GEO 2004 Conference Abstracts

The abstracts of the GEO 2004 Conference presentations (March 7-10, 2004, Bahrain) are published in alphabetical order based on the last name of the first author. Only those abstracts that were accepted by the GEO 2004 Program Commi�ee are published here. Abstracts were submi�ed online and were subsequently edited by GeoArabia Editors and proof-read by the first author. The names of companies and institutions to which authors are affiliated have been abbreviated. For convenience, all subsidiary companies are listed as the parent company. A list of the organization abbreviations is on page 148.

(345-Poster) Characterizing sealing faults in (327-Oral) Maturity and geothermal history carbonates of onshore Abu Dhabi of the Silurian, Triassic and Jurassic source rocks, Saudi Arabia Abd El-Sa�ar, Mohamed M. (ADCO - msa�[email protected]), Rafael Rosell (ADCO), Saleh Bin Sumaidaa (ADCO), Abdelbagi, Sami T. (Saudi Aramco - sami.abdelbagi@aram Naema Al-Zaabi (ADCO), Jean F. Dervieux (ADCO) and co.com) and Mahdi A. Abu-Ali (Saudi Aramco) Marie-Odile T. Bockel-Rebelle (ADCO) Organic microscopic analysis were carried out on over There has been increasing interest in the role of faults in 400 samples of black shale, siltstones, and marls from the relatively gently deformed reservoirs of southeast Abu over seventy wells in eastern and central Saudi Arabia Dhabi, where fault-dependant plays were recognized. to determine maximum paleotemperature and thermal Evidence for sealing on faults includes differences in maturity of different source rocks. The results indicate hydrocarbon pressure, viscosity and water-contact heights that the organic components consist of liptinites, alginite across some faults, as well as seismic amplitude and of marine origin and vitrinite. Inertnites predominate impedance differences. There has been li�le published in the Silurian section. Vitrinite reflectance (% Ro) data work so far on the understanding of fault seal potential suggest that source rocks in the deepest part of the basin in carbonate rocks, which is the situation in onshore Abu are gas prone while the oil-generating potential increases Dhabi. Much seismic, well and production data are available from west to east and in the younger strata. At present, from the Abu Dhabi fields, this data made it possible to go the Silurian source rock in the deeper parts of all basins from observations to prediction of fault-seal mechanisms. has passed the oil window and is in the gas-expulsion Faulting and sealing mechanisms in the petroleum systems maturity phase. The wet gas is confined to basinal areas of Abu Dhabi have complicated movement histories. with depths equivalent to % Ro (1.2-2.0). At the west margin Also it is strongly influenced by the lithological nature of the basinal area the Silurian source is immature or has of the sequence offset by the fault. Therefore, to fully a�ained early maturity (% Ro = 0.45-0.50). The least mature assess fault-seal potential it is necessary to examine the Triassic source rock occurs along the western margin and evolution of faults through time and the stress history. its maturity gradually increases eastwards. To the east, this Extensive databases of all relevant information have source is at the peak oil maturity (% Ro = 0.7-0.9). In the been constructed. It involved painstaking integration north and in the Rub’ Al-Khali the main kitchen is mostly at between structural geology, sedimentology, geochemistry, wet and dry gas maturity (% Ro > 1.3). The Upper Jurassic geophysics, petrophysics, and reservoir engineering, source rock in the Rub’ Al-Khali Basin is at peak dry gas and which allowed many types of analyses to be carried out. wet gas generation. The central and eastern reaches of the This study also reviews fault-sealing mechanisms and Jurassic source are at peak-oil expulsion. The northern part fault seal risk analysis. Fault characterization showed of the ‘kitchen’ shows early to peak-oil maturities (% Ro = that they are segmented horizontally and vertically in 0.5-0.9). This data has allowed be�er modeling of the burial an echelon arrangement and featured by small throws. and hydrocarbon generation histories of the Saudi Arabian In such an environment, the concept of juxtaposition or basins. It has provided a good calibration tool to be�er fault membrane do not exist. Diagenesis/cementation seal predict geothermal histories and hydrocarbon occurrences should be the working mechanism. Almost all faults – even in undrilled locations. those beyond seismic resolution – form a deformation zone/ band (mainly fractures/fracture corridors) which is more continouos than the fault segments. This study introduces (222-Poster) Facies architecture and a new sealing mechanism, which is “Cemented Damages porosity/permeability patterns in Wajid Zone” (CDZ), where dissolution and re-precipitation Sandstone of calcite in the fault zone and in wall rocks caused the cementation of the damage zone. This framework and Abdullatif, Osman M. (KFUPM - database provides an understanding of fault-sealed play [email protected]) and risk that allows the comparison of success and failure Fadhel Al-Khalifa (KFUPM) scenarios in our future exploration. Facies architectural analysis and porosity/permeability determination were carried out on two-dimensional

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outcrops of Wajid Sandstone in southwest Saudi Arabia. (468-Poster) Effective integration of The facies are dominated by medium to large scale cross- reservoir heterogeneities, fracture stratified sandstone. Channel and basal lag conglomerate networks and fault communication and and mudstone facies occur in minor percentages. The sandstone is characterized by stacked fining-upwards their challenges in Bahrain’s Awali field sequences, tabular geometry and many reactivation simulation models surfaces. Facies architectural elements recognized include mainly sandy channels, sandy bedforms, laminated sand Abdulwahab, Ayda Essa (Bapco - [email protected]), sheets, and proximal overbank fines. The facies in the Wajid Kandaswamy Kumar (Bapco) and Sandstone suggest mostly proximal to medial depositional Ali Ebrahim Al-Mu�ah (Bapco) se�ing with laterally shi�ing low-sinuosity channels and Bahrain’s Awali field is an asymmetrical NS-trending bar sequences. The study revealed that stacked, layered, anticline that was discovered in 1932. The field is a multi- and compartmentallized sandstone body geometries are stack of carbonate and sandstone reservoirs, most of them characteristic in Wajid Sandstone. Facies heterogeneity and oil-bearing. The fluids range from tarry oil in the Aruma porosity/permeability development at macro- and micro- zone, to dry gas in the Khuff zones. The geology of the scale reflect depositional environmental control, as well field is extremely complex with a large number of faults, as post-depositional diagenetic changes. The evaluation of especially in the Wasia Group formations, which contain Wajid Sandstone heterogeneity at outcrop analog scale is the major oil reservoirs in the field. These reservoirs are important for facies and petrophysical modeling as well as at different stages of the production cycle. Following a 3-D fluid simulation studies. seismic acquisition campaign in the year 2000, Bapco took up an integrated study to develop numerical models as the (365-Oral) Paleozoic petroleum system of main tool to assess alternative production mechanisms. Kuwait This integrated study faced a significant number of challenges, which had to be overcome with innovative Abdulmalek, Salah A. (KOC - [email protected]), ideas. The challenges included representing communication Swapan K. Bha�acharya (KOC), Riyasat Husain (KOC), between reservoirs through faults, complex rock and fluid Abdul Aziz A. Sajer (KOC), Adel M.H. Ebaid (KOC) distribution from heavy oil to gas condensate, gas injection, and Jim Russel (KOC) aquifer encroachment and fracture intensity. Although the hardware required for handling the large simulation The Paleozoic petroleum system and its elements are models was meticulously selected based on benchmark established in most parts of the Arabian Peninsula, but data of the various machines, the geological complexities is poorly understood in Kuwait due to the paucity of posed serious problems while running the simulation exploration data. Recent drilling information and direct models. This poster describes the effective integration of gas indications in the NW Raudhatain area have provided the reservoir heterogeneities, fracture networks and fault valuable leads for understanding the Paleozoic petroleum communication in the simulation models built for different system in Kuwait. Although several regional Paleozoic zones of the field. It also highlights the challenges faced petroleum systems exist in the Arabian Peninsula, the during the history matching process and the approaches available exploration data suggests that a likely system in adopted to overcome these challenges. Kuwait is the Qusaiba–Unayzah (.) system. The existence of this system is indicated by the results of drilling, however no commercial production from this system has been (387-oral) Integration of regional petroleum established. The Lower Silurian Qusaiba ‘hot’ shale, the system elements and exploration play likely source for this system, is expected to be mature for gas fairway maps using GIS and might have entered the gas window by about 115 Ma. Tectonic activity associated with Late Cretaceous closure Abu-Ali, Mahdi A. (Saudi Aramco - mahdi.abuali@aramc of the Neo-Tethys Ocean (marked as an unconformity on o.com), AbdalHadi Al-Khalifa (Saudi Aramco), Jay Fares the top of Mishrif Formation) probably corresponds to (Saudi Aramco) and John Griffiths (Saudi Aramco) the critical time of this system. The Permo-Carboniferous Unayzah Formation is expected to act as the major Geographic Information System (GIS) is a powerful tool to reservoir rock. Khuff and Sudair carbonates are envisaged visualize and integrate geographic and geologic information as the minor reservoir rocks. While the anhydrites and on a single platform. A GIS application was successfully shale interbeds, at different levels within the Khuff, Sudair used to not only display information geographically, but and lower part of Jilh formations, can act as local seals for more significantly, to enable the interactive over-laying of this system, a major salt unit in the middle part of the Jilh maps from multiple sources to derive a play fairway map. Formation is expected to be the regional seal partitioning The application has facilitated the integration of maps into a the Paleozoic petroleum system from the Mesozoic one. single visualization platform due to its ease of accessibility, The stratigraphic limit of the system lies below the Jilh salt flexibility, excellent resolution of maps and features and down to the basement. Geographically it covers most of the ability to overlay multiple maps simultaneously. The onland areas of Kuwait. This petroleum system is poorly geo-data originated from different sources; such as: Z- explored and so far reserves are not established. Map, Petrosys, shape files, vector datasets, CAD maps, and scanned maps. Initially, much of the data had to be reforma�ed to various file formats compatible with the GIS,

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but newer releases of the underlying GIS so�ware allowed (144-Poster) Field studies of deformed the transfer of all the data into the corporate database. carbonates in northern Oman: implications The process of data transfer was a major task. Grids were for modeling structural permeability in converted to raster data with associated contours, faults and control datasets as vector data. Scanned maps were carbonate reservoirs geo-referenced and pertinent information extracted where Agar, Susan M. (ExxonMobil - susan.agar@exxonmobil. appropriate, by vectorization. The underlying GIS so�ware com), Jerry J. Kendall (ExxonMobil) and was customized to allow easy access to the data and their Rolf V. Ackermann (Beicip-Franlab) associated meta-data and display definitions. Regional petroleum system maps that include structure, source rock Cretaceous outcrops in northern Oman provide an thermal maturity, well tests and hydrocarbon show data, opportunity to investigate the different processes that structural growth history, paleogeography and reservoir accommodate strain variations in carbonates and the isopach grids were generated for three petroleum systems: factors that influence their timing and distribution. (1) Permo-Carboniferous Unayzah; (2) Devonian Jauf; and Such knowledge is critical for predicting the impact of (3) Jurassic Arab-D formations. These three integrated structures on carbonate reservoir performance. Preliminary petroleum systems maps were combined with migration field observations in the Jebel Akhdar region emphasize pathways and structural growth history maps to generate several important factors for flow modeling in deformed regional play fairway concepts that can be used to help carbonates. Mechanical stratigraphy is an important control assess future exploration plays. on fracture heights and densities. However, fractures confined to individual beds may not impact reservoir flow (423-Oral) Influence of sequence-boundary as much as higher-order fractures that have longer vertical duration and facies on porosity evolution, extents and wider spacing. Stratal stacking pa�erns as well as the mechanical properties of individual beds are Early Cretaceous, Saudi Arabia important controls on these distinct fracture populations. Our observations of fractures in gently folded strata Adams, Roy D. (Saudi Aramco - [email protected]), indicate that curvature does not always provide a suitable G. Wyn Hughes (Saudi Aramco), Nassir S. Alnaji (Saudi proxy for fracture densities or orientations. The folding Aramco) and Mokhtar M. Al-Khalid (Saudi Aramco) mechanism and the timing of fracture formation relative Core and outcrop provide excellent data on two sequence to folding are key controls on fracture density gradients boundaries that extend from the Tuwaiq Escarpment, around some folds. Fracture corridors and discrete, low- near Riyadh, to the Gulf. These sequence boundaries displacement faults are also potential fluid-flow conduits. approximately coincide with formational contacts between Preliminary estimates of the displacement-height scaling the Sulaiy and Yamama formations, and between the relations for the very tall but narrow faults indicate that Yamama and Buwaib formations. Although the Yamama- faulting mechanisms in carbonates may differ from those Buwaib sequence boundary is well established, the Sulaiy- in clastics. Such differences could impact the reliability of Yamama sequence boundary is subtle, possibly due to sub-seismic fault prediction in carbonates. Seismic imaging a relatively brief period of sea-level fall and subaerial is also unlikely to resolve these faults, which may therefore exposure. The Sulaiy-Yamama sequence boundary probably be omi�ed from flow simulations. These observations, represents no more than a few hundred thousand years combined with the style and scale of strain partitioning and of missing time and produced some karsting. Evidence variable fault zone characteristics are key considerations for of caverns is found within 20 feet of the boundary and representing structural permeability in flow simulations of includes cave-sediment fill and collapse breccia. In contrast, deformed carbonate reservoirs. the Yamama-Buwaib sequence boundary represents several million years of missing time. This extensive exposure (302-Oral) Hydrocarbon source rock produced a heavily karsted surface and intense vadose correlations of the Saudi Arabian petroleum dissolution that extended more than 200 � below the sequence boundary. With burial, extremely vuggy intervals systems collapsed, creating extensive fracture networks. Producing Ahmed, Abdelghayoum (Saudi Aramco – abdelghayoum. reservoirs beneath these two sequence boundaries differ, [email protected]), Mahdi A. Abu-Ali (Saudi Aramco), primarily due to differences in duration of exposure Adnan A. Hajji (Saudi Aramco), Peter D. Jenden (Saudi associated with the overlying sequence boundary. Porosity Aramco) and Michael J. Moldowan (Stanford U) beneath the Sulaiy-Yamama sequence boundary is predominantly inter- and intra-particle. Porosity beneath Saudi Arabia’s Eastern Province holds the greater part of the Yamama-Buwaib sequence boundary is predominately the Arabian Basin which is the world’s major oil producing fracture porosity related to intense vadose dissolution province. Three major petroleum systems are confined to and subsequence collapse. Depositional facies provide a the Paleozoic and Mesozoic sections. These systems are secondary control on porosity development in the Sulaiy discussed with respect to source rock potential and their Formation: be�er porosity development correlates with hydrocarbon genetic relationships. The Paleozoic petroleum coral- and Lithocodium-rich, shallow-shelf, depositional system consists of the Early Silurian Qusaiba shales of the facies. Depositional facies have less influence on porosity Qalibah Formation as the principal source rock, particularly development in the Yamama Formation, due to pervasive the basal ‘hot’ shale unit. Biomarker and isotope data have and intense vadose dissolution. established the genetic link between the basal Qusaiba ‘hot’

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shale and the reservoired hydrocarbons. This system is (373-Poster) Reservoir geometry and quality dominated by the non-associated gas and sweet extra light across a Triassic alluvial plain: an outcrop oil, essentially in Central Arabia. The Jurassic petroleum analog for the Gharif play? system includes: (1) argillaceous carbonates of the Tuwaiq Mountain and Lower Hanifa formations in the Arabian Aigner, Thomas (U Tuebingen - t.aigner@uni- Basin; (2) Hanifa-equivalent deposited in relatively open tuebingen.de) and Jens Hornung (U Darmstadt) marine, clay-rich source environment in the Rub’ Al-Khali Basin; and (3) Sargelu/Najmah carbonates in the Gotnia This outcrop analog study investigates Triassic fluvial Basin. The Cretaceous petroleum system comprises of the sandstones (Stubensandstein Formation) deposited on Wasia Formation in the Rub’ Al-Khali Basin, and both the a terminal alluvial plain under semi-arid to sub-humid Wasia and Sulaiy formations and their equivalents are climatic conditions in the land-locked German Keuper Basin. indispensable source facies offshore Arabia. To address The Stubensandstein may serve as an analog for reservoirs hydrocarbon origin and preservation (oil cracking), several in parts of the Gharif Formation of Oman. The reservoir Saudi Arabian oils were analyzed by high-resolution properties change drastically over tens of kilometers from geochemical methods using diamondoids and compound proximal and distal paleogeography positions: (1) lithofacies specific isotope analysis of biomarkers. Diamondoids types vary along paleogeographical gradient from proximal indicated some samples were thermally altered (‘cracked’), erosion and non-deposition to fluvial bed-load, to distal some were mixtures of cracked and non-cracked oil, and suspended-load deposits and finally to playas with lacustrine others were composed entirely of normal oil. Biomarker carbonates; (2) sandbody geometries change from ribbons to isotopes strongly differentiated presumed Jurassic and sheets; (3) the average permeability of sandbodies decreases Cretaceous sourced oil samples. This had been difficult to by two orders of magnitudes from about 700 mD to 1 mD distinguish by other conventional methods. along paleogeographic proximal to distal trends. Within a three-fold hierarchy of cyclicity, the (probably autogenic) (229-Oral) Fracture characterization using micro-cycles could not be correlated while the meso- and macro-scale cycles could be correlated regionally using the mode-converted shear waves from dual approach of stratigraphic base-level changes. The observed offset VSP in Minagish field, Kuwait sedimentary pa�erns, together with paleosol types, their stable isotope signals and palynological data, indicate that Ahmed, Shabbir (Schlumberger - [email protected]), paleoclimatic fluctuations exerted the principal control on the Abdullatif Al-Kandari (KOC), Pradyumna Du�a (KOC) stratigraphic architecture and cyclicity. Shorter and longer- and Osama Osman (Schlumberger) term paleoclimatic fluctuations cause systematic changes in The Najmah-Sargelu Formation in the Minagish field is a reservoir and seal geometries, extent, and interconnectedness fractured reservoir in which fracture alignment controls oil of sandbodies. Thus knowledge of the overall paleoclimatic production. Fractures cause the formation to be anisotropic trends in comparable continental basins such as the Gharif such that seismic shear (S) waves get decomposed into fast may allow predictions on the regional reservoir architecture. and slow components, one aligned parallel to the natural axis of the fracture and the other aligned perpendicular (374-Poster) Geometry, poroperm and to it. Three-component downhole data recording enables sequence stratigraphy of ‘shoal’ the recording of mode-converted shear waves from a geobodies: outcrop analogs for Middle East compressional (P-wave) source, which can be used for detecting anisotropy. As part of an ongoing drilling effort carbonate reservoirs in the Minagish field, one well in its southern portion Aigner, Thomas (U Tuebingen - t.aigner@uni- provided an excellent opportunity for understanding tuebingen.de), Sassha Braun (U Tuebingen), Boris Kostic the shear wave spli�ing behavior of the Najmah-Sargelu (U Tuebingen) and Michael Ruf (U Tuebingen) Formation. Seismic ray trace modeling results revealed that a dual offset VSP would determine the anisotropic This outcrop analog study was designed to provide input trend. Two offset sources, located at 260°N and 350°N, for static reservoir models of shoal bodies on carbonate each at 2,000 � from the well, were used to acquire 3- ramps. The Germanic Muschelkalk represents excellent component downhole data. Zero-offset VSP data was also outcrop analogs for epeiric carbonate systems in the Middle acquired to calibrate and estimate vertical velocities. Field East, such as the Khuff, Hanifa or Arab reservoirs. The quality control showed that the signal quality in general studied shelly-oolithic carbonate shoals are up to 30 km was good, indicative of reasonable borehole conditions. P- long and 15 km wide. They correspond in dimensions to and S-wavefields were separated from the total wavefield both modern analogs and to several Middle East oil fields. using the Parametric Wavefield Decomposition technique. Meter-scale fundamental sequences are stacked into large- The shear wave data was projected in the fast and slow scale regressive-transgressive cycles. Porous intervals within directions utilizing the rotation technique. The results the shoal facies are concentrated around the tops of the showed that despite a limited offset, several interfaces fundamental shallowing-upward sequences. Pure separate generated converted shear waves, which in turn split vug porosity samples are characterized by relatively low into fast and slow shear components. The determined permeabilities (0 to about 10 mD) but can reach up to 20 anisotropy direction was in close agreement with the other percent porosity. In general, a combination of separate data. The mode-converted shear analyses using offset VSP vuggy and interparticle porosity leads to higher permeability added a new dimension to couple this information with the (several tens of mD). Maximum porosity and maximum future surface seismic measurements in the area. permeability zones follow the cyclic seaward-stepping and landward-stepping of the shoal geobodies. Two factors

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control the evolution of carbonate shoal-complexes with and making optimal data interpretation and therefore reservoir potential: (1) cyclicity, controlled by hierarchical exploration difficult. The examples shown here involve eustatic oscillations. The best and most voluminous reservoir datasets which are contaminated with high-amplitude bodies are developed during the peak of the large-scale multiples. Therefore a correct estimation of the multiples regression, whereby meteoric leaching enhances porosity; and their subtraction from the original data is of importance and (2) regional differential subsidence of basement for optimal subsurface model building and interpretation. blocks. Subtle paleotectonic upli� or low subsidence causes The approaches discussed in this study are different for preferred accumulation of shoals on local paleohighs. marine and land environments. For the marine data, the surface-related multiples generated between the surface and various subsurface reflectors (including the shallow, (139-Oral) Regional core-based strongly reflecting water bo�om) appear the strongest. sedimentological review of the glacially- They have been estimated with a multi-gate prediction influenced Permo-Carboniferous Al Khlata filter and the multiples are subtracted with a multi-gather Formation, South Oman Salt Basin, Oman subtraction process. The simultaneous suppression of different types and orders of multiples appears tobe Aitken, John F. (Badley Ashton - [email protected]), crucial in these environments. The recorded land data is Nigel D. Clark (Badley Ashton), Peter L. Osterloff (Shell), characterized by numerous types of multiples without Randall A. Penney (ResLab) and Uzma Mohiuddin (PDO) velocity discrimination and strong varying near-surface statics. For this data, a combination of data-driven surface- The Al Khlata Formation of the subsurface South Oman Salt related and internal multiple removal was employed in a Basin is a significant hydrocarbon-bearing succession within quasi pre-stack approach using the CMP domain. Since Oman. Previous sedimentological models have a�ributed its the land dataset suffers from a poor signal-to-noise ratio, formation to direct deposition from glaciers during Arabian supergathers have been constructed for be�er signal Plate G3 Gondwanan glaciation. Primary depositional identification prior to sequential multiple estimation and processes were thought to be responsible for perceived a�enuation. As a result of the successful a�enuation of the extensive and unpredictable lateral sedimentological and multiples, a be�er velocity analysis was facilitated leading reservoir quality heterogeneity. All Al Khlata Formation cored to more precise subsurface interpretations. wells in the study area were redescribed in order to determine the stratigraphic and palaeogeographic distribution of facies associations and depositional environments, and to establish (390-Oral) The E&P legacy data: a step- controls on reservoir quality variability in relation to the change in information discovery, retrieval sedimentary organization and the existing palynozonation. and use Approximately 2.5 km of core has been described, and all existing petrographic and conventional core analysis AlFaraj, Tawfeeq A. (Saudi Aramco - tawfeeq.faraj@aramc data reevaluated against these core observations. Twelve o.com) and Peter A�ewell (Saudi Aramco) lithotypes have been identified, which build into ten lithofacies associations defining three main depositional Throughout the history of Saudi Aramco (1933–present), environments: glaciofluvial, glaciodeltaic and glaciolacustrine large amounts of exploration data were kept as hardcopy environments. The controls on reservoir quality are grain reports, maps and other hardcopy products across various size, sorting and mud abundance. However, as there is a wide storage locations. Maintaining, sharing and dissemination variation in these primary depositional features at all scales of of information on these hardcopy products were o�en sedimentary hierarchy, reservoir quality prediction remains tedious and time-consuming. In order to provide easy enigmatic. Glaciolacustrine and glaciodeltaic deposits access to the information on these hardcopy products are volumetrically more important than has previously and to enhance the day-to-day vital functions of the been recognized. In particular, Al Khlata diamictites were geoscientists, Saudi Aramco undertook a major indexing entirely deposited by rainout and debris flow and there is no and scanning project for the conversion of all legacy evidence for the preservation of true tillites. Consequently, it (hardcopy) exploration products that were identified is hypothesised that ice never over-ran the South Oman Salt to have added value to the geoscientists’ day-to-day Basin, although it was certainly present in the Huqf outcrop operations or with a historical value to the corporation. area to the northeast, as evidenced by striated pavements. The important considerations involved in the indexing, The absence of an ice cover suggests that there is be�er scanning and quality checking of the digital products predictability of Al Khlata facies that permits more reliable are presented. The importance of defining and capturing correlation and reservoir modeling. sufficient metadata, which is information about the data, to support finding and retrieving the digital products are also major considerations. Sound procedures and best-practices (459-Poster) Multiple attenuation on shallow for ensuring a fast and most-economical data conversion marine and land data from the Middle East operation were employed. In addition, the data access rules and sensitivity classification that apply to these digital Ala’i, Riaz (Anadarko - [email protected]) products, which are stored in a document management system, are implemented. With the completion of this This study discusses some methodologies and strategies major project, geoscientists at Saudi Aramco are benefiting for successful multiple estimation and a�enuation on from quick and easy access to a wide variety of information shallow marine and land data recorded in the Middle that was previously difficult to access. The success of this East. Multiples can be a major problem in seismic data project had created a high quality web-enabled electronic interpretation: they may obscure crucial target structures data library using a single database model for the converted

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hardcopy data. Also, a large amount of storage space was assessed such hydrodynamic effects on hydrocarbon flow freed up for other uses. magnitude and direction. The results of the analyses show that significant hydrodynamic forces do occur and need to be considered in addition to buoyancy driving forces. The (392-Oral) Reflection tomographic depth hydrodynamic effects can become most significant in areas conversion in Saudi Arabia of groundwater flow energy sources, which are strongest in areas of highland surface topographic relief, areas of tectonic Aljanoubi, Emad (Saudi Aramco - [email protected] compression, or near breaches of aquitards. Thus, based on om), Aldo L. Vesnaver (Saudi Aramco) and the observations made in present-day hydrogeological Muhatresh F. Al-Mutairi (Saudi Aramco) systems of sedimentary basins, as demonstrated by Over a large area in Saudi Arabia, the most challenging this study, explorationists may assess the possibility of part of depthing is the hanging horizon depth estimation. hydrodynamic effects to determine exploration fairways. The geological framework is smooth and predictable between 100 and 800 m subsea, making a�ractive the (404-Poster) Shear-wave processing of zero- use of so-called hanging horizon as a depth reference offset VSP for lithologic analysis for calibrating structural trends. The shallow formations are extremely heterogeneous, including sand dunes, Alkhater, Salman (Saudi Aramco - carbonate with cavities and collapses, and paleocanyons, [email protected]) and o�en filled with sand. In addition, the P-wave velocity can John C. Owusu (Saudi Aramco) drop from 3,000 to 600 m/s within a short distance, with possible velocity inversions. There are uphole, velocity- In conventional zero-offset VSP seismic processing, the hole, and structural-hole that cover most of the Kingdom, emphasis has been on the enhancement of the P-wave. but unfortunately, not all of them penetrated the hanging The shear wave recorded by the three-component receiver horizon, and those that did are sparsely sca�ered in some is usually of limited benefits due to a variety of factors areas. Reflection tomography is a viable tool for estimating including: low signal-to-noise ratio, interference from other the velocity-depth model down to the hanging horizons. wavefields and limited dynamic range of the downhole We experimented with multi-layer refraction and joint receiver. However, the shear wave information, used in tomography. Refraction tomography did not produce conjunction with the compressional waves, can enhance a stable model, probably due to the shallow subsurface our understanding of the reservoir by providing a�ributes complexities. On the other hand, the hyperbolic inversion such as pore fluid, lithology and the structural image. down to the hanging horizon produced a stable model Additionally, this information can be utilized in modeling for individual 2-D lines. To avoid possible misties, we and processing of multi-component surface seismic data. inverted a grid of 2-D lines, as a single 3-D, in two areas. In this study, we show that shear wave recorded in a zero- The combined inversion in both areas demonstrated that offset VSP survey can be enhanced by performing hodogram reflection, rather than refraction, tomography was able to analysis on the vertical and horizontal component datasets. generate a geologically reasonable velocity depth model First, the two horizontal components (X and Y) are rotated that tied all wells with a minor bulk shi� due to the wavelet into horizontal radial (HR), and horizontal transverse phase inconsistency. (HT) components by maximizing the direct P-wave. This is followed by a rotation of the horizontal radial and transverse components by maximizing the direct S-wave. (303-Oral) Significance of assessing The P- and S-wave interval velocities and Vp/Vs ratio hydrodynamic forces in secondary computed from this analysis correlated very well with hydrocarbon migration analyses those from dipole sonic log. Even more important, this procedure could provide S-wave velocities in the absence Alkalali, Arif I. (Saudi Aramco - [email protected]) of dipole sonic data. Hydrodynamic forces are a direct manifestation of subsurface fluid energy gradients that can significantly (114-Poster) Computing fracture attributes affect the migration of hydrocarbons in a sedimentary from azimuthal velocity and AVO seismic basin, in addition to the traditionally considered buoyancy data in Saudi Arabia driving forces. The potential significance of such forces has been previously demonstrated theoretically by Almarzoug, Ahmed M. (Saudi Aramco - mathematical relationships and basin-scale fluid-flow [email protected]), Fernando A. Neves (Saudi numerical simulation models. The aim of this study was Aramco), Jung J. Kim (Saudi Aramco) and to determine if such significant hydrodynamic forces Edgardo L. Nebrija (Saudi Aramco) actually occur in nature. Their occurrence in present- day hydrogeological systems of sedimentary basins can Determination of intensity, orientation, and distribution give an insight of past hydrogeological systems at the of open fractures is a critical task for optimal location of time of assumed secondary hydrocarbon migration. horizontal wells in fractured reservoirs. For a horizontal well Using a specially developed technique programmed in a to be most productive in tight (low permeability-porosity) spreadsheet, maps of present-day subsurface fluid potential reservoirs, it should cross large vertical fractures (faults) distributions were analyzed for several subareally exposed with significant amounts of associated micro-fractures. basins in different parts of the world that span known depth Mapping fractured areas is known to be a real challenge ranges of secondary hydrocarbon migration. The analyses to the geoscientist. Several studies indicate that the search

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for vertical fractures with vertical core is fruitless, since the Hydrocarbon shows were encountered while drilling chance of intersecting fractures is quite low for a typical and petrophysical evaluation indicated the presence of 4-inch core experiment. Secondly, these fracture zones are hydrocarbon pay within the favorable primary reservoir not easily observed tectonic structures (unlike major faults) facies (parallel/crinkly laminites and thrombolites) but on on post-stack seismic data. P-wave amplitude versus offset testing the well failed to produce hydrocarbons. A detailed and azimuth (AVOA) and azimuthal velocity analysis using examination of the core revealed extensive salt plugging 3-D wide-azimuth full-offset pre-stack seismic data usually throughout the reservoir interval with prevalence of black provide a detailed map of the fracturing pa�ern away substance (i.e. bitumen). Analysis of core plugs and thin from well control. This study estimated fracture direction sections confirmed the extensive plugging of pores with and relative fracture density using azimuthal anisotropy halite, and bitumen. Preliminary studies conducted on salt measurements of P-wave velocities and amplitude data. We plugging indicated that the halite, which is diagenetically noted a small azimuthal variation in P-wave velocity and a late, is deformed with rare primary fluid inclusions. significant variation in AVOA response at the reservoir. The Bitumen is found in pore space and within halite crystals. estimated fracture azimuth computed either from velocity Several generations of solid bitumen are thought to exist. or AVOA data is spatially variable, but generally east-west Petrophysical evaluation of wireline logs indicated a poor and north-south, in agreement with the regional tectonic quantitative correlation between the log response and the trend and borehole breakout analysis. AVOA analysis amount of bitumen seen in cores. Although many stringer showed a more consistent estimate of fracture orientation wells in the SOSB are known to contain bitumen at various than velocity analysis. percentiles (such as Dhahaban South-1H1 or Dafaq-1H1), bitumen plugging was not believed to present a problem to hydrocarbon flow. However, in Minassa-1H1, bitumen (186-Oral) Gas detection by extended elastic plugging coupled with salt plugging seems to form a major impedance barrier to the hydrocarbon flow by reducing the effective porosity and permeability values in the A1C reservoir. AlMustafa, Husam M. (Saudi Aramco - husam.mustafa@a Specialized studies are now focussing on resolving the ramco.com), Edgardo L. Nebrija (Saudi Aramco) genesis and regional distribution of halite and bitumen. The and Saied Zahrani (Saudi Aramco) studies will also clarify their wireline log response. Searching for optimum seismic pore-fluid indicators should concentrate on elastic moduli rather than wave-propagating (140-Oral) Hanging-horizon depth estimation velocities since it is the moduli that govern the behavior of using geostatistical tools rocks. Extended elastic impedance derived from elastic impedance, allows us to derive curves proportional to Al-Ali, Mustafa N. (Del� U – [email protected]�.nl) and various elastic parameters such as bulk modulus, Lame’s Abdulnasser M. Khusheim (Saudi Aramco) constant of incompressibility, rigidity and Poisson’s ratio. Our analysis concentrates on the incompressibility-rigidity The reliability of ‘hanging-horizon’ depth map is important approach because incompressibility is sensitive to pore when dealing with low-relief structures (15 to 30 msec). fluids and rigidity is unaffected by fluids. Combining these In this study we briefly describe the application of two into one measurable parameter should provide an geostatistical tools in estimating a hanging-horizon depth effective tool for delineating gas-bearing zones in sandstone map via integration of velocity wells and seismic data in an reservoirs. The value of incompressibility divided by rigidity area east of Ghawar field in Saudi Arabia. The main objective at three well locations showed smaller values in gas-bearing of this task was to produce a depth map to the top of the reservoirs than those in tight or water-bearing reservoirs. Aruma Formation. The section above the Aruma Formation We applied this extended elastic impedance approach to is characterized by lateral and vertical heterogeneities. the Upper and Lower Unayzah Sands for gas interpretation Although there are many velocity wells in the area that and obtained a fluid and lithology impedance volume reach the bo�om of the Rus Formation, and a few that highlighting possible gas-bearing regions previously reach the Aruma Formation, they are not adequate to overlooked by conventional acoustic impedance inversion. independently resolve the existing complexities. Therefore, It has been found that the extended elastic impedance is an high-resolution 2-D seismic data (2.5 m subsurface a�ribute sensitive to gas accumulation and thus an essential sampling) was used to improve the time mapping between factor to consider for optimally placing future development the wells. The first step was to tie all the velocity wells to the wells in the region. seismic at critical horizons that can be interpreted over the entire area. Next, ordinary cokriging was used to integrate well times with seismic times (referenced to surface) for (175-Oral) Salt and bitumen plugging: their every mapped horizon. The resultant time maps were used combined effect in carbonate stringers, as markers to guide the 3-D kriging of velocity data from South Oman Salt Basin all wells in the area. This produced a 3-D velocity model with each voxel having a velocity value and a time isochron. Al-Abry, Nadia (PDO - [email protected]), Janos Therefore, a depth map can be obtained by summation of all L. Urai (Aachen U), Ralf Li�ke (Aachen U) and voxels thicknesses in each column. Finally, to assure perfect Peter A. Kukla (Aachen U) tie to all the well depths, collocated cokriging of well depths and this map was performed. Geostatistical tools proved as Minassa-1H1 well was drilled to test for moveable a useful means for integrating shallow seismic data with the hydrocarbons in the A1C carbonate stringer cycle in the associated well information. Dhahaban area of the South Oman Salt Basin (SOSB).

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(318-Oral) A novel technique for near- identified at the crestal part of the Burgan Dome–one of surface macro-velocity model estimation three main structural highs in the Greater Burgan field. The other two structural highs, Ahmadi and Magwa, show Al-Ali, Mustafa N. (Del� U - [email protected]�.nl) much lower levels (in most cases zero concentrations of H2S). The variation between the concentrations in these This abstract briefly describes a novel technique for three areas appears to be a consequence of off-take and improving near-surface macro-velocity model estimation. intrareservoir seals controlling the migration of H2S from It is based on integration of uphole velocity data and a deep-seated source. Over a four-year period we have a velocity a�ribute derived from vibrator baseplate identified areas where H2S appears to be decreasing, information. As it pushes against the earth, the vibrator increasing, and staying relatively constant. A model for this senses the earth’s response to the applied force through variation has also been proposed. the movements of the baseplate. Therefore, by knowing the dynamics of the vibrator (the reaction mass and baseplate accelerations) estimates can be obtained for the underlying (215-Oral) Evaluation and testing of earth properties. Consequently, a P-wave velocity a�ribute bypassed oil accumulations in the Burgan can be derived from these estimates. This a�ribute has the field, Kuwait same spatial sampling rate as the source grid in the seismic survey, which is considerably finer than the sparse uphole Al-Azmi, Saleh F. (KOC - [email protected]), Abeer K. grid. It reliably defines the lateral boundaries of near- Al-Ali (KOC), David Jackson (ChevronTexaco-KOC), surface velocity variations. Integration of this a�ribute Saleh A. Al-Rasheedi (KOC) and and uphole velocity data using geostatistical tools, may Obaid M. Al-Shammari (KOC) lead to improvements in the near-surface macro-velocity The acquisition and interpretation of 3-D seismic over model. An important application of this model is in the the Greater Burgan oil field led to a be�er understanding calculation of seismic statics. The technique outlined above of the distribution of unswept oil accumulations. These was used to build models in several areas followed by accumulations range from simple a�ic closures in massive application in seismic stacking. Results exhibited consistent sand reservoirs–normally associated with simple structural improvements in seismic stacks compared to those obtained closures, to more complicated accumulations comprising from conventionally calculated models. Using the new of combined structural-stratigraphic traps in the more technique, medium and long wavelength statics anomalies interbedded sandstone reservoirs. The Burgan Sandstone were be�er resolved. This is a�ributed to the guidance Reservoirs are divided into 4 zones: 4th Sand, 3rd Sand provided by the vibrator velocity a�ribute to determine the Lower, 3rd Sand Middle, and 3rd Sand Upper. Above the lateral influence zone of each uphole in the area. Finally, Burgan Sandstone reservoirs lies the Mauddud muddy besides the achieved improvements, the data used to derive carbonate formation, above which lies another interbedded the velocity a�ribute is readily available in any land survey sand-shale reservoir, the Wara. Examples of bypassed that is acquired using vibrators. oil are discussed from all of the above clastic formations. The methodology applied involved the integration of well (52-Oral) Understanding the behavior of surveillance data (pnc/tdk logs, oil-water production data) with the geological and geophysical architectural data. hydrogen sulphide (H2S) in the reservoirs of the Greater Burgan oil field, Kuwait–an Although there are vast reserves remaining in the Greater integrated approach Burgan field, the stacking of reservoirs, combined with the increasing competition for wellbore usage, means that Al-Azmi, Saleh F. (KOC - [email protected]), David opportunities to sweep undrained oil needs to be assessed Jackson (ChevronTexaco), Reham Al-Houti (KOC) and and acted upon accordingly. This study concentrates Shymaa Al-Hazzaa (KOC) on the subsurface multi-disciplinary approach applied to the assessment of opportunities to drain bypassed The presence of H2S in the Greater Burgan field area oil. However, the interaction of the subsurface team became a problem in the 1990s when its presence in the with the surface production facilities and operations surface facilities became a prominent safety concern. departments, is highlighted. Examples of new wells to Therefore studies were set up both to cover the surface drain stratigraphically and structurally trapped downflank, occurrence, and the subsurface occurrence of H2S. This bypassed, oil are given; together with workovers which study describes the subsurface occurrence, and shows how have been carried out to drain both a�ic oil accumulations in an integrated approach covering geochemistry, geology, massive sands, and bypassed oil trapped in the interbedded geophysics and engineering has led to the presently sand-shale reservoirs. favored model for H2S encroachment. The model is vital for providing a framework for asset decisions regarding (415-Oral) Eigenimage footprint removal shut-in priorities and allowables, providing qualitative predictions for future H2S behavior, and provide a basis for Al-Bannagi, Muhammad S. (Saudi Aramco - mohammad. the development of concepts to mitigate H2S encroachment. [email protected]), Kangan Fang (Saudi Aramco) and Following initial studies to ascertain the size and nature of Panos G. Kelamis (Saudi Aramco) the H2S phenomena, it was decided to run annual full-field sampling programs; there are now four consecutive years Geometry acquisition footprints are linear spatial grid of H2S measurements in gas samples at the wellhead. By pa�erns seen on seismic time slices. Essentially, they simply mapping the data, an overall ‘H2S Plume’ was mirror the acquisition geometry used for acquiring

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the seismic survey. Their presence tends to mask key (152-Oral) Contrasting styles of salt geological features introducing uncertainty at the final structures in the South Oman and Ghaba interpretation stage. Although dense seismic acquisition Salt Basins geometries eliminate the footprint signature, they are rarely employed in the field due to the high cost involved. Al-Barwani, Badar H. (PDO - [email protected]) Thus, processing techniques are usually applied aiming and Ken McClay (Royal Holloway, U London) to reduce the footprint effect. Pre-stack reconstruction and regularization algorithms, based on Fourier/Radon Three major salt basins occur in Oman: (1) South Oman transforms and combined with apriori information, can Salt Basin (SOSB); (2) Ghaba Salt Basin; and (3) Fahud be quite effective. Their performance however, depends Salt Basin. Although the Late Proterozoic Ara salt on spatial sampling, spatial bandwidth and the choice of controls the structural evolution of these basins, they parameterization. Alternatively, post-stack methodologies differ in styles, geometries and driving mechanisms for based on FK filtering principles, are used but they tend to halokinesis. In the SOSB, mini-basins and salt ridges suffer from the well-known mixing and worming artifacts. are the main features with interconnected salt ridges In this study, a new post-stack approach is introduced to and no circular diapirs observed. Differential loading remove the seismic acquisition footprint. The method during the Nimr Group sedimentation was dominant at is based on eigenimage filtering and offers several the early stage of halokinesis to the west of the SOSB. advantages over the conventional FK and F-XY prediction Later blanket sedimentation during the Ordovician filtering techniques while preserving the data character. It prevented further halokinesis in the SOSB. In contrast only assumes that the number of distinct dips is limited to the north of the SOSB, in the Central Oman High and unlike many eigen-based approaches can work well and the Ghaba Salt basins 8 salt diapirs are found as a with dipping reflectors. Additionally, it removes random result of ‘thick-skinned’ compression of reactivation of noise and makes a modest a�empt to restore missing data basement faults. These diapirs are interpreted to form at shallow depths. Its performance is demonstrated with as a result of two phases of compression rather than field land data from the Arabian Peninsula. ‘thin-skinned extension’ as previously documented. The first phase formed during the ‘Hercynian’ Orogeny (Late (151-Oral) Tectonic evolution of mini-basins Devonian to Late Carboniferous) as a result of the Huqf Upli�, which triggered further halokinesis. The second in the Thumrait block (South Oman Salt phase of contractional salt tectonics occurred during Basin): implications from physical analog the Cretaceous in the Central Oman High, the Ghaba modeling Salt Basin, and the Fahud Salt Basin, as a result of the emplacement of the Semail and the Masirah Ophiolite in Al-Barwani, Badar H. (PDO - [email protected]) northern and eastern Oman, respectively. The contrasts and Ken McClay (Royal Holloway, U London) between diapirs developed in the different tectonic regimes are illustrated in details. This study presents structural evolution of the Thumrait block in the southwestern part of the South Oman Salt Basin, and a series of scaled analogue models designed to (95-Oral) Calculating long wavelength statics simulate development of mini-basins. The Thumrait block in the Sirte Basin is characterized by a series of salt ridges and associated salt withdrawal mini-basins. It shows a complex interaction of Al-Dabagh, Hazim H. (Schlumberger - salt and sediments. The salt withdrawal mini-basins are [email protected]) and Khaled Khabbush (Consultant) circular to oval in shape, 1-12 km wide, and encircled by narrow, elongated salt ridges. Four different types of A new approach has been developed to tackle the mini-basins formed at different time intervals. Most of problem of calculating long-wavelength statics from the deformation associated with halokinesis occurred at conventional exploration seismic data. The method uses an early stage during the deposition of the Early/Middle the pre-stack reflection data from shot records and an Cambrian Nimr Group and the Amin Formation. Pulses initial near-surface model as input to an algorithm using of sediment loading manifested by alluvial fan and the ray-tracing technique. The appropriate statics value is braided river deposits from the west are the main trigger that value which produces maximum stack power along and driving mechanism for halokinesis. Results from the travel-time curves generated by ray-tracing through the analogue modeling show that mini-basin formation can model. The technique has been tested successfully on be caused by differential loading of the type generated both synthetic and real seismic data acquired in a hilly by alluvial fan systems. Differential loading of a ductile and noisy environment. The procedure does not require polymer created localized extension forming radial and the picking of seismic refraction events on shot records. It axial grabens. These grabens are sites of reactive rise provides a practical alternative to conventional methods of the ductile substrate producing ridges that bound in those areas where refraction events cannot be picked withdrawal basins. The results of the physical modeling reliably on pre-stack data. This method is able to cope are compared to the Thumrait block during the early with the vertical and lateral variation in the physical phases of halokinesis during the deposition of the Early– properties of the near-surface layers and produces Middle Cambrian Nimr Group. reliable results for the conventional seismic data example described in this paper.

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(434-Poster) Using high-resolution sequence has been done for North Oman, with emphasis on the stratigraphy for field-scale characterization Shu’aiba Formation. The review included: (1) a compilation of Permo-Triassic Khuff carbonate of the regional tectonic evolution and structural framework of Oman from selected key publications and internal reservoirs, Ghawar field, Saudi Arabia reports; (2) construction of a GIS database, which brings together structural and other geological data from the Al-Dakhil, Ra’id K. (Saudi Aramco - regional to the well scales, together with field-scale [email protected]), Ghazi A. Al-Eid (Saudi production data; and (3) the creation of a 3-D regional Aramco), Aus A. Al-Tawil (Saudi Aramco), Rick R. Davis structural model for the whole of North Oman area (North (Saudi Aramco) and Shoaib M. Rawasia (Digicon) Oman Common Earth Model - NOCEM) based on seismic The Khuff Formation overlies the Permo-Carboniferous data in depth interpreted by PDO. The 3-D regional model siliciclastic Unayzah reservoir bearing, and is overlain by is a base to define regional structural domains from the the fine siliciclastics of the Triassic Sudair Formation. The interpretation of structure and kinematic indicators. This Khuff C carbonate reservoir contains three high-resolution enables be�er understanding of the structural evolution sequences; whereas the Khuff A and B carbonate reservoirs both regionally and per domain, which may include one are each made up of one bearing (third-order?) sequence. or more fields. A total of five regional tectonic domains Sub-tidal, high-energy, and open-marine facies, overprinted have been defined. The main characteristics used to define by early diagenetic fluids form high porosity reservoir these domains were: (1) amount of halokinesis (salt-related compartments. Intra-formational seals are anhydritic/ deformation); (2) amount of upli�/burial; (3) fault signature dolomitic carbonate coastal successions and form thick, (intensity, as far as it can be qualitatively assessed, and non-reservoir intervals between the Khuff C and B, and dominant orientations). The distinction of the tectonic the Khuff B and A, during longer-term possible third or domains allows, for example, for an assessment of the second-order highstand system tracts (HST), overprinted expected style(s), directions, intensities, etc. of fractures by extreme inland climatic aridity, coincident with the and faults, both from an exploration and field development assemblage of the supercontinent Pangea. Sequence and point of view. cycle-set boundaries are marked by exposure surfaces during periods of sea-level drops, which in turn have a (433-Oral) Proximal-to-distal facies corresponding gamma-ray signature on wire-line logs. variability within a high-resolution Using these regional markers on over 15,000 � (5,000 m) in 50 cored wells and wire line logs in 200 closely-spaced wells, sequence stratigraphic framework defining allowed mapping high-resolution (fourth order?) sequences, syndepositional structural activity of as well as deciphering of onlap geometry of the high- Ghawar field during the deposition of the frequency transgressive systems tract (TST) and prograding Permian Khuff-C carbonates geometry of the high-frequency HST. Glacio-eustacy during the Permo-Triassic times, which are transitional from global Al-Eid, Ghazi A. (Saudi Aramco - [email protected]), ice-house to global green-house times, resulted in moderate Ra’id Khalil Al-Dakhil (Saudi Aramco), Aus A. Al-Tawil amplitude sea-level fluctuations, giving rise to regionally (Saudi Aramco), Rick R. Davis (Saudi Aramco) and mappable, high-resolution (4th-order) sequences and their Shoaib M. Rawasia (Digicon) component systems tracts and cycle sets. This controlled the vertical partitioning of reservoir facies within Khuff C, The up to 90 m thick, gas-bearing Late Permian Khuff C B, and A carbonates. The active Ghawar structure during carbonate reservoir is made up of three high-frequency the Permian, lead to lateral partitioning of these facies from sequences bounded by sharp, regionally mappable proximal on the crest, to distal on the flanks. Furthermore, boundaries with varying degrees of exposure features and subtle highs and saddles along the crest, furthered the regionally mappable flood-backs. These sequences and lateral portioning of the reservoir. Reservoir facies formed component cycle-set boundaries are marked by regionally during the retrograding oolitic shoal belts of the late TST mappable gamma-ray signatures, facilitating their mapping (Khuff A, B, and C) and the shallow subtidal burrowed in non-cored wells. The transgressive systems tract (TST) of facies of the prograding HST of each of the high-resolution each sequence is made up of back-stepping cycle-sets (3 to sequences (Khuff C only). This high-resolution stratigraphy 10 m each), which remain horizontal and can be traced for allowed very precise mapping of facies down to the cycle- over 200 km; onlap geometry can be recognized regionally set level at a very high resolution of 15 � (3 m) at the scale over locally high areas. Flooding cycle sets are made up of the Ghawar field. of peritidal, lagoonal, and back-barrier facies, which pass into the late TST belt of overlapping ooid shoal facies that thicken northward. The associated fore-shoal and (106-Poster) Tectonic evalution of North storm-influenced facies are time-transgressive from south- Oman from regional scale to field scale to-north. High-energy, fore-shoal/deep marine bryozoan mud are the most distal Khuff facies in Ghawar field, and Al-Dhahab, Salah H. (Shell - [email protected]), form the maximum flooding (MF) of the high-frequency Pascal Richard (Shell), Martin de Keijzer (Shell), sequences. The prograding highstand systems tract (HST) Safia al Mazrui PDO( ) and Jacek Filbrandt (PDO) of each high-frequency sequence is made up of shingled cycles of open marine flooding facies that pass upward A regional review of those aspects of the structure and into shallow subtidal (reservoir) and minor intertidal (non- tectonic evolution, which potentially affect and control reservoir) facies. Slopes of prograding packages are subtle reservoir quality and reservoir performance at a field scale,

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(0.01 degree), and can only be recognized by mapping the (20-Oral) Integrated static and dynamic high-resolution sequences over the scale of the Ghawar modeling approach in one of Thamama gas field. High-resolution sequence stratigraphy constrains reservoirs of onshore Abu Dhabi the distribution of facies within regionally mappable units down to 15 � (3 m), within which, proximal facies are to Al-Habshi, Ali H. (ADNOC - [email protected]), the north and along the present-day Ghawar crest, and Amr M. Badawy (ADNOC), Abdel Rahman R. Darwish distal facies to the south and on the present-day Ghawar (ADNOC), Adham K. Hathat (ADNOC) and flanks. This indicates an active Ghawar structure that Thanaa E. Hamdy (ADNOC) was plunging to the south during the deposition of Khuff carbonates/evaporites. Crestal variability formed proximal The ability of integrated so�ware to present solutions is facies over subtle highs to distal facies over subtle lows, evolving rapidly and has shi�ed to emphasize on what a best- whereas local, fault-bounded, down-dropped blocks practice modeling approach should be. One of the issues o�en led to thicker accumulation of sediments as well as local raised is the link between a facies-based model incorporating restriction and deposition of salinas and sub-aqueous depositional and sequence stratigraphic characteristics, and anhydrite. Delineation of such intervals within the high its use during dynamic simulation. This study suggests an frequency sequence framework leads to constraining local approach that introduces the concept of modeling based on areas of degraded reservoir quality due to cementation the reservoir rock type. The example used is one of the major and plugging by remobilized anhydrite. High-frequency producing gas reservoirs in a giant field in central onshore (third-/fourth-order) eustacy (low-to-moderate amplitude) Abu Dhabi where the general structure trends is NE-SW, and during a transitional time from the Permo-Carboniferous has dimensions of 40 x 30 kms. Its main reservoir zones are glaciation into Permo-Triassic greenhouse gave rise to the part of the Lower Cretaceous Thamama Group. The overall regionally mappable high-frequency sequences, their TST, depositional environment is characterized by its location on HST, and component cycle-sets. the Arabian carbonate platform within an intrashelf basin. Applying the sequence stratigraphy principles, the reservoir is (249-Oral) Contracting a complex 3-D survey divided into two parasequence sets. The lower part comprises a progradational interval overlain by a retrogradational Al-Ghamdi, Turki M. (Saudi Aramco - turki.ghamdi.8@ara package, with the boundary between each package marking mco.com) and Richard Hastings-James (Saudi Aramco) a stillstand. Six lithofacies were identified in the reservoir: (1) bioclastic peloidal grainstone; (2) algal packstone/floastone; The Qatif 3-D survey is Saudi Aramco’s most complex (3) bioclastic peloidal packstone; (4) algal wackestone/ 3-D survey ever, involving Ocean Bo�om Cable (OBC) floastone; (5) bioclastic peloidal wackestone/packstone; and dual sensor, transition zone (TZ), and land vibroseis (6) argillaceous bioclastic wackestone. These lithfacies are and dynamite operations. The aims of the survey are to believed to have been desposited on a homoclinal carbonate accurately image both the shallower carbonate reservoirs ramp that dipped gently seaward. Porosity and permeability for development purposes, as well as deeper clastic gas are well developed in the reservoir section due to a lack of reservoirs for exploration purposes. The survey area pore-filling cement. In the field, a clear general trend occurs of encompass various types of surface conditions varying down-flank porosity reduction of more than 10 percent from from deep-water to mangrove and tidal areas, sand, sabkha, the crest down to the water-bearing zone. This is mainly due cities, old towns, highways, industrial areas, restricted to the increased abundance of stylolite formed during burial areas (military bases, airports, farms), and a high density diagenesis, hydrocarbon migration, and infill of the structural of various categories of pipelines and power lines. In order trap. Analysis of both thin-section descriptions and high- to investigate and assess the required effort, Saudi Aramco pressure mercury injection, led to the identification of five conducted five feasibility studies, of which one is internal distinctive rock types. Each reservoir rock type has a certain and the rest by four different recognized international effective pore throat size distribution which will produce a seismic contractors. The studies assessed the distribution particular capillary pressure curves, relative permeability of various surface conditions, identifying possible source curves and constrained porosity/permeability estimation. and receiver types’ distributions, exclusion zones, high- risk operating areas, and types of permi�ing issues. (438-Oral) Effective reservoir management of Furthermore, Saudi Aramco conducted a 2-D test line with a mix of explosives and vibroseis sources to determine Bahrain’s mature oil field: a case study the explosive source configurations, test various receiver Al-Haddad, Abdulla M. (Bapco - abdulla_ configurations, and assess required drilling efforts. Along [email protected]) and Challa R.K. Murty (Bapco) with the 2-D test, a Peak Particle Motion (PPM) study was run in different site locations throughout the survey area Bahrain’s Awali field, discovered in 1932, is a highly-faulted to establish critical safe operating distances from various asymmetrical anticline trending in a NS direction. The types of buildings, pipelines, power lines, plants, and water field produces from seventeen oil and three gas reservoirs wells. Finally a contract was developed incorporating the within Jurassic to upper Cretaceous formations, as well as above information to optimize the survey area, specify from the Permian-Triassic Khuff limestone gas zones. These the crew configuration and acquisition parameters, and to reservoirs occur with divergent lithology, rock and fluid specify operational procedures. properties. Some of them are saturated, while other are highly undersaturated. Some of them are oil wet and some water wet. They operate under various drive mechanisms and pressure maintenance schemes. Gas injection in the

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Mauddud reservoirs, which is one of the major oil producing laterally for a few kilometers where the lower contact zones in the field, has been in operation for the last 65 years. is an unconformity marked by a prominent limestone Gas injection in the Arab-D reservoir has been in progress escarpment. Six distinct lithofacies have been described from 1986. Pilot peripheral water injection is in progress in as follows: cherty conglomerates, sandstones, siltstones, the Wara sands in the northeastern area of the field since 1995. gley-type paleosols, oyster-rich limestones and coal seams. Additionally, different production mechanisms have been The cherty conglomerate facies is encountered at three applied including gas li�, pumping and stop cocking for GOR major (> 4 m thick) stratigraphic levels and represents an control. The field being mature and structurally complicated, unusual case due to its coarseness and the absence of such naturally demands an integrated approach for effective deposits in the Central Oman Mountains. The sandstones reservoir management to ensure maximum recovery. Due to are predominantly quartz arenite although locally chert the application of diverse reservoir management techniques, clasts can be as much as 20 percent. Siltstone is the most reservoir characterization, geostatistical application for dominant facies while gley-type paleosols occur in the anisotropy, and increased accuracy for simulation, the field southern outcrops. Most of the coal seams are found in the has been producing with minimum annual decline. By northern outcrops showing increasing pyrite content up- integrating the geological, seismic and reservoir/production section, a typical signature of marine influence as recorded data, the productive limits of various reservoirs have been in the literature. Foraminifera microfauna associated with extended adding substantial reserves. This presentation the siltstones above the coal seams comprise Nummulities discusses the approach adopted in the effective reservoir fabianii, N. Stritatus, N. Garnieri, Pellatispira sp., Amphistigena management of this giant mature oil field. sp., Silvestriella sp., Calcarina sp., Borelis vonderschmi�i, Gypsina globules, Fabiania cf. saipanesis, together with rare miliolids and fragments of inderminate encrusting (191-Oral) Geochemical analysis to identify foraminifera (dominantly acervulinids). The stratigraphic prospectivity of Makhul Formation in Kuwait ranges of these taxa indicate that the upper part of the Musawa Formation is Upper Eocene, Priabonian (arguably Al-Hajeri, Mubarak M. (KOC - [email protected]) and early to middle Priabonian) in age. The absence of the Swapan K. Bha�acharya (KOC) larger foraminiferal genera Assilina and Aalveolina, which The Makhul Formation has been evaluated geochemically are common in the Eocene section of Oman and are known to establish its hydrocarbon potential as a future exploration to have become extinct at the end of the Middle Eocene, target. So far the Makhul Formation in Kuwait is considered also indirectly supports a Priabonian age. The occurrence to be a localized source rock for selective Cretaceous of these thick siliciclastic sediments is interpreted as the reservoirs and also tested oil-bearing in one of the wells in result of activation of the North Ja’alan Fault resulting in Minaghish field. In this present work one a�empt was made a strike-slip basin in the Late Eocene. The forces associated to reevaluate the source characterization using TOC, rock- with the strike-slip movement are believed to be related to eval, kerogen composition, thermal maturity and pyrolysis the ri�ing of the Red Sea and Gulf of Aden during a time GC data. This study is further extended to compare the of global sea-level fall where a maximum regression took compositional variations between oil and extract and isotopic place (about 34 Ma). variations between kerogen and pyrolysate. Results indicate that although TOC and rock-eval data show selective source (362-Poster) Micropaleontology and potential, other detailed analysis do not justify the inference. sedimentology of the Late Paleocene-Early Integration of the results indicate that the Makhul Formation Eocene Abat Formation of southeast Oman is a poor source even if it has sufficient organic carbon in selected horizons. A second study was conducted to identify Al-Harthy, Abdul Rahman (SQU – [email protected]) any prospective horizons within the Makhul Formation and Abdulrazak S. Al-Sayigh (SQU) using gas composition from mud log gas chromatogram. For this purpose an unconventional methodology–use of New micropaleontological data is presented for the we�ability of mud log gases–was used, and correlated Abat Formation of southeast Oman. The formation is of over the structures. The correlation was then validated with Late Paleocene to Early Eocene (Thanetian to Ypresian) proven hydrocarbon-bearing horizons in Minaghish field. in age. It comprises a thick (114 m) sequence of open A certain high percentage of we�ability of mud log gas marine, resedimented and basinal deposits. The base was chosen as a criteria for prospect identification. It was of the formation begins with thin interbeds of shales observed that the lower part of Makhul is prospective in and planktonic foraminiferal wackestones, which are selected areas in Kuwait. progressively overlain by resedimented algal and foraminiferal packstones and grainstones. The planktonic (360-Oral) The sedimentology of the upper foraminifera include Morozovella and Subbotina species, especially in the lower part. This lower part is in turn part of Musawa Formation: a Late Eocene overlain by an amalgamation of at least 17 m of graded intracontinental basin of eastern Oman limestone beds with sharp scoured contacts. The meter- scale limestone beds are made of stacks of at least six Al-Harthy, Abdul Rahman (SQU- [email protected]), Ali resedimented algal-dominated limestone beds with no S. Al-Rajhi (SQU) and Abdulrazak S. Al-Sayigh (SQU) shale interbeds. Towards the top of the formation, typical The upper Eocene succession of the southeastern Oman shallow-marine fauna are common, especially larger Mountains contains an exceptionally thick fluviodeltaic foraminifera such as Discocyclina, Daviesina, Miscellanea, siliciclastic sequence. The outcrops represent the upper Nummulites, Alveolina, Miscellanea, Assilina and Operculina part of the Musawa Formation and can be traced musawaensis nov. sp. together with smaller benthonic

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foraminifera including Lenticulina, Nodosaria, Glandulina, performed on prospect areas. Each area was interpreted Anomalinoides, and Pullenia are also present. Calcareous and the uphole location average velocities were contoured red algae together with echinoid plates and corals occur with appropriate parameters to reduce artifacts. All the sporadically throughout the upper part. The formation prospects were merged into one grid. Derivation of static unconformably overlies Maastrichtian sandstone turbidites corrections is from the ‘frozen’ model velocity grid. The grid of the Fayah Formation, and is conformably overlain by is sampled at the source and receiver coordinates. Given sandstones and conglomerates of the Musawa Formation the thickness from surface to datum, the static correction with which it interdigitates in its upper part. is calculated. Advantages of this method are: (1) speed, quick to produce model static corrections; (2) consistency, all static corrections are derived from a single model; and (115-Poster) Perseverance in stringers (3) ties, all 2-D and 3-D locations should have time horizons exploration: the Dafaq discovery at the same time. Problems occur when: (1) datum is above the surface; (2) weathering is below the datum; (3) rapidly Al-Hashimi, Rashid A. (PDO - rashid.raa.hashimi@pdo. changing near-surface velocity and inversion; and (4) co.om), Robert Gardham (PDO), Abdullah Al-Shamakhi under-sampled areas and shallow upholes. A common (PDO), Aida Al-Harthi (PDO), Jack Filbrandt (PDO), expression of a problem in a time section is a cycle skip, Hisham Al-Siyabi (PDO), Xavier Maasarani (PDO), Leon and other medium-wavelength effects that can be seen in Hoffman PDO( ) and Jean-Michel Larroque (PDO) the near offsets. A simple horizon-tracking approach is The Intrasalt Ara Group Carbonate Stringer play of used to overcome these short-wavelength problems on 2-D Neoproterozoic to Early Cambrian age is developed over lines. The shallow time horizon is tracked and moved to a large parts of the South Oman Salt Basin (SOSB). Six carbonate reference time. Caution has to be observed as the method cycles (A0C to A6C) have been identified and are correlated can be used to create or mend time structures. The concern on the basis of facies, paleogeography, chemostratigraphy over the legitimacy of moving time horizons and the and absolute age datings on volcanic tuffs. Oil and gas difficulty of applying the method to 3-D blocks lead to more discoveries have been made in several of these carbonate rigorous methods in deriving near-surface models. cycles, encased and sealed by Ara salt, across a variety of carbonate facies and pressure regimes. Well Ambrah-1 was (497-Oral) Integration of depositional, drilled in 1991 to target both the A3C and A2C stringers. The diagenetic and seismic tools to predict well was sidetracked down-dip a�er finding out that hole 1 reservoir quality of Khuff Formation in had been drilled through a fault zone. Ambrah-1H2 found a 10 m hydrocarbon-bearing pay zone only, in the A2C and eastern Saudi Arabia tight A3C. A detailed post-drill remapping of the area with Al-Jallal, Ibrahim (Saudi Aramco - [email protected] new pre-stack imaging-reprocessed 3-D seismic data has om) and Shiv N. Dasgupta (Saudi Aramco) revealed another potential fault zone separating the northern part of the A2C stringer (Dafaq area) from the part penetrated The Khuff Formation, a major source of gas in Saudi by AMB-1H1 and AMB-1H2. Furthermore, the borehole Arabia, was studied in detail both locally and regionally. image analysis derived from these two wells show the A2C The study shows how to use depositional and diagenetic is very highly deformed. Dafaq-1H1 was drilled in 2001 two tools from cores and logs integrated with seismic to kilometers down-dip of Ambrah-1H1 and H2, based on the predict reservoir extension around the wells. The seismic assumption that the fault separating Ambrah-1H2 and the waveform is calibrated at the well and can be used in other Dafaq area is sealing. Dafaq-1 found highly overpressured areas with no well control to estimate reservoir quality. The oil in the A2C, was tested in 2002 and produced at stable study explains how integrated analysis between multiple commercial rates. Dafaq oil has a low bubble pressure point disciplines in Geology and Geophysics can be achieved compared to its initial high reservoir pressure. The discovery The Khuff depositional se�ing was defined regionally, is currently being appraised by PDO and early production is lithostratigraphic units were correlated, major facies were planned for mid-2004. recognized, and anhydrite footage and average porosity were mapped. Areas of good reservoir potential around (46-Poster) Single-layer velocity model to the Gulf Area were defined. Sour gas areas were explained derive near-surface correction statics in and areas of poor reservoir facies were predicted. Locally, diagenetic and depositional tools were used to interpret Saudi Arabia good reservoir areas. Dolomitization in this example Al-Homaili, Mohammad A. (Saudi Aramco - mohammad enhanced the original porosity in grainstones and created [email protected]), Ralph Bridle (Saudi Aramco) and intercrystalline porosity, creating the best reservoir facies Robert E. Ley II (Saudi Aramco) in north Ghawar. Careful study of these features lead to the identification of a marine embayment or large Until 1994 upholes were drilled and logged every 4 km channels that brought saline water through the layers along 2-D seismic lines. Having acquired over 42,000 above, dolomitizing the rocks beneath. Other diagenetic upholes, the near-surface is generally well-sampled. The factors, including cementation by anhydrite or calcite and ‘frozen’ model is a single-layer velocity model from surface leaching, were defined and their destruction of porosity to datum. At uphole locations, the average velocity to datum and permeability were recognized and explained. Recently, is derived. For upholes that penetrate the datum, average seismic inverse modeling was done for the Khuff using the velocity is calculated from the depth and time to datum. recently acquired high-fold 3-D seismic data constrained Some upholes are shallow; in this case the last high velocity by the available petrophysical data from wells. The is extrapolated to datum. Creation of the ‘frozen’ model was computed seismic impedance and porosity from well

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logs and cores were plo�ed for the Khuff reservoirs and the recovery factor increased due to be�er understanding a good linear relationship was obtained. Analyses at well of fracture connectivity and recovery process; (2) STOIIP locations described above, have confirmed the usefulness uncertainty was be�er defined; (3) existing performance of the integration and the importance of 3-D seismic as a limitations related to current well completion and not to predictive tool if used carefully with well data. Careful reservoir productivity; (4) recommendation to stimulate examination of wells beneath channels, mentioned above, existing well resulted on increased production by 10 revealed a major difference in the acoustic impedance values fold at sustained reservoir pressure; (5) opportunity to between wells that are dolomitized with good porosity further development by drilling a new crestal well; and (6) and permeability, wells that are cemented by anhydrite recommendation to perform an interference test to reduce and wells that have moldic porosity with calcite cement. uncertainty on porosity and connectivity. Lower impedance matches the higher reservoir quality. The acoustic impedance a�ribute is mapped laterally around the well locations and in the interwell space. The (267-Oral) Wide-azimuth 3-D OBC seismic areal distribution of this seismic impedance provides an from acquisition to interpretation, offshore estimate of the regional porosity and permeability to find Abu Dhabi: a case study hidden reserves and could verify large Khuff reservoir potential both north and southeast of Ghawar. The future Al-Kaabi, Musabbah H. (ADNOC - [email protected]), challenge is to determine if these predicted good-reservoir Johan M. Wi�e (ADNOC), Omar A. Suwaina (ADNOC) areas contain hydrocarbons using other seismic tools, such and Atef Ebed (ADNOC) as AVO techniques. The examples explained in this study In the last few years, ADNOC has acquired several high- illustrate the procedure that was used and may be applied quality, wide-azimuth 3-D OBC seismic surveys. The for other reservoir predictions. main objectives were to address key exploration and development challenges like accurate structural imaging, (275-Oral) Al Kharrata field–a highly lateral variation in reservoir quality, contact identifications heterogeneous, tight fractured carbonate: and fracture analysis through pre- and post-stack analysis. data integration solving the puzzle This case study covers a wide range of challenges and achievements from survey planning to data interpretation. Al-Jeelani, Omar (ADCO – [email protected]), The selection of wide-azimuth patch geometry was the Stephen Bourne (Shell), Maria Boya Ferrero (Shell), result of an extensive and elaborate feasibility study. The Anna Dombrowski (Shell), Ahmed Khouri (ADCO), Jan survey was acquired with high geophysical parameters in Manoharan (Shell), Jürg Neidhardt (Shell), Pascal Richard terms of fold, offset and azimuth. Key challenges in data (PDO) and Ben Stephenson (Shell) processing included aliased energy along the receiver lines due to coarse sampling, multiple contamination The Al Kharrata field is probably one of the most lithologically and imaging of the deep Khuff and pre-Khuff reservoirs heterogeneous, intensely fractured reservoirs in the world. in a structurally complex area. To facilitate the structural The producing formation R’mah is unique as it can act as interpretation various noise reduction and coherence-type a source rock, a seal or a reservoir. The challenge of this filters were applied a�er migration. The final pre-stack study was to understand and develop a field that due to its time-migrated cube showed excellent imaging of the fractured nature, its low porosity and unusual mechanical radial faulting at the Lower Cretaceous Thamama level properties cannot be characterized by stand-alone standard and enabled interpretation of the linear fault pa�ern in techniques. It was crucial to approach the characterization the Palaeozoic clastic interval below. Seismic quality was in an integrated fashion. Prior to the study, despite 14 years deemed sufficient to carry out a detailed quantitative of production AKE STOIIP was poorly constrained, as data seismic reservoir characterization study, which was used from logs, core and production seemed contradictory. Two for selecting the location of an appraisal well. out of the four wells drilled failed to produce hydrocarbons. Lacking a generic model to explain good/bad well behavior further development of the field was hindered. The reservoir (73-Oral) 3-D Pre-stack depth migration on a model was developed from an integration of petrophysics, laptop: travel-time compression reservoir engineering and geology. It incorporated the results Al-Khalifah, Tariq A. (KACST - [email protected]) of the wells and an outcrop study in Syria, which observed an intimate relationship between fracturing-style and Now through the magic of compression, one can perform lithology. The model predicts that most of the STOIIP resides 3-D Kirchoff pre-stack migration on a laptop. Specifically, in two intensely fractured chert layers, which could not be travel-time table compression is key for the practical characterised by standard techniques such as logs, core and efficient implementation of pre-stack Kirchhoff 3- plugs or borehole images. Given the limited data set and the D migration. Kirchoff 3-D pre-stack migration requires heterogeneous nature of the reservoir, the unknowns greatly repeated access to a large travel-time table. Access to this exceed the constraints. Some of the uncertainty remains table implies either a memory intensive or I/O bounded unresolved. Therefore the approach taken was to capture solution to the storage problem. Travel-time tables in 3-D uncertainty by establishing discrete geologically plausible media are five-dimensional, resulting in files with sizes scenarios and assigning probabilities to their occurrence o�en exceeding 50 GB. Loading such files in memory for the based on the available data. This study provided a significant application of pre-stack migration is virtually impossible improvement in the understanding of the reservoir, which on many machines, resulting in slower implementations of led to recommendations on options for further development migrations based on continuous access of the computer’s and data gathering. In particular the study identified: (1) much slower hard-drive. Proper compression of the travel-

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time table allows us to efficiently perform 3-D pre-stack potential Haima/Huqf play concepts have been proven, migration. Such compression also allows for faster access these intervals are usually not specifically targeted and to desirable parts of the travel-time table and more accurate consequently, no economic volumes have been found to travel-time interpolation. The compression is applied to the date. This is to a large extent related to lack of good quality travel-time field for each source on the surface using 3-D seismic imaging of these intervals. Seismic data quality polynomial or cosine transforms. This allows for practical varies considerably due to the terrain conditions and compression up to and exceeding 20 to 1. Additional acquisition history. Sand dunes cover the western half of the compression is obtainable through bit-encoding methods area and the data quality suffers from statics problems. An in which we represent the typical 32-bit floating point extensive 2-D seismic grid, and some 3-D seismic surveys numbers by lower bits. Using travel-time compression we cover central Oman High. Most of the reflectivity below the managed to pre-stack 3-D migrate portions of the SEG/ Gharif lacks definition and suffers serious contamination EAGE salt model as well as portions of a 3-D image from of multiples. A 1998 2-D regional grid of long offset data the Middle East on a laptop. provides be�er resolution for the deeper strata, but it is still severely affected by multiple contamination below the Gharif. New reprocessing tests of the long-offset lines, (246-Poster) Sedimentology and including multiple a�enuation techniques based on pa�ern geostatistical modeling of Quwarah Member, recognition, like SUPERCHEAT and SPLAT applied at both Qasim Formation: Paleozoic sandstone pre- and post-stack stages, show that the imaging of the pre- reservoir outcrop analog, Saudi Arabia Gharif sequence can be improved significantly. Additional reprocessing tests are currently addressing the statics Al-Khalifah, Fadhel A. (KFUPM - [email protected]), and the ‘sand-dune’ effects. This improved data shows a Osman M. Abdullatif (KFUPM) and variety of steeper Haima structures below relatively flat Mohammad H. Makkawi (KFUPM) younger strata; dipmeter data support the steeper Haima geometries. Relatively weak steeper Haima reflectors can The increasing demands to maximize recovery from oil now be mapped with confidence as primary events, which and gas fields and recent technological advances have led has already helped to recognize additional (faulted-) dip to an increased application of reservoir characterization closures. Moreover, this improved seismic data provide a and qualitative geological modeling of rock properties. be�er grip on acoustic impedance contrasts in the Lower These techniques are limited in representing reservoir Haima, which possibly can be linked to reservoir- and heterogeneity in the subsurface. In contrast, surface outcrop seal-prone sections, which are clear from a review of analogs provide information about rock body dimensions, the available well data. Based on these results additional size, and orientation; and therefore new insights for reprocessing and seismic infill are now being considered. geological modeling, understanding and predicting the behavior of fluid flow in the reservoir. This study aims to establish from outcrop, a geological and petrophysical (180-Poster) Analysis of micro-seismic data model for the Quwarah sandstone in central and eastern and the b-value distribution in Yibal oil field Saudi Arabia. The model is intended to provide a database in northern Oman and enhance the understanding and prediction of the sandstone in the subsurface as a reservoir. The study was Al-Mahrooqi, Said S. (PDO - [email protected]), carried out at Qasim areas where the Quwarah Member of Ahmed Al-Abri (SQU), Issa Al-Hussain (SQU), Ali Al- the Middle to Late Ordovician Qasim Formation. The study Lazki (SQU), Harry Rynja (PDO) and Guy Mueller (PDO) includes field sedimentological facies analysis on outcrop sections, permeability measurements, and sample collection Micro-seismicity was monitored continuously by PDO in for petrographic analysis and porosity measurements from the Yibal field in northern Oman since September 1999, thin sections. The porosity and permeability data are used using a network of five seismographs. The temporal and in the quantitative reservoir model using geostatistical spatial distribution in the oil field and the b-value of the techniques. The analog model is expected to provide a micro-seismicity activity were examined to determine if be�er understanding of the reservoir heterogeneity, and a correlation exists between micro-seismicity, oil and gas have a significant impact on reservoir development and production, and water injection. In the Yibal field, oil is management strategy. produced from and water is injected into the Shu’aiba reservoir, and gas is produced from the Natih Formation. A total of 1,061 micro-seismic events were recorded between (135-Oral) Multiple elimination reveals new October 1999 and July 2002 with the largest magnitude of Deep Haima opportunities in northcentral 2.24 Ml occurring in June 2000. A b-value of 0.85 (± 0.033) Oman and a maximum possible magnitude of 3.15 were calculated for these seismic events. The b-value is consistent with b- Al-Lawati, Mohamed H. (PDO - mohamed.m.lawati@pdo. values calculated elsewhere for a fluid-dominated seismic co.om) and Pieter Spaak (PDO) system. The spatial distribution of b-values over the entire field was found to decrease away from its center. This could Exploration success in the Central Oman High has been be an indication of a rock with high pore pressure and an confined mainly to the Gharif sandstones and it isfrom ambient stress near the point of failure at the center of the this interval that the main Central Oman oil fields produce. field. The majority of events occurred between 700 to 1,100 The Mesozoic sequences are devoid of any hydrocarbons, m depth which is the depth of the Natih gas accumulation in while penetrations into the Haima and Huqf supergroups the field. The foci of a larger number of events occurred near are limited in number. Although the main ingredients for the gas producing wells, suggesting that micro-seismicities

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are induced by the gas production process more than oil to correspond to the transgressive sequence set (TSS) of production. Micro-seismicity locations migrate towards the a second-order supersequence that ranges from the top east northeast and in the upward direction with time. This Habshan Formations (upper Valanginian) to the base of trend matches the NE strike of the fault system beneath the the so-called ‘Lower Dense Zone’ of the Kharaib Formation field. It also suggests that the pressure wave front migrates (Barremian). The TSS is build by a third-order sequence northeast in the direction of preferred permeability. (uppermost Valanginian) that is composed by three fourth- order, high-frequency sequences, comprising three reservoir and three non-reservoir (dense) units. The uppermost high- (455-Oral) Discovery of a potential source frequency sequence, the focus of this study, can further be rock level within late Campanian Sawwaneh subdivided into five fi�h-order parasequences. Third- and Formation in Bardeh area, southern fourth-order sequence boundaries, fourth-order maximum Palmyride, central Syria: petroleum flooding surface, as well as fi�h-order flooding surfaces implications were identified in core material from wells of Abu Dhabi and tied to well logs. On the basis of sedimentary textures Al-Maleh, Ahmed K. (Damascus U - [email protected]), and sedimentary structures, as well as grain types, seven Francois Baudin (Pierre and Marie Curie U), Mikhail reservoir lithofacies and four non-reservoir (dense) lithofacies Mouty (Damascus U ), Youssef Radwan (AECS) and have been identified. The analyzed lithofacies range from Carla Muller (Consultant) open platform, middle ramp to restricted platform subtidal to intertidal environments. Bacinella/Lithocodium packstones The Rmah and Shiranish formations (Campanian- to floatstones, floatstones to rudstones, and boundstones, Maastrichtian) are proven source rocks in eastern and dominate the reservoir zone. Good reservoir quality is further northeastern Syrian (Euphrates Graben and Djezerah). The developed within skeletal, peloidal packstones to grainstones Sawwaneh Formation, Erk marl equivalent, defined in the and algal, skeletal rudstones. Intensively bioturbated Palmyride in the 1980s, lies above the upper Campanian wackestones and packstones, and interbedded argillaceous Rmah Formation and is overlain by the marly Maastrichtian- limestones characterize the ‘dense units’. Based on geological Lower Eocene Bardeh Formation. Generally, the Sawwaneh (lithofacies) and petrophysical (porosity/permeability Formation is marl-limestone of variable thickness (17-320 and mercury injection) data, five reservoir facies have m) with important facies changes, and local-enrichment been defined. Each reservoir facies shows deterioration of by phosphate. Detailed sedimentological and geochemical reservoir quality from crest towards flank position. Reservoir studies conducted in the last two years uncovered the deterioration is also observed directly below the sequence presence of a 10-m-thick black shale level at the top of the boundary (erosive surface) on top of the reservoir. Diagenesis Sawwaneh Formation in the Bardeh area, Southern Palmyride. (cementation and compaction) is interpreted to play a major It is clayey biomicrite rich in hyaline small benthonic role in reservoir quality distribution within the established foraminifera, with a matrix heavily impregnated by organic high-frequency sequence stratigraphic framework. ma�er with microscopic pyrite crystals. Coccolithes dated the entire formation as late Campanian and pin-pointed its boundaries with the Maastrichtian. The analysis of samples (178-Oral) Defining the main heterogeneities taken from this bituminous level confirmed a 25 percent within ADCO’s fields calcium carbonate content and 4.4 percent total organic carbon, with high hydrogen-index value (690 mg HC/gm Al-Maskari, Shamsa S. (ADCO - [email protected]) TOC) suggesting a type II organic ma�er. Temperatures of and Marie-Odile T. Bockel-Rebelle (ADCO) maximum Pyrolytic yield (Tmax) is of 423°C, indicating that Diffuse fracturing, for a number of years, has been understood the organic ma�er did not experience high temperatures to be one of the main heterogeneities within a great number during burial and are still immature with respect to oil- of the Middle East carbonate fields. However, diagnosis generation. However its total petroleum potential is good made on ADCO developed Cretaceous reservoirs weakened with 32 kg per ton of rock in average. The level’s petroleum this assumption. Using both available static understanding prospectivity should be considered through a regional (mainly core and borehole image log interpretation) and context in which the Sawwaneh Formation thickens north dynamic analysis (well tests, Production Logging Tool, and westward (Ad Daww Basin and Homs Depression) production histories), the diagnosis highlighted the fact that where it is buried beneath thick Maastrichtian-Neogene the dynamic impact of diffuse fracturing is never clearly sedimentary cover that may reach 2,000 m. observed. Therefore, this fact raised the need to adequately define the main heterogeneities within these reservoirs. In (205-Poster) Lower Thamama (Lower order to achieve such a goal, it is necessary to build a good Lekhwair Formation) sequence stratigraphy geological comprehension of the reservoirs, supported by and reservoir characterization (Lower sequence stratigraphy, diagenesis, and the latest knowledge in faulted/fractured reservoirs. Such defined heterogeneities Cretaceous, United Arab Emirates) will then be confronted to the dynamic data. Within ADCO’s Al-Mansoori, Abdullah I. (ADCO - [email protected]), fields, two major types of heterogeneities have been identified; Christian J. Strohmenger (ADCO) and these include: ‘high K streaks’, and/or large-scale vertical Ahmed Ghani (ADCO) objects (defined as seismic or sub-seismic faults and fracture corridors). The high K streaks, within the undeveloped ADCO Significant hydrocarbon accumulations have been found Cretaceous reservoirs, were studied using core, thin-sections, in the Lower Lekhwair Formation (Lower Thamama logs, and Mercury Injection Capillary Pressure (MICP) Group, Valanginian). The succession studied is interpreted data. The results indicated that these high K streaks are

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mainly products of diagenesis. As a result, bimodal porosity facies and reservoir quality. The characterization of pre- distribution was their strong character. Moreover, the nature Khuff clastic reservoirs requires integration of data and of the major porosity system, such as pore-throat and the knowledge from various types, and various scales of lateral extension of these streaks were found to greatly impact geological and geophysical properties. A major problem in their dynamic behavior. Prediction of their lateral extent is a mapping reservoir quality from seismic characters is that challenge that is owed to good geological understanding the continuity of seismic events is o�en weak. In order to and the availability of good production data. On the other overcome this problem, acoustic logs and VSPs from key hand, understanding faults and fractures within the ADCO wells were used to develop relationships between wells environment is essential to predict their distribution and and seismic characters. We a�empted to explore these characterize their dynamic impact. Thus, study of the faults relationships by using the learning ability of ANN. The and fracture corridors together with their associated damaged relationships learned using this approach were used to zone is currently ongoing, using well data, seismic a�ributes predict seismic characters for different seismic windows. analysis, analogs and dynamic synthesis. The different approaches ranged from unsupervised to supervised training methods, conducted over a constant seismic window to produce seismic facies and reservoir (320-Oral) Arabian Platform structural quality prediction maps. A new technology application growth and its impact on facies distributions of classifying seismic intervals parallel to a horizon based and hydrocarbon occurrence on the shape of the wiggle traces and its geological use was developed. Trace shape, in addition to other seismic Al-Qahtani, Abdelmu�aleb M. (Saudi Aramco - abdelm a�ributes such as reflection strength, phase and frequency u�[email protected]), Abdel G. Ahmed (Saudi is a fundamental property of the seismic data. Different Aramco), Pierre J. Van Laer (Saudi Aramco) and trace shapes are used to classify and map seismic facies. Tariq U. Usmani (Saudi Aramco)

The Arabian Platform has experienced about six major (317-Poster) Geological evaluation and tectonic events that are responsible for the development of wellbore stability of gas-bearing Barik reservoir facies and hydrocarbon accumulations throughout Sandstone reservoir: Saih Rawl field, Oman geological history. Recent 2-D/3-D seismic depth imaging and deep wells have enabled us to understand the growth Al-Raisi, Muatasam (Schlumberger - muatasam@musc history in the Arabian basins. These tectonic events were at.oilfield.slb.com), Ibrahim El-Moula PDO( ), Mayya the prime contributors to trap formation and evolution, Al-Rawahi (PDO), Paolo Giacon (PDO), Aimen Amer as well as reservoir development and hydrocarbon (Schlumberger) and Zed Al-Khathiry (Schlumberger) accumulation. The major tectonic events that affected the Arabian Platform are: (1) Precambrian extension event; (2) The Cambrian-Ordovician Barik Sandstone Member in Carboniferous or ‘Hercynian’ event, represented by regional northern Oman is one of the main gas reservoirs within tilt and compressional forces; (3 and 4) Permo-Triassic and the Haima Supergroup. The Barik Sandstone Member Triassic growth (Zagros Suture and the opening of Neo- comprises alternating, sharply-delineated sheets of Tethys Ocean); (5) Late Cretaceous (collisional event–First fluvial sandstone, shoreface sandstone, coastal sediments Alpine event) further enhanced the growth of older traps, and mudrock of overbank and marine deposits. Such inverted platform tilts and created new traps; and (6) variability in depositional environments and paleocurrent Middle to Late Tertiary growth (Red Sea opening and orientations resulted in deposition of laminated sandstone Second Alpine event) or Neogene NNE-dipping tilt that and shale intervals, some of which can not be recognized formed the final hydrocarbon traps of Arabian Platform on conventional open-hole log measurements. These structures. Major stability of the Arabian Platform led to the alternating sandstone and shale units have an impact on accumulation of thick carbonate reservoirs and platform- hydrocarbon production and borehole stability. This study wide anhydrites that made it favorable to form different integrates conventional core measurements with borehole plays. Several of these tectonic events had substantial images, dipole shear and nuclear magnetic resonance to contributions to the facies distribution, trap creation, be�er understand variation in reservoir quality and to be�er modification and hydrocarbon migration. Geoseismic and diagnose borehole stability issues. Detailed analyses shows isopach maps in combination with the basin history and that image logs can be used to successfully resolve many source rocks maturity elucidate the multi-phase generation of the sedimentological features identifiable in core. A total and migration of hydrocarbons in the Arabian Basins. of six key image facies are recognized and these may be rationalized into a genetic element scheme (similar to that applied to the core). A neural network technique was used (322-Poster) Application of neural networks to predict the vertical occurrence of different lithotypes in a to predict pre-Khuff seismic facies in given well. The cross-bedded facies exhibit the best porosity Eastern Saudi Arabia and permeability and reveals fluvial channels deposits. Both compressive wellbore failures (wellbore breakouts) Al-Qahtani, Abdul Motaleb M. (Saudi Aramco - abdelm and tensile failure were observed in the images and used u�[email protected]), Riyadh S. Al-Saad (Saudi to estimate near-wellbore stress orientations. Most of Aramco) and Husam M. Mustafa (Saudi Aramco) shear failure seems to be occurring near bed boundaries. Determining reservoir quality sand intervals, wellbore Recent applications of Artificial Neural Networks (ANN) conditions and local variability in the stress orientations are to seismic studies have demonstrated its effectiveness in very important in the field hydro-fracture completions and prediction, estimation, and characterization of seismic pressure point selections.

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(129-Oral) The Rabab, Sakhiya, Zalzala be resolved by high-resolution measurements. The base of ‘stringer’ discoveries of South Oman, one each cycle represents coarse-grained sediments with high large field? permeability streaks, which has direct implication on field development plans. An a�empt was made to detect this Al-Rawahi, Saada (PDO –[email protected]), cyclicity from image logs to aid the correlations in un-cored Jean-Micheal Larroque (PDO), Rashid Al-Hashmi (PDO), wells. Other factors that contribute to heterogeneity of the Khairan Al-Mauly (PDO), Robert Gardham (PDO), carbonate reservoirs include cementation, mouldic porosity Hisham Al-Siyabi (PDO), Mark Newall (PDO), Fahar Al- and leached-out rudist shells, bioclasts and algae. In the Rabeei (PDO), Joao Rodrigues (PDO) image logs these features are identified and quantified as and Nadia Al-Abry (PDO) resistive and conductive anomalies. Through this analysis the macro-porosity system can be quantified and discriminated The Neoproterozoic to Early Cambrian, Intrasalt Ara Group as primary and secondary porosity and pore-size effects on Carbonate Stringer Play is developed over a large part permeability can be be�er defined as a continuous curve. of the South Oman Salt Basin. Six carbonate cycles have This study illustrates a methodology to quantify vuggy and been identified and are correlated on the basis of facies, cemented texture of the carbonate rocks at a resolution that is paleogeography, chemostratigraphy and absolute age the closest to actual core scale. datings on volcanic tuffs. Oil and gas discoveries have been made in several of these carbonate cycles, across a variety of (416-Oral) Application of PSDM/Tomography carbonate facies and pressure regimes, encased and sealed by Ara salt. The Zalzala, Sakhiya and Rabab discoveries, for modeling near-surface velocity exhibiting homogeneous reservoir properties and hydrostatic Al-Rowaili, Turki Z. (Saudi Aramco - turki.rowaili@aramc pressures, contain some significant volumes of oil and gas in o.com) and Alex Litvin (Paradigm) a single carbonate cycle – the A2C platform. This carbonate platform was initially explored by targeting seismically In Saudi Arabia, complex surface topographic features such different prospects disconnected by fault zones and/or as escarpments, sand dunes, and wadis, strongly affect poorly imaged data zones. The exploration and appraisal structural information on the deeper seismic section. The drilling of these prospects followed by detailed geological main objective of this study was to estimate the near-surface studies and improvements in seismic processing suggest velocity via pre-stack depth imaging (PSDM) workflow. The that the Zalzala, Sakhiya and Rabab discoveries were once workflow was applied to high-density 2-D data and included a single hydrocarbon accumulation. This accumulation was a tomographic velocity inversion procedure to reveal more subsequently segmented into three blocks. PVT data are still realistic subsurface images. The initial velocity model for consistent with one continuous hydrocarbon column. This PSDM was derived via a coherency-inversion approach. model explains the unexpected discovery of gas in Rabab, Ray-tracing was performed from a buried reflector to the and if known upfront, would have affected the exploration smoothed version of the actual topography for best-fi�ing strategy of the area. PDO has now started early development the picked travel-time. A�er the PSDM main flow, residual of the recently discovered accumulations with first production moveout of the depth-imaged gathers was analyzed for planned in early 2004. This development phase will test the key horizons with a tomographic inversion procedure to feasibility of gas injection to maximize oil and condensate refine the initial velocity model. PSDM with tomography recovery in these challenging reservoirs. inversion clearly reduces apparent pull-down structures due to thickening from outcrops and sand dunes. These velocity (218-Oral) Lithology and heterogeneity corrections lead to a more realistic (geologic) subsurface quantification from image logs and core: image for interpretation. implications in carbonate reservoir, offshore oil field, Abu Dhabi (136-Oral) East-Ghaba Basin: unlocking Haima Supergroup potential Al-Rougha, Hamad Bu (Zadco - [email protected]), Hedhili B.M. Gossa (Zadco), Muatasam H. Al-Raisi Al-Sadi, Yaqoob M. (PDO - [email protected]), (Schlumberger), Toshiaki Shibasaki (Zadco), Ishtiaq A.K. Omar S. Al-Jaaidi (PDO, currently JVR Centre for Jadoon (Schlumberger) and Carbonate Studies) and Pieter Spaak (PDO) Sandeep Chakravorty (Schlumberger) The Ghaba Salt Basin lies east of North Oman’s major gas Most of the carbonate reservoirs in offshore Abu Dhabi are fields and was considered to form a major boundary for characterized by complex textural heterogeneity that requires deep (Haima) charge. Although several large prospects high-resolution log data, such as borehole image logs. This were identified on the eastern basin flank, results of earlier textural heterogeneity corresponds to extreme permeability hydrocarbon modeling pointed to a major charge risk. variation that is the controlling factor in reservoir production. As a consequence, exploration activities were minimized. This study illustrates an approach to improve the carbonate The hydrocarbon modeling documented two phases of reservoir characterization of an offshore oil field in Abu hydrocarbon generation. An early (Ordovician) oil charge Dhabi, by quantifying small-scale heterogeneity using was expelled during deposition of the Haima Supergroup borehole image logs and core measurements. The reservoir from deeper, central parts of the Basin from pre-, intra and under study ranges from mud-supported to grain-supported post-salt source rocks. During this phase, hydrocarbons rocks with variable grain sorting and cementation. Detail core migrated onto the basin flanks where most present-day analysis indicates the presence of small-scale, fining-upwards Haima closures were not yet formed. A second Late Jurassic cycles in the order of 0.5–5 � thick, some of which can only phase occurred a�er formation of major Haima structures,

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and is linked to the charge of Oman’s large gas fields. This stratigraphic sequence of the Partitioned Neutral Zone second charge is thought to have originated from shallower (PNZ), Kuwait and Saudi Arabia. The Neocomian Ratawi Ara salt pockets, on the basin flanks, going through the Formation of the Thamama Group in the PNZ is divided gas generation window. These so-called ‘rim basins’ were into three sequences: (1) lower Ratawi Oolite; (2) middle only recognized from 3-D seismic on the western basin Ratawi Limestone; and (3) upper Ratawi Shale. The South flank. Their distribution, combined with overall upli� Umm Gudair field produces from a thick oil column of the of East Oman during late Paleozoic and early Mesozoic, Lower Cretaceous Valanginian Ratawi Oolite reservoir, significantly increased charge risk east of the basin axis. following its discovery in 1966. The Hauterivian Ratawi Several disappointing exploration wells have been drilled on Shale Member is 350 � thick and lies 500 � above the the eastern flank of the Ghaba Salt Basin. Lack of success was mature oolite reservoir. Distinctive sandstone streaks generally a�ributed to lack of charge. However, a number of were identified within this Ratawi Shale Member. The these wells have proven hydrocarbon shows, and recent 3-D average thickness of these sandstone stringers is about remapping revealed the existence of several new ‘rim basins’ 10 �. An integrated approach involving detailed log and located on the eastern basin flank which may have provided petrophysical analyses from old and modern log suites, local gas charge. Geochemical analysis and basin modeling together with geologic data interpretation, indicated the has been initiated to review the regional charge and migration Ratawi Sand was deposited both in a very shallow-marine history of North Oman. It is planned to drill a deep well to test environment (regressive shoreline) and as channel sand this local charge concept. during the Hauterivian lowstand system tract (LST). Delineation of the main axis of the channel was the challenge for reservoir prospectivity. The main axis of the (490-Oral) Connectivity between the Ghazal channel was observed to be more than 50 � thick and to run and Mazalij fields, Saudi Arabia in a NW direction, diagonal to the main axis of the South Umm Gudair field Ratawi structure. A�er perforating 6 � Al-Saggaf, Muhammad M. (Saudi Aramco - muhammad.s of the channel sand, the discovery well flowed clean and [email protected]) and low-sulphur oil at a very good rate. The provenance of the Ma�er J. Al-Shammery (Saudi Aramco) Ratawi Sand is from the southeast. It is a pure stratigraphic The target reservoir of the Ghazal and Mazalij fields is the trap that is unrelated to the main structure of the field. Paleozoic Unayzah Formation. The Mazalij gas reservoir This channel sand exhibits fining-upwards sedimentation. was discovered in 2000, on the down-thrown block of a The highstand system tract (HST) of the lower part of succession of faults that separate it from the crestal area of the Ratawi Shale was eroded by an incised valley that the field, where the reservoir was missing. The Ghazal field sculptured, scoured and formed the NW-running trend of was also discovered in 2000, where it encountered a thick the main channel, which was subsequently filled during the Unayzah reservoir with excellent sand quality. The two transgressive system tract (TST) with mixed clastic Ratawi fields were initially thought to be disconnected. However, Sand facies. On top of the channel sand, the maximum several pieces of evidence (including depositional growth, flooding surface (MFS) of the Ratawi Shale represents structural depth, pressure regimes, and geochemical a very good, distinctive correlation marker. The MFS is analysis), which are discussed in this study, indicated considered as the main vertical seal above the Ratawi that the fields may be connected. A delineation well was Sand. A localized unconformity is observed at the base of proposed to test the connectivity between the two fields. the Ratawi Sand main channel that reflects its scouring In order to select the optimal location for the well, accurate nature and the intensity of erosional effects of the Ratawi depth maps of the entire Ghazal/Mazalij region were Sand tepees into the lower Ratawi Shale and Limestone produced. The goal was to generate not only a map of the clinoform. More geologic data is required to delineate depth structure of the Unayzah, but also maps of the depth the southeastern extension of the discovery reservoir, and isopach structures of all key layers in this region. This is outside the current boundary of the field. Similar studies, vital to understanding the growth structure of the reservoir utilizing the proposed geologic model, are recommended and to obtaining a good assessment of the depositional elsewhere in the PNZ for the delineation of the Ratawi Sand environment in this area. The location of the delineation reservoir. well was selected on the saddle between Ghazal and Mazalij in order to directly se�le the issue of the connectivity of (12-Oral) Humma Marrat oil field, a unique the two fields with a high degree of confidence, andto Jurassic reservoir in the PNZ, Kuwait and afford a much more accurate assessment of the reservoir Saudi Arabia compartmentalization in this region. The results of this well helped confirm the connectivity between the two fields. Al-Shaarawy, Osama A. (KOC-JO - [email protected]), Jim D. Ming (SAT-JO), David L. Barge (SAT-JO) (11-Poster) The Ratawi Sand, a newly- and Ali S. Abul-Hassan (KOC-JO) discovered stratigraphic reservoir in the The Humma oil field is situated in the southwestern corner mature South Umm Gudair field, PNZ, of the Partitioned Neutral Zone (PNZ), between Kuwait and Kuwait and Saudi Arabia Saudi Arabia. It is the only Jurassic producer in the PNZ. It was discovered in 1998 following several unsuccessful wells Al-Shaarawy, Osama A. (KOC-JO - [email protected]) targeting Cretaceous reservoirs beginning in the 1950s. An and David L. Barge (SAT-JO) integrated approach utilizing 3-D seismic interpretation, oriented core data, open hole and borehole image logs, The Lower Cretaceous Ratawi Sand is a newly discovered CMR (Combinable Magnetic Resonance), ECS (Elemental reservoir introduced herein for the first time to the

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Capture Spectroscopy), and Stonely Permeability (DSI) by exploration drilling with discouraging results. This is data was used for the evaluation and understanding of the despite evidence for adequate reservoir quality, trapping complexity of the Jurassic Marrat reservoirs in the field. The and hydrocarbon migration pathways. In northeast Abu structural configuration of the field is an elongated NW- Dhabi (Al Dabbiya/Rumaitha and Arjan areas), this complex plunging anticlinal feature with steeply-dipping flanks. has been covered by 3-D seismic (3,340 sq km) which has The structural closure of the field was produced from a subsequently been reprocessed for be�er imaging of the shear couple that culminated during the Early Cretaceous Habshan sequences. Clinoforms of the Habshan Sequence-1 and continued through the Late Cretaceous. The simple are readily recognizable from seismic data, and a four-way shear tectonic model applied to the Humma field is well structural closure was mapped with the ooid grainstone expressed by a flower structure associated with both shoal as the main target. These grainstones show higher the Jurassic Marrat and Cretaceous Shu’aiba formations seismic amplitude compared with the lagoonal part of the as interpreted from the 3-D seismic, oriented core, and sequence. However, the observed amplitude changes and borehole image log data. This tectonic model may have the brightening on the seismic do not indicate the presence analogs elsewhere in the Gulf Region. The complexity of hydrocarbons. The four-way structural closure is of the Marrat reservoirs is a�ributed to the rapid change considered as a high-risk exploration target. Our sequence in facies from the north to the south, as well as from the stratigraphic model indicates that the shoal complex of base to the top of the Marrat reservoir units. The Lower each sequence is overlain by the shallow intertidal and Marrat succession comprises two overall cleaning-upward logoonal deposits of the younger sequences. Therefore, the cycles of packstones with anhydrite streaks. Depositional existence of laterally continuous and competent seals above environments are predominantly low energy inner shelf the shoal complex is unlikely. Accordingly, hydrocarbons (inner ramp to lagoonal) se�ings. The evaporites at the top will migrate freely upwards and charge more competently appear to be penecontemporaneous with the dolomitized sealed traps. limestone. Hydrocarbon potential for the Lower Marrat reservoir is confined largely to dolomitized sediments. These possess a combination of intercrystalline and moldic (461-Poster) Petrophysical and geochemical porosity with local fracture to breccia porosity. The Upper identification of the heavy oil/tar in clastic Marrat reservoirs are composed of a stacked succession reservoir, Saudi Arabia of individual and overall shallowing-upward cycles. Deposition was in a protected sub-tidal, open-shelf lagoon Al-Shobaili, Yousif M. (Saudi Aramco - yousef.shobaili@ar to largely filled intrashelf basin as part of a progradational amco.com), Edward A. Clerke (Saudi Aramco), parasequence set. Open fractures of massive dolomite Henry Halpern (Saudi Aramco) matrix is the target for the Middle Marrat reservoirs. The and Peter J. Jones (Saudi Aramco) understanding of the Jurassic Marrat reservoir in the Areal and vertical distributions of the heavy oil (tar) Humma field is required prior to drilling delineation wells. zone within the reservoir is important in designing well The last well drilled in the field has been naturally flowing completions, optimizing field development and enhancing at a very good rate since early 2002. The development reservoir modeling and simulation. The purpose of plan for the Humma field will include the drilling of both this study is to provide petrophysical and geochemical vertical and deviated wells. guidelines for a heavy oil (tar) case study, and to summarize our experiences in the execution of the petrophysical and (33-Oral) Hydrocarbon potential assessment geochemical analysis. The petrophysical investigation of of the Habshan Sequence-1 shoal complex, a heavy oil (tar) interval started with an inventory of the northeast Abu Dhabi, United Arab Emirates physical property variations found within the heavy oil (tar) in a clastic reservoir and evaluating the impact of these Al-Shekaili, Fatema (ADCO - [email protected]), variations on the formation’s petrophysical and geochemical Azhari Abdalla (ADCO), Abdullah Al-Aidarous (ADCO) data. Next our study looked at the indicators of tar presence and Christian J. Strohmenger (ADCO) in core description, core plugs, capillary pressure data and core geochemical data. From the wireline log data, we Integrated seismic interpretation and sequence stratigraphic analyzed well logs, formation pressures, PNL data, and analyses were used to assess the hydrocarbon potential of test data for the clastic reservoir. The goal of the study was an ooid shoal complex within the Habshan Formation. The to identify, characterize and map the distribution of the Habshan Formation (uppermost Tithonian to Valangenian) heavy oil within the clastic reservoir, and to understand is the lowermost member of the Thamama Group. It is the hydrocarbon mobility within this zone. Certain composed of several relatively thin reservoir units engulfed geochemical pyrolytic techniques were developed at Saudi in a thicker mud-dominated successions. The Habshan Aramco and are highly useful for reservoir characterization Formation comprises two second-order supersequences, and heavy oil tar zone identification. Parameters derived which can be further subdivided into five third-order include Pyrolytic Oil Productivity Index (POPI) that is sequences. Depositional environments within each used to determine productive intervals in oil reservoirs and sequence range from lagoonal and shallow intertidal in the Apparent Water Saturation (ASW), which gives an estimate west, to slope and deep-marine in the east. Best reservoir of the water saturation in the pore space based only on the quality is developed within the eastward prograding pyrolytic data. In addition, an estimate of the API gravity ooid shoal complex of each sequence. The shoal complex of the oil-in-place is possible. Finally, a Compositional of Habshan Sequence-1 has been targeted several times Modeling program (CoMod) was wri�en, whereby complex reservoirs can be assessed.

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(5-Oral) Estimation of thickness in a sand time gaps), that rapidly pinch out onto the Hadramawt dune with a vertical velocity profile Arch. During the late Paleozoic to the early Mesozoic times, the trends of the basement rocks were oriented NS, Al-Shuhail, Abdullatif A. (KFUPM - NW, NE, and subordinately EW. These trends influenced [email protected]) interbasins ri�ing directions or elevated upli�/high regions, as differing stress fields built-up during various phases of Previous field and mathematical studies have shown Gondwana fragmentation. However, the Mesozoic basins that sand dunes may have vertical velocity profiles (i.e. vary spatially and temporally from the west to the east continuous increase of velocity with depth). Therefore, of the country. Widespread sedimentary deposition over computing the dune’s thickness using conventional seismic most of Yemen (except for the persistent paleoupli�s and refraction methods that assume a vertically homogeneous highs) took place from the Early Jurassic and continued layer will likely produce some errors. The purpose of this with only short, relatively local interruptions into the late study was to quantify the effect of the vertical velocity Paleogene. During the Late Jurassic to the Early Cretaceous profile in a sand dune on the process of thickness estimation the ancient NW-trending Najd faults were rejuvenated, using seismic refraction data. First, the time-distance (T-X) with final separation of the Arabian and African plates in data of the direct wave in the dune is calculated using a the Neogene along ENE (Gulf of Aden) and NNW (Red vertical velocity profile V(z), derived from Hertz-Mindlin Sea) trends. The sedimentary cover of the Mesozoic and contact theory. Then, the thickness is estimated from the Cenozoic basins shows lateral and vertical facies variations calculated T-X data, intercept time, and velocity of the from fully marine to terrestrial. refractor at the dune’s base assuming a constant velocity in the dune. The error in the estimated thickness due to the constant-velocity assumption increases with increasing (252-Oral) Pre-stack depth migration through thickness and decreasing porosity of the dune. For sand deep salt dunes with porosities greater than 0.2 and thicknesses less than 200 m, the error is less than 14 percent. Al-Yarubi, Saeed A. (PDO - [email protected]) and Uwe Asmussen (PDO)

(81-Oral) The Phanerozoic geology of Yemen The South Oman Ara Salt Basin lies in the Block 6 concession held by PDO. This Cambrian salt basin is explored for Al-Thour, Khalid A. (Sana’a U - [email protected]) intrasalt carbonate stringers. The Stringer play is actively supported by the acquisition and processing of 3-D seismic Using extensive surface and subsurface data, the Phanerozoic surveys. Complex salt domes with steep flanks, sometimes geology of Yemen was synthesized in this study. The results associated with salt overhangs, are very challenging to have important implications for the tectonic evolution of the imaging of deep intrasalt carbonate stringers targets. southern Arabia and hydrocarbon exploration strategies. The main seismic processing challenges are to image The tectonic deformation of Yemen is focused in five major the continuity, correct positioning, and fault pa�erns of sectors that have been repeatedly reactivated throughout these stringers. Pre-Stack Depth Migration (Pre-SDM) has the Phanerozoic in response to movement on nearby plate greatly helped to resolve some of these challenges. For boundaries. They are: (1) Tihama Plain including the Red example, imaging of steep salt flanks and the definition Sea; (2) Western Highland Triangle; (3) Rub’ Al-Khali of fault pa�erns across existing stringer discoveries has Desert (Empty Quarter); (4) Eastern Highland Rectangle; significantly improved. PDO has a dedicated Pre-SDM and (5) Southern Plain including the Socotra Archipelago. team working for the stringer exploration and development These sectors show the main Phanerozoic sedimentary and sufficient inhouse computing power to run projects basins and interbasinal upli�s in Yemen. Most basins, exceeding one thousand square kilometers of Pre-SDM however, are broken up into a varying number of sub- output area. Until recently, Prestack Time Migration was basins and separating highs in consequence to the response the standard processing product that was supplied for to initial and subsequent ri�ing phases and/or to horizontal seismic interpretation. However, it was realized that Pre- movements along bordering master faults with resultant SDM provides a more robust approach, less sensitive to transpressional and transtensional adjustments along velocity picking. The Pre-SDM technique is gaining ground different sectors. The geological history of Yemen has been with the development and maturation of the stringer play reconstructed by combining the vast amounts of integrated and is close to becoming a standard seismic product. and detailed geophysical and geological data of the major basins with tectonic and lithostratigraphic analyses from the remainder of the country. Specific deformation episodes (108-Oral) An integrated subsurface model were penecontemporaneous with regional plate tectonic of the Amin Formation in the context of the events. Sedimentation commenced in the infra-Cambrian Kauther field cluster development in North but li�le remains of these or of Paleozoic deposits in outcrop Oman except for what is preserved in fault-bounded small basins along the Gulf of Aden border, or the northern part of the Al-Zadjali, Ibrahim (PDO – [email protected]), western highland triangle. Paleozoic sediments have been John A. Millson (PDO) and Mark Li�le (PDO) encountered in the subsurface only in: (1) the northwestern part of the country; (2) within the Saba’tayn Basin (in Wadi Recent exploration activities in the northeast Afar area Al Jawf-Marib Basin); and (3) along the southern flank of of PDO Concession Block 6 have resulted in significant the Rub’ Al-Khali Basin. They consist mainly of coarse hydrocarbon discoveries in the Kauther Cluster. clastics with several major unconformities (representing Accumulations contain wet gas in continental reservoirs of

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the Cambrian Amin Formation at about 4,000 meters below (441-Oral) Optimal technique in imaging sea level. In the cluster, substantial gas-initially-in-place deep salt structures (GIIP) has been booked from the Kauther-1 well results, and there is scope for more to be booked from the subsequent Amarasinghe, Diwin (Saudi Aramco - diwin.amarasingh Harmal-1 and Fakhr-1 wells. An active drilling, testing and [email protected]), Hashim A. Hussein (Saudi Aramco) and study program for the cluster is currently underway to Dwight Gustafson (Saudi Aramco) define robust volumes GIIP and Ultimate Reserves (UR), and to provide input into a field development program The validation of relatively shallow low-relief structures with first gas production planned in 2007. With limited on seismic sections is a difficult task in areas of complex time available for stepwise appraisal activities, studies near-surface geology and topography such as those in and uncertainty management form key components of Saudi Arabia. The deep salt can be optimally imaged this work program. Depositional and structural modeling and structurally correlated with shallower horizons, thus of the discoveries utilizes a workflow developed for minimizing the risk of discarding potential structural previous activities calibrating outcrops to subsurface (well, reservoirs as long wavelength static anomalies. With the seismic, fields) to ensure all data are fully integrated. An recent advances in the seismic processing technology, and improved understanding of the Amin reservoir is being increase in computer resources, pre-stack time migration incorporated in static reservoir modeling for the cluster to (PSTM) can now be routinely performed on recorded improve understanding of in-place hydrocarbon volume time that can even exceed 5 seconds. Also, the design and distribution, recoverable volumes, and hydrocarbon types. acquisition of composite sparse 3-D surveys developed by Elements of the work may facilitate a be�er understanding Saudi Aramco, provide wide-azimuthal coverage and a of remaining exploration and appraisal opportunities in relatively higher fold, because of the increased number of North Oman. far-offset traces by design. In processing, these a�ributes contribute to be�er a�enuation of multiples, as well as linear and random noise. With deep far-offset data being (452-Poster ) Dip/Azimuth attribute as a tool less sensitive to velocities, they are used to produce a more to map structures reliable static solution. Be�er statics and less noise obviously help in picking be�er velocities for PSTM which, in turn, Al-Zahrani, Mohammed S. (Saudi Aramco - mohamme reduces the noise and optimally delineates the geometry of [email protected]), Stephen Bremkamp (Saudi deep salt reflectors. The far offsets allow the use of large Aramco) and Bhoopal Naini (Saudi Aramco) migration apertures in PSTM which also contributes to The South Ghawar 3-D encompasses an area of the same imaging goal. Furthermore, we incorporated approximately 20,000 sq km and as such is one of the gravity data as a spatial constraint in order to verify the largest land 3-D dataset globally. Within South Ghawar and presence, or absence of salt domes. This study shows a surrounding areas, the Triassic Mid-Jilh gives rise to the case history, where the above procedures are implemented. strongest of all seismic reflections in the entire stratigraphic The data example belongs to the Quwaysim area of Saudi section. This reflection results due to the encasement Arabia, which, as interpreted from our seismic data, is now of shales, overpressured in part within predominantly characterized as having deep salt buildups. dolomite/anhydrite section. Seismic a�ribute ‘dip-azimuth’ analysis of the Mid-Jilh reflector yields a coherent and (279-Oral) Fracture and in-situ stress complex pa�ern of linear to sub-linear trends. Detailed characterization of the Unayzah Reservoir, structural analysis of the area shows a one-on-one Wudayhi field: an integrated approach relationship between the seismic a�ribute derived lineations and the ‘Hercynian’ structures located within the Ameen, Mohammed S. (Saudi Aramco - mohammed.am deeper stratigraphic section. Some of these faults extend as [email protected]), Khalid A. Al-Hawas (Saudi Aramco), far up the section as the Permian-Carboniferous Unayzah Mohammad Wahab (Saudi Aramco), Edgardo L. Nebrija Formation. Very rarely do some of these faults propagate (Saudi Aramco), Faisal Al-Thawad (Saudi Aramco) and up to and above the Jilh Formation. Since seismic data in Colin Macbeth (Heriot-Wa� U) the pre-Khuff section tends to be of poorer quality due to the presence of noise and embedded interbred multiples, it The Wudayhi field was discovered in Saudi Arabia in is difficult to map the pre-Khuff structures unambiguously. 1998, with gas reserves in the Unayzah clastics (Upper We demonstrate that the a�ribute dip-azimuth computed Carboniferous-Lower Permian). Well tests indicate that over the Mid-Jilh reflector is a quick tool that can be used production rates and levels cannot be explained solely by by the interpreters to generate regional fault-trend maps. matrix porosity. It is therefore assumed that fractures are Recognition of the fault trends provides valuable insights present and essential to production, particularly in the into the location of potential closures, vertical hydrocarbon lower section of the reservoir. In addition, borehole stability migration conduits and regions of fracture-enhanced is an issue in the Unayzah reservoir. Thus an optimal reservoirs. A regional structural interpretation based on the development necessitates field-scale characterization of dip-azimuth analysis is presented for the first time. fractures and in-situ stresses in the reservoir. Geological characterization using core and borehole images from key wells indicate the occurrence of open micro-fractures. These occur mainly in the lower part of Unayzah (Unayzah-

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B). The fractures in the Unayzah-B have two dominant (37-Oral) Integrated fracture characterization sets trending ENE and ESE, respectively. Insitu stress using calibrated seismic data characterization shows that the maximum horizontal in-situ stress trends at EW to ENE direction, nearly parallel to the Angerer, Erika (CGG - [email protected]), Pierre ENE-trending fracture set. To detect field-scale distribution Lanfranchi (CGG), Xin-Quan Ma (vsfusion) and pa�erns of the open fractures and the in-situ stresses, and Stephen F. Rogers (Golder) we applied azimuthal seismic. Wide-azimuth 3-D seismic data is processed and interpreted to detect the azimuthal Reliable sub-seismic scale fracture characterization requires signature in the reservoir, covering the Unayzah-A and the a consistent workflow including wide-azimuth acquisition Unayzah-B. Sweet spots of high anisotropy are detected. of surface and VSP data, calibrated data pre-conditioning, These spots show good agreement with the borehole-scale robust a�ribute generation, and analysis of fracture-related observations on fracture density and in-situ stress pa�ern. azimuthal anisotropic effects. Using surface seismic and Furthermore it is supported by well test analysis. VSP data examples, we present an innovative workflow of which the main characteristic features conmsist of three steps. The first step involves an ‘azimuth-friendly’, pre- (305-Oral) Integrated reservoir modeling of processing sequence that produces amplitude preserved a complex carbonate reservoir, Al Huwaisah azimuth sectored images. A geostatistical method is applied field, North Oman to decompose the data into: (1) a ‘geological’ common part, (2) the anisotropic signal, and (3) noise. VSP data helps to Amthor, Joachim (PDO - [email protected]), correct for true amplitudes and refine velocity models. It Huw A. Davies (PDO), John Keating (PDO), Mohammed also provides independent measurements of azimuthal Al-Mughairy (PDO) and Charles Kerans (U Texas) anisotropy and hence fracture properties, which are used to calibrate surface seismic estimates. The second step consists The billion barrel Al Huwaisah oil field is a large, faulted of n azimuth-dependent, 3-D stratigraphic inversion dip-closure with locally significant fracture swarms, which where we apply a layer-based inversion technique to each produces from heterogeneous rudist-dominated limestones azimuth sector. In order to ensure an overall consistency, of the Aptian Shu’aiba Formation. It is the most complex field the same initial model is used for all sectors. The 3-D nature within the Shu’aiba of Oman in terms of facies distribution, of the algorithm produces a set of impedances that are stratal geometry and flow unit architecture, which is more robust and accurate than conventional AVO-based reflected in the historical well and field performance. To a�ributes. The third step is an impedance ellipse-fi�ing address the key uncertainties for long-term development of procedure, calculating fracture intensity and orientation the Al Huwaisah field beyond its primary depletion phase, models. This information is subsequently integrated into an integrated modeling approach was adopted. Improved a layer-based Discrete Fracture Network (DFN) model. 3-D seismic definition resulted in: (1) a reduction in top The DFN approach allows the validation of the static reservoir uncertainty; (2) improved imaging of faults and model, through the simulated sampling of well fracture fractures; and (3) improvement in imaging the depositional intersections. Furthermore, it provides an environment geometry through the use of seismic facies and a�ribute for simulating pressure transient responses and a route to analysis. Integration of 3-D seismic data with extensive upscaling grid cell permeabilities. borehole image log data led to the development of a fault/ fracture model which greatly improved the understanding of the water movements in the field. Interpretation of the (59-Poster) Dolomitization of the subsurface complex reservoir architecture is based on the integration Asmari Formation (Oligocene-Lower of seismic and well data (cores, high-resolution image Miocene), SW Iran: suggested models and logs, dipmeter and conventional open-hole logs) with the reservoir quality controls available production performance data. Outcrop data and field analogs were reviewed and integrated into alternative Aqrawi, Adnan A.M. (Statoil - [email protected]), geological models to account for the complex reservoir Mohammad Keramati (NIOC), Neil Pickard (CCL), architecture. To address the range of uncertainty in Gillian Darke (Statoil), Ali Moallemi (NIOC) reservoir architecture and to allow planning of uncertainty and Tore Svånå (Statoil) mitigation, a number of static reservoir models were constructed using a multiple realization approach. For The sedimentological characterization the Asmari reservoir each of the four field areas, different realizations were required a detailed analysis of the facies coupled with the constructed to account for variable top structure, fault/ interpretation of the diagenetic overprints. This has been fracture architecture, depositional architecture, porosity achieved mainly through thin-section analysis (of cores and permeability distribution and oil saturation models. and cu�ings) and electric logs interpretation, in addition to These area models were then upscaled and exported for the detailed core description and core analysis (i.e. porosity reservoir simulation. The simulation models suggest that and permeability measurements). Taken together these further development of the Al Huwaisah field through infill data have led to a be�er understanding of the depositional drilling supported by waterflood-pressure maintenance can and diagenetic history of the subsurface Asmari Formation, significantly increase oil rates in the next decade. and the prediction of its reservoir units across two studied giant fields. It appears that dolomitization is one of the most important factors controlling porosity and permeability in

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the Asmari reservoir of southwest Iran. It was necessary to low oil-saturated intervals must be classified as heavy to characterize the origin of the various dolomite fabrics, residual oils. These are mainly located in the northeastern because some non-dolomitised intervals provide very part of the field; their presence explains the apparent tilted good reservoir too, whereas other dolomitized intervals OWC. The study of the structural evolution of the field act as seals. Although dolomite is present throughout suggests that the present distribution of the residual oil is the reservoir successions in the selected fields, two due to the field having had a higher closure and a higher dolomite fabrics can be clearly recognized. Fine-grained oil leg. Based on structural reconstruction, a model of this dolomites, o�en dolomudstones/wackestones, are typically geological scenario led to a distribution of fluids (water, associated with anhydrite nodules that are interpreted as moveable oil and residual oils) that is close to the observed pseudomorphs of former displacive gypsum nodules that present-day ones. This predicted residual oil distribution grew from hypersaline brines under sabkha conditions. can be used for optimizing the location and efficiency of the The fine-grained and thinly bedded nature of the sabkha wells injectors. dolomites that cap the depositional cycles (0.5-5 m thick), results in high intercrystalline micro-porosity but generally low permeability, unless the rocks are fractured. The best (422-Oral) Reservoir characterization of reservoir quality is o�en associated with coarser dolomite complex Upper Jurassic Carbonates fabrics that have replaced subtidal bioclast-rich packstones Azer, Samir R. (ADMA-OPCO - [email protected]), and grainstones that form the base of the shoaling-upward Alasdair M. MacKenzie (ADMA-OPCO), cycles. In addition to intercrystalline micro-porosity, these Shawket G. Ghedan (ADMA-OPCO) and dolomitized subtidal facies typically possess interconnected Douglas Alexander Boyd (ADMA-OPCO) biomoulds that enhance the overall reservoir quality. The bulk stable isotopic analysis of oxygen and carbon The Upper Jurassic (Kimmeridgian/Tithonian), is of selected dolostone samples, revealed one main sample composed of four carbonate anhydrite cycles (from top- grouping, regardless of their original depositional facies base: A through D) that constitute the dominant reservoirs type (i.e. grainy or muddy). All the analyses have positive and caprocks of the Arab Formation. These are overlain 18 δO PDB signatures (up to +3.3) suggesting that they by the Hith Formation anhydrites and subordinate formed from either hypersaline fluids or seawater. On the carbonates, and underlain by the Diyab Formation source 13 other hand, δC PDB varies to a greater extent (-3.56 to + rock. This study summarizes the results of an integrated 13 4.66) with depleted δC PDB values indicating an organic multi-disciplinary reservoir characterization study of the carbon input. This grouping may either indirectly indicate Arab C and D members. The objectives of the study were that the dolomitization timing or process occurred for the to describe, characterize and model the Arab C and D in subtidal facies and supra-tidal facies together, and/or later a mature offshore Abu Dhabi field, to ultimately enhance diagenetic modifications have affected both dolomitized production and improve reservoir management. Based on fabrics. However, the dolomitization mechanism might sequence stratigraphic concepts, the Arab C and D were have dominated by sabkha pumping for muddy supra-tidal subdivided into four sequences, ten parasequence sets facies and reflex evaporation for the grainy subtidal facies. and 47 shallowing upwards cycles or layers, 5 to more than 40 feet thick. Thick highstand and thin transgressive (411-Oral) Bitumen Oocurrence in a giant oil systems tracts characterize the Arab C and D. Based on field offshore Abu Dhabi: identification and petrographic analysis and mercury injection data, a rock typing scheme was developed. Capillary pressure and impact on fluid behavior relative permeability curves were then generated for each Arab, Hani (Zadco - [email protected]), rock type for use in the simulator. Permeability estimators Bernard Carpentier (IFP), Eric Pluchery (Beicip-Franlab) were developed based on statistical methods, which and Jean-Marc Chautru (Beicip-Franlab) incorporate core measurements, geologic knowledge and well logs. All the data and interpretations were then Bitumens and tar mats are common features in Middle East integrated and a 3-D earth model was built. The 3-D oil fields and their presence in a reservoir can have adverse model was used for reservoir simulation, visualization and effects on its petrophysical properties and production reservoir management. The update of the model following efficiency. This study aims at assessing the distribution and recent drilling and geochemistry studies highlights water continuity of the bitumens in the Lower Kharaib Formation saturation changes as well as tar mat occurrence for the of a giant oil field, offshore Abu Dhabi, in order to improve benefit of reservoir evaluation and management. the reservoir production. Geochemical methods (Rock-Eval, gas chromatography and solvent separation) were used in (405-Oral) Sedimentological and rock-typing order to identify the different organic materials present in the reservoir and define their typical signatures on definition of the Khuff Formation of an wireline logs. Apart from the ‘normal’ moveable oil, which offshore Abu Dhabi field is produced from the field, two types of heavy organic Azzam, Ibrahim N. (ADNOC - [email protected]) and materials have been recognized: (1) bitumen-rich reservoir Arnaud Meyer (Total) intervals associated with high resistivities and high oil saturations. These intervals are characteristic of classical A reservoir facies (lithotypes) classification and Core Rock tar mats levels. These levels are located at the base of the Typing (CRT) study was carried out on the Khuff Formation reservoir layer and are restricted to the crestal area of the of an offshore Abu Dhabi field. This study was a part of the present-day structure. No relation with the present day oil- full-field simulation model, and aimed at improving the 3- water contact (OWC) was detected. (2) Bitumen associated D geological model of this gas field. The CRT approach was

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conducted on: (1) a sedimentological description of 2,482 � of (36-Oral) Well planning for implementation cores from six wells and mainly representative of the Upper of optimum development of a complex Khuff Formation (K1 to K4 reservoir units; K5 reservoir carbonate reservoir unit was also investigated); (2) the observation of 1,330 thin sections of rocks; and (3) the analysis of 2,480 CCAL and 87 Badri, Abdelmoneim B. (QP - [email protected]) MICP measurements. The first part of the study consisted of the definition of the depositional facies based on lithology, Proper and accurate well planning has played a major texture, and sedimentological features, deduced from both role in anticipated implementation of an integrated macroscopic and microscopic descriptions of cores and thin development plan involving a major capital project with sections. This resulted in proposed sedimentary lithofacies, marginal economics. The objective of this presentation is reservoir layering (based on sequence stratigraphy to review the premise of well planning to most efficiently analysis), and reservoir lithofacies property description. recover oil and condensates from a gas-recycling project The second part of the study defined: (1) rock types with in offshore Qatar as well as details of the plan to reduce observed differences of porosity networks; (2) diagenetic uncertainty. The objectives included: (1) production of evolution of sediments; and (3) qualitative interpretation liquids first for maximum recovery efficiency without of petrophysical data. Core-to-log matching and the CRT drilling of additional wells for gas recycling; (2) penetration recognition and identification on wireline logs was difficult of all reservoir layers; (3) maintaining a constant stand-off and sometimes biased, especially in the dolomite intervals. to gas and water contacts; (4) optimum well completion for The application of the CRT approach to the uncored zones flow; and (5) addressing corrosion concerns. Procedures remains uncertain, particularly in K4 and K5 reservoir included use of an updated, integrated, multi-disciplinary, units. Lithofacies and CRT descriptions for the six wells rock and fluid characterization to guide plans which would were used to build the 3-D geological model. The 3-D grid meet the objectives. 3-D seismic mapping that used the also incorporated the sedimentological layering based on techniques of depth-conversion using the interval velocity facies description, and the sequence stratigraphy analysis. approach, and also facies, rock typing and layering were Maps of lateral variations of core type were used in the 3-D incorporated. ‘ZmapPlus’ and ‘Stratamodel’ were used model to provide constraints for depositional orientation, in preparing and checking the surface and property facies changes, etc. This study contains a full analysis grids, water saturation modeling, and ended with oil/gas and integration of all sedimentological and petrophysical volumetric calculation on layer basis. The well targets available data. were then optimally selected using this information. The results achieved all the objectives and were incorporated (165-Oral) Petroleum system evaluation, in a full-field compositional simulation, which indicated that performance forecasting a�ests to the effectiveness Strait of Hormuz, Iran of well trajectories and completion planning. This study shows that careful well planning using updated integrated Badics, Balazs (Norsk Hydro - [email protected]), characterization and guided by the project objectives, can Michael Erdmann (Norsk Hydro) and be achieved. Such planning significantly contributes to Thomas Hardt (Norsk Hydro) reducing risk and improving economics. The petroleum systems of the Strait of Hormuz were investigated using basin-modeling techniques. (346-oral) Cost-effective ‘dynamic’ static Geographically-separated occurrences of oil, gas-condensate corrections in the Arabian Peninsula and gas discoveries in this tectonically complex area indicate distinct differences in hydrocarbon generation and charge. Bagaini, Claudio (Schlumberger - [email protected]) and The emphasis of the study was put on matching predicted Tariq Alkhalifah (KACST) and observed fluid properties in known accumulations, in order to predict fluid types in undrilled prospects. Several We derive the analytical expression of a new pre-stack source rocks are known in the greater area and have been operator, the Topographic Datuming Operator (TDO). correlated to accumulations during the decade. The Silurian This datuming operator generalizes the operation of Gakhum source rock, proven at Bandar Abbas (80 km to the static corrections, which is well known in the seismic north of the area), is thought to have sourced the Gavarzin, exploration community, and widely used in land seismic Salakh and Suru fields. The high2 N and CO2 content in data processing. TDO eliminates the essential assumption these gas fields suggest a highly-mature source rock. The of vertical incidence to the earth’s surface of the downward- Aptian Bab Member and the Cenomanian Shilaif source and upward-propagating reflected wavefield, which is rocks most likely charged the Henjam, Hangam, Mubarek, not valid in the presence of high-velocity shallow layers and Tusan fields. Both intervals are thin, but organic-rich. and/or large offset-to-reflector depth ratios. TDO applies The maturation of the Aptian-Cenomanian source rocks kinematic corrections, which are to a large extent equivalent occurred from the Middle Miocene to present-day. The to those obtained with ‘dynamic’ statics using ray-tracing, Upper Cretaceous Gurpi and the Paleocene-Eocene Pabdeh in a cost-effective way. The weighting function used in the marls are deeply-buried likely source rocks in the eastern Kirchhoff implementation of TDO produces redatumed Strait of Hormuz. Trap formation predated charging in seismic sections that can either be amplitude-preserving or the observed cases. Hydrocarbon migration modeling, true-amplitudes depending on the requirements. The TDO which includes multi-component PVT analysis, correctly introduced here, fills the gap between the simple but o�en matched all known accumulations and their fluid types, inappropriate surface-consistent static corrections, and the with uncertainties arising from, for example, the applied more rigorous but computationally-expensive Kirchhoff kerogen transformation kinetic model. pre-stack redatuming. In addition, TDO does not require

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a detailed depth-defined velocity model, but processing (35-Oral) Facies modeling within Fateh field, parameters that can be updated by applying iteratively the Ilam case study, Dubai, UAE operator itself. This study presents the application of TDO to land seismic data representative of the Arabian Peninsula Balke, Sco� C. (DPC - sco�[email protected]) and near-surface seismic challenges. Sand dunes, wadis, Fateh Development Team (DPC) velocity inversions in the overburden, and shallow high velocity layers were considered. The study also compares A�er the first successful well has been drilled, the results obtained using standard static corrections and the fundamental challenge in the development of ‘dynamic’ statics performed by TDO. any hydrocarbons is accurate distribution of the reservoir properties. In order to preserve the reservoir heterogeneity, the development geoscientist takes the (235-Poster) Geochemical studies and detailed understanding of the vertical data and applies source rock evaluation of Lower Cretaceous that knowledge in a 3-D spatial arrangement within a Sulaiy Formation in Kuwait geocellular model. In the case of the Ilam Formation, a productive carbonate reservoir of the Gulf’s Fateh field, Bahman, Fatema K. (Kuwait U - [email protected]), numerous wells had been drilled and the field is in an Fowzia H. Abdullah (Kuwait U) and advanced stage of development. This study presents a case Abbas A. Saleh (Kuwait U) example of the effects on the static model using various methods in order to distribute petrophysical information. Most of the oil reserves in Kuwait is produced from clastic Reservoir properties within a carbonate rock can vary sandstones and carbonates reservoirs of early and middle considerably. The Ilam reservoir was modeled using several Cretaceous age. Many studies were carried out to evaulate different methods in order to capture the range of geologic some of these oil reserves. The Upper Jurassic-Lower uncertainties. The most effective approach, which provided Cretaceous (Tithonian-Berriasian) Sulaiy Formation is the most likely distribution of porosity and permeability, one of these source rocks. The purpose of this study is was based upon a precise understanding of facies within to evaluate the depositional environment of the Sulaiy the Ilam from core information. Facies delineation was Formation by correlating its lithological variations and then determined from a sonic and density log cross-plot. organic ma�er content in Kuwait. A total of 114 core Facies maps were constructed and used to populate samples were collected from Sulaiy Formation wells in porosity and permeability within the geocellular model. Burgan, Minagish, Mutriba, Ritqa and Raudhatain oil The objective in building this static model was not only fields in Kuwait. Analytical procedures were carried out to analyze the various distribution techniques of porosity for organic ma�er evaluation using LECO analyzer and and permeability, but also to develop the upscaled dynamic transmi�ed-light microscope. Petrographical studies of reservoir model, which provided a full-field reservoir thin sections and chemical composition of rocks were simulation of the field. A development program for the done using EDS, ICP and XRD. The study also analyzed Fateh field was based upon this dynamic model. Drilling 21 core samples from the Hith, that underlies the Sulaiy results as well as reservoir performance were compared Formation, and 38 from the overlying Minagish Formation. with the various methods of property distribution. The evaluation of the physical and chemical conditions of the depositional environment variation, above and below the Sulaiy deposits, completed the time deposition of the (334-Oral) Tectonic evolution of Alborz (Iran) whole series. The Sulaiy Formation is mainly composed of since Mesozoic gray to dark, highly-bituminous, pyrite-rich carbonate. The carbonates alternate with massive and laminated mudstone Barrier, Eric (CNRS-MEBE - [email protected]), Marie- that contains sponge spicules and foraminiferas, and is most Françoise Brunet (CNRS-MEBE), Abdollah Saïdi (GSI) obvious in the northern part of Kuwait. The Hith Formation and Alireza Shahidi (GSI) is composed of anhydrite intermixed with gray to brownish bituminous limestone forming a chicken-wire structure. The The Alborz Range constitutes the southern margin of the Minagish Formation is composed of light gray to brown, South Caspian Basin. The analysis of bri�le deformations in poorly bituminous, massive carbonate. The results of TOC the Mesozoic and Cenozoic Alborz sedimentary sequences measurements range between 0.46 - 6.0 % wt, and may reach enabled us to reconstruct the regional tectonic evolution. as high as 11.0 % wt. The kerogen shows an amorphous A�er the Middle-Late Triassic Eo-Cimmerian tectonic organic ma�er (AOM) mixed with well-preserved zoo- phase resulting from the collision of the Cimmerian and phyto-plankton (algae) with rare humic particles. The blocks with Eurasia, an extensional event developed elemental composition of organic ma�er indicates type-II during the deposition of the Shemshak Formation (Late kerogen. The maturity level and kerogen type indicate Triassic to Middle Jurassic). We assign this extension to a potential source rock especially in the northern part the ri�ing phase of the South Caspian Basin that probably of Kuwait, where the organic ma�er is well-preserved opened in Late Jurassic. During the post-ri�ing period of amorphous marine type-II kerogen. The accumulation thermal subsidence, minor compressional tectonic events of deposits was controlled by a fluctuation of rising and intercalated, especially at the Jurassic-Cretaceous boundary dropping sea level within the general transgression of the and latest Cretaceous. Regional unconformities and the sea starting from the supra-tidal-intertidal in the lower part deposition of clastic sediments provide evidence for these (Hith Formation) to deeper subtidal to more open marine compressional phases. In Eocene time, a strong extension offshore environment at the top (Sulaiy Formation) with an lasted, associated with EW-trending normal faulting, anoxic depositional condition giving rise to overall on lap originating the thick volcano-clastic Karaj Formation. We transgressive sequence.

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assume that this regional sub-meridian extension is related of the Mut Basin is appropriate as an outcrop analog to to the back-arc opening behind the northward subduction the Asmari and Euphrates formations because of four of the Neo-Tethys oceanic lithosphere beneath the Eurasian similarities; namely: (1) depositional geometries; (2) facies margin. The next major orogenic period developed during and fauna (notably foraminifera); (3) interaction between the Late Cenozoic in relationship with the Arabian-Eurasia sands and carbonates; and (4) influence of paleotopography collision. This study is part of the Middle East Basins on stratigraphic development. A variety of depositional Evolution Programme (MEBE). geometries are observed in the Mut Basin; including: (1) tidal carbonate bioclastic ramp; (2) a low-relief carbonate platform that transitions during flooding to an isolated (74-Oral) Integration of explicit fracture platform complex; (3) rimmed platform with steep slope; networks in field flow models for a higher and (4) low-relief, intraplatform banks. These are similar to reliability of multi-phase production profiles many of the morphologies described in the literature from Kirkuk field. The facies described in the Mut Basin have Basquet, Rémy (IFP - [email protected]) and been closely tied to their position on the depositional profile Bernard Bourbiaux (IFP) by direct observation of stratal geometries. Characteristic foraminiferal assemblages exist in each depositional Seismic and sub-seismic faults or fracture swarms generally environment from the lagoon, through margin banks and have a major impact on the hydrodynamic behavior of a shoals, to the slope and the basin. A mixed-system develops reservoir. Early water breakthrough or crossflow between on one flank of the basin where an active delta underwent layers are the main effects observed in the presence of rapid flooding and became an estuarine system with such objects. Due to their large scale, the integration of carbonate reefal banks lying just beyond the estuary mouth. these fractures into a field flow model as homogenized The Early Miocene transgression flooded a complex relict flow properties defined at the hectometric gridblock scale, topography in the Mut basin that is similar to the onlapping generally leads to inaccurate predictions of the multi-phase geometries of the Middle Oligocene units in Kirkuk onto production behavior. To overcome these limitations, the the underlying Eocene strata. While the similarities are present work proposes a reservoir simulation method striking, two features typical of the Asmari or Euphrates based on the dual-medium concept, but keeping the formations have not been studied in the Mut Basin, and explicit representation of large-scale fractures as identified should not be considered as part of the analogy; these are: or modeled by the geologist. This modeling approach (1) diagenetic history; and (2) development of evaporites. is applied for the simulation of water encroachment Lastly, one exceptional aspect of the Mut area as an analog in a typical fractured oil field model. The results are for the Asmari and Euphrates formations, is that all these compared to several conventional approaches based on aspects of the Miocene shallow-marine deposits are the single porosity concept or the dual porosity concept, reassembled in one geographically small area. It remains to and involving different methods of homogenization of be seen whether this also is typical of the Gulf equivalents! the fracture network. The explicit modeling of the actual large-scale fracture network geometry enables an accurate prediction of the progression of fluids within the fractures (471-Oral) Sequence stratigraphy of the Late while minimizing the number of fracture cells. The method Oligocene-Early Miocene mixed siliciclastic is promising as it enables a straightforward use of realistic and carbonate sediments in the southwest geological fracture models in reservoir simulators, for any of Iran field study where flow channeling along highly-conductive geological features is suspected. Beiranvand, Bijan (RIPI, NIOC - [email protected])

(355-Oral) The Miocene of the Mut Basin The Late Oligocene-Early Miocene sediments in the southwest of Iran, especially in the Dezful Embayment, (southern Turkey): an analog for Oligo- are one of the most important reservoirs in the world. Miocene reservoirs of the Middle East These sediments are predominately carbonate, but in the central area of the Dezful Embayment, it consists of a Bassant, Philip (ChevronTexaco - phil.bassant@chevrontex mixed siliciclastic and carbonate reservoir. The amount of aco.com) and Frans van Buchem (IFP) siliciclastic material varies from less than 5 to more than Early Miocene and Oligocene oil-bearing limestones of 50 percent. In the upper part of the sequence, a sandstone Iran (Asmari Formation) and northeastern Iraq (Euphrates complex (sandy dolomites, medium grained, poorly Formation) are characterized by complex lateral and vertical consolidated sandstones, dolomitic calcareous sandstones, facies variability. These are described in the literature as an calcareous sandstones, carbonaceous shales and sandstones) alternation through time between ramp and rimmed shelf rapidly increases in thickness and apparently coalesces, platform morphologies for the Oligocene limestones in but in the lower part, the fine- to medium-grained loose the Kirkuk field (northeast Iraq). Mud-flat, bioherm and sands, poorly consolidated sandstones, greenish to black bank, foreslope and basinal depositional environments shale, silty shale and thin intervals of silty sands are not have also been described in the literature. The Mut Basin regionally extensive and the thickness development on in southeast Turkey contains excellent-quality outcrops of the central part. This mixed siliciclastic and carbonate Early Miocene shallow-marine limestones, sandstones and sequence deposited within a relatively low relief carbonate basinal sediments. These were deposited during a time of platform se�ing. These sandstone intervals have high rapid marine flooding of a complex antecedent topography permeability and constitute a major aquifer system in the during the Early Miocene, Burdigalian stage. The Miocene region. The sequence stratigraphical analysis logs that

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have been created by using a systematic core description, hinge lines had perceptible influence on facies distribution biostratigraphic data integrated with sedimentological, and stacking pa�erns. and lithological data, and so wireline log criteria by the application of sequence stratigraphic concepts in this carbonate ramp and platform se�ing show the following (487-Poster) The interpretive stratigraphy results: 1) because of the low angle of the shelf and its broad of a regional traverse dip section from the nature, even small changes in relative sea level, caused by Khuff outcrop belt in central Saudi Arabia to the interaction of sediment supply, tectonics, and eustasy Al-Jawb in Eastern Saudi Arabia changes, has a major impact on depositional pa�erns. 2) The thick carbonate intervals produced while the relative Billing, Ian M. (Saudi Aramco - [email protected]), rise in sea level is very rapid and the “weak” clastic systems Denis Vaslet (BRGM), Yves-Michel Le Nindre (BRGM), are completely over whelmed and pushed right back Abduljaleel Abubshait (Saudi Aramco), Raid Dakhil into the hinterland. 3) In the upper part of the sequence, (Saudi Aramco), Rami Kamal (Saudi Aramco), Aus Tawil sediment supply from the low relief hinterland is weak but (Saudi Aramco), Randy Demaree (Saudi Aramco), as the sea level rise is slow, the clastic system can aggrade Geir Ytreland (Saudi Aramco) and and prograde. Slow sea level rise also allows the broad Alastair Gray (Saudi Aramco) carbonate ramp developed outboard of the clastic system to aggrade. So the fluvially derived clastic sediment supply is The Permo-Triassic Khuff Formation in the subsurface sufficient to maintain the clastic shoreline systems in more of Saudi Arabia acts as a significant gas reservoir, and a or less the same position. 4) In the middle and lower parts detailed sequence stratigraphic scheme has recently been of the sequence, a rapid rise in sea level overwhelms the completed for the Khuff in the supergiant Ghawar field in available clastic sediment supply, and pushes the clastic eastern Saudi Arabia. The challenge then facing carbonate shoreline system back (Forced Regression System Tracts, geoscientists was to evaluate this model outside of the FRST) on to the shelf. Ghawar structure, and produce a regionally-consistent geological framework for this formation. A significant amount of core has been taken in wells outside of Ghawar, (63-Oral) The creation of late Proterozoic and moderately well-exposed outcrops of the Khuff basement highs and their subsequent Formation also exist within the Kingdom. This is the result influence on sedimentation patterns of the of a detailed geological study of the Khuff Formation to Arabian Peninsula the south of Ghawar as a step in the creation of a regional Khuff Formation model across the entire Arabian Shelf. Bell, Andy (Shell - [email protected]) The Khuff Formation outcrops in a narrow 600-km-long arcuate N-S belt in central Arabia, to the west of Riyadh. A model of late Proterozoic accretion and cratonization While providing good information on potential reservoir has been developed which can be extended across the geometries and an insight into the stacking pa�erns of Arabian Plate. Shell in conjunction with SRK Consulting these shallow-water to supra-tidal carbonates, linking the of Australia, has used gravity and magnetic data, outcrops to the subsurface has proved challenging, due calibrated by seismic and well data to produce a series to down-dip facies changes and the paucity of diagnostic of kinematically constrained tectonic models. A model of evaporite markers, which act as significant units for basement topography was developed across the entire correlation in the subsurface. By compiling a 250 km-long Arabian Peninsula using the SEEBASETM methodology dip-section traverse, utilizing extensive and detailed core of SRK, which inverts the gravity and magnetic data, descriptions, micropaleontological analysis and wireline allowing a be�er visualization of basement relief. log integration, a consistent correlation has been compiled. The model of basement topography shows a series of This presentation illustrates the results of this traverse predominantly NS-oriented ridges which are then off-set from the Qassim outcrops in central Arabia, through by NW-trending lineaments. This NS-orientated basement shallow-cored water wells, into exploration wells, tying grain is interpreted as a result of terrane accretion during up with the Ghawar field, and terminating at Jawb. This the late Proterozoic Pan-African Orogeny which was study represents a major advancement in the regional subsequently affected by an anastomosing array of NE- understanding of the sequence stratigraphy and lateral trending continent-scale shear zones corresponding to the facies distribution of the Khuff Formation, and will aid infra-Cambrian Najd Event. Evidence from the sub-crop future exploration efforts throughout the Arabian Gulf. of the Angudan unconformity in Oman and the subcrop of the ‘Hercynian’ unconformity in other parts of the Arabian Peninsula suggest that these highs are bounded by (264-Oral) Fold and fracture relationships localized zones of more intense deformation. The bounding in carbonate anticlines in the Zagros fault zones to these highs are interpreted as closely spaced Mountains and Oman near-vertical faults, rooted in basement shear-zones, which have been subjected to both transtension and transpression Blanc, Eric J.-P. (Cambridge U - [email protected]), during various episodes through geological history. The Christopher A.J. Wibberley (Antipolis U), Mark B. Allen amount of lateral movement on these faults is limited. (CASP), Hossein Hassani (Amir Kabir U) and These long-lived basement positive features act as relative Govand Sherwani (U Salahaddin) ‘buoyant’ highs independent of the tensile or compressive Fractures play a significant role in both the porosity and stresses acting on the plate. As the basement ridges were migration pathways of Middle East carbonate reservoirs. increasingly buried, subtle differential subsidence and/or Fracture distribution in folded carbonate reservoirs is

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controlled by a combination of the tectonic evolution impedance models and invert post-stack seismic to acoustic and the mechanical properties of the strata. In order to impedance that honors all available information (actual improve prediction of fracture distributions in Middle East and pseudo wells); and (5) transform acoustic impedance carbonate reservoirs, we are performing studies of fracture to reservoir porosity. This new methodology has been development in folded carbonates in the Zagros fold and successfully tested on a carbonate field, where available thrust belt in Iran, Iraq, and the Adam Foothills of Oman. log data is sparse. Synthesized logs were estimated Scales of observation range from satellite imagery studies, from facies-dependent regression analyses, where rock through fieldwork, to micro-structural analysis. The property differences were identified by superposing orientations and spatial distribution of fracture sets mapped independent cross-plot analyses of existing log data (in around fractured/faulted anticlines are correlated to the vertical and spatial domains). This resulted in synthesized deformation history, particularly with respect to folding impedance logs that, when modeled, statistically honored mechanisms and the likely evolution of stresses during known carbonate stratigraphy. The end result is inverted folding. Such genetic controls are thought to be important in impedance transformed to reservoir porosity (via rock estimating likely reservoir fracture geometries from large- property relationships) that honors known heterogeneity of scale, regional information such as tectonic deformation vertical and spatially varying rock properties in a complex history and evolution of stress regime. Also important carbonate reservoir. in controlling fracture development during folding are the presence of pre-fold and syn-fold faults, whilst late or post-fold faulting commonly develops independent (209-Oral) Evaluation of a fractured fracture clusters. The relationship between lithofacies and carbonate reservoir with integrated seismic fracture properties is discussed, from a number of points and image data, onshore Abu Dhabi of view. Firstly, strain partitioning along weak beds during folding may affect the vertical continuity of fractures. Bloch, Gérard (ADCO - [email protected]), Maged Al- Secondly, fracture characteristics (e.g. density and aperture) Deeb (ADCO) and Ishtiaq Jadoon (Schlumberger) depend on the mechanical properties of a given lithology. In one of the major onshore oil fields in Abu Dhabi, the Thirdly, diagenetically altered units along key surfaces presence of a large number of fractures and minor faults such as hardground surfaces or paleokarstified units exert o�en leads to higher production and/or water-cuts and a geomechanical control affecting the development of later mud losses in the Upper Cretaceous carbonate reservoir. fracture arrays. An important issue in fractured carbonate Therefore, these features need to be well-constrained for reservoirs is whether much of the fracture porosity has optimum field development. Seismic data is successfully been destroyed by calcite cementation. Nevertheless, used to predict the presence and distribution of faults, micro-structural observations show that even cemented but can also be used to predict sub-seismic deformations. fractures can reopen, under certain stress conditions, to act However, due to relatively coarse seismic resolution, these as conduits to fluid flow or as surface fissures held open predictions require validation with well data. Electrical during reburial by porous sediment infill. Such diagenetic image logs such as Formation MicroImager (FMI), allow controls highlight the sensitivity of final fracture array viewing the reservoir along the borehole for fault and properties to the burial and upli� history in relation to fracture analysis (characterization and distribution). This folding and fracture generation. study shows examples of how integrated seismic and borehole log image data can be used to constrain sub- (208-Oral) Log synthesis and pseudo-wells seismic features along the borehole. In one example of a for optimal impedance inversion of a horizontal well, the presence of a fault is confirmed by carbonate reservoir, onshore Abu Dhabi the borehole image analysis. Image data, coupled with the open-hole logs, were used to draw a balanced structural Bloch, Gérard (ADCO - [email protected]) and Michael cross-section and to calculate about 25 to 43 � of throw at Shoemaker (Jason) the fault. In another case, an inferred sub-seismic fault was not observed in the borehole image. However, a kink was Prior to a post-stack model-based inversion to acoustic recognized between two panels of structural dip, based impedance, it is critical that the geoscientist execute a on the image analysis. The location of the kink was found reservoir well log data consolidation and rock properties to be in agreement with the location of the inferred fault. analysis, with the ultimate objective of modeling reservoir The low number of fractures observed over the kink area porosity. Available wells and log data (sonic and density) is explained by the deformation being consumed by the however, can be sparse, and may require log synthesis bending of the layers. In another example of a horizontal and the emplacement of pseudo-wells prior to impedance well, four sets of open fractures were interpreted by the modeling and inversion. Here, we introduce a systematic borehole image analysis. This information is found to be approach in achieving the objectives of: (1) statistically consistent with the detailed seismic interpretation of minor synthesize log data from existing information, independent faults. Higher mud losses were observed in this well that of both layers (vertical) and well locations (spatial); (2) are a�ributed to the be�er connectivity between fracture derive and tie synthesized (and available) impedance networks. In conclusion, fracture analysis based on borehole logs to seismic amplitudes for the accurate estimation of images, integrated with seismic interpretation, is essential wavelets and seismic synthetics; (3) add pseudo-wells to resolve or reduce many structural uncertainties in the with appropriate pseudo-logs to properly constrain the reservoir. Integration closes the scale gap between log and well-derived, low-frequency part of the inversion in order seismic data, and is a key element for improved reservoir to conform the model to the known carbonate geology characterization leading to be�er field development. in both space and time; (4) interpolate (via log data)

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(232-Oral) Evaluation of salt domes for to the northeast. The compilation of the recent structural, Mesozoic and Paleozoic targets, offshore stratigraphic, sedimentological, paleogeographical and Abu Dhabi geophysical studies, of the central part of the Oman Mountains, resulted in the interpretation of the following Boekholt, Martin P. (ADCO - [email protected]), events: (1) The detachment initiating the subduction of Erik B. Kleiss (ADCO) and John Mariano (ExxonMobil) the autochthonous was intracontinental and occurred in the proximal part of the continental margin, south of the Part of the ADCO concession lies in offshore Abu Dhabi external part of the shelf. (2) Between the intraoceanic around several islands in the Gulf. This offshore area detachment initiating the Samail ophiolitic nappe and is part of the Hormuz Salt Basin and the discovered the intracontinental detachment, the part of the margin hydrocarbon accumulations are related to movement of consisting of the external shelf, the continental slope, and the infra-Cambrian salt during the Mesozoic and Cenozoic. the whole Hawasina Basin formed an independent North Continuous growth of the offshore structures was Muscat micro-plate. (3) From early Turonian to the end established by back-stripping the depositional packages of Santonian, obduction and intracontinental subduction through geologic times. The continuous diapirism resulted operated in the same direction and the same time. The in shallow-marine conditions over and around some salt northeast part of the micro-plate plunged below the domes, and hence in the localized deposition of good Samail nappe and its southwestern part emerged part- reservoir facies surrounded by deeper-water deposits. thrusting the autochthon. (4) At the Santonian-Campanian This study evaluated the hydrocarbon potential of two transition, obduction and intracontinental subduction islands that appear to be realted to salt diapirism. Tha stopped a�er the Samail nappe front overpassed the fairway analysis included: (1) evaluation of all potential southwest border of the micro-plate. (5) During the final reservoirs; (2) salt body detection and modeling with stage of the intracontinental subduction, the lower part newly acquired, high-resolution, 3-D gravity data; (3) of the subducted continental crust delaminated upwards imaging of sedimentary structures around the salt domes the overlaying part under buoyancy effect, marking the using pre-stack Depth Migration (PSDM); and (4) sub- first stage of the autochthonous exhumation. (6) From regional mapping of key intervals used for charge analysis. early Campanian to early Maastrichtian, the North Muscat Two high-resolution 3-D gravity surveys confirmed the micro-plate moved back to the northeast; its northeast existence of salt diapirs close to both islands, and their size part plunging by gravity into the asthenosphere, and the and shapes. Both salt domes reach close to the surface and subducted autochthonous exhumed by unfolding and have feeders to the south, and salt overhangs to the north. upli�, which caused the emersion and partial erosion of the The feeder for one salt dome is deep (at least 10 km), and ophiolitic sequence. (7) The local crustal thickening, related therefore is likely a�ached to the Hormuz salt. In contrast, to the delamination of the subducted continental crust, the maximum depth of the second, smaller salt body is only formed the Saih Hatat Dome, in which erosion reaches the 4 km, and indicates a detachment from the Hormuz salt. In pre-Permian succession. addition to PSDM, the seismic data was processed through several iterations of tomographic updates and anisotropic (48-Oral) Multi-layer statics modeling using imaging. The resulting images of the sedimentary layers around the domes were significantly improved, including upholes or first breaks their approximate termination against the salt dome. Bridle, Ralph M. (Saudi Aramco - ralph.bridle@aramco Potential exploration targets were verified in the depth .com), Robert E. Ley II (Saudi Aramco), Mohammad A. domain. The interpreted salt body geometries derived Al-Homaili (Saudi Aramco), Bryan Maddison (Saudi by PSDM and gravity modeling are consistent. Both salt Aramco) and Kurt Janssen (Saudi Aramco) domes are located in small NNE-striking salt-withdrawal basins, which are confined by structural highs on both For most of the exploration area in Saudi Arabia, a single- sides. In one syncline, the relevant source rocks for shallow layer velocity model is adequate. In areas of complex near- targets are buried deep enough to be mature for present- surface topography and where the datum is above surface day oil generation. the simple single-layer approach can be in error. These time errors create cycle skips or medium to long wavelength (185-Poster) Eoalpine geodynamic evolution structure problems. Multi-layer models can be built on 2-D of Omans Tethyan continental margin lines, the control being from the 42,000 upholes that were drilled prior to 1994. For individual 2-D lines a reasonable Breton, Jean-Paul (BRGM - [email protected]), François model may be built, however there are problems tieing Béchennec (BRGM), Joël Le Métour (BRGM), Laure the models. The method is to interpret the upholes, and Moen-Maurel (Total) and Phillipe Razin (U Bordeaux) then use the knee points as definition for the base of the layer. The velocity is interpolated linearly between upholes A revised interpretation of the successive stages of the and the base of the layer can be interpolated linearly by eoalpine evolution of the northeastern margin of Oman thickness or elevation. Though versatile, this layer-building is presented through seven cross-sections of the same method requires good quality representative upholes that lithospheric transect at five million year intervals, from penetrate through the base of the weathering on a regular late Albian (100 Ma) to early Maastrichtian. This SW-NE grid. In areas of severe and complex topographic variations, transect starts on the southwest border of the Hamrat the uphole multi-layer model becomes inadequate as the Duru Range, crosses the eastern part of Jabal Akhdar, 4-km spacing only captures the aliased low-frequency Saih Hatat and the Tethys Ocean, up to the Samail Basin component of these high-frequency changes. The

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acquisition of high-resolution seismic data with high group subsurface uncertainty and risk. Quantitative methods density, in some cases 5 m intervals, gives the opportunity in stratigraphy are important in addressing this problem to use shot gathers for refraction information. By using the because they allow more objective analysis. A particular classic refraction spread method the first three horizons quantitative method, stratigraphic forward modeling can be interpreted from shot gathers of suitable quality. (SFM), represents sedimentary processes by equations, These first-break interpretations create a depth/time model rules and algorithms and makes quantitative predictions consisting of computed velocity control points that are of the products likely to result from given initial conditions input into the layer model builder. Assuming the refractors and process parameters. Because a SFM is a quantitative to have zero or small dips, the majority of the problems tool, and because good models are based on sound seen in the near-surface can be solved. This is not a severe understanding of physical processes, they can to some assumption in most areas of Saudi Arabia, particularly in extent address the problem of quantifying and providing the Eastern Province, since surface layers are essentially an independent challenge to sequence stratigraphic flat-lying. Layer modeling has created models with less models. Do SFMs behave in a way consistent with sequence static uncertainty, and can be applied to both 2-D and 3-D stratigraphic concepts, and make similar predictions? acquired seismic data. Dionisos is a stratigraphic forward model, developed by IFP and a consortium of companies including Total and Shell. It is being tested and applied throughout Shell in 2003-2004. (32-Poster) Post-inversion uncertainty It is a 3D SFM, includes many important processes known analysis for post-stack acoustic impedance to operate in carbonate systems, and can be applied to both inversion siliciclastic and carbonate systems either at the exploration or the production scale. Constrained model results can be Broadhead, Michael K. (Saudi Aramco - michael.broadhea useful at the exploration scale, helping reduce uncertainty [email protected]) in reservoir, seal and source rock prediction, and at the production scale, predicting probable inter-well reservoir In order to produce a quantitative confidence estimate for properties. Dionisos has been applied to various subsurface post-stack seismic inversion for acoustic impedance, one challenges, e.g. a Cretaceous carbonate field Asab in the would ideally incorporate the uncertainty analysis into UAE, carbonate buildups in SE Asia, and Cenezoic deltas the inversion process itself, which would take into account on the Atlantic margins, and plays an important role in data covariance and prior probabilities. This methodology helping to assess and reduce subsurface uncertainty. is published elsewhere based on a Bayesian approach. However, it may also be desirable to produce uncertainty estimates for existing impedance volumes. Such estimates (403-Oral) Impact of surface-consistent would necessarily be crude, but should have value in processes on pre-stack seismic attributes at least a relative sense. This new approach exploits the well known series expansion of variance approach in the Burnstad, Roy M. (Saudi Aramco - [email protected] theory of propagation of errors. To first order, the forward om), Tim Keho (Saudi Aramco,) and problem gives the variance of the seismic amplitudes in Patrick Ru�y (Saudi Aramco) terms of a convolution between a function of the wavelet and a function involving the acoustic impedance, and its The Permo-Carboniferous Unayzah Formation has been an associated variance (the uncertainty in impedance which exploration target in Saudi Arabia for over a decade, with we desire to estimate). To invert this equation amounts to oil and gas production from the unit now well established. solving a deconvolution problem, where it is assumed that Still the Unayzah remains a challenging objective, in everything is known except the impedance variance. This large part due to the complex interplay of continental deconvolution problem is complicated by the need for a depositional environments it represents. Braided stream, positivity constraint on the solution, hence we developed an wadi fill, playa lake, interfluve, alluvial fan and eolian dune approximation to the inverse problem that leads to a simple systems have all contributed to the Unayzah. In the study algebraic expression applied in a sliding window. The area, where the Early Permian Unayzah-A2 is the primary study also developed a procedure for estimating the seismic target, exploration efforts are now focusing on combination amplitude variance, which uses ensemble averaging over structural-stratigraphic traps. The success of these efforts a neighborhood of seismic traces within the range of the hinges on precise delineation of sandstone trends. To this variogram. The study shows how one could, in principle, end, 3-D surface seismic data presents the best opportunity incorporate wavelet uncertainty into the formulation. to extract and map a�ributes that help define the target trends. The methodology used in this study was a�ribute analysis of near and far stacks at key stages of target oriented (369-Poster) Dionisos: a stratigraphic 3-D seismic re-processing. Key processing decisions were forward-modeling tool for reducing reservoir guided by these analyses. The study included three major and trap uncertainty pre-stack processing procedures routinely applied to land 3-D seismic data: surface consistent amplitude analysis, Burgess, Peter M. (Shell - [email protected]), Henne linear noise removal, and surface consistent deconvolution. Lammers (Shell), Cees van Oosterhout (Shell) Parameterization of shot, receiver, common depth point, and Kees van der Zwan (Shell) and offset operators were evaluated. The study results indicate operators chosen for surface consistent pre-stack Many conceptual geological models and methods, such as processing procedures should be carefully analyzed before sequence stratigraphy, tend to overestimate information application. Use of offset-dependent seismic a�ributes and knowledge about the subsurface, and underestimate

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assisted the analysis and ensured that the overall objectives (328-Oral) Geochemical characterization of re-processing were met. Subsequent interpretation led to of the Mauddud Formation reservoir, an improved understanding of the sandstone trends in the Raudhatain and Sabiriyah fields, North targeted Unayzah Formation. Kuwait

(439-Poster) Stratigraphic architecture and Chetri, Hom B. (KOC - [email protected]), Peter reservoir quality controls on the Shu’aiba Cameron (KOC), John Isby (BP), Abid Bhullar (BP) and reservoir, Shaybah field, Saudi Arabia Tony Barwise (BP) Geochemical evaluation of produced oils and core Cantrell, David L. (Saudi Aramco - dave.cantrell@aramc extracts from the Mauddud Formation reservoirs in o.com), G. Wyn Hughes (Saudi Aramco), Roy K. Sadler North Kuwait were carried out to evaluate the possibility (Saudi Aramco ), Robert F. Lindsay (Saudi Aramco) and of compartmentalization and predict oil quality in Peter K. Swart (U Miami) flank positions. GC, GC-MS, and Iatroscan analysis was Recent efforts by a multifunctional team within Saudi performed on produced oils. Iatroscan analysis was then Aramco has provided new insights into the stratigraphic carried out on nearly 1,000 core extracts. Additional GC architecture and depositional framework of the Shu’aiba analysis was then performed on select core extracts. The reservoir in Shaybah field, Saudi Arabia. Within this geochemical data was then integrated with the 3-D reservoir reservoir interval, three major early Aptian sequences models, to develop an interpretation of the geochemical and one late Aptian sequence have been identified, character of these reservoirs. GC and GC-MS data show which record changes in water depth and depositional that both Raudhatain and Sabiriyah oils are derived from energy from a shallow-marine platform interior and shelf the same source. Raudhatain is more thermally mature than margin environment in the southern and central portions Sabiriyah. Varying degrees of biodegradation is observed of the field, to a deeper-marine offshore se�ing to the in both oils and core extracts from both fields. Iatroscan northeast. Initial topography was established during the has proved to be a valuable, yet inexpensive geochemical lowermost sequence, and influences the distribution evaluation technique. Biodegraded oil is found in less of paleoenvironments in later Shu’aiba sequences. The permeable intervals of the reservoir. The correlation of lowermost sequence is initiated above an unconformity and low permeability to more altered oils explains the PVT karst surface at the top of the Buwaib (Kharaib) Formation, oil profiles observed in these fields. In Raudhatain field, and begins with a major flooding event (recorded by a the heavier oil leg tested in the flanks of the reservoir can cyclic succession of argillaceous orbitolinid packstones and be related to reduced reservoir quality in these positions. Lithocodium wackstones (informally named the Biyadh at In Sabiriyah field, GOR differences of oils tested in flank Shaybah), which is typically overlain by a succession of wells can be related to be�er reservoir quality throughout Lithocodium-coral wack-packstones. The second sequence the Mauddud interval in these wells. A simple ‘fill and typically sharply overlies the first sequence, and is highly spill’ migration history is proposed for these North variable in character, containing a differentiated rudist Kuwait reservoirs. As the reservoirs filled, early oil became bank complex in the central and northwestern part of the biodegraded and reduced the effective permeability of the field along the platform margin, which separates restricted lesser quality reservoir layers. More mature oil topped-up platform interior facies in the south from deeper water the reservoirs by migrating through the more permeable planktonic foram-rich packstones to the northeast. Again layers. Oil quality maps can be produced for these reservoirs sharply overlying this sequence is a third sequence, which by following porosity and permeability maps in existence. contains a diversity of environments that reflects earlier depositional topography, although it overall represents (388-Oral) Log responses, anhydrite a relative deepening from the previous sequence below. detection and reservoir property Finally, the fourth (late Aptian) sequence only occurs as a restricted basinward wedge of foram-rich packstones to implications in the anhydritic carbonate of the east of the field. Diagenesis has extensively modified the Khuff Formation the original properties of these sediments. Petrographic and geochemical evidence suggests that the top of the Clerke, Edward A. (Saudi Aramco - edward.clerke@aram Shu’aiba Formation is a major karst surface, in which co.com) meteoric diagenesis has selectively altered portions of the The Permian Khuff Formation is a varying lithology, reservoir up to 180 � below the top-Shu’aiba sequence low porosity gas reservoir in Saudi Arabia and is a gas boundary (which is interpreted to represent a composite and oil reservoir in other areas of the Gulf. Lithological sequence boundary). Other sequence boundaries locally complexities, regionally and locally include: (1) reservoir display evidence of limited meteoric diagenesis. Specific can be either limestone and/or dolomite; (2) anhydrite in diagenetic modifications include coarse blocky calcite all of its modes (bedded and coalesced nodular, nodular, cements, compaction, and microporosity development. pore filling and matrix replacement) is present in both the The interplay of stratigraphic architectural elements and limestone and the dolomite, o�en in significant volumes, diagenesis controls reservoir quality in the Shu’aiba at as well as beds of various thicknesses (2 to 35 � thick) of Shaybah field. 100 percent anhydrite, extending over large areas. A visual estimate of anhydrite content may be misleading as some of the anhydrite may be microscopically disseminated.

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The varying lithology of the Khuff Formation has been (353-Poster) Use of model based K-L addressed by performing slab-veneer-homogenize- filtering to attenuate interbed multiples in powder X-ray diffraction mineralogic studies of 600 � of seismic reflections of the Devonian Jauf core from two wells in the Ghawar area. The goal of our bulk mineralogy study is to quantify the Khuff Formation reservoir, Eastern Saudi Arabia minerals for improved reservoir modeling and log Cook, Douglas J. (Saudi Aramco - calibration. Anhydrite volumes are especially important [email protected]) and Ching Chang J. Tsai for the modification of reservoir quality by cementation on (Saudi Aramco) the depositional rock fabrics and for the significant effect on the log analytical determination of porosity. Certain The use of K-L filtering has been successfully used to combinations of well logs and borehole drilling mud can be a�enuate interbed multiples interfering with seismic used to overcome the log analytical problems. In particular, mapping of the Devonian Jauf reservoir to help expand the ECS (Elemental Capture Spectroscopy) well log yields the success of Saudi Aramco’s gas exploration. Velocity excellent determinations of anhydrite as compared to the discrimination to stack-out multiples does not work veneer XRD data. When a reliable indicator of anhydrite satisfactorily. Since there is o�en an angular discordance volume is available, improved diagenetic models of of the Paleozoic interval with the interbed multiples, the reservoir can be constructed and more complete approaches were sought to a�enuate the multiples by petrophysical interpretations are enabled. One of these, the dip-discrimination. Model-based K-L filtering was applied Anhydrite Boost, computes the reservoir carbonate porosity to find a method of dip-discrimination that did not smear rather than the total formation porosity. This approach the desired primary reflections below the ‘Hercynian’ grounds the comparison of reservoir quality in rocks with unconformity reference horizon. The process uses the the same amount of porosity but with different amounts of interpreted reference horizon to fla�en the seismic anhydrite; since the porosity is a property of the carbonate data and operate only below that horizon. The process and not the anhydrite cement. transforms the data into various principle components, each representing a different portion of the data. The (389-Oral) Beyond porosity-permeability largest principle component represents the most similar relationships: determining pore network energy such as flat events, whereas the smallest principle component the least similar energy such as random noise. parameters for the Ghawar Arab-D using the When the multiples are flat and the primaries dipping, the Thomeer method K-L reconstruction process using principle components, can recover the primary reflections without the presence Clerke, Edward A. (Saudi Aramco - edward.clerke@aram of the interbed multiples. The same reconstruction can also co.com) exclude the principle components representing noise in the J.H.M. Thomeer of Shell Oil Company developed a powerful data. Thus, the final reconstructed data have a be�er signal- method for the analysis of mercury injection capillary to-noise ratio. Model-based K-L filtering does improve the pressure data and published this method in 1960. This imaging of primary events in the Paleozoic section in the procedure has been used extensively by Shell for the last 40 exploration target areas. It has increased the confidence of years but has not been used widely outside of Shell, except directly mapping the truncation of the Jauf reservoir using by a few Shell-trained practitioners. At Saudi Aramco, the seismic data. The method successfully a�enuates interbed Thomeer method has been used to analyze the mercury multiples only when there is dip discordance between the injection capillary pressure data (MICP) from 125 samples multiples and the primary reflection events of interest. from the Arab-D reservoir at Ghawar that are part of the Hagerty-Cantrell Data Set. Two complete passes of analysis (474-Oral) Near-surface challenges keynote: have been completed on the data using the Thomeer static corrections in the 21st Century analysis procedure. Of 125 samples, 43 are monomodal, 78 are bimodal and 4 are trimodal. The quality of the Cox, Mike (Geophysical Consultant - [email protected] analysis is evaluated by generating a Thomeer Permeability on.co.uk) using the Thomeer fi�ing parameters and comparing it to the actual measured sample permeability. The results Static corrections are routinely applied to almost all are quite good over a wide range from 0.1 to 2,000 mD, surveys. Their main emphasis has been the computation consistent with the result that Thomeer found for a similar and application of datum and residual static corrections on comparison performed on the Shell Rock Catalog data set land and transition zone surveys, and simple corrections of 279 rock types; an uncertainty of a multiplicative - 1.8x on marine surveys. Model data, incorporating a wide . This method offers significant advantages over Levere� J weathering trough, are used to demonstrate the current function and FZI methods. Key advantages for the Ghawar approach and show the impact on structural and isopach Arab-D reservoir are the direct handling of micro-porosity times. In this analysis, the issue of cross-domain leakage in using the superposition of Thomeer hyperbolae and the use residual static corrections is discussed. Raypath analyses of the measured and Thomeer empirical permeabilities as a demonstrate that vertical raypaths assumed by static consistency check. Finally, permeabilities computed using corrections are incorrect, as near-surface layer raypaths the empirical Thomeer equation compare exceedingly well are rarely vertical, although vertical travel is a good with the measured permeabilities in the Ghawar Arab-D approximation in many areas. The relationship of static over the wide range from 0.1 to 2,000 mD. corrections to other data processing techniques also needs to be considered. We should compensate for near-surface features and elevation differences with corrections that 54 55

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take nonvertical near-surface raypaths into account; that pressure is maintained by peripheral water injection in the is, dynamic corrections should be applied so that the aquifer, which is the primary driving mechanism for oil time shi�s are functions of reflector depth and source-to- production. As the Arab-D reservoir becomes progressively receiver offset. Various techniques have been proposed, mature, early water encroachment, anomalous production, such as wave-equation datuming and pre-stack depth faults and fractures create production problems. In order to migration. However, as with datum static corrections, these monitor such irregularities in fluid movement and increase techniques require an accurate near-surface model. Many oil recovery, installation of permanent downhole multi- techniques used in geophysical data analysis are based component seismic sensors has been proposed. The recorded on approximations, but generally constitute a practical data could be used to update reservoir models, make or pragmatic approach to solve specific problems; this is predictions and optimize production by providing consistent certainly the case for static corrections which, in spite of time-lapse images of fluid movement, sweep efficiency, their shortcomings, have served the industry extremely by-passed hydrocarbons and other phenomena. Permanent well. Is it now time to phase out their usage for certain seismic sensors can also detect microseisms caused by the types of near-surface conditions so that their application is changing stress state of the reservoir during production and consistent with the wave equation? injection. Micro-seismic events in the reservoir can delineate fluid-flow paths and define conductive fracture geometry at interwell scale. The key factors that dictate time-lapse (447-Oral) High-fidelity vibroseis for subtle seismic application for reservoir monitoring are sensitivity stratigraphic feature detection and repeatability. If the sensitivity of seismic time lapse a�ribute is low, the repeatability issue becomes important. Crisi, Peter A. (Saudi Aramco - [email protected]) A feasibility study was conducted recently for time lapse and John L. German (Saudi Aramco) seismic monitoring using permanent downhole sensors. High-Fidelity Vibroseis (HFVS) is a technique designed Synthetic time lapse seismograms were computed from to optimize vibroseis imaging. It has been used by Saudi reservoir flow simulation model and rock physics data from Aramco on a test line over an older vintage 2-D seismic line wells. Comprehensive analyses of different, possible, seismic at Abu Markhah/Nuayyim fields. The objective of the test line monitoring methods, including both active and passive was to improve the imaging of subtle stratigraphic features in measurements for micro-seismicity were performed over the the Unayzah reservoir and to address the observed changes Uthmaniyah sector, a mature area in Ghawar field. Well log in wavelet character between the three wells on the line. In and core analysis data were used to build the rock physics the test, the same 2-D line was acquired three times. First, it and petrophysical models that relate reservoir properties was acquired with conventional 2-D acquisition parameters, (porosity, lithology, fluid saturation) to the elastic rock including five vibrators sweeping six sweeps on each VP properties that impact the seismic response (bulk modulus, with conventional source arrays. Next, it was acquired in shear modulus, density). This provided elastic properties HFVS mode with point sources sweeping five times on in each cell of the dynamic model. For time-lapse steps each VP, vibrators spaced cross-line. The third acquisition of the dynamic simulation model, a corresponding elastic scheme was in HFVS mode with point sources sweeping model and its seismic response for each cell were computed. six sweeps each VP, and vibrators spaced in-line. Production Changes in seismic response produced the synthetic time- rates were comparable with the three techniques. This study lapse seismic a�ribute data that would quantitatively relate will examine the relative strengths and weaknesses of each to changes in fluid saturation. Results of the study provided technique from processed results. The HFVS technique the most practical approach for seismic monitoring and involves inversion of the sweep to minimum phase, using one design specifications in a field trial. accelerometer on the baseplate and one on the reaction mass of the vibrator. Harmonic distortion, phase errors, and surface (482-Oral) Effect of basement tectonics on transmission variations are handled more accurately than hydrocarbon prospective in Zagros, Iran with conventional acquisition, resulting in improved wavelet processing. This HFVS dataset showed improved wavelet Davoodi, Zeinab (Tarbiat Modarres U - stability relative to the conventional datasets. Stacked data [email protected]) and results show improved stratigraphic imaging on the cross- Ali Yassaghi (Tarbiat Modaress U) line HFVS dataset. This dataset also showed a channel feature in the Unayzah reservoir section that was not imaged on the The studied area is located in the northwest Zagros Fold- conventional dataset. HFVS was successful on this dataset in Thrust Belt (Dezful Embayment). This structurally complex the imaging of subtle, low-impedance stratigraphic features. region was affected by subsurface tectonic lineaments possibly during the late Alpine Orogeny. A detailed assessment of Landsat images, together with geomagnetic (426-Oral) Permanent seismic sensors in and earthquake data, resulted in the identification of monitoring Arab-D reservoir: case study in subsurface transverse faults. Three sets of faults were Ghawar field, Saudi Arabia identified using the curved geometry of foreland folds and newly developed folds. The first is a right-lateral Dasgupta, Shiv N. (Saudi Aramco - strike-slip set of faults oriented NW-SE. The second is a [email protected]) less-developed, le�-lateral strike-slip set of faults that is oriented NE-SW. The third set is oriented nearly N-S but The Ghawar field in eastern Saudi Arabia produces oil from is less obvious on Landsat images than the other two sets; the Jurassic Arab-D reservoir. The northern Ghawar sector however it can be clearly detected using geomagnetic has been under production for over 50 years. Reservoir data. There are similarities between the orientation of

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these lineaments and the geomagnetic lineaments, and limited wider application (i.e. “to get more out of remote with previously identified basement faults in the northern sensing data”) was recognized and addressed through margin of Arabian Platform. This data, together with technological initiatives such as InSAR (reasonably accurate the depth of earthquakes related to reactivation of these Digital Elevation Model information and subsidence lineaments, implicitly reveals that they are deep-seated measurements) and Hyperspectral. However, the aim is basement faults. Major oil fields within the Zagros Belt to maximize the value of current sensors by integrating occur as structures within the NW-trending folds within them with other available information. Recognizing the Tertiary sediments. However, in the Arabian Platform this potential, PDO has joined the SAR-View project, an oil fields are in NS-trending anticlines within the Middle industry project between GAFAG, a company for applied Jurassic-Cretaceous sediments. The Arabian anticlines remote sensing services based in Munich Germany, and have been a�ributed to movement along basement faults the European Space Agency (ESA). The purpose of the before the Zagros Collisional Orogeny. This suggests that project was to develop customized data products based older oil-bearing anticlines have been overprinted by the on SAR/multi-spectral earth observation data for the oil younger NW-trending Zagros structures. Therefore it is and gas industry. The end result consists of two products: proposed that the older NS-trending anticlines can also be near-surface and upli� probability mapping. Near-surface exploration targets in the Zagros Fold-Thrust Belt. mapping is useful as Oman’s oil concession areas mainly consist of flat gravel plain with braided wadis that are filled with loose sand and gravel, and areas of sand dunes. Such (19-Oral) Cyclostratigraphic correlation near-surface geology with diverse ground types, disparity application on the Arabian Plate in surface ruggedness and stiffness, or any other subtle surface/near-surface alteration, can strongly affect seismic de Coo, Jan (Shell - [email protected]), Cees van data quality. Integrating interpreted remote-sensing data Oosterhout (Shell) and Maarten Wiemer (Shell) as a ‘false’ horizon into a seismic trace interpretation Cyclostratigraphy studies the influence of periodic climatic system clearly demonstrated good correlation between changes on the stratigraphic record, which is thought to be seismic data quality and changes in the surface topography. determined by earth orbital forces with a periodicity between Further work will be required to establish the actual impact 20,000 to half a million years. The challenge is to extract the of surface changes on the seismic quality. Upli� probability cyclostratigraphic signal from the complex stratigraphic mapping is designed as a hydrocarbon exploration tool records, to arrive at a sound chronostratigraphic for the detection of upli� structures in the subsurface. correlation. A tool to study cyclostratigraphy is the PC- It considers geomorphology combined with geological, based application CycloLog (ENRES), which enables the stratigraphical information and the tectonic se�ings. The mathematical manipulation of wireline logs to recognize upli� probability map over a pilot area in Oman was and enhance cyclic bedding amplitude and frequency. A validated against interpreted structures from 3-D seismic pilot project across a Permo-Triassic evaporitic carbonate data. With good correlation between upli� mapping sequence in a number of wells from the Arabian Plate, and subsurface structures, it was decided to apply this showed that analysis of spectral a�ributes with the help inexpensive technology to the whole of the PDO concession of an integrated predictive error filter (INPEFA) provides area (113,500 sq km). Progress made so far clearly indicates a means of detailed correlation. Inflection points on the that the integration of Remote Sensing information delivers spectral a�ribute curve indicate correlatable geological more than pre�y wall paper, and can provide value adding events related to facies changes and/or basin dynamics. information at all stages of seismic acquisition, processing Maximum entropy spectral analysis (MESA) suggested and interpretation, particular in arid countries like Oman. that the dominant observed wavelength is associated with a cyclicity frequency coinciding with a period of 37,000 years, (171-Poster) Organic geochemistry of oils which may correspond with the obliquity periodicity in and condensates associated to sour gas in Triassic times. The interpreted dominant periodicity was Gulf used to convert depth logs to geologic time. Subsequently, with the help of a trapezoidal band pass filter a synthetic Dessort, Daniel (Total - [email protected]), Francois insolation curve in geologic time could be derived. Results Montel (Total), Gerard Caillet (Total) and showed that CycloLog provides additional tools to improve Marc Lescanne (Total) correlation between wells both on reservoir and regional geological scales. The results with respect to climatic Hydrogen sulphide and carbon dioxide in reservoirs can pa�erns and cyclic sedimentary sequences however, must be generated by different ways: (1) thermal decomposition be considered speculative, particularly in the absence of of IS or IIS sulphur-rich kerogens at low maturity; (2) oil detailed chronostratigraphic control. biodegradation in reservoirs by sulphate reducing bacteria (SRB); (3) thermal decomposition of sulphur-rich oils; and (117-Oral) From pretty wall paper to value (4) abiological thermochemical sulphate reduction (TSR). Sour gas, and especially hydrogen sulphide concentration adding image technology in the Gulf varies widely. It is thought that most of the de Lestrange, Vianney (PDO - vianney.mr.delestrange@p hydrogen sulphide concentration greater than 5 percent do.co.om), Peter Engbers (PDO), Rashid Al-Hinai (PDO), was produced by TSR occurring from about 100 degrees Tobias Wever (GAFAG) and Ulrich Steiner (GAFAG) C. In petroleum reservoirs, SRB activity appears negligible up to 80 degrees C and is known to produce less hydrogen Remote Sensing data has been in use for many years as a sulphide than TSR. As the by-products of TSR and SRB are backdrop for maps and for general planning purposes. The similar, gas analysis alone cannot easily discriminate which

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process was responsible for the production of sour gas (238-Oral) Pre-stack seismic analysis for when its relative concentration is low. For these reasons, fracture and rock property prediction over a it is important to study at the same time gas composition large Abu Dhabi carbonate field: a feasibility and characteristics of associated liquid fractions. Oils and condensates were studied using detailed molecular study analysis: (1) the thermal maturity of the liquid fraction Dong, Wenjie (ExxonMobil - wenjie.dong@exxonm was estimated; (2) markers such as thia-adamantanes and obil.com), William Soroka (ADCO), David Y. Wang mercaptans (formed as by-products of TSR) were measured; (ExxonMobil) and James S. Schuelke (ExxonMobil) and (3) specific biodegradation of light compounds was sought. In addition, analysis of carbon isotope ratios of The 3-D seismic data acquired recently over a large specific compounds was achieved, TSR and BSR alteration carbonate field in Abu Dhabi, United Arab Emirates, 13 12 showing different effects on the C/ C ratio of specific provide an opportunity for evaluating the feasibility and compounds. value of azimuthal AVO (AZAVO) analysis over carbonate reservoirs. In addition to the familiar AVO intercept and (376-Oral) Automated facies characterization gradient a�ribute volumes, AZAVO analysis produces of deep-water fan-channel complexes, two azimuthal a�ribute volumes: azimuthal amplitude variation intensity and the principal direction of this western Nile Delta, Egypt variation. In general, these two azimuthal a�ributes are related to fracturing intensity and fracture orientation Dight, Michelle (Paradigm - michelled@paradigmgeo when the data are processed properly. Therefore, an .com), Robert M. Bond (Paradigm), Gavin J. Baldwin integrated approach for interpreting the four AZAVO (Paradigm), David W. Phelps (Apache) and a�ribute volumes can reveal valuable fracture and rock John Bedingfield Apache( ) property information for reservoir characterization and Over the past 35 years approximately 3.8 BOE have been potentially reservoir flow simulation. However, in order to discovered in the Nile Delta of Egypt, primarily as gas gain confidence over the AZAVO results and their range of and gas condensate. Between 2000 and 2002, an Apache- validity, rigorous azimuthal AZAVO feasibility work must led partnership acquired 2,600 sq km of high quality 3-D be carried out. In our study, we address AZAVO feasibility seismic data in the deep-water portion of Apache’s West for fracture and rock property prediction by detailed Mediterranean Concession in the western Nile Delta. examination of the following four fundamental aspects: Subsequent drilling resulted in four new field discoveries (1) Seismic acquisition adequacy for AZAVO, source/ and one successful appraisal well in the deep-water portion receiver coupling and directivity, overburden anisotropy of this concession. Multiple a�ributes from the seismic effects. (2) Pre-stack seismic data quality, nature of noise, survey have been analyzed, classified and calibrated against azimuthal integrity of the pre-stack data. (3) Rock physics data from recently drilled wells. The aim of this project was support for AVO analysis and angle stacks evaluation. (4) to predict, identify and quantify good quality reservoirs in Validation/calibration with geological and engineering the Pliocene deep-water, fan-channel complexes. During data and modeling techniques. This study describes the the analysis, several a�ribute volumes were generated for quantitative approaches, analysis methodology, results and the area of interest by applying geometric and post-stack, recommendations rendered from the study. wave-equation based algorithms. Principle Component Analysis (PCA) was used to gain a be�er understanding of (24-Oral) Basin analysis and hydrocarbon a�ribute correlations, data redundancy and noise. This was potential of the Darag-Lagia Basins, Gulf of followed by the application of a number of sophisticated multi-a�ribute volume classification techniques including Suez, Egypt Multi-Resolution Graph Clustering (MRGC). MRGC is a Douban, Adel F. (Sipetrol - [email protected]), dot-pa�ern recognition method based on non-parametric Ahmed M. Abu Khadra (Cairo U), Mohamed Darwish graph data representation. It works by analyzing the (Cairo U) and Mounier H. El-Azabi (Cairo U) underlying structure of the data to determine the natural data groups within it. Importantly these groups may This study involved a comprehensive review of the have very different densities, sizes, shapes, and relative hydrocarbon habitat of the Gulf of Suez ri� basin, and separations. The program automatically determines a prediction of its remaining hydrocarbon potential. The optimal number of clusters while allowing the geoscientist present hydrocarbon occurrences in the northern part of to control required level of detail. A cross-check was then the Gulf of Suez are compared to the assessed potential performed to determine if the seismic data could identify reserves to highlight areas for future exploration activities. these facies, and the optimal barycentres were used for The study consisted of a basin analysis and an evaluation supervised classification. Application of MRGC and of the petroleum system (e.g. reservoir quality, source rock PCA, in conjunction with visualization of the 3-D dataset, distribution, geothermal gradient, maturation history). The resulted in an enhanced understanding of the facies study also reviewed: (1) reservoir lithology, distribution, distribution within the deep-water, fan-channel, reservoir quality and porosity; (2) source rock distribution, organic complexes. These results will provide useful input into richness, type and maturity; (3) geothermal gradient maps, the optimal placement and design of future appraisal and burial/maturation history models; (4) sealing rock; and (5) development wells. timing of hydrocarbon generation, migration pathways and entrapment style. The study area was subdivided according

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RedSea advert

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to the interpreted hydrocarbon migration trends into two (85-Poster) Regional controls on reservoir major clusters. The northern cluster includes the Darag properties in the Shu’aiba Formation of and Nebwi basins that generally dip to the southwest. The North Oman southern cluster includes the Lagia Basin that generally dips to the northeast. The proven recoverable reserves in Droste, Henk H.J. (JVR Centre for Carbonate Studies - Sudr, Matarma, Asl and North Darag fields cumulatively [email protected]) are 0.119 BOEB; while the ultimate recoverable reserves in Darag and Nebwi basins are 1.204 BOEB, which is ten times The construction of a regional sequence stratigraphic greater than the proven reserves. The ultimate recoverable framework significantly improved the understanding of reserves in Lagia Basin are 1.479 BOEB. Structural or regional variations in reservoir properties and geometries stratigraphic traps, which exist along the migration path of the Aptian Shu’aiba carbonates in Oman. A distinct should be expected full to the spill point and might be relationship between systems tracts and reservoir facies considered for future exploration. Five prospective areas and architecture has been recognized which is related to: have been identified over the northern Gulf of Suez area, (1) changes in stacking pa�erns in response to variations which are: Area I: North Darag, Area II – South Darag, Area in available accommodation space; (2) the response of the III – Nebwi, Area IV – Ras Lagia and Zaafarana and Area V carbonate factory to variations in the influx of clays and – West Lagia. nutrient content of the water; and (3) duration of exposure at the sequence boundary. Within the Shu’aiba Formation a (83-Oral) Sequence stratigraphic framework Transgressive (TST), Highstand (HST) and early Lowstand (LST) Systems Tract has been recognized. Reservoirs within of the Aptian Shu’aiba Formation in Oman the early TST are laterally extensive but hardgrounds and condensed intervals form horizontal baffles significantly Droste, Henk H.J. (JVR Centre for Carbonate Studies - reducing vertical permeabilities. The reservoirs did not [email protected]) experience significant early fresh-water leaching but The Shu’aiba Formation consists of Aptian platform interior transgressive lags may form high permeability streaks. The carbonates and is an important oil reservoir in Oman. early HST reservoirs consist of rudist biostrome mounds A sequence stratigraphic framework was constructed to with a highly complex internal architecture. They show assess regional controls on reservoir development. Two strong variations in permeability related to progradational third-order sequences can be regionally correlated. The geometries, channeling and impact of early fresh water lower sequence starts with a transgressive systems tract diagenesis on the rock fabric. The late HST reservoirs (TST) of laterally extensive very shallow marine to intertidal show a more simple reservoir architecture with a gradual sediments, followed by shallow marine algal limestones shallowing-upward trend towards higher energy be�er transgressing over exposed limestones of the Kharaib reservoir facies. Low angle clinoforms, however, may Formation. During the late TST the development of algal affect the lateral connectivity. The gradual vertical change mound complexes led to a differentiation on the platform. in reservoir properties also results in long transition zones. Between these mounds fine-grained, in places organic- Reservoirs in the early LST consist of porous pelletoidal rich deeper-water sediments were deposited related to pack/grainstone wedges with a strong impact of early a maximum flooding surface (MFS). During the early fresh water diagenesis on rock fabric. Interbedded clays highstand systems tract (HST) rudist biostrome complexes and hardgrounds related to flooded exposure surfaces colonized the mounds. In the late HST the rudistic growth however significantly reduce vertical permeabilities. decreased, distal ramp sediments filled in intermound Horizontal permeability may be affected by progradational depressions, and the mounds merged into a platform geometries. Wedges and pinch-outs are common and there surrounding an intraplatform basin. A regional drop in is a high potential for stratigraphic trapping. sea level associated with subaerial exposure and influx of fine-grained clastics terminated deposition on the platform. (62-Oral) Sequence stratigraphy of the First The early lowstand systems tract (LST) contains offlapping Eocene Reservoir, Wafra field, PNZ, Kuwait wedges of argillaceous carbonates and carbonate-rich claystones along the margins of the intraplatform basin. and Saudi Arabia Ultimately, the whole platform interior was exposed and a Dull, Dennis W. (ChevronTexaco - dennisdull@chevrontex late LST wedge was deposited along the ocean margin of aco.com) and William S. Meddaugh (ChevronTexaco) the platform. The basal clays of the Nahr Umr Formation form the TST overlain by an MFS formed by the Marker Located in the Partitioned Neutral Zone (PNZ) between Limestone Bed. The sequence stratigraphic framework Saudi Arabia and Kuwait, the First Eocene Reservoir is can be used as a template which: (1) Explains the regional the youngest of five producing intervals that range in age variation in reservoir/flow properties. (2) Allows grouping from Eocene/Paleocene to Lower Cretaceous at Wafra field. of fields according to stratigraphic se�ing for comparison The First Eocene dolostones were deposited in arid to and analogs in reservoir studies. Incorporation of seismic semi-arid conditions on a shallow, low to moderate energy data allowed significant refinement and improvement of inner shelf or ramp se�ing. The presence of evaporites the previous sequence stratigraphic models, which were suggests restriction was sufficient for the development based on well data only. of hyper-saline lagoons and sabkhas. The sequence stratigraphic interpretation of the First Eocene Reservoir is based on five recently cored wells. These wells have

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numerous hardgrounds that increase in frequency to the matrix material, the Sr method is ideally suited for dating north. Intraclastic rudstones occasionally overlay the Asmari stratigraphy. Age-depth profiles in Ahwaz, Bibi hardgrounds and subaerial exposure surfaces. In some Hakimeh, and Marun oilfields show that a distinct decrease cases brecciation is observed beneath the hardgrounds in sediment accumulation rate occurred abruptly at around indicating intermi�ent sub-aerial exposure and incipient 24.5-24.0 Ma (near the Oligocene/Miocene boundary). soil formation. The shallowing-upward cycles are capped Accumulation rate decreased from 41-93 meters/million by mud-dominated rocks, hardgrounds and exposure years (m/my) in Oligocene time to 14-28 m/my in early surfaces that are correlative with gamma ray (GR) highs that Miocene time. Major depositional sequences defined from help define the cycle tops on well logs. Many of the cycle facies relations and cycle-thickness pa�erns have durations tops and associated GR highs can be correlated across the of 1.1-2.6 my, whereas depositional cycles represent average entire length of the Wafra field (approximately 20 km). The time intervals of 100-300 thousand years. The Sr-age ability to correlate the fine-scale GR pa�ern and correlative profiles allow correlation of sequence boundaries between cycles likely indicates that the First Eocene Reservoir was the fields, supporting a pa�ern of progradation and basin deposited in an aggradational-progradational portion of a infilling from Bibi Hakimeh field toward the northwest. Sr tectonically stable shelf where subsidence kept pace with analyses of most anhydrite and dolomite samples plot close carbonate deposition. The First Eocene reservoir has been to or below (at slightly younger ages than) the macrofossil subdivided into ten interpreted high-frequency sequences age-depth trend, indicating formation from seawater, either (HFS) bound by hardgrounds, subaerial exposure surfaces, on the seafloor or by shallow (up to several tens of meters or lithofacies tract offset. Placement of the ten observed depth) reflux of hypersaline brine. An exception to this is HFS into the regional sequence stratigraphic framework is anhydrite of the base-Gachsaran cap-rock and dolomites on-going. in the top 25 m of the Asmari Formation, where Sr ages older than the macrofossil age-depth trend may indicate contribution of Sr from older evaporite beds, possibly (481-Oral) Enhanced signal-to-noise ratio recycled from the basin margins. and bandwidth through explosives design

Egan, Mark S. (WesternGeco - mark.egan@westerngeco. (429-Poster) Geological aspects of the 3-D com), Glen-Allan Tite (WesternGeco), Patrick Thompson geocellular model of Thamama reservoir in (WesternGeco) and Jim Brookes (Schlumberger) an offshore field, Abu Dhabi

The signal-to-noise ratio and bandwidth of explosive- Elsaid, Mohamed Elhami (ADMA-OPCO - sourced seismic data are the direct results of the properties [email protected]), Faisal Al-Ginaibi (ADMA-OPCO) of the explosives used and the near-surface conditions. and Adel Belgaid (ADMA-OPCO) Some of the current properties of seismic explosives may not be the most desirable. Multi-variant testing has A Lower Cretaceous carbonate reservoir in an Abu Dhabi confirmed that in many environments, the efficacy of offshore field was characterized with a 3-D-geocellular seismic explosives can be improved. These tests indicate model. A total of 7,241 � of core and thin sections were that the design of the explosive utilized is critical to the described in detail and tied to the petrophysical log data. ultimate quality of the seismic data, and that data quality Based on detailed semi-quantitative thin section and can be improved through customized explosives. Current core description, Mercury injection and petrophysical data suggest that 3 to 6 dB of signal enhancement may parameters, a rock-typing scheme composed of 11 rock be achieved in the seismic bandwidth through the use of types was identified and validated. Depositional and metalized explosives. Examples of these improvements will diagenetic models were also generated to provide a be presented in this study. predictive tool for reservoir quality and its distribution. The depositional model represents a shallow-water carbonate (253-Oral) Strontium-isotope dating of the platform with a set of facies that characterize each tract. The diagenetic model comprised surface, subtidal, shallow, Asmari Formation (Oligocene-Miocene) in and deep burial diagenetic events, such as micritization, Ahwaz, Bibi Hakimeh and Marun oil fields, fringing calcite marine cement, vadose grain leaching, southwestern Iran compaction, stylolitization, dolomitization, anhydrite cementation and fracturing. A sequence stratigraphic Ehrenberg, Stephen N. (Statoil - [email protected]), John framework was implemented based on core and log M. McArthur (UC London), Ma�hew F. Thirlwall (Royal data. The reservoir model is that of a distally steepened Holloway, U London), Neil A.H. Pickard (CCL) and carbonate ramp characterized by thick regressive events Gi�e V. Laursen (Statoil) or highstand systems tracts (HST), and thin transgressive systems tracts (TST). It is composed of three stacked high- The strontium-isotope method of dating minerals resolution sequences, which were further subdivided into precipitated from sea water has been applied to core 43 high-order depositional cycles, that constitute the basis samples from the Asmari Formation using micro-analyses of the layering model. These eustatic cycles represent the of mollusk shells and lime mud matrix. The Asmari scale at which changes in petrophysical properties occur. Formation consists of about 400 m of cyclic platform The quality of the geological model: (1) has a direct impact limestone, dolostone, sandstone, and shale. Due to the on reserves estimates; (2) helps to improve the reservoir rapid and steady rate of change of the global Sr-isotope development scheme; and (3) affects reservoir management curve during Asmari time (31-18 Ma = Rupelian- and well placement. Burdigalian), and the presence of well-preserved shell and

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(230-Oral) New approach to analysis was recalculated with a be�er accuracy. This technique behind casing using cased hole resistivity, resulted in an increase of the total porosity. One last geochemical, and epithermal neutron application is mainly used for carbonate reservoirs with a small percentage of anhydrite. Quantifying the right logging percentage of anhydrite was one of the requirements of the oil company. That was easily achieved from the sulfur yield Elsherif, Ahmed (Schlumberger - [email protected] of geochemical logging. This technique is not suitable when lb.com), Mohammed Al-Haimer (KOC-JO) and the oil in the reservoir has a large percentage of hydrogen Waleed Al-Awadi (KOC) sulfide; in this case the tool will measure the sulfur from Evaluation behind casing was achieved several years ago both the oil and anhydrite, giving an incorrect answer. using thermal neutron decay time measurements. Recently, several breakthrough technologies have improved and (266-Oral) Oil viscosity measurement expanded the ability to see behind the pipe. Cased hole on continuous basis using magnetic resistivity, geochemical logging, cased hole density and epithermal neutron logging are the main tools used for resonance: a new approach from Kuwait these evaluations. In this study, we illustrate several Elsherif, Ahmed (Schlumberger - [email protected] examples in which these technologies were used for lb.com), Mariam Al-Saeed (KOC) and successful evaluations. The first example covers a well that Mona Al-Rushaid (KOC) was logged in open-hole conditions, and then relogged a�er casing was set. A comparison of the results confirmed Measuring the oil viscosity during open-hole logging was the accuracy of formation evaluation behind casing. The one of the main requirements of KOC. This requirement was geochemical results were used in combination with the triggered by the presence of different oils across the same epithermal neutron data to predict a density measurement reservoir or by the local variation of oil viscosity versus behind casing. The second example illustrates the case of depth. The technique used to accomplish that requirement a well that could not be logged in open-hole conditions was based on NMR logging. It is well-known that different because of bad hole conditions. Results of the cased hole hydrocarbons will diffuse with different amplitudes based evaluation gave the client the essential answer to complete on their viscosity at down-hole conditions. The idea the well successfully. The third example covers an old well used in this study was based on acquiring two different that was analyzed using the cased hole resistivity and the passes of NMR logging with two different values of echo thermal neutron decay time technique. The comparison spacing. When the logarithmic mean of the two pore size with the very old resistivity log on the well was rather distributions are displayed linearly, they will coincide interesting since it showed more oil at present which could or separate depending on the hydrocarbon viscosity have migrated. The evaluations described in the study present in the formation. The more separation between represent the first use of this technology in Kuwait. Wells the two logarithmic mean times, the less viscosity the oil were operated either by KOC, or Joint Operations, which is. Furthermore, the results were confirmed using another covers the neutral zone between Saudi and Kuwait. technique of stationary measurement acquisition using different wait times and echo spacing on selected points in (231-Oral) Different applications of the the reservoir. A new technique of processing was also used geochemical logging over sandstone and to process the results of the stationary measurement based on the relation between the amount of diffusion and the carbonate reservoirs in Kuwait transverse relaxation time. The different fluid saturations along with hydrocarbon viscosity determination, were Elsherif, Ahmed (Schlumberger - [email protected] achieved from the stationary measurements. The above .slb.com), Mariam Al-Saeed (KOC), Shaikh Abdul Azim technique was used in different reservoirs from Kuwait (KOC), Osama Elgendi (KOC-JO) and with good results. Ahmed Abdullatif (KOC)

During the last years, geochemical logging has increased (260-Oral) Sequence stratigraphy, reservoir dramatically in Kuwait. Several applications have been layering and palaeogeography of the Wara introduced for both sandstone and carbonate reservoirs. For sandstone reservoirs, the true shale volume is critical Sandstone Formation, Khafji field for proper reservoir characterization. The presence of ‘hot Emerson, Paul F. (Sco� Pickford – [email protected]), sands’ makes it difficult to correctly determine the shale Keiichi Miyazawa (Al-Kha�i JO), Kenji Kaneko (Al-Kha�i volume, because the gamma ray measurement is not a good JO) and Mousa Ali (Al-Kha�i JO) shale indicator. In these sands, geochemical logging plays an importnat role in evaluating the true shale volume from The Cretaceous-aged (Albian) Wara Sandstone Formation the aluminum concentration in the formation. Another forms one of the less well known reservoirs of the Kha�i application is the use of the computed grain density of field in the offshore Partitioned Neutral Zone between the formation to calculate the total formation porosity Kuwait and Saudi Arabia. A recent study to achieve a from the bulk density. Historically, a constant value of be�er understanding of the reservoir layering zonation grain density was used for that purpose. As a result of within a sequence stratigraphic framework recognized impurities in the sandstone such as siderite and pyrite, the a cyclical pa�ern of deposition. The pa�ern consists of matrix density is no longer a constant value across different a series of prograding deltaic/estuarine units: Zones 2B, layers of the reservoir. Using the computed grain density 3B and 4B (broadly highstand system tracts) that are from geochemical logging, the total formation porosity

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Schlumberger advert

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vertically separated from one another by estuarine/marine (113-Oral) Intrasalt carbonate stringer mudstones: Zones 2A, 3A and 4A (broadly transgressive volume interpretation in Oman systems tracts). These overlie Zone 2V (lowstand system tract), an economically-important incised-valley filled Engbers, Peter (PDO - [email protected]), Ahmad with fluvial and later marginal-marine tidal sands. Early Zulkifli (PDO), Fahar Rabeei (PDO) and deposition appears to be controlled by structural elements, Saada Rawahi (PDO) which principally created a topographic high to the south of the main valley fill. The channel system drained in an The intra-Ara salt carbonate stringers of the Huqf ENE direction, which was maintained during a subsequent Supergroup are one of the more complex deep oil plays highstand tract (Zone 2B). During this period a broadly in South Oman and presently constitutes a significant part tidal deltaic/estuarine depositional se�ing was developed PDO’s exploration prospect portfolio. Because conventional in the Kha�i area, with more fully-marine se�ings seismic interpretation is difficult and time-consuming, postulated to the east and northeast. Channel systems were novel seismic interpretation techniques are being applied generally low-energy and were laterally equivalent to mud- to improve current exploration mapping methodology. prone marsh, interdistributary bay, tidal flat and localized Seismic volume interpretation is one of these opportunities. shoreface environments. A later rejuvenation of the fluvial/ We herein highlight this technology and its role in the tidal system, during the deposition of Zones 3B and 4B, stringer exploration workflow. The volume interpretation appears to reflect a slight adjustment of the palaeoflow to workflow first subsets data on the basis of continuity (not a more northeasterly direction, perhaps indicating that the all stringers are identifiable by high amplitudes) and then early topographic high to the south had broadly ceased to uses body checking and unravelling on impedance data control the channel systems. to find and analyse the stringers. The stringer bodies are automatically ranked by volume (through a voxel-GRV relation). Further in the unravelling process, the stringer (112-Oral) The poor seismic data quality bodies are broken into subbodies subject to more restrictive challenge: new techniques in volume amplitude thresholds. This is effectively an internal interpretation to improve delivery of connectivity analysis of the stringers using a range of structural frameworks thresholds to identify a range of connectivity scenarios. This method discriminates bodies into meaningful fault Engbers, Peter (PDO - [email protected]), Jack and/or stratigraphic compartments, and estimates sizes Filbrandt (PDO), Andrew Growco� (PDO), Martin and shapes of potential production cells. Subsequently, Roberts (PDO) and Awfa Al-Amri (PDO) 3-D visualization of the identified stringers is done using semblance and other discontinuity volumes to evaluate Seismic interpretation is challenging in Oman due to faults in order to test various connectivity scenarios. In pilot overburden complexity, structure, and reservoir geology. studies, resulting bodies have compared well with hand- Many areas, particularly in South Oman, have poor seismic interpreted stringer horizons. It is now envisaged to fast- data quality at reservoir level due to multiples, and noise, track the interpretation of new unmapped datasets using which impart a chaotic seismic image. This makes mapping this technique. It is faster, and provides an essential first of top reservoir and faults difficult. Improvements in step in evaluating new data sets prior to detailed mapping. multiple elimination techniques, although successful at removing multiples, also destroy primary energy. As a result other techniques have been developed to tackle (393-Oral) Pre-stack migration velocity the poor seismic data quality challenge. Recently, seismic analysis in the Tau domain volume image processing and interpretation has been the focus to improve seismic data quality for production and Erickson, Kevin E. (Saudi Aramco - kevin.erickson@aramc exploration purposes. In particular the ‘vanGogh’ filter o.com), Emad Aljanoubi (Saudi Aramco) and (structurally-oriented noise reduction filter with edge Tariq A. Al-Khalifah (KACST) preservation) is used to enhance seismic images, and to highlight structural features (faults and fractures) using Due to the inherent ambiguities involved in performing so-called ‘stopper-voxels’ based on the edge detection pre-stack migration velocity analysis in the depth domain, concept. The interactive environment ‘FaultWorld’ has it is o�en difficult to converge to a proper estimate of the recently been developed to facilitate fault and fracture interval velocities. An error in the initial velocity results in interpretations through selection of dip/azimuth ranges migration of events to incorrect depth, which then makes of automatically extracted structural discontinuities. Using it difficult to estimate the correct velocities in the following these toolkits, PDO and Shell are developing various iterations. In order to avoid this issue we explore a new volume interpretation workflows to deliver fast track algorithm in which the migration and velocity analysis are ‘structural frameworks’ i.e. top reservoir interpretation done in the vertical time, or tau domain, and the conversion with faults networks. Data conditioning at various levels is to depth is performed at the end of the process once the key to developing a robust approach for these poor quality best estimates of the velocities have been achieved. Even seismic data. Improved coherency of reflections is seen as if inaccurate velocities are used to begin the process, or well as improved fault detection. Using ‘FaultWorld’ and chosen during one of the velocity analysis iterations, the new, robust structurally-oriented trackers, a structural data will migrate to the correct time. A Kirchhoff migration framework can then be generated and exported to static algorithm is employed for its flexibility, efficiency and reservoir modeling packages in a relatively short time, ability to handle inhomogeneous media. The capability of where these models can be validated with other datasets. the method to focus small parts of the data makes it ideal for use in velocity analysis. The algorithm has been modified to

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operate in the space-tau domain by calculating the travel- from 1972 until 1975, and since then has been under full times with kinematic and dynamic ray-tracing equations. In water injection. Logged contrasts in rock characteristics a synthetic model with a strong shallow velocity anomaly, showed that the water sweep was effective in the be�er- tau migration has reproduced the model in depth a�er two quality Upper Mishrif reservoir. Logs also indicated that iterations. For a land field data example, conventional depth parts of the Lower Mishrif reservoir were unswept and migration and velocity model updating did not completely overlain by water; they were ‘over-ride’ areas. A series resolve some of the shallow complexities. Velocity updating of horizontal wells drilled since 1996 in ‘over-ride’ areas in the tau domain, however, converged to the desired has made a major contribution to the actual production velocity, with fewer iterations, and produced a reasonable profile and the expected final recovery. The positioning of depth section. the horizontal wells was based on the integration of 3-D seismic, geological model, dynamic reservoir modeling, and a static reservoir model. The presentation describes (26-Oral) Structural growth control of the successes and surprises from the horizontal drilling Khuff exploration play in eastern Saudi program and the technology used by the team to manage Arabia the reservoir. The current challenge is to reevaluate all static and dynamic reservoir data in order to predict remaining Faqira, Mohammad I. (Saudi Aramco - areas of unswept oil. This is not a trivial task a�er 30 years [email protected]), Murdy M. Al-Zahrani (Saudi of production and water-injection by more than 120 wells. Aramco), James L. Rico (Saudi Aramco), Khalid M. Shokair (Saudi Aramco), Michael A. Zinger (Saudi Aramco). Nezar A. Al-Talhah (Saudi Aramco) and (80-Poster) Discovery of a new play William B. Stone (Saudi Aramco) fairway in Yemen: the Late Jurassic Madbi Limestone Well and seismic data studies document that the Khuff gas play is primarily controlled by several structural Ferguson, Sco� (Nexen - sco�[email protected]), growth periods from Carboniferous to Neogene time. The Jonn H. Calvert (Nexen) and John D. Smewing (ERL) play is sourced by the Silurian Qusaiba hot shale, whose distribution is controlled by ‘Hercynian’ structural growth In 2002 a new oil discovery was made by Nexen Petroleum and is seismically mappable in eastern Saudi Arabia. International and partners on Block 14 in Yemen. The Khuff A, B, and C reservoir development was controlled discovery was made in the upper Oxfordian-lower by the Permo-Triassic structural growth over Ghawar Kimmeridgian Madbi Limestone, a stratigraphic interval field and other trends in the area. The syn-depositional deposited just prior to, and during, the earliest period of growth of these trends during the Khuff time contributed Late Jurassic ri�ing in this area. This discovery is significant to reservoir development for two reasons: (1) relatively in that it is the first oil produced from this stratigraphic high paleotopography may have developed a high-energy interval in the Say’un Basin of Central Yemen, and has environment, which set the reservoir quality framework opened up a major new play trend outside of ‘traditional’ of the Khuff reservoir; and (2) higher magnitude growth Lower Cretaceous reservoirs. The Madbi Limestone records of these relative highs may have controlled the early depositional and structural events that spanned the pre-ri� dolomitization process and the porosity and permeability to early-ri� time frame in the Late Jurassic. The lowermost enhancement. The structural growth maps of the Khuff Madbi sediments (pre-ri�) are typically hemipelagic mud- Formation suggest that most four-way dip closures in dominated carbonates, deposited in water depths of 100 eastern Saudi Arabia developed in the Late Cretaceous m or greater. Initial ri�ing had a major impact on Madbi and Early Neogene times. During these times the base depositional pa�erns. In the footwalls of the faults, the Qusaiba source rock was generating wet and dry gases. Madbi was upli�ed to the point where the hemipelagic Fluid inclusion results from Ghawar field Khuff reservoirs carbonates were exhumed and eroded, sometimes confirm the timing of the trap development by showing completely, exposing basement. Rotation of fault blocks in condensate fluids dated between 96 to 106 Ma. The high the hanging walls of the faults simultaneously led to vast magnitude of the Late Cretaceous and Neogene growth thicknesses of mixed clastic-carbonate sediments adjacent reactivated some of the ‘Hercynian’ faults that provide to the fault and forced regressions on the outer upli�ed an excellent conduit between the Qusaiba source and the part of the block. Typical stratigraphic development Khuff reservoirs in the area. in these outer margin se�ings comprises a coarsening- upward succession with hemipelagic carbonates at the base passing up through foraminiferal wackestones and (89-Oral) Rejuvenating a mature reservoir packstones into coarse skeletal grainstones at the top, with 3-D modeling, and horizontal drilling: o�en succeeded by exposure. The primary Madbi reservoir the SW Fateh, Mishrif case study, Dubai is developed in these grainstones. Porosity types are primarily intergranular and biomoldic. Repetition of this Faugeras, Xavier (DPC - [email protected] forced regressive sequence and the stacking of reservoirs m), Jeffrey W. Yeaton (DPC) and Philip J. Rorison (DPC) is a�ributed to pulsed movement on the master faults. The primary technical challenge to exploiting this play further The SW Fateh field in offshore Dubai, is located on a salt- is to define the trend of the platform margin facies through induced dome. Production is from three different carbonate geological and seismic means. reservoirs. This case study shows how a multi-disciplinary team created a step change in the asset’s production profile. The Mishrif reservoir produced under natural depletion

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Nexen advert

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(367-Oral) Jurassic to Cretaceous Aruma Group and Natih Formation below the base Tertiary sedimentation and tectonics in Lebanon and unconformity. Velocity and porosity anomalies from Lekhwair Syria in the northwest to the Huqf-Haushi High in the southeast, provide support for the areal distribution of this event. NE- Ferry, Serge (U Lyon - [email protected]), oriented maximum horizontal stress during the late Tertiary Catherine Homberg (U Paris), Eric Barrier (CNRS), led to the formation of major folds resulting in, for example: Mustapha Mroueh (Lebanese U), Anis Matar (Lebanese the surface anticlines over Natih and Fahud fields, as well as U), Yann Merran (U Lyon), Louaï Machhour (Total), Walid inversion of the Maradi Fault Zone. The regional northward Hamdan (Lebanese U), Fathi Hijazi (Lebanese U) and tilt associated with crustal loading of the Arabian Plate by the Rafik Hamzeh Lebanese( U) Iranian Plate modified traps during the Plio-Pleistocene from Lekhwair to Fahud and south to Musallim. On the coastal chains of Lebanon and Syria, regional extensional tectonics in latest Jurassic created roughly EW- (154-Poster) Sequence stratigraphy of the oriented grabens that would later host the fluvial Rutbah sandstones in Central Lebanon (Chouf area). Syn-depositional Fiqa Formation and proposed subdivision, EW to N120E normal faults have been recognized in both the North Oman Syrian Coastal Range and Lebanon. They are associated with a N30-oriented, extensional tectonic element controlling the Filbrandt, Jacek B. (PDO - [email protected]), development of the Chouf Basin until the late Albian time. Safia Al-Mazrui PDO( ), Peter Osterloff (Shell), Stephen The up to 350-m-thick Barremian Rutbah sandstones in Packer (Millennia), Aida Al-Harthy (PDO) and central Lebanon corresponded to a very powerful river with Uzma Mohiuddin (PDO) amalgamated large deep channels that constitutes a good Biostratigraphy, seismic data and field observations have been potential reservoir in the central part of the basin. Laterally, integrated to develop a model of evolving paleoenvironments deposits are more clayey, bearing only unconnected small in the Coniacian to Campanian foreland basin of the sandy point bars. The overlying Aptian carbonates (Jezzine Oman Mountains, southeast of the Suneinah Trough. The Formation) are also thickest in the Chouf area. They pinch depositional sequences of the Fiqa Formation represent part out to the east (Anti-Lebanon). A major stratigraphic gap of the Aruma Group, unconformably overlying the platform covers the early to middle Albian. The subsequent carbonate carbonates of the Wasia Group (Natih Formation). The older system (late Albian to early Turonian) is regularly sloped to units of the Fiqa Formation are informally referred to as the the west. It consists of alternating massive or layered platform Lower and Upper Shargi members, overlain by the carbonate carbonates, and of planktonic-bearing laminated carbonates; and/or marl-prone Arada Member. The informal subdivision it bears the same number of sequences in Lebanon, Syria and is based on micropaleontological dating of drill cu�ings. in the Gulf. Coastal sections of Lebanon show spectacular Biostratigraphic correlation allows further subdivision of Cenomanian slump scars and large calcarenitic sand waves the lower part of the Fiqa Formation. This forms the basis for prograding down-slope within slope carbonates. delineation of deep-water stratigraphic traps, and improved resolution promotes real-time zonal indentification whilst (153-Oral) Kinematic interpretation and drilling. The Wasia carbonate platform became submerged structural evolution of northern Oman, Block in the Coniacian. The Shargi depositional system comprised 6, since the Late Cretaceous a Santonian to Campanian age deltaic complex and a Campanian turbidite basin fill. The shale-prone Lower Shargi Filbrandt, Jacek B. (PDO - [email protected]), units prograded northward from central Oman during the Salah Dhahab (Shell), Kester Harris (PDO), Abdullah Santonian. The shelf-slope break was stationary in the early Al-Habsy (PDO), John Keating (PDO), Salim Al-Mahruqi Campanian. Campanian-aged cyclic, turbidite deposits filled (PDO), Ismael Ozkaya (Baker Hughes), Pascal Richard the basin east of the Maradi Fault Zone and south of the (PDO) and Tony Robertson (PDO) emplaced nappes. The turbidites onlapped the north-facing delta slope and filled some 400 m of accommodation space. The structural characteristics of the northern margin of the The turbidites are laterally extensive, forming sheet sands, Late Cretaceous carbonate platform in Oman differentiate and have moderate to good reservoir properties, derived the tectonic evolution of this region from the continental primarily from exposed Gharif and older sandstones in margin now exposed in the Oman Mountains. Imbrication the emergent Huqf-Haushi High. An ophiolite-derived associated with the emplacement of the Semail Ophiolite component increases upwards through the early Campanian and NE-oriented telescoping of the Arabian Platform as the foreland basin became filled and the Huqf provenance margin culminated in the Campanian. The structural grain area was transgressed. contrasts markedly with that of the region immediately to the south, and implies strong strain partitioning. Kinematic (145-Oral) Shu’aiba rudist build-ups and indicators from subsurface data, combined with the age of growth faulting, provide the basis for the interpretation that sequence stratigraphy in offshore Qatar maximum horizontal stress was NW-oriented in this foreland Fischer, Klaus C. (Wintershall - klaus.fischer@wintershall region. The dominant tectonic control on the formation of .com), Ismail A. Abdulla (QP), Mamdouh E. Zahran (QP) faults is believed to have been a ‘collision’ of the Arabian and Martin Lehmer (Martin-Luther U) Plate with the Indian Subcontinent during the Santonian- Campanian. Deformation was dominated by distributed Rudist build-ups within the Aptian Shu’aiba Formation are a strike-slip faulting. Late Maastrichtian to Paleocene upli� and prolific reservoir in the southern Gulf. These rudist build-ups erosion, in excess of 500 m, is recorded in the truncation of the were formed along the rim of a shelf interior basin during

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relative sea-level highstand conditions. The southern limit of integrated approach that includes geology (borehole image this basin is well-defined and comprises major hydrocarbon logs–≠BHI, cores, wireline logs), geophysics (seismic facies accumulations, e.g. the Bu Hasa field in Abu Dhabi, the analysis), and reservoir engineering data (PLT, Welltest, Shaybah field in Saudi Arabia, and several fields in Oman. production data). Field ‘A’ is a giant Upper Cretaceous The northern limit of the basin is less well-defined, there are carbonate reservoir, onshore United Arab Emirates, in which only few somewhat regional publications. Recent exploration fractures and highly permeable layers play an important role work in offshore Qatar added a new piece of information in hydrocarbon production and early-water break-through. to the existing view of facies distribution. Primarily based The study combined a set of selected ‘fracture-relevant’ on seismic data, a pronounced Shu’aiba reef build-up was a�ributes in a multi-variable statistical process called Seismic identified. The build-up is part of a discontinuous trend of Facies Analysis (SFA). Each seismic facies was mapped and minor build-ups running more or less in a north-northwest the delineated areas were validated against interpreted well direction. Seismic sequence analysis identified several cycles data (BHI, core and dynamic data) to deliver an accurate map of eastward progradation and locally vertical aggradation. of fracture occurrences. The seismic facies map was then used Following these highstand deposits, a relative fall of sea level to interpret structural lineaments and to constrain stochastic resulted in subaerial exposure of the Shu’aiba build-up that realizations of the fracture model. The second step consisted generated increased porosity. The Nahr Umr shale/sandstone of a detailed analysis of dynamic dataset (Welltest, PLT, and was deposited above the Shu’aiba Formation. The model production data) with specific innovations used to measure was supported by seismic inversion: a distinct decrease of hydraulic fracture properties from Welltest interpretation acoustic impedance was observed at the crest of the build-up. and from PLT data. Results of the dynamic analysis were Sequence and facies analysis of existing well data supported combined with the stochastic fracture models to produce the model and added more details. The investigations finally full-field reservoir models with fracture properties (porosity, allowed for a correlation of sea-level history with other parts permeability and block sizes), which can be used for single- or of the Shu’aiba basin. dual-media reservoir simulations.

(261-Oral) Salt occurrence in the Gulf region (161-Oral) Approaching vertical permeability issues in fractured fields: an extensive Folle, Stefan (Schlumberger - [email protected]. analysis com) Foulon, David J. (Total - [email protected]) and The construction of cavities in local salt deposits for the Sylvie Delisle (Total) strategic and commercial storage of oil, oil products and gas provides economic benefits in the Gulf countries. This Additional world reserves are increasingly due to new involves, for example, salt production in combination with developments of current fields. Specific issues arise when hydrocarbons for ethylene-dichlorine-plants. This study applying these sophisticated development schemes to shows the salt deposits in the Gulf region and focuses on fractured reservoirs. One such issue, improperly addressed by the areas in the vicinity of the marine basin. Beside natural current so�ware, but of fundamental impact on IOR schemes, outcrops, some salt deposits have been penetrated by solution is the characterization of vertical permeability (Kv) throughout mining and conventional mining operations. Other deposits the fractured field. This study presents a way to solve this were explored but did not progress into the development weakness. The vertical permeability in a fractured field is phase. Oil and gas exploration has provided additional governed by: (a) the vertical extension of the different sets of information on salt occurrences. Iran has the largest evaporite fractures; (b) the proportion of cross-bedding fractures; and deposits, primarily of infra-Cambrian and Tertiary in age. (c) the exchange area of bedding-terminated-fractures at the Jurassic salt deposits are rare. Diapirism is widespread in Iran interfaces between layers. Several steps have been performed and li�s the evaporites to extractable depths. The salt deposits toward a proper evaluation of this aspect of reservoir of Iraq are primarily characterized by Tertiary bedded salt characterization: (1) Innovative data analysis methods have which lies at relatively shallow depths and extends into Iran. been developed to be�er characterize these three features. (2) In southern Iraq and Kuwait flat-bedded and relatively deep New ways to calculate the vertical permeability from these Jurassic salt occurs in the United Arab Emirates as well as in data have been formalized, which allow automatic calibration Oman. Cambrian–infra-Cambrian salt structures are stratified on the available dynamic data through multi-realizations. as well as diapiric, some of them at suitable depths. (3) Routines for extrapolation at field scale respecting the geological understanding of the fracture network, result in (372-Oral) A fully-integrated approach for realistically Kv-filled geomodels directly usable for rock- fracture characterization using geological, typing or upscaling into reservoir models. These advances are currently being applied to a Middle Eastern field. geophysical and reservoir engineering data in ‘A’ field (159-Oral) Converted shear-wave anisotropy Fonta, Olivier (Beicip-Franlab - [email protected]), for fractured reservoir management Maged Al-Deeb (ADCO), Salem El-Abd Salem (ADCO), Loic Godail (Beicip-Franlab) and Gerard Bloch (ADCO) Gaiser, James E. (WesternGeco - [email protected] co.slb.com) and Richard R. van Dok (WesternGeco) Fractured reservoir analysis requires: (1) spatial delineation of fractured areas; (2) evaluation of fracture intensity; and Fractured reservoirs have been encountered worldwide (3) determination of the hydraulic properties of the different and in general they are profitably produced, however it is fracture sets. This study presents a multi-disciplinary safe to say that none of them have been depleted efficiently.

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As the petroleum industry focuses less on exploration, and (349-Oral) Satellite gravity reveals the ‘big in a market of rising costs, it is becoming more important picture’ under the northern Gulf to recognize the presence of fractures for optimal reservoir management. Fractures can significantly complicate the Glenn, William E. (Larch - [email protected]), Erwin behavior of reservoir porosity and permeability, o�en J. Ebner (ELS), Rick Morgan (Consultant) and resulting in numerous dry wells and higher production Aavo Taal (Al-Kha�i JO) costs. A key strategy for fractured reservoir management is a quantitative description of the geology, geophysics One of the most under-utilized tools available to and petrophysical a�ributes obtained from seismic explorationists working in offshore exploration is Satellite methods during production and development. 3-D Gravity. Recent advances in satellite positioning and gravity multi-component seismic surveys, where compressional instrumentation have progressed to the point where the waves excite shear-wave reflections (PS-waves), can quality of satellite gravity data rivals that acquired by ship- provide complimentary surface-seismic information to borne gravimeters. Satellites can now deliver high-quality, help identify fracture properties early in the production low-cost gravity data to provide an enhanced understanding history of a reservoir. Based on measurements of shear- of the regional structure of offshore areas. In 2002, a series wave azimuthal anisotropy, PS-waves can identify fracture of satellite gravity maps were created for the northern Gulf density and strike, and because of their asymmetry they region north of latitude 27. Sandwell 9.2 satellite gravity are also sensitive to fracture dip. Examples from both data were used, and 3-D Bouguer correction was applied land and marine 3-D PS-wave surveys demonstrate using ETOPO-5 bathymetry and GTOPO-30 land data; grid- the potential of using these a�ributes to characterize spacing was 500 m. The series comprised a map of Bouguer subsurface stress variations that are important for open- Gravity, three horizontal and vertical derivative maps, a fracture development. The intermediate-scale seismic band pass filter map, and a final interpreted Bouguer Gravity anisotropy properties obtained from PS-waves will be map. The parameters and data filters used to generate the critical for solving specific production problems associated processed maps were selected to optimize signals from with different fractured reservoir types, and could improve depths of interest to oil and gas explorationists. The mapped reservoir modeling: production-history and pressure-test data show at least four distinct structural domains in the matching, and fluid-flow simulation. From an economic northern Gulf region. Bouguer gravity anomalies have a point of view, if PS-wave surveys acquired over the life of strike, wavelength and shape that are somewhat different a field can prevent a small fraction of unproductive wells, in each of these domains. Data resolution allows for the they are worth the expense. detection of gravity anomalies with anomaly widths as small as 6 km, depending on geometry and density contrast of rocks in the subsurface. These maps provide a valuable tool (306-Oral) Permeability modeling, up-scaling for refining the regional geology of this important area. They and dynamic simulations in a complex can be used to project onshore geological features (terrains, carbonate reservoir, Al Huwaisah field, North boundaries, faults, structures, lithology, and stratigraphy) to Oman the offshore, to help in understanding and interpretation of existing offshore fields, and to plan the location of marine Gauthier, Philippe (PDO – [email protected]), seismic surveys. The satellite data is of sufficient quality to Dave Brooks (PDO), Nada Al-Kindy (PDO), Ebufegha serve all these purposes well. Akposeiyifa (PDO) and Subrata Sen (Shell)

The main reservoir of the Al Huwaisah oil field is the (150-Oral) The Jurassic Najmah/Sargelu Aptian Shu’aiba Formation comprising rudist-bearing shelf petroleum system of West Kuwait: a margin deposits with a complex depositional architecture. producing fractured carbonate source rock An iterative routine using log data and saturation height reservoir functions was developed to estimate permeability in this complex carbonate reservoir where standard porosity- Goff, Jeremy BP( - [email protected]), Fahed A. Al-Medhadi permeability relationships do not exist, and where facies (KOC), Hamad N. Al-Ajmi (KOC), Naveen K. Verma identification is only possible in cored wells. The resulting (KOC), Anthony J. Barwise (BP), Tim D. Needham (U well permeability profiles compare favourably to well test- Leeds), Johnathan M. Henton (BP), Norman Oxtoby derived, effective permeability and preserve significant (Royal Holloway, U London) and permeability contrast. Local sweep pa�erns identified Joyce Neilson (Carbonate Reservoirs Ltd) from time-lapse saturation data were integrated with the calculated permeability, production log data, and well- Deep exploration drilling by KOC in the Gotnia Basin, scale pressure profiles, to aid in the identification of key West Kuwait, has led to the discovery of light oil (35-40 dynamic reservoir characteristics. Up-scaling for reservoir degree API) in a new reservoir in the Jurassic Najmah and simulation was done in such a way to maintain critical Sargelu formations. Challenging drilling problems due to permeability contrast and well-test permeability averages. convergence of pore pressure gradients (up to 0.99 pounds One aim of the dynamic simulation is to reproduce the local per square inch per foot) and fracture pressure gradients sweep pa�erns identified in the wells in over 30 years of (1.0-1.02 pounds per square inch per foot) in the reservoir production. This will allow targeting unswept areas of the and overlying Gotnia Formation evaporite caprock have field with greater confidence and consequently increase the been successfully overcome. Extensive core data has been ultimate recovery. acquired to facilitate reservoir description. The reservoir is 100-170 m thick and comprises four carbonate source rock units, and three non-source shelf/slope carbonate reservoir

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units. Average porosity in the non-source carbonate (173-Poster) Mid Triassic-Neogene layers determined from log and core (helium) analysis is tectonostratigraphic evolution of the 2.3 percent; secondary porosity up to 8 percent is locally northeastern active margin of the Arabian present. Fractures are developed at all scales: from micro- fractures visible in thin sections, hairline fracture networks, Plate and its control on the evolution of the bed-confined vertical fractures, and large vertical fractures Gotnia Basin cu�ing bed boundaries. Geochemical analyses indicate that oil expulsion has been very inefficient: (1) 90 percent of the Goff, Jeremy BP( - [email protected]), Saad Z. Jassim U( Leeds) oil generated has been retained within the Najmah/Sargelu and Dogan Perincek (Kuwait U) formations; and (2) 10 percent has migrated downwards A new interpretation of the Mid≠ Triassic-Neogene evolution through the underlying Dhruma and Upper Marrat of the northeastern active margin of the Arabian Plate is Formations into the Middle Marrat Formation carbonate presented, based on correlation of tectonostratigraphic reservoir. Fluid inclusion data from fracture cements record sequences along the Zagros Suture Zone from Southeast generation of oils of progressively lighter oil gravity; oil Turkey through Northeast Iraq and into Western Iran, using generation occurred in mid-Cretaceous-Early Tertiary time. field observations and review of published geological maps. Fractures formed in response to overpressuring associated Triassic ri�ing with deposition of deep-water carbonates and with oil generation, Kimmeridgian and Turonian folding eruption of basalts occurred within the northeastern part of and Late Tertiary upli�. High-angle wells are being used the Arabian Plate; a ridge with shallow water carbonate to locate productive fracture systems and collect additional platform deposition separated this ri� from the newly- data on fracture distribution and spacing. Surveillance formed restricted Gotnia Basin to the southwest. Following data indicates a slow recharge of the productive fracture renewed extension in the Late Jurassic along the line of the network occurs following production due to expansion of Triassic ri�, a narrow ocean basin opened in latest Jurassic- oil in micro-fractures. Early Cretaceous time between the Arabian Plate and the Bitlis/Bisitoun micro-plate with widespread deposition of (155-Poster) Discovery and geology of a radiolarian cherts on the continental slope of the Arabian giant fossil Jurassic oil field in the Zagros Plate. From Cenomanian time this ocean subducted to the Mountains, southwest Iran north and northeast below the Bitlis/Bisitoun micro-plate with deformation of oceanic sediments and the formation Goff, Jeremy BP( - [email protected]), Masoud Shamshiri of a Late Cretaceous calc-alkaline volcanic arc and forearc (NIOC), Salman Jahani (NIOC), Farid Farmani (NIOC), basin. In the late Campanian, ophiolites were obducted Mehrab Rashidi (NIOC), Nicholas J. Whiteley (BP), onto the Arabian Plate forming a narrow foredeep filled Claudia Ruiz (BP), Christoph Lehmann (BP), Alexis S. by flysch and carbonates. In Paleogene time, eruption of Anastas (Devon), Abid Bhullar (BP), Norman Oxtoby andesitic and basaltic volcanics occurred, associated with (Royal Holloway, U London), Joyce Neilson (Carbonate deposition of marine carbonates and flysch, north east of Reservoirs Ltd), Bob W. Jones (BP) and the suture zone between the Arabian Plate and the Bitlis/ Richard Diggens (Deloi�e and Touche) Bisitoun micro-plate. Foredeeps migrated to the southwest across the northeast part of the Gotnia Basin in response to In 1931 geologists from the Anglo Persian Oil Company compression and continental collision in Palaeogene and visited remote valleys cut into the core of a large anticline mid-Miocene-Quaternary time. in the Zagros Mountains. They discovered outcrops of a thick section of bituminous dolomite. Seventy years later, (176-Oral) Seismic stratigraphy of the Lower a team of geologists from NIOC and BP retraced the steps of these pioneers to relocate and log these outcrops and Cretaceous Shu’aiba Formation of Abu determine the significance of the bitumen. The bitumen is Dhabi contained in secondary porosity in a Middle-Upper Jurassic platform margin dolomite reservoir that has formed during Gombos, Jr., Andrew M. (ADCO - [email protected]), deep burial at temperatures of up to 130 degrees C. Fluid Jason B. Sco� (ADCO), Christian J. Strohmenger (ADCO) inclusion data integrated with basin modeling indicates and Khalid Al-Amari (ADCO) that medium-light gravity oil migrated into the reservoir A new sequence stratigraphic framework has been (synchronous with dolomitization) during the burial of a established for the Lower Cretaceous Shu’aiba Formation of paleostructure in early Late Miocene time. Oil migration Abu Dhabi, integrating core, well-log and 3-D seismic data. continued during late Late Miocene folding. During later The Shu’aiba Formation is a second-order supersequence upli� and erosion in Pliocene and Quarternary time, the (base ‘upper dense zone’ = Hawar Shale to top Shu’aiba), limestone caprock failed. Low-temperature calcite fracture comprised of five third-order sequences. These third-order and matrix cements associated with low-salinity aqueous sequences are tied to the most recent global cycle chart and fluid inclusions record the invasion of meteoric water into correspond to Aptian sequences Ap1 through Ap5. The the reservoir, degradation of the oil, and leakage of the oil overlaying Bab Member is interpreted to start with upper accumulation. Logging of the bitumen bearing reservoir Aptian sequence Ap6. Biostratigraphy and nanno-fossil integrated with structural mapping, indicates that the fossil data support the proposed correlation. Seismic stratigraphic oil field originally contained an oil column over 500 m thick. interpretation, using geometric observations and internal The final trap was an asymmetric anticline, with a gently- reflection pa�erns, allows the identification of the dipping back limb, and a steeply-dipping to overturned second-order supersequence as well as the six third-order fore limb. The back limb has locally been thrust over the sequences from 3-D seismic data. Lower Aptian sequences forelimb due to late structural movement.

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Ap1 through Ap2 show retrogradational and aggradational (64-Oral) Geological modeling at Humma parasequence stacking pa�erns (transgressive sequence field, PNZ sets) whereas lower Aptian sequence Ap3 (early highstand sequence set) shows aggradational to progradational Griest, Stewart D. (ChevronTexaco - griessd@chevrontexac parasequence stacking pa�erns. The upper Aptian o.com), W. Sco� Meddaugh (ChevronTexaco), sequences Ap4, and Ap5 (late highstand sequence sets) Joseph Mason (ChevronTexaco) and clearly display progradational parasequence stacking Sherilyn Williams-Stroud (ChevronTexaco) pa�erns. Furthermore, 3-D seismic interpretation allows the identification of third-order transgressive systems The Middle/Lower Jurassic Marrat carbonate reservoir at tracts (dense zones) and highstand systems tracks Humma field was discovered in 1998 in the southwest part (predominantly reservoir zones) within the prograding of the Partitioned Neutral Zone (PNZ), between Kuwait and Aptian sequences Ap3 to Ap5. Amplitude maps tied to Saudi Arabia. Three wells are producing 32 degree API oil reservoir data allows the prediction of enhanced reservoir from multiple reservoir zones distributed throughout the quality within the Shu’aiba prograding sequences Ap3 (late hydrocarbon-bearing section. The structure at Humma is highstand systems tract), Ap4 and Ap5. In addition, dense a high-amplitude, four-way closure formed along a major zones (termed ‘I-Dense’) within the transgressive systems regional block-faulted ri� system that was initiated in the tract of Aptian sequence Ap3 can be predicted using Precambrian Period. All regional tectonic events until the amplitude and discontinuity maps. The proposed new present day have resulted in persistent upli�, folding and sequence stratigraphic framework allows a more accurate faulting of the structure that was contemporaneous with prediction of reservoir quality away from well control, and deposition. Jurassic Marrat carbonates exhibit some faulting will thus improve both the static geological and dynamic and fracturing, while shallower Cretaceous carbonates and reservoir models. clastics exhibit complex transtensional faulting within a keystone graben. Marrat reservoir distribution at Humma was influenced by a paleotopographic and paleogeographic (211-Oral) Low-resistivity pay carbonate configuration associated with the structure. Individual reservoir, Lower Cretaceous, United Arab reservoir zones are best developed along a paleotopographic Emirates high that closely conforms to the present-day structural configuration. Reservoir intervals are best developed at the Gomes, Jorge S. (ADCO - [email protected]), tops of shallowing-upwards (progradational) parasequences Sunarnyoto Soenarwi (ADCO), Michel J.M. Rebelle where inner ramp and inner shelf environments existed (ADCO), Maria T. Ribeiro (ADCO), Youssef Dabbour within a predominantly transgressive megasequence. The (ADCO), Khalid Al-Marzouqi (ADCO), Mario Petricola deepest Marrat reservoir interval exhibits dolomitization. (Schlumberger) and Paolo Ferraris (Schlumberger) An earth model for Humma field based on a geostatistical approach, was used to assess the distribution and degree This study discusses the evaluation of a low-resistivity of uncertainty related to reservoir properties within the pay carbonate in the Middle East, and presents the field. Structural configuration was based on 3-D seismic approach used for the proper geological and petrophysical and regional 2-D seismic interpretations. Each interval characterization of this reservoir. Log data exhibit a very throughout the reservoir sequence was modeled based on the low resistivity (0.3-0.4 ohm-m), which translates into an structure and well data. Reservoir properties were measured erroneous Sw (Archie) of more than 80 percent. However and interpreted from log analysis, core and production data. this reservoir produces dry oil at a reasonable rate (5,000 Semi-variograms were developed to simulate the lateral bopd with no water cut) without any fracture as evidenced distribution of reservoir properties. Porosity was modeled by well tests. A petrographic investigation on thin sections using sequential Gaussian simulation (SGS). Water saturation shows high micro-porous facies. The micro-porosity results and permeability were modeled using collocated cokriging from large abundance in peloids and micritized organisms, with SGS using porosity as secondary data. The earth model and is associated with a meso- to macro-porosity developed was used to evaluate oil-in-place uncertainty and as input to as moldic porosity (dissolution of foraminiferas internal fluid-flow simulation for field development planning. cavities) and/or framework porosity (dissolution of Bacinella internal structures). The micro-porous network traps irreducible formation water which will give a low (16-Poster) Integrated redevelopment of resistivity response, even if oil occurs within meso- to the Soroosh and Nowrooz fields, northern macro-porosity. A NMR porosity-partitioning method Gulf and remaining subsurface development is used to resolve the computation of Sw, by using the uncertainties T2-distribution from NMR, for porosity partitioning into micro-, meso- and macro-porosity. The result of porosity Guit, Fer (Shell - [email protected]), Alex Huerlimann partitioning will be dependent on the T2-cut off which is (Shell), Nariman Noori (Shell), Hein de Groot (Shell), used in the evaluation. NMR core measurements were used Parvin Ahmadi (NIOC), Sadjad K. Shiroodi (NIOC) and to calibrate T2 cut-off. A saturation equation modelling Ali Hassani (NIOC) non-Archie behavior, and solving for saturation in each individual pore type, through a sequential method that The Soroosh and Nowrooz fields located in the northern reproduces the oil migration process into the various pore Gulf were redeveloped by Shell Exploration BV. Early types, was used. production in excess of 60,000 bopd was achieved from Soroosh in December 2001 and main production is expected to start in 2004 with the availability of the integrated new production facilities. On Soroosh field, a total of 10

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horizontal production wells and two water disposal wells (472-Poster) Reservoir characterization and were drilled from two platform locations. The wells target modeling in the fractured basement plays of crestal oil volumes in excellent multi-Darcy permeability Yemen Burgan reservoir sands. Production will be by depletion drive using ESP’s and wells are designed to deal with Gutmanis, Jon (GeoScience - [email protected]) a steady drop in reservoir pressure. Crude analyses and Sylvie Delisle (Total) demonstrate the presence of a density gradient from 20 to 10 degree API over the oil column; also lateral variations in Hydrocarbons have been under production from the oil quality have been demonstrated. Weak aquifer support is fractured basement plays of Yemen since the early 1990s inferred from past production and is due to high viscosities when Canadian Occidental Petroleum Ltd. (now Nexen over the base of the oil column. In addition aquifer support Inc.) made discoveries in the Masila Block. Subsequently has further been reduced by depletion of some 200 psi of other operators have also developed basement plays, such as the regional Burgan aquifer by massive production from Total in the East Shabwa Block. This presentation describes the various other fields in the region. On Nowrooz field a reservoir characterization and modeling work carried out total of 17 horizontal production wells were drilled crestally in the fractured basements of the Masila and East Shabwa from 2 platform locations. The structure is heavily faulted blocks. These blocks are located within a major ri� system along the crest; however, historic production indicates which contains marly Cretaceous to Tertiary ri� and post- strong pressure support by the volumetrically large aquifer. ri� sediments. From well penetrations, the basement rocks Although the net-to-gross of the Burgan reservoir is lower are a complex series of metasediments and metavolcanics, than in Soroosh field, the drilling campaign was successful with granitic intrusions, generally at a depth of some 2,500 to in targeting relatively high proportions of sand in relatively 3,000 m. They are believed to be part of the Arabian-Nubian undisturbed fault blocks. This study describes the findings Shield, which extends through much of northeast Africa of the production drilling and early production phase and and Arabia and is of Archean-Proterozoic age. Reservoir remaining subsurface development uncertainties. characterization primarily involved detailed analysis of well data, especially borehole image logs, core and fluid (174-Poster) Paleokarst and porosity flow information at a range of scales from individual flow entries to cross-hole interference tests. The objectives were development in Cretaceous carbonate to understand the producing fracture system, especially the reservoirs, central Oman types of porosity, their a�ributes, and their distribution at local to reservoir scale. A key requirement was to determine Guo, Li (CASP - [email protected]), Michael D. ranges of values for the key parameters (e.g. porosity, Simmons (Ne�ex) and Eric J.-P. Blanc (CASP) thickness) in order to support volumetric calculations. Dissolution associated with subaerial exposure is thought The well data was integrated with reservoir scale litho- to be responsible for much of the secondary porosity in structural and dynamic data to develop conceptual models the Lower-mid-Cretaceous carbonates of the Arabian of the fault and fracture system. A vital component was Platform. However, the presence of subaerial exposure the use of analog information from literature and outcrop surfaces in much of the succession has not been well- to help constrain the models and the range of parameter recognized. Outcrops in the Central Oman Mountains values. In general, the studies indicated that faults and provide an excellent opportunity to detect the existence their damage zones are the main source of production, and of paleokarst and understand their potential influence on that fault geometry and intersection relationships are an reservoir development. A well-preserved karst profile is important influence on permeability distribution. Reservoir recognized at the top of the Natih Formation in southeast stress, more specifically the orientation of the maximum Jebel Madar, characterized by the occurrence of solution horizontal stress axis, was also identified as an important hollows, fissures, and breccias. A brecciated unit marks influence on fracture permeability. For the volumetric the top Shu’aiba Formation in southern Jebel Madar and calculations, faults at seismic and sub-seismic scale were provides evidence of subaerial exposure features; including modeled, using constraints from well data, while the brecciation, incipient calcrete fabrics, clay-infiltration and smaller-scale ‘background’ fracturing was included in the secondary porosity with meteoric cements. Irregular down- matrix properties. Sensitivity evaluations were run for each cu�ings and solution hollows, associated with lithoclasts parameter to assess their impact on the OOIP calculations, and clayey matrix, truncate tops of the meter-scale cycles allowing uncertainties in volumetrics to be ranked. in the lower part of the Kharaib Formation. Some of the features are original hardgrounds modified by diagenesis, (199-Oral) Lithology and fluid prediction in and others are likely to be created by desiccation, dissolution Cretaceous clastics using 3-D simultaneous and replacement during subaerial exposure. The subaerial angle stack inversion: results from a pilot exposure surfaces at the top Shu’aiba and Kharaib formations are supported by stable isotopic compositions, area, Burgan Field, Kuwait which show negative shi�s, suggesting an incorporation Haas, Stephen A. (ChevronTexaco – of soil-gas CO into the carbonates and early meteoric 2 [email protected]) and Yousef Al-Zuabi (KOC) diagenetic overprint during the subaerial exposure. These subaerial exposure surfaces have played direct and indirect In this study, we test simultaneous inversion of seismic roles in enhancing reservoir quality. Karstification and angle stacks as method to delineate reservoir sands and burial corrosion, together with fracturing, appear to have fluid contacts in the Wara and Burgan reservoirs in a pilot been the key factors contributing to the development of area in Burgan Field. These two clastic reservoirs account reservoir quality in this study.

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for the majority of Kuwait’s oil reserves, so any direct (6-Oral) Characterization of fractures within method that identifies lithology and fluids has tremendous Dammam Dome, eastern Saudi Arabia value. Simultaneous inversion incorporates AVO effects into the traditional full offset inversion process. This Hariri, Mustafa M. (KFUPM - [email protected]) additional input be�er constrains predicted lithology and and Osman A. Abdullatif (KFUPM) fluid solutions. In our workflow, we first analyzed well logs, including dipole sonic logs, and determined that using both Dammam field is located in eastern Saudi Arabia and is one P (compressional) and S (shear) impedances would improve of the major domes resulted from salt emplacement. The identification of reservoir sands and, to a lesser degree, dome hosts the first oil discovery in Saudi Arabia (Dammam- fluids. We selected a 280 sq km pilot area in the southwest 7 well). It covers an area of about 100 sq km, and encompass flank of Burgan Field, based on optimal seismic and three major cities; Dhahran, Khobar and Dammam. The well data quality, gentle structure, and constrained fluid dome is characterized by gentle sloping topography in all contacts. Next we reprocessed the 3-D seismic into three directions with four hills that stand out. Outcrops within relative amplitude angle stacks, completed log editing and the dome range in age from Paleocene to middle Miocene, modeling, and then calculated P impedance, S impedance and consist, from base upward: Umm Er Radhuma, Rus, and density volumes using simultaneous inversion. Finally, Dammam, Hadrukh and Dam formations. Fractures within we tested various transform combinations of these volumes the Dammam Dome can be divided into three categories to best identify sands and fluids. The results of the pilot according to their size and nature. The first are regional and simultaneous inversion test are encouraging, but clearly large size (Mode I or extensional) fractures which extend limited by our seismic data quality. Comparing these for more than 500 m and may be related to the doming. The results with earlier full stack deterministic and stratigraphic second category consists of local fractures (Mode I and III, III inversion results indicates we have improved predicted = dip-slip) with a length of 1 to 10 m. The block movements lithology, but not predicted fluids. We are incorporating between the regional fractures mainly produce these types our lessons learned into planning for next generation 3-D of fractures. The third category consists of more localized, surveys. small-sized fractures (< 1 m) which develop within rock blocks and are mostly related to the nature of the rock types. These fractures are of different Mode. Each type of fracture (297-Oral) 3-D anisotropic reflectivity in the has distinctive characteristics and formation mechanism. Gulf region This study is aimed at characterizing these fractures and defining their regional and local nature. The output of the Hall, Mike (GX - [email protected]), Jim Simmons (GX) and study will help in understanding the mechanism that formed Ghiath Ajlani (ADNOC) the fractures within the dome, and the prediction of their A multi-component (3-C, 4-C, 9-C) anisotropic reflectivity- occurrence and pa�ern. Moreover, the findings of this study modeling tool was used to simulate the seismic response of are important to the field of fractured reservoirs. an earth model common to the Gulf region: an anisotropic overburden overlying a fractured carbonate reservoir. The (110-Oral) Unconventional Shu’aiba traps overburden is a thin-layered sequence of interbedded and tilted or stepped oil-water contacts in anhydrites and clastics that can exceed 1,000 m producing eastern Arabia a layer-induced VTI (vertical transverse isotropy) seismic response. Thick shale underlying this is intrinsically Harris, Kester (PDO - [email protected]), Gerard VTI. A carbonate reservoir is represented as an HTI layer Bloch (ADCO), Martin Boekholt (ADCO) and (horizontal traverse isotropy). The seismic response of Jean-Denis Bouvier (Daleel) the anisotropic overburden and reservoir was simulated. The model is restricted to plane, homogeneous layers, There are several Late Cretaceous carbonate fields in the but each layer can be arbitrarily anisotropic. A modeling northwest of Oman and onshore United Arab Emirates, simulation produces a cube of pre-stack seismic traces which are considered to be combined structural- equally sampled in x, y and t, for negative and positive stratigraphic traps, and where faults are interpreted to form inline and crossline offsets. As a result, 3-D wide-azimuth, the lateral seal in the up-dip direction. This area of Oman multi-component data is modeled. Vertical and horizontal and the southern fringe of the Arabian Gulf has undergone force sources represent vertical and horizontal vibrators, regional tilting in Late Tertiary times, generally down to the respectively. Anisotropic modeling indicates the particular northeast. The tilting significantly modified the geometry of type of seismic data (P-P, P-S, SH-SH, SV-SV) needed to preexisting fields, and has led to the partial remigration of best illuminate the fractured reservoir, recover estimates of trapped hydrocarbons. There is a new explanation for the shear-wave spli�ing, and evaluate the sensitivity of AVOA ‘fault-trapped’ oil in these fields: the tilted compartments (Amplitude-versus-Offset-versus-Azimuth) analysis. of the field have not yet reached equilibrium and donot Simulated 9-C data was analyzed in acquisition coordinates have flat oil-water contacts. This is due to a combination (inline-crossline) as well as in radial-transverse coordinates. of low permeability of the reservoir, hysteresis in the It demonstrated how the la�er yields a clear separation drainage-imbibition process, and (possibly) insufficient of the elastic waves whereas the former does not and can time since tilting. One of the characteristics of the lead to false interpretations of shear wave spli�ing. This preexisting fields is that early hydrocarbon fill prevented modeling provides insight into how to properly record and the destruction of porosity, by inhibiting stylolitization. process 3-D seismic data to determine fracture orientation Consequently the reservoir porosities are relatively high at beneath a complex VTI overburden. the paleoculminations. This is proven by well data, and is occasionally visible on seismic. The diagenetic destruction

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of porosity in the water leg below the paleocontacts has led advantages of using geochemical logging was the use of to a significant change in reservoir properties across these the output grain density for calculating the formation total surfaces. These surfaces are now also tilted, and so form porosity from the bulk density measurement. Historically, permeability barriers which prevent–or at least hinder–the a constant value for the matrix density was a common remigration of hydrocarbons. These two separate processes approach to calculate the density porosity. Due to the (tilting, and the formation of diagenetic barriers) have an presence of impurities in the sandstone such as siderite impact on the production geology of fields, and give rise and pyrite, it was found that the matrix density is no longer to unconventional targets for exploration. The Late Tertiary a constant value across different layers of the reservoir. tilt is a regional event across eastern Arabia, and needs to Using the above-mentioned technique in the fields of North be accounted for when evaluating stepped or dipping oil- Kuwait resulted in an increase of 1.5 percent in the total water contacts in this area. porosity on average. That was very important because an accurate total porosity is essential for accurate calculation of water saturation and total oil-in-place. A second application (213-Oral) An integrated picture of faulting of geochemical logging was the accurate calculation of and fracturing using image logs and shale volume. This is important specially when ‘hot sand’ 3-D seismic in a giant Lower Cretaceous is present in the reservoir. In this case, the GR is no longer carbonate field, Abu Dhabi a reliable shale indicator. When this technique was used, an increase of the net pay of the reservoir was achieved. Hassall, John K. (ADCO - [email protected]), Jason Sco� (ADCO), Andrew Gombos (ADCO) and Khalid Al-Amari (ADCO) (485-Oral) Geostatistical distribution of eolian facies using a modern analog as Fi�een wellbore image logs (mainly FMI) are available in a modeling template, Permian Unayzah horizontal wells in the field. These logs allow fracturing Formation, Tinat field, Saudi Arabia and faulting in the field to be assessed. The interpretation of a recent high-resolution 3-D seismic survey has shown Heine, Christian J. (Saudi Aramco - christian.heine@aram that more than one hundred and twenty faults are present co.com), Jim Wilkins (Saudi Aramco), John Melvin (Saudi in the field. The faults mainly show limited vertical throw, Aramco), Brian Wallick (Saudi Aramco) and frequently less than 12 �, but may have some strike-slip John Cole (Saudi Aramco) component. The wellbore image logs show that faults were penetrated in five wells. A comparison between the Ancient and modern analogs have long been used in faults as seen on the image logs, and the faults as mapped reservoir modeling to add shape, size and areal extent on the seismic, shows that they are consistent once the to geological a�ributes such as lithofacies, porosity and ability of image logs to detect sub-seismic faults is taken permeability. Consistent with this practice, a modern analog into account. Images of the fault planes show variable has proved invaluable in constraining the distribution fault plane disruption. Disrupted zone thickness ranges of reservoir quality sandstones in the eolian reservoir of between a few inches and many tens of feet. The image the Unayzah Formation at Tinat field. Sedimentological logs show the majority of the fractures are closed, and run analysis of image log and core data clearly identified parallel to the faults. Weak fracture clustering is apparent dune, interdune and sheetsand deposits. The regional and fracture intensity is enhanced in the neighborhood of eolian depositional model incorporates a variety of dune some faults. Some of the seismically-identified ‘faults’ may forms that display consistently eastward-dipping foresets. be more properly described as fracture swarms, at least The reservoir is layered in stratigraphic units that utilize towards their tips. The image logs suggest the impact of a detailed correlation of successive relative rises in water faults and fractures on water-flood performance is likely to table. Ten units are identified. These range from 25 to 50 be minor, and this is confirmed by a review of data such as � in thickness, and each unit has been further subdivided water front maps and production log data. These show very into layers approximately 5 � thick. Facies mapping using li�le evidence for fault/fracture influence on flow pa�erns image logs and available core has been carried out for a�er more than thirty years of waterflood. However, the each unit within the eolian reservoir. The modern eolian impact of fractures and faults on gas injection schemes environment analog was selected from Landsat and Spot (WAG and GI pa�erns) now being implemented is yet to satellite images from the Rub’ Al-Khali of Saudi Arabia, be determined. These current developments are highly and the selected image was scaled and oriented based on susceptible to the reservoir a�ributes being discussed. the interpreted Permian wind direction. An object-based template was drawn for each of the three lithofacies honoring the available well data. The templates were used (278-Oral) Utilizing grain density and clay in a geostatistical method to distribute the three lithofacies volume from geochemical logging for types in a 3-D model. The resulting layer-specific lithofacies improving reservoir characterization in were then used in modeling the porosity and permeability North Kuwait fields distribution that corresponds to the eolian depositional environment. Other a�ributes such as 3-D seismic Hassan, Tharwat F. (Schlumberger - [email protected] amplitude extraction and impedance will be integrated ld.slb.com), Shaikh Abdul Azim (KOC) and during the template building process. Waleed El Awadi (KOC)

Geochemical logging was highly utilized in Raudhatain and Sabryiah fields of North Kuwait. One of the main

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(336-Oral) High-fidelity 3-D processing for despite the inherent limitations of subsurface data? Yes, the high-density Qarn Alam survey it can be done! However, limitations in the resolution and uncertainty in correlation have to be accepted, Herman, Gérard C. (Shell - [email protected]) and managed, and communicated. Only a clear identification Colin Perkins (Shell) and documentation of the procedure and uncertainty in the correlation process can make it reproducible by other Many of the factors influencing land seismic data quality workers and counteracts the growing discrediting opinion are related to the near surface. These problems include that “HRSS is not useful because every worker comes up sca�ered surface wave noise and surface-consistent with his own scheme”. wavelet variations. In order to address these issues PDO has acquired a unique dataset in the Qarn Alam area of Oman, with shots and receivers on the same 25 x 25 (243-Oral) Oil and gas prospecting by ultra- m grid. In addition to the high-density CMP stack fold sensitive optical gas detection with inverse generated by this data volume, a new array of processing gas dispersion modeling techniques became applicable that address the very near- surface issues described above. This study discusses two of Hirst, Bill (Shell - [email protected]), Steve Gillespie these new methods and describes how they were applied (Shell), Ian Archibald (Shell), Olaf Podlaha (Shell), to this original acquisition. The techniques are mixed- Graham Gibson (Glasgow U), Johannes Courtial (Glasgow phase, surface-consistent deconvolution, and deterministic U), Steve Monk (Glasgow U), Ken Skeldon (Glasgow U) prediction and removal of sca�ered coherent noise. The first and Miles Padge� (Glasgow U) technique addresses surface-consistent wavelet variations We report the development and testing of a new oil and gas with an amplitude and mixed-phase wavelet deconvolution prospecting technique ‘LightTouch’ that combines real-time approach. The mixed-phase nature of the algorithm allows sub-part-per-billion ethane concentration measurements for residual statics to be calculated in an effective manner. in the atmosphere with inverse gas dispersion modeling The second technique addresses the long-standing problem to locate sources. The extreme sensitivity of the sensor of sca�ered coherent noise. It uses a mathematical model of permits detection, at a range of several km, of the naturally the near-surface wave propagation to predict and remove occurring ethane plumes that accompany hydrocarbon the sca�ered noise. Therefore, this method a�enuates all reservoirs. Using wind and concentration data, the gas aspects of this noise type, whilst preserving the signal. The dispersion process can effectively be inverted to provide theoretical details, and performance of these techniques, remotely-determined ethane flux maps over the ground, compared with existing processing techniques, are thereby assisting in the search for hydrocarbon reservoirs. discussed, and a way forward for land seismic data is We present results from a recent 240 sq km survey in a presented. Middle East desert se�ing, showing good correspondence between our results and those obtained from a targeted (28-Oral) High-resolution sequence geochemical soil sampling survey performed in a parallel stratigraphy in the Shu’aiba Formation, blind trial. Oman: lessons learned from the outcrop (420-Oral) Yibal field petrophysical Hillgartner, Heiko (Shell - [email protected]) integration: a case study in a low High-resolution sequence stratigraphy (HRSS) aims to permeability, fractured carbonate field identify repetitive sedimentological and stratigraphical pa�erns and interpret them in terms of changes in Hogarty, Patrick (PDO - [email protected]) and environmental conditions (commonly bathymetry) of Gareth Henderson (PDO) variable frequency and intensity. HRSS analyses of the This study shows the results of a value driven, data Lower Shu’aiba Formation in outcrops of northern and gathering and analysis campaign on a mature high central Oman show an internal architecture with several porosity, low permeability carbonate reservoir. The Yibal smaller orders of depositional sequences. Potentially this field commenced oil production in 1969 and is located in has significant implications for subsurface correlations and North Oman, about 450 km west-southwest of Muscat. interpretation of facies and property distribution in Shu’aiba One of the key issues in Yibal field is proper water reservoirs. Learning points are: (1) Depositional sequences saturation measurement and monitoring for determination are laterally continuous at least on a regional scale, but of stock tank oil initially in place (STOIIP) and reserves lateral facies changes are common in environments with reconciliation. This study discusses the data gathering unfilled accommodation space. (2) Although a general strategies using open hole suites, cased hole pulsed neutron pa�ern of vertical facies evolution on different scales is saturation monitoring and high precision sponge coring present, superposition of sea-level trends on different scales technology. The first sponge core cut in Oman was acquired and different depositional regimes result in a large variety in the Yibal field in 2002. Integration of this low-uncertainty of small-scale facies stacking pa�erns. (3) Relationships data is discussed in the context of building saturation between high-resolution sequence architecture and height profiles in the reservoir. The impact of we�ability petrophysical properties are not straightforward and uncertainty is also discussed in relation to saturation cannot be used as generally applicable templates. (4) Clear profiles. A novel technique (Micro Computed Tomography) bathymetric markers are important to establish a reliable for petrophysical and geological modeling will also be and reproducible high-resolution sequence framework. Can presented. a HRSS framework be established in Shu’aiba reservoirs

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(330-Oral) The influence of basement Tertiary paleogeographic maps, based on sequence lineaments on the basin architecture of the stratigraphic concepts, was raised and became an objective. overburden in the Iranian sector of the Gulf The other objective was that these maps should provide a regional basis for studies on the Asmari Formation Hoogendijk, Folco F. (Shell - folco.hoogendij[email protected] reservoirs of Iran in order to resolve problems such as m), Ian Glenister (Shell), Mourad Mehenni (Shell) and locations and orientations of shelf margins, directions of Mehran Mohammadi Faridan (Shell) clastic input into different parts of the basin, and therefore likely stratigraphic geometries. These in turn are critical for The present-day Gulf Basin architecture is that of a understanding internal variations (heterogeneities) within foreland basin to the Zagros Orogenic Belt. This north to different oil fields. A set of 12 Tertiary paleogeographic NE-dipping mono-clinal basin is intersected by a series maps was prepared. These maps represent distinct sequence of basement-controlled tectonic lineaments trending NS stratigraphic events (usually MFS + HST, LST + TST) during to NNE-SSW, i.e. more or less perpendicular to the basin the depositional period (Oligocene-Early Miocene) of the dip. These lineaments, however, differ greatly from each Asmari Formation in southwest Iran. They start with the other in their appearance and timing of reactivation. demise of the Jahrum/Dammam shelf carbonate system The most striking of these lineaments is the Qatar Arch and end with early Gachsaran (or Lower Fars) Formation which remained a broad arch formed over a basement deposition in Early Miocene. The sequence stratigraphic high throughout its existence from Early Paleozoic times framework was established using a modified version of onwards. The Nowruz-Hendijan Ridge, however, is a much the Arabian Plate maximum flooding surface. However, narrower and steeper anticline. The appearance of this in contrast to this model, the sequence definition used is ridge seems to suggest a Hormuz Salt induced upli� over a sensu Vail, rather than sensu Galloway, because the former reactivated basement lineament that formed during Albian- definition keeps all continuously deposited sediment Cenomanian times, coinciding with the onset of ophiolite together within one packet and therefore relates be�er to obduction along the Neo-Tethys Margin. The other, roughly the establishment and infill of accommodation space. The NS-trending tectonic lineaments identified have a more maps were initially constructed by composing the best subtle appearance. No ridges or large fault zones were existing published paleogeographies for each sequence, formed but instead they appear as subtle hinge zones or whilst paleontological/stratigraphic calibration was then as a series of infra-Cambrian Hormuz Salt diapirs lining- achieved by posting data for individual localities from key up above basement lineaments. The salt diapirs are more papers. Tens of published articles in addition to textbooks abundant in the southern Gulf and show a whole array and stratigraphic lexicons of the countries of the region of shapes as well as rates and timing of growth. Besides were considered. Age definitions were largely taken from the roughly NS-trending tectonic lineaments, another set key stratigraphic papers but it was found that work done on of NW-trending lineaments have been identified based Iraq’s stratigraphy was generally be�er documented than on isochore maps. On the seismic data these reactivated that performed on Iranian stratigraphy, and therefore, an basement lineaments appear only as subtle hinge zones. In Iraq model was used to calibrate the basin. This stratigraphy the southern Gulf, salt diapirs also seem to line-up along was later confirmed by fieldwork on the Khaviz anticline in this trend. These lineaments were active from mid to Late southwest Iran, where the Pabdeh, Asmari, and Gachsaran Cretaceous to Early Tertiary times. The tectonic reactivation outcrop. The main difficulty encountered was the poor of the Proterozoic basement lineaments had a perceptible distinction of the Aquitainian in Iran, and the position of influence on sediment facies distribution and stacking the Ghar/Ahwaz sandstone units within the stratigraphy. pa�erns in the overburden. It therefore becomes essential Broadly speaking, the Aquitainian of Iran appears to to unravel in detail the tectonic history of this basin in order embrace both the uppermost part of the Oligocene and to assess its remaining hydrocarbon potential. the Aquitainian. This problem was initially resolved by applying the paleontologically be�er-constrained northeast Iraqi sequence stratigraphic model to Iran. In addition to (60-Poster) Paleogeography of the Asmari a simple reevaluation of the paleontological data, certain Formation in southwest Iran based on the guide-horizons were used, which almost certainly are sequence stratigraphic concepts isochronous and correlative with formations in Iraq (e.g. the Kalhur and Basal Anhydrite). To some extent, entry of the Horbury, Andrew D. (CCL - [email protected]), major Ahwaz sandstones in Iran on sequence boundaries Adnan A.M. Aqrawi (Statoil), Neil Pickard (CCL), Tore can also be taken to be relatively isochronous. Svånå (Statoil) and Ali Moallemi (NIOC)

Although paleogeographic maps of many different (437-Poster) The Arab-D biofacies of Saudi vintages can be traced within any publication survey about Arabia - their paleoenvironment and new the Middle East, there is usually only limited agreement biozonation between any two sets of such maps. This is mainly because the objectives for which maps were made vary in Hughes, G. Wyn (Saudi Aramco - geraint.hughes@aramco. terms of quality of data input, interpretation, geological com), Abdullah G. Dhubeeb (Saudi Aramco), Osman Varol time covered and area of interest. Most of these maps (Varol), Robert Lindsay (Saudi Aramco) and have not been updated with recent geological concepts Harry Mueller (Saudi Aramco) and developments such as sequence stratigraphy, plate tectonics and biostratigraphy. Due to recent exploration and Despite the maturity of the Arab-D reservoir in the Ghawar development activities of some international oil companies field of Saudi Arabia, unexpected reservoir behavior has in southwest Iran, the need to establish a series of updated caused a reassessment of the depositional model using a

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sequence-based approach. As the Arab-D reservoir has Late Jurassic time during the separation of South America relatively short chronostratigraphic duration, conventional from Africa. Another system of lineaments that trend NW- biostratigraphic marker species are unavailable, and local SE from Kenya to Sudan, are believed to be an older fracture appearance and disappearance events are a�ributed to pa�ern related to the Pan-African Orogeny that became paleoenvironmental influence. Nevertheless, biocomponent active during the separation of Africa-Madagascar and distribution can provide valuable information on India. The Melut Basin is one of the four major ri� systems paleoenvironmental variations that may be geologically in southcentral Sudan. The ri� system trends NW and is synchronous between relatively closely-spaced wells. controlled by Central African shear zones. The depositional Semi-quantitative analysis of the macrobiofacies, sequence in Melut Basin includes lacustrine shales with microbiofacies and quantitative nannobiofacies of the fluvial-alluvial sandstones and conglomerate. The basin Arab-D reservoir carbonates has been used to assist to complex exhibits ri� tectonic features with strike-slip decipher this problem. This study provides the lateral compressional effects resulting in complex fault-bounded variations in the various biocomponents across the region, anticlines. The major fault trend through the basin is NNW but especially in the Ghawar and adjacent fields, in an and parallel to Aswa Lineament that extends from Kenya a�empt to provide assistance towards depositional model to Sudan. Twelve cross-sections across the Melut Basin using a sedimentologically-based sequence stratigraphic were restored, and they suggest an Early Cretaceous ri� approach. Core samples have been analyzed from Abqaiq, phase. The associated structural elements were influenced Abu Safah, Ain Dar, Dammam, Hawiyah, Haradh, Khurais, by the northward propagating Atlantic Ocean. The Tertiary Fazran, Qatif, Shedgum, and Uthmaniyah fields, and ri�ing in Melut Basin is characterized by periodic pulses outcrop samples from the Tuwaiq Escarpment. There is a of extensional deformation. During this time the basin remarkable similarity in the vertical stacking of the various was probably influenced tectonically by the Tethys- biofacies, from the deeper spicule-Lenticulina biofacies Mediterranean, as well as the Red Sea-Gulf of Aden ri�. In in the base, through the domed/encrusting sclerosponge, the late Tertiary, the basin was affected by normal faulting branched sclerosponge (Cladocoropsis mirabilis) biofacies that was accompanied by a significant component of strike- into the shallow Clypeina jurassica, Mangashtia vienntoi, slip faulting. The development of the basin during this Pfenderina salernitana, Trocholina alpina and final gastropod stage was most likely affected by Arabia and Asia collision. biofacies. A series of discrete nannopaleontological Also there may be a close link between the cessation of events accompany the macro- and micropaleontological fault activity in the Red Sea-Dead Sea transform and the events, based on coccolith and didemnid ascidian spicule transtensional faulting in the Melut Basin. The Miocene variations. These events are now documented in an failed ri� system propagating from Kenya and truncated objective, uninfluenced, objective digital database format at the border of Sudan, is just to the southern part of this that will enable ease of access and use by Arab-D reservoir basin. During the Tertiary, the basin was affected by the sequence stratigraphers. volcanism, which was widespread in the Ethiopian Plateau to the east, and Darfur volcanic swells to the west. Several basic volcanic rocks are recognized in the Melut area. The (380-Oral) Unconformable stratigraphic trap Quaternary in Melut Basin was calm, and only interrupted potential of South Iraq by the reactivation of normal the fault. Ibrahim, Muhammad W. (Target - [email protected], ) (163-Oral) Integrated reservoir engineering: Several unconformable stratigraphic trap plays were from geological concepts to multiple detected below major unconformities in the Phanerozoics production history matches of Iraq through regional mapping of the stratigraphic sequences of South Iraq. The trap models involve the Inizan, Marielle (Total - [email protected]), juxtaposition of various seal rock facies over several Raffaele Di Cuia Total( ), Patrick Henriquel (Total), types of reservoir rock facies across structurally modified Philippe Lapointe (Total), Florence Vieban (Total) and regional unconformities. In this study the sequences across Gilles Vincent (Total) 10 regional unconformities where potential cap rock facies are unconformably super-imposed on potential reservoir Subsurface uncertainties concerns Geophysics, Geology rock facies were mapped to illustrate: (1) four play fairways and Reservoir (2G&R). The Subsurface Uncertainty below two Jurassic unconformities; (2) seven plays fairways Management process is now a standard methodology in below five Cretaceous unconformities; and (3) seven play Total for non-developed fields. However, as a growing fairways below three Tertiary unconformities. number of fields in our portfolio are mature reservoirs, it becomes essential to assess and manage uncertainties (338-Oral) Structural and tectonic evolution for already developed fields. This implies to match the real production history data. This presentation describes of Melut Basin, Sudan a carbonate field case where the entire process of 2G&R Imam, Abdul-Mageed M. (PDOC - uncertainties quantification and ranking was performed imageed@petrodar.com) leading to several reservoir models that honor the production history. The key messages of this study are: (1) The sedimentary basins of interior Sudan are characterized geological concepts are tested through the history match by thick non-marine clastic sequence of Jurassic (?), process, i.e. the production data should be used to select Cretaceous, and Tertiary age. These basins form a major the most suitable ones. (2) Stochastic modeling and multi- segment of the Central African ri� systems that extend realization allow multiple production history matches and from Nigeria to Sudan. These systems began to develop in thus constitute a true risk assessment for forecasts. (3) Such

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a study can only be achieved by a total integration of the of existing reservoirs, the Khuff Formation needs to be 2G&R engineers and tools. understood at all scales from regional understanding of the platform paleography and stratigraphy, to the fine- scale reservoir heterogeneity at a micro-facies level. In (142-Oral) The upper Arab Formation: is the order to address these issues a large multi-disciplinary present really the key to the past? and multi-scale study has been launched on a large Gulf-scale database. The database includes data from: Insalaco, Enzo (Total - [email protected]), Thierry (1) Zagros outcrops; (2) onshore and offshore Iranian Boisseau (Total), Steve Glover (Total), Florence Viéban wells; (3) offshore Qatari wells; (4) offshore Abu Dhabi (Total) and Fredéric Walgenwitz (Total) wells; and (5) seismic data. Conceptual geological models The upper Arab Formation is one of the most important have been constructed for the large-scale stratigraphic reservoir formations in the Middle East Gulf Region, and architecture, sedimentological organization and the one of the world’s biggest reserves. The complex, fine-scale paleoecological systems. At the reservoir-scale, models for intercalation of dolomitic and anhydritic units poses a the diagenetic overprinting (including models for poroperm number of operational challenges at both exploration and development/occlusion, and dolomitization), and its production scales. These are linked to two fundamental links to the sedimentological, stratigraphic and fracture issues: (1) the sedimentological and sequence stratigraphic framework, have been constructed. These have been interpretation of evaporites, and their relation to the supported by geochemical studies on the carbonates and carbonates; and (2) the diagenesis and remobilization of anhydrites, and micro-structural studies on the fractures. anhydrites. In order to address these issues a core, thin- These regional to reservoir-scale conceptual models have section and geochemical synthesis of a number of cored been used to constrain the reservoir models and to improve upper Arab wells has been studied. The 3-D facies mosaics the integration of the geological uncertainties. A suite of are extremely complex, especially for the evaporites where modeling tools have been used to integrate the conceptual complete gradations between facies types are present. A information and assess uncertainties at all scales. At the simple supra-tidal sabkha versus deep subtidal salina model regional scale Forward Stratigraphic Simulators have been is too simplistic – there are numerous types of evaporitic used in a multiple scenario approach to assess large-scale facies, complete gradations between evaporite types and platform organization. Inhouse reservoir-scale modeling they can occur across the whole depositional profile. tools have been used to model the fine-scale reservoir Moreover, late stage anhydritization and development heterogeneity, and create multiple realizations of the static ‘later’ replacive nodules can also cause problems – not all reservoir properties. Finally these are modeled dynamically nodular anhydrite-rich units are syn-sedimentary or early to assess the impact of the geological parameters on the diagenetic in origin. The majority of the evaporites in the production profiles. study window are various types of ‘sabkharized’ shallow salina and sabkha deposits. Also important are zones of (450-Poster) Fractures identification and later replacive nodules. The sabkha and salina deposits their contribution to production in khuff-3 of the study window appear to be significantly different Reservoir - a tight deep gas dolomite - in the to the sabkha deposits of the present-day Gulf in terms of facies characteristics and facies cycles. The principal Bahrain field conclusions are: (1) understanding the anhydrite facies and Janahi, Layla A. (Bapco - [email protected]) and diagenesis are key in mixed dolomite-anhydrite reservoirs; Adel A. Al-Madani (Bapco) (2) do not over-rely on uniformitarianism (actualism) for understanding the evaporites deposits and anhydrites The Khuff Formation (Permian age) is a major gas reservoir, (not all evaporites are sabkhas, not all anhydrites are which has been producing since 1970 under depletion drive syn-sedimentary/early diagenetic); and (3) there can be mechanism. The Khuff Formation is considered to be the significant amounts of anhydrite mobilization and post- principle gas producer in the Bahrain field since 90% of depositional changes. These issues will have an impact at the gas reserves are contained in it. The remainder of the the regional-scale by providing a predictive stratigraphic reserves is believed to be in the pre-Khuff sequence. Khuff model in terms of facies organization and reservoir quality; Reservoirs produce around one BSCFD of non-associated and at the reservoir-scale, by refining reservoir layering gas. The Khuff Formation is divided stratigraphically into schemes and petrophysical groupings. four reservoir units: K0, K1, K2 & K3. Matrix porosity and permeability are restricted to K0 to K2 units, with the best (143 -Oral) The Khuff (Dalan/Kangan) reservoir quality in K2 whereas reservoir development in Formation: from regional models to the K3 is associated with fracturing. Recently acquired 3- D seismic survey over Bahrain field, calibrated with wells reservoir simulations information, has allowed – to far extent – the recognition of Insalaco, Enzo (Total - [email protected]), Catherine the structural style at Khuff levels. The evaluation of fractures Baglinière (Total), Roger Brousse (Total), Christian at K3 level was carried out by integrating well logs, borehole Fraisse (Total), Jean-Paul Gomez (Total), Pierre Masse imagery and drilling information. This multidisciplinary (Total) and Fredéric Walgenwitz (Total) approach has improved the understanding of the fractures distribution nature and occurrence in the Bahrain field at the The Khuff Formation (Dalan/Kangan) is one of the most Khuff level. It is believed that this approach would reduce important reservoir formations in the Middle East Gulf the drilling risk to developing the K3 reservoir and ensure Region and one of the world’s biggest gas reserves. In order that gas resources from this tight reservoir are well defined to guide investment decisions and to optimize production and optimally exploited and targeted.

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(270-Oral) Reducing turn-around time of the well-known Jurassic and Silurian petroleum systems structural interpretation through Volume (74 and 33 MMbbl per sq km, respectively). Source rock Interpretation: the Yibal example maturity data show that the Jilh Formation has reached peak oil-generation in sub-basins around the Ghawar Jauffred, Jean-Claude E. Shell( - jean-claude.jauffred@s field high. Jilh oils and oil-stained rock extracts are hell.com), Peter P. Bakker (Shell), Peter Engbers (PDO), readily distinguished from Silurian- and Jurassic-sourced Maartje M.D. Koning (Shell) and Guy G.F. Mueller (PDO) oils using standard geochemical analytical tools such as gas chromatography, stable carbon isotope ratios and Although seismic interpretation is o�en carried out in a biomarker analyzes. Although properties vary widely, Jilh conventional way, Volume Interpretation technology is oils have characteristics suggesting a restricted, frequently ge�ing more widely accepted. Many tools are available hypersaline, shale or marl source rock. Reasonably good in the industry to help seismic interpreters to go beyond correlations have been obtained between Jilh oils and simple visualization of data in three dimensions. These extracts of potential Jilh source beds at Shaden and Mazalij tools can be combined into workflows to address specific fields. We conclude that minor accumulations of Jilh oil at aspects of interpretation. They help to reduce turn-around Ain Dar, Qirdi and Sahba fields were generated within the time and take full advantage of the amount of detail Jilh Formation. provided by modern 3-D seismic data. This is particularly the case for fault interpretation, which is always a lengthy (169-Oral) Structural characterization of part of the interpretation. Volume Interpretation tools such as structural dip and azimuth or coherency have greatly carbonates in the United Arab Emirates: improved the quality of structural interpretation. Still, from regional to reservoir scale interpretation of faults has up-to-now been done mostly manually. Automatic fault tracking tools are however under Johnson, Christopher A. (ExxonMobil - christopher.a.joh development in the industry. In Shell, a new methodology [email protected]), Mary Johns (ExxonMobil) and for fault interpretation has been developed based on the Susan Agar (ExxonMobil) patent pending vanGogh technology: the stopper-voxels. High-quality 3-D seismic data of carbonate reservoirs of Stopper-voxels represent discontinuities in the seismic data the United Arab Emirates (UAE) provide an excellent that usually correlate well to faults and can be extracted for opportunity to relate the deformation response to Late analysis and editing. The results are exported as fault sticks Cretaceous compression. At the regional scale, anticlinal or surfaces to a Trace Interpretation System or a reservoir culminations form arrays along prominent subsurface modeling package. The method is used at any stage of the ridges. The arrangement of the anticlines, their size and interpretation. In exploration, it can be used to quickly asymmetry, and the character of internal deformation are analyze fault trends and structural styles at different levels consistent with a basement-involved origin through oblique in a survey. In field development, it is used to speed-up the compression and inversion of deep-seated (probably building of fault models at reservoir level or analyze small Proterozoic) grabens. At the field scale, the anticlines are discontinuities for fracture trends detection. This study cut by numerous vertical fault zones that strike at a high illustrates this novel approach on the Yibal field in Oman, angle to the anticlinal axes. The fault zones display pa�erns where the tool was used to automate fault modeling and of segmentation at all scales down to the resolution of fracture study. the seismic data. Their orientation and sense of oblique offset suggests they formed as large-scale, conjugate (412-Oral) Petroleum potential of the Triassic shear bands. Fault-zone spacing and offset reflect local System, Saudi Arabia strain partitioning, whereas fault zone strikes (dominantly N75W and N45W) are compatible with regional WNW-ESE Jenden, Peter D. (Saudi Aramco - [email protected] compression during fold growth in Late Cretaceous time. m), Adnan A. Al-Hajji (Saudi Aramco), William J. Carrigan The limited offset (usually less than 30 m) and segmentation (Saudi Aramco), Abdelghayoum S. Ahmed (Saudi of the fault zones indicate that the fault zones are unlikely Aramco) and Mahdi A. Abu-Ali (Saudi Aramco) to form major seals within the reservoir. Investigations of the relationships between faults and fractures in seismic Triassic oil and gas-condensate has been recovered data, borehole image logs, and core for one Abu Dhabi throughout a large part of the Eastern Province of Saudi field indicate that the faults have not developed major Arabia. In order to address the origin of these liquids, damage zones. Borehole image logs show local clustering pyrolysis data were compiled for over 700 Triassic core of fractures near some, but not all faults. A correlation and cu�ings samples. Oil- and gas-prone source rocks are between fractures in borehole image logs and those in recognized in the lower Minjur Formation but are most core provides preliminary insights to the relative impact widespread in the Jilh Formation. Samples with the highest of different fracture sets on production. The dominant organic carbon contents (up to 7.4 percent) have excellent NW-trending, fault-parallel fracture set includes grain- oil yields but net source bed thickness is limited. Petroleum size reduction surfaces that are likely to baffle flow. The potential has not been integrated over the entire Triassic NE fracture set appears to be dominated by open fractures section because source beds are difficult to recognize in that are likely to enhance flow. All of these interpretations bulk cu�ings. Individual cores have potentials up to 800 provide the structural framework integrated over multiple Mbbl of equivalent 35 degree API oil per sq km. Although scales that is essential to evaluate structural risk in reservoir sufficient to produce widespread oil and gas shows, these performance. are quite small when compared to petroleum potentials in

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(170-Oral) Structural styles and tectonic fluid contacts, calibrating hydrocarbon saturations in the evolution of onshore Abu Dhabi drainage and imbibition cycles in the presence of variable salinities and in providing detailed hydrocarbon saturation Johnson, Christopher A. (ExxonMobil - christopher.a. profiles in the productive portions of reservoirs and through [email protected]), Brian West (ExxonMobil), the oil-water transition zones. Results from pyrolysis are used Mohamed Sa�ar (ADCO) and in an integrated interpretation using core, logs, and dynamic Andrew M. Gombos (ADCO) data from well tests. CoMod provides new capabilities that greatly assist in tar mat identification and characterization Deformation in onshore Abu Dhabi has been studied using and can be used to correct data for problems caused by 3-D seismic data from multiple fields. The structures studied background organic ma�er from disseminated kerogen, coal, are large anticlines that grew during Late Cretaceous, or drilling contaminants. The methods provide powerful, basement-involved foreland compression. The high-quality rapid, and cost-effective tools to confirm interpretations, subsurface imaging allows an unprecedented opportunity to assist when well logs are ambiguous, and to provide to relate faulting and fold growth over a wide area of the parameters that cannot be obtained through log analysis Arabian Platform. The number and individuality of the alone. structures enables comparative analysis of fold geometry and internal deformation. A consistent structural framework can be constructed that explains deformation observed at (483-Oral) “Real-Time” Pyrolytic Methods scales ranging from the deep crust and lithosphere (plate to Geosteer Horizontal Development Wells: scale), through field-scale growth of anticlines, down to Qatif Field, Saudi Arabia. the smallest faults and flexures that are imaged at reservoir scale on seismic data. The integrated picture results in the Jones, Peter J. (Saudi Aramco - [email protected]), linking of regional tectonics and plate kinematics, foreland Henry I. Halpern (Saudi Aramco), Ma�hew W. Dahan deformation character, fold growth and deep geometry, (Saudi Aramco), Gurhan Aktas (Saudi Aramco), Ishak B. structural timing, and internal faulting and deformation. Ishak (Saudi Aramco), Salman M.M. Al-Qathami (Saudi The anticlines are crossed by systematic sets of small-offset Aramco) and Khalid R. Malki (Saudi Aramco) fault zones arranged in an apparent conjugate relationship. Novel pyrolytic methods developed by Saudi Aramco Fault zone directions (approximately N75W and N45W) are to quantitatively assess reservoir quality from residual interpreted to result from regional WNW-ESE compression hydrocarbon staining on drill cu�ings have been applied during fold growth. Fault zone spacing and offset bear a in ‘real-time’ to assist with geosteering horizontal oil field strong relationship to the magnitude of local strain within development wells. The subject methods include: the bri�le Mesozoic carbonates. The observations are consistent Pyrolytic Oil-Productivity Index (POPI), the Apparent Water with overburden behavior above obliquely inverted deep- Saturation (ASW) Method, and the Compositional Modeling seated grabens. From a production perspective the limited Method (CoMod). Pyrolytic methods have been used at Qatif offset (usually less than 30 m) and segmentation of the fault field primarily to assist in geosteering horizontal power water zones have significant implications for fluid flow within and injection wells (HPWI) that have been drilled in the Arab-C across the zones. The ubiquity of faulting, its geometry, and and Arab-D reservoirs. Placement of HPWI wells at Qatif is its consistent orientations are of interest to explorationists, complicated due to the presence of tar mats that exist on the particularly in areas where 3-D data are unavailable. flanks of the structure. HPWI well placement is designed to be downdip from all sweepable oil, i.e., in the oil-water transition (465-Oral) Advanced pyrolytic techniques zone and below the SW cut-off for moveable oil. However, to characterize oil reservoirs from core the presence of tar mats on the flanks of the structure have samples resulted in a very narrow tolerance for positioning these wells between oil productive and tar occluded reservoir, where Jones, Peter J. (Saudi Aramco - [email protected]), li�le or no water injection can be accomplished. The analysis Henry I. Halpern (Saudi Aramco), Edward A. Clerke is carried out by the POPI Field Analyzer at the wellsite, (Saudi Aramco) and Stephen G. Cheshire (Saudi Aramco) with the following objectives: (1) confirm well placement in O/W transition zone; (2) identify/characterize/quantify Saudi Aramco has developed three novel methods to tar intervals that may be encountered; (3) assess successful quantitatively assess reservoir quality from residual staining geosteering out of tar mats once encountered; and (4) identify on drill cu�ings and core; the Pyrolytic Oil-Productivity reservoir intervals that are favorable for water injection. Index (POPI), the Apparent Water Saturation (ASW) Real-time pyrolysis has proved a valuable tool for reservoir Method, and the Compositional Modeling Method (CoMod). development by quantitatively assessing tar presence and POPI provides an independent assessment of oil-reservoir fluid movability in complex reservoir systems. productivity. The ASW Method provides an independent assessment of water saturation (SW) that corresponds closely to standard calculations via the Archie Equation. Finally, the (162-Oral) 3-D azimuthal tomography on CoMod Method provides assessment of the relative amounts OBC data of various organic ma�er types present in multi-component systems. Pyrolysis methods have proven reliable on 40+ Julien, Philippe L. (Total - [email protected]), year-old unpreserved core samples and are used extensively Philippe Berthet (Total) and Jean-Pierre Dunand (Total) in development planning to assess reservoir productivity This study proposes an original approach for quantifying and changes in reservoir facies. ASW has been an extremely the anisotropy that may occur in a fractured carbonates valuable and rapid input into the integrated study of reservoir reservoir. Wide azimuthal seismic datasets o�en exhibit

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an azimuthal dependency on the normal moveout and (488-Poster) The Permo-Triassic section at the AVO gradient measurements. The success of the Wadi Bih and Wadi Hagil in Ras Al Khaimah, methodology for determining azimuthal interval velocity United Arab Emirates variations is here based on a robust seismic processing, on a robust automatic picking of azimuth/offset events and on an Kamal, Rami A. (Saudi Aramco - adequate depth tomography. The acquisition of the Ocean [email protected]), Ian M. Billing (Saudi Aramco), Bo�om Cable (OBC) 3-D seismic dataset was designed so Abduljaleel A. Abubshait (Saudi Aramco), Denis Vaslet that the elementary bin has a full azimuthal coverage. The (BRGM), Yves-Michel Le Nindre (BRGM), Christian J. efficiency of the methodology was enhanced by applying Strohmenger (ADCO), Abdullah Al-Mansoori (ADCO) the azimuthal tomography in the depth domain. The and Randy Demaree (Saudi Aramco) depth domain avoids azimuthal structural effects and enhances the seismic event coherency for the picking. The Composite geological sections of approximately 3,800 � depth domain also offers a good resolution in the moveout of continuous bedded deposits of the carbonate Permian discrepancy, mainly for non-hyperbolic measurement, and Bih and Hagil, and the Triassic Ghail formations at even for thin layers. Based on the elliptically variation of the Wadis Bih and Hagil in eastern Ras Al Khaimah, in the NMO velocity, the highest interval velocity axis direction United Arab Emirates, have been prepared. The sections was derived first. This axis direction correlates to other include a comprehensive documentation of bedding, study results such as Amplitude versus Azimuth (AVAZ) composition, rock texture, mineralogy, sedimentary or Azimuthal High Resolution Velocity Analysis (AHRVA). structures, depositional facies and facies stacking pa�erns. A�erwards, the medium is considered to be horizontally Lateral variation and porosity were also carefully noted. transversely isotropic (HTI). Thus, the parameters of the The stratigraphy/sedimentology was complemented by a medium were inverted using depth tomography. The VTI description of structural features including faults, folding, tomography was subsequently adapted for HTI media. collapse features and brecciation. Additionally, two teams Since non-hyperbolic measurements were achievable, the of geologists took gamma ray readings along fixed intervals tomography resolves the three parameters Vp0, δ and ε. along the described composites. The resultant traces were The time-to-depth conversion of the reservoir map was compared to wireline gamma ray logs from select wells in consistent with the azimuthal measurements. the subsurface of eastern Saudi Arabia and offshore Abu Dhabi. This has resulted in a correlation scheme with (77-Oral) Permanent downhole seismic the time equivalent Khuff Formation in the subsurface of eastern Saudi Arabia. The outcrop geology rendered from sensors in flowing wells the descriptions was also compared with core descriptions of the Khuff Formation in the subsurface of Saudi Arabia Jupe, Andrew (ABB - [email protected]) and with a bias towards understanding the geometries of Will Wason (ABB) Khuff reservoirs. Finally, the Ras Al Khaimah section was It is generally accepted that the ‘Oilfield of the Future’ compared to Khuff Formation outcrop sections over 1,000 will incorporate distributed permanent downhole seismic km to the east in central Saudi Arabia. The implications sensors in flowing wells. However, the effectiveness of these of this breadth of data capture are invaluable in concurrent sensors will be limited by the extent to which seismic signals efforts to create a unified model for the Khuff formation can be discriminated, or decoupled, from flow-induced across the Arabian Shelf. acoustic noise originating within the production tubing. A specialized test facility has been developed in order to (489-Oral) A comparative study of visually understand and characterize the acoustic noise generated estimated mineral composition, X-ray by fluid flow within a production borehole, with the goal of developing the next generation of seismic tools suitable for diffraction, and trace element determination permanent deployment in flowing wells. By eliminating or from cores across the Khuff-C carbonate in reducing the signal contamination due to the flow, the noise Hawiyah, Ghawar field, Saudi Arabia floor of the system could be improved, enabling smaller seismic signals to be resolved. This study presents the test Kamal, Rami A. (Saudi Aramco - facility design and the results of both physical experiments [email protected]), Ghazi Al-Eid (Saudi Aramco), and numerical modeling aimed at the management of Bruce W. Sellwood, (U Reading) and flow-induced acoustic noise, for permanently deployed Edward A. Clerke (Saudi Aramco) seismic sensors in flowing hydrocarbon wells. From the flow noise experiments, a tool has been developed for A 180-�-long cored interval through the Khuff-C permanent deployment into flowing wells. The tool is depositional cycle, which includes the Khuff-C reservoir, designed to allow the seismic sensors to be acoustically de- was subjected to a key study to compare four techniques coupled from the flow noise, whilst being well coupled to of mineral composition determination of the same rock, the formation. A number of seismic sensor packages can be namely from: full core description, thin section descriptions, distributed at various intervals along the deployed tubing trace element analyses, and X-ray diffraction analyses. to monitor passive and active seismic data. The system has Cored footage from the Khuff-C carbonate in a northeastern been designed so other types of sensors (eg; pressure and Hawiyah area well, was veneered along a length of 180 �. temperature) can also be incorporated if necessary. The thin veneered slabs were ground in one-foot length batches. Homogenized samples from the batches were then X-ray analyzed for mineral composition. Separately, visual estimates of mineral composition were made for the same rock from thin sections taken from core plugs taken at 6-

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inch intervals in addition to mineral composition estimated GIS users. The database contains over 100,000 structurally- from the regularly performed core descriptions. Finally, related, surface and subsurface records of the Arabian Plate. small samples were acquired from the same plug ends and The project is specifically designed to permit the integration of were pulverized and run through automated trace element geoscience information from GIS and non-GIS users. Besides detection processes. Data from all four methods were the scientific value of documenting the regional structural tabulated, plo�ed and compared. Visual determinations of evolution of the Arabian Plate, this rapidly growing database bulk mineral compositions portray the lithology trends in also yields economically important information; e.g. about the rock, expressed in the X-ray determined mineralogy and the possible occurrence and orientation of sealing and non- trace element analyses. Detailed comparisons showed that sealing faults in a particular formation or field. calcite percentages compared the best. Dolomite percentage compared fairly. Anhydrite percentage trends were correct but values were systematically low compared to mineralogy. (102-Poster) Permian Upper Gharif The anhydrite discrepancy can be explained by observing Sandstones of Oman: a new approach to that a large percentage of the Khuff anhydrite is concentrated predict them on seismic in small to medium sized nodules. Hi�ing or missing a nodule during the core plugging process can make the Kazdal, Recep A. (PDO - [email protected]) and difference between a high visually estimated percentage and Glen William (CGG) an almost negligible percentage of the mineral. Although Prediction of Permian Upper Gharif channel belts is a major the anhydrite trend is not jeopardized, X-ray diffraction challenge for the exploration and field development activities is recommended for studies where accurate anhydrite in Central and North Oman. The declining portfolio of percentages are necessary. X-ray diffraction revealed the Gharif exploration opportunities and increasing constraints occurrence of minor and trace elements, namely: feldspar, for additional oil production are pushing geoscientists pyrite, siderite, fluorite, and celestite (0.1 – 2.9 percent of bulk for an in-depth understanding of the distribution of these rock); that were not recognized by the optical petrographers. sands. The Upper Gharif sand units are discontinuous thin Minor element recognition can play an important role in channel bodies, difficult to correlate at field scale and not correlation, determination of environments of deposition, always in pressure communication. At a time when most and diagenetic sequences. This comparative study reveals of the Gharif fields in Central Oman are entering secondary the variance between visually estimated mineral composition recovery activities (water flood), identification of connected and what is instrumentally detected. Secondly, the study has sand bodies through geophysical and geological means, is shown the variance between geochemical mineral analyses of utmost importance. The main challenge is to image the taken from a homogenized ground sample taken across a complex distribution of intertwining channels on seismic. foot of core and spot measurements taken six inches apart The approach presented here is a combination of forward along the same foot of core. modeling of the well data and visualization of the seismic data. A convergence between the expected seismic response (1-Oral) Arabian Plate structural evolution: and what is observed, allows the geoscientist to make GIS application inferences about the likely presence of sand. The individual sand bodies are quite thin (2-5 m) and below seismic Kapka, Be�ina (GeoTech - [email protected]) and resolution, but variations of the net-to-gross of stacked Joerg E. Ma�ner (GeoTech) channels may be seen on seismic. One example shown is from Mabrouk field in North Oman. The seismic response Comprehensive surface and subsurface structural data of suggests a good correlation with the synthetic seismogram the Arabian Plate are captured in a Geographic Information models. Sand development appears to be associated with System (GIS) database framework. The structural environment troughs (negative) on the seismic, and shales with peaks and activation history of features (such as faults, folds, (positive). Moreover, wider troughs seem to correspond with halokinesis and volcanism) is documented, mapped and higher net-to-gross. Hence, visualization of troughs might interpreted. The GIS system allows for: (1) the visualization help to detect the net-to-gross distribution. This observation of geological features in different map displays; (2) statistical needs further confirmation, but may open avenues for analysis and interactive querying; (3) the exchange and improved picking of injector or producers well locations. collaboration of data and interpretations between different Similar observations have been made at Barik, Hasirah, parties; (4) on-line access of data; and (5) high-quality output Hawqa Saih Rawl, and Zauliyah fields, where wide troughs of results for possible publishing purposes. The system, can be correlated to high net-to-gross systems, whereas tram- for example, answers questions like: (1) “which structural lining pa�erns correspond to low net-to-gross. features are reactivated or newly-created on the Arabian Plate in the Permian”; (2) “what is their orientation and geometric relationship”; and (3) “what local and regional (137-Oral) Seismically constrained stress direction and stress conditions could have caused these integrated reservoir modeling of the Al features”. This can be achieved interactively on screen, or via Huwaisah field, North Oman standard formulated expressions. Computer Aided So�ware Engineering (CASE) tools were used to design the database Keating, John (PDO – [email protected]), using Unified Modeling Language (UML) diagrams. This Mohammed Mugheiry (PDO), Chia Fu Hsu (Shell) and strategy has advantages such as: (1) built-in documentation Ron Nelson (Shell) and visualization of the relationships between the a�ributes of the data; (2) updating and modification of the existing The billion barrel STOIIP Al Huwaisah field is a large, low- database structure; and (3) transfer of that structure to other relief, faulted dip closure with a thin oil column. It produces

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from the Aptian (Lower Cretaceous) Shu’aiba Formation, depth level, also called gridpoint gathers, from which the which consists of complex, rudist bearing, shelf margin anti-causal part is used to predict the upward reflecting part deposits. Matrix heterogeneity is locally compounded of the internal multiples. A series of land field datasets from by faulting and fracturing giving rise to highly variable Saudi Arabia was used to demonstrate the effectiveness of production behavior. Integrated study of the field was the proposed technique, as well as its impact in exploration driven by a need to understand and improve production and developmental drilling. performance and plan for future field development. The field is covered by 3-D seismic of 1990-2001 vintage. Volume interpretation and image processing techniques enable a new (247-Oral) Reducing drilling risk in the interpretation of key horizons and faults. A new structural Tertiary and Upper Cretaceous using framework, velocity model and depth model for the field have refraction processing and visualization of been developed. Seismic inversion was also used to constrain 3-D seismic data porosity modeling. Seismic facies, a�ribute analysis and inversion help to identify gross depositional environments Kellogg, Stephen C. (Saudi Aramco - stephen.kellogg@a (large channels, shoal, lagoon) and determine reservoir/non- ramco.com), Ean Craigie (Digicon) and Barton A. Payne reservoir. Faulting and fracturing have a major impact on (Saudi Aramco) fluid movement through the reservoir and are important for well targeting and completion. Seismic a�ributes were Shallow karsts that are present in parts of the Arabian integrated with abundant well data (approximately 60 km Peninsula pose significant risks to exploration and Borehole Image log) to provide multiple fracture realizations development drilling. At the very least, drilling programs for reservoir modeling. Integrated reservoir modeling must plan on encountering sudden circulation losses and/or allowed the historical performance of the field to be matched bit drops as the drill string approaches a void space. This for the first time. A number of wells have been drilled to drives up drilling time and costs. The worst case is the realize opportunities in newly mapped structural highs total loss of a well, abandonment, and redrilling. Current and reservoir sweet spots based on the current study. These production 3-D seismic data is designed for deep reflection were also picked to avoid seismic discontinuities. Successful targets, from about 5,000 � down to 17,000 �. Due to wells show high production rates (increase in net oil of about parameters such as bin and array dimensions, very shallow 300 cubic meters/day) and have opened new areas of the reflection resolution is inadequate to image these voids. We field. All wells are now targeted with reference to seismic have developed an alternative, simple, and fast method of a�ribute volumes to minimize drilling losses and maximize detecting these shallow karst features by employing seismic production by avoiding potential water bearing features. refraction data, and then performing a series of a�ribute analyzes, taking advantage of the latest 3-D visualization techniques. Conceptually, ray-paths will be highly-distorted (382-Oral) Data-driven internal multiple when encountering a karst feature, with back-sca�ering/ elimination targeted for land data absorption. As a result, the energy recorded at receivers near karsts will be substantially reduced relative to receivers Kelamis, Panos G. (Saudi Aramco - panos.kelamis@ara where no karsting is present. Using multiple refractors, mco.com), Kevin E. Erickson (Saudi Aramco), Daniel A. we have found that it is possible to track these differences Nietupski (Al-Khaleej) and Robert L. Clark (Digicon) and map them in the near-surface a�er a simple and fast processing flow. The results can then be passed on to the The prediction and subsequent elimination of internal drilling engineers, who can alter their well plan accordingly, multiples in land data is probably one of the most challenging to minimize the risk of drilling through these problematic subjects in seismic data processing. The time and space zones. The results have proven very encouraging when variability of the multiples, their small velocity discrimination compared in a ‘blind’ manner against well histories. These compared to primary events, combined with low signal- techniques were applied in a problematic area of the to-noise ratio and weak reflectivity at the target, are a few southern Ghawar field. of the key obstacles which make the multiple elimination process complex and quite o�en cumbersome. Using principles from Common Focus Point (CFP) technology a (469-Poster) Depositional environments data-driven, internal multiple prediction approach, targeted and diagenesis of Cretaceous (Albian to for land data was developed. It requires no assumptions Maastrichtian) strata of Abadan plain of the about the earth model and can be applied pre- and/or Persian Platform, southwestern Iran post-stack. The kinematics of internal multiples generated by a specific boundary are computed by convolutions of Keyvani, Forooz (NIOC - [email protected]) the corresponding CFP gathers. These CFP gathers are and Ezat Heydari (Jackson State U) essentially half-redatumed shots with sources at the surface and receivers at datum. Thus, in order to compute internal Sedimentology, diagenesis, and reservoir quality of multiples, a layer-stripping, top-down procedure is required Cretaceous (Albian to Maastrichtian) strata were investigated that can handle all the interfaces above the target of interest. in Azadegan, Kooshk, Khoramsahr, Darkhuain, Mahshahr, As an alternative to the boundary-related approach, a layer- and Tangu oil fields of the Abadan Plain province of the related scheme is also introduced in which all the downward Persian Platform in southwestern Iran. Formations studied reflecting effects of the overburden can be accounted for. The include (oldest to youngest) Kazhdumi, Sarvak, Ilam, Gurpi, application of the layer-related internal multiple algorithm and Tarbur. The overall characteristics of these formations requires, besides CFP gathers, a fully re-datumed version of were controlled by relative sea-level fluctuations, although the surface data with both sources and receivers at a chosen compressional tectonics associated with the closing of

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the Neo-Tethys Ocean and basement faulting also played and perforations. Pre-processing included the generation of minor roles. A relative sea-level rise initiated deposition of a bias log from all the production dataset. A 3-D parameter organic-rich shales of the Kazhdumi Formation (Albian- was generated from this log by interpolation to co-condition Cenomanian). The limestones of the overlying Sarvak the carbonates in object modeling. This bias log was also Formaton (Albian-Turonian) formed during the highstand. used during the upscaling of the well data at grid resolution. A major sea-level fall at the Cenomanian-Turonian boundary A 3-D shale volume parameter generated from more than exposed carbonates of the Sarvak Formation. However, 300 wells by interpolation, was used as a co-conditional the uppermost portion of the Sarvak Formation was parameter for locating shales in the 3-D geomodel. A deposited during an early Turonian sea-level rise, and was general markedpoint process algorithm was used to model subsequently exposed due to a minor sea-level fall. The shales the lithofacies picked from wireline log interpretation. of the Laffan Member (Coniacian) of the Ilam Formation Core descriptions provided the input for the definition of covered the Cenomanian- Turonian unconformity during lithofacies. Petrophysical modeling was performed on the the early stages of a major sea-level rise. The limestones of results of the object modeling to simulate effective porosity the Ilam Formation (Coniacian-Santonian) were deposited and log-derived permeability. Water saturation was modeled during the highstand and possibly early lowstand. A major using a J-function for different lithofacies. The resulting transgression resulted in deposition of dark gray shales simulation model matched the vertical static pressure and of the Gurpi Formation (Campanian-Maastrichtian). The major saturation distribution for 228 wells quickly during Tarbur Formation (Maastrichtian) formed patch reefs along initialization. the shelf margin. A disconformity separates Maastrichtian and Danian (Early Paleocene) in this area. The study revealed a variety of lithofacies indicative of strand plain, tidal flats, (207-Oral) Onshore Abu Dhabi 4-D seismic coastal plain, carbonate sand shoals including tidal bar pilot test survey 1998-2003 belts, inner shelf, middle shelf, patch reef, barrier complex, Kleiss, Erik B.J. (ADCO - [email protected]), Peter outer shelf, mounds, distal deep marine pelagic depositional Melville (ADCO), Samer Marmash (ADCO), Abu Baker environments. Major diagenetic alterations occurred along Al-Jeelani (ADCO), Majid Al-Mirza (ADCO), William the Cenomanian-Turonian unconformity. Meteoric processes Soroka (ADCO), Andrew Sewell (WesternGeco), Hafez Al- resulted in karstification, generation of porosity and Kamal (WesternGeco) and Paul West (WesternGeco) permeability, and dolomitization, forming good reservoir quality strata in the Sarvak Formation. Burial diagenesis In 1998 a first high-spec onshore 3-D seismic survey was affected all units, in some cases increasing porosity and acquired over a major onshore oil field in Abu Dhabi, permeability and in others decreasing them. covered at surface by sand dunes up to 60 m high. A repeat test in 1999 confirmed that short-term repeatability was good, (271-Oral) Integration of geological and noise levels low enough to detect seismic differences and dynamic data for constructing 3-D predicted from reservoir modeling. It showed that for a successful 4-D, the 1998 acquisition parameters should geological models: an IOR study from the be repeated as-perfect-as-possible and surface conditions Ahwaz field, southwest Iran should not have changed too much. In 2003, a dedicated 4- D survey was acquired over part of this field. Since the first Khanna, Mohit (Statoil - [email protected]), Arne survey, surface conditions have changed and new wells and Linjordet (Statoil), Torgrim Jacobsen (Statoil), Tor surface infrastructure came in place, so not all vibrator and Røsaasen (Statoil), Mohammad Sharafoddin (RIPI) and geophone locations could be exactly repeated. All this leads Ahmad Miryaan (NISOC) to small variations in recorded signal and noise. The main An IOR study has been performed on the Asmari Formation purpose of the 2003 pilot survey is to confirm the expected of the Ahwaz field. As a part of this study a 3-D geocellular good seismic repeatability a�er five years, and if successful, model was constructed based on reservoir characterization to verify and adjust the dynamic reservoir model. This study from 338 wells and a regional interpretation of the presents how the 2003 repeat survey was acquired using depositional systems of the Asmari Formation. The model economized–yet well-repeatable–acquisition parameters. was used as a basis to match 40 years of production history Data examples illustrate local changes in source and receiver and to predict the outcome of different drainage strategies. spread, surface conditions, statics, recording procedures This study describes the construction of the 3-D geological and instrument changes. Some tests compared 1998 to 2003 model. The Ahwaz field spans 420 sq km in the Zagros data, and also differences resulting from different source area of southwest Iran with 400 m-thick Asmari Formation configurations in 2003. as the main oil-producing reservoir unit. It consists of interbedded sandstone, shale and carbonate intervals of (350-Oral) Enhanced productivity of Oligocene to Miocene age. 3-D geomodeling was performed fractured carbonate reservoir through cross- on a simulation grid design with more than one million cells to avoid upscaling, thereby saving time, cost and avoiding dipole shear-wave logging in the Bakr-Amer mathematical inaccuracies. The main input to the model field, Gulf of Suez, Egypt was core data, petrophysical log interpretation and dynamic Klimentos, Theodore (Schlumberger - [email protected]), data. In the current model a multi-stage modeling technique Tahe Elzefzaf (GPC) and Maher Omara (GPC) was used to include all the wells in the field. Another unique technique that was implemented involved the use of Earth stress pa�erns give a general indication of the most production data to constrain the distribution of sands and likely fracture orientation or maximum stress trend. carbonates. The production data was comprised of PLT, PI,

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Nonetheless, local variations and the effects of localized equation was developed for the determination of α as a structures, such as large faults, can modify the stress function of permeability and rock elastic moduli. Then, rock pa�ern, counter-acting or adding to the regional stress. permeability and elastic moduli, which were derived from Thus, such a local stress and fracture profile information can NMR and dipole sonic imaging logs, were used as inputs be useful to many petroleum exploration and development into the empirical equation for the determination of α. This related aspects; such as; (1) selecting perforation intervals process led to a more accurate evaluation of geomechanical and strategy; (2) planning hydraulic fracturing operations; applications (effective earth stresses, wellbore stability (3) optimum well placement; (4) wellbore stability; (5) sand and sand-free maximum drawdown pressure). Moreover, production; and (6) hydrocarbon migration. In this study, it was found that the NMR-derived capillary pressure cross-dipole shear-wave anisotropy logs, acquired in several in conjunction with permeability may be very useful in wells of the Bakr-Amer field in the Gulf of Suez, were used determining a sand-free maximum drawdown pressure, to enhance the productivity of the Nullipore carbonate especially when there is water influx, which commonly reservoir by determining the orientation and magnitude causes sand production by reducing the capillary pressure of the principal horizontal stresses and detecting major between sand grains. fractured intervals. Currently, the Bakr-Amer field accounts for 55 percent of the General Petroleum Company’s (GPC) daily oil production. Approximately 40 percent of this (407-Poster) Prospecting for the upper amount is solely produced from the uppermost reservoir Wasia Mishrif Member in Eastern Saudi known as the Nullipore. The cross-dipole shear sonic data Arabia were processed to obtain oriented fast and slow shear- waves. This information was then used to determine the Knowlton, Andrew M. (Saudi Aramco - andrew.knowlton direction and magnitude of the insitu earth stresses and the @aramco.com.sa) and Tariq U. Usmani (Saudi Aramco) orientation of fractures. Zones showing significant shear- The Mishrif Member of the late Cretaceous Wasia Formation wave anisotropy were detected as open-fracture systems has been largely overlooked as an exploration target since using the shear-wave anisotropy data in conjunction with the early days of drilling in the Eastern Province of Saudi the Stoneley-wave chevron pa�erns and other available Arabia. The first exploration wells found sweet gas in logs. These intervals were subsequently perforated and the Mishrif Member at Dammam Dome and this remains produced significant amounts of hydrocarbons. Further the only producing field from the Mishrif in the Eastern application of this technique in several wells of the Bakr- Province. The Mishrif was deposited as an alternation Amer field, proved that the Nullipore reservoir productivity of transgressive, highstand carbonates and clastics in a is primarily controlled by the flow contribution from natural relatively quiescent marginal to shallow-marine se�ing. fractures. New highly-deviated wells were completed The widespread mid-Turonian tectonic event disrupted this over the Nullipore on the basis of the newly-acquired depositional cycle and the upper Wasia was subsequently information, and excellent results were obtained. Moreover, eroded over many emerging structural highs in Eastern older wells were restudied and recompleted on the same Arabia. The pre-Aruma unconformity defines the boundary basis, and a large increase of production was a�ained. between the subcropping Mishrif Member and the overlying Aruma Formation. Many potential hydrocarbon (351-Oral) NMR applications in traps occur on the flanks of Turonian-activated structures geomechanics where the Mishrif Member subcrops and is sealed by the shales of the Aruma Formation. Major play risks include Klimentos, Theodore (Schlumberger - [email protected]) hydrocarbon charging of the Mishrif reservoir and sealing capacity of the Aruma Formation. The Biot elastic constant (α) of a rock is a poroelastic parameter that relates stress and pore pressure (Pp). It describes how compressible the dry skeletal frame is with (400-Oral) Providing easy, quick and secure respect to the solid material composing the dry skeletal access to exploration data on the intranet frame of the rock. According to Biot, α measures the ratio of the fluid volume squeezed out to the volume change Kok, Al A. (Saudi Aramco - [email protected]), Ibrahim of the rock if the la�er is compressed while allowing the A. Al-Ghamdi (Saudi Aramco) and fluid to escape. This implies that α should be a strong Sa’id A. Al-Hajri (Saudi Aramco) function of permeability, although other factors such as Geoscientists require quick and easy access to data for rock compressibility, lithology, and cementation may also their day-to-day decision making process. For large be influential to some degree. In petroleum-bearing rocks, organizations, these seemingly simple and straight-forward Terzaghis effective stress principle may not always be valid. requirements are o�en complicated by data stored in Accordingly, a modified effective stress (σeff) is a function disparate databases with very li�le integration. This study of the Biot constant: σ = σ - α * P . Despite the great eff tot p discusses the challenges, benefits and the technologies used significance of α, only a limited amount of laboratory work for providing unprecedented access to exploration data on its determination has been reported in the literature. easily, quickly and securely. By leveraging developments in Our recent experimental results showed that permeability web-enabling technologies, the goal of providing easy and has a much stronger effect on a than porosity. Laboratory quick access to exploration data anytime and anywhere experiments on two Middle Eastern rock samples having on the intranet was accomplished at the Saudi Aramco the same porosity (18 percent) but different permeability Exploration organization. Virtually all strategic data exhibited very different values of static α. Based on stored in disparate databases can be queried and viewed extensive laboratory measurements, a novel empirical

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easily, along with a map display via a web browser. In significant. In such situations, minimizing cable feathering addition, tens of thousands of on-line documents stored during acquisition by appropriate survey design and the in a document management system were made easily use of steerable streamer technology would be beneficial accessible. Also, by providing the capability to visualize for improving multiple a�enuation results. the data via a map display, quality checks have been made easier, thus improving data quality. This implementation, called E-Data, was accomplished by utilizing the web (88-Oral) The role of mechanical stratigraphy and light-weight GIS technologies as well as the spatial in structural evolution and trap styles in the database and document management technologies. E-Data Zagros is designed to be cross-browser compliant and platform independent. Data access security is implemented by Koopman, Anton (Shell - [email protected]) leveraging the Oracle database authentication mechanisms. Deformation styles in Alpine compressive belts are To minimize implementation effort, a widely-used, off-the- critically influenced by stratification and multi-layered shelf light-weight GIS was used to facilitate the web map characteristics of lithological units, at a variety of scales. display and to access spatial data in the spatial database. Distribution and intensity of fractures correlate with the specific characteristics of mechanical stratigraphy at any (272-Oral) 2-D SRME performance in the of these scales. Dedicated outcrop studies contribute to presence of streamer feathering and understand the complex structural relationships in the structural dip prolific hydrocarbon province of the Zagros Mountains, where double plunging anticlines constitute the primary Koeninger, Chris (WesternGeco - chris.koeninger@wes trap style. These folds are neither periodic nor cylindrical terngeco.com), Ian Moore (WesternGeco), Dave Monk along their axes, and did not develop by any single growth (Apache), John Bedingfield Apache( ) and mechanism. At trap scale, most anticlines resemble models Ron Roberts (Apache) of conjugate kink bands, composed of conjugate pairs of externally rotated, relatively planar limbs, with kinked but Wave-equation based, data-driven multiple prediction relatively rounded hinges at either side of a moderately algorithms, such as DELPHI’s SRME, can provide a arched and generally broad crestal zone. Relatively box- highly-accurate prediction of surface multiples regardless shaped or chevron-like fold shapes prevail in well-bedded of the complexity of the medium. While acquisition and stratified intervals, whereas more rounded shapes prevail processing methods for 3-D prediction of multiples are in the competent members of the mechanical multi- an active area of research, the prediction of multiples layer. Thrusts are secondary and subordinate to folding, from conventional (narrow azimuth) 3-D marine data propagating beyond the locking position of the folds. using enhancements to the 2-D SRME method is of Localized volume constraints associated with excessive considerable practical importance. It is well-known that external rotation across primary mechanical boundaries 2-D implementations of SRME can be subject to significant within the fold limbs leads to secondary accommodation kinematic errors in the presence of 3-D effects, such as cable of shortening by flexural slip, stepped bedding plane feathering or cross-line structural dip. However, much less thrusting and generally disharmonic parasitic folding, is known about the combined effect or relative importance controlling details of trap geometry, fracture distribution, of these sources of error. The widespread use of the method and fracture bedding relationships. Effects of deep-seated indicates that, in many cases, the data pre-conditioning strike-slip, primarily organized according to preexisting and adaptive subtraction steps applied before and a�er the basement fabrics, are diffusely distributed across the major computation of the multiple model compensate effectively detachments and appear to overprint the progressively for these errors, though the performance of the method evolving detachment folds in the cover. There are can be difficult to predict. This study discusses the results indications that this overprint resulted in spaced corridors obtained on a data set from the Middle East with emphasis of small-scale faulting and enhanced fracturing, positively on illustrating the effects of cable feathering and structural affecting permeability and production performance of the dip on 2-D SRME models of free-surface multiples. A main reservoirs in the Zagros Mountains. recently developed tool is used to predict the timing errors associated with specific modes of surface multiples, taking into account the relevant geological, data acquisition, (343-Poster) Paleosedimentary environment and data processing characteristics. The error prediction of the Burgan sandy tongues in the Arabian method is extremely fast compared to an SRME-type Plate prediction of the multiples themselves. There are many uses for the errors predicted by such an analysis, including Kordi, Masoumeh (IOOC - [email protected]) and input to the survey design, prediction and QC of the Sayed H. Kazemeini (IOOC) performance of the demultiple algorithm, optimization of Burgan sandy tongues of the Albian Kazhdumi Formation data processing parameters, and even potentially, correction are major productive reservoir in the Middle East. High of the predicted multiples for the errors involved. The main porosity and permeability of these sandstones and the conclusion of the study is that when the cross-line dips existence of shales layers–either as source rock or caprock of the multiple generators are small, 2-D SRME predicts in this formation–have provided all the required conditions the travel-times of free-surface multiples accurately for hydrocarbon accumulation. Extension of the Burgan and is reasonably insensitive to cable feathering. As the sands was determined by producing subsurface maps cross-line dip increases beyond a few degrees, travel-time and stratigraphic cross-sections. Well log correlation, errors become large, and sensitivity to cable feathering is

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petrophysical properties and petrography were studied defining and correlating the various flooding surfaces and to determine lateral and vertical facies variations, basin sequences boundaries. Transgressive, highstand, lowstand analysis and sedimentary environment modeling. Based system tracts were identified and named from bo�om to top on lithology and reservoir characteristics, the Kazhdumi as MR_00 to MR_70. The new stratigraphic framework not Formation is divided into five members (from bo�om to only forms the basis for reservoir correlation within various top): C (poor reservoir); B (main reservoir); A (secondary Marrat fields discovered in the past two decades, but also reservoir); Dair limestone; and Upper Kazhdumi (Nahr provides a tool for inter-field reservoir correlation in the Umr member). Structural, isolith, sand-to-shale ratio, and Divided Zone and Kuwait. A depositional model for each sandstone percentage maps show that the thickness of of the sequences was also developed on a semi-regional sandstones increase to the west, and this trend is roughly scale. This study is likely to enhance the understanding perpendicular to the main NW-trend of the basin. Lobate of Marrat depositional environments and contribute to pa�ern and interfingering development of sands on resolving some of the outstanding Marrat boundary issues subsurface maps show that they were formed in a river- in the Arabian Plate. dominated, foot bird delta. Paleocurrent and source of sediments in this delta originated from the area of Kuwait and Saudi Arabia. Stratigraphic cross-sections illustrate (49-Oral) Right-lateral wrench fault system in the wedge shape development of sandy tongues and offshore ex-divided zone confirm the deltaic environment. Petrographic studies Kusaka, Hajime (Al-Kha�i JO - [email protected]) show that the C member contains black shales, siltstone, glauconite and phosphate grains that indicate deposition The Kha�i, Hout and Dorra fields are located in offshore in the pro-delta. In this member layers of sandstone are ex-divided zone in the Gulf. The three fields are elongated recognized. The B member mainly contains loose sands and asymmetrical domal structures aligned in a NE-SW with more than 75 percent quartz, which become coarser direction. The discovery of three fields are based on 2-D and cleaner from bo�om to top that confirm a deltaic seismic data. However be�er understanding of the tectonics environment for these sediments. Roundness, sphericity of the area was obtained a�er acquiring 3-D seismic data and abundance of quartz grains show that the source of in the late 1990s. KJO conducted a 3-D seismic survey sands was dominantly sedimentary rocks older than Albian over Kha�i and Hout fields in 1997 and over Dorra field in that have undergone more than one sedimentary cycle. 1999, for a total of about 1,000 sq km. Advanced processing The succession of sandstone, siltstone and claystone in techniques and extensive interpretation of the 3-D data the A member indicates a deltaic environment. Towards provided the structural relationship between the three the east of the Arabian Shield, the Burgan sandstones pass fields and among the fields and tectonic origin. Two major to shale and limestone with an interfingering pa�ern in a right-lateral wrench faults trending in a NE direction were river-dominated delta. The great extent and thickness, and identified. The northern fault runs through the Dorra and favorable reservoir conditions in the Burgan paleodelta, Hout fields. The southern fault runs through the Kha�i created the most prolific sandy oil fields in the world. field and is believed to extend to the south into the Safaniya field. The two faults were generated at the Aruma-Wasia (399-Oral) Integrated Marrat sequence unconformity in late-middle Cretaceous time with NE- stratigraphy-depositional model of Divided directed compression. The trend of the northern wrench fault plane changed in the middle of the Hout field from Zone and Kuwait in relationship to key NE to NNE in direction. A couple of flower structure planes Marrat boundaries of Arabian Plate branched out from the main wrench fault, and extend up to the Rus Formation in the central part of the Hout field. Kumar, Sukhdarshan (KOC - [email protected]) and An antithetic fault striking in a NW-SE direction divides the Hanan B. Al-Qanaei (KOC) field. A structural ridge between the two main wrench faults An integrated sequence stratigraphic study of the Marrat trends in a NNE direction, and extends from the southern Formation in the Divided Zone between Kuwait and Saudi part of the Hout field to the northern part of the Kha�i field. Arabia and Kuwait was undertaken. It used all 96 wells Coherency cube reveals several faults along this ridge. The and improved our understanding of the depositional facies, Kha�i, Hout and Dorra trend was generated by a pair of correlativity and distribution of the key Marrat producing wrench faults trending in a NE direction. reservoirs. The study focused on building depositional environment models for each of the sequences, and relating (347-Oral) Geomechanical reservoir them to the key flooding surfaces and sequence boundaries characterization of a giant fractured of the Arabian Plate (AP). The study positions the Upper Marrat of Kuwait with the Middle and Lower Dhruma carbonate field, offshore Abu Dhabi elsewhere in the plate. The age dating of the Marrat Ku�y, Abdurahman (Zadco - aku�[email protected]), Chawki sequences is limited by scarce biostratigraphic data, and A. Dabbouk (Zadco), Hamad Bu Al-Rougha (Zadco), is based primarily upon correlation. Due to the impact Mauro Cimolai (CoreLab), Ned Etris (CoreLab) of tectonic movements, some of the sequence boundaries are sharp, not completely preserved, or correspond to A geomechanical reservoir characterization was performed non-deposition. Within the Jurassic sequence stratigraphic in two carbonate reservoirs in an offshore Abu Dhabi field. framework, five sequences are identified in the Marrat The ultimate objective for this study was to develop a succession, and are named from bo�om to top as JSEQ-1 fully-coupled geomechanical simulation model that more to JSEQ-5. A suite of composite logs, core and ditch cu�ing accurately identifies the controls on fluid flow within the data, and selected master logs for key wells, were used for

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reservoirs. The giant field is a very low-relief anticlinal non-reservoir ‘dense’ bodies embedded in it. Stochastic structure consisting of distinct, stacked carbonate reservoirs inversion was carried out with inhouse so�ware GeoInv. that hold billions of barrels of light oil. A�er a primary The stochastic approach enables us to compute a family of production phase that started in 1968, a pa�ern water-flood equi-probable impedance inversion volumes that are both was introduced in 1983. However, substantial early water constrained by seismic and well data. For this inversion, breakthrough prompted a range of comprehensive studies to a family of 100 realizations was computed using 22 input assess the reservoir performance drivers. The present study wells and a mean wavelet extracted from 6 high-quality was initiated to understand the influence of geomechanical wells. Each inversion contained 785,000 traces. The mean effects on reservoir performance, due to variations in and the standard deviation (Sigma) were computed from reservoir pressure, saturation and temperature caused the 100 realizations and analyzed. Next, the probability of a by production and injection operations. Geomechanical cell to be higher than a described threshold was computed factors could potentially dynamically change the from the inversion family. From these probabilities, the permeability within the formation, thus controlling fluid locations of the high impedance or low density zones in movement over the field’s history. This study presents the the reservoir were delineated and their volume calculated. characterization workflow for geomechanical a�ributes in The results were entered into the geomodel built in time at the reservoirs. Geomechanical a�ributes like elastic Young’s a one millisecond sampling. The 38 million cell impedance modulus, Poisson’s ratio, bulk modulus, compressive and cubes were read in the same stratigraphic time grid, in tensile strengths, in-situ stresses, shear moduli, and rock proportional layers of the reservoir formation, and then compressibilities from 233 wells were computed using read into depth into the geomodel. The depth model was various log data. Direct hard data, like core mechanical then converted into porosity, estimated stochastically properties and minifrac tests available in limited wells, were using over 100 wells present in the geomodel. The models used to calibrate and validate the log-derived geomechanical corresponding to mean impedance cubes, mean plus properties. Mapping and 3-D modeling were subsequently and minus a proportion of Sigma were prepared for an used to ensure spatial consistency and geologic feasibility. uncertainty approach. The porosity models were produced A mapping of the initial stress state of the reservoirs was with different methods either deterministic or stochastic, generated. The geomechanical characterization of the constrained at the wells and then pore volumes computed reservoirs formed the necessary input for the coupled flow for these different options. simulation to investigate the effects of rock mechanics on regional flow performance. The results of the geomechanical characterization suggested that the dominant directions of (217-Poster) Iran’s Balal field development: stress have changed significantly over time, and that the full subsurface integration within a buy-back current stress field is that of a strike-slip stress regime as contract opposed to the extensional regime that existed in the past, as revealed from the seismic record. Arising from this study, Legorjus, Claude (Total - [email protected]), a newly identified conjugate fault/fracture system across the Pierre Bergey (Total), Sabrina van de Beuque (Total), field was established which proved to be consistent with the Fabrizio Bolondi (Agip Iran BV) and pa�ern of water breakthrough from field operations. This Khosrow Farhangi (NIOC) insight added significant complexity to the structural model The Balal field, located offshore Iran, has been developed of the field. Clarification of the geomechanical influence on for oil production from the Upper Arab reservoir by Elf the reservoir dynamics of the formation has proven to be Petroleum Iran (Total Group) in association with Bow Valley a complex issue with extended requirements for accurate Energy and AGIP Iran BV. The development was carried out reservoir data. under the terms of a buy-back contract signed in April 1999 with the National Iranian Oil Company. The discovery well (172-Oral) Integration of seismic impedance 3W-1, drilled in 1967 identified three oil-bearing reservoirs inversion into the geomodel (Upper Arab, Khatiyah and Shu’aiba). Two appraisal wells were drilled in 1968 and 1972. Following acquisition of a 3- Lalande, Severine (Total - [email protected]), D high-resolution seismic survey in 2000 and the drilling of Youssef Al-Mehairi (ADCO), Shakir Al-Kowaildi (ADCO), the first development well (BL-1P) in 2001, a comprehensive Dominique Chenot (Total), Jean-Luc Piazza (Total), study of the reservoirs and the overburden was conducted Philippe Prat (Total), Jo An Hegre (Total) and by an integrated subsurface team for risk assessment and Leon Barens (Total) development optimization purposes. A 3-D geomodel was built encompassing state-of-the-art micro-structural core This study describes the final part of a joint integrated analysis, structural seismic interpretation, stratigraphy, seismic reservoir characterization project on a major sedimentology, seismic impedance inversion, petrophysics, carbonate reservoir of an onshore Middle East field. The fluid synthesis, tests interpretation and reservoir static reservoir geomodel building captured well information, and dynamic modeling. Major uncertainties identified the 3-D structural and seismic information obtained prior to the development included OWC positions, through seismic interpretation and impedance inversion. compartmentalization, fracture network behavior, aquifer The aim of this seismic characterisation project was to strength and flank dip. Based upon the subsurface study improve the reservoir management by optimizing well the major identified risks were losses while drilling, shale placement, geosteering and geomodeling. These goals instability, pressure maintenance and water breakthrough. imply: (1) deriving the lateral and vertical heterogeneities in The development strategy was optimized on a few key the reservoir; and (2) characterizing the reservoir porosity aspects (reservoir target locations, data acquisition, well variations, including the location and volume of some drilling and completion design, reservoir monitoring

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design, pump installation timing, etc). Recommendations spatially which was applied to the data. However this is have been proposed to further reduce uncertainties during very interpretive and difficult to apply to 3-D. So rather the field production life. Within the frame of the buy-back than acquiring expensive uphole data, conventional seismic contract, the development of the Upper Arab reservoir records were analyzed for near-surface velocity layer occurred between 2001 and 2003 with the successful drilling information. From these analyzes a multi-layer velocity/ of a total of 10 production and water injection wells. During depth model can be created. Adding the layer travel-times the development drilling static and dynamic appraisal from surface to datum gives the static correction. For 3-D was conducted on the economically un-proven Khatiyah acquisition 2-D shot gathers have been extracted and the and Shu’aiba reservoirs. Well results confirmed the major thickness, and the velocity has been contoured. Using findings of the subsurface study: extension of the fracture grid manipulations, the 3-D model was determined. The network toward the flanks of the structure, and well layer models have improved the focusing of the horizons deliverability. in many difficult areas. However, there are always more problems to solve. Large amplitude and short wavelength local anomalies can still be present. Other methods were (332-Poster) Salt movement, tectonic events tried to get a be�er handle on the near-surface statics, and structural style, in the central Zagros including a geostatical approach using vibrator base plate fold and thrust belt, Iran data, refraction statics and tomography.

Letouzey, Jean (IFP - [email protected]) and Shahram Sherkati (NIOC) (224-Oral) Frequency-dependent anisotropy and implications to fracture characterization Structural analysis of surface and subsurface data in the Dezful Embayment, the northern Fars, and the High Zagros Li, Xiang-Yang (BGS - [email protected]), Enru Liu (BGS) and provinces shows that the presence of the infra-Cambrian Mark Chapman (BGS) Hormuz and the Miocene Gasharan salt layers has a direct control on the structural style. Both are levels of major Fractures are critical for ensuring economic oil and disharmony and decollement during the Neogene Zagros gas production in tight formations of otherwise low folding. There is some evidence of Hormuz salt movements permeability reservoirs (e.g. carbonates). A�empts have triggered by tectonic events: Permo-Triassic Tethyan ri�ing been made to infer fracture properties from seismic data along High Zagros NW-trends, and Cretaceous-Paleogene through the use of fracture-induced seismic anisotropy, obduction and compressive events with basement which has achieved considerable successes in the reactivation of NS Arabian trends. The emergence of estimation of fracture orientation and intensity. However, Hormuz evaporitic plugs in this zone, is closely associated this approach is limited to fractures at the micro-scale, and with major fault zones related to the Zagros folding event. reveals li�le information about the facture system at the Sandbox models analyzed with X-ray tomography suggest meso- (formation-) scale. Moreover, there is no control of that thrust and wrench fault occurrences were influenced by the fracture size and its distribution. Recently, it has been preexisting salt domes (weak zones). Driving mechanisms observed in several cases that anisotropy may change of Hormuz salt rising and extrusion was the squeezing of with seismic frequency. As usual, this phenomenon of preexisting salt domes. Local pull-apart and wrench fault frequency-dependent anisotropy is o�en treated as noise deflection probably also allowing for rapid salt-piercing. and has not been utilized properly for fracture analysis. Our recent modeling development reveals that the frequency-dependent anisotropic behavior depends on (45-Oral) Evolution of near-surface models a characteristic fracture size. Thus it is possible to fit this for correction of statics in Saudi Arabia parameter to the observed frequency-dependent changes and to measure the fracture sizes with seismic data for the Ley II, Robert E. (Saudi Aramco - [email protected]), first time. This model has been calibrated against laboratory Mohammad A. Al-Homaili (Saudi Aramco), Mike A. measurements and verified by numerical modeling, which Zinger (Saudi Aramco), Ralph Bridle (Saudi Aramco), provides a basis for the application to field data. We invert Robert W. Rowe (Saudi Aramco) and the field data for fracture size and fracture density from a Ameera Al-Mustafa (Saudi Aramco) multicomponent VSP, and find that the resulting fracture size matches geological evidence. This reveals the potential Prospective structures in Saudi Arabia are ge�ing both to create fracture length ‘maps’ using multi-component deeper and of smaller relief. Thus the methods for seismic data in addition to the standard fracture density determining near-surface correction statics have to evolve and orientation maps, effectively filling gaps in imaging to meet the challenge. Several approaches have been used sub-seismic fractures. or developed to resolve near-surface issues: (1) single- and multi-layer modeling; (2) refraction statics; (3) tomography; and (4) geostatistics. One of the first methods used in Saudi (225-Poster) Static correction in desert and Arabia was the single-layer velocity model. All of the loose terrain 42,000 upholes were interpreted and the average velocity to datum at the uphole location calculated. These uphole Li, Xiang-Yang (BGS - [email protected]), Xiucheng Wei (BGS) average velocities were then contoured to create the single- layer model. This model has worked well for most of the Static correction is a major challenge for seismic exploration prospective area. For complex near-surface conditions in mountains and desert terrain with loose soil, such as and topography this simple model requires some extra in the Middle East. Desert terrains with loose soil are corrections, for 2-D lines in the form of a time shi� varying characterized by significant lateral variations and lack of

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clear vertical layering. The first breaks in seismic records (381-Oral) Impact of high-fidelity Radon from such terrains usually show characteristic features transform on multiple and noise removal of bending events at near offsets and linear events at far offsets. Furthermore, the geo-pressure at the near- Liu, Qinglin (WesternGeco – [email protected]) and surface o�en varies continuously with depth, resulting in Panos G. Kelamis (Saudi Aramco) continuous depth-dependent velocity variation. Assuming an equivalent medium with quadratic velocity variation in The Radon transform is one of the most commonly depth (called the quadratic velocity model), we present a used algorithms in seismic data processing with specific travel-time inversion method to perform static correction in applications in multiple and linear noise elimination. It desert and loose terrains. The method includes fi�ing first transforms seismic data from the time-offset domain into break times using the quadratic velocity model, separating a model space in which signal and noise can be separated the first arrivals into turning-wave arrivals at the near by a simple muting process. Thus, the wanted signal can offsets and refracted-wave arrivals at the far offsets, and be reconstructed by the inverse transform. Alternatively, inverting for the near-surface quadratic velocity model. the noise can be modeled followed by a subtraction step This method is simple to implement and fast to compute in order to recover the signal. The conventional Radon compared with the existing method based on tomographic implementation is characterized by two main drawbacks: approach. Applications to real data from northwest China (1) lack of resolution due to the finite aperture of the show significant improvements in subsurface imaging, and recorded data; and (2) failure to properly handle aliased confirm that the method is particularly useful for static data due to poor sampling in the offset axis. High-fidelity corrections in desert terrains with loose soil. Radon transforms address both these issues and deliver improved resolution and increased performance on aliased input data via the integration of prior information in the (276-Oral) Improved reservoir algorithm. The derivation of the prior information is an characterization of a giant reservoir: Asmari important step in the performance of the high-fidelity Formation in the Ahwaz field, southwest Iran Radon transforms. In this study, the prior information is based on a Cauchy function in the model parameters to Linjordet, Arne (Statoil - [email protected]), Neil Pickard enforce sparseness. In principle, the Gaussian, least-squares (CCL), Mohit Khanna (Statoil), Daniel Berge Sollien based distribution, is replaced by a distribution that induces (Statoil), Tor Røsaasen (Statoil), Khosrov Haidari sparseness in the model space. The significant improvement (NISOC), Ahmad Miryan (NISOC), Bijan Beiranvand of resolution offered by this implementation makes it (RIPI), Ali R. Shakeri (RIPI) and possible to separate signal and noise with small differences Zahra K. Mosadegh (RIPI) in addition to overcome issues related to aliased data. Both high-fidelity parabolic Radon transform for multiple An IOR study has been performed on the Asmari Formation suppression and high-fidelity linear Radon transform for of the giant Ahwaz field in southwest Iran. This study strong linear noise removal have been developed. Their presents integrated reservoir description of the Asmari performance is demonstrated with a series of synthetic and Formation as input to the construction of a 3-D geomodel field data examples. In particular, the new algorithms can used as a basis for the IOR drainage strategy. Structural handle irregular sampled and aliased data and offer true definition was established by seismic interpretation on amplitude preservation. 26 2-D seismic sections. Improved volume control on the flanks was obtained. The Ahwaz Asmari Formation consists of interbedded carbonate, sandstone and shale (401-Oral) Multi-azimuth far-offset VSP: data of Late Oligocene to Early/Mid Miocene age. The Asmari processing and application Formation is penetrated by 338 wells, out of which 16 wells have recovered cores. The mixed siliciclastic/ Liu, Qinglin (WesternGeco - [email protected]) and carbonate depositional environment plus post-depositional John C. Owusu (Saudi Aramco) diagnesis, make macroscopic lithologic core description difficult. Evaluation of more than 6,000 thin-sections in A multi-azimuth large offset vertical seismic profile (VSP) three key wells support the geological and petrophysical survey was carried out near the town of Haradh, Saudi interpretation. The petrophysical interpretation included Arabia. The purpose of the survey was to provide a be�er mineralogy, porosity, permeability and water saturation. image of the target Khuff-C reservoir away from the well A water-saturation versus depth relation (J-function) was location. A time structure map from 3-D seismic indicates combined with fluid contacts to identify the flooding a very complex reservoir which is poorly imaged. The pa�ern. Strontium isotope age dating combined with reflection from the reservoir is very weak and there isa biostratigraphy, show that the Ahwaz Asmari Formation significant mistie between the 3-D seismic and synthetic was deposited from 30 to 18 Ma. Sequence stratigraphic seismogram generated from well logs. The VSP data was correlations combined with Strontium age dating in acquired along four azimuths radiating from the well and neighbouring fields, have improved the characterization intercepting three other proposed drill islands. Along each of how the Ahwaz Asmari sand/carbonate/shale arcitecture azimuth, two offset VSPs at 6,000 � and 11,000 �were develops internally and towards the surrounding oil fields. acquired. In addition to the offset VSPs, a zero-offset VSP The Lower Asmari sands were deposited in a restricted area was acquired to tie all the offset data at the well location. during sea level lowstands, while the Middle and Upper Information derived from the VSP data would be used to Asmari were deposited over a widespread carbonate ramp determine the location of future developmental wells in and contain transgressive and highstand sands. The results the area. The processing of the data posed a number of were used to construct the Ahwaz Asmari geo-model. technical challenges. Because of the very large source offset,

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the data quality–particularly in the shallow part–was poor, (Ghawar field) and the Western Province (Red Sea) of and therefore a high resolution three component processing Saudi Arabia using lab measurements on core plugs, flow was adopted. The processing flow included horizontal seismic stacking velocity analysis, mud weight profiles rotation, parametric wavefield decomposition, predictive and formation pressure tests. The lab tests were used to deconvolution, VSPCDP mapping and Kirchoff migration. define a velocity-pore pressure relationship which was The results of the P-wave and PS-wave VSP migrated images then used to predict the impact of overpressure on stacking show a be�er spatial resolution and improved structural velocities in well-indurated rocks. Stacking velocity image at the target reservoir due to the higher bandwidth of fluctuations were compared to compaction trends in the the VSP data. There is a very good tie between the synthetic Western Province, and velocity changes predicted from seismogram, the zero-offset and offset VSP. The combined well cemented rocks in the Eastern Province. Mud-weight P and PS images provide a be�er understanding of the profiles and formation-pressure tests were used to locate stratigraphy within the reservoir. vertical and lateral changes in overpressure. It was found that overpressure-induced changes in stacking velocity, which approximates Vrms, should be on the order of 100 (200-Oral) Jurassic stratigraphic boundaries m/s in the Eastern Province. Stacking velocity a�ributes of the southern Mesopotamian Basin, were mapped, to determine if they correlate to presence Kuwait of geopressure as indicated by mud weight logs. Li�le correlation to geopressure-induced drilling hazards was Lomando, Anthony J. (ChevronTexaco - found. Data from the Western Province revealed a more [email protected]), Sunil K. Singh (KOC), Aref Al- optimistic scenario. Because the sonic log behavior in the Doheim (KOC), AbdulAziz Ali Sajer (KOC) and Naema Western Province seems driven primarily by compaction, Hussain Al-Ajmi (KOC) as opposed to lithology, overpressure detection from stacking velocity seems feasible in this region. The stacking The Jurassic Period in the Kuwaiti sector of the Mesopotamian velocity profile at the overpressured location has a distinct Basin is a complex, highly cyclic suite of carbonates, evaporites decrease in slope at the onset of the overpressured zone. and shales. A recent KOC exploration review was tasked with The use of stacking velocities as drilling hazard indicators challenging previously published paradigms of stratigraphic in the Eastern Province should probably be directed at zonation, sequences and the occurrence of local and regional mapping the anomalous occurrence of high porosity and/or unconformities. Critical importance was placed on evaluating permeability in the Jilh formation. This could be the point of major sequence boundaries. The Early Jurassic is characterized future anisotropy-related studies. by several depositional cycles within the productive Marrat Formation. Biostratigraphy, cyclostratigraphy and seismic data were used to test the notion of a late Toarcian-Aalenian (408-Poster) Future petroleum systems of unconformity (base AP7) reported in many regions of Arabia. Iraq The Middle Jurassic Dhruma-Sargelu cycle was tested to see if the late Bathonian–Callovian hiatus extends from Lunn, Grenville (PGA – [email protected]), John Sco� the basins of central and northern Saudi Arabia, across the (PGA) and Augustus O. Wilson (Saler) Rimthan Arch into the southern Mesopotamian Basin. The Late Jurassic Najmah Formation, the regional organic-rich Many parts of the stratigraphic succession and many carbonate source rock, reflects more of a basinal anoxic areas of Iraq are only sparsely explored. This poster will restriction than a major deepening event, but culminates summarize the main potential future petroleum systems of in a series of carbonate debris flow units. These terminal Iraq with emphasis on seal-source-reservoir relationships in units may be the initial indicator of a Late Jurassic tectonic the under explored sections of the Mesozoic and Paleozoic. pulse in combination with a low-stand ice house spike in the Individual intervals to be presented will range from Jurassic green house world. This pulse, probably reactivated Cretaceous basinfloor/lowstand sequences through the along some Paleozoic structures, was the cause of continued Late Jurassic source-seal couplet, models for Triassic source basin restriction and segmentation, and controlled the systems to the Early Paleozoic oil and gas system. The poster deposition of the thick Gotnia-Hith evaporite system. The will present data and interpretations based on petrographic, boundary between the evaporitic Hith and transgressive paleontological and geochemical analyses undertaken on Makhul Formation shales was tested for evidence of a Late more than 40 key Iraqi wells over the last 20 years. Jurassic regional unconformity (top AP7). The approach of target testing pre-existing paradigms has clarified the nature (316-Poster) Reservoir characterization and of the Jurassic section in Kuwait in support of continuing exploration efforts. history matching of a fractured carbonate and highly permeable sandstone reservoir

(409-Oral) Stacking velocities as Lyslo, Kellfrid B. (Statoil - [email protected]), Tone geopressure indicators in Ghawar and Red Nedrelid (Statoil), Kjersti Håland (Statoil), Michael Sea areas, Saudi Arabia Hovdan (Statoil), Claus von Winterfeld (PDO), Mehran Azizzadeh (RIPI), Javad Honarmand (RIPI) and Lore�o, Thomas (Saudi Aramco - thomas.lore�o@aramco Ghorbanali Sobhi (RIPI) .com) The studied field is located at the foothills of the Zagros The feasibility of overpressure detection from seismic Mountains, near the Gulf. The reservoir consists of data is assessed and compared in the Eastern Province interbedded limestones, dolomites and clastic sediments.

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The aim of this study was to build a 3-D reservoir are consistent with previous studies performed in other model describing the matrix properties and the fracture areas of the world. This study describes the state-of-the-art distribution in the reservoir. Further, the aim was to technology and techniques used to gather representative generate a history-matched, dual-porosity reservoir reservoir samples. All job details, from the planning phase simulation model, from which predictions of improved to the execution phase are discussed, and the main results oil recovery could be made. A new reservoir zonation built from the formation testing and sampling job are presented. on a sequence stratigraphic framework was developed to improve the modeling of flow units in the field. A 3-D corner point grid was built in a reservoir model simulator (216-Oral) Origin and magnitude of over- (RMS) with near-orthogonal grid cell geometry. The grid pressured regimes in subsurface Kuwait and is laterally identical with the simulation grid, only the their implications in well planning vertical resolution differs. The 3-D grid was populated with stochastic realizations of a well and trend constrained Manowar, Ahmed A.M. (KOC - [email protected]) and facies model. The distributed facies objects (dolostone, Ahmed Al-Edan (KOC) limestone, sandstone, shale) were then populated with Pore pressure data acquired from deep wells in the their specific petrophysical properties, again conditioned to Valanginian Ratawi Shale Formation indicates the onset of well data and observed spatial data trends. Based on static overpressure in most of onshore Kuwait. The formation also geological and dynamic well data, in addition to outcrop represents the initiation of clastic influx a�er predominantly analog data, a conceptual fracture model was established, carbonate Early Cretaceous sedimentation. The Ratawi representing the general understanding of the distribution Formation is a sand/shale sequence with more or less and formation of fractures. Using this conceptual fracture consistent thickness between 350 and 425 �. Sand content model, a 3-D discrete fracture network (DFN) model was decreases from the southwest towards the northeast, where generated using ‘FRACA’. The DFN model was upscaled thin stringers of marine sands are embedded in thick to ‘Full-Field Equivalent’ fracture parameters for the shale beds and pore pressures increase rapidly. Pressure ‘ECLIPSE’ model. The reservoir simulation model was gradients show a depth-to-magnitude relationship, which tuned to match the initial highly-tilted oil-water contact varies from 0.51 psi/� to 0.62 psi/� at 9,300 and 12,100 �, created by a dynamic aquifer (preproduction) and tuned to respectively. The onset of over-pressuring is primarily match the overall energy distribution suggested by material related to static loading (overburden) and originates out of balance. Matching criteria for the production history were compaction of predominantly shale sections in the north, set for three main issues: (1) pressure development; (2) where expelled water entrapped in discontinuous sand produced gas/oil ratios; and (3) contact movements. These stringers of the Ratawi Formation are over-pressured. criteria made it easy to identify deviations and problem Pore pressure increases steadily in older Cretaceous areas, and the worst-offending ma�ers were continuously carbonate formations in the southern part of Kuwait, improved. The result was a high-quality history matched but shows an abrupt rise in the north, probably related dual porosity reservoir simulation model. to varying degrees of diagenesis of these sediments. A sharp rise of pore pressure approaching lithostatic occurs (379-Oral) Overcoming the challenges of within the regionally extensive Jurassic Gotnia evaporites, sampling heavy oil in unconsolidated sands where water-bearing limestone stringers are subjected to in the Gulf maximum confining pressures. Multiple pressure reversals occur below the Gotnia, and are of varying magnitudes Maizeret, Pierre-David (Schlumberger - in different areas of the country. In the Greater Burgan [email protected]) and Hendrik I. de Groot (Shell) area in south Kuwait, a normal pressure profile has been observed within the Najmah/Sargelu and the underlying Wireline formation testing is preferred by many operators Dhruma/Marrat sections. In Minagish field of west Kuwait, because the technique is more cost effective than most types these formations are encountered deeper, both absolute of well testing, and yet can gather much useful reservoir pressures and gradients appear to be higher within the information such as representative formation pressures, Najmah/Sargelu section. The Najmah/Sargelu pressures are permeabilities, and fluid samples. But, when applied related to generation and expulsion of hydrocarbon within to unconsolidated sands containing heavy oil, certain this source-reservoir unit bounded by the Gotnia and difficulties o�en occur, which can only be overcome by Dhruma formations that provide excellent top and bo�om careful planning and application of advanced approaches. seals. Careful collection and analyses of pore pressure data The Burgan reservoir in Nowrooz field in Iran, is an epitome over the country enabled us to optimize casing strings and of such a formation. The challenge was to withdraw some be�er formulate well test strategies. representative reservoir fluid while avoiding breaking the rock. The operation was made even more difficult by the fact that the sampling time had to be minimized to avoid ge�ing (421-Oral) Some aspects of the stack differentially stuck. The results were critical to optimize the response concept for acquisition geometries production strategy to revitalize this under-developed Marschall, Roland (RUB - [email protected]) field. In order to constantly control the drawdown applied to the formation, the ‘low-shock sampling’ technique was The fundamental properties of a given 3-D acquisition used. Moreover, the optical properties of the fluid flowing geometry (preferably symmetric) can be evaluated based on through the tool were constantly monitored during the its stack response, where the reference geometry is defined operation in order to check the mud filtrate contamination by the corresponding 3-D full-fold geometry (for which level of the sample. The results observed for this heavy oil

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we have a receiver-line as well as a shot-traverse on each (201-Oral) Optimization of a complementary gridline, within a certain maximum offset from the centre field development plan by assessing = source position). For 3-D full-fold geometries this stack subsurface uncertainties response is called the stack array. The stack response usually is established in the time domain. However, transform Maubeuge, Frederic (DEZPC - frederic.maubeuge@to domains may also be used as there are the frequency tal.com), Jean-Michel Guemene (Total), Gilles Vincent and the wavenumber domains, and additional weighting (Total), Thierry Charles (Total), Said Hunedi (DEZPC) and schemes may be applied in each domain as well. A method Frederic Paux (DEZPC) will be presented and discussed, which (by using the model of having the same signal–but with different delays–on For the first time on a mature field, an entire stochastic the input channels including different noises) allows for workflow has been used for optimizing a complementary optimum array forming by applying differential statics, development scheme. The first part of this study presents therefore avoiding the conventional straight stack approach the uncertainty management process developed for this for array forming. The method also takes into account field, with the quantification and the ranking of the main variations of the incoming signal’s amplitude spectra, and subsurface uncertainties. The important conclusion of therefore is applicable to both, i.e. source- and receiver- this stage was that the uncertainties on fluid contact and related effects. The proposed algorithm may be used not petrophysics were of second order in terms of impact on only for P-wave but also for S-wave data. Special filters the well productions, compared to uncertainties affecting may be implemented in addition to the above mentioned the gross rock volume. The structural map was therefore improved array-forming method: multi-component point a very important parameter for matching 10 years of grid data (i.e. vertical component and horizontal inline production history. Accordingly the most suitable maps component data) allow the use of the phase shi� of the were selected within the uncertainty ranges of the structural Rayleigh wave (on the vertical component as compared to interpretation. Results of forecast simulations had strong the horizontal component) to design such a special filter for operational consequences for the late stage complementary improved ground roll suppression. A particular version of field development: decision of infill producer drilling. Based such a special filter will be presented as well. on several defined history matching reservoir models, a well architecture was selected and a true risk assessment was (292-Oral) Static and dynamic modeling performed for the economics of the new infill well. Static and dynamic results of the infill producer, drilled a few months of oil in transition zones: improving oil a�er completion of the study, are presented. Although recovery predictions from carbonate fields more time is required to clearly quantify the impact of the with large transition zones well on the field performances, positive effects (additional oil recovery) are already foreseen and the operation was Masalmeh, Shehadeh K. (Shell - shehadeh.masalmeh@she revealed to be economic. The achievements of such a study ll.com) was only possible by the total integration of the subsurface engineering and the dedicated tools. Oil-water transition zones may contain a sizable part of a field’s STOIIP, specifically in low permeable carbonate reservoirs. The field development plan may be heavily (130-Oral) 4-D evolution of fold and thrust influenced by how much oil can be recovered from the belts: comparisons of analog models with transition zone. The amount of recoverable oil in a transition the Zagros Fold Belt, Iran zone depends–among other things–on the distribution of initial oil saturation (Soi) against depth and on the McClay, Ken (Royal Holloway, U London - residual oil saturation (Sor), capillary pressure and relative [email protected]), Tim Dooley (Royal Holloway, U permeability characteristics as a function of initial oil London), Paul Whitehouse (Royal Holloway, U London), saturation. Due to the general lack of relevant experimental Jose de Vera (Royal Holloway, U London) and special core analysis data, modeling both the static and Adam Pugh (Royal Holloway, U London) dynamic properties of fields with large transition zones remains an ongoing challenge. This study will discuss the This paper presents a series of scaled analog models limitations of the common practices in modeling transition designed to simulate thrust development in oblique zones and present laboratory measurements which show subduction se�ings such as the Zagros fold belt in Iran. that oil mobility in transition zones can be much higher The models were constructed to produce doubly-vergent than traditionally assumed. In addition, examples will be Coulomb wedge thrust belts with a pro-wedge and a retro- shown to address the following questions: (1) Do log and wedge separated by an upli�ed orogenic core. Models core data give the same saturation height function when were constructed from homogeneous layered sandpacks using drainage capillary pressure curve and saturation in a 2 x 2.5 m deformation rig. Progressive evolution of the exponent measured on water-wet samples? (2) How should orogenic wedges was monitored using digital photography the static reservoir model be initialized? (3) What is the and animated for analysis. The analog experiments have impact of imbibition capillary pressure curves on sweep investigated subduction obliquities from orthogonal (90°) to efficiency in heterogeneous reservoirs with large transition as low as 50° obliquity. Variations in sandpack thicknesses zone. One of the main conclusions of this discussion is that and basal detachment frictional characteristics and syn- the common practice of initializing static model may lead tectonic erosion and sedimentation were also investigated. to erroneous saturation height functions and oil in place Orthogonal subduction models produce long, linear, calculations due to the effect of we�ability and resultant critically tapered pro-wedge fold thrust belts parallel to the fluid redistribution in the pore space. subduction margin together with a narrow, upli�ed core

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and a steep retro-wedge thrust system. Oblique subduction field produces from five intervals of which the Lower models produced doubly-vergent, thrust wedges with thrust Cretaceous Ratawi (Minagish) Oolite reservoir is the faults parallel to the margin. There was li�le evidence of oldest. The reservoir produces from grainstones and discrete strike-slip faulting with oblique displacements being packstones deposited on a gently dipping carbonate accommodated along low-angle thrust systems. Variations in ramp. The Ratawi reservoir has produced more than 950 sandpack thicknesses, basal detachment frictions and syn- MMbbls since 1956. A 12 million cell reservoir model was tectonic erosion produced along-strike variations in thrust generated using a 143 x 200 areal grid with 417 fine layers and fold geometries. Analysis of animations of these models distributed among 34 stratigraphic intervals. Porosity shows how the thrust systems nucleate and propagate. In was distributed using sequential Gaussian simulation particular, it is clear that at any one time several thrusts are (SGS) constrained by stratigraphic interval. Porosity semi- moving simultaneously. Animated models together are used variogram range parameters average 2,700 m with trend to demonstrate the variations in structural styles in these varying significantly by stratigraphic layer. Permeability thrust belts. Map pa�erns in the models are compared with was added using layer specific transforms derived from the those in the Zagros fold and thrust belt in Iran using Landsat core data. The reservoir model was modified to include the TM data. cross cu�ing 6,400 � Barrier which exists in the Wafra Main Area. The origin of this flow barrier is uncertain, but may be a ‘fossil’ OWC. The 6,400 � Barrier was defined as a separate (402-Oral) GIS in the oil and gas exploration region in the reservoir model. The porosity in the barrier workflow was distributed using the SGS technique constrained by data and a semi-variogram for the barrier. Permeability McLay, Kevin (PDO - [email protected]), Roland was added using a barrier specific transform derived from Muggli (PDO) and Safia Mazrui PDO)( core data. Water saturation (Sw) was added to the final An oil and gas exploration portfolio contains a multitude model using a J-function that takes into account three ‘rock of data on potential hydrocarbon accumulations. Major types’ based on permeability (> 900 mD, 12-900 mD, and < challenges in managing such a portfolio are that of ensuring: 12 mD). The earth model has been used as input for fluid- (1) data is kept up-to-date; (2) a consistent evaluation with a flow simulation, for well location, and related reservoir clear audit trial is applied throughout; and (3) that data are management decisions, and for OOIP appraisal. available for the ongoing lead/prospect evaluation process. In PDO’s frontier exploration, GIS-based portfolio management (358-Oral) Sequence stratigraphy of an tools and processes have been introduced to address these eolian gas sand: layering in the Permian challenges. These tools support the exploration workflow Unayzah-A reservoir at south Ghawar, from initial play generation, through data acquisition (e.g. seismic) and onto identification of leads which can Eastern Saudi Arabia then be matured into drill-ready prospects. Key datasets Melvin, John (Saudi Aramco - [email protected]) are now either stored and maintained via GIS or made and Christian J. Heine (Saudi Aramco) available within it. This includes play, lead and prospect, well, geophysical and geological data. The ability to now In the gas reservoirs of the Unayzah-A Formation in eastern ‘evergreen’ this data, together with the strength of GIS in Saudi Arabia, lithostratigraphic correlations based on integrating data, has played a key role in the successful conventional wireline logs have historically failed to provide adoption of the technology. Enhanced reporting and analysis a geologically robust stratigraphy. Recent core and Image is now possible which in turn assist in the quality assurance Log-based studies have identified a complete depositional of the exploration portfolio and the generation of new sequence within the Unayzah-A. Thus, a base-Unayzah-A opportunities. Key to the successful implementation of GIS Sequence Boundary is marked by a ‘significant desiccation tools has been the close cooperation between the geomatics surface’ (SDS) that is overlain by a widespread, thin sheet discipline, the evaluation teams, and the portfolio managers. of eolian sand. It is superseded by an extensive deposit of This cooperation has ensured the tailoring and adoption of irregularly laminated and locally highly disrupted, silty, very the tools to meet the objectives of the workflow. Having joint fine-grained sandstones with rare thin siltstones. These reflect ownership has greatly facilitated the rapid development very shallow water deposition with periodic desiccation and subsequent deployment of these tools. The ultimate suggesting a shallow ephemeral lake environment. They aim for all parties is that the GIS environment will be used terminate in a thin but widespread upward-fining unit as an effective data and knowledge management system that represents the ‘maximum extent of the lake’ (MEL). throughout the exploration workflow. Above that horizon, facies relationships vary among wells, representing a number of terrestrial environments including (34-Oral) Stochastic reservoir model for the erg-centre, eolian cross-bedded sandstones; erg-margin, Ratawi Oolite Reservoir, Wafra field, PNZ dune and interdune deposits; deflation plain; and ephemeral lake. Cycles of deposition are recognized within each of these Meddaugh, W. Sco� (ChevronTexaco - sco�meddaugh@ major facies associations. Most significantly, these can be chevrontexaco.com), Dennis W. Dull (ChevronTexaco), shown to be regionally correlatable within and between the Stewart D. Griest (ChevronTexaco), B. Blake Sherman various facies tracts. When the intra-Unayzah-A stratigraphy (ChevronTexaco), Daniel Justin (KOC), Sukhdarshan is datumed on the MEL, these correlatable cycles are seen Kumar (KOC) and John Weston (KOC-JO) to be essentially flat-lying ‘parasequences’ whose origin is a�ributed to a fluctuating water table within the regional The Wafra field is located in the Partitioned Neutral Unayzah se�ing. The stratigraphy is therefore clearly Zone (PNZ) between Saudi Arabia and Kuwait. The pseudo-chronostratigraphic in character, i.e. it is justifiably

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founded on sequence stratigraphic principles. This permits a geometry consisted of 20 receiver lines, 3,840 channels, and clearer understanding of the distribution of reservoir bodies 60 m intervals. Twelve uncorrelated records were acquired within the Unayzah-A, and predicts the occurrence of intra- in three different field surface conditions (sand and gravel reservoir variability and potential compartmentalization. plains). The sweep parameters were linear upsweep, 8 to Reservoir characterization of these deposits is thus 80 Hz, and 12 seconds. The listening time was extended optimized. Outcrop analogs occur in the Permian Cedar to 12 seconds thus enabling the generation of 36-second Mesa and Jurassic Entrada Sandstones of Utah. correlated records extending from -12 to +24 seconds. Time- frequency plots were generated from near-offset traces that showed consistent and relatively high level of harmonic (383-Oral) Post-glacial rebound noise. Distortion was significantly stronger in the gravel unconformity within the Baq’a Member of plains, while sub-harmonics were greater in the sand areas. the Sarah Formation (Ashgill): sequence We had designed a tool for fast harmonic noise evaluation stratigraphic implications at the Ordovician- using solely the sweep equation. These theoretical analyses, Silurian boundary in Saudi Arabia in combination with the time-frequency plots, led to a precise prediction of harmonic noise leakage. Analyses of Melvin, John (Saudi Aramco - [email protected]), the full 36-second correlated records showed contamination Merrell A. Miller (Saudi Aramco), Owen E. Sutcliffe of the following record with airwave and sub-harmonic (ResLab) and Thomas W. Ferebee (Saudi Aramco) noise. This noise was of the same magnitude as harmonic noise contamination of previous record. With current The recently redefined Hawban and overlying Baq’a members sweep parameters, a slip time of 12 seconds presents no of the Sarah Formation were reexamined at outcrop and in real risk of harmonic noise contamination. In addition the shallow subsurface at several locations in Saudi Arabia. to these tests, energy tests were also conducted. Various The Hawban Member comprises a chaotic, syn-sedimentary combinations of sweep lengths and number of vibrators deformed, interval of green-gray, very poorly-sorted sandy were tested. They showed that in this area and under these diamictites supporting large boulder-sized contorted clasts conditions, ambient noise is not the major problem and that of sandstone derived from the underlying Sarah Formation. data quality improvement should come from an increase in Palynologically, it is characterized by a stratigraphically source density rather than source strength. A slip-sweep admixed assemblage comprising taxa reworked from older operation with four fleets of three vibrators and double Ordovician sediments, as well as indigenous Ashgill marine source density is a possible way to upgrade the current flip- species. Thus Hawban deposition occurred in a glacimarine flop operation with two fleets of five vibrators. se�ing at the end of the Gondwanan glaciation. The overlying Baq’a Member consists of two units. The lower of these is a pale gray silty shale that passes upwards into fine- (54-Poster) Applications of GIS in regional grained hummocky-stratified and wave-rippled sandstones. geological interpretation: examples from the Palynologically, this gray shale is characterized by marine Arabian Plate taxa dominated by leiospheres, with only rare reworked assemblages. It has variable thickness and infills topographic Middleton, David (Shell - [email protected]), lows in a post-glacial, shallow marine environment upon Sundaresan T. Ramamurthi (Shell) Andy Bell (Shell) and the post-Hawban surface. This shale unit is overlain by a Arjen de Kam (Fugro) Baq’a sandstone unit that comprises stacked, cross-bedded sandstones with numerous sharp, erosional basal bed As the significance of the Arabian Plate as the world’s premier contacts, of probable braided-fluvial or estuarine origin. The hydrocarbon province continues to grow, an understanding uppermost beds of this facies become more argillaceous and of the geological evolution of the region is vital to the are intensely bioturbated, suggesting the onset of marine development of new play concepts and exploration conditions. The basal contact of this Baq’a sandstone is opportunities. Any such regional-scale geological demonstrably unconformable across both the Baq’a shale and evaluation requires the compilation, visualisation, analysis the Hawban Member. The Baq’a sandstone is considered to and interpretation of large volumes of disparate geological have developed in response to post-glacial isostatic rebound data. Geographic Information Systems (GIS) represents (upli�) of underlying units. Stratigraphically, there is clearly a unique and invaluable tool to the geoscientist in this a hiatus between it and the older units. It is proposed that respect. Although traditionally used in surface evaluation, the Baq’a sandstone represents the basal unit of a major new the application of GIS to the subsurface environment has stratigraphic sequence that may ultimately be developed in become widely used in recent years. The power of GIS the Qusaiba Member. lies in the ready visualisation and detailed numerical and spatial analysis of georeferenced geological information, including depth, well, outcrop, seismic and structural (251-Oral) Slip-sweep simulation and energy data. The applications of GIS include the generation and test experiment interpretation of regional structure, depth, and play maps. The ability to query elements in their spatial context and on Meunier, Julien J. (CGG - [email protected]) and a�ribute information is a fundamental and most important Turki M. Al-Ghamdi (Saudi Aramco) application of the tool for geologists. 3-D functionality allows enhanced visualisation and analysis, such as the Records of correlated and uncorrelated shot gathers were ability to ‘drape’ facies maps over structural contours of key acquired by a Saudi Aramco seismic crew in southwest reservoir intervals to delineate play fairways. Advanced Yabrin, Saudi Arabia. The experiment was designed applications include the generation of depth contour maps and analyzed in cooperation with CGG. The recording in the absence of seismic data, using georeferenced surface

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geology maps, fault data and Digital Elevation Models. linked to improved understanding of the Barik Sandstone This study demonstrates the power and suitability of GIS (reservoir types, distribution, connectivity and quality) and functionality in regional geological interpretation, with fluid distribution over the area of the accumulation. The examples from across the Arabian Plate. Barik Sandstone incorporates a variety of continental braid plain to marginal marine/offshore reservoir types. The main reservoir developments in Khazzan are contemporaneous (375-Oral) Distinctive cone-in-cone horizons, with those in the producing Saih Rawl field to the south. macrofossil beds and palynomorph diversity Paleocurrents suggest that in addition to a well-established, events: their significance to the Silurian fluvial-dominated source component prograding from the sequence stratigraphy of Saudi Arabia southeast, one or more westerly sources may have been important. The preferred depositional model suggests Miller, Merrell A. (Saudi Aramco - merrell.miller@aramco. that repeated regressive episodes were driven by relative com) and John Melvin (Saudi Aramco) sea-level fall (forced regressions). An intra-Barik layering scheme has been developed which provides a potential A number of thin (< 10 cm) carbonate horizons displaying correlation resolution of less than about 1 my giving distinctive cone-in-cone mineralization are identified in dark some control on likely intra-Barik reservoir distribution, gray, organic-rich mudstones of the Lower Silurian Qusaiba connectivity and distribution through time. Intra-Barik Member of the Qalibah Formation in eastcentral and paleogeographic models and provenance studies hint at a northwestern Saudi Arabia. They are thought to have formed distinct but subtle source/depositional control on reservoir as a result of early diagenesis close to the sediment-water quality. The more productive Barik reservoir in the Khazzan interface, and are remarkable because: (1) they are extremely Gas Accumulation is a�ributed to a significant component widespread considering their thin stratigraphic thickness; (2) of secondary porosity associated with feldspar leaching. they are commonly associated with fossiliferous horizons Meaningful evaluation of the Khazzan Barik reservoir rich in intact orthocone nautiloids and bivalves; (3) they occur intervals that are likely to contribute to production in close association with regionally-correlative palynomorph has been developed using an in-situ stress-corrected events. The most widely correlatable of these is associated poroperm transform defined from special core analysis. with cone-in-cone mineralization without macrofossils. This The Khazzan Barik reservoir is a ‘tight gas’ reservoir with mineralized bed formed in an environment of minimum typical permeabilities in the < 5 mD range. Crest to flank clastic input and/or the deepest water se�ing, suggesting that compositional variations between the Khazzan and Saih that particular event indicated by a palynomorph diversity Rawl fields hint at complex intra-Barik hydrocarbon charge ‘spike’ represents a maximum flooding surface (MFS) in this and flushing between the two areas. part of the Arabian Silurian. This inference is substantiated by its concurrence with the Monograptus convolutus graptolite zone, which is globally recognized as a time of sea-level (50-Poster) Characteristics of seismic wave highstand. Above this MFS, downlap is indicated by another fields in the offshore area between Saudi correlatable horizon of high palynomorph diversity. This Arabia and Kuwait is also considered to represent a marine flooding event, separating discrete prograding clinothems of a highstand Minegishi, Masato (Al-Kha�i JO - [email protected]), systems tract. The available evidence suggests that associated Katsuya Watanabe (Al-Kha�i JO) and cone-in-cone diagenesis is most fully developed in the most Falah Al-Anazi (Al-Kha�i JO) distal (i.e. sediment-starved) muds of the basin. Traverses in a proximal direction identify an increased association of The seismic vintages obtained by KJO have not been cone-in-cone with macrofossils that ultimately dominate, sufficiently qualified for detailed geophysical and prior to disappearing as the most proximal recorded of the geological study of the existing reservoirs. The difficulties diversity events become associated only with silt turbidites mainly come from the complex nature of acquired seismic indicative of high clastic input of these clinoforms. wavefields, so that the conventional seismic method has failed to extract reflection signals appropriately. For achieving quality improvement, it is necessary to fully (203-Oral) Towards improved geological understand the characteristics of seismic wave propagation understanding of an Early Paleozoic (Barik systematically and to define the problems clearly. Such a Sandstone Member) stratigraphic trap - the task requires a seismic wave simulation study based on Khazzan gas accumulation, Sultanate of an expected velocity model. In this study, the velocity Oman model was estimated from several checkshot and VSP data, seismic velocity, and well marker information. Then, the Millson, John A. (PDO - [email protected]), Jamie model was used for the Finite Difference and Ray-tracing G. Quin (Repsol), Erdem F. Idiz (Shell), Peter Turner simulation. Finally, the calculated synthetic seismograms (Birmingham U) and Ahmed K. Al-Harthy (PDO) were analyzed in various ways. The result shows that strong heterogeneity of seismic interval velocity in a vertical The Khazzan gas accumulation is a combination structural/ direction causes strong multiple reflections. In addition, stratigraphic trap with gas reservoired in lower Paleozoic the relatively weak primary reflections around reservoir siliciclastics of the Cambrian Barik Sandstone Member. zones are hidden by those multiples. From snapshot views Evaluation of significant in-place gas volume have been of seismic wave propagation simulation, it can be seen that tempered by issues of reservoir quality and productivity, two high velocity layers, as well as sea surface, are the main with major remaining uncertainties in gas distribution and cause of the multiple reflections. The amount of Normal ultimate recovery. Uncertainties to be addressed are closely Moveout (NMO) is almost the same for both multiple and

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primary reflections, and any multiple elimination methods SE fault corridors in the Sohag-Asyut-Minia area forming that relied on NMO difference, have not worked well. The a large, Late Oligocene–Early Miocene delta near Faiyum. study results can be useful in the planning a new seismic Transfer of the throw at the northern tip of the Gulf of Suez data acquisition and processing. For example, a multiple into the Cairo-Suez area created a number of fault blocks elimination method based on this study can do a be�er that formed local drainage basins in the northern Eastern job if the velocity function of primary reflections can be Desert. These also flowed into the Nile Delta area. A major estimated. The elimination result shows the effectiveness of drop in the Mediterranean Sea level, during the Tortonian- the proposed method in the absence of other noise. Messinian, lowered the base level of erosion of the onshore areas. This led to an eastward shi� in the Nile and exposure of the old Syrian-arc folds, a�er erosion of the intervening (280-Oral) Vertical hydrophone arrays for Eocene and younger rocks. Deposition of a large coarse transition zone seismic exploration clastic section of the Tortonian Qawasim Formation over thick shale of the Cretaceous-Lower Tertiary continental Moldoveanu, Nick (Schlumberger - moldoveanu1@housto slope loaded that slope area and led to its northward tilting. n.westerngeco.slb.com) and Mike Spradley (WesternGeco) Associated growth faulting, parallel to the shelf edge, The near-surface geology for a typical transition zone formed the Nile Delta hinge zone. The arcuate outline of the environment consists of a water layer covering a mud layer. hinge zone and its related growth faults formed a very large, The water layer depth ranges from very shallow to over southward plunging antiform on the downthrown side. 10 m, and the mud layer thickness could also be variable, Collapse of this antiform by normal faults formed a central from very thin layers to tens of meters. The traditional way (keystone) NS-oriented graben in which the Messinian Abu to acquire seismic data in transition zone environment is Madi channel flowed towards the north and northwest. to deploy receivers, typically marsh phones, on the water Excellent reservoir sands of the Abu Madi Formation were bo�om or to push them in the mud layer. The presence of deposited in this channel, which later formed several gas the water layer and the unconsolidated sediments at the fields of the Baltim Trend. Top Serravallian erosion of the surface could affect the quality of the seismic data due to hinge zone area and northern Egypt supplied Tortonian receiver ghosts, strong seismic reverberations and mud roll and Messinian sediments into the low areas to the north. that very o�en contaminate the seismic records and generate a poor signal-to-noise ratio. The objective of this study is (277-Oral) Fluid transfer mechanism using to present a new method of acquiring and processing the geochemistry in shallow oil zones of seismic data in transition zone environment that is based Bahrain’s Awali field on the use of the vertical receiver arrays. A vertical receiver array is implemented with two hydrophones separated by Murty, Challa R.K. (Bapco - [email protected]), a certain distance and deployed in the water layer or buried Hisham K. Zubari (Bapco), Mark A. Beeunas (OilTracers), in the mud layer. The vertical hydrophone array gives the Mark A. McCaffrey (OilTracers) and possibility to separate the upgoing seismic wavefield, which Keith F. Thompson (Petrosurveys) typically contains the primary events, from the downgoing seismic wavefield, which contains the ghosts and receiver Geochemical analyses integrated with geological side surface related multiples. Examples of application of and engineering data has substantially improved the vertical hydrophone arrays acquisition will be shown from understanding of the mechanisms of hydrocarbon seismic surveys conducted in transition zone Louisiana and emplacement and fluid movement in shallow oil reservoirs Argentina. The technique could also be used in the Middle of Bahrain’s Awali field. The field is an asymmetrical East where multiples affect seismic data. The conclusion anticline, which is intensely faulted and fractured in the of the study is that the vertical hydrophone array method shallow and Bahrain zones. The shallow zones include three could be used successfully to improve the seismic data marine limestone reservoirs (Rubble, Ostracod, and Magwa) quality in a transition zone environment. which belong to Upper Cretaceous Asia group. In general, the Rubble zone is composed of massive carbonates while (118-Oral) Early history of the Nile Delta the Ostracod and Magwa have muddier limestone. These reservoirs contain heavy and light oil distributed areally region and vertically. Divergent rock types and fluid properties, Moustafa, Adel R. (Ain Shams U - and stratigraphic and structural features could impact fluid [email protected]) and Farid Abou-Shadi (Shell) transfer between reservoirs. It is strongly suspected that syn- depositional faulting might have affected these reservoirs in Detailed study of borehole, seismic, and outcrop data of addition to a major unconformity which formed during the northern Egypt (including the Mediterranean offshore Late Cretaceous. This erosional event completely removed area) has led to a good understanding of the early history of the Rubble and part of the upper Ostracod in the central the Nile Delta region since the Oligo-Miocene. Upli� of the part of the field. Further, fault compartmentalization and the eastern and western shoulders of the Gulf of Suez – Red Sea extent of fluid transfer from the three zones due to faulting ri� basin controlled the Oligo-Miocene drainage around the affect the fluid properties. It is required to know the current ri� shoulders. Upli� of the shoulder area in southern Sinai oil distribution of light and heavy oil and if these phases formed a large drainage basin in the central and northern occurred during migration or later, a�er reactivation of Sinai that flowed into Wadi El Arish contributing a large faults and reservoir compartmentalization, the knowledge sedimentary budget with good reservoir potential into the of which is essential for developing these reservoirs. There is offshore Sinai region, east of the present-day Nile cone. also a question whether gravity segregation or de-asphalting Similar drainage of the Red Sea Hills area flowed into NW- or bio-degradation was responsible for separation into heavy

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and light oils across the three zones. To investigate the lateral directly correlated to the well stratigraphy. However, at and vertical reservoir continuity, a geochemical study was present in seismic industry, the choice of surface seismic initiated involving advanced gas chromatography techniques processing parameters relies on human judgment, skills on oil samples from 11 wells. The methods include: (1) and experience of the processing analyst only. Examination review of abundance of ‘interparaffin’ peaks identifiable; of this conventional processing technique shows that it and (2) ‘Star Diagrams’ for finger-printing the oils with the fails in many cases to provide a good tie with borehole ratios of peaks compared with the nearby wells. The C8 to data, which in turn, does not allow reliable stratigraphic C20 range is typically the most diagnostic range for reservoir interpretation of the seismic data. This study demonstrates continuity assessments using these diagrams. The other an alternative processing method for integrating borehole technique used was the ‘Slope analysis’, wherein the molar data with processing parameter selection from the earliest concentration profiles were used to know the accumulation stage. The present processing technique is subdivided into and alteration. The analyses have provided compositional two steps. The first step involves proper editing of the data that: (1) characterize the difference between oils in the well acoustic data (sonic and density). The log editing is shallow zones; (2) verify reservoir compartmentalization; based on a multi-log approach and is carried out by direct (3) support specific geological models which explain the interaction between borehole and seismic data. The second inter and intrareservoir fluid communication; (4) reveal step is based on quantitative and objective evaluation reservoir oil bio-degradation events; and (5) indicate at least of the processing parameter selection obtained from the four discrete episodes of hydrocarbon migration into the integration of borehole and seismic data by means of reservoirs based on the Slope Factor (SF) analysis and several statistical a�ributes calculation of the extracted wavelets. geochemical parameters. The a�ribute’s values define both the best correlation between the well trace and the corresponding seismic trace, and the complexity of the extracted wavelet. The present (413-Oral) Near surface velocity estimation processing methodology is illustrated with data from using ground-roll the prospective concession NC186 in the Murzuq Basin, Libya. The main challenge for seismic technology in this Muyzert, Everhard (Schlumberger - [email protected]) area is to afford the best image of subtle unconformities. Near-surface velocities are used in statics and applications The methodology offers three major advantages over the such as survey design and wavefield separation. In particular, conventional processing approach. First, seismic data show the near-surface shear velocity is difficult to determine. In a be�er resolution and actual definition of sediment onlaps this study we show how ground-roll can be used to estimate and evidence of the underlying unconformity surface. the near-surface P- and S-velocity. A two-step method is Second, it provides an improvement in the tie between the used. First, the local phase-velocity of the ground-roll is surface and the borehole seismic data so that events on the measured. This can be done in the FK-domain or with a local processed seismic data can be easily identified in terms of spectral estimate such as FK-music using spatially unaliased polarity and time. Third, it a�enuates the multiple energy ground-roll such as recorded by single sensor acquisition within the surface seismic data, so that the identification of geometries. Second, the phase-velocity curves are inverted subtle stratigraphic traps can be identified more accurately for a near-surface P- and S-velocity model as a function of from the newly processed seismic data. depth. Tests show that it is difficult to independently resolve the P-velocity and therefore it is tied to the S-velocity model. (91-Oral) Seismic challenges in early gas The model is sensitive to the velocities in the top 50-100 development m, and depends on the frequency range of the measured phase-velocities; the model depth can be extended with Nebrija, Edgardo L. (Saudi Aramco - edgardo.nebrija@ara increasing lower frequencies recordings. The method also mco.com) allows for determining the local direction of the shallow shear wave anisotropy. We have applied the method to a Saudi Arabia’s gas deposits occur in Permian carbonate 2-D 3C seismic line from North America. The near surface reservoirs and Permo-Carboniferous and Devonian clastic shear wave velocities vary up to 100 percent along a line that reservoirs at depths of 12,000 to 17,000 feet. The main crosses a dry sand area (Vs = 300 m/sec) and a wet area (Vs challenges for the geophysicist are to resolve these deep =150 m/sec). The obtained near-surface velocity model has an reservoirs and extract information about their porosity, gas excellent correlation with a nearby shallow VSP. content, and the fractures in them. The limited frequency bandwidth of surface seismic data o�en fails to resolve these deep reservoirs. Since many of the future producing (147-Oral) A well-driven processing wells will be drilled horizontally, it is critical to determine approach for seismic imaging of subtle reservoir continuity away from the pilot hole. The higher stratigraphic traps: case history from resolution possible with offset VSP surveys allows these Murzuq basin, Libya gas reservoirs to be resolved, so that a horizontal well may be steered in a direction that ensures maximum reservoir Nafie, Tarek Y. (WesternGeco - [email protected] contact. In both the carbonate and clastic gas reservoirs, lb.com), Didier Wloszczowski (Repsol), Mohamed Kawan well logs indicate a strong inverse correlation between (WesternGeco) and Ali Bengheit (Repsol) acoustic impedance (product of density and velocity) and reservoir porosity. The impedance is obtained from Accurate correlation between well synthetic, borehole, seismic data through inversion and it serves as ‘so� data’ and surface seismic data in key wells is a fundamental for the geostatistical estimation of the 3-D distribution of prerequisite for interpreters, so that reflections can be porosity. This integrated 3-D model of reservoir porosity

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forms the basis for the placement of gas development log analysis, and the regional tectonic stress direction in wells. In Saudi Arabia, acoustic impedance senses porosity, the field. A time delay of 18 milliseconds occurs between but not the fluid content of the reservoir. To detect gas, the fast and slow shear wave arrivals and shear-spli�ing (or elastic impedance must also be known because it gives fracturing) starts in the lower part of the Khuff section. a measure of the rock’s compressibility. Since gas is compressible and water is only slightly compressible, elastic impedance detects gas in the reservoir. From P-wave (363-Oral) Multi-attribute seismic analysis seismic data, information about elastic impedance comes for deep gas exploration in Saudi Arabia from off-normal incidence seismic energy. Many of these Neves, Fernando A. (Saudi Aramco - reservoirs, particularly the clastics, have low porosities [email protected]), Timothy H. Keho (Saudi Aramco) due to diagenesis. Core and borehole image logs indicate and Patrick M. Ru�y (Saudi Aramco) the presence of fractures in these reservoirs. The probable orientations and relative intensities of these fractures can Gas exploration in the Permian Unayzah Formation in be determined from wide-azimuth 3-D seismic data since central Saudi Arabia is a technically challenging mission. seismic velocity, amplitude, and AVO vary as a function of In order to reduce the exploration risk in an area of li�le direction in the presence of vertical fractures. This study well control, advanced geophysical techniques were shows, through field examples, that seismic data contribute applied to a 1,350-sq km 3-D high-quality seismic dataset. significantly to the early development of Saudi Arabia’s gas These included acoustic and elastic impedance inversion, reservoirs because they yield critical reservoir information seismic facies analysis using neural networks, spectral unavailable otherwise from the few wells drilled to date. decomposition, and coherence analysis. Since seismic data plays an instrumental role in guiding the exploration (92-Oral) Fracture characterization using effort in the area, great care was taken in preparing it for transmitted shear waves in a 3-C azimuthal analysis. The pre-stack time migrated data were processed to preserve relative true amplitudes, thereby making offset VSP the dataset suitable for seismic a�ribute investigation. Nebrija, Edgardo L. (Saudi Aramco - edgardo.nebrija@ara Multi-a�ribute seismic analysis revealed the existence mco.com), Bhoopal R. Naini (Saudi Aramco) and of several meander belts and incised channels, be�er Shabbir Ahmed (Schlumberger) delineated faults, and provided useful insight about the depositional style in this area. In order to take advantage In the presence of vertically aligned fractures, seismic data of the complementary information provided by the various exhibits anisotropic behavior. The observed propagation seismic a�ributes, we employed volume interpretation and velocity, reflection amplitude, and AVO response of simultaneous visualization of these a�ributes. This study compressional waves vary as a function of direction, being will show that the integration of all these methodologies largest parallel to these fractures. But, the most diagnostic and analysis techniques highlighted both structural and seismic confirmation of the presence of fractures consists of stratigraphic information that could not be readily derived the spli�ing of incident shear waves into two orthogonal from conventional seismic amplitude analysis. components that travel at different speeds – the fast shear wave polarized parallel to the fractures and the slow shear (116-Oral) Surface-piercing salt domes of wave polarized perpendicular to them. A three-component, azimuthal, offset VSP survey was acquired over the Unayzah Interior North Oman and their significance sandstone gas reservoir at Wudayhi field in central Saudi for intrasalt hydrocarbon prospectivity Arabia to determine the orientation of fractures that were Newall, Mark J. (PDO - [email protected]), Jeroen suspected to contribute to gas productivity. Two multi- Peters (PDO), Jacek Filbrandt (PDO), John Grotzinger offset VSPs at orthogonal azimuths, and four single-offset (MIT), Mark Shuster (PDO) and Hisham Al-Siyabi (PDO) VSPs at other azimuths, were acquired. Zoeppritz modeling using dipole sonic and density logs showed that significant The six surface-piercing salt domes of Interior North Oman compressional (P) to shear (S) conversion should occur at form prominent topographic and geological features in a the top of the overlying Khuff carbonate section due to its flat, rocky desert environment. These salt domes, situated large P-wave velocity contrast with the Sudair Shale above in the central part of the large Ghaba Salt Basin, have it. The survey results confirmed this expectation. Other been known since the 1950s. A geological survey of the interfaces higher in the section and similarly characterized salt domes in 2001 yielded significant new lithological, by large velocity contrasts, also generated shear waves. stratigraphical and sedimentological information on the Thus, when borehole receiver arrays placed below the rocks exposed in these outcrops. This new field data has Unayzah reservoir were analyzed for shear-wave spli�ing, been placed in the context of ongoing exploration efforts for several transmi�ed shear events could be analyzed. The deep hydrocarbon plays in Interior Oman. A wide variety resulting combination of multiple shot azimuths and of rocks is exposed in the salt domes: carbonates, clastics, offsets with multiple shear events passing through the volcanics, and evaporates. Constituent rocks and structural same fractured reservoir, yielded redundant measurements style vary considerably from dome to dome, but at surface, of the fast shear-wave directions, all of which consistently the main lithological elements of the diapirs are carbonates pointed in the EW direction. This orientation matches the and evaporites belonging to the Late Precambrian- results derived from surface P-wave anisotropy analyses Early Cambrian Ara Group, the highest element of the of the wide-azimuth 3-D seismic data, the orientation of Huqf Supergroup. Large exotic blocks of bedded Ara borehole breakouts and maximum horizontal stress from carbonates are well-exposed and form marked hills and

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ridges, allowing detailed field observations to be made on are assumed to be controlled by the interaction of climatic intrasalt carbonate ‘stringers’ which were carried upwards changes and regional and/or local tectonic processes. by rising diapiric salt. The close correlation of facies of the Problems and uncertainties inherent to lithostratigraphic carbonate exotics in the salt domes of North Oman with correlations, with or without biostratigraphic age control, Ara ‘stringer’ carbonates penetrated and extensively cored are largely overcome by using spectral a�ribute analysis in deep exploration wells in the South Oman Salt Basin of facies-sensitive wireline logs. Spectral a�ribute analysis demonstrates the regional significance of the salt dome is a mathematical tool which enables a time-efficient and outcrops for the intrasalt ‘stringer’ hydrocarbon play in acurate construction of a near-synchronous high-resolution Oman. This work has implications for the prospectivity of stratigraphic correlation framework. The science behind other infra-Cambrian evaporite basins in Oman, and also this method is cyclostratigraphy, and is being used to for time-equivalent (Hormuz) salt basins in the Middle interpret the results of the spectral a�ribute analysis. The East. cyclostratigraphic correlations extend across facies belts and enable the evaluation of regional and/or local tectonic activites during the Early Cretaceous and Jurassic. A (262-Poster) Synthesizing the density log unifying nomenclature is proposed for the study area, which using other wireline logs and artificial neural is known for its many, o�en confusing, lithostratigraphic networks technique nomenclatures. The correlations show the large-scale architecture of the carbonate platform sedimentation, Nikjoo, Mahmood (NIOC - [email protected]), with intrashelf basins, onlap pa�erns and hiatuses. Cyclic Mohammad Reza Rezaee (U Tehran), Bahram Movahhed depositional pa�erns in important reservoirs such as the (NIOC) and Nader Sabeti (NIOC) Sarvak and Arab are easily recognisable as well as the lateral lithofacies variations within these cycles. Important The density log is normally used for determination influxes of clastic sediments within the predominantly of porosity as one of the most basic characteristics of carbonate successions can be recognised and are correlated hydrocarbon reservoirs. This log is also used in seismic with time-related non-clastic intervals in the basin. This interpretation of reservoir rocks. Without it basic problems detailed and time-related cyclostratigraphic correlation may occur in reservoir characterization. Because of through the Iranian offshore area of the Gulf contributes to operational and technical limitations, the density log is a be�er understanding of the geological development of the not available in some zones especially in shallow depths area and supports advanced exploration. where well diameter is large. There are also some zones and layers where bulk density readings are not reliable, e.g. the washed out zones. In our study, synthetic bulk (366-Oral) Sedimentology of the density log was derived using the artificial neural networks hydrocarbon-bearing Miocene Asmari technique in combination with other logs including sonic, Formation, Zagros Mountains, Iran gamma ray, resistivity and neutron porosity log. The correlation coefficient between synthetic density log values Noad, Jon J. (Shell - [email protected]), Heiko and measured density log values is about 0.912 with a slope Hillgartner (Shell) and Ali Moallemi (RIPI) of about 0.816. Mean relative error between synthetic bulk density log values and measured bulk density values was The Oligo-Miocene Asmari Formation of the Zagros about 1.2 percent. These values for correlation coefficient, Mountains of southwest Iran is one of the world’s most slope and mean relative error prove that the artificial neural important reservoirs. Despite this, its sedimentology has networks technique can synthesize the density log from received relatively li�le a�ention, particularly in terms of other logs. outcrop studies. This is surprising, as it can be examined in exposures within ravines cu�ing through the huge and striking whaleback anticlines that make up the Zagros (226-Oral) Cyclostratigraphy of the Lower Fold Belt. Many of these exposures occur close to existing Cretaceous and Jurassic of the offshore fields, allowing the opportunity to see the reservoir at Gulf in Iran: new approach in advanced surface. Recent fieldwork has been undertaken measuring exploration sections through the Asmari Formation, in wadis cu�ing through anticlines situated close to the super giant Nio, Djin S. (ENRES - [email protected])), Mat G.G. De Gachsaran oil field. The Asmari limestone is typically Jong (ENRES) and Peter Wigley (Lynx) around 500 m in thickness, and is generally subdivided into three parts. The Lower Asmari is marly in character A cyclostratigraphic well-to-well correlation framework was near the base, overlain by foraminiferal and coralline algal established for the Iranian offshore from the northern Gulf limestones. The Middle Asmari comprises dolomitized, across the South Pars (Qatar) Arch through the southern lagoonal limestones, while the Upper Asmari is more Gulf to the Strait of Hormuz. Spectral a�ribute analysis of evaporitic. The detailed sedimentological data collected facies-sensitive wireline logs was used for the downhole during the fieldwork has been used to develop a sequence prediction of cyclostratigraphic bounding surfaces. The stratigraphic framework, subdividing the Asmari limestone spectral a�ribute curves were mostly generated from into four cycles, and then into 33 subordinate cycles. This gamma ray logs and show the hierarchical order of cycle framework has been applied regionally to explain the boundaries as well as flooding surfaces in each well. distribution of lithofacies within the Asmari Formation Trends in the spectral a�ribute curves show time-related across the Zagros. The deposition of the contemporaneous lithofacies variations. The cycles and lithofacies variations Ahwaz sandstone member is examined, and may allow the

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potential stratigraphic position of lowstand wedges to be the model based on seismic data interpretation. Different predicted. The development of the thick Kalhur evaporites simulation grids were realized to preserve the geological to the northwest has also been addressed. The implications heterogeneity and the RRTs a�er upscaling of the geological of these findings for undiscovered hydrocarbons are model, and the dynamic model was optimized to minimize explored. the run time. Mercury injection data was based on RRTs, while SCAL data was screened to honor the RRTs. The dynamic model was initialized using mercury injection (71-Poster) A new depositional model of the capillary pressure (MIPC), but gave erroneous initial water Lehwair-Kharaib formations in Abu Dhabi saturation distribution. The task was to develop a method based on thickness and lithofacies trends to generate log-derived capillary pressure based on RRTs. A multi-regression technique was developed using Rock Obara, Hidenori (JODCO - [email protected]) and Quality Index (RQI), depending on the petrophysical Yasutaka Shirakura (JODCO) properties, as a correlation parameter to generate J-function per RRT. The dynamic model was successfully initialized. The Lekhwair and Kharaib formations have long been Seventy wells were used to compare the model initial interpreted to represent a featureless carbonate platform water saturation (Swi) profiles versus log Swi. The STOIP which developed seaward (east) of a siliciclastic shoreline calculations were in good agreement (within 2 percent) in western Arabia. Recent work, however, demonstrates with the geological model. Relative permeability scanning that the platform was not flat nor featureless, but curves were generated to represent the fluid displacement, comprised a relatively complex westward-facing ramp and especially in the transition zone for each RRT. Average of shallow intrashelf basin in western Abu Dhabi. This new seven scanning curves per RRT were generated. In addition, interpretation is based upon an analysis of the distribution scanning curves were also generated for imbibition of grain types and thickness trends of log- and rock-based capillary pressures, with and without negative pressures. sequence stratigraphic units. Examination of gamma-ray A history match run with imbibition capillary pressures (no logs in the offshore areas of Abu Dhabi revealed that the negative pressures) gave the best results. History matching Lekhwair and Kharaib formations consist of relatively is continuing and good results have been achieved so far. “hot” and “cool” log signatures and that these signatures commonly matched with grain types and textures. For example, grain-supported rocks tend to have a “cool” (25-Oral) Applications of terrestrial gamma-ray response and mud-supported rocks tend to photogrammetry for 3-D geological structure have a “hot” gamma-ray response. Thus, we were able modeling to recognize shallowing- and deepening-upward trends to develop a high-frequency sequence stratigraphic Oeldenberger, Stefan (Intergraph - [email protected]) framework. Regional correlation and mapping of sequence and Vianney de Lestrange (PDO) stratigraphic units showed a consistent relationship between thickness, texture and grain types (e.g. Bacinella, In recent years, the rapid development of computer Hensonella, rudists, miliolids, orbitolinids, etc.). Thick technology has substantially decreased cost, effort and time stratigraphic units are made up of grain-supported rocks required for 3-D data modeling. A variety of data sources, with shallow-water fossils and thin stratigraphic units are such as remote sensing satellite data, 3-D seismic logs and muddy and/or made up of deeper-water fossils. In general, borehole data have found their way into GIS databases for increasing thickness (mainly to the east) corresponds to cross-correlation, data analysis and advanced visualization. shallow-marine, high-energy carbonates and decreasing Terrestrial Photogrammetry is an important source of 3-D thickness (mainly western offshore Abu Dhabi) corresponds modeling data. It provides the tools and methodologies to deeper water. These trends suggest that the Lekhwair for the rapid and safe acquisition of accurate structural and Kharaib formations accumulated in a westwardly geology data from o�en inaccessible outcrop locations. deepening ramp into offshore western Abu Dhabi. Lightweight, highly portable digital cameras are available today with very high-resolution and geometric accuracy, facilitating the capture of images under field conditions. In (294-Oral) Application of reservoir rock the Middle East, the first digital terrestrial imaging trial was types in dynamic modeling successfully conducted in May 2003 for PDO. A dedicated geological visualization and analysis package was used to Obeida, Tawfic A. (ADCO - [email protected]), Avar I. geocode the images and to autocorrelate digital models Vohra (ADCO), Yousef S. Al-Mehairi (ADCO) and of the cliff surfaces. Draped onto the digital surfaces, the Karry S. Suryanarayana (ADCO) images were converted into freely rotatable 3-D image A dynamic model was constructed by upscaling a 3-D models. Multiple images were merged and transformed geological model (31 million cells) of the Lower Cretaceous into planar, orthorectified image mosaics, for 2-D display/ Carbonate build-up in one of ADCO’s oil fields in the plo�ing purposes and to accurately measure the heights United Arab Emirates. The carbonate formation is the most of stratigraphic columns. The 3-D image models were also prolific and geologically complex oil reservoir. Seventeen the basis for measurements to determine the extent and Reservoir Rock Types (RRT) were described based on facies, orientation of sedimentary and discontinuity lineaments. porosity and permeability. Log-derived permeability (based The dip and strike measurements were used to extrapolate on a Neural Network), honoring the core permeability, was bedding and tectonic planes in 3-D space and to display the used in the 3-D geological model. Thirty faults and an measurements in a variety of geostatistical representations, areal distribution of a dense RRT were incorporated into for instance as histograms and stereonet projections.

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(103-Oral) Thief zones are not fractured faults are actually tear faults associated with thrust faults. layers in the Yibal field, North Oman These faults are characterized by buckling on one side only. This is a�ributed to regional tilting in NW direction during Ozkaya, Sait Ismail (Baker Hughes - ismail.ozkaya@baker Late Miocene time. Time of fracturing, oil emplacement and hughes.com) and Guy F. Mueller (PDO) fracture cementation suggest that the faults of Lekwhair and Dhulaima were re-activated during Late Eocene- Oligocene The role of faults and fault related fracture corridors as times and before the Late Miocene tectonic event. This major flow conduits is well established in the Yibal field. analysis of the structural evolution allows an improved Reservoir flow dynamics are dominated by faults and the understanding of the fractures critical for field development high permeability thief zones in this carbonate reservoir. by relating fracturing to structures and time of multi-phase Water rises through the faults and moves into thief zones. fracturing to structural evolution. A key uncertainty is the connection between the thief zones and layer-bound fracturing. Water stays within the thief zones without slumping by gravity even at great distances (457-Oral) High-resolution, 2-D, 2,880 away from injectors, raising the possibility of a dual porosity channel production seismic acquisition: system. A fracture study was undertaken to investigate the what happened to the signal? distribution of layer bound fractures and their correlation to water fingering. The study was based on borehole image Pecholcs, Peter I. (Saudi Aramco - [email protected]), logs, water saturation from open-hole logs of recent wells Bob Vincent (WesternGeco), Richard Hastings-James and surveillance data. It confirms previous well test results (Saudi Aramco), Bryan R. Maddison (Saudi Aramco) and and points to three important conclusions. (1) At least two Stephen Kellogg (Saudi Aramco) very high permeability strata are present in the Yibal field Three years ago, Saudi Aramco mobilized a 2-D, 2,880- (the top Shu’aiba thief zone and mid-Upper Shu’aiba thief channel, high-resolution seismic crew. This was achieved zone). (2) The reservoir has a few fractured layers. One such by converting the conventional 480-channel configuration fractured layer occurs at the reservoir top and corresponds to from 72-geophones/channel at a 30 m group interval a cemented interval below Nahr Umr. (3) The thief zones are to 12-geophones/channel at a 5 m group interval. Tests not, coincident with the fractured intervals but follow layers confirmed that the digital group formed seismic image was with high porosity and permeability. Such high permeability equivalent to the analog sum, only if the cross-line receiver layers are o�en only sparsely fractured. Conductive fractures pa�ern dimension was the same. The initial 2,880-channel within the fracture layers do not contribute to horizontal configuration used a single source and receiver line with permeability because layer-bound fractures within these a maximum offset of 7,200 m, and a source/receiver in- layers are not interconnected. Further improvement on the line group interval of 5 m. If the cross-line receiver pa�ern understanding of the interrelation between the thief zones dimension was reduced to 5 m, it was virtually impossible to and fractures can be achieved by displaying generated flat- recover the signal. We were not prepared to process seismic top geological cross-sections for all horizontal wells, against shot records with a signal-to-coherent noise (S/N) ratio water saturation and faults. Furthermore, understanding less than one. This design was replaced by a single-source/ reservoir we�ability is essential as it may be the cause of the dual-receiver line design with an in-line group of 10 m and apparent dual porosity behavior of the thief zones since they 60 or 120 m cross-line (group-formed). Using a variable are not fractured. cross-line dimension proved to be very effective because optimal processing parameters could be designed for the (104-Oral) Origin and evolution of Lekhwair near-surface (60 m cross-line receiver array) and the deep and Dhulaima structures, North Oman Basin target (120 m cross-line receiver array). A common medium- wavelength static was derived to couple the two seismic Ozkaya, Sait Ismail (Baker Hughes - ismail.ozkaya@baker images. Although the new design offered improved S/N ratio hughes.com) and Kester Harris (PDO) seismic images, the seismic processor was still challenged by significantly high levels of ambient coherent noise in the pre- Structural interpretation based on seismic and borehole stack shot records. For this purpose, Saudi Aramco selected image data reveal that the Lekhwair and Dhulaima Fields of an 18 km portion of an existing production 2-D line to record North Oman Basin are located on a regional fault propagation single sweep uncorrelated split-spread shot records at a 5 m fold structure over a deep seated thrust fault. The regional interval. Application of pre-correlation signal enhancement thrusting and associated folding took place in the Late filters will be presented and compared to conventional post- Cretaceous. Thrust direction was from SE to NW. Some local correlation seismic processing algorithms. structural highs such as Lekhwair represent fault bend folds over blind thrust faults, which are splinters of the main sole thrust fault. Other local structures such as Lekhwair East (315-Oral) Burial history reconstruction and and Dhulaima A are associated with back-thrust faults. thermal modeling in offshore southwest Iran All of these thrust fault structures are asymmetric in the direction of thrust faulting and elongate in NE-SW direction Peymani, Mohsen (U Tehran - [email protected]), perpendicular to thrust faulting. The NE-SW asymmetric Mohammad Reza Kamali (NIOC) and fold structures of Lekhwair and Dhulaima are intersected Mohammad Reza Rezaee (U Tehran) by two rhombic sets of WNW and NNW faults which can be Burial history reconstruction and thermal modeling studies interpreted either as a system of conjugate strike slip faults were carried out on 76 wells located in the northern Iranian or rhombic normal faults. There is evidence in Lekhwair A part of the Gulf. The results indicated that sediments in North and Dhulaima Fields, in particular, that some WNW

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the center of the Gulf (around the Qatar Arch) have lower (82-Oral) Tectonic control over Shu’aiba depth of burial compared to northwest and east. The depth Formation depositional facies of burial is maximum in the vicinity of the Strait of Hormuz. The predicted maturity model shows a good fit with Pierson, Bernard J. (ADNOC - [email protected]), maturities obtained by measuring vitrinite reflectance. In Rafael M. Rosell (ADCO), Naema Obaid Al-Zaabi (ADCO) the northwest of the Gulf the Pabdeh Formation is immature and Mohamed Mahmoud Abdulsa�ar (ADCO) and Gurpi Formation is early mature. The Kazhdumi, Dariyan and Gadvan formations are in the oil-generation Integrating in play fairway reviews, the wealth of geological window. The Surmeh Formation is at the end of the oil and geophysical data available in Abu Dhabi, including window and beginning of the gas-generation window. The new 3-D seismic data, has led to a be�er understanding Kangan Formation is in the gas-generation window and of the tectonic evolution of the Arabian Platform. This it is estimated that the Sarchahan (Silurian shale) is also understanding is key to predicting the distribution of in the gas-generation window. In the east of the Gulf, the depositional facies and play elements for any given play Pabdeh and Gurpi formations are in the oil window, and fairway. During the Paleozoic and early Mesozoic, a well- near the Strait of Hormuz they are in gas window. The defined set of NS basement faults, bounding a number Kazhdumi, Dariyan, Gadvan and Surmeh formations are of NS, sub-parallel basement highs and lows, controlled at the end of oil window and in the vicinity of the Strait of zones of preferential subsidence and determined the Hormuz they are in gas window. The Kangan Formation distribution of depositional facies in the eastern part of the chiefly lies in the gas window and it is estimated that the Arabian Plate. In early Aptian, at the onset of deposition of Sarchahan Formation is completely in the gas window. In the Shu’aiba, a NW-SE regional trend of strike-slip faults, the center of Gulf only the Kangan Formation has reached which had so far li�le influence on the depositional facies, the oil window, therefore the Sarchahan Formation must be became a predominant tectonic feature. This set of faults at the end of oil window in this area. The Pabdeh, Gurpi, determined the location of the Shu’aiba shelf margin at the Kazhdumi, Dariyan and Gadvan formations reached the southern edge of the Bab intrashelf Basin. Rudist colonies oil generation window in about Early Eocene. Timing of lined the windward, southern shelf margin, but were more oil generation for the Surmeh, Kangan and Sarchahan prolific on local highs, at cross points between the NS and formations are late Early Cretaceous and Middle Jurassic, the NW-SE regional fault pa�erns. There, spectacular rudist respectively. accumulations generated the excellent Shu’aiba reservoirs found in several giant fields in Abu Dhabi, Saudi Arabia and Oman. The eastern margin of the Bab Basin was (167-Oral) Imaging complex reservoirs using located along a broad, subtle NS basement high, possibly single sensor seismic acquisition offset locally by NW-SE transfer faults. Low-angle ramps lined the edge of this broad high. This morphology coupled Pickering, Stephen (WesternGeco - [email protected] with a leeward position of the eastern margin led to local esterngeco.slb.com), Stephen McHugo (WesternGeco) and and poor development of rudist reefs. The western margin Anthony Cooke (WesternGeco) was probably also controlled by a NS basement high, which Syn- or early post-deposition tectonism can o�en result may have generated a gentle ramp on which only patchy in complex reservoir distributions, and contain a variety rudist colonies grew. The northern part of the Bab Basin of lithofacies types which are not easily identified or may have seen the development of isolated rudist platforms mapped using seismic data. Some of these reservoirs can over salt-cored highs. be a significant source of economic hydrocarbons, yet their exploitation is o�en hampered by the difficulty in (223-Oral) Facies analysis and organic identifying the distribution and quality of net pay within geochemical study of the Middle Oolitic the field. Because they are seismically difficult to image, Member of the Minagish Formation, Kuwait these reservoirs are o�en found relatively late in the economic history of the basin–all too o�en by serendipity southern oil fields in the search for deeper reservoir objectives. In this study, Qabazard, Suad A.K. (Kuwait U - we describe a complex sandstone injectite reservoir. The [email protected]) and gross structural and lithological complexity of the reservoir Fowzia H. Abdullah (Kuwait U) was previously only comprehended from borehole image data. This study describes the design and execution of a The Lower Cretaceous middle (oolitic) member of high-resolution point-receiver seismic survey acquisition, the Minagish Formation is one of the major carbonate and the resulting pre-stack inversion workflow of the data. reservoirs in the southern oil fields of Kuwait and This dataset was used to predict the lithology and visualize Partitioned Neutral Zone (PNZ) between Kuwait and the morphology of an extremely complex field. The study Saudi Arabia. The scope of this study was to deduce: (1) revealed that high-resolution seismic data can provide a the depositional environment of the Minagish Formation; greater understanding of the reservoir, revealing in this (2) the post-depositional diagenetic processes; and (3) to case structural detail that supports the geologic model of estimate the distribution and variations in source rock the field. The study also confirmed the operator’s concerns potential. The investigations of the depositional and post- about reservoir complexity. The results revealed good depositional processes were based on: (1) petrographical predictions of reservoir facies using reservoir a�ribute studies using transmi�ed-light and scanning-electron analysis, and evidence regarding the mode of origin of the sandstone distribution in the basin.

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microscopy; (2) mineralogical analyses by X-ray diffraction pressure data, cores from 6 wells and wireline logs from and an energy dispersive analyzer in order to determine the 33 wells. Complex pore systems of the carbonate reservoirs mineral composition; (3) and to study the micro-fabrics and were characterized in terms of pore throat aperture. A strong diagenetic features. These analyses were complemented by correlation was found between R35 and core permeability. inorganic geochemical studies using an ICP-OES analyzer The available mercury injection samples taken from for major and trace metal contents. Organic geochemical different lithofacies naturally fell in same separate classes techniques were performed based on determinations of deduced from R35 thresholds: Mega (> 10 micros), Upper total organic carbon (TOC) elemental composition of the Macro (5-10 microns), Lower Macro (2-5 microns), Meso organic ma�er (kerogen) using a LECO analyzer. Kerogen (0.5-2 microns), Micro (0.2-0.5 microns) and Nano (< 0.2 petrography was carried out under transmi�ed-light to microns). An excellent fit was achieved between calculated identify the type of the organic ma�er incorporated during and measured permeability based on porosity-permeability sedimentation. The middle oolitic member of the Minagish transforms created for each of the above classes. To establish Formation contains a laminated organic carbonate the same rock classes in non-cored wells, a neural network wackestone facies that grades into peloidal and ooidal was trained using log data along with core R35. Upon packstones and grainstones. Based on the differences in the achieving a very good match, the respective transforms micro-facies present, this member is classified into grain- were applied yielding permeability values that compared and mud-supported textural types, and consequently is well with measured permeability. A�er further validation, interpreted to represent a protected shelf-lagoonal se�ing the network was applied on the 26 noncored wells. Results interbedded with high-energy oolite shoals. The micro- were deemed robust for permeability characterization. Flow facies of the Minagish limestones consist of ooids, peloids units were combined into 18 layers, which were used to and intraclasts with skeletal grains of foraminiferas, build 3-D porosity and permeability geocellular models for echinoderms, calcareous algae and shell fragments, reservoir simulation. In conclusion, this methodology can reflecting their deposition under oxic marine conditions. be used effectively for robust permeability characterization Significant amounts of framboidal pyrite are restricted to and establishing flow units in heterogeneous carbonate the mud-supported micro-facies, indicating that reducing reservoirs with few cored wells and data. conditions were established through bacterial sulfate and enhanced the preservation of organic ma�er during the deposition of facies. The rocks are dominantly composed (9-Oral) A study of natural gas origins in of carbonates, with the absence of high percentages of southern Iran silicates and clay minerals, indicating limited clastic influx Rabbani, Ahmad R. (Amir Kabir U - [email protected]) into the Cretaceous Arabian Platform during periods of transgression. The micro-facies contain marine, amorphous The Upper Permian Dalan and Lower Triassic Kangan type II kerogen, providing another piece of evidence of lack formations contain extensive gas reservoirs in southern in terrestrial input. The sedimentological and geochemical Iran. Gas fields in southern Iran (for example as Aghar, results show that both the coarse- and fine-grained Kangan, Nar, North and South Pars and others) contain carbonates in the middle Minagish Formation serve as a more than 18 percent of the proven gas reserves. Gas good reservoir. This is reflected in the high percentages samples from Upper Permian and Lower Triassic gas of secondary porosity and micro-porosity. The high TOC reservoirs are composed of methane-dominated light (0.53 to 2.546 percent) contents and the abundance of high hydrocarbon: CO2, N2 with minor quantities of noble quality (type II), algal-derived marine (C/N = 4.6-25.1) gases. The analytical results demonstrated fairly uniform organic ma�er in the grain- and mud-supported micro- chemical compositions for gases and isotopic compositions facies indicate high potential source beds but the low of methane and its homologues in the section overlying maturity level of kerogen shows that the oil accumulated in the anhydrite zone (Nar Member of Dalan Formation). the pore spaces is not indigenous. For example, the carbon isotope composition of methane in samples from the Dalan zones D, C, and E, and Kangan (69-Oral) Estimation of flow units using Formation varied from -39.95 to -41.28‰. This allows us to neural networks as a key to calculate conclude that gas accumulations in the Kangan and upper part of Dalan constitute a single reservoir. Quite different permeability in a carbonate reservoir characteristics are displayed by gases from the lower zone Raafat, Khaled T. (QP - [email protected]) (below the anhydrite) of the Dalan Formation (zone G). This gas is characterized by considerable depletion in the Permeability characterization is an integral part of robust light carbon isotope. For example, methane from the lower reservoir characterization, reservoir simulation and part of the Dalan Formation has 26.22‰. They also show a performance forecasting. The objective of this presentation number of other distinctive features: significant enrichment is to demonstrate a methodology using neural networks in nitrogen; occurrence of isotopically light CO2 (-21.87‰); complementing other petrophysical work for calculation and an inversion in the isotope relationships of ethane and of permeability and definition of flow units. Procedures propane. These peculiarities suggest that the composition included using Winland H.D. equation, which established of gases in this zone was modified by the process of the that pore throat radii at the 35th percentile mercury thermal chemical reduction of anhydrite. The source rocks saturation (R35) correlated well with core porosity and of the gas could be either the Dalan Formation itself, or air permeability. R35 was used in a petrophysical model Ordovician-Silurian shales. integrating sedimentological, rock and fluid properties,

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(53-Oral) Organic geochemistry of crude oils (499-Oral) Maximizing remaining value from the northwestern part of the Gulf through integrated reservoir modeling and reservoir management: Yibal Shu’aiba Rabbani, Ahmad R. (Amir Kabir U - [email protected]) reservoir, Oman and Mehdi S. Afrapoli (Amir Kabir U) Razali, Mohammed A. (PDO - mohammed.a.razali@ Mesozoic and Tertiary source rocks and crude oils from pdo.co.om), Daniel Rayes (PDO), Said Abri (PDO), the northwestern Iranian sector of the Gulf have been Hassan Behairy (PDO), Guy Mueller (PDO), Robbert characterized by means of a variety of organic geochemical Nieuwenhuijs (PDO), Patrick Hogarty (PDO) and techniques. The Biomarker characteristics (molecular Hamed Al Sharji (PDO) fossils) were combined with other geochemical data to interpret the sources, depositional environments, diagenesis The Yibal field is one of the cornerstones of Oman’s oil and catagenesis processes, migration and alteration. Oil production. The field has contributed 23 percent of PDO’s fields investigated include Abouzar, Bahrgansar, Dorood, total cumulative oil production and is currently supplying Foroozan, Hendijan, and Norowz fields. Two groups of 17 percent of PDO’s daily production. Oil production is petroleum can be recognized on the basis of carbon isotope, from the Cretaceous carbonate Shu’aiba Formation that is biomarker investigation and statistical cluster analysis. considered to have been deposited in a deep-water se�ing. Group 1 includes the Abouzar, Bahrgansar and Hendijan The giant Shu’aiba reservoir is faulted and relatively oil fields and based on the biomarker and other parameters, fractured, with good porosity but low permeability. The field these oils were sourced from the Upper Jurassic to Lower has been on production since 1969 and on water injection part of the Cretaceous shaly rocks. Group 2 includes the since 1972 reaching peak production in 1997 at 225 Mbbl/d. Dorood, Foroozan and Norowz oil fields and these oils Since then the field has been experiencing a rapid decline. were sourced from the Upper Permian to Middle Jurassic In November 2000, a Volume-to-Value exercise was started carbonate rock. to focus on a reservoir study and reservoir management, aiming to arrest the decline and maximize the remaining (310-Poster) Facies and sequences of producible volume; an extensive effort was placed on Devonian Jauf Reservoir, Ghawar Field, data acquisition and data management. This resulted in two dedicated teams, Study and Reservoir Management, Saudi Arabia working together in parallel. The study team is focusing Rahmani, Riyadh A. (Saudi Aramco - riyadh.rahmani@ara on evaluating the reservoir’s uncertainties by integrated mco.com) modeling, and the reservoir management team is focusing on voidage and pressure maintenance using analytical and The Devonian System of Saudi Arabia is part of a thick reservoir models from the study team. A well-to-fieldwide Paleozoic succession of essentially siliciclastic rocks that modeling approach was applied for the reservoir study. were deposited across North Africa and the Arabian Plate. The first step was to build a Single Well Model (SWM) to Deposition of the Paleozoic succession occurred along a very understand the key parameters on production mechanism: broad, shallow and relatively stable ramp shelf, extending a total of 17 SWMs were built that were selected across the for several thousands of kilometers along the northern and field. The second step was to build a Conceptual Model northeastern margins of Gondwana Supercontinent. In (CM) to verify the findings from the SWM: two CMs were the greater Ghawar field area of eastern Saudi Arabia, the built, at the crest and flank. The next step was to build the Devonian Jauf Formation is a very important gas reservoir. models that could be used as a tool for identifying the A detailed sequence stratigraphic and sedimentological opportunities and reservoir management. This was done study of the Jauf in the area revealed a complex in two ways: Focus Area and Full Field Model (FFM). The depositional history, and a highly variable stratigraphic two techniques were tested in parallel. For the FFM, it architecture. However, applying sound concepts of facies was foreseen to be impossible, due to the size of the field and sequence analysis resulted in predictive facies and and the limitation on computing power. Hence the coarse sequence stratigraphic models that were proven useful in 5-layer ‘cake’ model was built. Both methods were very both exploration and development. The Jauf Formation fruitful and successful and the end-products led to more comprises two third-order sequences, referred to as SQ55 opportunities in determining the new oil, and helped focus and SQ60. Each one of these two third-order sequences on reservoir management strategies. Several new wells for consists of several higher-frequency sequences of the fourth- oil production and water injection have been identified and order. Third-order sequence SQ55 is dominated by a falling drilled successfully as predicted from the models. Other stage systems tract (forced regressive shoreface) which activities such as additional perforations, ESP conversions prograded from west to east across a distance of 150-200 km. were also successfully carried out. On the other hand, for The overlying SQ60 comprises a transgressive systems tract further re-development of the field and ge�ing maximum and a highstand systems tract. Depositional environments reserve, the decision was made to build a detailed FFM that of the various facies were mostly nearshore and coastal could be used for well-to-well planning. This is currently plain and ranged from wave-dominated shorefaces, to ongoing and shows a promising outcome. As a whole, the estuarine embayment fills of tidal channels and bars to tidal current strategy seems to work well and has reduced the and fluvial-dominated coastal plain channels. Reservoir decline considerably by a third. quality rocks were mostly those deposited during the TST of SQ60 in tidal estuarine environments as channel-fills, bars and bay-fill deltas.

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(210-Poster) Lower Cretaceous Upper between 360–440 �. The youngest Ca member consists Thamama reservoir high-resolution of sideritic nodules and gluconitic sands with limestone sequence stratigraphy, United Arab Emirates streaks. Its thickness varies between 10–20 � and is hydrocarbon bearing. The Cb member consists of sideritic Rebelle, Michel J.M. (ADCO - [email protected]), nodule layer, claystones and sandstones to argillaceous Christian J. Strohmenger (ADCO ), Ahmed Ghani sandstones with thickness of 15–25 �. The Cc member is (ADCO), Khalil Al-Mehsin (ADCO) and a well-sorted sandstone with thickness ranges of 45–70 � Abdulla Al-Mansoori (ADCO) and it is the main hydrocarbon producer of the Nahr Umr Formation. The Cd is the oldest and thickest member and The Upper Thamama reservoir is part of the Lower its thickness ranges between 250-360 � with a wide variety Cretaceous Kharaib Formation (Barremian) and one of the of lithological assemblages such as argillaceous siltstone, major oil reservoirs of Abu Dhabi. It consists of outer to inner argillaceous to gluconitic sandstone, sideritic layers with ramp platform carbonates, starting with orbitolinid, skeletal abundant coal laminae. The porosity and permeability wackestones and packstones overlain by algal Bacinella-rich of Nahr Umr sands range between 20–40 percent and floatstones with high micro-porosity. Towards the top of the 20–2,500 md, respectively. In order to bring out the sand reservoir, rudist (Toucasia) floatstones and rudstones become body geometries of the Nahr Umr Formation, 3-D seismic abundant grading into skeletal grainstones and rudstones a�ributes were generated by integration of petrophysical of a high energy depositional environment. The top of and reservoir data. Individual sand body geometries could the reservoir is marked by an exposure surface showing not be discerned with 3-D seismic a�ributes; however, root imprints, desiccation cracks, and reddish staining. composite-window a�ributes were generated on Ca/Cb and The Upper Thamama reservoir is underlain and overlain Cc levels. The horizon amplitude, instantaneous frequency by so-called dense zones, representing restricted lagoon and phase data provided circumstantial evidence and deposits (orbitolinids wackestones rich in pyrite, clay, and a meaningful relationship between acoustic amplitudes quartz grains). Traditionally, the Upper Thamama reservoir and sand thicknesses. The 3-D seismic a�ributes were subdivision is based on lithostratigraphic correlation, reasonably corroborated with the Nahr Umr sands in the using the vertical distribution of stylolites. As such an axial part of the Awali field. The study brought out a small approach is not tenable for building geological (static) but distinct a�ribute anomaly in the southern as well as and reservoir (dynamic) models, a new high-resolution on the eastern margin, which is well validated with Khuff sequence stratigraphy framework was established. It is wells. The study suggests exploratory/stepout locations to based on core and well-log data from different ADCO fields test the prospectivity and hydrocarbon potential of these as well as outcrop data from Oman and the United Arab anomalies. Emirates. The so-called stylolitic intervals correspond to major facies changes related to third-, fourth-, and fi�h- (177-Poster) Subsurface uncertainty order sequence boundaries, parasequence set boundaries, and parasequence boundaries. Early diagenetic processes management in the Sakhiya A3C reservoir in follow the sequence stratigraphic framework and therefore South Oman can be predicted away from well control. The high- resolution sequence stratigraphic framework allows a Riyami, Qassim M. (PDO - [email protected]), be�er prediction of the vertical and lateral distribution of Asya Rawahi (PDO) and Mike O’Dell (PDO) reservoir quality and reservoir continuity. There has been a string of exploration successful oil discoveries in the past five years in the Harweel Cluster in (456-Poster) 3-D Seismic characterization of South Oman. One of these discoveries is the A3C reservoir Nahr Umr reservoirs in Awali field, Bahrain in Sakhiya field. This reservoir is 4 km deep, lithostatically pressured, and the oil is sour. Two wells penetrate this Reddy, Bapu C. (Bapco - [email protected]), Waleed reservoir, but only one has been tested. A large degree of A. Jawad (Bapco), Jonna D. Rao (Bapco) and subsurface uncertainty exists in gross rock volume and oil- Masoud M. Faqihi (Bapco) water-contact, reservoir architecture, faults and fractures, reservoir compartmentalization, permeability level The prolific hydrocarbon producers of Awali oil field and heterogeneity, fluid properties, and other reservoir are the reservoirs of Cretaceous Wasia Group, Jurassic parameters. Li�le is known about the scale and relative Arab Formation and Permian Khuff Formation. The Nahr importance of each of these uncertainties. An uncertainty Umr Formation of Wasia Group is one of the main clastic management scheme developed in PDO for other reservoirs hydrocarbon producers in the Cretaceous System. It is in this cluster was applied to Sakhiya A3C. This scheme overlain by the Mauddud Formation with intervening uses sensitivity simulation studies to guide the selection of shale and unconformably overlies the carbonates of the realizations, which are used in further simulation studies Shu’aiba Formation. The widespread occurrence of clastic to determine the optimum development scenario. It was sediments in the Nahr Umr Formation clearly manifests determined that there is a low uncertainty for recovery the prevalence of a marginal marine to deltaic regime on depletion, but there is low recovery in a depletion with an easterly progradation in a north-south oriented development, also. For the case of miscible gasflood depositional strike. The Nahr Umr Formation is comprised development, there is high recovery and high uncertainty. of four clastic reservoir facies; namely: Ca, Cb, Cc and Cd The result of the work clarifies the data gathering with intercalated shale laminations. It ranges in thickness requirements prior to the next phase of development.

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(313-Oral) The Tethyan Margin of Oman: production was flowing from a conductive fault network. long-term control (10–40 Ma) of the Early In order to implement these results in the simulation model, Triassic to Late Cretaceous turbiditic reservoir zones with increased permeability multipliers were defined: (1) for the flanks, (2) central graben, and (3) sedimentation proximal to seismic faults. Thus the impact of the fractures on the reservoir was modeled using a single porosity system Robin, Cécile (U Rennes - [email protected]), François with permeability multipliers. This resulted in an accurate Guillocheau (U Rennes), Spela Gorican (Ljubjana U) and history match that was achieved within a fraction of the time François Béchennec (BRGM) that a dual porosity model would have taken. The Oman Tethyan paleomargin is a Maastrichtian inverted passive margin (ophiolites obduction) showing a continuous (84-Oral) Integration of 3-D seismic, turbidictic sedimentation from the Early Triassic to the Late reservoir and production data to revitalize Cretaceous time. The exact paleogeographic se�ing is still debated: thinned continental crust versus oceanic crust, assets: Thamama case study, Rashid field, isolated basin versus open ocean, among other models. Dubai Major changes in the turbiditic systems occur in the 10 to 40 Ma time scale. Multiple systems can be defined: pure Rorison, Philip J. (DPC - [email protected]), siliciclastic deep-sea lobes (Lower Jurassic), pure carbonate Xavier Faugeras (DPC) and Jeffrey W. Yeaton (DPC) (ooïdic) deep-sea lobes (Middle/Upper Jurassic), carbonate The Rashid field is located in offshore Dubai, on a low- slope-apron systems (Lower Cretaceous), deep-sea plain relief, salt-induced dome. Production is from two carbonate siliceous (‘radiolarite’) and carbonate turbidites. They record reservoirs. This presentation concentrates on the subsurface major events: (1) widespread siliceous sedimentation during team’s approach to reevaluating the Thamama reservoir and Ladinian/Carnian, Toarcian, Kimmeridgian and Cenomanian the results of the horizontal drilling program. The integrated times; (2) major siliciclastic input at the Late Triassic/Early study provided a be�er understanding of the reservoir and Jurassic; (3) major progradation around the Middle/ proved to be a solid base for recommending new wells to Upper Jurassic boundary; and (4) major facies shi� and be drilled on the structure in a phased redevelopment of the disconformity during the Late Jurassic (late Kimmeridgian?). asset. Production from the Thamama reservoir began in 1979. They record both local and global control, from local tectonics Since then, it has produced continuously from vertical wells to global sea-level variations, climate or sea-water chemistry under natural depletion without significant water production. changes. The spatial variation (facies, thickness) along this In 1999, a 3-D seismic survey provided an improved image margin, and a correlation with the Arabian Platform, provide of the reservoir’s 3-D geometry and fault architecture. The information to discriminate these factors. Of particular data were interpreted and, together with reservoir property interest for this study is the Middle/Upper Jurassic Guwaysa data, were integrated into a fine-scale geocellular model. Formation that consists of pure carbonate (ooïdic) deep-sea Finally, a dynamic model was constructed. At each stage lobes. In the most proximal se�ing it is 300–350 m thick and of the study, structural, static and dynamic information (as consists of a repetitive motif of coarse-grained sandy units well as uncertainties) was reconciled. The results showed (30 to 100 m thick) overlain by a more muddy one (20 to 50 that horizontal drilling and water injection would add value. m thick) that had a duration of 1 to 10 million yeas. These Implementation of the phased redevelopment began in 2002 features can be explained by a change in both sea level and with a first multi-lateral, 18 years a�er the last development carbonate production on the shelf. well was drilled. As results supported the model, phase 2 was implemented with the drilling of three more laterals in 2003. (166-Oral) Developing a validated fractured Phase 3, water injection would involve conversion of the first reservoir model: an example from the Awali multi-lateral to reverse ESP assisted dumpflood. In conclusion, Field, Bahrain revitalization of the Rashid Thamama started with gaining a be�er understanding of the reservoir, its uncertainties and Rogers, Steve (Golder - [email protected]) and development options. A phased redevelopment approach Yahya Al-Ansari (Bapco) was necessary to reduce risk, allowing the model to be verified by drilling results and reservoir performance before A naturally-fractured Cretaceous carbonate reservoir in the making value based investment decisions. We estimate Awali field in Bahrain was modeled. Because the reservoir that redevelopment of Rashid Thamama will increase the is relatively thin and predominantly penetrated by vertical expected ultimate recovery of the field by 30 percent. wells, only limited information exists with which to develop the fracture model. The limited borehole image log and core (440-Oral) Khuff and pre-Khuff imaging data, surface fracture data, along with other indirect static and dynamic observations, were synthesized into a number improvement by integrating well and seismic of possible conceptual models that describe the distribution velocities to create a PSTM velocity field and performance of the various fracture components. Discrete Fracture Network (DFN) models were built and used to Rowe, Robert W. (Saudi Aramco - conduct flow simulations in order to help establish which [email protected]), Hashim A. Hussein (Saudi of the static fracture models best explained the dynamic Aramco), Gregory Douglass (Saudi Aramco) and flow behavior of the reservoir. The results of the simulations Michael Zinger (Saudi Aramco) revealed that two distinctive fracture models existed across The success of deep gas exploration in the Eastern Province the reservoir layer: one for the flanks and another for the of Saudi Arabia relies largely on the imaging accuracy of the crestal graben. Both models indicated that significant

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pre-Khuff seismic section. Unfortunately, the abundance of was deposited in a foredeep synchronous with nearby multiple energy, low reflection coefficients, and the depth compressional folding; it was derived by upli� and erosion of of the target make it difficult to obtain a clear image on the underlying sequence. Folds have evolved as detachment the seismic data. Utilizing well velocity and a preliminary folds or fault propagation folds with a major detachment geologic interpretation of key seismic horizons in the horizon in Lower Paleozoic or infra-Cambrian sediments, estimation of pre-stack time migration velocities, allows and additional more localized detachments in Paleogene, the geophysicist to create a more accurate velocity field. Cretaceous and Triassic sequences. The Pliocene sequence, Seemingly, minor enhancements in the stack and migration comprising up to 1,000 m of alluvial fan conglomerates, velocity field can lead to significant improvements in was deposited synchronously with further compressional the seismic interpretation. An analysis of regional well deformation and folding. Intense deformation of the post- velocities showed a consistent velocity trend at the Jilh Early Miocene sequences has occurred above a second and below. This, combined with strong seismic response, major detachment at the base of the Gachsaran Formation and easily interpreted velocity of the Jilh dolomite horizon, evaporites, with thrusting of the Gachsaran over younger enabled calibration of the well velocity to the 3-D seismic formations. Rapid upli� in Quaternary time led to the at that level. Using the calibration, the velocities of the incision of deep valleys (tangs) into the rising folds. Sudair, Khuff, and pre-Khuff horizons can be very closely estimated. Once estimated at a particular location, the layer velocities can then be extrapolated spatially throughout the (220-Oral) Using 3-D seismic data to define survey, based on the horizontal velocity analysis of the Jilh Cretaceous transpressional features in the dolomite event and preliminary interpretations of the Jilh, Bahrah area of north Kuwait Khuff, and pre-Khuff horizons. The extrapolated velocities serve as a spatial 3-D guide function for conventional Russell, David J. (KOC - [email protected]), Khalid detailed velocity analysis. This technique allows the Abdul-Rahman (KOC), Ahmed Manowar (KOC), Thakur geophysicist to correctly interpret the deep primary Sanjeev (KOC), Ghaida Al-Sahlan (KOC) and velocity without being distracted by the strong velocity Meshal Al-Wadi (KOC) semblance response of the overlaying multiples. Use of The Bahrah area lies geographically between the Greater the improved velocity field for pre-stack time migration is Burgan and the North Kuwait Sabriyah fields. The Jal al a key step on the path to correct imaging of the pre-Khuff Zoor Ridge, Kuwait Bay and tidal flats are located within the section. In this study, we show in detail the steps required to Bahrah area making good quality seismic data acquisition implement the velocity integration/extrapolation procedure very difficult. Bahrah structure is a plunging anticlinal and view data examples at each step. We demonstrate the segment of the Kuwait Arch, intersected with faults related regional stability of the calibrated well velocities, as well as to Late Cretaceous and Paleogene tectonism. Interpretation the stability of the Jilh dolomite seismic reflection velocity. of old (pre-1995) 2-D seismic data in this logistically For two surveys, the 3-D pre-stack time migrated (PSTM) difficult region has presented a challenge to define the local velocity model resulting from the use of this procedure will structural elements. A few wells have encountered oil pools be shown in conjunction with the PSTM data. with significantly different oil-water contacts indicating compartmentalized reservoirs within the Albian Burgan (410-Poster) Mid Miocene-Recent and Mauddud formations. The acquisition of 3-D seismic tectonostratigraphic evolution of the data covering the northern oil fields, including Bahrah has northeast Dezful Embayment, southwest aided in the interpretation of positive flower structures and other related features. During Late Cretaceous, le�-lateral Iran transpression caused the formation of these approximately Ruiz, Claudia C. (BP - [email protected]), Stephen J. 1 x 3 km mildly-asymmetric, positive flower structures. The Ma�hews (BP), Jeremy C. Goff BP( ), Bob W. Jones (BP), Mishrif sediments (Turonian) are the youngest formations Nicholas J. Whiteley (BP), Masoud Shamshiri (NIOC), that exhibit drape over the flower structures, indicating that Farid Farmani (NIOC) and Salman Jahani (NIOC) the transpression ceased in Turonian. A post-Cretaceous graben is superimposed on the flower structure creating An interdisciplinary study by NIOC and BP has focused an interesting but difficult to interpret image of the on the tectonostratigraphic and burial history of post-Early subsurface. Although the old 2-D seismic data detected Miocene sedimentary sequences in the northeast Dezful these features it is only with modern 3-D seismic data that Embayment. Progressive southwestward advancement we can confidently map these various structural elements of Late Tertiary compressional deformation was the main within the Bahrah area. Although many of the faults are control on differential subsidence. Old basement-involved interpreted conventionally, spectral decomposition of the NS-trending fault systems, such as the ‘Izeh Lineament’, seismic data helps define the limits of the faults as well as appear to have been important in localizing the development revealing more fault zones. Areas with high fault density of oblique thrust ramps. The complex interaction of this and structural elements of a tensile nature are considered basement structural inheritance, with several potentially prospective in the Mauddud limestone. With the additional active detachment levels, has resulted in substantial lateral fault detail afforded by the 3-D seismic data, the Burgan variation in thickness and facies of the Middle Miocene to clastics are being evaluated in terms of isolated oil pools Recent stratigraphic section. The Middle Miocene–early separated by faults. Current interpretation is that these Late Miocene sequence is up to 4,000 m thick in the Dezful faults provide the necessary barriers between the up-dip Embayment; to the northeast this sequence thins to 1,500 water and the down-dip oil accumulations. These types m with pinchout of evaporites. The late Late Miocene of plays have good potential where traditional four-way sequence (comprising up to 2,000 m of clastic sediments) structural closures are not developed.

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(449-Oral) Applications of image log (27-Oral) Chasing Permian dune sandstones analyses to reservoir characterization, in Central Saudi Arabia Ghawar and Shaybah fields, Saudi Arabia Ru�y, Patrick M. (Saudi Aramco - patrick.ru�[email protected] Russell, S. Duffy (Saudi Aramco - steven.russell@aramc m) and Martin Rademakers (Saudi Aramco) o.com), R. Kumbe Sadler (Saudi Aramco), Wang Weihua (Schlumberger), Pete Richter (Schlumberger), Interpretation of a 3-D seismic volume from central Saudi Ramsin Eyvazzadeh (Saudi Aramco) and Arabia has revealed a remarkably linear valley filled Edward A. Clerke (Saudi Aramco) with eolian dune sandstone of the Unayzah Formation. Studies of well logs, cores and test data have further The complex relationship between porosity and permeability, enhanced our understanding of the valley trend and its particularly in carbonate reservoirs, is mostly a�ributed to significance to exploration. The valley first formed inthe the extreme range in heterogeneity of porosity types–from mid-Carboniferous, when upli� along basement faults micromatrix to vuggy. Small-scale porosity and permeability caused a drop in base level, emplacing drainage systems heterogeneity significantly affects reservoir productivity. that eroded at least 3,000 feet of Silurian and Devonian Conventional wireline logs lack the fundamental vertical sediments (‘Hercynian’ unconformity). Far to the southeast, resolution capability and quantification of heterogeneity aggradation in an intracratonic basin filling with glacial to provide the needed reservoir characterization database. meltwater decreased the slope of the entire system and High-resolution image logs have ideal small-scale resolution generally changed the depositional style from braided fluvial capability as well as azimuthal borehole coverage, and can and alluvial fan, to more meandering fluvial, lacustrine and be processed to quantify extreme heterogeneity in reservoir eolian. In the study area, the Unayzah Formation has been porosity and permeability. Recent work in the Arab-D found to consist almost exclusively of dune sands that reservoir has shown that the major control on permeability developed during this latest episode of deposition. These is the size of the largest pore throats of the pore system sands fill the valley incised during the ‘Hercynian’ tectonic (Archie C 0.1–2.0 mm and D size > 2.0 mm pores). A new event, extending in thinner accumulations outside the methodology of processing borehole image data is applied valley. It is not known whether the sands were transported to distinguish porosity in various pore size ranges, and into the area by eolian processes or were instead reworked hence, permeability variations and stratigraphic rock types fluvial sediments, but it is clear that reservoir-quality rock through interpretation of specially-processed image log data lies only within the confines of the valley. Identification and a�er initial calibration with cores. First, azimuthal borehole mapping of this areally restricted Unayzah dune field–only total porosity is quantified. The contribution of large size possible with 3-D seismic–and the concurrent improved pores (vugs) to total porosity is quantified and used as understanding of its origin, has allowed us to focus later input to constrain permeability values. Porosity now exploration efforts in the area. distributed by size range is transformed into permeability. Results from the permeability analyses are used as input into (158-Poster) Regional distribution, lithologic the identification of rock types. A training set of lithofacies is identified on conventional logs and used to initiate a neural characterization and petroleum potential of network analysis of rock types. In a pilot study, wells in the Oligocene strata in the Arabian Basin the Lower Cretaceous Shu’aiba Formation of the Shaybah Sadooni, Fadhil N. (UAE U - [email protected]) and field and the Upper Jurassic Arab-D Formation of the Abdulrahman N. Alsharhan (UAE U) Ghawar field were analyzed in separate applications of the methodology. Image log-based porosity measurements have The present-day Oligocene sediments over the Arabian a significant impact on hydrocarbon pore volumes because Basin are found only as sca�ered surface and subsurface of the improved resolution of the extreme range in porosity patches. They were either never deposited or removed by as classified by pore size. Shu’aiba rudist rudstones exhibit subsequent erosion. In the northern parts of the Arabian a clear bimodal porosity distribution and the broadest Basin, these sediments were described from the supergiant range of pore sizes, which is not detected by conventional field of Kirkuk and the neighboring outcrop of Qara Chauq wireline logs. Hence in this facies, conventional wireline Mountain, North Iraq; as well as from some oil fields in log porosity calibrated to core data at the plug sample northern Iran such as Masjid-i Sulaiman. In the North Iraq scale is pessimistic. The areal distribution of the bimodal localities, these sediments are formed of three vertically- porosity and corresponding permeability of 10 Darcies or stacked cycles of lagoonal, reefal, fore-reefal and basinal more, which accounts for high production flow rates and facies collectively known as the Kirkuk Group. In Iran, low pressure drawdown, is limited to one part of the field these sediments are assigned to the Asmari Formation most affected by meteoric diagenesis. In the upper Arab- which consists of coral and coral-algal boundstone with D, small-scale vertical reservoir heterogeneities, which are foraminiferal limestones. In the Syrian Tichreen field, characterized by high image log-derived porosity, correlate the Oligocene Chilou Formation is a major reservoir. In to diagenetically altered dolomite and vuggy Cladocoropsis southern Iraq, mainly in the oil fields along the Iraqi- and stromatoporoid-rich intervals that are major contributors Iranian borders, the Oligocene sediments are represented to production. Permeability derived from image log analyses by a clastic succession of fluvial to lacustrine deposits that incorporate the role of the large pore throats, and are termed the Mesan Group, which is partially equivalent independent of porosity, result in a permeability estimation to the Ghar Formation. In the southern parts of the at least one order of magnitude higher than the permeability Arabian Basin, the Oligocene sediments are represented calculated from conventional porosity-only log-permeability by reefal-large foraminifera carbonates outcropping in transforms in Arab-D Zone 2.

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Hafit Mountain along the Oman-United Arab Emirates Zubair, and Nahr Umr formations. Other formations such (UAE) border, and designated as the Asmari Formation. as the Hartha, Ahmadi, Khasib and Mauddud may prove to Oligocene carbonate sediments were also encountered in be productive outside the presently prospective areas. offshore UAE. The remnants of the Oligocene sediments indicate that only part of the basin-margin coral build-ups and the basinal facies were preserved, and only in small (124-Oral) Using seismic inversion and sca�ered areas. It is very probable that these sediments techniques to optimize drilling through hard were removed by later erosion or were never deposited in Amin conglomerates of South Oman other areas. The fractured reefal and fore-reefal limestones of the Kirkuk Group is the main reservoir rocks in Kirkuk Said, Dhiya (PDO - [email protected]), Robert oilfield where they have been producing since 1927. Gas Gardham (PDO) and David Conroy (Sii-ASE) seepages from these relatively shallow reservoirs (average The conglomerates of the Cambrian Amin Formation pose depth is 800 m) are responsible for the phenomenal ‘eternal considerable drilling challenges in the exploration for fire’ that remained glowing since the dawn of civilization. hydrocarbons in the underlying intrasalt carbonate stringers Heavy-oil accumulation (24 degree API gravity) occurs of South Oman. The Amin sediments comprise a series in the Asmari Formation in Mandous field (offshore Abu of hard conglomerates (unconfined compressive strength Dhabi). Future exploration work should be directed for the > 24 kPsi) interbedded with so� sandstones (unconfined delineation of the basin-margin build-ups in other parts of compressive strength < 10 kPsi). Drilling through the hard the basin, where they may contain significant amount of conglomerate layers is very slow (averaging > 30 minute/ hydrocarbons in both structural and stratigraphic traps. meter) compared to the relatively fast drilling in the so�er sandstones (averaging < 15 min/m). Rig time consumed in (364-Oral) The Cretaceous oil systems of the drilling the Amin section is therefore a major contributor to Mesopotamian Foredeep Basin, southern the total cost of carbonate stringer wells, to the extent that, Iraq whenever possible, wells were located where the Amin was least thick above domal salt structures. It was observed that Sadooni, Fadhil N. (UAE U - [email protected]) the drilling rate of penetration (ROP) in the Amin formation exhibited a trend of increasing ROP (min/m) with increasing The Mesopotamian Foredeep Basin of southern Iraq acoustic impedance (AI), as obtained from the wireline logs hosts more than 90 percent of Iraq’s proven oil reserve. of carbonate stringer wells. Hence, a deterministic acoustic The supergiant fields are the result of a combination impedance inversion of the seismic data was performed to of contemporaneous growth due to the Hormuz salt provide a prediction of ROP from AI at the location of an diapirism, and the relative basement-blocks displacement. appraisal well, Rabab-2. One of the nearby wells was used The basin was dominated during the Early Cretaceous by as input to the computation, and another well was used as a a low-energy carbonate ramp that underwent frequent blind calibration point, where the inverted AI was found to gradual clastic invasions reflected in fluvial-deltaic- mimic the ROP trend. Successful utilization of the inverted marine clastic sequences. The ramp was converted into a AI at Rabab-2 as a prediction tool for ROP resulted in using block-faulted shelf/platform by the end of the Cretaceous. three drill bits as opposed to a planned eight to drill through Some of these rimmed shelves were characterized by the the Amin Formation. Furthermore, continued advances in presence of basin-margin rudist build-ups and associated drill bit technology when combined with AI’s predictive with sabkhas and lagoons to the west. Within the three characteristics resulted in more efficient planning and groups of the lower, middle and Upper Cretaceous referred drilling of the Amin conglomerates (estimated saving of to as the Thamama, Wasia, and Aruma groups in the Gulf 20 rig days). Crucially, teamwork and close communication region, seven major sedimentary cycles are recognized. between the geoscientists and the drilling team ensured Three of these cycles are a�ributed to the Lower Cretaceous that optimal decisions were made with regards to bit trips. Thamama Group, and each of the Wasia and Aruma groups The drilling success realized by using AI to predict ROP are divided into two cycles. Each cycle contains well- at Rabab-2 has made the tool a necessity for future wells recognized stacked carbonate and sandstone reservoirs in this area. To date, this drill-bit optimization has been overlain by multiple, tight carbonate, shale and evaporite successfully implemented in five further wells, yielding seals. Potential source rocks are either the marly limestones substantial savings. and shales of the Jurassic Sargelu, Naokelekan and the Chia Gara formations, or the Lower Cretaceous Balambo Formation. Indigenous source rocks within the above cycles (339-Oral) Fracture modeling of the Shu’aiba may also generate some of the hydrocarbons. Production Formation, Idd El Shargi North Dome field, started during the 1940s from the fields of Zubair and Offshore Qatar Rumaila South by the Basra Petroleum Company (BPC). Other fields were developed later by Iraq National Oil Sa�erfield, Will (Occidental - will_sa�[email protected]), Company or as joint ventures with foreign contractors Charle Gamba (Occidental), Sco� Burns (Occidental), Tim during the late sixties and seventies. Most of the production Davis (Occidental), Avnish K. Rajvanshi (QP), Paul La comes from structural traps in gentle, structurally simple, Pointe (Golder) and Raed Nasr (Schlumberger) long, homoclinal structures such as Rumaila or West Qurna. Image log, lost circulation, and seismic data were used to The Mesopotamian Basin might contain more potential oil construct a discrete fracture network model (DFN) of the systems within the deeper strata of the present fields. More Shu’aiba limestone reservoir at Idd El Shargi North Dome reserves are likely in the stratigraphic traps of the Mishrif,

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field (ISND), Qatar. The purpose of the modeling wasto (352-Poster) An assessment of undiscovered capture both the large-scale fracture corridors mapped oil and gas resources of the greater Silurian from seismic and well penetrations as well as background Qusaiba-Paleozoic total petroleum system of micro-fracturing visible in image logs. With the use of this method, a robust model of fracture intensity and the Arabian Peninsula orientation was constructed to guide water-flood planning. Schenk, Christopher J. (USGS - [email protected]), Thomas The Shu’aiba reservoir at ISND is a high porosity limestone S. Ahlbrandt (USGS) and Richard M. Pollastro (USGS) with low matrix permeability. The presence of fractures both along conductive fault corridors and interspersed The Qusaiba Member of the Silurian Qalibah Formation in the matrix creates enhanced permeability. Wells which was deposited over the northern and eastern part of the intersect fracture trends typically produce at high volumes Paleozoic passive margin that now forms the eastern part and recoveries relative to wells located solely in the matrix. of the Arabian Peninsula. The Qusaiba Member is a major An extensive database of horizontal image logs was used marine source rock for hydrocarbons from the Wadi Sarhan as the primary basis for the model. Fluid losses while Basin in the north, to the Rub’ Al-Khali Basin to the south. drilling and production data were used to further constrain The Qusaiba source rock interval in these basins is as much placement and orientation of conductive fracture trends. as 75 m thick, with TOC values ranging up to 20 percent Following calculation of fracture intensity and orientation, and averaging about 4 percent. Qusaiba source rocks are the model was calibrated against available dynamic data. generally thermally mature or overmature for gas in the As a final step the DFN background fracture model was central parts of the basins, and are thermally mature for combined with the large scale fracture a�ributes to create oil along the margins of the basins, as demonstrated by simulation grid properties. The DFN model incorporated the recent oil fields discovered in central Saudi Arabia. all available geologic and engineering data to calculate, on Reservoirs are mainly carbonate rocks of the Permian Khuff a cellular basis, directional fracture permeability, fracture Formation and clastic rocks of Ordovician, Devonian, porosity, and sigma factor. The DFN approach in this and Permian age. Six assessment units defined within example, is a successful method of modeling a complexly the Greater Silurian Qusaiba-Paleozoic Total Petroleum fractured reservoir, which serves as the basis for dual System in the Arabian Peninsula were assessed for permeability simulation. undiscovered petroleum resources, providing total mean estimates of 808 TCFG, 37 BBO, and 51 BBNGL. Most of (308-Poster) 3-D visualisation for non- the hydrocarbons discovered and produced to date from conventional wells in Kuwait this petroleum system have been conventional gas fields from the Qatar Arch and from the extension of the Qatar Saxby, Ian P. (BP - [email protected]), Hanadi Al-Qallaf Arch in Iran, indicating that significant potential may exist (KOC) and Thomas Radford (BP) in other basins of the Arabian Peninsula. In the central part of the Rub’ Al-Khali Basin, rocks of this petroleum In 1996 KOC acquired 3-D seismic surveys to cover the system may host an unconventional or basin-centered gas major producing fields. The total surface area covered accumulation, although a definitive interpretation of an 4,835 sq km (> 50 townships). Analyzing each seismic unconventional basin-centered gas accumulation cannot dataset alone ‘amputates’ the regional structural geology. be made with data available to us. Production ‘sweet spots’ Structurally, the fields are predominately faulted anticlines within the postulated basin-centered gas accumulation with four-way closure. The structures are a result of large- may be associated with fractured reservoirs along regional scale strike-slip movement. Simultaneous visualization structural lineaments. of multiple seismic a�ributes (coherency, spectral decomposition, acoustic impedance, and amplitude) on the (228-Oral) Central Oman field static dune merged 3-D volumes allows identification of subtle faults and increased quality of well placement. Generally, the solution faults have li�le vertical offset, but act as pressure barriers Schjolberg, Kolbjorn (PDO - [email protected] and flow baffles. Calibration of the reservoir properties .om), Christine Huegen (PDO) and Nigel Benjamin (CGG) across the faults requires the detailed integration of all available data. During 2002, several non-conventional wells Recently, the Central Oman area has seen increased have been drilled in Kuwait in three different horizons. The exploration activity at the Gharif level corrsponding to wells had different technical objectives for different projects. reflections at 900–1,500 milliseconds (msec) two way time The first project was a horizontal water disposal well in the (TWT). Gharif traps are low-relief structures (10-15 msec), Cretaceous Shu’aiba carbonate. The well was planned to and the reservoirs consist of thick sand bodies in the lower penetrate a tight carbonate and then drill into a region of Gharif member, and channel sands of complex distribution karsting. The second project was a deep sub-horizontal in the middle and upper Gharif members. Resolving bedding parallel well into the Jurassic Najmah-Sargelu medium and long-wavelength statics has emerged as a over pressured fractured shale. The objective was to access critical success factor in determining structural closures. high gravity oil below the Gotnia salt. The third project This is complicated by the fact that part of the area is was a horizontal infill drilling program also conducted in covered by sand dunes. Historically in PDO, sand dune the Cretaceous Mauddud carbonate in conjunction with related static anomalies have been resolved by application a seawater injection scheme. The wells were designed to of an elevation static, followed by a constant one or two- avoid the faults that have been mapped from the new layer sand velocity correction, and a pass of refraction seismic efforts. In all cases, the final location was chosen picking. Results were not always satisfactory, so an from the 3-D visualization of the seismic. improved solution was needed for the Gharif exploration

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campaign. A pilot project was initiated as part of a joint (299-Poster) Wadi effect on seismic PDO/CGG effort. A refined dune static solution was derived interpretation based on the old method. Subsequently, the method was improved by more accurate definition of the dunes, both Sedgeley, David (Saudi Aramco - david.sedgeley@aramco. in terms of sand velocity and dune distribution, as well as com), Ching-Chang J. Tsai (Saudi Aramco) and application of residual refraction statics followed by two Khalid Al-Mahmoud (Saudi Aramco) passes of reflection static picking. An alternative method was tested based on first break picking (GLI3-D), but did In a geophysical sense, a wadi is a near-surface channel not give satisfying results due to the variable distribution filled with very low velocity sediment. Depending upon of near offsets. This is mainly caused by the 3-D acquisition the size of the wadi with respect to the seismic acquisition method, combined with variable topography of incised geometry, it can cause static and dynamic time distortions river valleys, escarpments, sand dunes and gravel plains. that may eventually lead to interpretation errors. The The refined dune static solution has been applied to 2,250 extreme effects of a large wadi are o�en unresolved by sq km of newly acquired 3-D data, as well as old existing production seismic processing and must be addressed 3-D surveys. Results show improved stack response and by more detailed analyses. In this project, the effects of seismic-to-well matches. In the Hawqa 3-D survey, where a wadi were studied by forward ray-tracing a model of upholes were drilled, a good match between the seismic the wadi. Model acquisition parameters are based upon and uphole statics was observed. Once the new method actual field parameters previously used to acquire a high- was established and proven, it was applied with success on fold 2-D dataset over an existing major wadi in eastern existing 3-D surveys in dune-free areas as well. Saudi Arabia. The model is constructed using structural and rock property information from the seismic data and surrounding well control. The location of drainage systems (194-Oral) Integrated 3-D static reservoir is o�en controlled by underlying structure, and in this modeling of a giant carbonate field in the model a vertical fault with 200 � of throw has been inserted Lower Cretaceous of Abu Dhabi beneath the wadi. The ability to correctly interpret this fault is used as a primary measure of the accuracy in processing Sco�, Jason (ADCO - jsco�@adco.co.ae), Andrew Gombos the model seismic data. The results of several processed Jr (ADCO), Karri Suryanarayana (ADCO) and versions of the model demonstrate its sensitivity to Khalid Al-Amari (ADCO) parameter analysis and application. In particular, the initial velocity analysis must be accurate beneath and adjacent Recently acquired 3-D seismic data over a giant onshore to the wadi. The correct stacking velocity field becomes field in Abu Dhabi reveals new insights from the extremely highly distorted across the wadi, and cannot be derived by high-resolution images of the reservoir structure and averaging adjacent velocities from unstructured areas. Use internal architecture. The important aspects of this data of laterally-smoothed velocities is especially damaging to were captured in a 3-D static reservoir model and combined the stacking at deeper times where more offset ranges are with a new neural network based Reservoir Rock Typing incorporated. Errors in velocity application are exacerbated (RRT) scheme. Seismic a�ribute analysis within the seismic by the application of autostatics; the combined effect is sequences allows the identification of various rock quality to add spurious faults and cause segmentation of true trends and anomalies. In the back-reef portion of the field faults. This happens regardless of whether shallow or deep a series of high amplitude bodies define the location and cross-correlation windows are used. If the initial velocity geometry of low porosity/permeability tidal channels and application was inaccurate, adding random noise to the ponds. In the prograding fore-reef portion of the field, model signal may also cause the application of autostatics seismic amplitude can be correlated with transitions from to create erroneous structures that are significantly different good reservoir quality nearshore high-energy grainstone from the noise-free case. facies, through to deeper-water, low-reservoir-quality wackestones and packstones. Based on a limited number of cored wells in the field 15 separate RRTs have been (146-Oral) Nahr Umr sand reservoir defined. A recent log-based study utilizing neural networks development in the Al Shaheen field: has allowed the existing RRT scheme to be successfully reservoir characterization enhancement migrated into about 350 vertical uncored wells on the using long horizontal wells field. The new static reservoir model has been calibrated with various dynamic data to improve the confidence in Sehested, Charlo�e L. (Maersk - [email protected]), its validity. Production spinner logs display marked inflow Kenneth A. Nielsen (Maersk) and anomalies that correspond to RRT boundaries. Open-hole Troels Albrechtsen (Maersk) pressure measurement data collected in recent wells, display numerous large pressure barriers that correspond The Al Shaheen field is situated in Block 5 offshore Qatar and to seismic sequence boundaries and changes in RRTs. is operated by Maersk Oil Qatar under an EPSA with Qatar The final calibrated static model successfully captures all Petroleum. The mid-Cretaceous Nahr Umr reservoir is one of relevant new data sources for the field. Co-visualization three main reservoirs in the Al Shaheen field. The reservoir, of various model properties allows rapid understanding which is time-equivalent to the muddy argillaceous Nahr Umr of the field complexities and generates new insights into Formation in the United Arab Emirates, has a total thickness the mechanisms controlling fluid flow and by-passed oil. between 5 and 20 � and comprises several thin, oil-bearing The model is being utilized to enhance the ongoing field sands. The reservoir sands represent a transgressive sand development, geosteer horizontal wells and is the basis for sequence deposited in a marginal-marine se�ing. The sand an improved dynamic simulation model. sequence has proven to be continuous but highly variable,

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with occasional pinch-outs of individual sands. Development models for use in waterflood simulation studies. Large of these thin oil-bearing sands with long horizontal wells has permeability multipliers were required to match well been highly challenging. The pre-drilling characterization tests, production logs did not match those one might of the sands was mainly based on data from vertical wells produce from the permeability distribution in the spread over the large area covered by the field. Drilling and well, and history matches were difficult to obtain. The logging results of new long horizontal wells have provided Mauddud is now interpreted as a reservoir bearing short, significant improvements to the characterization of the Nahr sub-vertical fractures that are: (1) not measured with Umr sand reservoir. In the very thin-layered sand reservoir, routine core analysis programs; (2) difficult to detect with the horizontal wells have provided first class information borehole imaging techniques; and (3) act as thief zones regarding the lateral variability of reservoir quality. Further, to injected water. This lead to a challenge of modeling they have provided insights into areal variations in sand permeability in the well that matched both well test and thickness through detailed interpretation of horizontal well production logs, and was useable in the 3-D reservoir undulating within the reservoir. The latest development model. A model of porosity contrast is used to vertically plan includes drilling of 18 long horizontal production and distribute fractures in the reservoir. Permeabilities are injection wells targeting the Nahr Umr reservoir. This study assigned to these intervals through an iterative process presents the geosteering data gathering and the integration using values determined from production logs. In this of these data to enhance the reservoir characterization in manner, fracture permeability is placed in tighter reservoir order to optimize well placement. intervals whenever it occurs between more porous layers. This methodology has been used to match both well test results and production logs profiles. It forms the basis for (125-Poster) Revised structural distributing permeability in two reservoir models. Recent interpretation of Sabiriyah field, Kuwait drilling results from horizontal wells have added a much needed third dimension to the well model. Successful Sercombe, William J. (BP - [email protected]), Ian P. borehole imaging in these wellbores show there is nearly an Saxby (BP) and Talal S. Al-Failakawi (KOC) order of magnitude increase in fractures interpreted in low The structural geology of the giant Sabiriyah field in North porosity layers. Stoneley waveform analysis in horizontal Kuwait has undergone a significant reinterpretation. wells shows more reflections and higher permeability in The Sabiriyah field is a low amplitude four-way closure low porosity layers. We believe these results confirm the twenty kilometers in length on the Burgan Arch system. tendency for this reservoir to have significant fracture The principle oil reservoirs are in the Cretaceous carbonate permeability in tight reservoir layers. Mauddud and clastic Burgan formations. Depth slice interpretations of amplitude, spectral decomposition and (29-Oral) Integrated reservoir description coherency from regionally merged 3-D seismic volumes and geostatistical modeling in Upper Burgan indicate a more complex and intense fault pa�ern than Reservoir, Raudhatain field, North Kuwait previously recognized. The complexity from seismic is supported by quantitative dipmeter analysis that also Shaikh, Abdul Azim (KOC - [email protected]), Craig indicates significant structural domain variance. The fault Rice (BP), Haifa Al-Ajeel (KOC), Peter F. Cameron (KOC) grids from seismic were mapped with fault-cut position and and Shehab Abdullah (KOC) throw in all wells. All the datasets were integrated in order to ensure consistency. The Sabiriyah field is interpreted as The Upper Burgan paralic to marine sedimentation process a restraining bend on an overall NW-SE sinistral strike-slip represents a complex cycle of transgressive-regressive fault system. Fault movement is associated with a number sequences during late Albian period in North Kuwait. of Mesozoic and Cenozoic tectonic events overprinted on an The shoreface and channel sandstones deposited in this earlier infra-Cambrian structural framework. The resultant environment hold significant quantity of in-place oil. NW-SE and NE-SW conjugate fault system and associated The reservoir has a production history of more than 40 Reidel faults within the field are new inputs to the revised years with peripheral water flood. An integrated study 3-D geologic model. The revised structure model will incorporating static and dynamic data has been carried be used to improve the static and dynamic models. The out to characterize the reservoir for flow simulation so as complex fault pa�ern will assist with the fluid flow and to formulate alternative development plans suitable for the compartmentalization issues associated with production, mature reservoir. Depositional history of the reservoir has well planning and water flooding. been described under three broad categories. The lower Upper Burgan reservoir consists of cycles of shoreface (326-Oral) Distributing fractures in well sands and marine shales. The marine shales are laterally extensive reflecting important high frequency sea-level models in the Mauddud Formation changes. A lowstand systems tract (LST) is interpreted in reservoirs, Raudhatain and Sabiriyah fields, the Middle Upper Burgan and represents a time during North Kuwait which a complex pa�ern of stacked channels were deposited. The estuarine shales are discontinuous and act Sercombe, William J. (BP - [email protected]), Ian P. as local baffles. The upper Upper Burgan of the sequence Saxby (BP), Craig Rice (BP), Deryck Bond (KOC) and was deposited during an overall transgressive event. The Talal S. Al-Failakawi (KOC) Upper Burgan depositional unit has been divided into 13 major layers bounded by laterally extensive markers. The Mauddud Formation reservoir experienced a case of A fine scale, faulted, geological framework captures the fracture denial during the construction of 3-D reservoir key depositional heterogeneity observed within the flow

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units. The main flow units were derived from correlations (494-Poster) Lithostratigraphy, between petrophysical properties and dynamic data. Fuzzy biostratigraphy, sedimentary environment logic was used to derive the flow units in terms flowfacies. and paleogeography of Nesen Formation 3-D facies models were generated using stochastic object modeling constrained by paleocurrent and general (Upper Permian) in central Alborz, northern distribution of channels. Flow facies exhibiting very high Iran: new sight to P/Tr boundary permeability were identified from well logs and specifically incorporated within the facies model to realize the water Shokravi, Gholamreza (Petropars - [email protected]) movement within reservoir. Seismic a�ributes were used and Ebrahim Ghaseminegad (Tehran U) as trends to guide the distribution of individual facies. The Upper Permian Nesen Formation outcrops in the Petrophysical parameters were generated using stochastic central Alborz Mountains, northern Iran. This formation simulation within the facies parameters. The paper was deposited on the passive margin of the northern side of describes the approach to reservoir characterization and the Lut Block, which was a part of Cimmerian Block. Plate building geostatistical models in detail. tectonics played an important role in the deposition of this formation, and the formation is closely related to the Abadeh- (304-Oral) Variation of structural style and Djulfa range. In order to study this formation two sections basin evolution in the Izeh Zone and Dezful were sampled: (1) Siah-Bisheh section, located near a small Embayment, Central Zagros, Iran village along the Tehran-Chalus road; and (2) Amol section, located 35 km from Amol along the Tehran-Amol road. The Sherkati, Shahram (NIOC - [email protected]) and study focused on the lithology, paleontology, microfacies Jean Letouzey (IFP) and sedimentary aspects of the Nesen Formation. In the Amol section, subaerial exposure, claystones and lateritic The Izeh Zone and Dezful Embayment are located in sediments of the basal Nesen Formation overlie the the central Zagros Mountains of Iran. This region was Ruteh Formation. In the Siah-Bisheh section, volcanic and tectonically affected by the Late Cretaceous Neo-Tethys- volcanoclastic rocks of variable lithology were divided Zagros obduction episode and the early Miocene Zagros into three units (lower, middle and upper). The underlying Orogeny when Eurasia collided with the Arabian Plate. New Ruteh Formation is covered by shale and limestone of fieldwork, geological maps, seismic data interpretation, the Nesen Formation. In total 11 microfacies (from lime and well information were used to prepare: (1) a regional mudstone and shales of deep sea to pisolitic packstone) balanced transect; (2) several updated isopach maps; and were recognized; these can be a�ributed to four different (3) tectonic subsidence curves. The analysis revealed the environments: (1) open sea; (2) bar; (3) lagoon; and (4) tidal structural style and its relationship to sedimentary facies flat. Vertical changes in microfacies and fossil evidence and the evolution of sedimentary depocenters. Furthermore indicate that the Permian sediments in central Alborz it shows compression and movements along NS-trending were deposited as a shallowing-upward cycle, consisting faults from Albian time, in addition to movements of higher frequency, meter scale, shallowing-upward along NW-trending faults in the Zagros basement which cycles (parasequences). The vertical and lateral changes predate the Neogene Zagros orogeny and influenced of the microfacies suggest that the Nesen Formation was the sedimentary basin. The depocenters migrated to the deposited in a rimmed shelf (Siah-Bisheh section) and southwest with time. During the Zagros Orogeny the a ramp (Amol section). The Nesen Formation deposits basement was involved in the main structures and below were diagenetically altered by several processes including: some folds. A new structural classification of the Zagros cementation, neomorphism, dissolution and replacement, sedimentary cover highlights the different mechanical silisification and bioturbation. Biostratigraphical studies behaviors of the formations in the stratigraphic column. It based on foraminifera show evidences for the existence of shows the existence of several local disharmonic horizons the latest Late Permian Changhsingian stage for the first that were activated during folding. These decollement time in central Alborz. levels separate lithotectonic units that accommodate shortening in different ways. The lower Paleozoic is the (419-Poster) Microbial sediment and basal decollement level throughout the studied area. The intermediate decollement levels are: (1) Triassic evaporites; chemostratigraphy in the Soltanieh (2) Albian shales; (3) Eocene marls; and (4) Miocene Formation, northwest Iran evaporites. The beds associated with the intermediate decollement have variable facies, and usually constitute Siabeghodsy, Aliasghar (U Urmia – [email protected] the most efficient caprocks. The wavelength, amplitude and rmia.ac.ir) style of folding is closely influenced by: (1) the lateral facies The Soltanieh Formation outcrops along the ridges east and thickness variations of the intermediate decollement of the village of Chapoghlu in the Soltanieh Mountains. horizons; (2) the sedimentary overburden; and (3) the Coordinates of base of section: 36°11’36”N, 48°55’29”E. inherited fault pa�erns. In many cases, surface structures Three major subdivisions are distinguished in the do not necessarily coincide with deeper hydrocarbon formation: (1) Lower Dolomite Member (123 m thick); structural traps where these disharmonic decollement (2) Chapoghlu Shale Member (274 m); and (3) Upper horizons were involved in folding. Exploration wells that (main) Dolomite Member (790 m). Stromatolites are fairly target reservoirs below the intermediate decollement levels common in the higher dolomites and dolomitic limestones should take these factors into consideration. of the type-Soltanieh section, and are common throughout

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the formation; they include forms of Microbial mat that variations caused by near-surface statics on the 3-D has been described at this study. The Microbial structure dataset. The high structural variations of the shallow is commonly recognized with stromatolite. A comparison horizons do not appear to be supported by wells drilled of Carbon–isotope (C13) chemostratigraphy versus the in the areas. Additionally, several prospective areas south stratigraphic column of the Soltanieh Formation shows and east of Ghawar structure include many subtle traps that Precambrian-Cambrian Boundary occurs in the Upper having only 10-20 milliseconds of structural closures. Dolomite Member of the Soltanieh Formation. The Soltanieh Small-order residual statics of less than 10 milliseconds Dolomite, with or without the intervening Chapoghlu becomes critical to correct for the structural dips in these Shale, has been traced through a great part of northern, areas. Conventional methods of solving the statics are not central and eastern Iran; the westernmost occurrences completely adequate. Implementation of state-of-the-art known so far are in the Lake Uromieh area. statics solutions and depthing techniques were applied to overcome these problems. A new method of computing the statics solution was implemented, where pseudo-upholes (370-Poster) Tectono-stratigraphic evolution were generated using the information from 3-D data. The of the southern Tethyan margin, North analysis involved creating a two-layer velocity model. Africa and Arabia: an updated sequence The seismic sections analyzed using the two-layer model stratigraphic interpretation mitigated the near-surface effects and accurately portrayed the dips on the subsurface seismic events. The computed Simmons, Michael D. (Ne�ex - mike.simmons@ne�ex.co static difference between the earlier velocity model and m), Peter R. Sharland (Ne�ex), Roger B. Davies (Ne�ex), two-layer model were applied to the time maps for key David M. Casey (Ne�ex) and David Boote (Consultant) horizons. The corrected time maps were used to make depth maps at the top of the reservoir using a ‘layer-cake’ Prior to the opening of the Red Sea in the Neogene, approach. The results from the corrected maps give be�er North Africa and Arabia were part of the same southern definitions of the structural configuration compared to the Tethyan Gondwanan continental margin. To be�er resolve maps based on the earlier velocity model. the tectono-stratigraphic evolution of this southern Tethyan margin, we present a chronostratigraphic chart, running from Morocco in the west to Oman in the east, (79-Poster) The Makran Accretionary which correlates the sequence stratigraphy of these two Complex: tectonic and structural hydrocarbon provinces against latest published timescale architecture of an active accretionary data. Refined sequence stratigraphic correlation allows complex the plethora of disparate lithostratigraphic schemes in use across this vast region, to be placed within coeval Skarpnes, Oddvar (Statoil - [email protected]), Oyvind second-order depositional sequences. The stabilization of Skinnemoen (Statoil), Seyed Mahdi Fazeli (NIOC), Alireza the stratigraphy at this scale also provides the framework Rostami (NIOC) and Bahman Soleimani (NIOC) to correlate and map higher-frequency surfaces (maximum flooding surfaces and sequence boundaries) between The Makran Accretionary Complex formed as a result of these continental plates. The sequence stratigraphic the northward subduction of the Neo-Tethys underneath interpretation presented here updates that published in the Eurasian Plate, a process that has been ongoing since GeoArabia Special Publication 2, and integrates recent Early Cretaceous. The accretionary complex extends for relevant literature. North Africa and Arabia were both more than 900 km, from the Zendan Fault in the outer part affected by the Hercynian, Cimmeride and Alpine of the Strait of Hormuz, to the Ornach Nal Fault in Pakistan. orogenies, and by synchronous glacial events in the end The width of the complex is about 500 km. The present Ordovician and Permo-Carboniferous. Throughout much accretionary front is located 230 km offshore. The Persian of the Mesozoic–Paleogene they occupied a position on the Carpet seismic survey acquired in 2000 (PC-2000) is the first tectonically quiescent margin of southern Tethys. In these seismic dataset covering the whole Iranian offshore part of later periods carbonate deposition prevailed, influenced the Makran Accretionary Complex. Based on the PC-2000 by global eustacy, although progradation of clastic systems seismic dataset, satellite gravity and bathymetric maps, from ancient shield areas at times of synchronous upli� are ten structural elements/provinces directly or indirectly notable features of both North Africa and Arabia. related to the accretionary processes have been defined in the outer Hormuz and the Iranian part of the Oman Sea. The offshore continuation of regional onshore strike-slip (244-Poster) Improving structural distortions faults play an important role in conveying the tectonic by mitigating near-surface effects and stress eastward, as continent-continent collision takes place modifying shallow velocity models in the western part of the area. The convergence/collision along the Zendan Fault is very oblique, resulting in right- Singh, Ravi K. (Saudi Aramco - [email protected] lateral transpressional tectonics and structuring. In the m) and Robert E. Ley III (Saudi Aramco) southwestern part of the survey area thrusting towards the north is interpreted as toe-thrusts related to large In Saudi Arabia, complex surface and near-surface scale listric faulting along the continental shelf of Oman. conditions prevent seismic reflections from properly The defined structural elements and provinces clearly imaging the seismic events associated with the subsurface demonstrate the continuity in the accretionary processes. formations. Presence of sand dunes, jebels, wadis and Defining structural events in an accretionary complex is sabkhas causes the heterogeneity of the near-surface therefore meaningless. ‘Structural events’ in an accretionary conditions. Shallow horizons exhibit high structural

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complex should be viewed as responses to subduction robust modeling algorithms able to take into account for rates, sediment properties, sedimentary thicknesses, and modal superposition are necessary. Acquisition has to be similar geological aspects. properly planned to obtain quality data in an adequate frequency range: (1) processing and inversion should allow the interpretation of the apparent dispersion characteristics (442-Oral) Reducing drilling risk using evaluating the local quality of the data; (2) filtering coherent seismic data processing attributes noise due to other seismic events; and (3) considering energy distribution, higher modes of propagation and Smith, Wayne (Saudi Aramco - a�enuation. [email protected]), Khalid Mahmoud (Saudi Aramco), Barton Payne (Saudi Aramco) and Hashim A. Hussein (Saudi Aramco) (183-Oral) Geochemistry and natural salt closure combine to prevent a costly Drilling locations, picked on structural seismic time data, workover: case study from a deep over- can be qualified as either high or low risk by using seismic processing a�ributes. The time dimension of a seismic pressured well in South Oman volume can be distorted by near-surface features, resulting Soek, Harry (PDO - [email protected]), Mark Laws in sub-optimal velocities, statics, and datum correction. (PDO), Paul Taylor (Shell) and Janos Urai (Aachen U) These near-surface artifacts o�en permeate deeper in the data, causing locally time-shi�ed horizons, which mislead A number of appraisal wells have been drilled to assess the interpretation of the seismic data. During the processing the economic viability of miscible gas injection to enhance sequence, we keep track and save many a�ributes such as oil recovery from intrasalt stringer reservoirs in the velocities, statics, elevation, datum corrections, and location Harweel cluster area in South Oman. The Precambrian of surface features. Later, the a�ributes are compiled in carbonate stringers are fully encased in salt, deep, highly such a fashion as to indicate these false time structures. over-pressured and contain sour light oil. Operational The advent of new, more powerful visualization tools difficulties whilst running a liner over the reservoir section allows us to easily merge these a�ributes with the seismic in one of the appraisal wells, combined with a sub-optimal time volume, giving a level of confidence in the validity of cementation, led to a gradual build-up in pressure on time structures. The same technique can be applied early the well’s A-annulus. This pressure build-up threatened in the processing sequence as a quality control, eliminating the integrity of the well and could have potentially lead many incorrect structures from the final data volume. We to a costly workover. A number of steps were therefore use a 3-D pre-stack time-migrated volume to demonstrate undertaken to determine the cause of this build-up and to the effectiveness of this tool. With careful selection of color plan remedial measures: (1) geochemical fingerprinting of maps and opacity, we superimpose the seismic a�ributes the leaking oil and comparison to similar data from cu�ings into the final amplitude volume. Cu�ing through this and core samples to be�er understand the origin of the oil. new composite time volume allows us to easily correlate The oil could have originated from any of the multiple horizon perturbations to near-surface anomalies. In this oil-bearing zones penetrated by the well, or it could have way, probable false time structures are highlighted and been introduced during well construction. (2) A pro-active passed on to the interpreters to assist them in lowering the annular pressure monitoring program; including pressure risk associated with planning well locations. build-up and bleed off cycles to investigate pressure behavior over time and under different conditions. (3) (473-Oral) Surface Wave Methods for near- A study into the behavior of salt as a means to provide surface characterization a natural seal against the liner instead of cement. The geochemical work allowed an unambiguous identification Socco, Laura V. (Politecnico di Torino - valentina.socco@p of the source of the oil. Study work on the salt has identified olito.it) and Claudio L. Strobbia (Politecnico di Torino) the likelihood and time required for the salt to close around the liner. The salt closure is mainly driven by the quality of Surface Wave Methods (SWM) are very powerful tools for the cement and the assumed liquids behind the liner. A pro- the near-surface characterization of sites: the shear velocity active pressure surveillance program has underpinned this and the damping ratio can be obtained overcoming, in some salt closure prediction. Recent observations have shown cases, the limitations of other shallow seismic techniques. that the pressure build-up on the annulus has ceased, which For complex near-surface applications, surface-wave results implies that the salt has crept and sealed off the annulus represent a useful integration of the information inferred by between the liner and wellbore. It has therefore effectively other seismic techniques. Information can be o�en a�ained, provided a secondary barrier hence restoring the integrity with no additional acquisition, by extracting the data from of the well. A clear understanding of the causes and sources the ground roll present in traditional P-shot gathers. But of the problem has emerged. This be�er understanding, in situations that are critical for other seismic methods, together with a surveillance program which supports SWM can even be an effective alternative to reflection and the annular pressure prediction (based on gradual salt refraction: data can be acquired also in noisy environments closure) has led to the recommendation not to work over and can be correctly interpreted also in the case of velocity this well for integrity reasons. It has saved the company inversions and hidden layers. The different steps of SWM a considerable amount of money and has triggered a have to be optimized considering the conditions imposed conceptual cementation design study to investigate how by the scale of near-surface problems that o�en allows salt can be exploited deliberately to provide well integrity only the acquisition of apparent dispersion characteristics: in future wells.

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(132-Oral) Learnings from a focused Norway and worldwide datasets. Multi-variate statistical exploration campaign in Central Oman analyses are used to evaluate the significance of these diamondoid hydrocarbons. Spring, Laurent (PDO - [email protected]) and Mohamed S. Al-Harthy (PDO) (273-Poster) Cenozoic sequence A�er the (re) discovery of the Hawqa field in 2002, the stratigraphy, Arabian Platform and Gulf most significant Gharif find in the last 10 years, PDO Exploration set a goal to evaluate and unlock the potential Steinhauff, D. Mark ExxonMobil( - mark.steinhauff@exxon of the Gharif Formation in Central Oman by undertaking mobil.com), Chengjie Liu (ExxonMobil) and the following activities. (1) Setup a multi-disciplinary team George J. Grabowski Jr. (ExxonMobil) of geoscientists, petroleum engineers, and other specialists Nine hiatuses or major sequence boundaries (SB) are to focus on various aspects of the Gharif play in Central recognized in Cenozoic strata throughout the Arabian Oman. (2) Embark on an extensive 3-D acquisition program Platform and Gulf: (1) a basal Tertiary (Danian to lower (approximately 2,250 sq km), coupled with uphole drilling Selandian) SB separating the Tertiary Umm Er Radhuma and Low Velocity Layer (LVL) surveys. (3) A�empt new (UER) Formation from the Upper Cretaceous; (2) a mid- approaches to (re) processing of seismic data by addressing Thanetian to upper Ypresian SB within the lower UER; (3) surface statics and multiples suppression problems that a lower Lutetian SB indicated by the absence of the ‘Rus’ traditionally blur seismic images of very low-relief (< 20 anhydrite from some anticlines; (4) a mid-upper Lutetian milliseconds two-way time) structures. (4) Undertake a SB; (5) an uppermost Lutetian to Bartonian SB; (6) a lower staged drilling campaign to test geological and geophysical Rupelian SB at the top of the Dammam Formation; (7) a models, with clear milestones to continue or stop lower Cha�ian unconformity separating Rupelian 2nd- exploration in the Gharif of Central Oman. One year a�er order sea-level highstand deposits from the mid-upper the onset of the project, an ‘A�er Action Review’ (AAR) Cha�ian second-order lowstand; (8) a lower Burdigalian was conducted. This very structured event helped PDO SB separating Asmari carbonates from overlying Asmari to understand how well the objectives of Central Oman siliciclastics; and (9) an upper Serravallian SB not prominent Gharif campaign were met, and what were the key learned over shelf areas. The Serravallian, Tortonian, and Messinian experiences–both positive and negative–that resulted from stages are represented by shale and evaporite in the this project. The structure of the AAR concentrated on: (1) foredeeps along the Iran and Oman margins. The Tortonian the objectives; (2) what actually happened; (3) what were the and Messinian are represented by mixed siliciclastics, learned experiences; (4) what should be done differently-if carbonates, and evaporite deposits across the shelf. anything-for the overall planning of the project; (5) the way Sequence boundaries are typically conformable in the subsurface uncertainties are approached; and (6) drilling foredeeps and subtle towards the Qatar Arch. For example, aspects of a focused exploration effort. tens of meters of strata are typically truncated from sequences over 100s of kilometers in the offshore United (307-Poster) Diamondoid hydrocarbons in Arab Emirates. Greater stratal thicknesses are truncated characterization and source-oil correlation from salt-cored anticlines (Dammam and Awali) including of secondary altered oils; results from the entire lower Lutetian sequence comprising ‘Rus’ subsurface evaporite. Paleogene through mid-Miocene onshore Iran sequences formed in response to global eustatic sea-level fluctuations in a slowly to moderately subsiding foreland Steen, Arne S. (Norsk Hydro - [email protected] se�ing. Post-mid Miocene deposition was influenced by the m) and Linda Schulz (Norsk Hydro) late Neogene Zagros Orogeny. Secondary alteration processes, like biodegradation, evaporative fractionation and cracking, affect the (319-Oral) Correlation of the Permian rocks hydrocarbon composition and consequently the geochemical of Oman and Saudi Arabia signature of the sample. Diamondoid hydrocarbons are known to be more resistant to thermal cracking or Stephenson, Michael H. (BGS - [email protected]), John biodegradation than most other petroleum components. Filatoff Saudi( Aramco), Uzma Mohiuddin (PDO), Randall Diamondoid signatures are used to report hydrocarbon A. Penney (PDO), Peter L. Osterloff (Shell) and maturity, source rock facies and levels of biodegradation or Moujahed I. Al-Husseini (GPL) thermal cracking. Diamondoid hydrocarbons are naturally occurring constituents in petroleum. These low-molecular- The recent publication of an integrated palynological weight hydrocarbons have a diamond-like cage structure. biozonation for Oman and Saudi Arabia has allowed the The simplest member of this class of compounds is the C10 sequences in those countries to be correlated throughout cage structured adamantane. The next homologue of the most of the Permian System. In the scheme, three biozones diamondoid hydrocarbon series is diamantane, followed are established in the palyniferous Lower Permian sequence by triamantane, etc. The hydrocarbon signature in outcrop in Oman, and to some extent these are recognizable in and seep samples are typically affected by biodegradation sequences of central and southern Saudi Arabia. These or evaporative alterations. The potential of this diamondoid biozones, OSPZ1 - OSPZ3 (Oman and Saudi Arabia hydrocarbon approach is demonstrated on a set of Iranian Palynological Zones), are associated with the Al Khlata samples, including outcrop samples from known source and Lower Gharif formations of Oman and the Unayzah C rock formations versus borehole source rocks and reservoir and B members of Saudi Arabia and are of Stephanian to fluids. The results are compared to regional studies offshore Artinskian age. The OSPZ3 zone itself is further subdivided

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into three subzones which are exclusively associated Dhabi as well as outcrop data, a sequence stratigraphic with the Lower Gharif member. The succeeding three framework has been established for the Barremian Kharaib biozones, OSPZ4-OSPZ6, are established in the episodically Formation. The Kharaib Formation can be described by palyniferous Middle and Upper Permian sequences. These a second-order supersequence (base lower ‘dense zone’ are associated with the Middle and Upper Gharif members to base upper ‘dense zone’ = Hawar Shale), built by two of Oman, and the Unayzah A member and the ‘basal third-order sequences. The lower third-order sequence Khuff clastics’ of Saudi Arabia. They range in probable starts at the base of the lower ‘dense zone’ and is capped age from Artinskian to Capitanian. The correlation and by a pronounced sequence boundary (exposure surface) characterization of OSPZ4-OSPZ6 has been rather tentative some ten feet below the middle ‘dense zone’. It is overlain until now, but work done since the publication of the new by a third-order sequence that is bounded on top by a biozonation has allowed: (1) subdivision of the OSPZ5 regionally correlative sequence boundary below the upper biozone; (2) improved palynological characterization of the ‘dense zone’. Second- and third-order sequence boundaries Upper Gharif member and the Oman Khuff Formation; (3) and maximum flooding surfaces, as well as fourth-order correlation between the surface Upper Gharif in the Huqf flooding surfaces were identified in core and tiedto outcrop area in Oman, and the subsurface in areas to the well-logs. Eleven fourth-order parasequence sets that west; (4) improved understanding of the paleoenvironments built the two third-order sequences show predominantly and paleoecologies seen in Gharif and Khuff sediments. aggradational stacking pa�erns, typical for greenhouse cycles. On the basis of faunal content, texture, sedimentary structures, and lithologic composition, thirteen reservoir (414-Poster) Delineation of faults lithofacies and eight non-reservoir (dense) lithofacies have and fracture zones using Spectral been identified. Lithofacies range from open platform, Decomposition analysis in the Idd El Shargi lower ramp, to restricted platform subtidal, to intertidal field, Qatar environments. Intensively bioturbated wackestones and packstones, and interbedded argillaceous limestones Street, Karl D. (Landmark – [email protected]), Sco� D. characterize the lower and middle ‘dense zones’ and Burns (Occidental) and Abdulla Seliem (Occidental) correspond to the early transgressive systems tracts of the two third-order sequences. Locally, mudcracks, blackened The geophysical analysis technique, Spectral grains, and rootlets have been observed. The reservoir Decomposition, enables the geophysicist to analyze the zones correspond to the late transgressive and, dominantly, seismic data in more detail than ever before. This technique highstand systems tracts characterized by parasequences uses the Discrete Fourier Transform to break down the that show shallowing-upward trends from open lagoon, broadband seismic wavelet into one Hertz (Hz) frequency burrowed skeletal wackestones to skeletal, peloidal slices enabling greater resolution and characterization packstones, algal, coated-grain grainstones/rudstones, of seismic data. This analysis tool has recently become and rudist, algal floatstones. Well-developed Thalassinoides available to the interpretive geophysicists across the world firmgrounds (Glossifungites surfaces) indicate temporary with the release of Landmark’s Spectral Decomposition cessation in sedimentation and cap several parasequences. so�ware. However, all publications to date have focused on using Spectral Decomposition for the stratigraphic analysis of clastic channel systems. The Idd El Shargi field consists of (204-Poster) Sequence stratigraphy and two elliptical, faulted domes, aligned approximately north- reservoir quality characterization of the south and is Qatar’s oldest producing offshore field. Oil Upper Jurassic Arab and Asab formations, production is from the Shu’aiba, Arab and Araej carbonate Abu Dhabi reservoirs. Spectral Decomposition has been used to delineate faults and fracture zones in these reservoirs in Strohmenger, Christian J. (ADCO - cstrohmenger@adco. more detail than any other geophysical analysis technique co.ae), Abdelfatah El-Agrab (ADCO), Rafael M. Rosell III tried before. Other techniques previously used to define the (ADCO), Suleiman Ali (ADCO), Jean Francois Dervieux faults include: dip-azimuth, coherency, and edge detection, (ADCO), Na’ema Al-Zaabi (ADCO), Ahmed Khouri but none have matched the quality and resolution of Spectral (ADCO), Tom Slater (RRI), Anna L. Ma�hews (RRI) and Decomposition. Since November 2002 all wells have been Marguerite J. Fleming (RRI) drilled using the Spectral Decomposition so�ware. A sequence stratigraphic framework has been established for the Kimmeridgian-Tithonian Jubaila/Arab and Asab (122-Oral) Sequence stratigraphy and formations offshore and onshore Abu Dhabi. A total of reservoir characterization of the Lower six third-order composite sequences have been identified Cretaceous Kharaib Formation, Abu Dhabi called J70 (Jubaila/Arab-D), J80 (Arab-C), J90 (Arab-B), J100 (Arab-A/Lower Asab Ooilite), and J105 (Hith/Upper Asab Strohmenger, Christian J. (ADCO - cstrohmenger@adco Oolite). The overall depositional environment envisaged .co.ae), Lawrence J. Weber (ExxonMobil), Ahmed Ghani for the Arab and Asab formations is that of a barrier (ADCO), Khalil Al-Mehsin (ADCO) and shoal complex with open marine, offshore sedimentation Omar Al-Jeelani (ADCO) to the east and a protected, evaporitic, intrashelf basin to the west. A barrier shoal complex developed along the Important hydrocarbon accumulations have been found platform margin and deposition was dominated by oolitic in platform carbonates of the Lower Cretaceous Kharaib grainstones. Concomitant deposition of sabkha, tidal Formation (Upper Thamama Group) of Abu Dhabi. By flat, salina and lagoonal sediments occurred westwards, integrating core and well-log data from a giant field of Abu and open-marine mudstones and wackestones were

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deposited eastwards of the barrier shoal complex. The J70 (57-Oral) Controls on reservoir performance: to J105 sequences belong to the highstand sequence set lessons learned from fracatured giant fields of the Upper Jurassic second-order supersequence and show progradation of the facies belts towards the east. Sun, Qing (C&C - [email protected]) and Through time, the lagoon behind the barrier bar complex, Jack Allan (C&C) became increasingly evaporitic being dominated by salina deposits during Hith deposition (J105 Sequence). The net One hundred fractured reservoirs from around the world reservoir and reservoir quality is strongly controlled by the were evaluated to determine the most important factors depositional environment and the lithofacies types. The controlling ultimate recovery. Fractured oil reservoirs best reservoir is present within grain-dominated lithofacies comprise four groups. Type I reservoirs have li�le matrix types of the barrier shoal complex. Relatively poor reservoir porosity and permeability. Fractures provide both storage quality is characteristic of mud-dominated lithofacies types capacity and fluid-flow pathways. Type II reservoirs have that occur in open-marine environments. In the intrashelf low matrix porosity and permeability. Matrix provides basin the dominantly dolomitized lithofacies types show some storage capacity and fractures provide the fluid- quite good reservoir qualities within thin intercalated flow pathways. Type III micro-porous reservoirs have packstone to grainstone layers, interpreted as tidal channels high matrix porosity and low matrix permeability. Matrix or washovers. The proposed sequence stratigraphic provides the storage capacity and fractures provide the correlation enhances the prediction of reservoir facies and fluid-flow pathways. Type IV macroporous reservoirs have reservoir quality distributions away from well controls. high matrix porosity and permeability. Matrix provides both storage capacity and fluid-flow pathways, while fractures merely enhance permeability. An analysis of controls on (212-Poster) Depositional setting, sequence recovery factor (RF) efficiency shows that Type I and Type II stratigraphy, and reservoir quality of the reservoirs (average RF = 21 percent and 26 percent) are easily Hanifa Formation in the eastern part of damaged by excessive production rates. In Type III reservoirs onshore Abu Dhabi (average RF = 24 percent), recovery factor is dependent upon lithology, we�ability, and fracture intensity. Enhanced Strohmenger, Christian J. (ADCO - [email protected] recovery techniques are essential for optimum exploitation. .ae), Abdullah Al-Aidarous (ADCO), Abdelfatah El-Agrab In Type IV reservoirs (average RF = 34 percent), recovery (ADCO), Martin P. Boekholt (ADCO), Rafael M. Rosell III factor is most sensitive to drive mechanism. Fractured (ADCO), Azhari Abdalla (ADCO), Marguerite J. Fleming reservoirs can achieve recovery factors comparable with (RRI) and Anna L. Ma�hews (RRI) those of conventional unfractured reservoirs when the correct reservoir management strategy is chosen. The Upper Jurassic (Kimmeridgian) Hanifa Formation is comprised of a barrier shoal complex (Hanifa reservoir facies) passing laterally into the Hanifa intrashelf basin (234-Poster) Sequence stratigraphy and (Hanifa source rock facies). Deposition within the intrashelf reservoir characterization of the Thamama basin ranges from shallow lagoonal to intertidal on top of reservoirs and outcrop equivalents: a core isolated topographic highs, to a deeper, restricted lagoonal workshop and field seminar environment. The la�er corresponds to the so-called Hanifa source rock facies. The Hanifa Formation represents a Suwaina, Omar A. (ADNOC - [email protected]), third-order sequence called J60. It is bounded at the base Lawrence J. Weber (ExxonMobil), Christian J. Strohmenger by sequence boundary J60-SB (exposure surface) and at (ADCO), Lee Vaughan (ExxonMobil), Abdulla Al- the top by sequence boundary J70-SB (exposure surface). Mansoori (ADCO), Sameer Khan (ExxonMobil) and The maximum flooding surface J60-MFS separates the Ahmed Ghani (ADCO) lowstand (LST)/transgressive (TST) and highstand systems tracts (HST). Within the Hanifa intrashelf basin As large producing properties in the United Arab Emirates five correlative high frequency sequences-parasequences (UAE) become more mature and require capital-intensive are identified, corresponding to the LST/TST. These secondary and tertiary methods to maximize oil and gas high frequency sequences-parasequences onlap onto recovery, greater emphasis is placed on building more sequence boundary J60-SB. Six correlative high-frequency accurate and predictive subsurface reservoir models. sequences-parasequences characterize the Hanifa HST. Sequence stratigraphy, based on sedimentary response to Potential source rocks are developed during the TST changes in relative sea level, provides the production and whereas reservoir facies dominate the HST of the Hanifa development geoscientist with a powerful predictive tool. Sequence J60. Depositional environment, lithofacies, and Application of sequence stratigraphic concepts to UAE the established sequence stratigraphic framework control subsurface seismic, core, well log, and outcrop data can reservoir quality and source rock distribution. The best lead to alternative, insightful, subsurface reservoir models. reservoir occurs within the barrier shoal complex of the Outcrop geology in the northern UAE is, in many ways, HST. Amplitude extraction a�er horizon interpretation of analogous to subsurface geology of large producing fields 3-D seismic data and rock properties analysis allow the in Abu Dhabi. Subsurface data is used to populate 3-D mapping of the lateral extend of the porous shoal complex. geologic models and conduct fluid-flow simulations using Potential source rocks, representing deeper-marine, the reservoir architecture developed from these outcrops. At restricted deposits of the intrashelf basin formed during the the outcrop, we will: (1) Investigate the impact of reservoir LST/TST and correspond to a good seismic reflector close to architecture (for example, lateral and vertical facies the base of the Hanifa Formation. changes, sequence boundaries, and flooding surfaces), diagenesis, variogram range, and porosity/permeability

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relationships on the development of quantitative geologic Carboniferous to Early Permian time. These sediments, models (2-D/3-D), using continuously exposed Thamama which were previously known in Abu Dhabi as the equivalent outcrop in Wadi Rahabah, Ras Al-Khaimah. Lower (PK-3), Middle (PK-2) and Upper (PK-1) pre-Khuff (2) Conduct fluid-flow simulations on selected geologic reservoirs can be correlated with the Unayzah and Berwath models of Thamama outcrops to examine interwell-scale formations of Saudi Arabia, which are of the same age. The heterogeneity issues that may affect recovery efficiency Unayzah depositional environment of western offshore for Thamama producing reservoirs. The focus of this Abu Dhabi is interpreted as sheet floods, deposited on an core workshop and field seminar is the description of the arid or semi-arid distal plain. Locally occurring braided reservoir and the role the description has on understanding channels, cu�ing into the stacked sheet flood sands, may reservoir performance. At the end of this workshop and form thick sand bodies with significant reservoir potential. field seminar, each participant should have an appreciation Structural growth and hydrocarbon generation histories for the set of sequence stratigraphic tools necessary to were modeled. Early growth and charge were identified construct subsurface reservoir models. as a significant condition for the formation of economic hydrocarbon accumulations. The Late Triassic to Early Jurassic period was found to be the optimum time for (344-Oral) Intrashelf basin development in hydrocarbon charge of the Paleozoic reservoirs. Structures the Sarvak Formation: example from the of later age were found either tight or water bearing due to High Zagros Mountains extensive diagenesis, which reduced reservoir properties by cementation. Quartz cement, illite and compaction were Taati, Farid (NIOC – [email protected]), Frans S. Van found to be the major diagenetic elements impacting the Buchem (IFP) and Philippe Razin (U Bordeaux) reservoir quality of the Unayzah Formation. The pre-Khuff section was explored in most of the prominent western The Sarvak Formation, of Cenomanian/Turonian age, offshore Abu Dhabi fields, but it positively tested sweet constitutes one of the major reservoir intervals in the gas only in one of these locations. The negative results in Central Zagros Mountains in Iran. A particular feature of the other pre-Khuff exploration wells are mainly a�ributed this carbonate system is the presence of intrashelf basins. to the fact that most of the wells were drilled in crestal Since they may play a significant role, both as the site of positions in these fields, where palynological studies have potential source rock deposition, as well as through their proven absence of the Unayzah Formation due to tectonic influence on reservoir properties in the adjacent carbonate upli� and erosion. In the successful well, only the lower platforms and their margins, our work has focused on the part of the Unayzah-A was found. However, the possible genesis, palaeogeography, and geometries of one such presence of Unayzah sediments on the flanks of the crestal intrashelf basin. The studied site is located in the High tested structures may alter the pre-Khuff section into an Zagros (Kuh-e Landareh), where, along a 10-km-long and a�ractive exploration play for sweet gas in western offshore 300-m-high transect, two margins of an intrashelf basin are Abu Dhabi. exposed. In combination with information of other outcrops in the area, a regional map of the basin was constructed. This intrashelf basin was probably formed during the last (68-Oral) Clay minerals in Cretaceous Nahr third-order depositional sequence of Cenomanian age. An Umr sandstone and their influence on overall backstep occurred well into the Turonian times, reservoir, Qatar followed by a strong progradation. This was terminated by the formation of extensive laterite soils in the region (Laffan Trabelsi, Ali M.S. (QP - [email protected]) and Formation). The intrashelf basin margins show an evolution Mirza A. Beg (QP) from a very low-angle geometry (1 to 2 degrees) to a steep margin geometry (upto 30 degrees). Facies changes are very In Qatar, the Nahr Umr Sandstone is oil productive in abrupt, both in a vertical and lateral sense. The platform several offshore fields. Located on the western flank of margin is constituted of coarse grained rudist-dominated the Qatar Arch, offshore Nahr Umr sands have sheet-like grainstone to rudstone, while the platform top consists of a geometry, covering an area of about 1.600 sq km. Nahr foraminiferal (mostly miliolids) wackstone, and the basinal Umr Sandstone occurs at an average depth 2,500–3,600 facies is a mudstone with oligostegina and planctonic � in onshore Dukhan field and 4,900–5,350 � in offshore foraminifera. This type of outcrop analogs provide us with Qatar. This sandstone was deposited in a shallow-marine geometrical information that is beyond the scale of seismic. environment as evident by glauconite peloids, orbitolinid They may help to be�er appreciate the lateral variability foraminifera, brachiopods and other shallow-marine fauna. and geometrical complexity in subsurface intrashelf basin Onshore, the Nahr Umr Sandstone appears to have a fluvial margins of the Sarvak Formation. origin as indicated by the presence of coal, plant debris and a paucity of shelled, invertebrate fauna. Overall, the Nahr Umr Formation comprises alternating intervals of (263-Oral) Sweet gas exploration potential of quartzarenite to sublitharenite sandstone, argillaceous the pre-Khuff reservoirs, western offshore sandstone, glauconitic sandstone and shale. In general, the Abu Dhabi quartzarenite sandstone consists of angular to sub-angular, moderately to poorly-sorted, fine-grained sandstone with Taher, Ahmed A.K. (ADNOC - [email protected]) and reasonable amount (about 20 percent) of predominantly Johan M. Wi�e (ADNOC) intergranular porosity. The argillaceous sandstone streaks have significantly lower permeability than clay-free The principal pre-Khuff hydrocarbon reservoirs in Abu intervals. This is due to the presence of detrital and pore Dhabi are the siliciclastic sediments deposited during Late

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throat blocking authigenic clay minerals. X-ray diffraction north-westwards towards Yibal field and the shallow-shelf (XRD) and scanning electron microscopy (SEM) analyses Bab Basin; southeastwardly towards a lagoon between reveal significant amounts of detrital and authigenic clays, Al Huwaisah and Saih Rawl fields). This lagoon, which especially kaolinite, chlorite, illite/smectite mixed layers contains the areas of both Burhaan and Musallim fields and illite. Detrital clay forms a significant portion of the only filled during another later early Aptian sequence. sandstone matrix. It is present at grain-to-grain contacts, Without control from chemo-, bio- or seismic stratigraphy, as laminae and clay wisps. Authigenic clay, especially it is difficult to define an order of depositional sequences kaolinite exhibits higher degree of crystallinity, has delicate or correlate over large distances using stacking pa�erns morphologies and predominantly coats sandstone (quartz) in cores or GR-logs. Carbon isotope stratigraphy offers a grains and partially fills and lines the intergranular pore robust and inexpensive tool to provide stratigraphic control spaces. Nahr Umr marine sandstone samples can contain both on reservoir and exploration scale. as much as 17 percent clay. In most samples kaolinite is the predominant type, followed in abundance by chlorite, illite and illite/smectite mixed layers. Some offshore marine (329-Poster) Stratigraphy of the central samples contain significant amounts (up to 32 percent) of Saudi Arabian Khuff Formation goethite as revealed by XRD analysis. Goethite occurs as Vaslet, Denis (BRGM - [email protected]), Yves-Michel well-rounded and sub-spherical micro-porous peloids (70- Le Nindre (BRGM), Daniel Vachard (CNRS), Sylvie 125 m). These peloids probably resulted from the diagenetic Crasquin-Soleau (CNRS), Jean Broutin (U Paris), alteration of originally chamositic grains. The Nahr Umr Mohamed Halawani (SGS) and Sandstones also contains smaller amounts of pyrite, dolomite Moujahed I. Al-Husseini (GPL) and siderite, occurring predominantly as replacement and cement. Volumetrically these constituents are relatively less The Permian-Triassic Khuff Formation outcrops of central abundant. While not a primary depositional and diagenetic Saudi Arabia are divided, from base to top, into five control on permeability, chlorite (chamosite) and other iron- members: Ash Shiqqah (formerly Unayzah member of rich minerals can create problems if Nahr Umr Sandstone the Khuff Formation), Huqayl, Duhaysan, Midhnab and is acidized without using iron sequestering materials and Khartam. According to benthic foraminifer and algae clay stabilizers. Smectites and mixed layer illite/smectite associations, the Ash Shiqqah Member is tentatively dated clays are sensitive to fresh water and low salinity fluids. as Capitanian (Midian). The Huqayl Member is assigned to They swell in contact with these fluids. The swelling a Wuchiapingian (Dzhulfian) age. The Duhaysan Member results in blocking of pore and pore throats and causes near remains undeterminated in age. The Midhnab Member is wellbore damage. The swelling problems can be avoided by dated as Changhsingian (Dorashamian). Within continental using oil base, potassium or ammonium chloride drilling, facies in the topmost part of the Midhnab Member, swamps completion and stimulation fluids. and crevasse splay deposits yielded the Upper Permian Midhnab flora. The lower Khartam Member contains (44-Oral) How sure are you that your rare Permian foraminifers, locally reworked. However, Shu’aiba stratigraphy is correct? New abundant ostracods of the Paleocopid group support a late Late Permian age. The disconformity between the Midhnab findings from chemical stratigraphy and Khartam members thus occurs during the Permian Vahrenkamp, Volker C. (PDO - volker.vc.vahrenkamp@pd Period. The upper Khartam Member is confirmed as Early o.co.om) Triassic Scythian in age based on the abundance of Spirorbis phlyctaena. The Permian-Triassic boundary is thus located Some 1,400 new data from 27 wells of the Shu’aiba within the Khartam Member. A sequence stratigraphic Formation in Oman have been collected to refine previously interpretation resulted in the identification of three main established correlations between carbon isotope profiles Maximum Flooding Intervals (MFI). The lower Huqayl in the Gulf region with isotopic variations proposed for MFI is located above the widespread subsurface Khuff-D Aptian seawater. Anchored by biostratigrahy, gamma anhydrite marker bed. The lower Midhnab MFI represents ray (GR) logs and a regional Shu’aiba correlation frame a the maximum inundation of the Arabian Platform during reference curve has been established for the Aptian, which Late Permian time. The lower Khartam MFI represents the significantly surpasses others from elsewhere in the world, last Permian inundation of the platform a�er a continental both in time resolution and definition. Surprisingly, the episode at the top of Midhnab Member. Secondary flooding carbon isotope composition of the Shu’aiba Formation intervals occur within the upper Huqayl, Duhaysan, and in the measured sections seems li�le changed from its upper Khartam members. The first Triassic MFI could occur original marine signature despite long term subaerial within the upper Khartam Member. exposure prior to burial and extensive early and/or late diagenesis. The new reference curve constrains the time (430-Oral) Removal of complex near-surface intervals during which individual sections accumulated. Correlation of time equivalent sections, both on a regional effects by semi-automatic data-driven and field scale, establishes a stratigraphic architecture of the focusing operator determination Shu’aiba Formation, which is significantly more complex Verschuur, Dirk J. (Del� U - [email protected]�.nl) than previously assumed. For example, during the early Aptian, complete infill of accommodation space by rudist A major problem in Middle East land data is the imprint build-ups at Al Huwaisah field caused multi-directional of complex near-surface effects on the subsurface image progradation into adjacent incompletely filled areas (e.g. of the seismic data. Current solutions mainly involve

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the assumption of vertical ray-paths through a relatively will help improve reservoir definition over the entire field, simple near-surface layer, imposing a static shi� on each and result in a more robust stochastic characterization. The seismic trace. As the propagation of seismic waves through reservoir model will be used in the sectorial development the unknown near-surface layer is more complex than that, of the field. the solution should come from an imaging-based approach. The Common Focus Point (CFP) technology may provide a solution to this problem without deriving a complex (149-Oral) Permian-Triassic anoxia, near-surface velocity model, as it approaches the problem carbonate productivity collapse and no in a pure data-driven manner. The basics and initial results consequences for reservoir rocks? with this methodology have already been demonstrated by a few authors. The current implementation still Weidlich, Oliver (U Kiel - [email protected]) and involves considerable user-interaction, which may prevent Michaela Bernecker (Erlangen U) this method from being used at large scale in the data The Permian-Triassic boundary (PTB) event encompasses processing stage. Therefore, the CFP iterative focusing the end-Middle Permian and end-Late Permian mass operator updating procedure is proposed to be replaced extinctions. The la�er is the most severe Phanerozoic by a global search through a solution space of possible event, which caused a complete breakdown of the marine focusing operators. Currently, genetic algorithms are carbonate-secreting communities during long-term oceanic employed for this purpose. Apriori information on the anoxia. Far-reaching consequences concern the marine propagation effects is included to constrain the solution. sediment composition during the Early Triassic on a This semi-automatic updating process can be formulated global scale, because a unique facies prevailed, which is for both the travel times as well as the amplitudes related to characterized by finely-laminated and horizontally-bedded the focusing operators. The end result should be a model- mudstones, enigmatic cement crusts, and thrombolites. independent true-amplitude wavefield redatuming of the Except for some ri� areas in the Neo-Tethys and the rim prestack data towards a selected datum reflector, below of the Arabian Plate, these Early Triassic limestones were which the seismic reflection energy can be handled by the deposited during a major transgression and, thus, lack conventional processing techniques. common features of karstification. These sediments with unique sedimentological and geophysical properties, cover (406-Poster) Sequence stratigraphy and productive hydrocarbon reservoir units in the Middle reservoir characterization of the Second East and other regions. While the impact of the PTB for Eocene Dolomite Reservoir, Wafra field, the marine biota is well-constrained, consequences for the reservoirs in the Middle East have rarely been considered. PNZ, Kuwait-Saudi Arabia Therefore, we tested the assumption that the Early Triassic Wani, Mohamad R. (KOC - [email protected]) and facies significantly contributed to reservoir heterogeneities: Sondos K. Al-Kabli (KOC) (1) by compilation of our own and published data, we show that Lower Triassic sediments are thick enough to The Second Eocene dolomite reservoir is one of the major be resolved by wireline logs. (2) Using our digital archive producers in the giant Wafra field of the Partitioned Neutral of the Saiq and Mahil formations (Saih Hatat, Oman), we Zone (PNZ) between Kuwait and Saudi Arabia. This present facies and petrographic data flanked by stable reservoir is of Paleocene age and occurs in the Tertiary Umm isotopes characterizing the rock properties. (3) Using Er Radhuma Formation. The reservoir has been producing available log data from the Middle East, we try to trace since the late 1950s under depletion drive. Recoveries, the Lower Triassic facies on larger scale. Based on our however, remain poor (about 5 percent of OIIP) mainly due integrated dataset, we regard Early Triassic carbonates as to low-gravity oil and reservoir heterogeneity. A geological an important benchmark in both, pure carbonate and mixed model that be�er defines reservoir heterogeneity is a pre- carbonate-evaporite systems and, thus, recommend further requisite for evaluating and implementing EOR techniques. studies on this unit. Primary porosity in subtidal dolomitized carbonates associated with evaporites as well as its modifications by (121-Oral) Fault zone morphology and dolomitization, dissolution and cementation typically occur in multiple zones that formed within shallowing-upwards, segment geometry of onshore Abu Dhabi high-frequency cycles. This study a�empts to identify these West, Brian P. (ExxonMobil - brian.p.west@exxonmobil. cycles in the Wafra Second Eocene reservoir, and place them com), Christopher A. Johnson (ExxonMobil), Mohamed in a sequence stratigraphic framework. Based on the study of Sa�ar (ADCO), Andrew M. Gombos (ADCO) and core material, core photomicrographs and descriptions, and Peter D. Melville (ADCO) correlations in more than 500 wells, seven high-frequency cycles, which are further divided into 13 ‘zones’, were Volume-based interpretation of extensive 3-D seismic data recognized. This zonation scheme be�er defines the poorer from onshore Abu Dhabi yields observations regarding reservoir units and the intervening non-reservoir sections the style and timing of deformation in this portion of in a systematic manner. It highlights the distribution the Arabian Plate. The most pervasive structural style is of grain-rich dolomites and evaporites, as well as the characterized by highly segmented, small-offset fault zones cyclicity of dissolution and cementation. The combination that we interpret as a conjugate shear set resulting from of (1) primary rock fabric, (2) diagenetic imprint, and (3) Late Cretaceous, NW-SE compression. The fault zones the zonation scheme introduced here, resulted in a be�er include a dominant, approximately N75W trend and a correlation of porosity versus permeability. This study subsidiary, approximately N45W trend, both of which are

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segmented laterally and vertically. The dominant trend (431-Poster) Horizontal development appears to be more through-going and exhibits both trans- of shallow shelf carbonate reservoirs: pressional and trans-tensional dextral offset. The subsidiary Cretaceous Saar Formation, Masila Block trend is more variable and exhibits almost exclusively sinistral, trans-tensional offset. The subsidiary trend is also 14, Yemen inferred to be associated with secondary stress-inducing Wilkinson, Kent (Nexen - [email protected]) factors that reinforce its expression; including; (1) torque at saddle point relays between non-parallel anticlines; (2) Oil was discovered on Masila Block 14, Yemen, in 1991 drape over anticlinal axes; and (3) reactivated, preexisting with first commercial oil production starting in 1994. Most structures. There is no evidence for significant offset along of the oil production has been from clastics in the Early either of these fault zones, despite their through-going map Cretaceous Upper Qishn Formation. The Tawila field is the pa�ern (10s–100s of km). Rather, numerous individual fault largest of the 15 existing fields in the Masila block. Over segments compose the fault zone and are on the order of the past three years greater emphasis has been placed on 100s of meters in length down to seismic resolution. The deeper secondary targets. The Tawila field is located on an morphology of the fault zones is strongly influenced by the isolated fault block structure within the NW-SE Say’un-al mechanical properties of the stratigraphy. Slight clockwise Masila Basin. The Saar Formation in the Tawila field is a reorientation of many fault segments from deep to shallow 600 � post-ri� succession consisting of a series of shallow is also analogous to clay-cake models of Riedel shears shelf carbonate sequences. Three reservoir facies have overlying deeper strike-slip faults. These observations have been identified within the uppermost portion of the Saar important implications for the evaluation of the fault seal Formation: (1) leached rudist biostromes; (2) sucrosic tidal risk in exploration se�ings and reservoir segmentation in flat replacive dolomite; and (3) leached bioclastic-peloidal production and development se�ings. grainstone shoals. Multiple subaerial exposure events can be identified in core by irregular contacts, shale-filled (289-Oral) The hydrocarbon potential of cavities, and karst-related breccias. A mud-supported rudist the underexplored Paleozoic and Triassic floatstone biostrome forms a significant reservoir facies due to the creation of secondary micro- and macro-scale moldic petroleum systems of Northwest Arabia and vuggy porosity (10-27 percent) related to an overlying exposure event. Dolomitization plays a key role in reservoir Whaley, Jane (IHS - [email protected]) development. The early formation of dolomite directly The majority of exploration in the northern Arabian Plate below the Valanginian Saar unconformity is associated has been directed towards late Mesozoic plays, leaving the with restricted, tidal-flat sediments. Fine-grained sucrosic Paleozoic and Triassic sections relatively under explored. euhedral dolomite forms an excellent intercrystalline Since 1936 there have been over 12 deep structures drilled reservoir. A horizontal development program initiated in in western Iraq with seven oil and gas discoveries, six in the early 2003 has demonstrated a four-fold improvement in Triassic and one in the Paleozoic. Similarly in Syria, since initial production rates (> 5,000 bopd) with a 30 percent 1940, there have been 120 structures drilled for Paleozoic increase in drilling cost compared with older vertical wells. and Triassic plays, with at least five Paleozoic and 52 Triassic oil, gas and condensate discoveries. In Jordan, (182-Oral) Managing uncertainties in two Ordovician gas reservoirs have been discovered since exploration and exploitation, Gharif 1984. In northern Saudi Arabia, one important Ordovician gas and condensate field/discovery was made in 1993. Formation, Central Oman When one considers the geographical size of the area, it Willoughby, John (PDO - [email protected]) is immediately apparent that these plays have significant and Mohamed Al-Lawati (PDO) potential. This paper describes the hydrocarbon potential of these sediments in northwest Arabia and introduces The Gharif is the most productive clastic reservoir unit in new play concepts to further unlock the potential in this PDO’s portfolio, but a�er almost 20 years of intense and prolific area. The paper covers Jordan, Syria, western Iraq successful exploration and exploitation, the play is now and northwestern Saudi Arabia to the west of 43 degrees considered to be mature. The current prospect portfolio is and north of 29 degrees. The paper is based on a recent dominated by subtle low relief closures, with vertical relief study that (1) illustrates the hydrocarbon potential of in the order of 10 -20m, and as such they are very sensitive the Paleozoic and Triassic sediments; (2) identifies the to uncertainties in the accuracy of depth conversion and location of the Paleozoic and Triassic petroleum systems; seismic imaging. Management of these is crucial if PDO (3) introduces new play concepts; (4) links plays and is to pursue a successful exploration and exploitation petroleum systems to known fields and discoveries; (5) program in the Gharif. This paper will focus on three of the analyses the proven hydrocarbon reserves of 67 Paleozoic principal uncertainties and will show how they are being and Triassic fields and discoveries; and (6) identifies, maps managed. a) Imaging Uncertainty: Superior statics solution and highlights the potential of the Paleozoic and Triassic in led to a reduction on the uncertainty of structural risk on more than 500 undrilled structures. the remaining opportunities, allowing PDO to polarise its portfolio. b) Velocity Uncertainty: By resolving the statics issues, we could demonstrate a marked improvement in our ability to establish “normal” time depth relationships

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which has led to an improvement in the accuracy of our (480-Oral) Processing, inversion, and depth conversion. c) Interpretation Uncertainty: Uncertainty interpretation of shallow seismic data exists in our ability to pick the Top Gharif in a reliable and consistent manner. Experience has shown that the expected Yilmaz, Oz (GeoTomo - [email protected]) seismic response of a strong Top Upper Gharif reflector is frequently not observed on reflectivity data, and it is The seismic method has three applications with different very difficult to interpret top Gharif with confidence. New requirements for band-width and depth-width: (1) risks and uncertainties have been identified, understood earthquake seismology with a bandwidth up to 10 Hz and are currently in the process of being mitigated. This and a depth of interest down to 100 km; (2) exploration should translate into an improvement of the quality of seismology with a bandwidth up to 100 Hz and a depth of the prospect portfolio. In the future, PDO’s Central Oman interest down to 10 km; and (3) engineering seismology with Gharif activities are expected to focus on field development a bandwidth up to 1,000 Hz and a depth of interest down and Near Field Exploration. to 1 km. Each of the three categories of seismology makes use of a specific wave type: (1) in earthquake seismology, dispersion of surface waves is used to delineate velocity- (202-Oral) 3-D boundary element modeling depth models for the oceanic and continental crusts. for fracture distributions in deep carbonate (2) In exploration seismology, reflected and diffracted intervals, northern Kuwait waves are used to derive an image of the subsurface. (3) In engineering seismology, refracted waves are used to Wu, Haiqing (ChevronTexaco - [email protected]), derive a velocity-depth model for the near-surface. For a Mohammed D. Al-Ajmi (KOC), Andrew Corley specific category of seismology, the associated wave type is (ChevronTexaco), Anthony Lomando (ChevronTexaco), considered signal, while other wave types are considered Lilian Skander (ChevronTexaco), Sunil K. Singh (KOC), noise. For instance, surface waves are essential for Nikhil C. Banik (KOC), Abdul Aziz H.A. Sajer (KOC), earthquake seismology, while they are treated as coherent Heyam M. Ammar (KOC), Moinuddin Didwai (KOC) and linear noise in exploration seismology, ground roll in land Meshary Ameen (KOC) seismic exploration, and guided waves in marine seismic exploration. I present a workflow for analysis of shallow This study used a Boundary Element Method (BEM) seismic data to estimate a near-surface model defined by to analyze reservoir scale deformation and build a layer geometries within the soil column, and the P- and S- geomechanical model to predict fracture distributions in wave velocities of the layers themselves. Specifically, I use the deep Jurassic carbonate intervals in northern Kuwait. reflected waves in recorded shallow seismic data to derive BEM is much more efficient than the Finite Element Method a seismic image represented by a CMP stack and refracted (FEM) in 3-D numerical analyses for faulted reservoirs. The waves to estimate a P-wave velocity-depth model of the BEM model is based on seismic interpretation of faults near-surface. I then use the P-wave velocity field resolved and horizons, boundary conditions on these faults, remote from tomography to guide the interpretation of the CMP stresses and overburden, and well control using image logs stack so as to delineate the layer geometries within the soil and cores. Stress tensors are calculated first at observation column in depth. Additionally, I use Rayleigh-type surface points around major faults. Coulomb failure criterion and waves to estimate an S-wave velocity profile in depth. I maximum principal differential stresses are then used to demonstrate the unified workflow for shallow seismic data determine the possible orientations and distribution of acquired for geotechnical site investigations, and coal and fractures or small faults. Borehole image logs and core data groundwater exploration. constraint the model for fracture density and orientation. Finally, fracture bubbles and rose diagrams are generated for be�er 3-D visualization and well planning in the area. (119-Poster) Integrated 3-D seismic analysis A specific workflow process including curvature analysis, and sequence stratigraphy of the Lower analog comparison, and geostatistical modeling was Cretaceous for a large carbonate field in Abu applied to validate the geomechanical modeling effort. We Dhabi collected acoustic borehole images, cores, logs, and seismic interpretations in the deep Jurassic carbonate intervals Yose, Lyndon A. (ExxonMobil - lyndon.a.yose@exxonm to detect fracture distributions from the Najmah/Sarjelu obil.com), Steve Bachtel (ExxonMobil), Andrew Gombos through Lower Marrat formations. An uncertainty model (ADCO), Jason Sco� (ADCO), Po Tai (ExxonMobil), was generated to show the influence of a variety of data Christian J. Strohmenger (ADCO), Nat Stephens types, ranges, and proportions. Finally, we analyzed (ExxonMobil), Ismail A. Al-Hosani (ADCO), Imelda present-day stress distributions and directions, built a 3-D Johnson (ExxonMobil), Jim Schuelke (ExxonMobil), Peter stress model, and calculated stress distributions on major Holterhoff ExxonMobil( ), Khalid Al-Amari (ADCO), Amy faults and fractures to indicate if they enhance or prevent Ruf (ExxonMobil) and Brian Coffey ExxonMobil( ) fluid flow in the carbonate intervals. Results include: (1) 3-D fracture density distribution and possible fracture New, high-effort 3-D seismic data collected for a field in orientations; (2) possible sub-seismic fault locations and Abu Dhabi provide some of the highest resolution images orientations; and (3) present-day stress distributions in the ever obtained for a carbonate reservoir. Seismic data were reservoir and on major and sub-seismic faults showing slip integrated with well and core data, and with available tendency and dilation tendency. age dates (biostratigraphic and isotopic), into a new

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sequence-stratigraphic model for the Lower Cretaceous ‘next generation’ strategies for reservoir management (Aptian/Albian). Third-order sequences stack to form and optimization in Abu Dhabi. High-effort, high- a complete accommodation cycle from transgressive, quality seismic data provide unparalleled imaging to highstand, to late highstand, to lowstand. Stratal and visualization of carbonate reservoir architecture architecture, facies distributions, and reservoir quality (stratigraphic and structural) that can be incorporated all vary predictably within the sequence stratigraphic directly into 3-D models. Prestack and poststack seismic framework and, at variable scales, are directly imaged a�ributes provide quantitative information on carbonate or detected by the new 3-D seismic data. The seismic porosity and fracture properties at the interwell spacing. workflow employed in this study included post-stack Time lapse (4-D) seismic shows promise for tracking data optimization, evaluation of multiple seismic a�ribute fluid front movement over time. Successful application of volumes for interpretation of reservoir architecture, seismic technologies and information, however, remains quantitative seismic facies classifications, multi-a�ribute highly dependent on calibration to appropriate outcrop porosity predictions, and calibration with well, core and subsurface data, validation with geologic models and and production data. Advanced visualization tools concepts, and integration within sequence-stratigraphic and volume co-rendering allow for imaging carbonate and structural frameworks. environments and architectural elements rarely seen in carbonate seismic data. In the early highstand of the composite sequence, a mosaic of rudist patch reefs and (105-Oral) Hawqa-revival of a Gharif shoals (flow units), tidal channels (flow baffles), and inter- field in central Oman shoal ponds (lateral flow barriers) are clearly observed in Young, Adrian (PDO - [email protected]), seismic images, comparable in detail to Landsat images Andrew Faulkner (Baker Hughes), Jonathan Strauss of modern carbonates. Seismic images of a prograding (Baker Hughes), Xavier Maasarani (PDO), Alan Wheeler shelf margin complex (late highstand) reveal remarkable (Baker Hughes), Abdullah Shamakhi (PDO) and detail on clinoform geometry and connectivity, and Walter Slijkerman (PDO) systematic architectural variations keyed to changes in accommodation and sediment supply. The integrated This study describes the issues regarding the subsurface seismic interpretations and reservoir framework provide development plans for the Hawqa field, located in new insights on carbonate sequence architecture, and the Bahja area of Central Oman. Hydrocarbons are for improved reservoir modeling and optimization structurally and stratigraphically trapped in several but strategies. relatively thin shallow marine and fluvial sandstones within the Permian Middle (MG) and Upper Gharif (120-Oral) Integrated approaches to members. There is evidence for multiple fluid contacts carbonate reservoir characterization and and fluid properties range from high gravity saturated oil in the MG3 reservoir to volatile oils in the MG2 units, prediction: examples from United Arab to rich gas condensates and oil in the Upper Gharif Emirates fields and outcrops member. The structure was perceived to be small at the time of discovery in 1989. Gross production from the Yose, Lyndon A. (ExxonMobil - [email protected] exploration well declined rapidly within weeks and orp.com), Lawrence J. Weber (ExxonMobil), Christian J. the well was closed in by mid-1990. A recent review Strohmenger (ADCO), Abdulla Al-Mansoori (ADCO) and of the Hawqa accumulation identified a significant Omar Suwaina (ADNOC) upside potential, which was subsequently proven by the Quantifying carbonate reservoir architecture and flow appraisal well Hawqa North-1 in April 2002. In particular, properties in 3-D geologic models requires integration MG3 production potential has been found to be prolific. of multiple types and scales of data within hierarchical However, recovery due to depletion is expected to be very sequence-stratigraphic and structural frameworks. low (about 5 percent) as MG3 reservoir pressure is near The present study highlights the following workflow bubble point and aquifer support is expected to be modest elements with examples from the Lower Cretaceous in at best. Thus, water flooding is planned from the start of Abu Dhabi: (1) integration of outcrop and subsurface production. A fast track development of the Hawqa field data to develop regional structural and sequence- is being pursued by a joint team from PDO and Baker stratigraphic frameworks that can be applied consistently Atlas. Major field-development risks have been identified from one field to the next; (2) volume-based enhancement and are being managed by an ongoing data acquisition and analysis of 3-D seismic data for quantification of and study program leading to a development plan by reservoir architecture and rock properties; (3) validation September 2003. Major subsurface development risks and calibration of reservoir predictions using outcrop, include structural definition and reservoir continuity. well, core and production data; (4) characterization of Reservoir structure has been delineated by aggressive sub-seismic (high frequency) variability in structural appraisal drilling and by newly-acquired 3-D seismic. and stratigraphic rock properties through integration A high degree of reservoir continuity in the MG3 has of outcrop and subsurface data into high-resolution been confirmed by interference testing between wells. An frameworks; and (5) hierarchical integration of all scales additional risk for the water flood is effective injectivity and types of data in static and dynamic 3-D reservoir near the wellbore of planned injectors. Full compatibility models for performance prediction. Special emphasis with injection water is planned by using the underlying is placed on the value of 3-D seismic in defining the Al Khlata Formation water as a source. Moreover, only

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low solids concentrations are being allowed in the effects. The RRS method involves three main steps: (1) injection water and, hence, high standard water filtering automatic picking of travel-times of a selected refraction is being planned. Currently, the choice between matrix event with some user-defined seed values; (2) the picked injection and injection aided by fraccing is being studied. travel-times with the same offsets are smoothed and Further study will decide on the optimum well placement used as the calibration curves for the next step; and (3) pa�ern and well type. Water flood in the Hawqa field is the differences between the raw picks and the computed planned to yield production in 2004. A rigorous technical calibration curves are inverted for the final statics at every and value assurance review process was put in place to shot and receiver location in a surface-consistent manner. assure that investments are secure. Full field development The RRS method can significantly improve the focusing will take place in subsequent years; whilst developing the of seismic data, and thus enhance the quality of time MG3, the overlying, complex MG2 and Upper Gharif stacked sections in areas with severe statics problems. reservoirs will be extensively appraised. The maximum statics value in our study reached up to 40 milliseconds. More importantly, it was found that refraction data from deep events, received at far offsets, (448-Oral) Next tomography for near-surface can be used to derive the correct statics values. Contrary imaging to most conventional refraction-based approaches that rely on near offset data, our methodology employs Zhang, Jie (GeoTomo - [email protected]) far-offset refraction data. This successful a�empt using During the past ten years, constraining and stabilizing far-offset data may have significant implications in most travel-time tomographic inversion has been a major areas of the Arabian Peninsula since near offset travel- research topic. As a result, tomography has advanced times are o�en difficult to pick automatically and/or even from ‘creeping’ inversion that damps model changes to manually. ‘jumping’ inversion that constrains the model itself. The objective function of a tomography problem no longer (94-Oral) Thin-skinned ramp promontory includes just a data misfit term. Model regularization model for the Dezful Embayment, Zagros becomes explicit. Even more, continuum inverse theory Mountains, Iran has been introduced into seismic tomography and the tomography solution becomes independent on initial Zweigel, Peter (SINTEF - [email protected]) models. These achievements have led to many successful applications of tomography in both the near-surface and The oil-prolific Dezful Embayment is a structural subsurface areas. However, the challenge for tomography depression in the outer part of the Zagros foreland fold accuracy still remains; in particular, in the near-surface and thrust belt. Formations in the embayment are several areas where lateral velocity contrasts are o�en great. thousand meter deeper than in its lateral neighborhood. Resolving these velocity contrasts is critical for making Publicly discussed theories for the origin of the accurate statics interpretation. Although the use of embayment include a tectonic half-window, thrusting continuum inverse theory for grid-based tomography into a preexisting depression, local post-thrusting validates a stable solution, imposing continuum o�en subsidence along fault zones bordering the embayment, lowers resolution across different geological units. The and basement faults active during Cenozoic convergence. truth is that there is really no continuum from soil to This study suggests an alternative model, which tries to limestone. Thus, we must develop the next tomography explain the structural depression as being caused by the that is not only well-posed, but also preserves high- presence of a footwall ramp promontory of about the same resolution contrasts. One of the proposed methods is size and shape, but presently slightly more hinterland- Geology-Regularized Tomography (GRT) that imposes ward position than the present embayment. A foreland- continuum only within the same geological unit and ward shallowing of the basal detachment onto the ramp breaks smoothing at interfaces. We may apply well logs would imply a correspondingly reduced thickness of and uphole interpretation to help define a priori geological the frontal part of the hanging wall. This model would zones. Initial tomography using continuum inverse theory explain interalia the following features: (1) plunge of will generate a globally-smooth solution, and different anticlines from the neighboring areas (thick hanging wall) geological units will be automatically identified from into the depression (thinner hanging wall); (2) tighter velocity contours. Subsequent tomography using GRT folding and thrusting, higher topographic position, and method will lead to a geology-consistent high-resolution erosion to deeper stratigraphic levels hinterland-ward of solution. the depression (the promontory acting as a bu�ress) as compared to the laterally neighboring areas; (3) higher (385-Oral) Refraction residual static topographic position and erosion to deeper stratigraphic levels in the foreland-ward parts of the areas laterally corrections using far offset data neighboring the depression (thick package thrusted onto Zhu, Weihong (Digicon - [email protected]) and ramp) as compared to their hinterland-ward part (normal Yi Luo (Saudi Aramco) thrusting of thick package). The hanging wall ramp flexure at the lateral margins of the embayment, which This study presents results of applying a novel, Refraction are oriented obliquely to the convergence direction, is a Residual Statics (RRS) algorithm to seismic data from preferred site for structural complications. Saudi Arabia in order to compensate for near-surface

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The names of companies and institutions to which presenters and chairpersons are affiliated have been abbreviated. For convenience, all subsidiary companies are listed as the parent company. The following is the list of abbreviations used.

Aachen University, Germany GUPCO: Gulf of Suez Petroleum Company, Petropars Ltd., Iran ABB Offshore Systems, UK Egypt PGA: Petroleum Geological Analysis Ltd., UK ADCO: Abu Dhabi Company for Onshore GX Technology Canada Ltd., GX PGS: Petroleum Geo-Services Oil Operations Technology Pierre and Marie Curie University, France ADMA-OPCO: Abu Dhabi Marine Heriot-Wa� University, UK Politecnico di Torino, Italy Operating Company IES: Integrated Exploration Systems, Dubai QP: Qatar Petroleum, Doha ADNOC: Abu Dhabi National Oil IFP: Institut Français du Pétrole, France Repsol, Spain Company IHS: IHS Energy Group, UK ResLab: Reservoir Laboratories, UAE AECS: Atomic Energy Commission, Syria Intergraph Middle East, UAE RIPI: Research Institute of Petroleum, Iran Ain Shams University, Egypt IOOC: Iranian Offshore Oil Company, Royal Holloway, University of London, Al-Kha�i JO: Al-Kha�i Joint Operations, Tehran UK Saudi Arabia Jackson State University, USA RRI: Robertson Research International, UK Al-Khaleej, Saudi Arabia Jason Geosystems Middle East, UAE RUB: Ruhr University at Bochum, Amir Kabir University, Iran JNOC: Japan National Oil Company, Tokyo Germany Anadarko Petroleum Corporation, USA JODCO: Japan Oil Development Company, Saler Geological Services, USA Antipolis University - Nice Sophia Tokyo Sana’a University, Yemen Apache Egypt Companies Joint Virtual Reality, Centre for Carbonate SAT-JO: Saudi Arabian Texaco-Joint Badley Ashton & Associates, USA Studies, Oman Operation Bapco: Bahrain Petroleum Company, Awali KACST: King Abdulaziz City for Science Selan Exploration & Technology Ltd., India BGS: British Geological Survey, UK and Technology, Riyadh, Saudi Arabia SGS: Saudi Geological Survey, Jeddah Birmingham University, UK Kelkar and Associates, USA Sii-ASE, Oman BRGM: Bureau de Recherches Géologiques Keyhan Exploration and Production SINTEF Petroleum Research, Norway et Minières, France Services, Iran Sipetrol International SA, Egypt C&C Reservoirs Limited, UK KFUPM: King Fahd University of SQU: Sultan Qaboos University, Muscat, Cairo University, Egypt Petroleum and Minerals, Dhahran Oman Cambridge University, UK KOC: Kuwait Oil Company, Ahmadi, Stanford University, USA CASP: Cambridge Arctic Shelf Programme, Kuwait Statoil, Norway Cambridge University, UK KOC-JO: Kuwait Oil Company-Joint Talisman Energy, Canada CCL: Cambridge Carbonate Limited, UK Operation Tarbiat Modares University, Iran CGG: Companie Générale de Géophysique, Kuwait University, Kuwait city Target Consultants, UK France Larch Consulting Ltd., Canada TEEC: Trappe Erdöl Erdgas Consultant, CNRS: Centre Nationale Recherches Lebanese University, Beirut Germany Scientifique, France Ljubjana University, Slovenia University of Aberdeen, UK CoreLab, Canada Lynx Information System, UK Université de Bordeaux, France Daleel Petroleum Company, Oman Maersk Oil Qatar AS University of Bremen, Germany Damascus University, Syria Martin Luther University, Germany University of Darmstadt, Germany Del� University of Technology, The Millenia, UK University of Kiel, Germany Netherlands MIT: Massachuse�s Institute of University of Leeds, UK Devon, Canada Technology, USA University of London, UK DEZPC: Der Ez Zor Petroleum Company, MMWR Oman: Ministry of Municipalities Université de Lyon: France Syria and Water Resources, Oman University of Miami, USA Digicon Geophysical Ltd., USA MPI: Max Planck Institute, Germany University of Milan, Italy DPC: Dubai Petroleum Company, United MVE: Midland Valley Exploration Ltd., UK Université Paris IV, France Arab Emirates Ne�ex Petroleum Consultants Ltd., UK University of Reading, UK ELS Consulting Ltd., Canada Nexen Petroleum International, Canada Université de Rennes, France ENRES International, The Netherlands NIOC: National Iranian Oil Company University of Salahaddin, Iran ERL: Earth Resource Ltd., UK NIOZ : Netherlands Institute for Sea University of Tehran, Iran Erlangen University, Germany Research University of Texas, Austin GAFAG: Gesellscha� fuer Angewandte NISOC: National Iranian South Oil University of Tuebingen, Germany Fernerkundung, Germany Company UAE U: United Arab Emirates University, GNPOC: Greater Nile Petroleum Operating Norsk-Hydro, Norway Al Ain Co. Ltd., Sudan OAPEC: Organization Arab Petroleum University of Urmia, Iran GeoScience Limited, UK Exporting Countries, Kuwait UC London: University College London, Geosystem Srl, Italy OilTracers, USA UK GeoTech Consulting, Bahrain Paradigm Geophysical Ltd., UK USGS: United States Geological Survey, Glasgow University, UK PDO: Petroleum Development Oman USA Golder Associates: USA PDOC: Petrodar Operating Company, Varol Research, UK GPC: General Petroleum Company, Egypt Khartoum, Sudan Vsfusion, UK GPL: Gulf PetroLink, Bahrain Petrosurveys, USA Zadco: Zakum Development Company, GSI: Geological Survey of Iran United Arab Emirates 148 149

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