IBP1111-12 Maximizing Reservoir Exposure with Proactive Well
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IBP1111_12 MAXIMIZING RESERVOIR EXPOSURE WITH PROACTIVE WELL PLACEMENT IN HIGH GEOLOGICAL COMPLEXITY FIELD OF VENEZUELAN ORINOCO BELT. 1 2 3 Luis Castaneda , Maryesther Leon , Antoine Meunier , 4 5 6 Manuel Lara , Yoanna Herrera , Miguel Granado Copyright 2012, Brazilian Petroleum, Gas and Biofuels Institute - IBP This Technical Paper was prepared for presentation at the Rio Oil & Gas Expo and Conference 2012 , held between September, 17- 20, 2012, in Rio de Janeiro. This Technical Paper was selected for presentation by the Technical Committee of the event according to the information contained in the final paper submitted by the author(s). The organizers are not supposed to translate or correct the submitted papers. The material as it is presented, does not necessarily represent Brazilian Petroleum, Gas and Biofuels Institute’ opinion, or that of its Members or Representatives. Authors consent to the publication of this Technical Paper in the Rio Oil & Gas Expo and Conference 2012 Proceedings. Abstract In 2010, Petrolera Indovenezolana S.A. (PIV), a joint venture between Corporación Venezolana del Petróleo (CVP) and the Indian company ONGC Videsh Limited (OVL), started planning for two horizontal wells in the Norte Zuata (San Cristóbal) field in the Orinoco belt of eastern Venezuela. The focus for this campaign was to evaluate the productivity of horizontal wells in thin sands and avoid areas of complex geology because of the high uncertainty in the structural behavior, applying technology that provided absolute control of the drilling process into the Oficina formation. Within the Oficina formation, thin sand reservoirs with variations in thickness and dip, geologically facies changes and subseismic faults presented the main challenge to geosteering a horizontal well. Because the project faced high geological uncertainties, a pilot hole was drilled as the first stage in the first well to verify the structural levels and the continuity of the sand bodies. To achieve the above challenges, the combination of a rotary steerable system (RSS) “point-the-bit” and a deep azimuthal electromagnetic resistivity tool (DAEMR) was used. The measurements provided accurate information to the well-placement engineers for proactive decisions in real time, mitigating the possible loss of the target by these geologic uncertainties. High-quality and valuable data for real time geological model update were the expected results obtained from the effort made by PIV in the Norte Zuata (San Cristóbal) field, and the data showed the oil-producing potential of one of the main reservoir (Sand F,G). This application of high-tier technologies demonstrated that drilling and data measurements can be improved and optimized to yield added value for reservoir development and 100% net to gross (NTG) targets. This reduces operational cost, makes it possible to drill in the right place the first time, and pushes forward the limit of the achievable in terms of reservoir exposure. 1. Introduction: Background The Orinoco Oil belt encompasses an area of 55,314 km2 and is the world’s largest source of liquid hydrocarbon reserves — an estimated 1,360 billion bbl oil originally in place (PDVSA Ministry of Energy and Petroleum, 2006). The area under development (11,593 km2) is located along the southern margin of the eastern Venezuelan basin, parallel to and north of the Orinoco River, and extends across the Guárico, Anzoátegui, and Monagas states. This oil province is divided, from west to east, into four regions—Boyacá, Junín, Ayacucho, and Carabobo—and is segmented into 29 blocks of approximately 500 km2 each and two additional block areas: Boyacá Norte and Junín Norte. In the development area, Petróleos de Venezuela (PDVSA) considers that, of the 513 billion bbl of oil in place estimated by the United States Geological Survey (USGS) in 2010, 316 billion bbl is recoverable (Schenk et al., 2009). ______________________________ 1 Mechanical Engineer – Schlumberger 2 Civil Engineer – Schlumberger 3 Master, Geological Engineering – Schlumberger 4 Petroleum Engineer – Petrolera Indovenezolana S.A. 5 Geological Engineering – Petrolera Indovenezolana S.A. 6 Geological Engineering – Petrolera Indovenezolana S.A. Rio Oil & Gas Expo and Conference 2012 To recover such reserves, multiple companies and diverse nations in joint agreement with PDVSA have participated in exploration and production (E&P) in the 31 blocks. The joint venture company Petrolera Indovenezolana has a share distribution of 60% CVP and 40% OVL. In 2006, OVL was the second company that started operations in Faja, in an area of 160.18 km2 from the 799 km2 of the Norte Zuata (San Cristóbal) field, located in the Junín Norte area. In April 2008 the CVP and OVL signed the contract for the joint venture company Petrolera Indovenezolana S.A. The Norte Zuata (San Cristóbal) field has eight (8) reservoirs, corresponding to the sands D, E, F, G and H (Oficina Formation), I (Merecure Formation) and J/K (Temblador Group). The range of API gravity is on the order of 10 °API to 18 ° API. Nowadays the field has 64 horizontal producing wells by a progressive cavity pumping system. The main challenges encountered by PIV in the development and exploration of the Norte Zuata (San Cristóbal) field, is the drilling of horizontal wells in a structural and sedimentological complex frame which is why its main reserves are associated with thin sand bodies of large lateral heterogeneity. Because of these challenges it requires drilling horizontal wells in an effective way to optimize and achieve the maximum production of the reservoirs, associated with lower drilling costs based on minor drilling times. In the Orinoco Oil belt, 30% to 40 % of the oil in place is located in thin deltaic sand units of less than 20 ft in thickness, which are difficult to explore with conventional technology (Machado et al., 2009). For this kind of sand lenses it is necessary to cross through long lengths of net pay thickness in the horizontal section of the well, optimizing the recovery due to factors such as variable gross thickness, lower horizontal permeability to vertical permeability ratio and a lower conductivity. The oil production in these thin and discontinuous layers needs more complex well designs to be economically profitable. On the other hand, the Geological Models has limited information, because the low density of drilled wells and the heterogeneity of the reservoirs. Therefore, for the reservoir characterization it is necessary to drill pilot holes to identify geological elements such as lateral continuity of the sands, pinchout zones, fault location and local dip variations that are not detectable in the seismic data. Besides, the ramp profile present in the sand resistivity, requires for exploration and development in the field a technology able to achieve absolute drilling control and continuous mapping of the reservoir boundaries (top and base) for precise positioning from 3 to 7 ft below the top of the reservoir. The borehole assembly used in these two wells was composed of three innovative technologies: a rotary steerable system (RSS) to create a uniform borehole without tortuosity, improve the rate of penetration (ROP) and measure the inclination close to the bit; a deep azimuthal electromagnetic resistivity tool (DAEMR) to provide enhanced well placement by mapping reservoir boundaries in real time so as to proactively steer the well; and a high-data- transmission measurement-while-drilling (MWD) tool to improve the telemetry capacity for real-time MWD capability. This technology was used in two horizontal wells by Petrolera Indovenezolana which has been the key to improve the efficiency of drilling (decrease drilling time overall 2 to 3 days) in the desired zone and allowed achievement of the objectives in terms of improved reservoir contact regardless of formation characteristics. Figure 1.Venezuelan Orinoco Oil belt. Norte Zuata (San Cristóbal) field is located in the Junín Norte block. 2 Rio Oil & Gas Expo and Conference 2012 2. Reservoir Model Knowledge The Sand G of the Norte Zuata (San Cristóbal) field in the Junín Norte block (Figure 1) geologically belongs to the Oficina formation, South flank of the Venezuelan Oriental Basin. These sand beds occur in the basal part of the Oficina formation, deposited in a braided fluvial setting as fluvial bar systems of braided plains/multistacked channels and channel-fill bars. The sand G is constituted by three (3) sand bodies separated by thin shale layers, coalescent in the East area, associated to the Deposit OFIG NZZ0035. The OFIG NZZ0035 reservoir (Figure 2), discovered in 1981, encompasses an area of 50 km2 and contains an estimated 734 million bbl oil reserves in place, of which 153 million bbl are considered recoverable oil. Until July 2011, 24 billion bbl (~ 3 %) has been produced; 129 million bbl remain. Twenty-nine wells have been drilled and are active producers. NZZ - 269 NZZ - 268 - OH Figure 2.OFIN ZZ0035 structural map. The reservoir characteristics are as follows: • thickness: ~ 49 ft • porosity: ~ 22% • permeability: ~ 1,014 mD • oil saturation: ~ 80% • original pressure ~ 1,290 psi at 2,680 ft • current pressure: ~ 900 psi • reservoir temperature: ~ 155 deg F. The preferential sedimentation direction is SW-NE and the sediments are principally sands, which are represented by a flooding zone and channels, separated by thin claystone layers of interdistributary bay environment. It has been interpreted that the sediments corresponding to the G sand are from a Low Deltaic plain/interdistributary bay environments, where CU sequences (coarsening upwards) represent probably deltas and brakeage fans. The sandstone bodies that are separated by thin shale layers and FU sequences (fining upwards) could be interpreted as distributaries channels, with a sandstone degradation East-West till finer sediments, from interdistributary bay environments, are reached. The reservoirs are framed by structural - stragraphic traps. The structural regime is extensive and corresponds to a homocline with a low dip angle to the N-NE that increases to the South. This homocline has an internal normal fault system, with general E-W trend.