The 17Th HGS-PESGB Conference on African E&P

Home , Anambra Basin, Geology of Namibia, Geology of Niger, Muglad Basin, Ogaden Basin

The 17th HGS-PESGB Conference Est. 1964

PES .org.uk on African E&P pesgb Oral Presentations – Tuesday, September 11, 2018 7:30 Registration and Coffee 8:15 Welcome and Opening Remarks: Brian W. Horn, General Chair 8:20 Session 1 Chairs: Paul Haryott, Rose & Associates and Brian W. Horn, ION Theme 1 - African Exploration in the Evolving Business Environment - Above Ground Risks and Rewards 8:25 Opening Keynote Address Tim O’Hanlon (Tullow) 8:50 The Golden Age of Super Basins - An African Perspective Charles Sternbach (AAPG Past President) 9:15 Entering the Next Phase of the Oil Price Cycle: What It Means for E&P in Emma Woodward (Drilling Info) Sub-Saharan Africa 9:40 Coffee and Posters 10:00 Theme 2 - New and Emerging Exploration Trendss 10:05 Why is Everyone Excited About the Sao Tome and Principe EEZ; the 4 Key Matt Tyrrell (PGS), J. May, E. Mueller, Reasons Why This Has Been One of the Hottest Areas for Exploration in O. D’Abreu 2017 10:30 Compelling Evidence for Oil Offshore Angoche, Mozambique Neil Hodgson (Spectrum), R. MacDonald, P. Hargereaves, K. Rodriguez 10:55 Chasing the TAGI Play into Morocco: Assessing the Contribution of Local Jonathan Redfern (University of Manchester), Versus Regional Drainage Systems on the Character and Provenance of J. Lovell-Kennedy, J. Argent and J. Canning Upper Triassic Fluvial Deposits 11:20 Palaeozoic to Present: Assessing the Petroleum Potential of the Offshore Sirt Lisa Fullarton (ION), E. C. A. C. Gillbard, Basin, Libya, Using Newly Reprocessed Regional-scale 2D Seismic Data K. G. McDermott, N. Clarke, P. Bellingham 11:45 Special Session: Exploration in Africa Past, Present and Future – Moderator: Paul Haryott (Senior Assoc., Keys to Exploration Success and Disaster Avoidance Rose & Associates) 11:50 Exploration in Africa Past, Present and Future – A Historical Perspective Bob Fryklund (IHS) 12:05 Lunch and Special Session: Round Table Panel Discussion Exploration in Africa Past, Present and Future – Keys to Exploration Success and Disaster Avoidance Moderator: Paul Haryott (Senior Assoc., Rose & Associates) Panel: Ernie Leyendecker (former EVP Worldwide Exploration, Anadarko), Bob Fryklund (Chief Upstream Strategist, IHS), Dorie McGuiness (VP Geology, Kosmos), Tim O’Hanlon (VP African Business, Tullow) 13:30 Session 2 Chairs: Bill Dickson, DIGs and Bryan Cronin, Tullow Oil Ghana Ltd. Theme 2 - New and Emerging Exploration Trends (continued) 13:35 Break-up Processes in the Presence of Plume Magmatism: New Insights Ken G. McDermott (ION), E. C. A. C. into the Tectonostratigraphic Development and Petroleum Potential of the Gillbard, P. Bellingham, B. W. Horn Austral South Atlantic 14:00 The Austral South Atlantic: Early Formation and Crustal Structure of the Dale E. Bird (Bird Geophysical), S. A. Hall, Orange and Cape Basins D. J. McLean, P. J. Towle, J. V. Grant, and H. A. Danque 14:25 Post-rift Potential Source Rock Correlations and Prospectivity of the Deep Ian Davison (Earthmoves), Duncan Wallace Atlantic Conjugate Margins South of the Walvis Ridge 14:50 Offshore Somalia: Source Rock Identification in a Frontier Margin Neil Hodgson (Spectrum), H. Kearns, K. Rodriguez, B. Allen, D. Paton, and A. Abiikar Hussein (Spectrum) 15:15 Coffee and Posters 15:45 Hunting the SNE in Guinea Bissau Neil Hodgson (Spectrum), A. Intawong, and K. Rodriguez 16:10 Gabon’s Wild West Frontier Promises a Golden Age of Discovery for the Tony Younis (Impact Oil & Gas), Deep Offshore M. Clutterbuck, P. Birch 16:35 Gabon Deep Offshore: New Petroleum System Insights from the Full Rob Crossley (CGG) and G. Duval Integration of Geology and Geophysics 17:00 Evening Reception

2 HGS – PESGB 17th Conference on Africa E&P The 17th HGS-PESGB Conference Est. 1964

PES .org.uk on African E&P pesgb Oral Presentations – Wednesday, September 12, 2018 8:00 Registration and Coffee 8:30 Session 3 Chairs: Ana Krueger, University of Houston and Onochie Okonkwo, Anadarko Theme 3 - Developing and Integrating Geological Concepts: Impact on Exploration in Africa 8:35 Entrenched Slope Channel Complex Systems: Reservoir Opportunities Bryan Cronin (Tullow) Through Understanding Architectural Element Distribution and Application to West Africa E&P 9:00 Towards the Development of an Integrated Central Atlantic Max Casson (University of Manchester), Tectono-Stratigraphic Framework J. Redfern, L. G. Bulot, J. Jeremiah 9:25 Reservoir Modeling of a Deep-Water West African Reservoir: A Fully Monica Miley (Anadarko), A. Dufournet, Integrated, Multi-Scenario Approach J. Villa, M. Bentley 9:50 Sedimentological Characteristics of Deepwater Sandstones Associated with Luisa Man (CoreLab), Tom Wilson, Simon Transgressive-Regressive Cycles Offshore Ghana Greenfield 10:15 Coffee and Posters 10:40 Magmatic Modification of African Crust: Implications for Strain Cynthia Ebinger, SarahJaye Oliva, Ryan Localization and Basin Subsidence Gallacher (Tulane University) 11:05 An Animated Model for the Mesozoic-Recent Tectonic Evolution of Sub- Jon Teasdale, C. Reeves, (Geognostics International Saharan Africa: From Plates And Structures to Basins and Paleogeography Limited, Earthworks BV) 11:30 Tracing the West and Central African Rift and Shear Systems Offshore onto William Dickson (DIGs) and J. W. Granath Oceanic Crust: a “Rolling” Triple Junction 11:55 Influence of Proterozoic Heritage on Development of Rift Segments in the Ana Krueger (University of Houston), Equatorial Atlantic M. Murphy, I. Norton, K. Casey, R. D. de Matos 12:20 Lunch and Posters 13:45 Session 4 Chairs: Luis Baez Shell and Ian Davison, Earthmoves Theme 4 - What We Thought We Knew: Exploration Concepts to Production Reality 13:50 Keynote - The Evolution of the Pre-Salt Play in the Kwanza Benguela Andrew Witt (BP), A. Bump, T. Love and Basins, Angola F. Setzer 14:15 A New Beginning: Remaining Potential and the Case for Investment Paul Bellingham (ION), J. Deckelman, in the Niger Delta B. W. Horn 14:40 Play Fairway and Petroleum Systems Analysis of Nigeria’s Cretaceous Benin Olusanmi O. Emmanuel (Acetop Energy), (Dahomey) Basin: Key to Unlocking Additional Hydrocarbon Volumes from K. Taiwo, O. Mojisola and E. Enu an Emerging Exploration Trend 15:05 Coffee and Posters 15:30 Jubilee Field: From World Class Exploration Discovery to Producing Asset. Kathryn E. Dawson (Tullow Ghana Ltd) Learnings from 7 Years of Production 15:55 Closing Keynote/Future Perspective – Jubilee to Liza: Lessons From a Keith Myers (Westwood Energy), E. Zanella, Decade of Exploration in the Central Atlantic J. Collard, H. Doran 16:20 Awards and Closing Remarks

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PES .org.uk on African E&P pesgb Poster Session Agenda Using Generative Adversarial Networks to Improve Deep Learning Fault Prediction Networks Matt Morris, Ping Lu, Anadarko South Gabon’s Pre-Salt Revelation Neil Hodgson, Karyan Rodriguez, Spectrum Geo Multi-Client Seismic Imaging Data-Driven Transformation in Geology, Geophysics and Engineering Mik Isernia, Paul Endresen, Ana Krueger, Bluewarre, University of Houston Is Namibia Really an Oil Province? W. Wo r n a r d t , Micro-strat The influence of Shale Ridges on Reservoir Development and Implications for Exploration – Syed Dabeer, Umar Ngala, PetroVision A Case Study from Onshore Niger Delta, Nigeria Evolution of East African Rift System (EARS) Sadat Sembatya, Makerere University – Kampala, Uganda The Next Phase of Exploration in Sierra Leone: A Closer Look at the Basinward Cretaceous Magenta McDougall, African Petroleum Plays in the Search for Improved Reservoir Quality An Atlas of Character: A Model For the Control of Passive Margin Development Neil Hodgson, and K. Rodriguez, Spectrum Geo Visualization of Vertical Hydrocarbon Migration Pathways in Seismic Data: Toward the David Connolly, dGB Earth Sciences USA Quantification of Seal and Charge Risk for African Exploration Plays JMA – The Hidden Treasure Below the Basalt Neil Hodgson, K. Rodriguez, J. Watson, Spectrum Geo Hidden Boundary Fault at East African Rift Basin Revealed with FALCON© Airborne Gravity Janine Weber, Ivonne M, Araujo, R. Yalamanchili, Gradiometry Data S. Maduhu, CGG Multi-Physics, TPDC Enhancing Gas Production in Nigeria’s Marginal Field. A Case Study of Ughelli-X Field Kemi Taiwo, O. O. Emmanuel, O. Aworanti, T. Ologun and U. Olorunmola, ND Western Limited, Acetop Energy Cape Fold Belt Fractured Basement Play Fairway Neil Hodgson, K. Rodriguez, and H. Kearns, Spectrum Geo The Underexplored Shelf-Edge Plays of the West Africa Transform Margin and the Opportunity Matt Tyrrell, M. Martin, A. Ashfield, A. Maioli and B. to De-Risk These on Merged 3D Seismic and Well Datasets Through Togo, Benin and Biaou, PGS, Société Béninoise des Hydrocarbures (Sobeh) Western Nigeria Hydrocarbon Potential of the Onshore Dahomey Embayment of Benin; Exploration of Emma Tyrrell, P. Elliot and M. Lofgran, Elephant Oil Ltd Devonian, Jurassic, Cretaceous and Tertiary Plays Using Integrated Seismic and High Resolution Airborne Gravity and Magnetic Data Conjugate Margin Chronostratigraphy – Comparison of Cretaceous-Tertiary Petroleum Katie-Joe McDonough, K. Reuber, B. W. Horn, K. G. Systems in Namibia and Uruguay McDermott, E. C. Gillbard, F. Brouwer, KJM Consulting, Pine, ION, 3 GEO Regional Reservoir Quality Trands in Cretaceous Sandstone Reservoirs in the Transform Margin Simon Greenfield, Dr. P. Cox, Core Laboratories UK Basins of Ghana Using Broadband 3D Seismic to Validate and Upgrade Satellite Seepage Data, Gabon Rowan Edwards, M. King and G. Duval, CGG

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PES .org.uk on African E&P pesgb Student Poster Session Agenda 3-D Crustal Model of Northwest Africa Naila Dowla, Dale Bird, Mike Murphy, Janusz Grebowicz, University of Houston Geometry and Kinematics of Seismically Active Border and Transfer Fault Systems in Pham, T.Q., C. Ebinger, S. Oliva, K. Peterson, P. the Malawi Rift, Africa Chindandali, D. Shillington, Tulane University Comparing Controls on the Formation of 27 Passive Margin Fold-belts from the Margins Malik Muhammad Alam, University of Houston of the Gulf of Mexico, South Atlantic and Africa Compilation of Widespread, Cretaceous OAE1, OAE2, and OAE3 Black Shale Horizons Nikola Bjelica, University of Houston Documented in Wells from the Gulf of Mexico, Caribbean, and Atlantic Passive Margins New Insights into the Assembly and Breakup of Pangea from a Mega-regional Compilation Marie-Nelsy Kouassi, Paul Mann, Joel Saylor, Kurt of 8,672 Detrital Zircon Ages from the Circum-Gulf of Mexico, Northern South America, and Sundell, University of Houston West Africa Constraints on Central Atlantic Rrifting Based on a Compilation of Low-temperature Geraldine Tijerina, University of Houston Thermochronology Ages from Rifted, Conjugate Margins of the East Coast of the USA and Northwestern Africa Is Africa Stationary? —A New Look at an Old Question Daniel Woodworth, Chengzu Wang, Nuhazein Mohamed and Richard G. Gordon, Rice University Rift History of the South Atlantic Ocean from Subsidence Histories of Offshore Wells Omar Zavala, University of Houston and Low-temperature Thermochronology (AFT) Cooling Ages from the South American and West African Conjugate Margins Plate Tectonic Framework for Petroleum Systems of Atlantic Conjugate Margins: Marcus P. Zinecker, Paul Mann, University of Houston Northwest Africa-Eastern USA and Northeast South America-Equatorial West Africa Application of Raman Spectroscopy for Determination of Natural Gas Composition Johnathan Torres, Sage Muttel, Dougles Syzdek, S, Nagy, Janusz Grebowicz, AGH University of Science and Technology; University of Houston- Downtown

HGS – PESGB 17th Conference on Africa E&P 5 Notes

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PES .org.uk on African E&P pesgb

Oral Presentations Day One Abstracts

September 10-13, 2018 Norris Convention Centre, Houston Texas Tuesday, September 11 | Opening Keynote Address | 8:25 Tim O’Hanlon Tullow Oil

Tim O’Hanlon is from Ireland. As a young Reservoir Engineer fresh from Imperial College London, he joined Ireland’s brand new start-up, Tullow Oil, in the mid 1980’s. He has been with this very exciting and ambitious company ever since, living in Africa for many years.

More recently as Vice President African Business, or Tullow’s Mr Africa, Tim has helped to drive Tullow’s rapid expansion on the Mother Continent. Whether it is targeting new company acquisitions in Africa, chasing new ventures or mending fences in the many African countries where Tullow operates, you can be sure that Tim’s fingerprints can be found on the files.

8 HGS – PESGB 17th Conference on Africa E&P widespread value to energy producers not just in super basins. Super basins are creating valuable contributions to our energy, economy, and environment. We will continue to enjoy abundant and affordable energy due to super basins. In addition, super basins will have a great impact on sustainability, security, and geopolitical factors.

We believe that: 1) our energy industry has made major contributionsTuesday, to global September prosperity, 11 2)| Theme 1 | 8:50 this prosperity will grow far into the future, and 3) professional societies will continue toCharles play a A. Sternbach key role in preparing men and women to provide this energy and prosperity longPresident into our of AAPGnext (2017/2018) century. Thus, we begin the super basins initiative.

The Golden Age of Super Basins Figure 1. Map of top 25 super basins, (courtesy IHS_Markit) An African Perspective

Figure 1. Map of top 25 super basins, (courtesy IHS_Markit)

Building on the success of AAPG Discovery Thinking well length in the realization of unconventional resources. These (individual game changing discoveries) and Playmaker basins are benefiting from multi generations of engineering Forums (exploration plays), we are up-scaling our efforts to refinements and breakthroughs. the basin scale and total petroleum system of the world’s most petroliferous basins. The introduction of the Global Super Basin Other basins, many offshore, are benefiting from improved Leadership Conference in March in Houston provided the seismic imaging to unlock deeper or hidden basins, sedimentary opportunity to share best practices among the world’s greatest packages previously obscured for various reasons. Many of the basins. AAPG plans to advance our mission to deliver science new resources are being found below salt or around basement and professionalism through multimedia presentations, a new highs. Examples include GOM, Brazil, and the European North initiative to publish papers on super basins in the AAPG Bulletin, Sea. Some basins benefit from both engineering and seismic. and other events. In all cases, understanding the geoscience architecture is key to success. Many super basins in Africa need further study. Super Basin Anatomy Many Super Basins were thought to be on their way out of The AAPG Bulletin Initiative sustainable production. Key enablers that have made possible The AAPG Bulletin introduces a new initiative for its second old basins reaching new production peaks include hydraulic century – the super basin series. The inaugural publication fracturing in horizontal wells and enhanced seismic imaging. features an overview of the super basin concept by Bob Each basin has unique geoscience architecture. A common Fryklund and Pete Stark (IHS_Markit). AAPG plans to roll out scheme includes multiple rich source rocks located beneath thick new super basin papers regularly in the months ahead. Together sedimentary packages containing many reservoirs and seals. with the AAPG Editor, Barry J. Katz, our plan is to build a legacy of foundational papers of the world’s top petroliferous Onshore basins like the Permian are dominated by perfecting areas that continue to produce prodigious amounts of energy multi-lateral multi-directional drilling, finding the right fluid (Figure 1). We anticipate that these papers will be revisited as a mix, varying hydraulic fracture stages, proppant materials, and valuable resource in the years and decades ahead. The authors

HGS – PESGB 17th Conference on Africa E&P 9 of these papers will be invited and acknowledged for their hydrocarbon production, each peak represents new technology expertise in their particular basin or region. It is also envisioned and ideas that resurrect a maturing or declining petroleum that super basins will be an important component of AAPG province. Many of the super basins that will be featured in this conferences and technical events. series discuss basins that only recently were thought to be played out but are now experiencing production peaks and in some These publications will show the importance of geoscience cases exceeding production peaks of previous decades, such as as these basins continue to have new life breathed into them in the Permian basin. The super basin series will also discuss by innovative geoscientists using new technology, and how the new technology driving this rejuvenation and the sharing of rocks tell the story. This series will frame the geoscience best practices of these new technologies that can be applied in architecture of the world’s most petroliferous basins including various super basins. an understanding of their petroleum systems, richness, distribution, and position in the stratigraphic column of the Topics the papers will address include: source rocks and their maturity and an appreciation of the • What makes a super basin special and unique and what can reservoirs, seals, and structural configuration. For example, the we learn from them? Permian Basin will be included in this series. It is endowed with • What are the critical geoscience elements that contribute to multiple rich source rocks (Simpson, Woodford, Barnett, and success? Permian/Pennsylvanian) deep within the sedimentary section that contains many reservoir seal pairs, all within the oil and • What is the exploration/ production history, and what are gas window, a shallow regional evaporite seal and a structural the major plays with remaining potential - conventional, evolution that prevents leakage to the surface, abundant surface unconventional, and field growth. infrastructure, open access to mineral rights, and favorable • What are key innovations in each super basin like: adoption regulation. of horizontal drilling, hydraulic stimulation, completion and drilling techniques, and seismic imaging that helped unlock “Petroleum Provinces of the Twenty-first Century” (Marlan the potential, and what is needed to grow it further? Downey, Jack Threet, and William Morgan 2001) AAPG • How do “above ground” issues like politics, access, mineral Memoir 74, was a landmark publication for frontier exploration. ownership, and geography influence realizing the full The super basins concept is a dramatically different focus in a resource potential of each super basin? return to established mature basins, where resources are known to be present, and will be a key resource for tomorrow’s oil and • Will the basin be a regional or global disrupter? gas supplies. In addition to their geologic energy endowment, super basins Super basins, as defined by Fryklund and Stark, are established have large scale and infrastructure to incubate new technology. producers with at least 5 billion boe produced and 5 billion Technology nurtured and proven in super basins has great boe remaining recoverable, two or more petroleum systems or relevance and application to basins of all sizes. Thus, super basin source rocks, stacked reservoirs, existing infrastructure / oil field papers will have widespread value to energy producers not just services, and access to markets. Horizontal drilling and multi- in super basins. Super basins are creating valuable contributions staged horizontal fracturing and their unconventional resource to our energy, economy, and environment. We will continue to potential are driving the onshore super basin renaissance. enjoy abundant and affordable energy due to super basins. In Improved seismic imaging, particularly below salt (or obscurred addition, super basins will have a great impact on sustainability, layers), is driving offshore super basins rejuvenation. The security, and geopolitical factors. Permian Basin, Gulf of Mexico, and Middle East basins are prototype oil and gas prone super basins. We believe that: 1. our energy industry has made major contributions to global Energy is where you find it. In many cases, the most promising prosperity reserves for today and tomorrow are in areas that have long been 2. this prosperity will grow far into the future, productive. The total petroleum systems concept guides our 3. professional societies will continue to play a key role in approach. Much has been said and written about peak oil. Peak preparing men and women to provide this energy and oil is a concept defined by a population of energy accumulations prosperity long into our next century. known, detectable, and producible at a particular time and place. When there are “multiple” peaks to a basin historical Thus, we begin the super basins initiative. n

10 HGS – PESGB 17th Conference on Africa E&P Biographical Sketch In addition, Charles created the AAPG Playmaker program in Charles A. Sternbach has 2012. These immersive 1-day forums on exploration creativity explored for and discovered have been presented 10 times in the US, Canada, and Europe. Energy in the US and around More than 1,500 professionals have attended and presentations the globe for 35 years. He was have received 10,000 web views around the world. More of these Staff Geologist for Shell Oil forums are planned. Company, Exploration Manager for Tom Jordan (Jordan Oil and Charles believes case histories of successful explorers and their Gas), President of First Place discoveries is a shortcut to wisdom. Every geologist around the Energy (International frontier globe raises the level of collective intelligence for all by sharing exploration) and is currently information and techniques. Critical insights fall into patterns President of Star Creek Energy. that can be recognized and anticipated. The legacy of exploration Charles has a PhD (and MS) literature forms a syllabus for future explorers. Technology enables in Geology from Rensselaer preservation and communication of critical knowledge via the Polytechnic Institute and a BA in geology from Columbia internet through programs like Search and Discovery, Datapages, University. He is also proudly a member of AAPG since 1980. and GIS spatial related databases. Prior to founding the Discovery Thinking forums, Charles founded the HGS Legends programs (as Charles has focused his efforts on Exploration Creativity, HGS president in 2000). He is a co-editor with Dr. Robert Merrill studying how explorers and their teams have found giant fields. on the fifth installment of the AAPG memoir series Giant Fields of He created and leads the popular AAPG Discovery Thinking the Decade 2000-2010 (Memoir 113). Forums which have been standing room only events at annual AAPG conventions in North America (ACE) and around the Charles resides in Houston, Texas. His wife Linda is also a world (ICE). These impactful programs integrate geology, distinguished geophysical advisor. Charles is a leader in the geophysics, and engineering into case studies of business success. global geological community: president-elect AAPG, past There have been 19 Discovery Thinking Forums since 2008 president Gulf Coast Association of Geological Societies, past with about 10,000 attendees. About 115 speakers have permitted president Houston Geological Society, and past president of their video presentations to be posted on the AAPG Search AAPG’s Division of Professional Affairs. He is an Honorary and Discovery Website with 40,000 viewings around the globe. Member of AAPG, HGS, GCAGS, and DPA.

HGS – PESGB 17th Conference on Africa E&P 11 Tuesday, September 11 | Theme 1 | 9:15 Emma Woodward Regional Manager – East, West & South Africa, DrillingInfo Entering the Next Phase of the Oil Price Cycle: What it means for E&P in Sub-Saharan Africa

After several years of industry downturn it appears we are finally Industries Bill being passed in Parliament, and militant activity entering into the next phase of the oil price cycle. At the time being curbed from its 2016 peaks. The government has signed of writing (March 2018), oil prices have stabilised at US$60-70/ a deal for new offshore multi-client seismic to take place, in bo and most oil companies have either managed to successfully preparation for a future offshore licensing round, for which there reduce their operational costs and budgets, or have gone under. has been significant interest. All legislative issues will need to However, service costs remain low, meaning it’s an ideal time for be resolved before this can be launched. There is also a renewed companies with a healthy balance sheet to be undertaking new sense of optimism surrounding Angola, where there have been exploration and development programmes. Renewed optimism signs that the government is willing to incentivise investment in the industry has resulted in a significant uptick in the number again, with new tax deals being signed with both producers of awards, acquisitions, and farm-ins being made. This has and explorers. Whilst it is unlikely companies will re-enter the been predominantly driven by the majors and supermajors, deepwater Kwanza Basin in the near future, much interest has but independents will follow. A corresponding increase in the been generated in the ultra-deepwater Lower Congo Basin. amount of seismic shot and number of exploration wells drilled is now expected, particularly through 2019. Long-delayed field E&P activity has also been increasing in Ghana, Cote d’Ivoire, development plans are also finally moving forwards again. This Equatorial Guinea, Sao Tome & Principe, Gabon, Namibia, will provide much needed relief for seismic and rig contractors. and South Africa. However, operations in East Africa have so far remained depressed. This is in part due to the inability In Sub-Saharan Africa, recent operations have generally been of governments to move quickly: with drawn-out decisions focussed in offshore West Africa, both in emerging basins such over infrastructure (for example the East African Crude Oil as the MSGBC (Mauritania-Senegal-Gambia-Bissau-Conarky), Pipeline and the onshore LNG plant in Tanzania) and the but also in more mature basins such as in Nigeria, Gabon, and delayed ratification of new awards (most notable in Tanzania Angola. East Africa has lagged behind the recovery. and Mozambique) leading to companies losing interest or changing operational strategy; Additionally, companies appear The MSGBC Basin has been one of just a handful of global less keen to invest in gas-prone basins, due to the longer-lead exploration hotspots to have emerged since 2014, and times to production, distance to markets, and in some cases lack supermajors such as ExxonMobil, BP, and Total, as well as Asian of clarity surrounding fiscal terms for gas. Many geologically NOC’s CNOOC and PETRONAS have worked hard to establish attractive areas onshore East Africa are also far from possible a footprint. The first mover advantage has now long gone, and markets, resulting in the need for substantial investment for smaller independents looking for a slice of the pie the only in infrastructure prior to first production. But plenty of remaining opportunities may be in Guinea-Bissau, historically opportunities remain, and with the right incentives companies seen as a riskier place to operate. will be attracted back to the region.

Nigeria remains the largest producer in Sub-Saharan Africa, This presentation will look at some of the main E&P events and as a result has severely suffered economically through of 2018, and will look forward to what Drillinginfo expects to the downturn. It has also suffered serious security problems: take place through 2019 and beyond across key countries in offshore piracy, militant attacks in the Niger Delta, and Boko Sub-Saharan Africa. There will be particular focus on major Haram activity in its northern provinces (where NNPC is trying legislative changes and other above ground risks, key asset to kickstart a frontier exploration programme). Uncertainty transactions, licensing rounds and awards, discoveries made, over the fiscal regime has also not helped the E&P outlook. important future wells, significant upcoming field development However, the situation is changing, with parts of the Petroleum plans, and options for gas utilisation. n

12 HGS – PESGB 17th Conference on Africa E&P Biographical Sketch Emma Woodward graduated from the University of Cambridge in 2012 with a BA in Natural Sciences and an MSci in Geological Sciences. She has been working at DrillingInfo since June 2013 and is currently the Regional Manager for West, East & Southern Africa. Prior to working at DrillingInfo, Emma completed a petroleum geology internship at BP.

HGS – PESGB 17th Conference on Africa E&P 13 outputs of all four of these fluvial systems resulting in a thick succession of well-sorted, distal fluvial outflow sediments with varying points of input (Figure 2). 4) Basin Modelling studies suggest that Cretaceous, syn-kinematic sediment fills are mature for oil: The revised crustal models and new sub-Akata play concepts of the outboard Niger Delta, together with temperature data from wells within the vicinity, have provided input for a recent basin modelling Tuesday, September 11 | Theme 2 | 10:05 Matt Tyrrellstudy, Joshua undertaken May, Eric Mueller by PGS (Figure 2). The study has modelled numerous pseudowell locations in STP- PGS EEZ with the results showing that both the syn-kinematic sediments and the early post-kinematic Ovsvaldo sedimentsD’Abreu (Cenomanian-Turonian) are mature for oil, and are able to have charged the multiple National Petroleumsandstone Agency reservoirs of São Tomé of the & PríncipeTertiary (ANP-STP) succession. WhyConclusions is Everyone Excited About the Sao Tome and The recent excitement that the industry has experience over STP-EEZ has its roots it recent advances Principein the understanding EEZ; the of the 4 petroleumKey Reasons stories of the Whydeepwater This Niger Delta Has and theBeen Northern Gabon Basin. As exploration advances and wells are planned, it may only be a matter of time before we see Onethe fruits of thatthe these Hottest new play conceptsAreas may for bear. Exploration in 2017

Exploration work conducted by PGS has sought to delineate the tectonic history and the nature of the crustal basement by calibrating both shipborne and public gravity data with Figuremulticlient 1. 2D Basemap seismic data showinginterpretations, the and multiclient then to use these seismicresults as input datasets and calibration that span for basin from models the to Nigerconstrain Delta,source rock through maturity STP and expulsion-EEZ to modelling. North Gabon Basin. The four key reasons why the Săo Tomé and Príncipe Exclusive Economic Zone (STP-EEZ) have been one of the hottest exploration areas of 2017 1. Continental and transition crust provides source and structure: Historic geological interpretations have predicted that the Figure 1. Basemap showing the multiclient seismic datasets outboard waters of the southern Gulf of Guinea, including that span from the Niger Delta, through STP-EEZ to North the Niger Delta, are underpinned by oceanic crust. Modern Gabon Basin. long-offset seismic Figuredata and its2. applicationAVO analysis in the calibration highlights Introduction of gravity data, has resulted in revised crustal models The Săo Tomé and Príncipe Exclusive Economic Zone that suggest these outboardanomalies areas containin sands a mélange associated of with (STP-EEZ) lies within the heart of a successful petroleum continental, transitional,transform and oceanic fracture crustal zonetypes controlled structures . neighborhood that in recent years has been the subject of by transform fracture zones. These revised crustal models significant attention from major oil companies scrutinizing have alerted oil companies to the potential for syn-kinematic the available multiclient datasets, and applying for exploration sediment fills that can provide restricted marine source rock licenses over multiple open blocks. deposits and accompanying structural plays. 2. Sub-Akata Shale plays in the distal parts of the Niger With a large multiclient seismic and well data library that reveals Delta: the subsurface geology of the Niger Delta (Figure 1), the distal In the Niger Delta, historic exploration efforts have parts of the Douala and Rio Muni Basins, and the North Gabon concentrated on thick Tertiary siliciclastic reservoirs charged Basin, PGS has conducted interpretation work to unravel the by the underlying Akata Shale source rock. An exciting prospectivity story and explain the recent excitement that the new play concept, that has captured the recent attentions industry has experienced over the STP-EEZ. of operators and explorers alike, is within the sub-Akata sedimentary succession of the distal or outboard parts of the Fitting into the regional geological picture Niger Delta, where a thinned Tertiary succession (and thus The STP-EEZ is bounded to the north by the Niger Delta with reduced overburden to the Akata Shale) lies atop continental its prolific Tertiary deltaic petroleum systems, to the east by or transitional crusts. This play that is yet untested, models Equatorial Guinea and Cameroon where the Rio Muni and syn-kinematic sediment fills to contain source rocks that are Douala basins have witnessed exploration success in Cretaceous mature for oil that has charged pre-Akata reservoirs with plays, and to the south by Gabon, the northernmost Aptian salt hydrocarbons trapping beneath the Akata Shale. basin with associated halokinetic plays and discoveries. Towards the south, this play continues into and is directly correlatable to the tectonic and sedimentary successions of STP-EEZ.

14 HGS – PESGB 17th Conference on Africa E&P outputs of all four of these fluvial systems resulting in a thick succession of well-sorted, distal fluvial outflow sediments with varying points of input (Figure 2). 4) Basin Modelling studies suggest that Cretaceous, syn-kinematic sediment fills are mature for oil: The revised crustal models and new sub-Akata play concepts of the outboard Niger Delta, together with temperature data from wells within the vicinity, have provided input for a recent basin modelling study undertaken by PGS (Figure 2). The study has modelled numerous pseudowell locations in STP- EEZ with the results showing that both the syn-kinematic sediments and the early post-kinematic sediments (Cenomanian-Turonian) are mature for oil, and are able to have charged the multiple sandstone reservoirs of the Tertiary succession. Conclusions The recent excitement that the industry has experience over STP-EEZ has its roots it recent advances in the understanding of the petroleum stories of the deepwater Niger Delta and the Northern Gabon Basin. As exploration advances and wells are planned, it may only be a matter of time before we see the fruits that these new play concepts may bear.

Figure 1. Basemap showing the multiclient seismic datasets that span from the Niger Delta, through STP-EEZ to North Gabon Basin.

Figure 2. AVO analysis highlights anomalies in sands associated with transform fracture zone structures.

3. Thick clastic sedimentary successions fed from long-lived fluvial systems: Within the Doula Basin, the long-lived fluvial systems of Figure 3. Results of Basin Modelling work show that maturity Cameroon and Equatorial Guinea such as the Sanaga River trends follow major fracture zones. and the Rio Del Rey River, which are understood to have Figure 3. Results of Basin Modelling work show that maturity trends follow major historic roots in the Cretaceous period, have resulted in fracture zones. thicker Upper Cretaceous and Tertiary sediment successions. Biographical Sketch To the south, the Ogooué River of Gabon is present day Matt Tyrrell attained an MSc the fourth largest river in Africa and again has a long-lived in Petroleum Geoscience from history, shedding large volumes of clastic sediments into the Oxford Brookes University North Gabon Basin. Located within the heart of the southern before joining Fugro-Aperia Gulf of Guinea, the waters of STP-EEZ have received the as an engineer, then Aceca as a distal outputs of all four of these fluvial systems resulting Geologist focused on North Sea in a thick succession of well-sorted, distal fluvial outflow stratigraphy. He joined TGS in sediments with varying points of input (Figure 2). 2006 where he was responsible for geoscience interpretation 4. Basin Modelling studies suggest that Cretaceous, syn- in Canada and Brazil, before kinematic sediment fills are mature for oil: joining the TGS Africa group The revised crustal models and new sub-Akata play concepts as Lead Geologist where he of the outboard Niger Delta, together with temperature data worked on new ventures and from wells within the vicinity, have provided input for a interpretation projects focused on East and West Africa. Matt recent basin modelling study undertaken by PGS joined PGS in 2015 as Principal Geologist for Africa where he (Figure 2). The study has modelled numerous pseudowell works on geoscience and business development tasks in West locations in STP-EEZ with the results showing that both Africa, with a focus on Cote d’Ivoire, Benin, Congo, and Angola. the syn-kinematic sediments and the early post-kinematic sediments (Cenomanian-Turonian) are mature for oil, and Matt is a principal geoscientist and project developer with over are able to have charged the multiple sandstone reservoirs of 18 years of industry experience. Responsible for delivering the Tertiary succession. exploration opportunities to clients through an understanding Conclusions of geoscience, project development, business development, and The recent excitement that the industry has experience over both client and Ministry relationships. He is responsible for STP-EEZ has its roots it recent advances in the understanding developing, scoping, and delivering integrated geoscience studies of the petroleum stories of the deepwater Niger Delta and the that provide our clients with exploration opportunities Northern Gabon Basin. As exploration advances and wells are planned, it may only be a matter of time before we see the fruits that these new play concepts may bear. n

HGS – PESGB 17th Conference on Africa E&P 15 Compelling Evidence for Oil Offshore Angoche, Mozambique

Neil Hodgson, Robert MacDonald, Phillip Hargereaves, Karyna Rodriguez, Spectrum Geo, United Kingdom

+44 1483 730201, [email protected]

INTRODUCTION The Rovuma Basin in northern Mozambique is a a well-established world-class gas province with over 100 TCF of gas discovered so far. The rest of the Mozambique margin remains unexplored with most oil companies trying to find the big oil prize. Spectrum is acquiring a 2D regional seismic grid designed to image the subsurface potential in the southern Rovuma Basin and the NE Zambezi Delta (Angoche) region, providing a more detailed understanding of the prospectivity where no wells have been drilled to date. Potential targets along the Mozambique margin have already been identified in both structural and stratigraphic trapping geometries. Several potential source, reservoir, and seal intervals have also been identified with Cretaceous and Tertiary play types including onlaps and drapes over basement highs, stratigraphic and structural traps of deep water slope channel and basin floor fan complexes, lowstand plays (both wedge and pro-delta fan), Tuesday, September 11 | Theme 2 | 10:30 syn-rift graben hanging wall and footwall plays, and strike slip structuralNeil plays. Hodgson Enhanced, Robert clastic MacDonald, reservoir Phillipquality Hargereaves,is expected Karyna Rodriguez from turbidite systems interacting with strong drift currents which are knownSpectrum to winnow Geo, United turbidite Kingdom channels leaving behind reservoirs of exceptional quality such as the Lower Grudja formation, a+44 recognized 1483 730201, significant [email protected] reservoir target, with sandstones exhibiting porosities up to 34% and permeabilities up to 5,000 mD. Recent understanding of the influence of active rifting and mantle plume activity causing elevated heat flow in the northern RovumaCompelling Basin, has explained the Evidence for Oil Offshore anomalously high geothermal gradient in that area which has resulted in significant gas generation. Spectrum’s acquisition area, east of the Zambezi and south of the Rovuma, is far from rifting and mantle plume activity such thatAngoche, geothermal Mozambique gradients are lower and so the main potential source rocks are modelled to be generating oil, as supported by onshore oil seeps. of deep water slope channel and basin floor fan complexes, lowstand plays (both wedge and pro-delta fan), syn-rift graben hanging wall and footwall plays, and strike slip structural plays. METHODOLGY Enhanced clastic reservoir quality is expected from turbidite systems interacting with strong drift currents which are known Two hundred forty two optical satellite images covering the central to winnow turbidite channels leaving behind reservoirs of Mozambique offshore have been examined for evidence of oil exceptional quality such as the Lower Grudja formation, a floating on the surface of the sea. These sea surface slicks, when recognized significant reservoir target, with sandstones exhibiting porosities up to 34% and permeabilities up to 5,000 mD. Recent appearing in persistent clusters can be indicative of a working understanding of the influence of active rifting and mantle plume subsurface hydrocarbon system. The principle takes advantage of activity causing elevated heat flow in the northern Rovuma Basin, the difference in surface texture between a natural sea surface and has explained the anomalously high geothermal gradient in that an oil slick floating on top of the sea. In suitable conditions the sea area which has resulted in significant gas generation. Spectrum’s acquisition area, east of the Zambezi and south of the Rovuma, is surface is slightly rougher than the oil slicks; sunlight reflects off far from rifting and mantle plume activity such that geothermal the slick in a different direction than the sea and this is captured by gradients are lower and so the main potential source rocks are the satellite image [1]. Distinguishing between pollution and modelled to be generating oil, as supported by onshore oil seeps. naturally occuring slicks is critical. By looking for locations with Methodolgy persistently occuring slicks (i.e. found in images of different dates) Two hundred forty two optical satellite images covering the forming a cluster over time we can rule out random pollution events central Mozambique offshore have been examined for evidence and be confident that the oils are indicative of a naturally occuring of oil floating on the surface of the sea. These sea surface slicks, thermogenic oil source. when appearing in persistent clusters can be indicative of a working subsurface hydrocarbon system. The principle takes advantage of the difference in surface texture between a natural OIL SEEP OBSERVATIONS sea surface and an oil slick floating on top of the sea. In suitable conditions the sea surface is slightly rougher than the oil slicks; In total 120 sea surface slicks were identified in the interest area, Figure 1. Regional Map showing analysis locations sunlight reflects off the slick in a different direction than the sea some comprised of clusters re-occuring over time. The majority Figure 1 : Regional Map showing analysis locations and this is captured by the satellite image [1]. Distinguishing follow the continental shelf edge along the East coast of Introduction between pollution and naturally occuring slicks is critical. By looking for locations with persistently occuring slicks (i.e. found Mozambique. Sedimentary facies from the Mozambique channel generallyThe Rovumadip gently Basin upwards in northern towards Mozambique the shelf is edge,a a well- so it established world-class gas province with over 100 TCF of gas in images of different dates) forming a cluster over time we can is thought that a mature oil source in the centre of the basin is responsible, with hydrocarbons migrating upwards and discovered so far. The rest of the Mozambique margin remains rule out random pollution events and be confident that the oils Westwards towards the mozambique coast. There is a very prominentunexplored cluster of withslicks most in the oil companiesregion of Angochetrying to find Island. the big oil are indicative of a naturally occuring thermogenic oil source. Observed on images from several different dates, these slicks are alsoprize. located Spectrum away is from acquiring the predominant a 2D regional marineseismic gridroutes. designed Oil Seep Observations They are evident near the onshore location slicks also identified at Angocheto image. Some the subsurface trends have potential been in observedthe southern in Rovumadeeper Basin and the NE Zambezi Delta (Angoche) region, providing a more In total 120 sea surface slicks were identified in the interest water, 185 km from the Mozambique coast. Image availability is much lower here, so identifying repeating trends is more detailed understanding of the prospectivity where no wells have area, some comprised of clusters re-occuring over time. The been drilled to date. Potential targets along the Mozambique majority follow the continental shelf edge along the East coast margin have already been identified in both structural and of Mozambique. Sedimentary facies from the Mozambique stratigraphic trapping geometries. Several potential source, channel generally dip gently upwards towards the shelf edge, reservoir, and seal intervals have also been identified with so it is thought that a mature oil source in the centre of the Cretaceous and Tertiary play types including onlaps and basin is responsible, with hydrocarbons migrating upwards drapes over basement highs, stratigraphic and structural traps and Westwards towards the mozambique coast. There is a very

16 HGS – PESGB 17th Conference on Africa E&P difficult. However, a large number of high confidence oil slicks are observed from a single image, grouped together over a 10km area, away from shipping routes (Figure 2, location E). This unusual distribution of oil slicks appears in correlation with the Grandidier seamount. Two similar groups of slicks are observed (Figure 1, locations E & G) difficult. However, a large number of high confidence oil slicks are observed from a single image, grouped together over a 10kmOIL area, SEEP away ANALYSIS from shipping routes (Figure 2, location E). This unusual distribution of oil slicks appears in correlation with the Grandidier seamount. Two similar groups of slicks are observed (Figure 1, locations E & G)

OIL SEEP ANALYSIS

Figure 2 : Example Seismic Line F [2] The distribution and re-occurrence of the slicks convincingly indicates that there is or has been a mature oil source in the Mozambique Channel. Persistently occuring oil slicks in Figure 2 : Example Seismic Line F [2] [2] correlationFigure 2 with: Ex athemple basin Seismic edge Linefrom F the north to the southThe of distributionthe study area and prominentre-occurrenceindicate cluster that ofof slicks thethe slickssource in the convincingly rock region is presentof Angoche indicate throughouts Island. that there the channelis or fracturedhas rather been andthana faulted. Observedmaturefocused on oil images source in smaller from in the several subMozambique basins. different Channel. dates, these Persistently slicks occuringThese oil slicksprovide in are alsocorrelation located withaway the from basin the edge predominant from the northmarine to routes.the south of the idealstudy conduits area for Theyindicate are Lookingevident that theatnear the source the some onshore rock of the is locationpresent available throughoutslicks seismic also (e.g. identifiedthe channelFigure 2) rather hydrocarbons it is easythan to see to why at Angoche.focusedslicks Some in maysmaller trends be subfocused have basins. been at this observed point. The in deeperbasin geolog water, y dips upwardsmigrate updip and and 185 km fromwestwards the Mozambique towards the coast. edge Image of the availabilitybasin. At least is much three sourceescape have through been the lowerLooking here,proposed so at identifying the insome the ba ofrepeating sthein, availablefrom trends Late seismic Triassic is more (e.g. Karoo difficult. Figure to sources 2) it is inaboveeasy the tomid geology. see Jurassic. why However, a large number of high confidence oil slicks are slicksThe may Triassic be focused and Albian at this stratapoint. moveThe basin up dip geolog towardsy dips the upwards shelf edge and so could well observed from a single image, grouped together over a 10km Conclusions westwardsexplain towards the assemblage the edge of seepsthe basin. found At thereleast threebut the source Cretaceous have been plays pinch out further offshore. These strata pinching out area, away from shipping routes (Figure 2, location E). This The distribution and re-occurrence of the slicks provides strong proposed in the basin, from Late Triassic Karoo to sources in the mid Jurassic. unusual distributioncould explain of the oil seaslicks surface appears slicks in correlation that were not with part the of theevidence main clusters. that there The isDFZ or hasis up been dip aof mature the potential oil source Triassic in the The Triassic and Albian strata move up dip towards the shelf edge so could well Grandidiersource seamount. rocks andTwo between similar groups the source of slicks and arethe observedGrandidier seamountMozambique are a Channel.series of onlapSlicks terminations,along the entire fractured shelf edge and andfault ed. (Figureexpl 1ainThese, locations the assemblageprovide E & idealG) of conduits seeps foundfor hydrocarbons there but the to Cretaceous migrate updiparound plays and pinch several escape out bathymetric throughfurther offshore. the highsabove These in geology. the strata study pinchingarea suggest out that could explain the sea surface slicks that were not part of the mainthe clusters. source Theis regionally DFZ is up prolific.The dip of the potential distribution Triassic does not allow Oil SeepsourceCONCLUSIONS Analysis rocks and between the source and the Grandidier seamountus to are isolate a series the ageof onlap of the terminations, hydrocarbon fractured source rock;and fault but ed.three The Thesedistribution provide and ideal re-occurrence conduits for hydrocarbonsof the slicks convincingly to migrate updip andpossible escape source through rock the intervals above havegeology. been proposed, from the Late indicates Thethat distributionthere is or hasand been re-occurrence a mature oilof thesource slicks in providethe s strongTriassic evidence (Karoo) that and there Mid is Jurassic.or has been New a 2Dmature data oilwill source play a in key the MozambiqueCONCLUSIONSMozambique Channel. Channel. Persistently Slicks occuring along theoil slicksentire inshelf edge androle around in refining several ourbathymetric understanding highs inof thethe studyhydrocarbon area sugge potentialst correlationthat with the thesource basin is edgeregionally from prolific.Thethe north to distribution the south ofdoes notof allow the areaus to and isolate accelerate the age hydrocarbon of the hydrocarbon exploration source activity rock; inbut the studyThe distributionthree area indicatepossible and that source re- theoccurrence rocksource intervals rock of the is have slickspresent been provide throughout proposed,s strong from evidencewhat the is Latebelieved that Triassic there to isbe (Karoo) or an has oil-dominated beenand Mid a mature Jurassic. region oil source Newwith 2Dexceptional in datathe will the channelMozambiqueplay rather a key Channel. than role focusedin refining Slicks in along oursmaller understanding the sub entire basins. shelf of edgethe hydrocarbon and aroundquality potentialseveral reservoirs. bathymetric of the n area andhighs accelerate in the study hydrocarbon area sugge explorationst that theactivity source in what is regionally is believed prolific.The to be an distributionoil-dominated does region not allowwith exceptionalus to isolate quality the age reservoirs of the hydrocarbon. source rock; but Lookingthree at possible the some source of the rock available intervals seismic have (e.g. been Figure proposed, 2) from theReferences Late Triassic (Karoo) and Mid Jurassic. New 2D data will it is easyplay toREFERENCESa keysee whyrole inslicks refining may our be understandingfocused at this ofpoint. the hydrocarbonThe potential[1] MacDonald, of the area I. R., and et al.accelerate (2015), Natural hydrocarbon and unnatural exploration oil basinactivity geology in dipswhat upwardsis believed and to westwards be an oil-dominated towards the region edge with exceptionalslicks in thequality Gulf reservoirs of Mexico,. J. Geophys. Res. Oceans, 120, of the basin.[1] MacDonald,At least three I. sourceR., et al. have (2015), been Natural proposed and in unnatural the oil 8364–8380,slicks in the doi:10.1002/2015JC011062.Gulf of Mexico, J. Geophys. Res. Oceans, 120, basin,REFERENCES from8364 Late–8380, Triassic doi:10.1002/ Karoo to 2015JC011062.sources in the mid Jurassic. The Triassic and Albian strata move up dip towards the shelf [2] Mahanjane, E.S., Franke, D., Lutz, R., Winsemann, J., edge[1] so MacDonald,could[2] Mahanjane, well explain I. R., E.S., et the al. Franke, assemblage(2015), D.,Natural Lutz,of seeps and R., Winsemann,foundunnatural there oil slicksJ., Ehrhardt,Ehrhardt, in the Gulf A., A., Berglar, of Berglar, Mexico, K. K. andJ. and Geophys. Reichert, Reichert, Res. C. C. (2014), (2014),Oceans, M Maturityaturity 120, and and but the8364 Cretaceouspetroleum–8380, doi:10.1002/ playssystems pinch modelling2015JC011062. out further in the offshore. offshore ZTheseambezi Delta petroleumdepression systems and Angoche modelling Basin, in Ntheorthern offshore Mozambique Zambezi . JournalDelta strata pinchingof Petroleum out could Geology, explain 37: the 329 sea– 348.surface doi:10.1111/jpg.12589 slicks that depression and Angoche Basin, Northern Mozambique. Journal were[2] not Mahanjane, part of the E.S.,main Franke, clusters. D., The Lutz, DFZ R., is Winsemann, up dip of the J., Ehrhardt,of Petroleum A., Berglar, Geology, K. and Reichert,37: 329–348. C. (2014), doi:10.1111/jpg.12589 Maturity and potentialpetroleum Triassic systems source modelling rocks and in between the offshore the source Zambezi and D elta depression and Angoche Basin, Northern Mozambique. Journal the Grandidierof Petroleum seamount Geology, are 37: a 329series–348. of onlap doi:10.1111/jpg.12589 terminations,

HGS – PESGB 17th Conference on Africa E&P 17 Assessing the provenance and contribution of local vs regional drainage systems for the Upper Triassic fluvial deposits, James Lovell-Kennedy, Jonathan Redfern, [email protected]

Challenges 1. Introduction 1. Was there a regional axial rift fluvial system linking Oukaimeden, Kerrouchen, the High Plateaux and the Oujda Mountains during the Upper Triassic?

2. To what extent did local drainage influence sediment deposition during the Upper Triassic?

3. Can proximal, medial and distal fluvial successions be identified and correlated across the Triassic basins across Morocco?

Aims of Study A. Analysis of heavy mineral assemblages from Triassic Basins to attempt to recognise signals from distinct source regions.

B. Build on previous work on regional uplift to identify Triassic source areas and drainage systems.

C. Compare the stratigraphy of the individual Triassic basins to assess the evolution of the depositional system and aid with correlation between basins.

D. Perform a High Resolution Heavy Mineral Analysis (HRHMA) to identify the provenance of the Triassic deposits

E. Combine heavy mineral analysis with field studies and subsurface data to reconstruct the Triassic paleodrainage and paleogeography Figure 1 : Map of the Triassic Basins, potential source areas and major faults in the study region.A heavy mineral study is being undertaken in order to constrain the provenance of these sediments. Paleocurrents data and published provenance studies suggest a drainage divide within the Massif 2. Geological Setting and Fieldwork Ancien, separating the Atlantic realm to the west from the eastern Tethyan domain. Key questions include whether a long distance axial system existed, running sub parallel to the main structural trend, Geological setting Fieldwork Figure 5: Paleocurrent data from transporting clastics from the Central High Atlas east-northeast toKerrouchen Tethys Basin. or Unitsif more K3 and southK4 to northward

feeder systems prevailed. The results also aim to address the rolerecord of a paleoflowintra-basinal flow toward topog the raphy through The inverted Mesozoic rift basins of the Atlas Mountains expose a thick Fieldwork and sampling of coarse clastic NNE, indicating a flow from the Triassic continental red-bed sequence. time: how this affected the distributionintervals hasof beenfluvial undertaken systems in the and theOukaimeden role of localBasin and sediment Central High source from basement blocks. Finally, the workKerrouchen will attempt Basin and to Oujda integrate Mountains the regionalAtlas and towards data the to Oujda evaluate evolution of the Mountains (Figure 6). The Triassic basin fill of the Central and Middle Atlas is predominantly basins as they mature, associatedto augment with rift previous linkage. work done in the ephemeral and perennial fluvial deposits, with alluvial fans, occasional Oukaimeden and Argana Basins. The conglomerates of the K2 units aeolian deposits and interbedded lacustrine and, playa mudstones and record variable paleoflows, away from the basinal highs from which rare carbonates deposited in a series of rift basins following the break up of Preliminary work on the composition of samples collected during recent fieldwork in the Kerrouchen Basin Whilst direct correlation between they are sourced. Pangea. The northern Oujda Mountains records a deltaic plain succession has identified a distinct variationthe in basinsclastic is hampered composition by the lack between the fluvial and alluvial systems. In the with a Carnian transgression of Tethys prior to the establishment of east, alluvial plain sediments containedof biostratigraphic granitic data, and similar carbonate clasts, likely derived from the local widespread marine conditions in the Jurassic. Hercynian basement of granitesdepositional and carbonates. processes can This be suggests a large alluvial plain, with deposits Tuesday, September 11 | Theme 2 | 10:55identified across the basins such Divergent paleocurrent measurements in the Massif Ancien indicate the Jonathanderived fromRedfern local, James basement Lovell-Kennedy paleohighs.as the K3 unit, Kerrouchen, and the F5 presence of a drainage divide, with flow to the west towards Argana and North Africa Research Group, School‘Oukaimeden of Earth and Sandstone’ Environmental within the Science, Manchester, UK flow to the east towards Oukaimeden (Figure 6). JohnThe Argentfluvial andsands Jason found Canning in the westOukaimeden contain Basin. metamorphic clasts of a schistose nature, with an absence of Soundgranitic Energy or carbonate PLC, Sevenoaks, clasts. UKIn thisFigure locality 4: Conglomeritic a contribution channels (A) at thefrom base an of Unit extra K3 outcropping-basinal in themetamorphic source is Kerrouchen Basin, Middle Atlas. The conglomerates are conformably overlain by mud Figure 2: Photo of the Hercynian 140 SE indicated, which based on paleocurrentclast conglomerates analysis, and stacked is most- fluvial sandstones.likely located The fluvial to sands the grade southwest into point of the basin. This Unconformity from within the Kerrouchen bar deposits with mud drapes near the top of Unit K3. Basin, Middle Atlas. The basement formed supports previous work in the region, which also indicated an extra-basinal (Anti Atlas) source for the a intra-basinal high. Debris flow deposits fluvialChasing deposits. the TAGI Play into Morocco: Assessing the (Unit K2) derived from the paleohigh onlap A B C the unconformity. Unit K3 and K4 are absent at this locality, as they were WorkContribution is ongoing, but initial investigation of Local suggests Versus that the linking Regional of the Late Triassic Drainage depositional deposited in basinward lows to the east. systems across Oukaimeden, Oujda and Kerrouchen Basins may offer analogues for facies distribution in The basement and conglomerates are Figure 3: Composite log of the Triassic 1m 5m capped by the massive red mudstones of sequencethe Eastern in theSystems Kerrouchen Meseta Basin.. on the2m Character and Provenance of Unit K5. Upper Triassic Fluvial Deposits

3. Future Work Figure 6 Map of Triassic Source areas and measured and Methodology and Sampling potential paleoflows. 5 potential source areas for

Triassic sediments have been identified; Initial heavy mineral analysis will be carried out on Hercynian Granites, Precambrian Granites, samples from the F5 and K3 units from Metamorphic, Volcanic and Precambrian and Oukaimeden and Kerrouchen, along with deltaic Paleozoic sediments. plain samples from Oujda and samples from the Tendrara Field provided by Sound Energy. Table 1: Table shows the age range of each Tendrara potential source for the Triassic sediments from Discovery These samples are believed to be coeval based on the published literature. For the Precambrian and environment of deposition. Paleozoic sediments, the age range of their detrital zircon population is given. The sedimentary deposits of the Anti-Atlas contain locally reworked Once the samples have undergone a heavy zircons from the Precambrian inliers. The combi- mineral separation, a QEMSCAN will be used to nation of petrographic analysis of the heavy min- identify the abundance of Apatite, Tourmaline, erals should be able to identify reworked grains, Garnet, Zircon, Rutile, Chrome and Monzonite. The which would help differentiate between a Precam- ratio of these minerals (specifically (ATi, GZi, RZi, brian granitic or sedimentary source for the Trias- CZi and MZi) are provenance sensitive. sic sediment.

Potential Source Region Radiometric Date Range As the potential source areas in the region could Hercynian Granites 275Ma - 326Ma Precambrian and Paleozoic Sedi- 570Ma-2093Ma* have significant overlap between heavy mineral ments *Detrital Zircon populations age populations, petrographic work will be done attempt Volcanoclastic Deposits 617Ma Metamorphic Units 617Ma – 660Ma to identify between reworked and first cycle grains. Precambrian Granites 617Ma – 2293Ma Figure 1: Late Triassic palaeogeography and potential clastic source areas in Morocco. Acknowledgements: Special thanks to I would like to thank the following for their support and advice with this project: Figure 1: Late Triassic palaeogeography and potential clastic source areas in Morocco. Emmanuel Roquette, Mustafa Oujidi, Nadine Mader and Ivan Fabuel-Perez. Results from the recent Tendrara wells drilled in Eastern on which to build further detailed work. Our study aims to Morocco prove economic flowrates from Late Triassic improve understanding of the local versus regional controls on continental sandstones. Sourced from the Palaeozoic and facies variation and in particular the prediction of sandstone trapped with post Hercynian rift structures, the play has many distribution and quality. similarities to the prolific TAGI play in the Berkine Basin and offers potential for extension of the petroleum system further This study compares the provenance and character of the west into Morocco. Triassic section outcropping in Oukaimeden Basin (F4, F5, and F6 sandstones) with the age equivalent units in the Reservoir quality and thickness is a key uncertainty and to Kerrouchen Basin, Middle Atlas, and east to outcrops in the better understand this, studies are ongoing to assess the main Oujda Mountains in the Eastern Meseta and to the subsurface, controls on the depositional systems and provenance. A complex accessing data from vintage exploration wells and core data from suite of Triassic facies are exposed along the inverted Mesozoic the Tendrara gas discovery. sequences of the Atlas Mountain Chain, providing an excellent opportunity to study the sedimentology of syn-rift sequences At Oukaimeden, in the High Atlas, the thick suite of Triassic that formed during the early break up of Pangea. Augmented clastics were deposited within an intra-montane basin, to by data from hydrocarbon exploration wells, the research is the east of a well-documented drainage divide. The main investigating how the basin fill changes both temporally and coarse clastic fluvial interval, Unit F5, contains thick, stacked spatially. The wealth of previous work undertaken on the channel fluvial deposits that record the presence of a large Triassic in Morocco provides a robust regional framework perennial fluvial system flowing to the east. Later, more

18 HGS – PESGB 17th Conference on Africa E&P ephemeral conditions prevailed, with thinner fluvial packages from the eastern Tethyan domain. Key questions include and interbedded aeolian, floodplain, and alluvial fans facies. whether a long distance axial system existed, running sub Toward the end of the Triassic a thin restricted marine to tidally parallel to the main structural trend, transporting clastics from influenced unit is recognised that is interpreted to mark the the Central High Atlas east-northeast to Tethys or if more south most westerly extent of the Tethyan transgression in the Triassic. to northward feeder systems prevailed. The results also aim to address the role of intra-basinal topography through time: how Further east, in the Kerrouchen Basin of the Middle Atlas, the this affected the distribution of fluvial systems and the role of fluvial packages observed at outcrop are thinner, and basin local sediment source from basement blocks. Finally, the work fill is dominated by alluvial fan and alluvial plain / playa will attempt to integrate the regional data to evaluate evolution deposits. Thick axial fluvial systems do not seem to be recorded, of the basins as they mature, associated with rift linkage. suggesting they are either absent or not exposed, possibly only located in the subsurface. Preliminary work on the composition of samples collected during recent fieldwork in the Kerrouchen Basin has identified a In the Eastern Meseta, outcrops are more limited, and thus distinct variation in clastic composition between the fluvial and understanding of facies distribution more uncertain. The alluvial systems. In the east, alluvial plain sediments contained few good sections in the Oujda Mountains record a distal granitic and carbonate clasts, likely derived from the local low-energy facies, composed of basal locally derived angular Hercynian basement of granites and carbonates. This suggests a conglomerates, overlain predominantly by mudrocks, with only large alluvial plain, with deposits derived from local basement very thin laterally restricted sandstones. The section shows an paleohighs. increasing marine influence, with interbedded shallow water carbonate sequences. The fluvial sands found in the west contain metamorphic clasts of a schistose nature, with an absence of granitic or carbonate How this correlates south, into the subsurface, where control clasts. In this locality a contribution from an extra-basinal points are more sparse and only limited to widely spaced metamorphic source is indicated, which based on paleocurrent exploration wells of varying vintages, is still uncertain. The analysis, is most-likely located to the southwest of the basin. This equivalent section in the Tendrara gas discovery displays an supports previous work in the region, which also indicated an increasing proportion of fluvial sandstones, with stacked fluvial extra-basinal (Anti Atlas) source for the fluvial deposits. channels interbedded with floodplain mudstone and laterally equivalent alluvial fan deposits. Work is ongoing, but initial investigation suggests that the linking of the Late Triassic depositional systems across A heavy mineral study is being undertaken in order to constrain Oukaimeden, Oujda and Kerrouchen Basins may offer analogues the provenance of these sediments. Paleocurrents data and for facies distribution in the Eastern Meseta. n published provenance studies suggest a drainage divide within the Massif Ancien, separating the Atlantic realm to the west

HGS – PESGB 17th Conference on Africa E&P 19 Tuesday, September 11 | Theme 2| 11:20 Lisa Fullarton, Elisabeth C. A. C. Gillbard, Ken G. McDermott, Nicola Clarke, Paul Bellingham ION, UK +44 1932 792283, [email protected] Palaeozoic to Present: Assessing the Petroleum Potential of the Offshore Sirt Basin, Libya, Using Newly Reprocessed Regional-Scale 2D Seismic Data

Introduction central Mediterranean. For the first time, deep imaging of The onshore Sirt Basin, Libya, has yielded some of the world’s the pre- and early rift basin is interpreted within a structural largest petroleum discoveries, with known reserves in excess of context to pull together the full tectonostratigraphic history of 40 billion barrels of oil equivalent. The offshore extent of this the offshore Sirt Basin and Cyrenaica Margin, from Hercynian system, however, is poorly constrained due to of the limited Orogeny to Mesozoic extension and Cenozoic inversion. amount of exploration activity. Recent wells have proven both equivalent and new petroleum systems in the offshore, Evaluation of Petroleum Potential but the extent, character, and full potential of these systems Regional stratigraphy from the Palaeozoic to present, has been is currently poorly understood. Furthermore, the structural interpreted in the context of assessing the petroleum potential complexities of the offshore area and the relationships between of this structurally complex region. Basin modelling of several the ancient crustal domains is only starting to be realized. proven and speculative source rock units shows the significant Placing the offshore Sirt Basin and adjacent Cyrenaica Margin offshore potential for both oil and gas maturation, and optimal into a regional context, and understanding the relationship timing of trap formation. Enhanced understanding of the with the onshore basins will be key to future exploration of this regional context of proven and speculative plays is presented, potentially huge yet underexplored province. extending the petroleum potential of the offshore along the Cyrenaica Margin and into the deeper water. Newly Integrated Mega-Regional Data Over 45,000 km of recently acquired and depth processed deep Conclusions regional seismic data and newly reimaged legacy 2D seismic data The regional stratigraphic interpretation is placed into a has been interpreted and integrated with offshore well data in a structural context in order to understand the deposition and mega-regional basin study. These data allow a well constrained development of reservoir facies, source rock maturation and crustal-scale structural and tectonic model to be defined and migration, and trap development to fully integrate the petroleum placed within the regional context of the tectonically complex potential of the offshore Sirt Basin and Cyrenaica Margin. n

20 HGS – PESGB 17th Conference on Africa E&P Paul Haryott has an extensive global background in oil and gas exploration that stretches over the 40 years since he began his career in the UK North Sea. Formerly a senior executive and member of senior management in Chevron, with responsibility for Africa and Latin America, he is now a Senior Associate with Rose & Associates. He has authored and co-authored numerous publications that include risk and uncertainty insights, and is a member of the AAPG and a Fellow of the Geological Society of Great Britain. Paul holds a BSc in Geology from Liverpool University and a MSc in Petroleum Exploration Studies from Aberdeen University. Tuesday, September 11 | Round Table Panel Discussion | 11:45 Paul Haryott, Rose & Associates Bob Fryklund, IHSMarkit Ernie Leyendecker, Anadarko Dorrie McGuiness, Kosmos Tim O’Hanlon, Tullow

Biographical Sketches Mr. Leyendecker recently Paul Haryott has an extensive retired as Executive Vice global background in oil and President, Exploration gas exploration that stretches for Anadarko Petroleum over theERNEST 40 years since he beganA. LEYENDECKER Corporation, one of the world’s his careerformer in the Executive UK North Sea. Vice President, Exploration largest independent oil and Anadarko Petroleum Corporation natural gas exploration and Formerly a senior executive and production companies. He took member of senior management on this role in October 2016. in Chevron,Mr. Leyendeckerwith responsibility recently retired as Executive Vice President, for AfricaExploration and Latin America, for Anadarko Petroleum Corporation,Mr. Leyendecker one of the has more than he is now a Senior Associate 35 years of experience in the with Roseworld’s & Associates. largest independent oil and natural gasoil explorationand natural gas andindustry. He production companies. He took on this role inbegan October his career 2016. in Midland, He has authored and co-authored numerous publications that Texas in 1982 with Marathon Oil Company, where he served include risk and uncertainty insights, and is a member of the in multiple engineering roles including drilling, completions AAPG Mr.and aLeyendecker Fellow of the Geological has more Society than of Great 35 Britain. years ofand experience reservoir engineering. in the oil After various assignments, he left to and natural gas industry. He began his careerpursue in aMidland, leadership roleTexas in the in start-up 1982 of with Enterprise Marathon Oil Gulf Oil Paul holds a BSc in Geology from Liverpool University and of Mexico. In 2002, Enterprise Oil was acquired by Shell, and a MSc inCompany, Petroleum Exploration where he Studies served from Aberdeenin multiple engineeringMr. Leyendecker roles joined including Kerr-McGee’s drilling, Gulf completions of Mexico team. and University.reservoir engineering. After various assignments,He served he in leftincreasing to pursue roles of responsibilitya leadership as Exploration role in the Manager before Kerr-McGee was acquired by Anadarko in 2006. start-up of Enterprise Oil Gulf of Mexico. In 2002,Since 2006, Enterprise he hasBob held Oilpositions Fryklund was of acquired increasing responsibilityby Shell, and Mr. Leyendecker joined Kerr-McGee’s Gulf ofat MexicoAnadarko, team.including He General served Manager in increasing for Worldwide roles of Bob Fryklund, Chief Strategist- Exploration, Engineering and Planning; Vice President Upstreamresponsibility , at IHSMarkit, as Exploration Manager before ofKerr-McGee Corporate Planning; Chiefwas Viceacquired Strategist President by of AnadarkoGulf- ofUpstream Mexico in 2006. , at IHSMarkit, has 38 has 38 Sinceyears of experience.2006, he A has held positions of increasingExploration responsibility and Senior atVice Anadarko, President, International including Exploration General proven oil finder and seasoned where he was responsibleyears for of the experience.company’s exploration A proven oil finder and Manager for Worldwide Exploration, Engineering and Planning; Vice President of Corporate executive Bob has worked for activities around theseasoned world. He most executive recently served as ExecutiveBob has worked for both majors both majorsPlanning; and independents. Vice President of Gulf of MexicoVice President,Exploration International and and Senior Deepwater Vice Exploration President, until He focusses on high impact his retirement in Juneand 2018. independents. He focusses on high impact global strategicInternational Upstream Exploration issues where he was responsible for the company’s exploration activities such asaround IPO’s, acquisitions, the world. He most recently served Mr.as Leyendecker Executive globalholds Vice a Bachelor President, strategic of Science International in UpstreamPetroleum and issues such as IPO’s, portfolio’s and expert witness Engineering fromacquisitions, Texas A&M University. portfolio’sHe is a member of theand expert witness assistance.Deepwater Exploration until his retirement in JuneSociety 2018. of Petroleum Engineers, the Association of Petroleum Geologists and theassistance. Houston Geological Society. Mr. Leyendecker He is a Mr.geologist, Leyendecker member of holds a Bachelor of Scienceserves in on Petroleum the Texas A&M Engineering Engineering Experiment from Texas Station’s A&M the AAPG, HGS, member of Board of ARPEL, Trustee of AGI He is a geologist, member of the AAPG, HGS, University. He is a member of the SocietyExternal of Petroleum Advisory Board Engineers, (TEES). the Association of and Chair of the IPAA Supply and Demand Committee. He was member of Board of ARPEL, Trustee of AGI and Chair awardedPetroleum the AAPG Presidents Geologists Award andin 2018. the Houston Geological Society. Mr. Leyendecker serves on the Texas A&M Engineering Experiment Station’s External Advisoryof the Board IPAA (TEES). Supply and Demand Committee. He was awarded the AAPG Presidents Award in 2018.

HGS – PESGB 17th Conference on Africa E&P 21 As an exploration geologist, Tim O’Hanlon is from Ireland. Dorie McGuinness has As a young Reservoir Engineer contributed to exploration and fresh from Imperial College appraisal of major discoveries London, he joined Ireland’s in the Gulf of Mexico, South brand new start-up, Tullow America, and Africa. During Oil, in the mid 1980’s. He has her early tenure at Kosmos been with this very exciting and Energy she contributed to ambitious company ever since, the exploration and appraisal living in Africa for many years. of the Ghanaian discoveries. After Ghana, she worked as a More recently as Vice President New Venture Senior Advisor African Business, or Tullow’s and led Kosmos’ entrance into Mr Africa, Tim has helped Mauritania & Senegal, and Suriname. During the last several to drive Tullow’s rapid expansion on the Mother Continent. years she served as a functional leader as VP, Geology across Whether it is targeting new company acquisitions in Africa, Kosmos’ portfolio, and has recently advanced to Senior VP chasing new ventures or mending fences in the many African of New Ventures. Prior to Kosmos, Dorie worked at Triton countries where Tullow operates, you can be sure that Tim’s Energy contributing to the exploration entry into Equatorial fingerprints can be found on the files. Guinea, and exploration and appraisal in the Cupiagua Field in Colombia. She began her career at BP Exploration, where, after her tenure in exploration and development, she served as a structural geology/salt tectonics technical advisor in the Gulf of Mexico. Dorie holds a BS in Geology from Bucknell University, and an MS in Geology from Virginia Tech.

22 HGS – PESGB 17th Conference on Africa E&P Break-up Processes in the Presence of Plume Magmatism: New Insights into the Tectonostratigraphic Development and Petroleum Potential of the Austral South Atlantic

Ken G. McDermott*1, Elisabeth C. A. C. Gillbard1, Paul Bellingham1, Brian W. Horn2

1ION, E & P Advisors, Chertsey, UK , 2 ION, E & P Advisors, Houston, TX, USA

INTRODUCTION

The conjugate rifted margins of the austral South Atlantic are classically magma-rich and display extremely well developed examples of all the volcanostratigraphic elements commonly observed on magma-rich margins globally: stretched continental crust, inner and outer SDR (seaward dipping reflector) packages, an outer (volcanic) high, a zone of high- velocity lower crust, and relatively thick early oceanic crust [1,2].

Rifted continental margins are often considered independently due to a paucity of conjugate high-resolution reflection seismic profiles. Here, ION’s South Atlantic mega-regional, conjugate seismic datasets are through paleogeographic reconstructions considered as they once were; a single basin through their shared geological history. Observations from these seismic data provide new and important insights into the principle mechanisms involved in highly magmatic Tuesday, September 11 | Theme 2 | 13:35 continental break-up. Ken G. McDermott, Elisabeth C. A. C. Gillbard, Paul Bellingham ION, E & P Advisors Chertsey, UK TECTONOSTRATIGRAPHIC MODEL OVERVIEW Brian W. Horn ION, E & P Advisors, Houston, TX , USA Through a well-correlated stratigraphic and crustal structure interpretation, a new tectonostratigraphic model for the formation of the austral South Atlantic is presented. This model describes the development of magma-rich margins influenced by plumeBreak-up magmatism and may Processes have global applications in to equivalentthe Presence margins. The model ofconsists of four distinct crustal domainsPlume (continental, magmatic, Magmatism: oceanic, and oceanic New plateau), withInsights two important crustal into boundaries the; the limit of continental crust (LoCC), and limit of oceanic crust (LoOC)[3] (Figure 1[3]). These crustal domains are delineated with respect to, andTectonostratigraphic reflect the effects of, variable melt volume during Development continental stretching and break and-up. Petroleum

Potential of the Austral South Atlantic

Figure 1. Geoseismic section[3] shown in TWTT details the a typical crustal configuration through the Namibian magma-rich margin. FigureThe margin1 Geoseismic has been sectionCC – continental[3] shown crust; in TWTT OC – detailsOceanic the crust; a typicalHVB – crustalHigh-velocity configuration body; SDR through – seaward the Namibiandipping reflectors; magma -SRrich – margin.syn-rift; The PR margin– Post-rift has sediments; been CC LoCC – continental – Limit of crust; Continental OC – OceanicCrust; LoOC crust; – Limit HVB of – OceanicHigh-velocity Crust. body; SDR – seaward dipping reflectors; SR – syn-rift; PR – Post-rift sediments; LoCC – Limit of Continental Crust; LoOC – Limit of Oceanic Crust. Introduction with two important crustal boundaries; the limit of continental The conjugate rifted margins of the austral South Atlantic are crust (LoCC), and limit of oceanic crust (LoOC)3 (Figure 13). classically magma-rich and display extremely well developed These crustal domains are delineated with respect to, and reflect Theexamples tectonostratigraphic of all the volcanostratigraphic model also describes elements stronglycommonly diachronous the effects post-rift of, andvariable drift phasemelt volume subsidence during continentaland highlight stretchings the roleobserved the Walvis on magma-rich Ridge – Rio margins Grande globally: Rise systemstretched played continental in the separationand break-up. of the central and austral segments of the South Atlanticcrust, inner Ocean and. outer SDR (seaward dipping reflector) packages, an outer (volcanic) high, a zone of high-velocity lower crust, and The tectonostratigraphic model also describes strongly 1,2 Analysisrelatively of thick subsidence early oceanic patterns crust on. both conjugates, compared todiachronous the drowning post-rift of the and Walvis drift – phaseRio Grandesubsidence Ridge and sys highlightstems, the role the Walvis Ridge – Rio Grande Rise system played in revealsRifted intriguingcontinental correlations margins are betweenoften considered distribution independently of major sourcethe rockseparation intervals of the and central evaporite and austral deposition segments in the of theLower South Cretaceousdue to a paucity through of conjugate time and high-resolution space. reflection seismic Atlantic Ocean. profiles. Here, ION’s South Atlantic mega-regional, conjugate CONCLUSIONSseismic datasets are through paleogeographic reconstructions Analysis of subsidence patterns on both conjugates, compared to considered as they once were; a single basin through their shared the drowning of the Walvis – Rio Grande Ridge systems, reveals geological history. Observations from these seismic data provide intriguing correlations between distribution of major source new and important insights into the principle mechanisms rock intervals and evaporite deposition in the Lower Cretaceous involved in highly magmatic continental break-up. through time and space.

Tectonostratigraphic Model Overview Conclusions Through a well-correlated stratigraphic and crustal structure The observations and processes described here underpin the interpretation, a new tectonostratigraphic model for the development of a regional petroleum systems model, allowing formation of the austral South Atlantic is presented. This model prediction of regional heatflow through time as well as the likely describes the development of magma-rich margins influenced location of source and reservoir lithologies across the entire by plume magmatism and may have global applications to austral South Atlantic Basin, reducing exploration uncertainty equivalent margins. The model consists of four distinct crustal for the discovery of commercial hydrocarbons. n domains (continental, magmatic, oceanic, and oceanic plateau),

HGS – PESGB 17th Conference on Africa E&P 23 References Brian W. Horn - Senior Vice 1Planke, S., Symonds, P.A., Alvestad, E., Skogseid, J. 2000. Seismic President and Chief Geologist volcanostratigraphy of large-volume basaltic extrusive compleses for ION E&P Advisors. Brian on rifted margins. Journal of Geophysical Research, vol. 105, no. has worked in exploration B8, pp. 19,335 – 19,351. and production for 27 years with Amoco, BP, and Maersk 2Barton, A. J., White, R.S. 1997. Crustal Structure of Edoras Bank Oil prior to joining ION in continental margin and mantle thermal anomalies beneath the 2010. In his current role he is North Atlantic. Journal of Geophysical Research, vol. 102, n. B2, responsible for the technical pp. 3,109 – 3,129. and commercial advisory group in support of E&P operators, 3McDermott, K., Gillbard, E., Clarke, N. 2015. From Basalt to NOC’s and government Skeletons – the 200 million-year history of the Namibian margin minsitries. His experience uncovered by new seismic data. First Break, vol. 33, pp. 77 - 85 includes integrating geological and engineering/production data for play-based exploration, and development, basin and Biographical Sketches play fairway analysis, petroleum systems, regional stratigraphic Ken McDermott was awarded and seismic correlations, prospect development and resource his Ph. D from the University potential assessments. In addition to exploration projects he of Birmingham in 2013 for has delivered exploitation/development programs generating his work on crustal hyper- prospects, development and reservoir characterization for extension at magma-poor rifted (infill) drilling designed to identify and evaluate critical geologic margins; and a B. Sc in Geology uncertainties focused on increasing recovery efficiencies and from University College reservoir management strategies. Dublin in 2007. From 2012 – 2014 Ken held a postdoctoral Dr. Horn received his Bachelors and Master degrees in Geology research position at University from The University of Colorado, Boulder and his PhD in College Dublin, working on Geology and Geological Engineering from the Colorado School the tectonostratigraphy of the of Mines, Golden, CO. North Atlantic. Since 2014, Ken has held the position of Structural Geologist at ION’s E & P Advisor service and is to a large extent focussed on the South Atlantic.

Ken has authored and co-authored numerous papers in internationally regarded peer-reviewed journals focussed on the formation, crustal structure, and tectonostratigraphy of continental margins around the world, and often speaks at national and international industry and academic conferences. Ken is a member of the PESGB and a fellow of the Geological Society of London.

24 HGS – PESGB 17th Conference on Africa E&P Tuesday, September 11 | Theme 2 | 14:00 Dale E. Bird Department of Earth & Atmospheric Sciences, University of Houston Bird Geophysical, [email protected] Stuart A. Hall Department of Earth & Atmospheric Sciences, University of Houston David J. McLean, Philip J. Towle, Hunter A. Danque Anadarko Petroleum Corporation James V. Grant Chesapeake Energy Corporation The Austral South Atlantic: Early Formation and Crustal Structure of the Orange and Cape Basins

New high-resolution marine magnetic anomaly data acquired more “normal” oceanic thickness and SDRs are either absent over the southwestern margin of South Africa, integrated with or more limited in areal extent. The modeled cross section reprocessed open-file marine magnetic anomaly data, displays through the Cape Basin indicates a change in crustal character a pattern of well-defined northwest-southeast striking linear from attenuated continental crust to normal thickness oceanic anomalies that can be traced with confidence over distances crust occurring over a much shorter distance, which suggests a greater than 150 km (Figure 1) (Hall et al., in press). We diminished influence of magmatic material. Magnetic anomalies interpret these anomalies to be M-series seafloor spreading over the Cape Basin are better correlated with those predicted anomalies M9 to M11, suggesting seafloor spreading initiation by our seafloor spreading model than the anomalies over the at about 135 Ma (Late Valanginian / Early Hauterivian). A two- Orange Basin. phase spreading rate, from seafloor spreading models (M11 to M0), matches the two-phase spreading rate for M-series Our reconstructions of the African and South American anomalies over the conjugate South American margin, offshore margins, south of 32°S at M11 and M4 times (i.e., ~135 Ma and Argentina. Importantly, the presence of M11 anomalies over ~131 Ma, respectively), successfully overlay magnetochrons both margins suggests an earlier opening for the austral South of the conjugate margins. In Figure 2 we compare seafloor Atlantic than previously recognized. spreading anomalies M4 and M11, as well as the inboard “G” anomalies over both transitional / continental margins. The We identify four breaks in the continuity of the linear magnetic new M11 rotation pole (38.86°N, 31.46°W) applies only to the anomaly pattern, oriented approximately northwest-southeast, southernmost margins of the Austral segment where the M11 which may be early fracture zones. One such discontinuity, anomalies are observed, because at this time the margins were which we have termed the “Cape Lineament” (CL) (“D2” in undergoing non-rigid deformation farther north, including Figure 2), marks a significant change in crustal character and crustal extension and magmatism. Cretaceous depositional history. Two northwest-southeast striking regional 2D modeled cross sections, integrating wells, The recognition of initiation of seafloor spreading earlier seismic reflection, seismic refraction and gravity data, were built than previously documented, together with the identification northwest and southeast of the CL. Northwest of the CL, the of differing crustal character northwest and southeast of CL, Orange Basin crust is characterized by greater thickness and carry important implications for heat flow and the subsidence / the presence of seismically-imaged seaward dipping reflectors depositional history of the margin. n (SDRs). The modeled cross section through the Orange Basin includes a region of rifted / attenuated continental crust; a wide Reference zone of underplated thin continental crust overlain by SDRs; Hall, S. A., Bird, D. E., McLean, D. J., Towle, P. J., Grant, J. V., and another wide zone of thick oceanic crust, associated with and Danque, H. A., in press, New constraints on the age of the smoother seafloor spreading anomalies, that thins progressively opening of the South Atlantic basin: Marine and Petroleum to normal oceanic crustal thickness at the seaward edge of the Geology. overlying SDRs. However southeast of the CL, the crust has a

HGS – PESGB 17th Conference on Africa E&P 25

. Total magnetic intensity anomalies and African topography (see Hall et al., in press, for additional informa- FigureFigure 1. 1 Total magnetic intensity anomalies and African topography (see Hall et al., in press, for additional information). Reprocessed tion). Reprocessed open-file marine magnetic anomalies (Bird Geophysical) are overlain by new, high-resolution magneticopen-file anomaliesmarine magnetic (Anadarko anomalies Petroleum (Bird Geophysical) Corporation); are overlain Interpreted by new, discontinuitieshigh-resolution magneticare heavy anomalies gray dashed (Anadarko lines (D1 throughPetroleum D4); Corporation); new high Interpreted-resolution discontinuities marine magnetic are heavy data gray survey dashed outline lines (D1 is white;through labelled D4); new magnetic high-resolution anomal mariney correla magnetic- tionsdata survey from thisoutline study is white; are blacklabelled lines. magnetic Two anomaly-dimensional correla-tions modeled from cross this study sections are black are lines.heavy Two-dimensional red lines; blue modeled and white circlescross sections posted are on heavy the redmodel lines; lines blue andcorrespond white circles to theposted extents on the ofmodel modeled lines correspond magmatic to underplating, the extents of modeled blue and magmatic green circlesunderplating, correspond blue and to green the modeledcircles correspond boundary to the between modeled oceanic boundary and between continental oceanic andcrust; continental onshore crust; outcropping onshore outcropping basement areasbasement are areas colored are colored black; black; the north the north-south-south and and east east-west-west oriented oriented lineslines over over South South Africa Africa trace trace the Cape the Syntaxis.Cape Syntaxis.

Figure 2. Africa – South America reconstructions of coast lines and 1 km isobaths (see Hall et al., in press, for Figure 2. Africa – South America reconstructions of coast lines and 1additional km isobaths information) (see Hall. a) et M4al., reconstructionin press, for additional (rotation poleinformation). = 45.5°N, 33.0°W, and angle = 54.2°), with our anomaly picks for Africa by blue (M4), black (M11), and yellow (“G”) circles; and red for South American magnetochrons and a) M4 reconstruction (rotation pole = 45.5°N, 33.0°W, and angle = 54.2°),“G” anomaly with .our B) M11anomaly reconstruction picks for Africa (rotation by poleblue =(M4), 38.86°N, black 31.46°W, and angle = 56.6°). (M11), and yellow (“G”) circles; and red for South American magnetochrons and “G” anomaly. B) M11 reconstruction (rotation pole = 38.86°N, 31.46°W, and angle = 56.6°).

26 HGS – PESGB 17th Conference on Africa E&P

Figure 2. Africa – South America reconstructions of coast lines and 1 km isobaths (see Hall et al., in press, for additional information). a) M4 reconstruction (rotation pole = 45.5°N, 33.0°W, and angle = 54.2°), with our anomaly picks for Africa by blue (M4), black (M11), and yellow (“G”) circles; and red for South American magnetochrons and “G” anomaly. B) M11 reconstruction (rotation pole = 38.86°N, 31.46°W, and angle = 56.6°). Tuesday, September 11 | Theme 2 | 14:25 Ian Davison Earthmoves Ltd., Camberley, Surrey, UK Duncan Wallace Chariot Oil and Gas Ltd., London, UK

Post-Rift Potential Source Rock CorrelationsShort cv and Ian Davison

Prospectivity of the Deep Atlantic Conjugate

Since 1999 Ian has been Managing Director of Earthmoves Ltd. a consultancy working frontier Margins South of the Walvisexploration Ridge areas and on salt tectonics He regularly gives industry short courses on Salt Tectonics and frontier exploration along the Atlantic margins and Mexico.. Ian is a co-director of GEO International Ltd. which specialises in African onshore rifts and East African Hydrocarbon Several isolated small half grabens (5-10 km wide and 1-2 km 2D/3D seismic data fromExploration. Namibia He willis also be Visiting used toProfessor characterise at Royal Holloway, University of London deep) are present along the conjugate margins of the South the source rock package, and compare with recently acquired Atlantic south of the Walvis Ridge which were produced by seismic from Argentina and Uruguay. n Early Cretaceous rifting. These can contain source rocks (e.g. AJ-1 well in South Africa). However, the areal extent of these Biographical Sketch grabens is restricted. The main accommodation space created Since 1999 Ian Davison has by Early Cretaceous extension is filled by magma which has been Managing Director of produced seaward dipping reflectors (SDRs). The upper part Earthmoves Ltd. a consultancy of the SDRs has been drilled in the Walvis and Pelotas basins working frontier exploration and consists of sub-aerial reddened basalts. No source rock areas and on salt tectonics He potential has been encountered, nor is any expected in such a regularly gives industry short sub-aerial sequence. Hence, the hydrocarbon prospectivity of the courses on Salt Tectonics and deepwater margins will largely rely on the presence of post-rift frontier exploration along source rocks. the Atlantic margins and Mexico.. Ian is a co-director Early drift, Barremian to Aptian age, marine source rocks were of GEO International Ltd. identified in several wells including the recent Murombe-1, which specialises in African Wingat -1, and Moosehead-1 wells, where residual TOC levels onshore rifts and East African up to 6% in source packages of up to 150m were measured. The Hydrocarbon Exploration. He is also Visiting Professor at Royal deposition of this source rock is interpreted to be widespread Holloway, University of London in the deep water and modelled to be oil mature in several large kitchen areas, situated in present day water depths from <500m to over 3000m. Additionally, good quality Cenomanian to Santonian age source rocks have also been identified in several wells offshore Namibia, such as the 1911/15-1 well with TOC levels reaching up to 10 % and a gross thickness of 170m, and the Kabeljou-1 well with average TOC of 5.3% and approximately 50m thickness.

The Barremian to Aptian age source rocks on the Namibian margin are now recognised to be the principal source rock for future exploration drilling and they are characterised by parallel-bedded, low amplitude, low frequency, continuous low- impedance reflectors, which lie above the SDRs. The equivalent Barremian to Aptian section above the SDRs in the deepwater (>2 km) Pelotas-Argentine margin has never been drilled, but seismic data indicates a similar stratal package. Recent

HGS – PESGB 17th Conference on Africa E&P 27 Offshore Somalia: Source rock identification in a frontier margin

Neil Hodgson¹*, Hannah Kearns1, Karyna Rodriguez¹, Benjamin Allen2, Douglas Paton2, and Abdulkadir Abiikar Hussein3

1Spectrum Geo Ltd, United Kingdom; 2School of Earth & Environment, University of Leeds; 3Ministry of Petroleum and Mineral Resources (MOPMR), Federal Government of Somalia

+44 1483 730201, [email protected]

INTRODUCTION

Offshore Somalia remains one of the last truly frontier passive margins in the world. Only two exploration wells have been drilled offshore along the 1000km long margin, and both are on the shelf in <100m water depth. Identifying potential source rocks on such an unexplored margin requires integration of multiple datasets to build a robust geological model that fits with our observations from seismic data. We use gravity and magnetic data to reconstruct tectonic plate positions, conjugate margin and onshore well information, regional geological understanding and records of Ocean Anoxic Events (OAEs), and we complement this with seismic observation and analysis including source rock characterisation, sequence stratigraphy models, and slick clusters on satellite imagery.

REGIONAL GEOLOGY Tuesday, September 11 | Theme 2 | 14:50 TheNeil initialHodgson Karoo, Hannah rifting of Kearns, Gondwana Karyna began Rodriguez in the Late Carboniferous/Early Permian[1]. Deposition of the continentally- derivedSpectrum Karoo Geo Supergroup, Ltd, United Kingdomcomprising both source and reservoir, occurred across Southern and East Africa at this time. BBenjaminreakup of Allen, Somalia Douglas and the Paton Madagascar-Seychelles-India (MSI) block occurred in the Early Jurassic[2] [Figure 1]. This coincidedSchool of withEarth an & initialEnvironment, marine transgression University of whichLeeds saw lacustrine to brackish-marine restricted basin sediments deposited Abdulkadir Abiikar Hussein inMinistry rifted half of Petroleum grabens formed and Mineral by fault Resources block rotation. (MOPMR), In the FederalMiddle toGovernment Late Jurass ofic, Somaliaa restricted seaway formed between the Indian+44 1483 and 730201, Somali plates. [email protected] Restricted marine marls were deposited in the basin at this time, and shallow water platform carbonate growth occurred on the continental shelf. From the Early Cretaceous, the northward movement of the Indian plate past the Somali plate coincided with the formation of large-scale transpressional and transtensional flower structures in the deep offshore,Offshore creating potentially Somalia: very large trapping Source structures, as wellRock as partial Identification barriers to oceanic circulation which may have facilitated the deposition of an organic-rich Late Cretaceous source rock. In the Late Cretaceous and Palaeogene, slope failure events occurred in the southernin a offshore.Frontier Margin

Figure 1. 1: The The EMAG2 EMAG2 V3 V3 dataset dataset was wasused usedto create to createa magnetic a magnetic plate reconstruction plate reconstruction from the Early from Jurassic the Early to present Jurassic day to present day

Offshore Somalia remains one of the last truly frontier passive and transtensional flower structures in the deep offshore, POTENTIALmargins in the SOURCEworld. Only ROCKS two exploration wells have been creating potentially very large trapping structures, as well as drilled offshore along the 1000km long margin, and both are partial barriers to oceanic circulation which may have facilitated Aon lack the shelfof drilling in <100m offshore water leavesdepth. Identifying the stratigraphy potential untested. source However,the deposition observations of an organic-rich from onshore Late Cretaceous well data, source seismic rock. characteristics,rocks on such an unexploredstructural deformation margin requires styles integration, and sequence of stratigraphyIn the Late Cretaceous models are and used Palaeogene, to build slope a consistent failure events framework for multiple datasets to build a robust geological model that fits occurred in the southern offshore. seismic analysis and characterization of potential source intervals. Source rocks are proposed at pre- syn- and post-rift with our observations from seismic data. We use gravity and levels.magnetic Pre data-rift to sources reconstruct may tectonic be pre platesent positions,in Permo conjugate-Triassic to LowerPotential Jurassic Source (Karoo) Rocks coals and lacustrine shales such as the Permianmargin and Bokh onshore Shale well which information, is the source regional for geological the Calub gas andA lackcondensate of drilling field offshore onshore leaves Ethiopia. the stratigraphy Lacustrine untested. sources are alsounderstanding well developed and records in the of Madagascan Ocean Anoxic conjugateEvents (OAEs), – particularly However, the onshore observations Karoo from sourced onshore oil wellfeilds data,. seismic and we complement this with seismic observation and analysis characteristics, structural deformation styles, and sequence Synincluding-rift sources source rock may characterisation, comprise Lower sequence to Mid stratigraphyJurassic shallow stratigraphy marine shales, models located are used on to the build southern a consistent extension framework of Tethys wheremodels, a and Tethyan slick clusters Ocean on Anoxic satellite E imagery.vent (OAE) occurred in the forToarcian seismic promoting analysis and the characterization development of of potential anoxic sedimentationsource . intervals. Source rocks are proposed at pre- syn- and post-rift Regional Geology levels. Pre-rift sources may be present in Permo-Triassic to The initial Karoo rifting of Gondwana began in the Late Lower Jurassic (Karoo) coals and lacustrine shales such as the Carboniferous/Early Permian1. Deposition of the continentally- Permian Bokh Shale which is the source for the Calub gas and derived Karoo Supergroup, comprising both source and condensate field onshore Ethiopia. Lacustrine sources are also reservoir, occurred across Southern and East Africa at this time. well developed in the Madagascan conjugate – particularly the Breakup of Somalia and the Madagascar-Seychelles-India (MSI) onshore Karoo sourced oil feilds. block occurred in the Early Jurassic2 (Figure 1). This coincided with an initial marine transgression which saw lacustrine to Syn-rift sources may comprise Lower to Mid Jurassic shallow brackish-marine restricted basin sediments deposited in rifted marine shales, located on the southern extension of Tethys half grabens formed by fault block rotation. In the Middle to where a Tethyan Ocean Anoxic Event (OAE) occurred in the Late Jurassic, a restricted seaway formed between the Indian and Toarcian promoting the development of anoxic sedimentation. Somali plates. Restricted marine marls were deposited in the basin at this time, and shallow water platform carbonate growth In the early post-rift, Upper Jurassic marine shales are a key occurred on the continental shelf. From the Early Cretaceous, source in the Ethiopian Ogaden Basin and in northern Somalia the northward movement of the Indian plate past the Somali (Uarandab Formation). Organic-rich shales of similar age are plate coincided with the formation of large-scale transpressional present in the Rovuma Basin and have moderate TOCs in the

28 HGS – PESGB 17th Conference on Africa E&P In the early post-rift, Upper Jurassic marine shales 2D seismic acquired in 2015 is interpreted within a areIn the a key early source post- inrift, the Upper Ethiopian Jurassic Ogaden marine Basin shales sequence stratigraphic framework to characterize andare ina keynorthern source Somalia in the Ethiopian(Uarandab Ogaden Formation) Basin. these potential source source using the methods of Organicand in northern-rich shales Somalia of similar (Uarandab age are Formation) present in. Loseth et al3. These results give further support for theOrganic Rovuma-rich Basin shales and of similarhave moderate age are presentTOCs in in the presence of thick sequences of effective source thethe Seychelles.Rovuma Basin In the and deep have basin, moderate an acoustically TOCs in rocks. quietthe Seychelles. homogeneous In the unit deep can basin,be mapped an acoustically at this Basin Modelling levelquiet and homogeneous is interpreted unit as can a deep be mapped marine organicat this - Leeds University carried out basin modelling richlevel marl and source is interpreted [Figure as2]. a deep marine organic- rich marl source [Figure 2]. considering four potential source rock intervals identified by the seismic characterization In the Cretaceous, global OAEs are known in the technique. Peak maturation maps for source rocks AptiaIn then Cretaceous,and Cenomanian global-Turonian OAEs are, and known localised in the Aptian and Cenomanian-Turonian, and localised at pre-rift (Karoo), syn-rift, Late Jurassic and Early restricted marine environments were created by Cretaceous levels indicate that where the sediment transformrestricted faultsmarine linked environments to the movement were created of the by Figure 2. Possible late Jurassic source rock identified in the deep basin transform faults linked to the movement of the column is thickest in the south, shallower Early Indian plate past the Somali plate in the Late Cretaceous and Late Jurassic sources are in the CretaceousIndian plate. Thesepast the may Somali have plate been in ideal the Lateanoxic oil window. Where the pre- and syn-rift is not so depositionalCretaceous .environments These may have for sourcebeen ideal rocks anoxic to deeply buried in the north, these source intervals developdepositional in [Figure environments 3]. Cretaceous for source and rocksTertiary to sit in the present-day oil window. sdevelophale décollement in [Figure surfaces3]. Cretaceous linked toand slope Tertiary failure eventsshale décollementin the southern surfaces offshore linked may to also slope have failure Conclusions sourceevents rockin the potential. southern Where offshore burial may is also sufficient have to Defining source rocks in untested frontier margins maturesource organicrock potential.-rich sediments, Where burial this canis sufficient reduce to can present a challenge, however by integrating multiple datasets and geological models developed viscositymature organic and increase-rich sediments, pore pressure this can sufficiently reduce to from seismic analysis, gravity and magnetic data, facilitateviscosity low and angle increase displacement. pore pressure sufficiently to facilitate low angle displacement. offset well information, satellite slick mapping, and sequence stratigraphy models we can propose 2D seismic acquired in 2015 is interpreted within a various scenarios in which organic-rich sediments sequence2D seismic stratigraphic acquired in framework2015 is interpreted to characterize within a sequence stratigraphic framework to characterize may have been deposited and matured. This is both these potential source source using the methods of Figure 3. Late Cretaceous restricted marine basins formed by transform a useful tool in de-risking frontier passive margins Loseththese potentialet al [3]. sourceThese resultssource giveusing further the methods support of Loseth et al [3]. These results give further support movement may have been ideal environments for source rock deposition where limited data exists, and also allows the key for the presence of thick sequences of effective prize for East Africa - the oil prone hydrocarbon for the presence of thick sequences of effective source rocks. Seychelles. In the deep basin, an acoustically quiet homogeneous system to be identified. n source rocks. unit can be mapped at this level and is interpreted as a deep marine organic-rich marl source (Figure 2). References BASIN MODELLING 1Macgregor, D., 2015. History of the development of the East BASIN MODELLING In the Cretaceous, global OAEs are known in the Aptian African Rift System: A series of interpreted maps through time, Leeds University carried out basin modelling consideringand fo Cenomanian-Turonian,ur potential source rock and intervallocaliseds restrictedidentified marine by the seismicJournal of African Earth Sciences, 101, 232-252. characterizationLeeds University technique carried out. P eakbasin maturation modelling maps considering for environmentssource four rocks potential wereat pre sourcecreated-rift (Karoo), byrock transform interval syn-rift, faultss identified Late linked Jurassic toby the the and seismic Early Cretaceouscharacterization levels technique indicate .that Peak where maturation the sediment maps forcolumnmovement source is thickestrocks of the at Indian inpre the-rift platesouth, (Karoo), past shallower the syn Somali-rift, Early Late plate Cretaceo Jurassicin the Late usand and Early2 Bosellini,Late A., 1992. The continental margins of Somalia – JurassicCretaceous sources levels are indicate in the oilthat window. where theWhere sediment the pre column-Cretaceous. and syn is thickest-rift These is not in may sothe deeplyhave south, been buried shallower ideal inanoxic the Early north,depositional Cretaceo these sourceus andStructural Late Evolution and Sequence Stratigraphy. In: Watkins, J., environments for source rocks to develop in (Figure 3). intervalsJurassic sitsources in the presentare in the-day oil oilwindow. window. Where the pre- and syn-rift is not so deeply buried in the north, these sourceZhiqiang, F., and McMillen, K. (Eds.) Geology and Geophysics intervals sit in the present-day oil window. Cretaceous and Tertiary shale décollement surfaces linked to of Continental Margins. American Association of Petroleum slope failure events in the southern offshore may also have Geologists, 185-205. source rock potential. Where burial is sufficient to mature CONCLUSIONS 3 CONCLUSIONS organic-rich sediments, this can reduce viscosity and increase Loseth, H., Wensaas, L., Gading, M. Duffaut, K., and Springer, pore pressure sufficiently to facilitate low angle displacement. M., 2011. Can hydrocarbon source rocks be identified on seismic Defining source rocks in untested frontier margins can present a challenge, however by integrating multiple datasetsdata? and Geology; 39 (12); 1167-1170. geologicalDefining source models rocks developed in untested from frontierseismic margins analysis, can gravity present and a magnetic challenge, data, however offset bywell integrating information multiple, satellite datasets slick and mappinggeological, and models sequence developed stratigraphy from seismic models analysis, we can proposegravity and various magnetic scenarios data, inoffset which well organic information-rich sediments, satellite slickmay have beenmapping deposited, and seq anduence matured stratigraphy. This is bothmodels a useful we can tool propose in de-risking various frontier scenarios passive in which margins organic where-rich limited sediments data exists may ,have and alsobeen allows deposited the key and prize matured for E.ast This A fricais both - the a usefuloil prone tool hydrocarbon in de-risking system frontier to passive be identified. margins where limited data exists, and also allows the key prize for East Africa - the oil prone hydrocarbon system to be identified.

REFERENCES REFERENCES [1] Macgregor, D., 2015. History of the development ofHGS the –East PESGB African 17th Conference Rift System: on Africa A series E&P of interpreted maps through 29 time[1] Macgregor,, Journal of D.African, 2015. Earth History Sciences, of the development 101, 232-252. of the East African Rift System: A series of interpreted maps through time, Journal of African Earth Sciences, 101, 232-252. [2] Bosellini, A., 1992. The continental margins of Somalia – Structural Evolution and Sequence Stratigraphy. In: Watkins, J., Zhiqiang,[2] Bosellini, F., andA., 1992 McMillen,. The continentalK. (Eds.) Geology margins and of SomaliaGeophysics – Structural of Continental Evolution Margins. and Sequence American StratigraphyAssociation .of In: Petrol Watkins,eum J., Geologists,Zhiqiang, F., 185 and-205. McMillen, K. (Eds.) Geology and Geophysics of Continental Margins. American Association of Petroleum Geologists, 185-205. [3] Loseth, H., Wensaas, L., Gading, M. Duffaut, K., and Springer, M., 2011. Can hydrocarbon source rocks be identified on seismic[3] Loseth, data? H., Geology; Wensaas, 39 L., (12); Gading, 1167 -M.1170. Duffaut, K., and Springer, M., 2011. Can hydrocarbon source rocks be identified on seismic data? Geology; 39 (12); 1167-1170. Hunting the SNE in Guinea Bissau

Neil Hodgson*, Anongporn Intawong, and Karyna Rodriguez

Spectrum Geo Ltd, Woking, United Kingdom. +44 1483 730201, [email protected]

INTRODUCTION

The recent eruption of giant oil and gas hydrocarbon discoveries on the North West African coast began in 2014 with the SNE-1 discovery by Cairn in Senegal (Figure 1; [1]). This play-making well targeted Albian sandstones and Aptian carbonates inTuesday, a structural September trap, 11 at | theTheme eroded 2 | 15:45 edge of the Early Cretaceous platform margin. Neil Hodgson, Anongporn Intawong, and Karyna Rodriguez Spectrum Geo Ltd, Woking, United Kingdom There are a +44number 1483 of730201, interesting [email protected] play elements at work in this play that suggest a play-model can be extracted and re-used elsewhere along the margin in the chase for analogue traps. At the southern end of the margin is Guinea Bissau, Senegal’s southern neighbour, where theHunting plays are as yet the unexplored SNE and in appear Guinea to have an Bissaueven more promising potential.

Figure 1. A west-east orientation PSDM seismic line through SNE-1 well1. Figure 1: A west-east orientation PSDM seismic line through SNE-1 well [1]. The recent eruption of giant oil and gas hydrocarbon discoveries Working Petroleum System on the North West African coast began in 2014 with the SNE-1 To the south of SNE, the carbonate platform margin is seen to WORKING PETROLEUMdiscovery by Cairn SYSTEMin Senegal (Figure 11). This play-making well extend through The Gambia and the Casamanche region of targeted Albian sandstones and Aptian carbonates in a structural Senegal into Guinea Bissau. Here, Albian sands of equivalent To the southtrap, of SNE,at the eroded the carbonate edge of the Early platform Cretaceous margin platform is seenmargin. to extendage to those through in SNE areThe seen Gambia prograding and towards the Casamanchethe bounding region of unconformity in a similar trapping geometry to SNE. Senegal intoThere Guinea are a Bissau.number of Here, interesting Albian play elementssands ofat workequivalent in this age to those in SNE are seen prograding towards the bounding unconformityplay that suggest in a aplay-model similar trappingcan be extracted geometry and re-used to SNE. Potential source rocks in the deep basin are likely to comprise elsewhere along the margin in the chase for analogue traps. Turonian and Aptian Ocean Anoxic Event (OAE) source rocks, Potential sourceAt the rockssouthern in end the of deep the margin basin is Guinea are likely Bissau, to Senegal’s comprise Turonianand consequently and Aptianwill be as Ocean rich and wellAnoxic developed Event offshore (OAE) source southern neighbour, where the plays are as yet unexplored and Guinea Bissau as they are offshore Senegal. The thick Cretaceous rocks, and consequentlydepositionappear to have from an northwill even be tomore southas promising rich along and this potential. well margin. developed However, variationoffshsectionore in Guineathe (up submarine to 4 kmBissau thick) erosion inas the thethat basiny generated are onlaps offshore against the PMU theSenegal. Earlywould The thick Cretaceous appearsection to (updramatically to 4 km change thick )the in prognosis the basin of theonlaps facies against of AlbianCretaceous thedeltaics Early andthat CretaceousJurassic one might carbonate encounter and platform Jurassic in the where trap. carbonate migration platform where migration through talus porosity and/or slope fan sands is envisaged to mirror the SNE example. The migration pathways are analogous and the tectonic tilting that generates the landward dipping carbonate platform, and therefore the structural dip of the trap, is also present from Senegal to Guinea Bissau.

Indeed all the play elements that work effectively in SNE also appear to be present and effective on the Guinea Bissau margin. In addition, on the shelf west of the SNE trend in Guinea Bissau lies a partially explored salt diapir province. Sinapa- 2 discovered 35° API oil in 2004 in Albian aged deltaic sands in the flanks of the Sinapa salt dome. This is one of 18 salt diapirs on the shelf that appears to have been tested in a definitive way, and it was successful. Two sand units were penetrated; an upper sand interval with 90m of locally poor quality sand above a second sand interval with 250m of excellent quality sands. The well was side-tracked up-dip and similar pair of Albian sand intervals were penetrated , defining Figure 2. Sea water compensated 2D conventional PSTM composite line in second TWT ties to the Sinapa-2 oil discovery well. The line a 500m oil columnFigurealso demonstrates 2: in Sea the water upper the compensatedpresence sand of theinterval 2DAlbian conventional. deltaicThe SinapaSNE PSTM (PMU) oil composite play proves along line thea working inshelf second margin. petroleumTWT ties to thesystem Sinapa o-2n oil the discovery shelf offshore Guinea Bissauwell,. andThe linethe also pair demonstrates of sands penetrated the presence byof the Sinapa Albian- delta2 canic SNE be correlated(PMU) play along to the the shelf shelf marginedge .where they comprise a double target30 in the SNE play (Figure 2 and 3). HGS – PESGB 17th Conference on Africa E&P CONCLUSION The appearanceAn analysis at the of beginningthe play elements of the within Albian our databaseof clastic that deltas have come that togetherthen dominate in the giant this SNE previously discovery, suggests clastic starvedthat carbonate platform marginthese is elements likewise are correlated also present andsouth indeed of the SNE the area same through sequence The Gambia stratigraphic and into Guinea processes Bissau. Hereappear the detail to have of the controlled trap suggests that multiple Albian sandstone targets may be present, with high quality sandstone facies comprising the majority of the trap volume.

PMU

Figure 3: Detail of west - east orientation 2017 reprocessed broadband data in second TWT, seawater compensated, demonstrates the SNE play in Guinea Bissau. Line length is 30 km.

REFERENCES

[1] De Boer, W., 2017. Geophysics of the SNE Field, Senegal. HGS-PESGB HGS PESGB 16th African Conference, September 2017, Abstract Volume.

[2] Cairn Energy PLC investor announcement dated 07/10/2014. deposition from north to south along this margin. However, variation in the submarine erosion that generated the PMU would appear to dramatically change the prognosis of the facies of Albian deltaics that one might encounter in the trap.

Figure 2: Sea water compensated 2D conventional PSTM composite line in second TWT ties to the Sinapa-2 oil discovery well. The line also demonstrates the presence of the Albian deltaic SNE (PMU) play along the shelf margin.

CONCLUSION

An analysis of the play elements within our database that have come together in the giant SNE discovery, suggests that these elements are also present south of the SNE area through The Gambia and into Guinea Bissau. Here the detail of the trap suggests that multiple Albian sandstone targets may be present, with high quality sandstone facies comprising the majority of the trap volume.

PMU

Figure 3. Detail of west - east orientation 2017 reprocessed broadband data in second TWT, Figure 3: Detail ofseawater west - compensated, east orientation demonstrates 2017 reprocessed the SNE play broadbandin Guinea Bissau. data Linein second length isTWT, 30 km. seawater compensated, demonstrates the SNE play in Guinea Bissau. Line length is 30 km. through talus porosity and/or slope fan sands is envisaged to platform margin is likewise correlated and indeed the same mirrorREFERENCES the SNE example. The migration pathways are analogous sequence stratigraphic processes appear to have controlled and the tectonic tilting that generates the landward dipping deposition from north to south along this margin. However, carbonate platform, and therefore the structural dip of the trap, variation in the submarine erosion that generated the PMU [1] De Boer, W., 2017. Geophysics of the SNE Field, Senegal. HGS-PESGB HGS PESGB 16th African Conference, is also present from Senegal to Guinea Bissau. would appear to dramatically change the prognosis of the facies September 2017, Abstract Volume. of Albian deltaics that one might encounter in the trap. Indeed all the play elements that work effectively in SNE also appear[2] Cairn to beEnergy present PLC and investor effective announcement on the Guinea datedBissau 07/10/2014.margin. Conclusion In addition, on the shelf west of the SNE trend in Guinea Bissau An analysis of the play elements within our database that have lies a partially explored salt diapir province. Sinapa-2 discovered come together in the giant SNE discovery, suggests that these 35° API oil in 2004 in Albian aged deltaic sands in the flanks elements are also present south of the SNE area through The of the Sinapa salt dome. This is one of 18 salt diapirs on the Gambia and into Guinea Bissau. Here the detail of the trap shelf that appears to have been tested in a definitive way, and suggests that multiple Albian sandstone targets may be present, it was successful. Two sand units were penetrated; an upper with high quality sandstone facies comprising the majority of sand interval with 90m of locally poor quality sand above a the trap volume. n second sand interval with 250m of excellent quality sands. The well was side-tracked up-dip and similar pair of Albian sand References intervals were penetrated, defining a 500m oil column in the 1De Boer, W., 2017. Geophysics of the SNE Field, Senegal. HGS- upper sand interval. The Sinapa oil proves a working petroleum PESGB HGS PESGB 16th African Conference, September 2017, system on the shelf offshore Guinea Bissau, and the pair of sands Abstract Volume. penetrated by Sinapa-2 can be correlated to the shelf edge where they comprise a double target in the SNE play (Figure 2 and 3). 2Cairn Energy PLC investor announcement dated 07/10/2014.

The appearance at the beginning of the Albian of clastic deltas that then dominate this previously clastic starved carbonate

HGS – PESGB 17th Conference on Africa E&P 31 GABON’S ‘WILD WEST FRONTIER’ PROMISES A GOLDEN AGE OF DISCOVERY FOR THE DEEP- OFFSHORE

* Tuesday, September 11Tony | Theme Younis 2 | 16:10, Michael Clutterbuck, Phil Birch; Impact Oil & Gas Limited Tony Younis, Michael Clutterbuck, Phil Birch Oil has dominated Gabon’s economy for decades, however, this mature province has seen its production Impact Oil & Gas Limited decline from a peak of 370,000 barrels per day in 1997 to around 200,000 in 2017. The Diaman, Leopard, Boudji, and Ivela discoveries made by Total, Shell, Petronas, and Repsol respectively, have opened up the deep water pre-salt play of South Gabon, and substantially moved the known limit of the active Gabon’spetroleum system “Wild westward West into the deepFrontier” offshore. Currently Promises other operators sucha Golden as Noble and Impact Age are continuing to push the limits of the deep water pre-salt play distally southwards along the South Gabon Marginof and Discoverystill farther west to the forocean -thecontinental Deep-Offshore boundary, aided by higher quality seismic

Data courtesy of CGG Multi-Client and New Venture

FigureFigure 1. NE-SW 1: NE- dipSW profile dip profile offshore offshore South GabonSouth showing Gabon a showinglarge inverted a large half grabeninverted preserved half graben as a sediment preserved filled outeras ahigh sediment whichOceanic divides filled the outer landward high whichinner Aptian divides salt the basin landward and theTransitional/Hyperextended oceanward inner Aptian hyperextended salt basin tectonic and the domains (Data Domain Outer High Inner Salt Basin courtesyoceanward of CGG hyperextended Multi-Client and tectonicNew Ventures) domains (Data courtesy of CGG Multi-Client and New Ventures)

Oil has dominated Gabon’s economy for decades, however, this There is evidence for the Outer High to be that of a large maturedata. province has seen its production decline from a peak of inverted half-graben, opening up the potential for not only a 370,000Along barrels the per western day in 1997 flank to aroundof the 200,000South Gabonin 2017. SaltThe Basin,series the of stackedpresence Barremian-Aptian of a prominent Dentale high, fluviatile (Figure 1)reservoir, has Diaman,frequently Leopard, Boudji,been identifiedand Ivela discoveries on various made vintages by Total, of 2D intervals,seismic. but The also exploration a substantial community section of transgressive has typically marine Shell, Petronas,considered and Repsolthis structure respectively, to behave b asementopened up or the igneous deep mid-Aptian in origin at Gamba least [4]reservoir, with sands,little or up no to 300mexploration in gross water pre-saltsignificance. play of SouthHowever, Gabon, with and the substantially advent of moved 3D seismic thickness, and the above latest the in syn-riftdepth imagingsequence. techniques The boundary, this between old the knownassumption limit of the has active now petroleum been turned system on westward its hea intod. these two clastic reservoir units can clearly be defined through the deep offshore. Currently other operators such as Noble and seismic stratigraphic analysis as an angular unconformity There is evidence for the Outer High to be that of a large inverted half-graben, opening up the potential Impactfor are not continuing only a seriesto push ofthe stacked limits of theBarremian deep water-Aptian pre- Dentale(Figure fluviatile 2). reservoir intervals, but also a salt playsubstantial distally southwards section alongof transgressive the South Gabon marine Margin mid and-Aptian Gamba reservoir sands, up to 300m in gross still fartherthickness, west to abovethe ocean-continental the syn-rift sequence. boundary, aided The byboundary West between of the Outer these High two lies clastic an adjacent reservoir marginal units trough, can 2 higherclearly quality seismicbe defined data. through seismic stratigraphic analysissuperimposed as an angular onto hyper-extended unconformity crust (Figure formed 2). through continued westward extension. Halokinetic activity is observed Along the western flank of the South Gabon Salt Basin, the within this narrow interval of the basin, yet is found below the presence of a prominent high, (Figure 1), has frequently break-up unconformity. Assuming that the salt identified within been identified on various vintages of 2D seismic. The the hyper-extended zone was deposited contemporaneously as part exploration community has typically considered this structure of the Aptian Ezanga evaporitic cycle, this finding demonstrates to be basement or igneous in origin at least4, with little or no the transient nature of continental extension, moving westwards exploration significance. However, with the advent of 3D seismic in the case of the West African Margin, suggesting that continental and the latest in depth imaging techniques, this old assumption separation occurred during the Early Albian3. has now been turned on its head.

32 HGS – PESGB 17th Conference on Africa E&P +ve Hard Carbonate build-ups located on outer high crest

-ve Soft

300m

Data courtesy of CGG Multi-Client and New Venture

Figure 2. NW-SE section of the outer high crest, highlighting an angular unconformity between the syn-rift Dentale and sag-phase GambaFigure Formations. 2: NW-SE Mapping section of the of high the quality outer Gamba high transgressive crest, highlighting sand shows thicknessesan angular up to unconformity 300m (Data courtesy between of CGG the Multi-Clientsyn-rift Dentale and New andVentures) sag-phase Gamba Formations. Mapping of the high quality Gamba transgressive sand shows thicknesses up to 300m (Data courtesy of CGG Multi-Client and New Ventures) Following continental separation, the Outer Margin underwent introduction. Geological Society London Special Publications 413 Wacceleratedest of the thermal Outer subsidence High lies allowing an adjacent for the accommodation marginal trough, superimposed onto hyper-extended crust [2] formedof high qualitythrough post-rift continued marine sourcewestward rocks ofextension. Albo-Turonian Halokinetic 3Péron-Pinvidic activity G., is Manatschal observed G., within Masini E.,this Sutra narrow E., Flament interval ofage. the This basin, interval’s yet seismicis found character below is recognisedthe break further-up uncon south formity.J. M., Haupert Assuming I., Unternehr that P.the (2015); salt Unravelling identified the within along- the hyperin Angola-extended and along zone the Brazilian was deposited conjugate, and contemporaneously is considered to strike asvariability part of of the Angola-Gabon Aptian Ezanga rifted evaporitic margin: a mapping cycle, thisbe the finding primary demonstrates generative interval the within transient these basins, nature but isof as continental approach. extension, Geological Society moving London westwards Special Publications in the case 438 of theyet Westuntested African in S. Gabon. Margin, suggesting that continental separation occurred during the Early Albian [3]. 4Unternehr P., Péron-Pinvidic G., Manatschal G., Sutra E. (2010); Following continental separation, the Outer Margin underwent accelerated thermal subsidence allowing Whilst the nearby discoveries demonstrate the presence of a Hyper-extended crust in the South Atlantic: in search of a forsyn-rift the accommodation petroleum system, the of Albo-Turonianhigh quality source post rocks-rift marinemodel. source Petroleum rocks geoscience, of Albo- Turonian16, 207-215 age. This interval’s seismicwithin the character Outer Margin is offerrecognised a significantly further higher south probability in Angola and along the Brazilian conjugate, and is consideredof oil generation to atbe the the present primary day [1], generative migrating laterally interval into withinBiographical these basins, Sketch but is as yet untested in S. Gabon. Tony Younis has a B.Sc. in Geophysics from the University of the pre-salt reservoir units of the Outer High. Furthermore, Tony Younis has a BSc in Edinburgh and a Masters in Petroleum Geology from the University of Aberdeen. Whilstwhilst thethe presence nearby of discoveriesAptian salt within demonstrate the inner South the Gabon presence Geophysics of a syn from-rift the pUniversityetroleum system, the Albo-Turonian sourceBasin is rocksconsidered within to be the an ideal Outer seal Marginto any trap, offer its absence a significantly of Edinburgh higher andprobability a Masters inof oil generation at the presentWith over 20 years industry experience, Tony began his career dayover [1], this migratingstructural high laterally is fortuitous, into allowing the pre the-salt gas generatedreservoir unitsPetroleum of the Geology Outer from High the . Furthermore, whilst the working in offshore seismic acquisition with Schlumberger as a Processing Geophysicist in 1997. In 2004, he opted to join Total’s presence of Aptian salt within the inner South GabonUniversity Basin is of considered Aberdeen. to be an ideal seal to any trap, from Neocomian-Barremian source rocks to migrate through UK subsidiary in Aberdeen as a Seismic Interpretation itsand absence out of the overstructure, this prior structural to the deposition high is of fortuitous, the Tertiary allowing the gas generated from Neocomian-BarremianGeophysicist where he played a key role in the Tormore discovery sourceshale seal. rocks Rather, to this migrate seal timing through is favourable and outfor the of capture the structure, of With priorover 20 to years the industry deposition of the Tertiary shale sealthat. eventually led to the Laggan-Tormore development in the Rather,Albo-Turonian this seal generated timing oil instead.is favourable for the capture ofexperience, Albo-Turonian Tony began generated his oil instead. West of Shetlands. From 2008, Tony took on various exploration career working in offshore roles within Total’s New Venture department in Paris as well as an operations role in Gabon in 2010. WithWith dwindlingdwindling reserves reserves and an and economy an economy heavily dependent heavily on dependent seismic acquisition on its hydrocarbon with wealth, the need to offset Gabon’sits hydrocarbon oil industry wealth, the decline need to isoffset ever Gabon’s more oil pressing. industry ExploringSchlumberger in asthe a Processing deep offshore for these very large In 2015 and after 10 years at Total, Tony decided to join the small plays, will be the key to halting and reversing that decline.Geophysicist in 1997. In 2004, and dynamic West African exploration company Impact, based in decline is ever more pressing. Exploring in the deep offshore for Woking, England, as the company’s Exploration Manager. these very large plays, will be the key to halting and reversing he opted to join Total’s UK Referencesthat decline. n subsidiary in Aberdeen as a Seismic Interpretation Geophysicist where he played a key role in the Tormore discovery that [1References] Anka Z., Séranne M., Lopez M., Scheck-Wenderotheventually M., Savoye led to the B. Laggan-Tormore (2009); The development long-term in evolution the West of the1Anka Congo Z., Séranne deep M.,-sea Lopez fan: M., A Scheck-Wenderoth basin-wide view M., Savoyeof the interactionof Shetlands. between From 2008, a Tony giant took submarine on various exploration fan and aroles matureB. (2009); passive The long-term margin evolution (ZaiAngo of the project).Congo deep-sea Tectonophysics, within Total’s 470, New 42- Venture56 department in Paris as well as an [2fan:] Gibson A basin-wide G.M., view Roure of the interactionF., Manatschal between aG. giant (2015); Sedimentaryoperations role basins in Gabon and in 2010. continental margin processes –submarinefrom modern fan and hyper a mature-extended passive margin margins (ZaiAngo to project).deformed ancient analgoues: an introduction. Geological Tectonophysics, 470, 42-56 In 2015 and after 10 years at Total, Tony decided to join the Society London Special Publications 413 small and dynamic West African exploration company Impact, 2 [3Gibson] Péron G.M.,-Pinvidic Roure F., G., Manatschal Manatschal G. (2015); G., Sedimentary Masini E., Sutrabased E., inFlament Woking, England,J. M., Haupert as the company’s I., Unternehr Exploration P. (2015); Unravellingbasins and continental the along margin-strike processes variability – from modernof the Angola-GabonManager. rifted margin: a mapping approach. Geologicalhyper-extended Society margins London to deformed Special ancient Publicationsanalgoues: an 438 HGS – PESGB 17th Conference on Africa E&P 33 [4] Unternehr P., Péron-Pinvidic G., Manatschal G., Sutra E. (2010); Hyper-extended crust in the South Atlantic: in search of a model. Petroleum geoscience, 16, 207-215 Tuesday, September 11 | Theme 2 | 16:35 Rob Crossley, Gregor Duval, Max Norman CGG Services (UK) Ltd Gabon Deep Offshore: New Petroleum System Insights from the Full Integration of Geology and Geophysics

Pre-Salt and Post-Salt section offshore South Gabon Pre-Salt and Post-Salt section offshore South Gabon New insights have been developed through the integration of GDE mapping integrated this control data with seismic regional geology, satellite imagery, potential fields geophysics, interpretation in the light of analogues from Brazil and the Red and the interpretation of a new basin-wide broadband 3D Sea. This led to new concepts regarding the changing hydrology seismic survey offshore South Gabon. of the basin and mechanisms driving some of the diapiric salt movement. This in turn led to new ideas regarding both the At the regional scale, the outer limit of continental crust has distribution of oil-prone verses gas-prone source facies, and the been mapped using gravity and magnetic data, calibrated with origin of the different sand systems at Dentale, Coniquet, and 3D seismic imagery, across the continental to oceanic crust Gamba Formation levels. transition zone. This helps mapping the extent of Pre-Aptian sedimentary basins where much of the petroleum potential The seismic resolution beneath the Aptian salt has driven greatly remains. Combined with this, a set of new gross depositional improved understanding of the tectonostratigraphy, with clear environment (GDE) maps, focussed on the Pre-Aptian Salt and evidence for multiple phases of rift fault block movement in Early Drift sedimentary units, have been compiled to help better the late syn-rift, and changing geometries within the sag phase. characterise reservoir and source facies distribution. Geological A suite of 1D basin models which tested a range of thermal data from wells and outcrops on the West African and Brazilian scenarios shows that oil-mature sections are widely-developed margins were used as control points and rotated into paleo- in the upper part of the pre-salt sequence, whereas the deeper position using Plate Wizard for six key time slices through the syn-rift section is in the gas window. These new observations, warp, rift, sag, and drift phases. coupled with recognition of fluid escape pathways, permits the

34 HGS – PESGB 17th Conference on Africa E&P development of exploration concepts which aim to target oil- Biographical Sketch charged traps, rather than gas charged traps, in the pre-salt. Rob Crossley graduated from Reading University in 1972 Furthermore, the NW part of the Congo fan buries the lower and gained his PhD from the part of the post-salt section and contains numerous turbidite University of Lancaster on the systems. The 1D basin models show that the lower part of the volcanic tectonostratigraphy post-salt section is oil-mature in several areas. The new image of the Kenya Rift in 1976. This quality gives a better basis for identifying potential charge was followed by 9 years as a pathways from the pre-salt and from depocentres in the post- lecturer in the University of salt, into potential traps in the turbidite sand intervals. n Malawi, where he extended his research into rift sediment fills, basin hydrology, sedimentation by termites and archaeology. He then joined Robertson Research in North Wales as a sedimentologist, where he worked at scales ranging from pore throats, through unitisation of North Sea Fields, to global Earth Systems modelling. Today, as Chief Geologist in CGG, he still occasionally finds himself looking down a microscope and interpreting seismic, as well as being involved in asset evaluations, regional-scale exploration projects and mentoring members of our up-and-coming technical staff.

HGS – PESGB 17th Conference on Africa E&P 35 Notes

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36 HGS – PESGB 17th Conference on Africa E&P The 17th HGS-PESGB Conference Est. 1964

PES .org.uk on African E&P pesgb

Oral Presentations Day Two Abstracts

September 10-13, 2018 Norris Convention Centre, Houston Texas

HGS – PESGB 17th Conference on Africa E&P 37

Entrenched slope channel complex systems: reservoir opportunities through understanding Wednesday, September 12architectural | Theme 3 element| 8:35 distribution and application to West Africa E&P Professor Bryan T. Cronin Professor Bryan T. Cronin, Tullow Ghana Ltd, North Dworzulu, Accra, Ghana Tullow Ghana Ltd, North Dworzulu, Accra, Ghana

Confined, entrenched, or simply slope channel complexes, have been described from a range of Entrenchedoutcrop, subsurface Slope and sea Channel floor settings. In the Complex West African context, theySystems: constitute a family of reservoirs that have a wide range of reservoir quality, reservoir connectivity, trapping style, and Reservoirrecovery Opportunities factor. Geological models all focusthrough on the architecture Understanding of the main channel belt and show that the phases of channel complex system occupancy pass from a bypass phase, through a stacked channel element phase of various character, through an aggradational phase with smaller, usually Architecturalmeandering Element channel elements, Distribution to an end phase of progressive and switch off Application of the system. A wide range of terms are now in common use that conflict in scale and usage, reflecting perhaps experience with specific case studiesto West, and belie the Africa true range of slopeE&P channel complex system expression. A unified model that allows true variability to be captured is needed. Confined, entrenched, or simply slope channel complexes, have been described from a range of outcrop, subsurface and sea floor settings. In the West African context, they constitute a family of reservoirs that have a wide range of reservoir quality, reservoir connectivity, trapping style, and recovery factor. Geological models all focus on the architecture of the main channel belt and show that the phases Figure 1. Planform and dip profile views of slope-basin floor showing the location of entrenched slope of channel complex Figurechannel 1. complexes, Planform andand leveedip profile growth views patterns of slope-basin floor showing the location of entrenched slope system occupancy pass channel complexes, and levee growth patterns may have a range of morphologies that reflect the evolution of from a bypass phase, through a stacked channel element phase Channel complex systems range widelythe in system,net sand, from net lateral thin bed, rotational or net mudfailure slump of the or wall debris (often flow made of various character, through an aggradational phase with volume. The channel complex systemsof also external vary widely master in levee the proportionmaterial), to of erosional channel elemententrenchment style. smaller, usually meandering Thesechannel styles elements, range to from an end (i) highlyphase amalgamated sand bodies that extend across the channel complex and other types of terrace, to passive onlap of underfit late stage of progressive switch off of systemthe system. but areA wide made range entirely of terms of individual are meanderform, or braidform, channel elements, sometimes called ‘confined sheets’, to (ii) more clearlymeanderform distinguished channel stacked internal channel levee. elements Lateral rotational that are underfitblock now in common use that conflict in scale and usage, reflecting to the channel complex system, and havefailure laterally and associated equivalent scalloped inside levees slump and scar terraces, wall morphology, to (iii) even is perhaps experience with specific case studies, and belie the true smaller scale skinny, later stage meanderformoften difficult channel toelements distinguish with fromhigher internal proportions levee ofand related associated range of slope channel complexvolumes system of expression.laterally equivalent, A unified smaller scale internal levees, internal crevasse splays, internal frontal meander cut banks, though either can co-exist. model that allows true variabilitysplays, to orbe passivecaptured drape. is needed. The lateral channel complex system wall may have a range of morphologies that reflect the evolution of the system, from lateral rotational failure of the wall (often made of external master levee material), to erosionalExternal entrenchment to many of theand slope other channel types of complex terrace, systems to passive Channel complex systems range widely in net sand, net thin onlap of underfit late stage meanderformare channel extensive internal master levee. levee complexes,Lateral rotational which blockare not failure always and bed, or net mud slump or debrisassociated flow volume. scalloped The slump channel scar wall morphology, is often difficult to distinguish from internal levee included in conventional models for slope channel complex complex systems also vary widelyand associated in the proportion meander of cut channel banks, though either can co-exist. system architecture. These external master levee complexes element style. These styles range from (i) highly amalgamated may themselves record multiphase occupancy of the main sand bodies that extend across the channel complex system but slope channel complex system, with each phase of levee build are made entirely of individual meanderform, or braidform, recording (i) a precursive phase of external crevasse splay build, channel elements, sometimes called ‘confined sheets’, to (ii) followed by (ii) the principal phase of spill cap aggradation of more clearly distinguished stacked channel elements that are the master levee, terminating in (iii) shutdown and hemipelagic underfit to the channel complex system, and have laterally drape of the external master levee complex. The timing of master equivalent inside levees and terraces, to (iii) even smaller scale levee build is also interpreted differently in current models, and skinny, later stage meanderform channel elements with higher needs further investigation here. proportions of related volumes of laterally equivalent, smaller scale internal levees, internal crevasse splays, internal frontal Beneath the slope channel complex systems, sedimentary splays, or passive drape. The lateral channel complex system wall

38 HGS – PESGB 17th Conference on Africa E&P

A unified model for entrenched slope channel complex systems is proposed that captures internal channel belt, external master levee complex, and precursive architectural element character, based on outcrop examples from the Cerro Torro Formation of southern Chile, various formations from southern and eastern Turkey, and the Eocene of the Spanish Pyrenees; seafloor examples from the Mediterranean and western California; and subsurface examples from offshore Myanmar, Equatorial Guinea, Angola, the North Sea, Colombia, and Ghana, to reflect commonality and contrast in slope channel complex architecture. The synthesis is long overdue. With the large amount of reservoirs of this style offshore West Africa and elsewhere have come an array of models that are mostly field specific without generic use. This paper draws on many years of work on a large number of global examples. n BRIEF BIO Biographical Sketch Bryan Cronin is a geologist with 28 years of technical experience with turbidites at outcrop, on the sea floor and in the subsurface. He is currently principal geologist for Tullow Ghana Ltd, based in Accra.

FigureFigure 2. 2. Unified Unified model model for fordeep-water deep-wa channelter channel complexes complexes He was an independent consultant (2005-2016), working on deep-waterBry reservoirsan Cronin in the North isSea, a geologist with 28 years of technical experience with turbidites at outcrop, on the architectureExternal to is many highly of variable, the slope reflecting channel the complex position systemsof the are extensive master levee complexes, which systemare not on always the slope included or shelf. in Some conventional systems are models highly entrenched for slope channel Africa, complex SE Asia, South system America, architecture. the former These Soviet Union and in andexternal have excavatedmaster levee headwards complexes on the uppermay themselves slope, where recordthey multiphaseother areas. occupancy He has running of the field main coursessea slope infloor the Alps, and Pyrenees, in the subsurface. He is currently principal geologist for Tullow Ghana Ltd, based in evolvechannel to canyons,complex cutting system, into with highstand each phaseshelfal systemsof levee such build recordingCalifornia, (i) aIreland, precursive Spain andphase Turkey of external for many years. He ascrevasse deltas, beach-barrier splay build, systems followed or offshoreby (ii) the bars. principal Further phase down of spillinstructed cap aggradation for Petroskills of andthe Nautilus.masterAccra levee,He is Honorary. Professor system,terminating in upper in (iii)to mid-slope shutdown settings, and hemipelagic slope channel drape complex of the externalat University master of Aberdeen,levee complex. The Robert The timingGordon University and of master levee build is also interpreted differently in current models, and needs further investigation systems are often preceded by mass-transport complexes, which Hangzhou Petrochina Institute for Petroleum Geology. here. may have initiated system entrenchment by providing diversion He was an independent consultant (2005-2016), working on deep-water reservoirs in the North Sea, andBeneath fairway the access slope to sandchannel on the complex shelf. Channel systems, complex sedimentary architectureHe is still involved is highly in education variable, and reflectingAfrica, training with SE MSc Asia, and PhD South America, the former Soviet Union and in other areas. He has running field systemsthe position may touch of the down system onto, on or theerode slope through, or shelf. such Somemass- systemsstudents are highly and oil entrenched company employees, and have with the PRACCS research transportexcavated complexes, headwards leaving on residualthe upper erosional slope, remnants where they of the evolve group to canyons, where he cutting is joint principalinto highstand investigator with Ben Kneller, shelfal systems such as deltas, beach-barrier systems or offshore bars. Further down system,courses in in the Alps, Pyrenees, California, Ireland, Spain and Turkey for many years. He instructed for mass-transport complex lateral to the slope channel complex working in southern Chile, Turkey, France, Argentina, Tibet and upper to mid-slope settings, slope channel complex systemsMexico. are often preceded by mass-transport margin.complexes, Channel which complex may systemshave initiated further systemdownslope entrenchment may by providing diversion and fairwayPetroskills access and Nautilus. He is Honorary Professor at University of Aberdeen, The Robert Gordon also touch down into or erode through precursive frontal splay to sand on the shelf. Channel complex systems may touch downProfessor onto, Cronin or erode was awardedthrough, the such William mass Smith- Fund by the complexes,transport complexes,that were initially leaving deposited residual outboard erosional of the remnants channel of the mass-transport complex lateral to the Geological Society, London, in 2007.University and Hangzhou Petrochina Institute for Petroleum Geology. system.slope channel Distinguishing complex precursive margin. frontal Channel splays, complex from unrelated systems further downslope may also touch down highstand deposits, and from crevasse splays, also requires His list of publications is extensive and in most mainstream peer further investigation here. reviewed journals. He is still involved in education and training with MSc and PhD students and oil company employees,

HGS – PESGB 17th Conference on Africa E&P with the PRACCS39 research group where he is joint principal investigator with Ben Kneller, working in southern Chile, Turkey, France, Argentina, Tibet and Mexico.

Professor Cronin was awarded the William Smith Fund by the Geological Society, London, in 2007.

His list of publications is extensive and in most mainstream peer reviewed journals. Wednesday, September 12 | Theme 3 | 9:00 Max Casson, Jonathan Redfern North Africa Research Group (NARG), Williamson Building, University of Manchester, UK. Luc G. Bulot North Africa Research Group (NARG), Williamson Building, University of Manchester, UK. Aix-Marseille Université, CNRS, IRD, Collège de France, Cerege, Site Saint-Charles, Marseille, France. Jason Jeremiah Golden Spike Geosolutions Ltd, Stevenage, Hertfordshire, UK. Towards the Development of an Integrated Central Atlantic Tectono-Stratigraphic Framework

The Central Atlantic region is an under-explored world-class Aptian) are recorded across the Atlantic. Multiple source rock hydrocarbon province. The recent oil and gas discoveries on facies are observed throughout the stratigraphy, characterised by the West African Atlantic margin and the Guyana/Suriname TOC and pyrolysis analysis, which are being integrated to better margin further confirm the significant resource potential understand the hydrocarbon generating potential of these rich of Central Atlantic basin. This paper presents results from source rock intervals. an ongoing multi-disciplinary project that aims to define a new stratigraphic framework for the Mesozoic in the Central High core recovery in DSDP 76-534a has permitted a new Atlantic by integrating a suite of geoscience data from outcrop interpretation of the Base Albian unconformity (BAU), and subsurface wells. The results are already identifying pan- recognised elsewhere across the Atlantic (Morocco - Luber et Atlantic sequence stratigraphic surfaces, improving stratigraphic al. 2017), suggesting there is a significant super-regional event resolution and providing insights into the geographical extent of at this time. This is associated with a major progradational source rock development. phase of deltaic systems on both sides of the conjugate margins during the Albian, delivering plant debris-rich sediment to During the late Mesozoic, the Central Atlantic region was a large the deep basin (Type III source rocks) and forming prolific enclosed basin; this offers the potential to compare the conjugate reservoirs on the shelf (i.e. SNE field, Senegal). Further work margins to provide a comprehensive assessment of basin by NARG defining exhumation rates from low-temperature evolution. The new biostratigraphically-constrained framework thermochronology data in northwest Africa, suggests a pulse of employs numerous dating techniques, including: calcareous source area uplift around 120Ma. Hence at this time, a source nannofossils, calpionellids, palynology, and ammonites, to build to sink approach is used to postulate the mechanisms for this a high resolution age model. New data includes detailed logging significant unconformity. and sampling of the exposed Mesozoic stratigraphy of Maio, Cape Verde, a re-evaluation of 7 IODP sites, integration of data Fieldwork data from Maio strongly supports this model and from available exploration wells across the region, and logging of a clear, refined stratigraphic correlation has been made to the exposed sections of Cretaceous sediments outcropping at Cap de DSDP-based framework. Multi-technique, biostratigraphical Naze, Senegal. This extensive dataset covers a broad geographical analysis has improved the dating of these sediments from area along the African and conjugate margin. previous work and a composite, fully integrated type- section from the island is presented. Early applications of the Cumulatively, over 400 samples have been collected and stratigraphic framework to seismic data in the West African analysed. Early results include a new interpretation from DSDP Atlantic margin strengthens our interpretations to allow Leg 41 Site 367 that highlights a previously unreported Lower better prediction of reservoir and source rock development, Berriasian unconformity (LBU), which removes much of the late understanding of the sequence stratigraphy, and regional Tithonian sediments. This scientific borehole is a key data point knowledge of the basin evolution. n in the basin. Detailed logging also identifies more extensive black shale development, indicating anoxia is more widespread Reference stratigraphically than previously recorded. In ODP 207-1258C, Luber, T.L., Bulot, L.G., Redfern, J., Frau, C., Arantegui, A., & DSDP 41-367, and 41-368 anoxia extends beyond the known Masrour, M., 2017. A revised ammonoid biostratigraphy for global anoxic events throughout the late Albian into the the Aptian of NW Africa: Essaouira-Agadir Basin, Morocco. Cenomanian. Similar observations at the OAE-1A event (earliest Cretaceous Research, 79, pp.12-34.

40 HGS – PESGB 17th Conference on Africa E&P Biographical Sketch Max Casson is working in the North Africa Research Group at the University of Manchester on his PhD project examining the regional geology of the NW African Atlantic Margin. Max’s research is sponsored by a consortium of oil companies active in NW Africa, as well as an ECORD research grant. Having spent his first year of the PhD collecting data in Senegal and Cape Verde, Max would like to share his initial thoughts towards an integrated tectono-stratigraphic framework for the Central Atlantic.

HGS – PESGB 17th Conference on Africa E&P 41 effective permeability in areas of contrasting depositional architecture. The number and location of these additional baffles were verified by history matching.

In two months of testing, the range of uncertainty was narrowed as several branches of the decision tree Wednesday, September 12 | Theme 3 | 9:25were eliminated. Remaining uncertainties such as transmissibility multipliers, petrofacies proportions, and correlation lengths were combined to generate a range of plausible models. From this range, Monica Miley, Amelie Dufournet, Jose Villaindependently derived low, mid, and high case models were selected. This approach is more valuable in Anadarko Petroleum Corporation the context of uncertainty assessment than creating a single base case model or generating an ensemble Mark Bentley of purely stochastic permutations of a single underlying concept. AGR-TRACS Conclusion The benefit of this workflow is to systematically create a range of reservoir models by identifying multiple complexities at different scales and testing them to understand which are the most important for fluid flow. Reservoir ModelingBy confining of a the Deep-Water work to a sector area, the team West quickly learned African which modifications needed to be made to the static model rather than applying more blunt modifications in the dynamic model. The sector model Reservoir: A Fullyworkflow Integrated, was employed to make multiple Multi-Scenario full field models by extending the seismic interpretation and incorporating all wells. These models have been used to optimize locations of infill wells and assess the value of accelerating production. There is greater confidence in the predictability of these models as minimalApproach adjustments to the dynamic model were required to achieve history matches. In the early stages of field development, there is a high degree of uncertainty in reservoir description. Creating a range of reservoir models allows proper assessment of reservoir uncertainties in a more rigorous way than using a single base case model. This is crucial in fields with significant geologic and production complexities where new in-fill wells are drilled to accelerate production, increase reserves, and maximize oil recovery. This case study demonstrates the application of a decision tree-based methodology to model multiple uncertainties for an off-shore field in West Africa. The goal was to understand which uncertainties have the most significant impact on fluid flow and create several dynamically tested reservoir models to represent them. Models were created quickly over a small sector area. Initial dynamic simulations provided feedback that improved the seismic interpretation and static model construction for subsequent iterations. An integrated team composed of a geophysicist, geomodeler, and simulation engineer were able to produce a set of geologically plausible, dynamically tested full field models. Figure 1. Location map for Enyenra field. The field is located 60 km off the coast of Background Ghana and 25 km west of the Jubilee field. From the northernmost to southernmost The subject of this study, the Enyenra field, is wells, the field extends 24 km and varies in width from 300-1000m. part of theTweneboa-Enyenra-Ntomme (TEN) complex of fields. It is located in the Tano (Figure 1). From the northernmost to southernmost well, the sub-basin of the Deep Ivorian Basin between the Romanche and field extends 24 km and is 300 to 1000 m wide. The Owo-1 St. Paul fracture zones. Basement-rooted extensional faulting discovery well, drilled in 2010, encountered 46 m of oil pay. created accommodation space for deepwater deposition. During Eleven wells have been drilled, six of which were completed as the Turonian, sediments comprising the Enyenra reservoir producer-injector pairs spaced 2 km apart. Production started were shed from the Tano high and deposited in the lower to in August 2017 and the current production rate is 35 MSTB/day. middle slope as a series of aggradational levee-confined channel As of May 2018, the cumulative oil produced is 18 MMSTB and complexes. The reservoir is trapped laterally by stratigraphic 26 MMSTB of water have been injected. Current recovery factor pinch-outs and updip by faults or pinch-outs. is 4%. Data used in this study include dual azimuth seismic data from 2014, three cores, well logs, pre-production drill stem tests, Enyenra is located 60 km offshore from Ghana and 25 km west interference tests, and production data. of the Jubilee field in water depths varying from 1400 to 1700 m

42 HGS – PESGB 17th Conference on Africa E&P Figure 1. Location map for Enyenra field. The field is located 60 km off the coast of Ghana and 25 km west of the Jubilee field. From the northernmost to southernmost wells, the field extends 24 km and varies in width from 300-1000m.

Figure 2: Sum of negative amplitudes extracted from an extended elastic impedance volume showing possible sand Figuredistribution. 2: Sum Four of negativechannel complexes amplitudes were extracted identified fromon seismic an extended data and elasticverified impedance with static pressure volume data. showing possible sand distribution. Four channel complexes were identified on seismic data and verified with static pressure data.

Figure 3. Wells inside and outside the channel axis show a highly variable net to gross. Figure 3. Wells inside and outside the channel axis show a highly variable net to gross. Due to the channelized nature of the deposits, there is a continuity are further validated through integration of seismic high degree of stratigraphic complexity and potential for interpretations, static reservoir pressures, and interference tests. compartmentalization. Multiple channel complexes have been Reservoir quality is highly variable in and outside the channel identified and interpretation of these is complicated by variation axis making the location and description of this boundary in erosion rates, stacking patterns, and sinuosity (Figure 2). critical in modeling (Figure 3). There are also finer-scale Individual reservoir intervals are identified by upward heterogeneities observed at the core scale: a range of facies fining successions on gamma ray logs. Reservoir extent and types from traction to muddy debrites to cement with varying

HGS – PESGB 17th Conference on Africa E&P 43

Figure 4. Facies identified from core were grouped into 8 primary petrofacies. Based on similarities in porosity-permeability trends, these were recombined into 5 groups representing different responses to fluid flow. porosity-permeability relationships that will exhibit different reservoir intervals, but some production allocation issues flow behaviors (Figure 4). have been observed. High-pressure water injection created hydraulic fractures in some injectors. In addition, there is a short Production from the Enyenra field has had a number of issues. production history and no evidence of water breakthrough. All Figure 3. Wells inside and outside the channel axis show a highly variable net to gross. Wells are currently equipped with inflow control devices of these factors impact the dynamic response of the reservoir allowing continued production/injection from different during the process of model calibration and history matching.

Methodology Given the large number of uncertainties, it was important to evaluate them systematically and understand which have the most significant impact on fluid flow. They were divided into geologic, modeling, and dynamic uncertainties, and organized in a decision tree with a range of possible values. These possibilities were combined in multiple ways to create a suite of reservoir models (Figure 5).

To quickly build and simulate these models, a subset of the field (15% of the total area) was selected for a sector model study. This area showed a variety of stratigraphic and production complexities, representative of the larger field. Various styles of seismic interpretation were created and multiple models were generated from these using different combinations of geologic Figure 4. 4. Facies Facies identified identified from from core corewere groupedwere grouped into 8 primary into 8 primarypetrofacies. petrofacies. Based on similarities in porosityBased on- similaritiespermeability in porosity-permeabilitytrends, these were trends,recombined these were into recombined 5 groups intorepresenting 5 and modeling different uncertainties. responses These to models were fluidgroups flow. representing different responses to fluid flow. dynamically tested and the simulation engineer, geomodeler, and geophysicist jointly analyzed the results in an iterative loop shown in Figure 6. Together, the team learned which factors were of most importance and focused on those for subsequent rounds of testing.

During this phase, only six months of production data were available. The dynamic models were constrained by daily production and injection rates. The difference between the simulated pressures and observed pressures were compared for the different scenarios from the decision tree.

Figure 5. Decision tree illustrating the seismic, modeling, and dynamic uncertainties considered in Figure 5. Decision tree illustrating the seismic, modeling, and dynamic uncertainties considered in model model construction. construction. 44 HGS – PESGB 17th Conference on Africa E&P

Figure 6. Integrated modeling workflow illustrating the loop from seismic interpretation to static modeling to dynamic Figuresimulation 6. Integratedand the feedback modeling provided workflow by history illustrating matching theto update loop from the seismic seismic interpretation interpretation and staticto static model. modeling to dynamic simulation and the feedback provided by history matching to update the seismic interpretation and static model.

Figure 7. Simplified decision tree after testing in sector area. Figure 7. Simplified decision tree after testing in sector area.

HGS – PESGB 17th Conference on Africa E&P 45

Figure 8. Comparison of actual bottom hole pressures (red circles) and simulated pressures for various scenarios (colored lines) over six months. These results indicated that the coarse-scale seismic interpretation (yellow lines) produced pressures that were too low, suggesting the models were too disconnected. Using curved layers in the fine scale seismic interpretation (pink lines) produced a better match between modeled and actual pressures.

Figure 7. Simplified decision tree after testing in sector area.

Figure 8. Comparison of actual bottom hole pressures (red circles) and simulated pressures for various scenarios (colored Filines)gure over 8. Comparisonsix months. These of actual results bottom indicated hole that pressures the coarse-scale (red circles)seismic interpretation and simulated (yellow pressures lines) produced for various pressures scenariosthat were too(colored low, suggesting lines) over the modelssix mont werehs. too These disconnected. results Using indicated curved that layers the in coarse the fine-scale scale seismic interpretation interpretation(pink lines) produced (yellow a linebetters) matchproduced between pressures modeled that and wereactual too pressures. low, suggesting the models were too disconnected. Using curved layers in the fine scale seismic interpretation (pink lines) produced a better Resultsmatch between modeled and actual pressures. Other fine-scale uncertainties evaluated were the vertical and The sector model testing reduced the number of plausible lateral extents of petrofacies derived from seismic and well data. models resulting in a simplified decision tree, shown in Figure 7. Testing showed longer correlation lengths, implying greater Following are some details on how various branches of the tree connectivity, led to better history matches. were retained or discarded. The proportion of petrofacies was also a major uncertainty due Seismic interpretation styles from channel sequence (coarse) to to limited sampling. Petrofacies were populated using a soft channel scale (fine) were tested along with different variations trend based on seismic amplitudes. Vertical proportion curves of channel geometries. Comparisons of predicted versus actual were implemented to distribute traction facies at the base of pressures indicated that a fine-scale (channel complex scale) channels and shalier facies at the top. interpretation of four continuous complexes produced the best match (Figure 8). The location of lateral baffles were derived from seismic amplitude extractions showing potential discontinuities in the Environments of deposition such as channel axis, margin and reservoir. Different global permeability adjustments were applied levee, were defined in various ways: using seismic amplitude to the straight and sinuous portions of the channels to account cutoffs or polygons interpreted on amplitude and thickness for varying connectivities and predictable contrasts in effective maps. History matching showed that 3D amplitude-based cutoffs permeability in areas of contrasting depositional architecture. produced models that were too disconnected, so this branch of The number and location of these additional baffles were the decision tree was discarded from future testing. verified by history matching.

Grid resolution was tested early so that simulations could be In two months of testing, the range of uncertainty was narrowed accelerated using a coarser grid without compromising the as several branches of the decision tree were eliminated. desired level of geological realism. Remaining uncertainties such as transmissibility multipliers, petrofacies proportions, and correlation lengths were combined Fine-scale uncertainties were also tested. The layering style of to generate a range of plausible models. From this range, the grid was especially critical for wells located near the channel- independently derived low, mid, and high case models were levee boundary. There is a large variation in net to gross in this selected. This approach is more valuable in the context of area which impacts how these regions are connected to each uncertainty assessment than creating a single base case model or other. History matching provided guidance on connecting these generating an ensemble of purely stochastic permutations of a regions into a single zone, indicating that layers should follow single underlying concept. the base of that zone (curved layers) rather than pinching out as flat layers (Figure 8).

46 HGS – PESGB 17th Conference on Africa E&P

Biographical Sketches Biographical Sketches

(for Reservoir Modeling of a Deep-Water West African Reservoir: A Fully Integrated, Multi- Scenario Approach) (for Reservoir Modeling of a Deep-Water West African Reservoir: A Fully Integrated, Multi-

Scenario Approach)

Monica Miley currently works for Anadarko Petroleum as a project geophysical advisor for the Ghana development team. Her experience also includes carbonatesMonica Miley in Brazil currently and onshore works for East Anadarko Texas. PetroleumShe was previously as a project employed geophysical at Chevronadvisor andfor theHouston Ghana Advanced development Research team. Center Her experiencein technology also groups includes focusing oncarbonates seismic attributes in Brazil and and data onshore processing. East Texas. She earned She was a Master’s previously degree employed in at GeophysicsChevron and at RiceHouston University Advanced and a ResearchBachelor’s Center degree in in technology Geology at groupsUniversity focusing of Rochester.on seismic attributes and data processing. She earned a Master’s degree in Geophysics at Rice University and a Bachelor’s degree in Geology at University of Amelie Dufournet currently works for Anadarko Petroleum as a contract Rochester. geomodeler in the Ghana development team. She was formerly employed by MaerskAmelie Oil Dufournet as a geomodeler currently on works fields for in WestAnadarko Africa, Petroleum and by Schlumberger as a contract. She earnedgeomodeler a Master’s in the degree Ghana at developmentUniversite Pierre team et .Marie She Curie.was formerly employed by Maersk Oil as a geomodeler on fields in West Africa, and by Schlumberger. She earned a Master’s degree at Universite Pierre et Marie Curie.

Conclusion Jose Villa currently works Jose Villa currently works for Anadarko Petroleum as a Senior Staff Reservoir The benefit of this workflow is to systematically create a range for Anadarko Petroleum as a Engineer for the Ghana development team. He previously worked for Shell of reservoir models by identifyingBiographical multiple complexities at SketchesSenior Staff Reservoir Engineer different scales and testing them to understand which are the for the Ghana development International E&P and PDVSA-Intevep in several teams including Integrated most important for fluid flow. By confining the work to a sector team. He previously worked ReservoirJose Villa Modeling currently (IRM), works Water for Anadarko Flood Deployment, Petroleum and as aModeling Senior Staffand Optimization. Reservoir area, the team quickly learned which modifications needed to for Shell International E&P Engineer for the Ghana development team. He previously worked for Shell be made to the static model rather than applying more blunt and PDVSA-Intevep in several His experience includes onshore and offshore fields in Venezuela, Norway, Brazil, modifications in the dynamic Biographicalmodel. The sector model workflow Sketches teams including Integrated Nigeria,International and USA. E&P He and earned PDVSA a MS-Intevep degree in at several Stanford teams University including and aIntegrated BS degree at was employed to make multiple full(for field Reservoirmodels by extending ModelingReservoir Modeling of (IRM), a Deep-Water West African Reservoir: A Fully Integrated, Multi- the seismic interpretation and incorporating all wells. These Water Flood Deployment, and CentralReservoir University Modeling of Venezuela, (IRM), Water both Flood in Petroleum Deploymen Engineering.t, and Modeling and Optimization. models have been used to optimize Scenario locations of infill Approachwells and Modeling) and Optimization. assess the value of accelerating production. There is greater His experience includes His experience includes onshore and offshore fields in Venezuela, Norway, Brazil, confidence in the predictability of these models as minimal onshore and offshore fields Nigeria, and USA. He earned a MS degree at Stanford University and a BS degree at adjustments to the dynamic model(for were Reservoirrequired to achieve Modelingin Venezuela, Norway,of a Brazil, Deep Nigeria,-Water and USA. He West earned a African Reservoir: A Fully Integrated, Multi- history matches. n MS degree at Stanford University and a BS degree at Central Central University of Venezuela, both in Petroleum Engineering. Mark Bentley is Training Director at AGR TRACS and an Associate Professor at the Scenario ApproachUniversity) of Venezuela, both in Petroleum Engineering. Biographical Sketches Institute of Petroleum Engineering at Heriot-Watt University in Edinburgh. He has Monica Miley currently works for Anadarko Petroleum as a Monica Miley currently worksspent for Anadarko most of his Petroleum career working as a projectin or leading geophysical integrated study teams and his project geophysical advisor Mark Bentleyadvisor is Training for the Ghana development team. Her experience also includes for the Ghana development Director at AGR TRACS specialistMark Bentley fields ofis Trainingexpertise Director are 3D reservoir at AGR TRACSmodelling and and an scenario Associate-based Professor at the team. Her experience also and an Associatecarbonates Professor in Brazil and onshoreapproachesInstitute East ofTexas. toPetroleum handling She subsurfaceEngineeringwas previously uncertainty at Heriot employed- Wattand risk. atUniversity He is co in- authorEdinburgh. of the He has includes carbonates in Brazil at the InstituteMonica of Petroleum Miley currently works for Anadarko Petroleum as a project geophysical and onshore East Texas. She EngineeringChevron at Heriot-Watt and Houston Advancedtextbookspent Research most ‘Reservoir of Centerhis careerModel in technologyDesign’.working Hein orisgroups aleading graduate focusing integrated of the University study teams of Wales and hiswith a was previously employed Universityadvisor in Edinburgh. for the Ghana development team. Her experience also includes on seismic attributes and dataPhDspecialist processing. in structural fields She geology.of expertise earned a are Master’s 3D reservoir degree modelling in and scenario-based at Chevron and Houston He has spentcarbonates most of his in Brazil and onshore East Texas. She was previously employed at Advanced Research Center in career workingGeophysics in or leading at Rice Universityapproaches and a Bachelor’s to handling degree subsurface in Geology uncertainty at University and risk.of He is co-author of the technology groups focusing integratedChevron study teams and and his Houston Advanced Research Center in technology groups focusing on seismic attributes and specialist fieldsRochester. of expertise are textbook ‘Reservoir Model Design’. He is a graduate of the University of Wales with a data processing. She earned a 3D reservoiron modelling seismic and attributes and data processing. She earned a Master’s degree in Master’s degree in Geophysics at Rice University and a Bachelor’s scenario-based approaches PhD in structural geology. degree in Geology at University of Rochester. to handlingGeophysicsAmelie subsurface Dufournet at Rice Universitycurrently worksand a forBachelor’s Anadarko degree Petroleum in Geology as a atcontra Universityct of uncertaintyRochester. and risk. He is co-author of the textbook Reservoir Model Designgeomodeler. He is a graduate of the in University the ofGhana Wales with a development team. She was formerly employed by PhD in structuralMaersk geology. Oil as a geomodeler on fields in West Africa, and by Schlumberger. She Amelie Dufournet currently Amelie Dufournet currently works for Anadarko Petroleum as a contract works for Anadarko Petroleum earned a Master’s degree at Universite Pierre et Marie Curie. as a contract geomodeler in geomodeler in the Ghana development team. She was formerly employed by the Ghana development team. Maersk Oil as a geomodeler on fields in West Africa, and by Schlumberger. She She was formerly employed by Maersk Oil as a geomodeler earned a Master’s degree at Universite Pierre et Marie Curie. on fields in West Africa, and by Schlumberger. She earned a Master’s degree at Universite Pierre et Marie Curie. Jose Villa currently works for Anadarko Petroleum as a Senior Staff Reservoir

Engineer for the Ghana development team. He previously worked for Shell JoseInternational Villa currently E&P works and PDVSA for Anadarko-Intevep Petroleum in several as teams a Senior including Staff Reservoir Integrated EngineerReservoir for Modeling the Ghana (IRM), development Water Flood team. Deploymen He previouslyt, and worked Modeling for Shell and Optimization. InternationalHis experience E&P includes and PDVSA onshore-Intevep and in offshore several teamsfields inincluding Venezuela, Integrated Norway, Brazil, ReservoirNigeria, andModeling USA. (IRM), He earned Water a Flood MS degree Deployment, at Stanford and Modeling University and and Optimization. a BS degree at His experience includes onshore and offshore fields in Venezuela, Norway, Brazil, HGS – PESGB 17th Conference on Africa E&P Central University of Venezuela,47 both in Petroleum Engineering. Nigeria, and USA. He earned a MS degree at Stanford University and a BS degree at Central University of Venezuela, both in Petroleum Engineering.

Mark Bentley is Training Director at AGR TRACS and an Associate Professor at the Institute of Petroleum Engineering at Heriot-Watt University in Edinburgh. He has Mark Bentley is Training Director at AGR TRACS and an Associate Professor at the spent most of his career working in or leading integrated study teams and his Institute of Petroleum Engineering at Heriot-Watt University in Edinburgh. He has specialist fields of expertise are 3D reservoir modelling and scenario-based spent most of his career working in or leading integrated study teams and his approaches to handling subsurface uncertainty and risk. He is co-author of the specialist fields of expertise are 3D reservoir modelling and scenario-based approachestextbook ‘Reservoir to handling Model subsurface Design’. uncertainty He is a graduate and risk. of He the is Universityco-author of of the Wales with a textbookPhD in structural‘Reservoir geology.Model Design’. He is a graduate of the University of Wales with a PhD in structural geology.

Wednesday, September 12 | Theme 3 | 9:50 Luisa Man, Tom Wilson Core Laboratories UK Sedimentological Characteristics of Deepwater Sandstones Associated with Transgressive-Regressive Cycles Offshore Ghana

Stratigraphic and sedimentological data from over 50 stacked channel sandstones, thin conglomerates, and pebbly wells, courtesy of the Petroleum Commission, Ghana, have sandstones, deposited as a result of alternating turbidity and been analysed to construct a stratigraphic framework and debris flows. Some of the conglomerates present pebble-sized sedimentological logs, enabling a series of paleogeographic sub-rounded to angular quartz particles. Conspicuous slumping, maps to be drawn. Detailed mapping of sand fairways through sand injection, and convolute lamination suggest unstable successive stratigraphically-defined packages provides a valuable settings and frequent slope and channel margin collapse. resource for successful exploration within this complex West African petroleum province. The data shows that in the Tano Regressive trends in the Upper Turonian-Lower Coniacian Basin a series of deepwater sands were deposited during (UK3) reflect the reservoir sandstones which were first found the Upper Cretaceous which are related to major sequence to be oil bearing in the Tano Basin, and grade into deep marine boundaries; these may be tectonically or eustatically driven. The mudstones at the top of this package. Coniacian sediments are maturity and grain-size of these sandstones varies up-section notable for variably containing the first downhole occurrence and is related to the tectono-stratigraphy of the Equatorial of Late Santonian, Early Santonian, and Coniacian microfossils. African margin. This clearly indicates the presence of a break in section and in many cases the Upper Santonian is seen sitting unconformably High resolution palynological, micro- and nannopaleontological on the Lower Coniacian. This period of non-deposition/erosion data have enabled a series of major sequence boundaries to be could be seen as an amalgamation of the Sa1 and Sa3 sequence identified in the deep water sediments offshore Ghana; these boundaries (Haq and Schutter 2008 / Hardenbol et al., 1998). include the Middle Cenomanian, Middle Turonian, Santonian, However, transpression is known to have occurred along the and top Cretaceous. The biostratigraphic data has been Equatorial African margin at this time and the unconformity integrated with the logs, including INPEFA curves generated in is regarded as at least partially tectonic in nature. It is notable CycloLog software, to assist with the stratigraphic interpretation. that despite this the lithological change at the boundary is The log trends have been used to erect a series of sediment minor and in many wells the contact occurs within marine packages (StratPacs) in the Upper Cretaceous, UK1 to UK7. mudstones. Within the Upper Turonian (UK3) interval, cored The rapid changes in sediment thickness and type associated sections intercepted significant sand deposited in a series of with deepwater sediments of this kind hinders log correlation channel-sheet/channel complexes composed of very fine to and make good quality biostratigraphic data crucial for well very coarse, locally pebbly sandstone beds, showing blocky to correlations. FU trends. The succession includes thick stacked amalgamated units deposited largely by dumping and waning of high-density Transgressive Middle-Lower Cenomanian limestones and shales turbidity currents, with some intervals of traction sedimentation are overlain by a unit of Upper Cenomanian silty mudstones developing cross-stratification and flat lamination. Conspicuous and/or sandstones within the lower part of UK2. Deep marine deformation, dewatering, and structureless features are mudstones and siliceous mudstones were deposited above this in interpreted as recurrence of debris flow, slump and channel the Turonian (upper UK2). margin collapse.

The top of the Middle Turonian is identified biostratigraphically The Upper Santonian to Campanian (UK5-UK6) comprises a within this transgressive section and commonly, but not always, thick mud dominated interval, which can be difficult to sub- is located at the base of a unit of gravity flow sands. Widespread divide biostratigraphically due to more hostile surface water erosion is not associated with this boundary and it appears to be conditions. The broadly regressive trend reflects a reduction in related solely to sea level fall. Within the Mid Cenomanian-Mid subsidence and gradual filling of the basin; multiple phases of Turonian succession (UK2), sedimentological analysis of logs sand deposition have been identified. Observed core material and core material from Tano Basin syn-transform succession, in the Upper Santonian-Upper Campanian succession (UK5) reveals a range of very thick bedded fine to medium-grained penetrated deep shelf-slope proximal to distal lobe facies

48 HGS – PESGB 17th Conference on Africa E&P presenting thick to thin bedded and amalgamated channel- Biographical Sketch sheet/channel complexes encased by low gamma, organic-rich to Dr. Luisa Man joined Core red-stained and slumped claystones. The sandstones are mainly Laboratories in 2011 as a fine to medium-grained with common carbonaceous drapes, sedimentologist in the regional locally interbedded with thin pebbly sandstones beds that fine studies group (Integrated upwards to sandy claystones, indicating gradual loss of sand. Reservoir Solutions), Analysed logs and cuttings material from Latest Campanian specializing in core description, (UK6) show mud-prone successions with isolated fine to reservoir sedimentology, and medium-grained slope channel sands present at several distal facies analysis. Since joining the locations. In some offshore wells recurrent bypass to the deeper group, she has been involved basin might occur. in recognition of depositional environments and facies The top of the Campanian is associated with a transgressive analysis from core and log data surface overlain by distinctly higher gamma mudstones in regional and proprietary of the Maastrichtian (UK7). No sandstones are present in studies with emphasis on the Atlantic Margin basins of West the Maastrichtian, and its top is marked by a significant Africa and Southern America. In her current position as Staff unconformity with Upper Paleocene (LT1) sediments sitting on Geologist, she specializes in the paleogeographic mapping a probably incomplete Maastrichtian interval. The Maastrichtian through the integration of all sedimentological, petrographical, lithologies reflect peneplantion of the hinterland, and the final stratigraphic, and structural data-sets. Dr. Man did her PhD in reduction of sand supply to the basin. the University of Bucharest, Romania studying sedimentary siliciclastic and mixed deposits of Upper Miocene shelfal The reduction in sand supply concomitant with sand maturation sediments from the western flank of the Focsani Basin. She (texturally and compositional) is evident when comparing frequently attends international industry conferences, at which the Cenomanian-Turonian to the Campanian deposits. Uplift she has presented a number of poster and oral presentations on and transpression in the Santonian probably rejuvenated the African Basins. hinterland and provided the coarser sediments seen in some wells, resulting in sand deposition throughout the Campanian. n

HGS – PESGB 17th Conference on Africa E&P 49 Wednesday, September 12 | Theme 3 | 10:40 Cynthia J. Ebinger, SarahJaye Oliva, Ryan Gallacher Department of Earth and Environmental Sciences, Tulane University, New Orleans, LA, USA [email protected] Magmatic Modification of African Crust: Implications for Strain Localization and Basin Subsidence

The Cenozoic East African Rift (EAR) and Cameroon Volcanic chambers beneath segment centers create new columns of mafic Line (CVL) formed on the slow-moving African continent, crust, as along slow-spreading ridges. Our comparisons suggest which last experienced orogeny during the Pan-African. We that transitional crust, including seaward-dipping sequences, synthesize primarily geophysical data to evaluate the role of is created as progressively smaller screens of continental crust magmatism in shaping Africa’s crust. In young magmatic rift are heated and weakened by magma intrusion into 15-20 km- zones, melt and volatiles migrate from the asthenosphere to gas- thick crust. In the 30 Ma-Recent CVL, which lacks a hotspot rich magma reservoirs at the Moho, altering crustal composition age-progression, extensional forces are small, inhibiting the and reducing strength. Within the southernmost Eastern rift, creation and rise of magma into the crust. Our syntheses show the crust comprises ~20% new magmatic material ponded in that magma and volatiles are migrating from the asthenosphere lower crustal sills (underplate), and as sills and dikes at shallower through the plates, modifying rheology, changing crustal density, depths. In at least one area, the rift topography and low density and enhancing strain localization to magma intrusion zones. intrusive bodies cause a local rotation in the regional stress field, We interpret lower crustal seismicity and seismic velocity enhancing transverse rift structures linking segments. In the patterns in the magma-poor Tanganyika rift as evidence for Main Ethiopian rift, intrusions comprise 30% of the crust below the onset of magma intrusion at the crust-mantle boundary, axial zones of dike-dominated extension. In the incipient rupture offering new insights into the time progression of strain zones of the Afar rift, magma intrusions fed from crustal magma localization, and geotherms. n

50 HGS – PESGB 17th Conference on Africa E&P Wednesday, September 12 | Theme 3 | 11:05 Jon Teasdale Geognostics International Limited Colin Reeves Earthworks BV An Animated Model for the Mesozoic-Recent Tectonic Evolution of Sub-Saharan Africa: From Plates and Structures to Basins and Paleogeography

Ever since its Paleozoic Gondwanan origin, Africa has never The resulting structurally constrained, animated plate tectonic been entirely stable. Progressive breakup and formation of model for the evolution of Africa explains how basins have Africa per se spanned more than 200 myr from Late Triassic been formed and modified. Importantly the model is globally to Neogene, forming and then modifying basins via a complex consistent as it is part of the Geognostics Earth Model series of tectonic events. This process has been fundamentally (GEM). Because of its structural constraints, GEM is by far controlled by pre-existing basement structure and rheology; most the most accurate plate model available – it can even be used basins have formed via reactivation of older structures under a to reconstruct wells, seismic lines, and play fairways from succession of different stress regimes. Understanding these events one conjugate margin to another. It is a powerful tool for and basin phases is key to exploring Africa effectively. understanding basin formation and paleogeography, particularly for source rock and reservoir prediction, as well as trap timing Here we present a “bottom-up” interpretation of Africa, and kinematics. starting with basement terranes and structural fabric. We have undertaken a rigorous interpretation of regional, Mesozoic In West Africa, Late Triassic to Early Jurassic rifting and to Recent map-view structures that explains the location and magmatism opened the early Central Atlantic, linked to the framework of basins, based on geological maps and publications, proto-Gulf of Mexico via a series of sinistral transtensional gravity, magnetics, and seismic. We have paid particular attention basins. This controversial new tectonic interpretation of Pangea to interpreting the oceanic fabric surrounding Africa to constrain breakup has significant implications for the kinematics, timing the Ourkinematics, model plate has motions, significant and timing implications of breakup. for We the have paleogeographic of basin development evolution and of segmentation the African of margins the West African and theninterior, worked backwith in consequent time to undo theseconstraints deformation on marinepatterns restriction,margin, source hence marine rock restriction,deposition, and salt source presence, rock and andreservoir accurately distribution,reconstruct Africa and to trap its Gondwana location origins. and timing. Wesalt encourage deposition. companies to get involved with this work as we endeavour to improve its accuracy and applicability.

FigureFigure 1. The 1: present-dayThe present starting-day point: starting the Geognostics point: the Earth Geognostics Model (GEM) Earth Model (GEM)

HGS – PESGB 17th Conference on Africa E&P 51

134Ma 101Ma Figure 2: Screenshots from the animated model illustrating its level of detail OurOur model model has has significant significant implications implications for for the the paleogeographic paleogeographic evolution evolution of of the the African African margins margins and and interior,interior, with with consequent consequent constraints constraints on on marine marine restriction, restriction, source source rock rock deposition, deposition, salt salt presence, presence, reservoirreservoir distribution, distribution, and and trap trap location location and and timing. timing. We We encourage encourage companies companies to to get get involved involved with with this this workwork as as we we endeavour endeavour to to improve improve its its accuracy accuracy and and applicability. applicability.

FigureFigure 1: 1: The The present present-day-day starting starting point: point: the the Geognostics Geognostics Earth Earth Model Model (GEM) (GEM)

134Ma 134Ma 101Ma101Ma FigureFigureFigure 2. 2:Screenshots 2: Screenshots Screenshots from the from fromanimated the the animatedmodel animated illustrating model model its illustratinglevel illustrating of detail its its level level of of detail detail

In East Africa we identify an Early Jurassic, NW-SE-directed Africa and the Red Sea, finally forming the present-day outline rift event that opened a series of narrow, isolated, salt-prone of the African continent in the Late Miocene. basins along the entire margin. A major kinematic change in the Kimmeridgian (~155 Ma) initiated N-S-trending dextral Our model has significant implications for the paleogeographic transpressional shear between East and West Gondwana, including evolution of the African margins and interior, with consequent the Davie Transform. Once Antarctica cleared SE Africa thus constraints on marine restriction, source rock deposition, salt “unlocking” the Falklands Plateau from Africa, Pacific-derived slab presence, reservoir distribution, and trap location and timing. rollback caused progressive opening of the South Atlantic through We encourage companies to get involved with this work as we n the Early Cretaceous, “unzipping” it from south to north. Two main endeavour to improve its accuracyBiographical and applicability. Sketch rift systems are interpreted, with an accommodation zone in the Santos Basin of Brazil. Significant internal deformation in Africa Biographical Sketch accompanied this phase of Gondwana breakup, via a tripartite After graduating as a geologist After graduating as a geologist in 1992, Jon Teasdale worked as a system of transtensional rifts that extended from Nigeria to Kenya, in 1992, Jon Teasdale worked as field geologist in remote areas in Australia and Antarctica, mapping and NW into Chad and Niger. a field geologist in remote areas in Australia and Antarctica, complex basement rocks and exploring for gold, uranium, and Formation of the Equatorial Atlantic occurred via a complex mapping complex basement diamonds. Jon obtained his PhD in Geology from The University of series of rotational extensional events in the Albian-Cenomanian. rocks and exploring for gold, Adelaide in 1997, during which he pioneered new methods for Early ~NE-SW-directed extension exploited end-Triassic dykes uranium, and diamonds. Jon and basement terrane boundaries to open a series of narrow obtained his PhD in Geology understanding poorly exposed geology. He has worked as a rift basins. At about 108Ma a shift in the pole of rotation from The University of Adelaide geological consultant for the past 20 years; initially with Etheridge between West Africa and South America initiated a significant in 1997, during which he Henley Williams and SRK Consulting serving the minerals industry in dextral shear couple between the two continents, forming a pioneered new methods for series of deep, oceanic pull-apart basins separated by dextral understanding poorly exposed Australia, Africa, and PNG. In 1999 he helped form SRK's Energy transpressional fold-thrust belts, culminating in progressive geology. He has worked as Services division and co-founded Frogtech in 2004, where he continental breakup through the Cenomanian-Turonian. a geological consultant for the past 20 years; initially with Etheridge Henley Williams and SRKconsulted Consulting servingwidely the in the oil, gas, coal, and geothermal energy sectors in more than 30 countries Collisions of the African plate with Europe have driven complex minerals industry in Australia, Africa,on alland continents.PNG. In 1999 he He joined Shell in 2007 as a Global Geological Consultant, where he advised inversion events through the Late Cretaceous to Recent. helped form SRK’s Energy Servicesand division mentored and co-founded all Shell exploration teams worldwide. Jon founded Geognostics in 2017, where A significant dynamic change in Tethyan subduction rates in Frogtech in 2004, where he consulted widely in the oil, gas, coal, the Santonian caused ophiolite obduction along the and geothermal energy sectors inhe more built than 30GEM countries (the on Geognostics Earth Model) as an innovative tool for exploring basins. Jon is an NE Afro-Arabian margin, as well as significant plate-wide basin all continents. He joined Shell in 2007expert as a Global in non Geological-seismic integration and interpretation, plate tectonics, structural geology, basin inversion, notably in Central Africa. Further inversion in the Consultant, where he advised and mentored all Shell exploration Maastrichtian was caused by the closure of Neotethys. The Mid teams worldwide. Jon founded Geognosticsmodeling in 2017,, and where exploration he risk management. Eocene onset of the Alpine collision between Africa and Europe built GEM (the Geognostics Earth Model) as an innovative tool caused widespread uplift and inversion in many Central and for exploring basins. Jon is an expert in non-seismic integration North African basins. and interpretation, plate tectonics, structural geology, basin modeling, and exploration risk management. Neogene Indian Ocean opening coupled with plume-related uplift caused widespread onshore and offshore rifting in East

52 HGS – PESGB 17th Conference on Africa E&P Wednesday, September 12 | Theme 3 | 11:30 William Dickson Reijers, T.J.A., Petters, S.W., & Nwajida, C.S. (1997) The Niger Delta Basin, in Sedimentary DIGs Basins of the World, V. 3 African Basins (R.C. Selley, ed), ch.7, p. 151-172. James W. Granath, PhD Schiefelbein, C.F., J.E. Zumberge, N.C. Cameron, and S.W.Granath Brown (2000& Associates) Geochemical comparison of crude oil along the South Atlantic margins, in M.R. Mello and B.J. Katz, eds., Petroleum systems of South Atlantic margins: AAPG Memoir 73, p. 15-26 Tracing the West and CentralShatsky, Nicolas (1946), African The Great Donets BasinRift and the Wichitaand System, Shear comparative tectonics of ancient platforms. Geology Series, #6 Akademiia Nauk SSSR Doklady, pp. 57-90. Systems Offshore ontoWeber & DaukoruOceanic (1975), Petroleum Crust: Geology of thea Niger “Rolling” Delta, 9th World Petroleum Congress, vol 2, p209-221. TripleFigures Junction Compared to the understood kinematics of its continental margins and adjacent ocean basins, the African continent is unevenly or even poorly known. Consequently, the connections from onshore fault systems into offshore spreading centers and ridges are inaccurately positioned and inadequately understood. This work considers a set of triple junctions and the related oceanic fracture systems within the Gulf of Guinea from Nigeria to Liberia. Our effort redefines the greater Benue Trough, onshore Nigeria, and reframes WCARS (West and Central African Rift and Shear Systems) as it traces beneath the onshore Niger Delta and across the Cameroon Volcanic Line (CVL), Figure 1. We thus join onshore architecture to oceanic fracture systems, forming a kinematically sound whole. This required updating basin outlines and relocating mis-positioned features, marrying illustrations from the literature to imagery suitable for basin to sub- basin mapping. The resulting application of systems structural geology explains intraplate deformation in terms of known structural styles and interplay of their elements. Across the Benue Trough and FigFigureure 1.1. WCARS features.features. a) a) General General location location map map (inset) (inset).. b) Countryb) Country names (bold); basins along WCARS, we infer variations in both structural (boldnames italics) (bold);, oceanic basins fracture(bold italics), zones (FZ,oceanic italics), fracture hot spot zones tracks (FZ, (HST). italics), Main hot spotbasins outlined in mauve; sub-basins in blue; intra-basin highs in red; possible sub-basins in grey dashes. COB = setting and thermal controls that require further tracks (HST). Main basins outlined in mauve; sub-basins in blue; intra-basin Continental-Oceanic Crust boundary. Basin abbreviations: A: Anambra Basin; AA: Abakaliki interpretation of their petroleum systems. highs in red; possible sub-basins in grey dashes. COB = Continental-Oceanic Anticlinorium;Crust boundary. BN: Basin Benue abbreviations: NE (sub-basin) A:; AnambraBS: Benue Basin; SW (sub AA:-basin) Abakaliki; D: Douala; GT: Grein Introduction Anticlinorium; BN: Benue NE (sub-basin); BS: Benue SW (sub-basin); D: Excellent work has defined Africa’s onshore geology Douala; GT: Grein Trough (Termit Basin); N’D: N’Dgel Edgi; R: Rio del Rey; and the evolution and driving mechanisms of the TB: Tefidet Basin (Termit Basin); TT: Tenere Trough (Termit Basin). FZ adjacent (particularly the circum-Atlantic) ocean abbreviations: Ng FZ: Ngaoundere FZ; S FZ: Sanaga FZ. Backdrop is the total basins. However, understanding of the oceanic realm horizontal derivative of the gravity isostatic residual (GI-THD). has outpaced that of the continent of Africa. This Africa: Prior and New “Big Pictures” paper briefly reviews onshore work. We then discuss theoretical Following mapping by the colonial surveys, a generation of geometry of tectonic boundaries (including triple junctions) and regional geologists applied ‘Big Picture’ integrative thinking our data (sources and compilation methods). Additional sections in Africa per the seminal work of, inter alia, Bosworth, Burke, discuss application of theory and data to the Gulf of Guinea Fairhead, Genik, Guiraud, and co-authors, establishing the system; and illustrate an updated interpretation of connecting basin-and-craton framework. The Ed Purdy Memorial GIS elements along WCARS via our remapped Benue Trough into project (Exploration Fabric of Africa or EFA) then offered a the Gulf of Guinea fracture system (Figure 1). We conclude continent-scale view derived from a 1:5MM scale compilation. by summarizing our efforts and suggest avenues to reassess Although EFA included key structural features such as faults hydrocarbon exploration along these features. and basin outlines, they were often generalized and mostly

HGS – PESGB 17th Conference on Africa E&P 53 Trough (Termit Basin); N'D: N'Dgel Edgi; R: Rio del Rey; TB: Tefidet Basin (Termit Basin); TT: Tenere Trough (Termit Basin). FZ abbreviations: Ng FZ: Ngaoundere FZ; S FZ: Sanaga FZ. Backdrop is the total horizontal derivative of the gravity isostatic residual (GI-THD).

Figure 2.

a) Simple representation of four triple junctions with different stability relationships. Rift-Rift- Rift (RRR) is stable under all circumstances. Rift-Rift-Transform (RRF) is inherently unstable Trough (Termit Basin); N'D: N'Dgel Edgi; R: Rio del Rey; TB: Tefidet Basin (Termit Basin); unless the boundaries are perpendicular and certain rate balances are met. Trench-Trench-Trench TT: Tenere Trough (Termit Basin). FZ abbreviations: Ng FZ: Ngaoundere FZ; S FZ: Sanaga FZ. (TTT) is stable under certain balanced rates of plate motion. Trench-Trench-Rift (TTR) can be Backdrop is the total horizontal derivative of the gravity isostatic residual (GI-THD). stable if rate balances or equal angles are met.

Figure 2.

b) Left-stepping arrangement of three RFF triple junctions along a generalized extensional plate margin. The triple junctions are formed from by three transform fault systems that penetrate into the right hand plate well beyond the tips of their respective rifts. This is a generalization of the analysis of the Gulf of Guinea triple junction region in this paper. Figure 2A. Simple representation of four triple junctions with different stability relationships. Rift-Rift-Rift (RRR) is stable under all circumstances. Rift-Rift-Transform (RRF)a) Simple is inherently representation unstable of unless four triple the boundaries junctions withare perpendicular different stability and certainrelationships. rate Rift-Rift- Rift (RRR) is stable under all circumstances. Rift-Rift-Transform (RRF) is inherently unstable balances are met. Trench-Trench-Trench (TTT) is stable under certain balanced rates of unless the boundaries are perpendicular and certain rate balances are met. Trench-Trench-Trench plate motion. Trench-Trench-Rift (TTR) can be stable if rate balances or equal angles are (TTT) is stable under certain balanced rates of plate motion. Trench-Trench-Rift (TTR) canFigure be 2B. Left-stepping arrangement met. stable if rate balances or equal angles are met. of three RFF triple junctions along a generalized extensional plate margin. The divorced from underlying genetic linkages. Our synthesis crustal blocks (e.g. Figure 3. Stability relationships for the Gulf of Guinea complex triple junction. Elements of the triple junctions are formed from by three (Tectonic Fabric of Africa, or TFA) uses more advanced data Dewey & Burke, triple junction: on the west side the fracture zones in blue, rift segments to south (or equivalently transform fault systems that penetrate to build upon EFA, connecting adjacent oceanic realms across 1974). If the third north) in black, and onshore African fault systems in red. into the right hand plate well beyond the continent in a kinematically sound fashionb) L eftto -suggeststepping and arrangement element of three is a rift RFF or triple a define missing tectonic elements. We previouslyjunctions discussed along athat generalized trough, extensional at its outset plate margin.the tips of their respective rifts. This is a work (Granath & Dickson, 2016a, b; 2017) Thefor both triple WCARS junctions and are formedthis system from formsby three transformgeneralization of the analysis of the Gulf of a less-recognized ‘Trans-Southern Africa Riftfault &systems Shear System’ that penetrate an intoaulacogen, the right sensu hand plateGuinea triple junction region in this paper. (STARSS), seen in eastern Africa as the Karoowell system. beyond the tips of theirShatsky respective (1946). rifts. This is a generalization of the analysisThe ofGulf the ofGulf Guinea of Gui providesnea a good example with the West Theoretical Geometries triple junction region in thisAfrican paper. Transform Margin (WATM) connected to the ridge Triple junctions, while integral to the kinematics of plate (or rift) segment running south and in which WCARS was the tectonics, also illustrate any geology where the relative motion abandoned arm. The Benue Trough is then likened to Shatsky’s of blocks is involved. Motions are described by the interaction aulacogen. of block boundaries with simple vectors. Boundaries may involve a) ridges, rifts, or extensional margins (R); b) transforms Development of such a system is illustrated by Figure 3, a or strike-slip fault systems (F); and c) trenches or convergent stability diagram a la McKenzie & Morgan (1969), drawn for marginsFigure 3. (T), Stability Figure relationships 2. Only some for junctions the Gulf are of inherently Guinea complex triplethe junction.Gulf of Guinea Elements system. of the Figure 3a shows a typical map stable,triple capablejunction: of on simultaneously the west side accumulatingthe fracture zones significant in blue, rift segmentsrelationship to south between (or equivalently FZ precursor in blue, an onshore fault displacementsnorth) in black, (McKenzie and onshore & Morgan, African 1969)fault systems while maintaining in red. system in red, and the continental margin rift in black. A the same vector relationship and so surviving for substantial connected string of these forms a sweep from, i. e. the West geologic time. When survival of a triple junction is limited, it African southern extensional margin to the West African usually fragments into two separate triple junctions or one arm Transform Margin. is essentially abandoned. Figures 3 b and c are in “velocity space” with arrows showing Plate divergence, as in the case of Atlantic opening, produced displacement vectors between blocks and dotted lines showing a series of rift segments that evolved into an ocean spreading orientations of boundaries between blocks. Symbol AvB signifies system composed of spreading-ridge segments linked by the vector motion of block A relative to block B (shown by the transforms. Beyond the neighboring ridge segment limits, arrow). For WCARS, we do not know exact angular relationships transforms became dormant as fracture zones (FZ). At between elements during the Cretaceous nor the displacement initiation of continental breakup, transform/FZ locations often rates on the faults involved, so these vectors are generalized to corresponded to pre-existing features within the marginal represent all the component triple “junctionettes”. Viewing the continental block, suggesting some (usually minor and rift- triple junction region in this way offers a twofold observation: restricted) reactivation. Nascent spreading segments may, however, link with a transform that actively extends into 1. For small displacements and low displacement rates (Figure the continent, thus forming a triple junction composed of a 3b), there is great latitude in configurations that retain transform, the spreading ridge/rift, and an intra-continental stability, i.e. a rift can connect to two divergent transform fault system. Unless two ocean basins develop between the segments with a wide angular relationship. If deformation continental blocks, the situation decays to a transform and a rift is concentrated at the intersection, internal accommodation segment with abandonment of the third element. The spreading can accommodate orientation mismatches, as for example, system then drifts away from the two separated continental within the Benue Trough.

54 HGS – PESGB 17th Conference on Africa E&P a) Map topology as three blocks: the north side of triple junction A, and the two sides B and C of the extensional basin. C will evolve into oceanic crust. Relative displacements between blocks are shown by a) Map topology as three blocks: the north side of arrows (e.g. AvB). triple junction A, and the two sides B and C of the extensional basin. C will evolve into oceanic crust.

RFigureelative 3. Stabilitydisplacements relationships between for the blocks Gulf ofare Guinea shown complex by triple junction. Elements of the triple junction: on the west side the arrowsfracture (e.g. zones AvB). in blue, rift segments to south (or equivalently north) in black, and onshore African fault systems in red. a) Map topology as three blocks: the north side of Figure 3A. Map topology as three blocks: the north side of triple junction A, and the triple junction A, and the two sides B and C of the two sides B and C of the extensional basin. C will evolve into oceanic crust. Relative extensional basin. C will evolve into oceanic crust. displacements between blocks are shown by arrows (e.g. AvB). b) While displacement rates between the three elements are relatively low and similar (upper Relative displacements between blocks are shown by right), the system can evolve if the rift segment is allowed to propagate, despite different relative directionsarrows (e.g. of AvB).displacement. b) While displacement rates between the three elements are relatively low and similar (upper right), the system can evolve if the rift segment is allowed to propagate, despite different relative directions of displacement. Figure 3B. While displacement rates between the three elements are relatively low and similar (upper right), the system can evolve c) As oceanic crust is born, and if the rift segment is allowed to propagate, despite different relative fast plate divergence rates (which b) While displacement rates between the three elements are relatively low and similar (upper directions of displacement. right), the system can evolve if the rift segment is allowed tousually propagate, exceed despite intraplate different rates relative) directions of displacement. begin to apply to the BvC c) As oceanic crust is born, and relationship, the triple junction stays stable if AvB and CvB are collinear. Otherwise the triple fast plate divergence rates (which junction becomes unstable and is abandoned or replaced with a different configuration. One usually exceed intraplate rates) replacement is the introduction of another rift segment, begin to apply to the BvC the mechanism by which the rift system propagates along relationship, the triple junction stays stableFigure if AvB 3C. andAs oceanic CvB are crust collinear. is born, andOtherwise fast plate the divergence triple rates (which usually exceed the continental margin and negotiates the plate margin junction becomes unstable and is abandonedintraplate or replaced rates) beginwith toa differentapply to the configuration. BvC relationship, One the triple junction stays stable bend in the Gulf of Guinea. replacement is the introduction of anotherif rift AvB segment and CvB, are collinear. Otherwise the triple junction becomes unstable and is c) As oceanic crust is born, and the mechanism by which the rift system propagatesabandoned alongor replaced with a different configuration. One replacement is the introduction fast plate divergence rates (which of another rift segment, the mechanism by which the rift system propagates along the the continental margin and negotiates the plate margin usually exceed intraplate rates) continental margin and negotiates the plate margin bend in the Gulf of Guinea. bend in the Gulf of Guinea. begin to apply to the BvC relationship, the triple junction stays stable if AvB and CvB are collinear. Otherwise the triple junction becomes unstable and is abandoned or replaced with a different configuration. One replacement is the introduction of another rift segment, the mechanism by which the rift system propagates along the continental margin and negotiates the plate margin bend in the Gulf of Guinea. 2. At higher displacements or displacement velocities (Figure CARS faults in western Cameroon. This reduces complexity 3c), CvA and AvB become collinear. As the rift widens and towards the simpler triple junction idea. oceanic spreading begins, CvA dominates and AvB becomes irrelevant. A triple junction may fit the initiation of these Data

tectonic elements but with time it decays to a rift and a Modern densely sampled data from ships (2D and 3D seismic transform, with spreading carrying the relationship away to especially) and satellites have driven forward the understanding the west. Blocks A and B are left behind, as C links with its of passive margin evolution and development of ocean basins counterpart in the next (adjacent) triple junction, and ocean and continental margins (Dickson et al. 2016 and references spreading fills the gap. therein). From want of regional tectonically-focused data and lack of incentive from big oil & gas discoveries, this progress This implies that motion in and around the triple junction on has lagged onshore. Still, adequate spatial resolution (to sub- African crust in the A or B block evolved with time, imparting basin or better scales) continent-wide grids have been compiled interesting structural relationships. Rotation of displacement of potential field data (Odegard et al., 2007b). These in turn vectors between A and B may cause inversion of early structure in constrained inversions for sediment and crustal thicknesses the triple junction. Indeed the Abakaliki Anticlinorium onshore (i.e., MARIMBA project depths to basement, Moho and Curie Niger Delta (Reijers et al., 1997) demonstrates such inversion. surfaces). This provided scaffolding for GIS-based geo-locating The second implication is that multiple triple “junctionettes” may and mosaicing of published material. evolve to a simpler geometry. The Yola and Doba Basins (Figure 1) Along the West African margin, the edge of magnetically striped may effect a connection between the CARS and WARS/Benue oceanic crust is defined on our magnetic imagery (TMI-THD or systems, so de-emphasizing or abandoning the lower (southerly)

HGS – PESGB 17th Conference on Africa E&P 55 total horizontal derivative of total magnetic intensity; Figure 4. Offshore Niger Delta not shown), along with a narrow bordering strip of feature correlations from ‘transitional crust’, be it exposed upper mantle and/or basement to surface (after hyperextended continental crust. However, the gravity isostatic residual anomaly (GI) and its total horizontal Dickson & Schiefelbein, 2015) derivative (GI-THD) have been most-used to locate, demonstrate reliability and revise, and connect known and interpreted tectono- precision of data employed to structural features both on- and near-shore. interpret basin floor offsets and long-lived basement control on The tectonic connection between the Bight spreading tectono-sedimentary evolution of system and WCARS has lacked clarity, being obscured the on- and offshore delta. by twenty-some km of Niger Delta sediments. A multidisciplinary approach, combining geophysical and Crustal features and gravity geochemical methods concluded that crustal features backdrop with overlays from could be well-imaged and accurately positioned Cobbold et al., 2009 (C) and (Dickson & Schiefelbein, 2015), identifying and Matthews et al., 2010 (M) of connecting offshore fracture zones (FZ) beneath the intra-Miocene structures on 3D delta both off- and onshore. A proprietary reprocessed seismic. Piston core (PC) data compilation of gravity data provided primary control for tectono-structural interpretation, augmented by (red, green & purple points), toe- similarly compiled magnetics, depth, and thickness thrust-belt (TTB) subcrops grids to define the deep rift-phase structure (Odegard (black) and BSR outlines (faint et al., 2007a & b described compilation and processing orange shading) represent at/near steps). Active hydrocarbon exploration meant that seafloorFigure 4. Offshore control. Niger Note Delta the feature density correlations of PC samplesfrom basement along to intrasurface-Miocene anticlines (Cobbold), broad coverages of detailed 3D seismic and surface demonstrating(after Dickson & accuracySchiefelbein, of2015) PC demonstratetargeting (PCreliability locations and precision normally test potential leakage paths). PC of data employed to interpret basin floor offsets and long-lived basement geochemical exploration (SGE) programs had been anomalies lie between the Matthews et al. 2010 (M) Miocene anticlines, suggesting a registration presented in cited papers. From a non-exclusive study control on tectono-sedimentary evolution of the on- and offshore delta. (used by permission), characteristic oil geochemistry errorCrustal in features the georeferencing. and gravity backdrop However, with overlays structural from Cobbold trends et onal., overlays C and M align closely with of the Niger Delta was matched to SGE results. Our PC2009 and (C) andTTB Matthews trends etand al., anticline2010 (M) of offsets intra-Miocene of overlay structures C fall on 3Dacross the trace of the Chain FZ which correlations from basement features up across intra- isseismic. mimicked Piston core by (PC)seafloor data (red,offsets green in & the purple TTB points),s. toe-thrust-belt sedimentary structuring through inferred hydrocarbon (TTB) subcrops (black) and BSR outlines (faint orange shading) represent leakage pathways terminating at the surface at/near seafloor control. Note the density of PC samples along intra-Miocene anticlines (Cobbold), demonstrating accuracy of PC targeting (PC locations demonstrated both precision and accuracy in defining Figure 5. the deeply-buried crustal architecture (Figure 4). normally test potential leakage paths). PC anomalies lie between the Matthews et al. 2010 (M) Miocene anticlines, suggesting a registration error Gravity (GI) Gulf of Guinea System in the georeferencing. However, structural trends on overlays C and M align underlay with A simple triple junction underlying the Niger Delta closely with PC and TTB trends and anticline offsets of overlay C fall across basin outlines. is usually pictured as having evolved into the Mid- the trace of the Chain FZ which is mimicked by seafloor offsets in the TTBs. Representation Atlantic Ridge, receding from the divergent African of WCARS keys off major Precambrian basement faults in Cote d’Ivoire at margin and abandoning the Benue Trough (onshore northern Nigeria) in its wake. With most of the lower Benue Trough the southern end of the Liberia coast. shears shows hidden beneath the Niger Delta, this evolution had largely been assumed. Our imagery indicated that the triple junction As described above, the oceanic FZs can now be traced nearly possible Benue was not a simple three-armed system as theory suggested, one-to-one to discrete onshore tectonic elements that were Trough but rather a west-stepped, progressive sweep in which a N-S significantly active during birth of the continental margin connections trending extensional system converted to the E-W trending (Figure 1). Some FZs connect to African tectonic elements and via Mamfe transform (trans-tensional) margin in discrete segments that some to Brazilian (Krueger et al., 2018, this conference). The (1?), Yola- Charcot FZ connects beneath the Niger Delta to the southern accommodated the overall larger “triple region” (Figure 2b). Doba (2?) and The serrated transform margin continued westward as strike- boundary of the Anambra Basin and Benue Trough. Hence Bongor (3?) basins, or a combination of these paths, likely masked by younger CVL activity. slip segments connected extensional segment step-wise to extension in the Chad-Niger Rifts is transferred to spreading extensional segment along the length of the coast across present- between the Romanche and Charcot FZs (including the Benin, day Nigeria to Liberia. One segment ran from Benin and Cote Chain, and Benue) which last is continuous with the northern D’Ivoire along the Romanche FZ, which keys off the Akwapim bounding margin of the Benue Trough. The Ngaoundere FZ Fault system bordering Ghana’s Neoproterozoic Voltaian Basin. connects to the main strand of the Central African shear zone The next step to the north connects to the St. Paul FZ, which across the Cameroon Volcanic Line (CVL). The Paraíba FZ

56 HGS – PESGB 17th Conference on Africa E&P Figure 4. Offshore Niger Delta feature correlations from basement to surface (after Dickson & Schiefelbein, 2015) demonstrate reliability and precision of data employed to interpret basin floor offsets and long-lived basement control on tectono-sedimentary evolution of the on- and offshore delta. Crustal features and gravity backdrop with overlays from Cobbold et al., 2009 (C) and Matthews et al., 2010 (M) of intra-Miocene structures on 3D seismic. Piston core (PC) data (red, green & purple points), toe- thrust-belt (TTB) subcrops (black) and BSR outlines (faint orange shading) represent at/near seafloor control. Note the density of PC samples along intra-Miocene anticlines (Cobbold), demonstrating accuracy of PC targeting (PC locations normally test potential leakage paths). PC anomalies lie between the Matthews et al. 2010 (M) Miocene anticlines, suggesting a registration error in the georeferencing. However, structural trends on overlays C and M align closely with PC and TTB trends and anticline offsets of overlay C fall across the trace of the Chain FZ which is mimicked by seafloor offsets in the TTBs. connects to South American Figure 5. features discussed by Krueger et al., 2018, this conference. Gravity (GI) underlay with Southwards along the West basin outlines. African margin from Douala to Representation Cape Town, fracture zones often of WCARS lie opposite tectonic features in northern the African continental crust, shears shows but they were not reactivated within the continent itself at possible Benue breakup and are not further Trough discussed in this paper. connections via Mamfe Niger Delta – CARS (1?), Yola- (Central African Rift Doba (2?) and System) Figure 5. Gravity (GI) underlay with basin outlines. Representation of WCARS northern shears Work by Weber & Daukoru Bongorshows possible (3?) Benue basins, Trough or a connections combination via Mamfe of these (1?), paths, Yola-Doba likely (2?) maskedand Bongor by (3?) younger basins, CVL activity. 1975 (citing Murat 1970) shows or a combination of these paths, likely masked by younger CVL activity. main tectonic features of the Niger Delta floor. Genik, 1993 width. Adjacent to the southwest, the onshore Niger Delta remains the key reference defining WCARS basins and shears of contains three deeply-buried sub-basins, from northwest to Chad, Niger, and Sudan. PGW flew Nigeria-wide aero-geophysics southeast being the Benue SW; the Awaizombe Low (squeezed surveys and published a depth-to-magnetic-basement initial between the southwest ends of the Onitsha High and the interpretation (Reford et al., 2010) particularly illustrating the Abakaliki Anticlinorium); and the two-part Afikpo Low. Roughly greater Benue Trough, and associated sub-basins. Dou et al., 2014 rhomboidal, the steep flanks of the Benue SW and Afikpo are illustrated the CARS shear system using an uncited rectilinear formed by vertical offsets along the Benue and Charcot FZs. Prior representation of the affected basins & sub-basins to emphasize to burial by the drift-age delta, they may have formed as early directional control via shear on the basin shapes. pull-aparts floored by highly-thinned continental crust. Because we need first to undo observed Santonian inversion and restore Our work refines these features and provides estimates of the the effect of Apto-Albian extension, our interpretation thus far crustal deformation involved. We observe that crustal thinning has no estimate for the amount of crustal thinning caused by is not a function of feature amplitude on our gravity imagery Barremian nw-se extension. (not shown). Prominent narrow, high-amplitude GI-THD anomalies associated with north-west and south-west flanks of To the north-east, the Yola and Doba Basins appear to have the Termit / Tenere Basin resulted from shallow depth to the formed a connection between the Doseo pull apart Basin in main sediment-basement density contrast. The much deeper (c. CARS and the WARS/Benue system (Figure 5). This would 14 km) basin center has a subdued gravity response as sediments transfer upper (northern) CARS motion directly into the have compacted, reducing the density contrast at the interface Benue Trough, thus de-emphasizing or abandoning the lower whose gravity signature at depth is also strongly attenuated by (southern) CARS faults in western Cameroon. The timing the inverse square law. would correspond to opening of the adjacent ocean as the “junctionettes” are de-emphasized or even abandoned in western Across our interpretation region, the cumulative ne-sw width Cameroon. The rectangular shape and substantial depths of of the Bida (Benue SW), Yola (Benue NE), and Termit basins is the Benue internal sub-basins (Benue SW and Afikpo Low) are about 500 km which implies ne-sw stretch of perhaps one-third consistent with such a history. of that. Published gravity inversion models across these basins and sub-basins indicate crustal thinning of about one-third, from Our interpretation confidence is lowest carrying these features a normal continental 30 - 35 km thickness to about 22 - 26 km. across the CVL with its thermal and volcanic activity masking the density changes so easily traced both east and west of the The ne-sw-trending Benue Trough present-day varies in width CVL. We rely more on principles of structural geology and less from about 140 - 260 km. It contains, as stated earlier, the on the weaker expressions in the potential field data in this inverted Abakaliki Anticlinorium, within the Anambra Basin, area to infer that early in the evolution of the passive margin lower Benue Trough (Reijers et al., 1997) plus the Onitsha High the lower CARS and perhaps also the Sanaga Fault made a and the Benue Folded Belt, implying a greater pre-inversion connection through to the fracture zones.

HGS – PESGB 17th Conference on Africa E&P 57 We suggest that the Benue SW and Afikpo sub-basins initially References filled with restricted lacustrine sediments, offering source Dewey, J.F., & K. Burke (1974) Hot spots and continental potential that may augment the well-known terrestrial and breakup: implications for collisional orogeny. Geology 2, p. 57- marine sources (Haack et al., 2000; Schiefelbein et al., 2000) of 60. the Niger Delta. Dickson, William & Schiefelbein, Craig (2015) Searching High Conclusions and Low: Correlating shallow (drift phase) and deep (rift phase) Triple junctions have interesting origins and histories, structural trends with surface and subsurface geochemistry developing for example within oceanic crust of the Gulf of in the Niger Delta, West Africa. GCS-SEPM Perkins-Rosen Guinea as a stepping series of “rolling triple junctions”. Linked Research Conference, Houston triple “junctionettes” may have evolved to a simpler geometry, reducing complexity towards the simpler, classic triple junction. Dickson, W., Schiefelbein, C.F., Odegard, M. E., & Zumberge, J. E. (2016) Petroleum Systems Asymmetry across the South Evolving motions in and around the initial Gulf of Guinea Atlantic Equatorial Margins. Geological Society, London, Special triple junction on African crust imparted varied structural Publications, 431, ch.13, pp15. relationships. Inversion resulting from rotation of the angular relationship required by the breakdown of initial displacements Dou, L., Shrivastava, C., Dai, C., Wang, J., Hammond, N., Anakwe, would explain the Abakaliki Anticlinorium, within the Benue C., Siddick, M., & Xu, B. (2014) Deciphering an Unconventional Trough, onshore Nigeria. African Reservoir: Geological Characterization of Granitic Basement from Bongor Basin, Chad, AAPG Search and Our kinematically-constrained structural interpretation of the Discovery Article 10673 West and Central African Rift System (WCARS) is consistent with our current understanding of the evolution of the adjacent Genik, G.J., 1993. Petroleum Geology of Cretaceous–Tertiary oceanic crust. The Yola and Doba Basins may have effected a rift basins in Niger, Chad, and Central African Republic. AAPG connection between the CARS and WARS/Benue systems, and Bulletin v77, 1405–1434. the previously obscured Benue architecture provides the key linkage between continental and oceanic systems. Granath, James W. & Dickson, William (2016a), Cross-Africa shear zones and their kinematic relationship to rift basins. HGS/ Deep pull-aparts beneath the onshore Niger Delta, likely of PESGB Africa Conference Sept. 2016. Barremian to Albian age, would initially have been lacustrine rather than marine, with implications for source rock deposition. Granath, James W. & Dickson, William (2016b), Regionally connected structural systems: the power of the big (continental- Basins belonging to the WCARS system can be re-evaluated scale) picture. AAPG Search & Discovery paper 2571578. based on their revised shapes, deformation history, and relationships to sources of thermal and sedimentary inputs with Granath, James W. & Dickson, William (2018), Organization of an eye to their hydrocarbon potential. n African Intra-Plate Tectonics, AAPG Search & Discovery 30555 from AAPG ICE, London Oct. 2017. Acknowledgements The Purdy Project (Exploration Fabric of Africa or EFA, Haack, R.C., Sundararaman, P., Diedjomahor, J.O., Xiao, H., Gant, www.efafrica.com) is now available from AAPG’s Datapages N.J., & May, E.D. (2000) Niger Delta Petroleum Systems, Nigeria. subsidiary as a non-exclusive adjunct to other DEO (Datapages AAPG Memoir 73, Ch.16, p. 213-231. Exploration Objects) material. Krueger, A., Murphy, M., Norton, I., Casey, K., de Matos, R. D. MARIMBA (Margins of the Atlantic Region Integrated (2018) Influence of Proterozoic Heritage on development of Multidisciplinary Basin Analysis) and TFA (Tectonic Fabric of rift segments in the Equatorial Atlantic, HGS/PESGB Africa Africa) are non-exclusive studies referenced with permission; Conference Sept. 2018 more at www.digsgeo.com McKenzie, D.P. & W.J. Morgan (1969), Evolution of Triple Map-based figures in this paper were generated as screen Junctions. Nature 224, p. 125-133. exports from ArcGIS(TM) 10 and annotated using PaintShopPro 9. Maps are in unprojected geographic coordinates Odegard, M. E., Dickson, W. G., & Schiefelbein C. F. (2007a) (lat-longs) using the WGS84 datum. The Application of New Developments in Geodynamics and Plate Tectonics to Hydrocarbon Exploration: Development An extended set of citations is available from the authors of Predictive Methods, COAS Marine Heat Flow Workshop, Oregon State U, September

58 HGS – PESGB 17th Conference on Africa E&P Odegard, M. E., Dickson, W. G., & Schiefelbein C. F. (2007b) Schiefelbein, C.F., J.E. Zumberge, N.C. Cameron, and S.W. Brown Structural and Lithological Inversion Using Gravity and (2000) Geochemical comparison of crude oil along the South Magnetic Data Integrated with Geological Information, 10th Atlantic margins, in M.R. Mello and B.J. Katz, eds., Petroleum International Congress, SBGf, Rio de Janeiro, Brazil, 19-22 systems of South Atlantic margins: AAPG Memoir 73, p. 15-26 November Shatsky, Nicolas (1946), The Great Donets Basin and the Wichita Reford, S. W., Misener, D. J., Ugalde, H. A., Gana, J. S., & Oladele, System, comparative tectonics of ancient platforms. Geology O. (2010), Nigeria’s Nationwide High-resolution Airborne Series, #6 Akademiia Nauk SSSR Doklady, pp. 57-90. Geophysical Surveys in SEG Annual Meeting Abstracts, p1835- 1839 Weber & Daukoru (1975), Petroleum Geology of the Niger Delta, 9th World Petroleum Congress, vol 2, p209-221. Reijers, T.J.A., Petters, S.W., & Nwajida, C.S. (1997) The Niger Delta Basin, in Sedimentary Basins of the World, V. 3 African Basins (R.C. Selley, ed), ch.7, p. 151-172.

HGS – PESGB 17th Conference on Africa E&P 59 Wednesday, September 12 | Theme 3 | 11:55 Ana Krueger University of Houston, Austin, TX, Bluware I. Norton University of Texas, Austin, TX K. Casey Actus Veritas, Houston, TX R. D. de Matos Nandy Oil and Gas, Rio de Janeiro, Brazil M. Murphy University of Houston, Austin, TX Influence of Proterozoic Heritage on Development of Rift Segments in the Equatorial Atlantic

The last phase of Atlantic Ocean opening involved Late Albian Offshore basins along the Brazilian Equatorial Atlantic margin rifting and separation of Africa and South America along were previously described as contemporary strike-slip basins, the Equatorial Atlantic. Prior to the Albian, initiation and separated by the Romanche Fracture Zone and the northern northward propagation of sea-floor spreading caused rotation and southern branches of Sao Paulo Fracture Zone (FZ). We of the South American plate and formation of two main rift integrated all newly published observations along the margin systems in NE Brazil and West Africa: The Northeast Brazilian into a New Plate Tectonic Model, which predicts diachronous Rift System, consisting of the Reconcavo-Tucano-Jatoba (RTJ); development and fits the data reducing misfit errors along the Sergipe Alagoas/Gabon (SAG), and Cariri-Potiguar (CP) rifts South American and African margins. in Brazil, and the West-Central African Rift System (WCARS) in Africa. The Brazilian basins developed inside and around the Methodology Borborema Province, a key Proterozoic structure that controlled This work consists of a compilation of multiple datasets that spatial and temporal differences between these rift systems. Our include: 2D seismic mapping (Krueger, 2012), digitized and analysis of a new compilation of onshore and offshore faults of edited onshore faults, new tectonic maps of South America the Equatorial Atlantic led us to the conclusion that the segment (Cordani et al., 2016) and Africa (Meghraoui, et al., 2016), bound by the Kribi and Bode Verde fracture zones south of combined with offshore maps from Matos (2000) South America Borborema acted as a link between intracontinental rifting to and Casey (2014) Africa. Using our combined seismic data the north and late rifting stages in the Central Atlantic. During interpretation (Matos, 2000, Krueger, 2012, and Casey, 2014) the Albian, this region acted as a ¨buffer zone¨, balancing, aided by free-air gravity interpretation (Sandwell et al., 2014) kinematically, in time and space, dextral strike slip rifting in the (Figure 1), we mapped the limit of oceanic crust on both sides Equatorial branch, with simultaneous sea floor spreading in the of the Atlantic. Our interpretation was used in the updates for Central segment. In this paper we tie sequence stratigraphic rift the UTIG PLATES model. We used PaleoGis software from the sequences to plate kinematic changes described in our new plate Rothwell Group L.P. and the UTIG PLATES Model to restore model. Attempts to consider the thermal and tectonic evolution basement structures and faults from Krueger (2012) together of the Central Salt Basins of the South Atlantic as an analog with Matos (2004) and Casey (2014) and new structural for the Equatorial Margin may lead to wrong predictions in interpretation of the faults onshore of South America to build hydrocarbon exploration. The differences in the development of the paleogeographic maps for the Lower to Mid-Cretaceous. these segments may explain the asymmetry in the distribution of oil and gas reserves along the South Atlantic Margin. Proterozoic Heritage West Gondwana was a collage of diversified Tonian terranes Introduction (1000 – 900 Ma) amalgamated during diachronic Brasiliano/ Onshore studies of Northern Brazilian basins (Amazonas, Foz Pan African orogenies (ca. 800 – 500 Ma, Brito Neves at al., do Amazonas, Marajo, Grajau, Sao Luis, and Ilha Nova basins) 2014). The Trans-Brazilian terranes (TBL) is a complex net of by Soares Jr. et al. (2008) and (2011), dated rifting phases from Neoproterozoic mobile belts of Neoproterozoic age, formed Late Triassic to Albian. The structural styles of the basins were as the Brazilian and African Cratons collided with the Congo interpreted to be controlled by an interplay between inherited craton (Brito Neves et al., 2014). This event is called Brasiliano geology during the early rifting stage and by readjustment of or PanAfrican. The Brasiliano/Pan African tectonic event the plates at the initiation of the seafloor spreading (Matos produced the main structures of West Gondwana; 1) the 3000 2017; Krueger 2012; Krueger et al. (2014, 2015a, 2015b). km-long Trans–Saharan (TSL) lineament and 2) its southward continuation: the Transbrasiliano Lineament (TBL, from NW

60 HGS – PESGB 17th Conference on Africa E&P (2014) and new structural interpretation of the faults onshore of South America to build the paleogeographic maps for the Lower to Mid-Cretaceous.

Figure 1. Equatorial Atlantic. Vertical gradient of the free-air gravity anomalies derived from Figuresatellite 1. Equatorial altimetry Atlantic. data (Sandwell Vertical andgradient Smith, of 2014).the free Onshore-air gravity fault anomalies interpretation derived modified from satellite altimetryfrom data the Commission (Sandwell and for Smiththe Geological, 2014). Onshoremap of the fault World interpretation (CCGM/CGMW) modified maps from ofthe South Commission for the GeologicalAmerica (Cordani map of theet al., World 2016) (CCGM/CGMW) and Africa (Meghraoui, maps of 2016).South America (Cordani et al., 2016) and Africa (Meghraoui, 2016). Ceará, in Brazil, all the way to Argentina), also a 3000 km-long caused rotation of the South American plate. To avoid confusion shear zone (FigureProterozoic 2). The TSL heritage borders the West African Craton, between the Proterozoic kinematic behavior of this Transversal with associated arc-relatedWest Gondwana Neoproterozoic was a collage rocks, of ophiolites, diversified TonianZone terranes and Cretaceous(1000 – 900 here Ma) we amalgamated refer to the Cretaceous during kinematic and accretionarydiachronic prisms. The Brasiliano/Pan TBL separates African the Amazon orogenies Craton (ca. 800segment – 500 Ma, as “ OrthogonalBrito Neves Zone at al.,”. 2014). The Trans- (Amazonian or pre-BrasilianoBrazilian terranes domain) (TBL) from is a complexthe Brasiliano net of Neoproterozoic mobile belts of Neoproterozoic age, formed as the Brazilian and African Cratons collided with the Congo craton (Brito Neves et al., 2014). This event terrains (Brito Neves at al., 2014). Linked with the TBL, the The OZ behaved as a large scale dextral transfer zone, balancing is called Brasiliano or PanAfrican. The Brasiliano/Pan African tectonic event produced the main structures rift development between the future Equatorial and Central Borborema Provinceof West is one Gondwana; important 1 )Neoproterozoic the 3000 km-long cratonic Trans –Saharan (TSL) lineament and 2) its southward nuclei, formed bycontinuation: a complex framework the Transbrasiliano of orogenic Lineament branching (TBL , fromAtlantic NW branches Ceará, in of Brazil, the South all the Atlantic. way to TwoArgentina), main rift systems system. We namedalso this a 3000large kmpolycyclic-long shear NNE zone shear (Fig. belt 2) in. Brazil,The TSL bordersin NE Brazil the West and WestAfrican Africa Craton, formed with exploiting associated these arc- zones and its continuityrelated in Africa, Neoproterozoic as the Borborema rocks, Horsetailophiolites Splay, and accretionaryof weakness: prisms 1). Thein Brazil; TBL separates the Northeast the AmazonBrazilian Craton Rift System, (BHS) (Figure 2(Amazonian). or pre-Brasiliano domain) from the Brasilianoconsisting terrains of the (Brito Reconcavo-Tucano-Jatoba Neves at al., 2014). Linked rifts with(RTJ); Sergipe the TBL, the Borborema Province is one important Alagoas/GabonNeoproterozoic (SAG),cratonic and nuclei, Cariri-Potiguar formed by a (CP) complex rift valleys framework of orogenic branching system. We named this large polycyclic NNE shear belt in Brazil, and its The Transversal Zone (TZ) is located in the central domain (Magnavita, 1992, Matos, 1999, Destro et al., 2003, and Burke continuity in Africa, as the Borborema Horsetail Splay (BHS) (Fig. 2). of the Borborema province (BHS) between Patos (LPT) and et al. 2003, Brito Neves and Cordani, 1991), and the West and Pernambuco (LPEThe) lineaments; Transversal the Zone LPT (TZ has) is been located recognized in the central Centraldomain Africanof the Borborema Rift System province (WCARS). (BHS 2)) inbetween Africa (Brown and as a continental Patostransform (LPT linking) and Pernambuco a recognized (magmaticLPE) lineaments; arc at theFairhead, LPT has 1983; been Fairhead recognized et al., as 2012, a continental 2013; Fairhead transform and Binks, the northern portion of the TZ (ca. 635-580 Ma), products of a 1991, Fairhead and Green, 1989, Hargue et al., 1992, Yandoka et Meso and Neoproterozoic plate-tectonic accretionary processes al., 2014, Yassin et al., 2017). Both rift systems aborted, and final (Brito Neves at. al (2016), rifting took place along the present day continental margins. This switch was driven by the presence of lithospheric keels The eastward extension of the TZ is represented by the Central under the Nigerian and Borborema Shields, not allowing rifting African belt or shear zone (CASZ), another Neoproterozoic to propagate through them. The last phase of Atlantic Ocean shear zone, the product of a continental collision during which opening finally took place in Late Albian. the Nigerian Shield was thrusted onto the Congo Craton. Opening of the Equatorial South Atlantic The Orthogonal Zone (OZ) exploited Neoproterozoic zones Initiation and northward propagation of sea-floor spreading of weakness and was active during the Early Cretaceous as in the South Atlantic caused rotation of the South American initiation and northward propagation of sea-floor spreading plate in respect to Africa, and formation of the two main rift

HGS – PESGB 17th Conference on Africa E&P 61 Figure 2. Tectono-structural map of the South Atlantic Ocean at 145 Ma, summarizing main geological Figureterrains 2. Tectono and structures-structural that map influenced of the South the lithospheric Atlantic Ocean rupture at 145 process. Ma, summarizingThis figure alsomain shows geological the terrainsdistribution and structures of Pre-rift that sedimentsinfluenced and the activelithospheric rift axes rupture at 145 process. MA. This figure also shows the distribution of Pre-rift sediments and active rift axes at 145 MA. systems in NE Brazil and West Africa. Oblique deformation Concluding Remarks requires less strain and as much as two times less force in order The Borborema Province – a Proterozoic element with a cratonic to reach theOpening brittle yield of the stress Equatorial (Brune et South al., 2012, Atlantic Brune and core and the frame of adjacent Pan African fold belts, (Figure 2) Autin, 2013, and Heine and Brune, 2014). Once yield is reached, acted as an obstacle to northward propagating rifting in the Initiation and northward propagation of sea-floor spreading in the South Atlantic caused rotation of the hot asthenosphericSouth American upwelling plate and in friction respect softening to Africa, andpromote formation Southof the Atlantic,two main thereby rift syste delayingms in NE rifting Braz iland and forcing a South extensive lithosphericWest Africa. weakening Oblique deformation (Heine and requiresBrune, 2014). less strain andAtlantic as much opening as two totimes the east,less followingforce in order zones to of weakness on the reach the brittle yield stress (Brune et al., 2012, Brune andorthogonal Autin, 2013, zone. and We Heine define and the Brune, term “buffer2014). zone” as a region Basins in anOnce around yield the is Borboremareached, hot Province asthenospheric record pre-rift upwelling and and friction softening promote extensive lithospheric weakening (Heine and Brune, 2014). where rifting was delayed or slowed as rifting followed a path of post-rift stages from 145 to 100 Ma. Strike slip movements in the thinner continental lithosphere, surrounding lithospheric keels. Equatorial BasinsMargin, in kinematically an around the linked Borborema to the finalProvince rifting record stages pre -Oncerift and the post driving-rift stages forces from from 145 the todivergent 100 Ma. plate movements Strike slip movements in the Equatorial Margin, kinematically linked to the final rifting stages in the in the Central South Atlantic segment, began during the Aptian Central South Atlantic segment, began during the Aptian (from(Matos the et evolvingal., 2017). Central Therefore, and South from AptianAtlantic) to reached a critical (Matos et al.,Albian 2017). time Therefore, (120 Ma fromto 110 Aptian Ma) the to SouthAlbian Atlantictime (120 path ofpoint, continental a lithospheric rifting moved cutting around shear zonethe developed around the Ma to 110 BorboremaMa) the South Province, Atlantic and path developed of continental into a rifting system of obliqueBorborema and narrow and Nigerian rifted basins cratons, floored defining by oceanic the silhouette of the moved aroundcrust. the Rifts Borborema exhibit episodes Province, of and transpression developed intoand transtensiona future during Equatorial this phase Atlantic. of deformationBecause of the, controlled Proterozoic heritage primarily by the degree of obliquity of each basin to the plate motion vector (Krueger, 2012). Oceanic system of obliquecrust emplacement and narrow riftedin each basins basin flooredwas diachronous. by oceanic Souththe of South the Romanche Atlantic Equatorial FZ, outboard margins of Rio developed Grande intricate crust. Riftsd oexhibit Norte episodesand Nigeria, of transpression oceanic crust and began transtension to form aroundNW-SE 112 Ma, geometries while north which of the combined Romanche with the South American during thiscontinent phase of- deformation,ocean transform controlled fault, oceanic primarily crust by emplacementthe plate occurred rotation aroundlead to the110 diachronicity Ma. Oceanic ofcrust the oceanic crust degree of obliquityformed outboard of each basin of the to South the plate-East motion corner vector of the Demeraraemplacement Plateau in French(Figure Guiana 3). and Guinea at 116 (Krueger, 2012). Oceanic crust emplacement in each basin was diachronous. South of the Romanche FZ, outboard of Rio References Grande do Norte and Nigeria, oceanic crust began to form Brown, S.E., Fairhead, J.D., 1983. Gravity study of the Central around 112 Ma, while north of the Romanche continent-ocean African rift system: a model of continental disruption. 1: the transform fault, oceanic crust emplacement occurred around Ngaoundere and Abu Gabra rifts. Tectonophysics, 94, 187–203. 110 Ma. Oceanic crust formed outboard of the South-East corner of the Demerara Plateau in French Guiana and Guinea at Brito Neves, B.B and Cordani, G., 1991. Tectonic evolution of 116 Ma; at Amapa and Sierra Leone at 114 Ma; in the northern South America during the Late Proterozoic. V. 53, P. 23-40 part of Para and Liberia; in Piaui, Maranhao, Ivory Coast, and Ghana at 110 Ma (Figure 3). Brune, S., Autin J. The rift to break-up evolution of the Gulf of

62 HGS – PESGB 17th Conference on Africa E&P Ma; at Amapa and Sierra Leone at 114 Ma; in the northern part of Para and Liberia; in Piaui, Maranhao, Ivory Coast, and Ghana at 110 Ma (Fig. 3). Concluding Remarks The Borborema Province – a Proterozoic element with a cratonic core and the frame of adjacent Pan African fold belts, (Fig. 2) acted as an obstacle to northward propagating rifting in the South Atlantic, thereby delaying rifting and forcing a South Atlantic opening to the east, following zones of weakness on the orthogonal zone. We define the term “buffer zone” as a region where rifting was delayed or slowed as rifting followed a path of thinner continental lithosphere, surrounding lithospheric keels. Once the driving forces from the divergent plate movements (from the evolving Central and South Atlantic) reached a critical point, a lithospheric cutting shear zone developed around the Borborema and Nigerian cratons, defining the silhouette of the future Equatorial Atlantic. Because of the Proterozoic heritage the South Atlantic Equatorial margins developed intricate NW-SE geometries which combined with the South American plate rotation lead to the diachronicity of the oceanic crust emplacement (Fig. 3).

Figure 3. Composite opening of the South Atlantic, restorations for 120, 115, 110, 105, 100 and 95 Ma. Figure 3. Composite opening of the South Atlantic, restorations for 120, 115, 110, 105, 100 and 95 Ma.

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HGS – PESGB 17th Conference on Africa E&P 63 Fairhead, J.D., Green, C.M., 1989. Controls on rifting in Africa Matos, R.M.D., 2004. Petroleum systems related to the Equatorial and the regional tectonic model for the Nigeria and East Niger transform margin: Brazilian and West African conjugate rift basins. Journal of African Earth Sciences, 8 (2/3/4), 231–249. basins. In: Post, P., Rosen, N., Olson, D., Palmes, S.L., Lyons, K.T., Newton, G.B. (Eds.), Petroleum systems of divergent Hargue, T.R., Heidrick, T.L. and Livinston, J.E., 1992. continental margin basins. Tulsa, Gulf Coast Section, Society for Tectonophysics, 213 (1992) 187-202.Elsevier Science Publishers Sedimentary Geology, pp. 807-831. B.V., Amsterdam Matos, R. D. de, Krueger, A., Casey, K., Norton, I., 2017. The Heine C., Brune S.; Oblique rifting of the Equatorial Atlantic: Equatorial Atlantic and the South Atlantic Margins: Cretaceous Why there is no Saharan Atlantic Ocean. Geology ; 42 (3): twins, but so different at birth. Fifteenth International Congress 211–214. doi: https://doi.org/10.1130/G35082.1 of the Brazilian Geophysical Society, SBGf - Sociedade Brasileira de Geofísica. Krueger, Ana. The Brazilian Equatorial Margin from Rift to Drift: Faulting, Deposition, and Deformation in the Offshore Meghraoui, M., P. Amponsah, A. Ayadi, A. Ayele, B. Ateba, A. Barreirinhas Basin. PhD Dissertation. University of Houston, Bensuleman, D. Delvaux; M. El Gabry, R.-M. Fernandes, V. 2012. Midzi, M. Roos, Y. Timoulali, 2016, The Seismotectonic Map of Africa, first edition, Commission for the Geological map of the Krueger, A., Murphy, M., Burke, K., and Gilbert, E., 2014. The world (CCGM/CGMW). Brazilian Equatorial Margin: A Snapshot in Time of an Oblique Rifted Margin. AAPG Search and Discovery Article #30325. Sandwell, D.T., R.D. Müller, W.H.F. Smith, E. Garcia, and R. AAPG 2014 Annual Convention and Exhibition, Houston, TX, Francis, 2014, New global marine gravity model from CryoSat-2 2014. and Jason-1 reveals buried tectonic structure:Science, v. 346, no.6205, p. 65-67. Krueger, A., Murphy, M., Burke, K., and Gilbert, E., 2015. The Brazilian Equatorial Margin: A Snapshot in Time of an Oblique SOARES Jr., A.V.; COSTA, J.B.S.; HASUI, Y. Evolução da Rifted Margin. The Houston Geological Society Bulletin, vol. 57, Margem Atlântica Equatorial do Brasil: Três Fases, Distensivas. no.7, pages 15 – 21. Geociências, v. 27, n. 4, p. 427-437, 2008.

Krueger, A., Casey, K., Burke, K., Murphy, M., and de Matos, SOARES Jr., A.V., HASUI, Y., COSTA, J. B. S., Machado, F. B. R.D., 2015. Transform Margin Rift Architecture: An Example Evolução do rifteamento e paleogeografia da margem atlântica from the Brazilian Equatorial Margin. In: Petroleum Systems in equatorial do brasil: Triássico ao Holoceno. Geociências, v. 30, n. Rift Basins. 34th Annual Gulf Coast Section SEPM Foundation 4, p. 669-692, 2011, São Paulo, UNESP. Perkins-Rosen Research Conference. Watts, A.B., Fairhead, J.D., 1999. A process oriented approach to Magnavita, L P., 1992, Geometry and kinematics of modelling the gravity signature of continental margins. SEG. The the Recôncavo-Tucano-Jatobá rift, northeast Brazil: Leading Edge, 258–263 (February, 1999). Yandoka, B. M. S., M.B. Ph.D.dissertation, University of Oxford, Oxford, United Abubakar, Wan Hasiah Abdullah, M.H. Amir Hassan, Bappah U. Kingdom, 493 p. Adamu, John S. Jitong, Abdulkarim H. Aliyu, Adebanji Matos R.M.D., 1992, The Northeast Brazilian rift system: Kayode Adegoke, 2014. Facies analysis, palaeoenvironmental Tectonics, v. 11, p. 766-791. reconstruction and stratigraphic development of the Early Cretaceous sediments (Lower Bima Member) in the Yola Sub- Matos R.M.D., 1999, History of the northeastern Brazilian basin, Northern Benue Trough, NE Nigeria. Journal of African rift system: kinematic implications for the break-up between Earth Sciences 96 (2014) 168–179. Brazil and West Africa. Geological Society of London Special publications, v.153, p.55-73. Yassin, M.A., Mustafa M. Hariri, Osman M. Abdullatif, Gabor Korvin, M. Makkawi, 2017. Evolution history of transtensional Matos R.M.D. 2000. Tectonic evolution of the Equatorial pull-apart, oblique rift basin and its implication on hydrocarbon South Atlantic, in W. Mohriak and M. Talwani, eds., Atlantic exploration: A case study from Sufyan Sub-basin, Muglad Basin, Rifts and Continental Margins: American Geophysical Union, Sudan. Marine and Petroleum Geology 79 (2017) 282-299. Geophysical Monograph, 115, p.331-354. DOI:10.1029/ GM115p0331

64 HGS – PESGB 17th Conference on Africa E&P Andy graduated from the Post Graduate Research Institute for Sedimentology at The University of Reading, UK in 2001. He joined BP in Aberdeen the same year working as a Petroleum Engineer in the North Sea, followed by a series of geoscientist roles in the North Sea business across exploration and development. This included working on the Clair field at the time of development start-up and many license round evaluations and exploration wells at a time of renewed interest in exploration Wednesday, September 12on the| Theme UK Continental 4 Keynote Shelf. | 13:50 Andrew Witt, Alex Bump, Tracy Love, Fabian Setzer He moved to London in 2012 to lead BP’s exploration campaign in the Great Australian Bight. In 2016 June 2016 he took the role of Exploration Manager in Angola, shaping the exploration programme in a high value area through the downturn. During his tenure he has helped to articulate the value of exploration within proven basins and contribute to the recent positive The Evolution of the Pre-salt Play in thelegislative changes.Kwanza

In 2018 BP’s exploration positions in Côte d'Ivoire and São Tomé & Príncipe were added to the Benguela Basins, Angola portfolio, both have seismic commitments. The original Angola pre-salt concept was an oil play targeting Biographical Sketch shallow water microbialite and coquina carbonate reservoirs Andy Witt graduated from accumulated over basement highs in the lacustrine rift basin, the Post Graduate Research sealed by Aptian salt, and charged from Barremian source rocks. Institute for Sedimentology at The University of Reading, As new seismic data were acquired, the geology began to come UK in 2001. He joined BP into focus. Crustal thickness tapers from >20km thick beneath in Aberdeen the same year the shelf, to <5km thick across much of the offshore basin. Tilted working as a Petroleum fault blocks were crowned with carbonate seismic facies; bright Engineer in the North reflectors within the inner pre-salt sag basin suggested source Sea, followed by a series rocks. Base-salt highs offered some large-volume traps, with of geoscientist roles in the robust salt seals. North Sea business across exploration and development. Initial drilling results were promising. Maersk confirmed This included working on the pre-salt oil at Azul, and Cobalt announced an oil discovery at Clair field at the time of development start-up and many license Cameia. As the industry drilling campaign continued, results round evaluations and exploration wells at a time of renewed were mixed: subsequent wells found marginal volumes of oil, interest in exploration on the UK Continental Shelf. others found gas, several found CO2 in reservoirs containing remnant bitumen. Many failed due to trap or reservoir. In 2015 He moved to London in 2012 to lead BP’s exploration campaign an industry data trade programme, supported by Sonangol, in the Great Australian Bight. In 2016 June 2016 he took the enabled the industry to build a broader subsurface picture of the role of Exploration Manager in Angola, shaping the exploration basin beyond their incumbent positions. programme in a high value area through the downturn. During his tenure he has helped to articulate the value of exploration The pre-salt stratigraphic section is observed to thin towards within proven basins and contribute to the recent positive the oceanic/continental boundary, where salt directly overlies legislative changes. basement and the source and reservoir sections are both absent. High temperatures caused by a post-rift heating event cracked In 2018 BP’s exploration positions in Côte d’Ivoire and São existing oil accumulations to gas and flushed some traps Tomé & Príncipe were added to the portfolio, both have seismic with CO2. commitments.

Thick intervals of vuggy, fractured, silicified carbonates have been encountered in several wells; this unexpected reservoir fabric directly impacts drillability and reservoir deliverability, key factors to be considered prior to development.

Structural complexities in the post-salt section have led to angular geometries above salt holes, which allow leaking and result in pre-salt hydrocarbon columns that are not filled to their mapped structural spill points.

Revisiting the original exploration model for the pre-salt play with the well data from drill-out offers points to consider in the exploration and development of other rifted margins. n

HGS – PESGB 17th Conference on Africa E&P 65 Wednesday, September 12 | Theme 4 | 14:15 Paul Bellingham ION Geophysical, UK James Deckleman, Brian W. Horn ION Geophysical, USA +44 (0) 1932 792 212; [email protected] A New Beginning: Remaining Potential and the Case for Investment in the Niger Delta

The Niger Delta is one of the most prolific petroleum provinces system containing many high quality reservoir sands. Seismic in the world. Since 1965, the Delta has produced over 34 billion imaging of these sequences is excellent; calibrated seismic barrels of oil and, since 1970, over 21 trillion cubic feet of gas (BP, quantitative interpretation reliably de-risks both hydrocarbon 2017). OPEC (2017) reports that Nigeria had 37.5 billion barrels presence and phase. These facts combine to produce a low risk of proved oil reserves and 194 trillion cubic feet of proved natural exploration environment, Nigeria has experienced a >50% gas reserves at year-end 2016. Nigeria currently produces ~2.0 exploration success rate over the last 60 years. Traps are generally million barrels of oil/day, implying an R:P ratio of 51. formed around gravitational collapse structures in both up-dip extensional and down-dip contractional systems (Figure 1). The Delta contains many volumetrically significant petroleum There is a complex relationship between the timings of source accumulations. Average field size ranges from 53 mmboe maturation, hydrocarbon expulsion and migration, and trap onshore to 232 mmboe in the deepwater (Wood Mackenzie, formation in the different structural domains which defines 2017). Offshore, field recoverable oil and gas volumes range as exploration and phase risk, highlighting the need to understand high as 1.2 billion barrels (Bonga field) and 7 trillion cubic feet the delta system holistically. Here, we investigate long offset, deep (Bosi field), respectively. Over 500 fields, of which more than regional 2D seismic and selected 3D data from the onshore and 30% are now producing (NAPIMS, 2017), have been discovered offshore delta to pull together an integrated story. in the Niger Delta to date. Well production rates of over 20,000 barrels of oil per day have been achieved (NAPIMS, 2017). We show how the deep, long offset data allows for a consistent With a mature service sector, established infrastructure, a new interpretation of the entire structure of the Delta with mulitple governance structure and the upcoming potential bid rounds for stacked thrust sheets within the Paleogene and major mappable marginal fields and exploration acreage providing access detachment surfaces. Many of the largest fields in the Delta are to opportunity, now is the time to take another look at the reservoired in younger Neogene sediments on these uplifted, Niger delta. folded and faulted highs. Improved imaging of the deeper Miocene and Oligocene sediments also demonstrates the likely Niger Delta Geological Setting presence of reservoir rocks within structural closures. The geological history of the delta has created an ideal petroleum system with the thick Akata shale oil-prone source Structural mapping clearly demonstrates the younger and less rock (with Type II and Type III kerogens) overlain by a deformed nature of the deep water Outer fold and thrust belt substantial succession of progressively shallower facies in a delta compared to the Inner belt (Figure 1) with only the deeper

Figure 1: Regional PSDM seismic line across the main provinces of the offshore Niger Delta. The extensional Figuredomain, 1 :Inner Regional fold PSDMand thrust seismic belt lineand across the Outer the foldmain and provinces thrust belt of theare offshoreall shown. Niger Delta. The extensional domain, Inner fold & thrust belt and the Outer fold and thrust belt are all shown. 66 HGS – PESGB 17th Conference on Africa E&P

Structural mapping clearly demonstrates the younger and less deformed nature of the deep water Outer fold and thrust belt compared to the Inner belt (fig. 1) with only the deeper of the two main detachment zones extending out to the outer belt. Exploration results in the Outer fold and thrust belt have been largely disappointing to date with most of the discovered hydrocarbons being on the inboard side of the Outer fold and thrust belt (e.g. Etan, Zabazaba and Kuro). These results drive a need to better understand the development of the area, timing of structuration, and maturation of the major source horizons. Through integrated petroleum system modelling we discuss the potential in the area and potential risks.

Remaining Potential

By viewing the Delta as an integrated system and taking a play fairway based approach, we have assessed the future exploration potential of both deeper plays within the Inner fold and thrust belt and the likely ultimate potential of the Outer belt. We also show the remaining value in discovered, undeveloped fields. We show how once a holistic understanding of the Delta is in place it is possible to simply evaluate and rank areas and blocks with remaining potential. We demonstrate how additional detailed evaluation of high graded areas supports the overall assessment.

Conclusions

Though Nigeria historically has had agressive fiscal terms, the low sulfur, high API crude (Bonny Light) is a high value product and Nigeria has excellent access to market leading to low and robust breakeven prices. The petroleum system is prolific and has yielded some of the largest reserves on the planet but the complexity of the system has also led to many exploration surprises. We show how an integrated approach can high-grade areas and support detailed, prospect specific risking and evaluations.

Pending regulatory changes and future opening of acreage that has been inaccesible for many years means that Nigeria could once again become a highly attractive investment option.

of the two main detachment zones extending out to the outer Brian W. Horn - Senior Vice belt. Exploration results in the Outer fold and thrust belt have President and Chief Geologist been largely disappointing to date with most of the discovered for ION E&P Advisors. Brian hydrocarbons being on the inboard side of the Outer fold and has worked in exploration thrust belt (e.g. Etan, Zabazaba and Kuro). These results drive a and production for 27 years need to better understand the development of the area, timing with Amoco, BP, and Maersk of structuration, and maturation of the major source horizons. Oil prior to joining ION in Through integrated petroleum system modelling we discuss the 2010. In his current role he is potential in the area and potential risks. responsible for the technical and commercial advisory group Remaining Potential in support of E&P operators, By viewing the Delta as an integrated system and taking a play NOC’s and government fairway based approach, we have assessed the future exploration minsitries. His experience potential of both deeper plays within the Inner fold and thrust includes integrating geological and engineering/production belt and the likely ultimate potential of the Outer belt. We also data for play-based exploration, and development, basin and show the remaining value in discovered, undeveloped fields. We play fairway analysis, petroleum systems, regional stratigraphic show how once a holistic understanding of the Delta is in place and seismic correlations, prospect development and resource it is possible to simply evaluate and rank areas and blocks with potential assessments. In addition to exploration projects he remaining potential. We demonstrate how additional detailed has delivered exploitation/development programs generating evaluation of high graded areas supports the overall assessment. prospects, development and reservoir characterization for (infill) drilling designed to identify and evaluate critical geologic Conclusions uncertainties focused on increasing recovery efficiencies and Though Nigeria historically has had agressive fiscal terms, the reservoir management strategies. low sulfur, high API crude (Bonny Light) is a high value product and Nigeria has excellent access to market leading to low and Dr. Horn received his Bachelors and Master degrees in Geology robust breakeven prices. The petroleum system is prolific and from The University of Colorado, Boulder and his PhD in has yielded some of the largest reserves on the planet but the Geology and Geological Engineering from the Colorado School complexity of the system has also led to many exploration of Mines, Golden, CO. surprises. We show how an integrated approach can high- grade areas and support detailed, prospect specific risking and evaluations.

Pending regulatory changes and future opening of acreage that has been inaccesible for many years means that Nigeria could once again become a highly attractive investment option. n

Biographical Sketches Paul Bellingham is an explorer with over 17 years of experience in the oil & gas industry as a geologist, exploration manager and director. Paul has experience with mega-regional to prospect scale projects and has worked across a wide variety of plays and provinces globally; he is currently Vice President at IONs E&P Advisors group responsible for the Eastern Hemisphere.

Paul has a PhD in Arctic tectonics from the University of Cambridge and is a fellow of the Geological Society and a member of the PESGB.

HGS – PESGB 17th Conference on Africa E&P 67 this abstract has two “Figure 2s” I changed the captions to reflect 5 figures in the file. please check the figure rreferences in the text. Figure 5 is not referenced. Wednesday, September 12 | Theme 4 | 14:40 Olusanmi O. Emmanuel Acetop Energy, Houston, Texas, United States of America Kemi Taiwo, ND Western Limited, Victoria Island, Lagos, Nigeria Emmanuel Enu, Olusoji Mojisola First Exploration and Petroleum Development Company Limited, Victoria Island, Lagos, Nigeria Play Fairway and Petroleum Systems Analysis of Nigeria’s Cretaceous Benin (Dahomey) Basin: Key to Unlocking Additional Hydrocarbon Volumes from an Emerging Exploration Trend

Nigeria is a major hydrocarbon province with known reserves shales and deep marine shales serve as the seals. Trap styles for exceeding 35 billion barrels of oil and 200 trillion cubic feet of this petroleum system are mostly structural, such as the four- gas. Much of these reserves and the already produced billions way dip closure at Aje field, but traps can also be stratigraphic of barrels oil equivalent were discovered almost entirely within and combinational structural/stratigraphic. As proven in the prolific Tertiary Niger Delta (Akata-Agbada Total Petroleum the Epiya 1 and Baba 1 wells, reworked marine and turbidite System) because there has been very little exploration focus on sands as well as confined channels and ponded turbidite sands the country’s other passive margin basin - the Benin basin. The are the main reservoir facies for the Late Cretaceous-Upper discovery of the 380 MMBOE Aje Field in OML 113 in 1996, Tertiary drift petroleum system. Traps styles can include 3-way by Yinka Folawiyo Petroleum initially sparked an interest in dip closures against rotated fault blocks, stratigraphic, and/or the Benin basin, and a decade of regional studies ensued, but combinational stratigraphic/structural traps, while 3rd and 4th no additional drilling took place in the basin until very recently order marine shales and claystones serve as the seals. when the 775 MMBOE Ogo Field in OPL 310 was discovered by Lekoil/Afren in 2013. However, integrated basin and play The essential elements of a working petroleum system are well fairway analysis involving regional 2D/3D seismic data, gravity developed within the Benin basin and they have been discussed. and magnetic data, electrical logs, core data, and geochemical The Cretaceous Play Fairway within Nigeria’s Benin basin is an data identified the existence of three working petroleum emerging exploration trend that could be of major significance in systems in the Benin basin that need to be further proven by the future. The Aje field and Ogo field discoveries as well as those more exploratory wells. These petroleum systems are; 1) Lower made in other Equatorial Atlantic margin basins with similar Cretaceous rift petroleum system sourced by lacustrine source evolution and tectonostratigraphic history, suggest that further rock of the Neocomian Ise Formation, 2) Upper Cretaceous exploration efforts should be targeted at the Cretaceous Fairway transitional petroleum system sourced by Albian-Turonian of Nigeria’s Benin basin to unlock additional hydrocarbon marine shales of the Abeokuta Group, and 3) Late Cretaceous- volumes from the basin. There are definitely several more Jubilee Tertiary drift petroleum system sourced by deepwater marine look-alike fields as well as numerous Aje and Ogo fields to be shales of the Araromi Formation and the Tertiary Akata discovered within the Cretaceous Fairway of Nigeria’s Benin Formation that sourced most of the oil in the Niger Delta basin. basin if additional exploration wells are targeted at the play.

Reservoir facies for the Lower Cretaceous rift petroleum system Introduction include fluvio-lacustrine, fluvio-deltaic and shallow marine The Benin (Dahomey) Basin forms one of a series of West sandstones interbedded with carbonates as proven in the Aje 4 African Atlantic Margin Coastal sedimentary basins in the well in the Aje field, by YFP and by Kerr McGee in Fifa-1 and Gulf of Guinea Oil Province (Figure 1). The basin occurs in Hihon-1 wells in the Seme field. Trap styles for this petroleum the eastern side of the Gulf of Guinea transform margin and is system include rifted fault blocks, unconformity traps, and bounded by Chain and Romanche Fracture Zones (Binks and stratigraphic pinchouts while interbedded lacustrine shales and Fairhead, 1992). It is one of Nigeria’s two passive margin basins, claystones (maximum flooding surfaces) serve as the seals. For the other being the prolific Niger delta, which it bounds to the Upper Cretaceous transitional petroleum system, fluvio- the west. deltaic to shallow marine sandstones, ponded turbidite sands, and tubidite fan facies proven in Aje 1, Aje 2, Aje 4, Ogo 1, and The basin was formed at the culmination of Late Jurassic to Early Ogo 1-ST wells are the main reservoir facies while transgressive Cretaceous tectonism that was characterized by both block and

68 HGS – PESGB 17th Conference on Africa E&P

FigureFigure 1.1: West West African African Atlantic Atlantic Margin Margin Coastal Coastal sedimentary sedimentary basins inbasins the Gulf in theof Guinea Gulf of Oil Guinea Province. Oil The Province. The DahomeyDahomey basinbasin is is the the colored colored polygon polygon that extendsthat extends from offshore from offshore SW Nigeria SW through Nigeria Offshore through BeninOffshore and TogoBenin to and Togo to eastern offshore Ghana. eastern offshore Ghana.

transformData faulting and during Metho theds breakup of the African and systems analysis carried out to better unlock the hydrocarbon American continents (Olabode, and Adekoya, 2008). The potential of the basin. It is hoped that a better understanding tectonic Theevolution data hasused been for linked this study with three includes stages regional of 2D/3D ofseismic the elements data, ofgravity the petroleum and magnetic system data,coupled electrical with a more development which also allows the stratigraphic section to robust knowledge of the play types in the basin will encourage a logs, core data, geochemical data, and drilling results from some of the wells drilled in the basin. Figure 2 be divided into three main sequences: (i) pre-transform stage sustained exploration interest that will help to unlock additional (Neocomianshows to Barremian),the seismic (ii) data syntransform coverage stage for offshore (Aptian toNigeria. hydrocarbon Additional volumesseismic fromdata themight basin. exist. latest Albian), and (iii) post-transform stage (Cenomanian to Holocene) (Omatsola and Adegoke, 1981). The formations as Data and Methods Results and Interpretation delineated in the Nigerian sector include Ise, Afowo, Araromi, The data used for this study includes regional 2D/3D seismic Ewekoro, Akinbo, Ososun, Ilaro, and Benin (Coastal plain sands) data, gravity and magnetic data, electrical logs, core data, Three working petroleum systems were identified in the Dahomey basin. These petroleum systems are; Formations. geochemical data, and drilling results from some of the wells 1) Lower Cretaceous rift petroleum system sourced bydrilled lacustrine in the basin. source Figure rock 2 of shows the Neocomianthe seismic data Ise coverage for There has been very little exploration focus on the Dahomey offshore Nigeria. Additional seismic data might exist. basin. However, the discovery of the 380 MMBOE Aje Field in OML 113 in 1996, by Yinka Folawiyo Petroleum and the 775 Results and Interpretation MMBOE Ogo Field discovery in OPL 310 by Lekoil/Afren Three working petroleum systems were identified in the in 2013 has led to renewed interest in the basin. This paper, Dahomey basin. These petroleum systems are; 1) Lower therefore, presents a summary of the play fairway and petroleum Cretaceous rift petroleum system sourced by lacustrine

HGS – PESGB 17th Conference on Africa E&P 69 Seismic Data Coverage offshore Nigeria

Dahomey Basin Dataset

Figure 2. 2: Seismic Seismic data data coverage coverage offshore offshore Nigeria. Nigeria. Red polygon Red polygon shows the shows seismic the data seismic coverage data within coverage the Dahomey within basin.the Dahomey basin.

TableTable 1:1. DahomeyDahomey basin’s basin’s petroleum petroleum systems systems and their and elements their elements Formation,Petroleum 2) UpperSource Cretaceous Rock transitionalReservoir petroleum Rock systemSeal sourced by AlbianTraps-Turonian marineAnalogues shales of theSystems Abeokuta Group, and 3) Late Cretaceous-Tertiary drift petroleum system sourced by deepwater Drift Deepwater marine Shelfal (bars/channels); Marine Structural (3-way Shelfal sands –Epiya marine(Maastrichtian shales & of theshales Araromi of Araromi Formation Slopal and(mass the transport Tertiary shales/claystones Akata Formation againstthat sourced rotated most ofand the Baba oil in rd th Tertiary) Formation deposits, debrites, (3 or 4 order fault) or Structural Slopal Sands - the Niger Delta basin(Maastrichtian) (Brownfield & and Charpentier,turbidites) 2006maximum). The elements flooding of/ theseStratigraphic petroleumLazendra systems canyon are Akata Formation surfaces) Basin floor (debrites – Espiritu Basin (L.Cre., presented in Table 1. (Tertiary) turbidites) Phi=9-30%* Brazil), Hackbury (Olig., Texas) PlayTransitional fairway analysis Albiansuggests and thatFluvial/Deltaic there are three to shelfal mainTransgressive play types shales present Structural in the basin: or 1)Proven Tertiary by Union slope Oil Cenomanian/ (Phi= 9-25%)*, Re-worked (MFS’s) capping Structural / (Seme field, Benin) and clastics,(Upper Cretaceous; 2) Upper Cretaceous shelf clastics, and 3). Lower Cretaceous syn-rift clastics (Figure 2). Albian – Santonian ) Turonian shales with localized mass autocycles and deep Stratigraphic (Aje YFP (Aje field, Nigeria). (deltaic to shallow transport deposits (Phi= marine shales above and Seme) Also suggested by Reservoir facies formarine). the Lower Penetrated Cretaceous 20-30%)*. Penetratedrift petroleum in systemSenonian include fluvio-lacustrine,piston fluvio cores-deltaic acquired in Aje & Seme fields Aje and Seme fields Unconformity (3rd east of Fifa-1 by Kerr and shallow marineas wellsandstones as Fifa-1 well interbedded with carbonatesorder as MFS) proven by Kerr McGee in theMcGee Fifa (Block-1 and 4, Benin) Hihon-1Rift wells in the SemeOrganic field. rich TrapFluvio styles - Lacustrinefor this petroleum Lacustrine system Shales include Rifted faultrifted blocks, fault Proven blocks, by drilling in the lacustrine shales - sandstones - Ise Fm. (interbedded or as unconformity Ceara - Portiguar unconformity(Lower Cretaceous traps and stratigraphic pinchouts while interbedded lacustrine shales and claystones – Neocomian) Neocomian Ise Lower Cretaceous autocycle MFS’s) traps, stratigraphic basin, Brazil, by Union (maximum flooding surfaces)Formation servefluvio as -thedeltaic seals sediments (Figure 3 and Figure 4). pinch-outs Oil (Seme Field) and (penetrated in Seme) proven in Ghana, Togo Kerr McGee (Block 4), and Brazil. Phi=11-13%*. Benin Possible carbonates as interbeds or as last phase of autocycle (Aje & Seme fields)

SW NE STRATIGRAPHIC COLUMN WITH PRINCIPAL PLAYS 70 OPL 332: HGS – PESGB 17th Conference on AfricaPlays E&P

3D PROFILE – SEME FIELD KEY HORIZONS

PALEOCNE- & PLAYS MIOCENE Marine Passive Margin Shales Progradation 1a (Agbada/ Akata Fmt.)

CAMPANIAN/ MAASTRICHTIAN Early drift, post-Senonian u/c 1b TURONIAN Early drift, pre-Senonian u/c TOP MIOCENE (Araromi Fmt.) PASSIVE ALBI AN- ALBIAN- MARGIN: CENOMANIANCENOMANIAN Transitional SLOPAL TRANSITIONAL TOP EARLY MIOCENE

EARLY MIOCENE 200 NEOCOMIAN NEOCOMIANSynrift SYNRIFT(Ise Fmt.) TOP CENOMANIAN 2 (ISE FMT.)

TOP ALBIAN TOP OLIGOCENE TOP BASEMENT BASEMENT TOP PALAEOCENE Principal Play Risks: 3 2b TOP CRETACEOUS 1 - Tertiary Slope Clastics: Reservoir & Area of Closure TOP SANTONIAN 2 - Up. Cretaceous Clastics: SYN-RIFT: OPL 332 - PLAYS CONTINETAL Trap, up-dip leakage 1 TERTIARY SHELF AND SLOPE CLASTICS 3 - Lr. Cretaceous Clastics: 2 UPPER CRETACEOUS SHELF CLASTICS & TURBIDITES Trap and Reservoir 0 1 2 km 3 LOWER CRETACEOUS SYN-RIFT CLASTICS For All - Source Maturity and Charge

Figure 2: Play types in the Dahomey basin with their principal play risks.

Table 1: Dahomey basin’s petroleum systems and their elements Petroleum Source Rock Reservoir Rock Seal Traps Analogues Systems Drift Deepwater marine Shelfal (bars/channels); Marine Structural (3-way Shelfal sands –Epiya (Maastrichtian & shales of Araromi Slopal (mass transport shales/claystones against rotated and Baba rd th Tertiary) Formation deposits, debrites, (3 or 4 order fault) or Structural Slopal Sands - (Maastrichtian) & turbidites) maximum flooding / Stratigraphic Lazendra canyon Akata Formation surfaces) Basin floor (debrites – Espiritu Basin (L.Cre., (Tertiary) turbidites) Phi=9-30%* Brazil), Hackbury (Olig., Texas) Transitional Albian and Fluvial/Deltaic to shelfal Transgressive shales Structural or Proven by Union Oil (Upper Cretaceous; Cenomanian/ (Phi= 9-25%)*, Re-worked (MFS’s) capping Structural / (Seme field, Benin) and Albian – Santonian ) Turonian shales with localized mass autocycles and deep Stratigraphic (Aje YFP (Aje field, Nigeria). (deltaic to shallow transport deposits (Phi= marine shales above and Seme) Also suggested by marine). Penetrated 20-30%)*. Penetrated in Senonian piston cores acquired in Aje & Seme fields Aje and Seme fields Unconformity (3rd east of Fifa-1 by Kerr as well as Fifa-1 well order MFS) McGee (Block 4, Benin) Rift Organic rich Fluvio - Lacustrine Lacustrine Shales Rifted fault blocks, Proven by drilling in the (Lower Cretaceous lacustrine shales - sandstones - Ise Fm. (interbedded or as unconformity Ceara - Portiguar – Neocomian) Neocomian Ise Lower Cretaceous autocycle MFS’s) traps, stratigraphic basin, Brazil, by Union Formation fluvio-deltaic sediments pinch-outs Oil (Seme Field) and (penetrated in Seme) proven in Ghana, Togo Kerr McGee (Block 4), and Brazil. Phi=11-13%*. Benin Possible carbonates as interbeds or as last phase of autocycle (Aje & Seme fields)

SW NE STRATIGRAPHIC COLUMN WITH PRINCIPAL PLAYS OPL 332: Plays

3D PROFILE – SEME FIELD KEY HORIZONS

PALEOCNE- & PLAYS MIOCENE Marine Passive Margin Shales Progradation 1a (Agbada/ Akata Fmt.)

EARLY MIOCENE 200 NEOCOMIAN NEOCOMIANSynrift SYNRIFT(Ise Fmt.) TOP CENOMANIAN 2 (ISE FMT.)

FigureFigure 3.2: PlayPlay types types in inthe the Dahomey Dahomey basin basin with theirwith principaltheir principal play risks. play risks. source rock of the Neocomian Ise Formation, 2) Upper sands as well as confined channels and ponded turbidite sands Cretaceous transitional petroleum system sourced by Albian- are the main reservoir facies for the Late Cretaceous-Upper Turonian marine shales of the Abeokuta Group, and 3) Late Tertiary drift petroleum system. Traps styles can include 3-way Cretaceous-Tertiary drift petroleum system sourced by dip closures against rotated fault blocks, stratigraphic, and/or deepwater marine shales of the Araromi Formation and the combinational stratigraphic/structural traps, while 3rd and 4th Tertiary Akata Formation that sourced most of the oil in the order marine shales and claystones serve as the seals. Niger Delta basin (Brownfield and Charpentier, 2006). The elements of these petroleum systems are presented in Table 1. Conclusion The essential elements of a working petroleum system are well Play fairway analysis suggests that there are three main play developed within the Benin basin and they have been discussed. types present in the basin: 1) Tertiary slope clastics, 2) Upper Cretaceous Play Fairway within Nigeria’s Benin basin is an Cretaceous shelf clastics, and 3). Lower Cretaceous syn-rift emerging exploration trend that could be of major significance clastics (Figure 3). in the future. The Aje field and Ogo field discoveries as well as those made in other Equatorial Atlantic margin basins with Reservoir facies for the Lower Cretaceous rift petroleum similar evolution and tectonostratigraphic history, suggest system include fluvio-lacustrine, fluvio-deltaic and shallow that further exploration efforts should be targeted at the marine sandstones interbedded with carbonates as proven Cretaceous Fairway of Nigeria’s Benin basin to unlock additional by Kerr McGee in the Fifa-1 and Hihon-1 wells in the Seme hydrocarbon volumes from the basin. There are definitely several field. Trap styles for this petroleum system include rifted fault more Jubilee look-alike fields as well as numerous Aje and blocks, unconformity traps and stratigraphic pinchouts while Ogo fields to be discovered within the Cretaceous Fairway of interbedded lacustrine shales and claystones (maximum Nigeria’s Benin basin if additional exploration wells are targeted flooding surfaces) serve as the seals (Figure 4 and Figure 5). at the play. n

For the Upper Cretaceous transitional petroleum system, References fluvio-deltaic to shallow marine sandstones, ponded turbidite Binks, R.M. and Fairhead, J.D., 1992. A plate tectonic setting sands and tubidite fan facies proven in Aje 1, Aje 2, Aje 4, Ogo for Mesozoic rifts of West and Central Africa. In: P.A. Ziegler 1, Ogo 1-ST wells as well as in Ghana’s Jubilee and Ten Fields, (Editor), Geodynamics of Rifting, Volume It. Case History are the main reservoir facies while transgressive shales and deep Studies on Rifts: North and South America and Africa. marine shales serve as the seals. Trap styles for this petroleum Tecto~mp#q~sic2s1, 3: 141-151. system can be structural, such as the four-way dip closure at Aje field (Figure 5), or stratigraphic and combinational structural/ Brownfield M.E and Charpentier R.R, 2006. Geology and Total stratigraphic as proven in the Jubilee field. As proven in the Petroleum Systems of the Gulf of Guinea Province of West Epiya 1 and Baba 1 wells, reworked marine and turbidite Africa U.S. Geological Survey Bulletin 2207-C

HGS – PESGB 17th Conference on Africa E&P 71

NWNW SESE

AggradingAggrading Complex Complex

PondedPonded sand sand lenseslenses

Structural:Structural: drape drape SynSyn-Rift-Rift overover basement basement highhigh

200Km200Km RegionalRegional2D2D LinLinee Figure 3: NW-SE regional seismic line showing trap styles in the Lower Cretaceous rift petroleum system. FigureFigure 3: 4. NWNW-SE-SE regional regional seismic seismic line lineshowing showing trap styles trap instyles the Lower in the Cretaceous Lower Cretaceous rift petroleum rift petroleumsystem. system.

X:X: 489962 489962 Y:Y: 680716 680716 AJEAJE 2 2 DepthDepth (ft.) (ft.) AJEAJE 3 3 W.D.:W.D.: 310’ 310’ Surf. Surf. Loc. Loc. ☼☼ X:X: 488848 488848 Y:Y: 674325 674325 W.D.:W.D.: 3,110’ 3,110’ PTDPTD - 8250-8250

Permeability Flag Permeability Flag

Hydrocarbon Pay Flag Hydrocarbon Pay Flag

Turonian:Turonian: 154 154 ft. ft. net net gas gas cond cond pay pay 3737 ft. ft. net net oil oil pay pay DSTDST #4: #4: 3,866 3,866 bopd bopd + +6.7 6.7 MMcfg/d MMcfg/d

T/CenomanianT/Cenomanian 450 450 ft. ft. high high to to Aje Aje-2-2 MaxMax Hydrocarbon Hydrocarbon column column height height 450 450 ft. ft. AJEAJE 1 1 ☼☼

T/TuronianT/Turonian

T/CenomanianT/Cenomanian

T/AlbianT/Albian

Cenomanian:Cenomanian: 29 29 ft. ft. net net oil oil pay pay DSTDST #3: #3: 3,473 3,473 bopd bopd + +1.4 1.4 MMcfg/d MMcfg/d Aje-Aje-2 2Turonian Turonian + +Cenomanian Cenomanian has has additionaladditional 480 480 ft. ft. net net wet wet reservoir reservoir sandssands that that could could be be productive productive at at Aje-3Aje-3 location location

TDTD 16189 16189 ft ftMD MD (11601 (11601 TVD) TVD) SWSW Arb.Arb. Line Line ‘D’ ‘D’ 1997 1997 3D, 3D, 2004 2004 PSDM PSDM Processing Processing NENE

Figure 5: Aje field seismic data showing the discovery well and the appraisal wells that proved the existence of both the Lower Cretaceous Rift and Upper Cretaceous Transitional petroleum systems

72 HGS – PESGB 17th Conference on Africa E&P Olabode, S.O. and Adekoya, J.A., 2008. Seismic stratigraphy scale perspectives in the successful identification, drilling, and development of Avon canyon in Benin (Dahomey) basin, and development of oil and gas prospects. He has over 14 southwestern Nigeria. Journal of African Earth Sciences 50, years industry experience working for major exploration and 286–304. production companies including ExxonMobil, Statoil ASA, Total, BG Group Plc., and Shell in Nigeria, Norway, United Kingdom, Omatsola, M. E. and Adegoke O. S. 1981. Tectonic evolution and and the USA. He has participated in the location, planning, and Cretaceous stratigraphy of the Dahomey basin. Nigeria Jour. drilling of several exploration and development wells on three Min and Geol. 18(01), p. 130 137. different continents: Africa, Europe, and America. Tunde has Biographical Sketch worked on the geological and geophysical evaluation of plays Biographical Sketch and generation of prospects in the Niger Delta, the Cretaceous Dr. Olusanmi ‘Tunde Emmanuel is a Certified Dr. Olusanmi ‘Tunde Dahomey/Benin, UK North Sea basin, onshore Libyan basins; Petroleum Geologist (CPG #6301) and Certified Emmanuel is a Certified theEarth US ScientistMuddy (J)(SIPES Sandstone #3501). play, He theis a Cretaceous Olmos Petroleum Geologist (CPG Sandstone,demonstrated the Austinexploration Chalk and (Gulf development Coast basin, Texas), as well as #6301) and Certified Earth shalegeoscientist plays including with skills the to Marcellus,integrate well Haynesville, control, Niobrara, Eagle Scientist (SIPES #3501). He is Ford,gross and-depositional Bakken Shale. environment Dr. Emmanuel models, holdsreservoir a B.Tech. Applied models, seismic attributes, risk assessment as well a demonstrated exploration Geologyas basin degree to play from and play the Federalto prospect University scale of Technology and development geoscientist Akure,perspectives Nigeria, in athe Master successful of Science identification, degree in drilling Integrated, with skills to integrate well Petroleumand development Geoscience of oil fromand gas the prospects.University He of hasAberdeen, United control, gross-depositional Kingdom,over 14 years and aindustry PhD degree experience in Geology working from for major the Colorado environment models, reservoir exploration and production companies including SchoolExxonMobil, of Mines, Statoil Golden, ASA, Colorado,Total, BG Group USA. Plc., and models, seismic attributes, risk Shell in Nigeria, Norway, United Kingdom, and the assessment as well as basin USA. He has participated in the location, planning, to play and play to prospect and drilling of several exploration and development wells on three different continents: Africa, Europe, and America. Tunde has worked on the geological and geophysical evaluation of plays and generation of prospects in the Niger Delta, the Cretaceous Dahomey/Benin, UK North Sea basin, onshore Libyan basins; the US Muddy (J) Sandstone play, the Cretaceous Olmos Sandstone, the Austin Chalk (Gulf Coast basin, Texas), as well as shale plays including the Marcellus, Haynesville, Niobrara, Eagle Ford, and Bakken Shale. Dr. Emmanuel holds a B.Tech. Applied Geology degree from the Federal University of Technology Akure, Nigeria, a Master of Science degree in Integrated Petroleum Geoscience from the University of Aberdeen, United Kingdom, and a Ph.D. degree in Geology from the Colorado School of Mines, Golden, Colorado, USA.

HGS – PESGB 17th Conference on Africa E&P 73 Wednesday, September 12 | Theme 4 | 15:30 Kathryn E. DawsonJubilee Field: From World Class Exploration Discovery to Producing Asset. Learnings from 7 Principal GeoscientistYears of Production Tullow Ghana Ltd, Accra, Ghana Kathryn E. Dawson [email protected] Principal Geoscientist, Tullow Ghana Ltd, Accra, Ghana

[email protected] Jubilee Field: From World Class Exploration Ghana’s world-class Jubilee field was discovered in 2007 by the Mahogany-1 (M-1) and Hyedua-1 (H- Discovery1) exploration wells by to the partnership Producing group comprised ofAsset. GNPC, Tullow LearningsGhana Limited, Kosmos from Energy Ghana HC, Anadarko WCTP Company, Sabre Oil & Gas Holdings Limited, and the EO Group Limited. 7 Years of Production

Figure 1. Field Location

Ghana’s world-class Jubilee field was discovered in 2007Figure by 1the: Field Locationdiscovered large net pays of 95m and 41m respectively in high- Mahogany-1 (M-1)Regional and studies Hyedua-1 had (H-1)highlighted exploration the strong wells potential by the withinquality the stackedCretaceous reservoir play in sands. this relatively partnership groupunder comprised explored area. of GNPC, The location Tullows Ghana of the wellLimited,s were selected to test a Turonian turbidite fan Kosmos Energyobjective, Ghana HC,identified Anadarko with early WCTP 3D Company,seismic data Sabre and supportedThe fieldby seismic is formed AVO of response. stacked slope Class turbidites 2 AVO partially ponded Oil & Gas Holdingssuggested Limited, oil bearing and the sands EO Group conformant Limited. to structure in awithin gross ansense embayment on two separate and break 3D insurveys slope within the Tano Basin. over the area with a “risky” gap between.

Regional studies63 hadkm offshore highlighted in 1300m the strong of water, potential the first within two wells wereIn drilledJuly 2009, some the 5 Ministerkm apart ofand Energy intersected approved the Phase 1 Plan the Cretaceouslarge play continuous in this relatively accumulations under explored of light sweetarea. crude oil. ofThe Development M-1 and H-1 which wells discoveredincluded the large use netof an FPSO with a The locationspays of the of 95mwells andwere 41m selected respectively to test ain Turonian high-quality stackedfacility reservoir capacity sands. of 120,000 bopd. In December 2010, the field turbidite fan objective,The field isidentified formed of withstacked early slope 3D seismic turbidites data partially and pondedcame on-stream, within an embayment setting an industry and break record in for the timeline from supported by seismicslope within AVO the response. Tano Basin. Class 2 AVO suggested oil discovery to first oil for this type development. bearing sands conformant to structure in a gross sense on two separate 3D surveys over the area with a “risky” gap between. The guiding principles underpinned the Phase 1 Development Plan and enabled the fast track delivery were: 63 km offshore in 1300m of water, the first two wells were drilled some 5 km apart and intersected large continuous • Employ industry best-practices and proven technology for a accumulations of light sweet crude oil. The M-1 and H-1 wells deepwater FPSO scheme

74 HGS – PESGB 17th Conference on Africa E&P

Figure 2: Early Seismic View & Later AVO View

In July 2009, the Minister of Energy approved the Phase 1 Plan of Development which included the use of an FPSO with a facility capacity of 120,000 bopd. In December 2010, the field came on- Figurestream, 2. Early setting Seismic an industryView and record LaterFigure AVO for 2: theView Early timeline Seismic Viewfrom & discovery Later AVO View to first oil for this type development. Figure 2: Early Seismic View & Later AVO View In July 2009, the Minister of Energy approved the Phase 1 Plan of Development which included the In July 2009, the Minister of Energy approved the Phase 1 Plan of Development which included the use of an FPSO with a facility capacity of 120,000 bopd. In December 2010, the field came on- use of an FPSO with a facility capacity of 120,000 bopd. In December 2010, the field came on- stream, setting an industry record for the timeline from discovery to first oil for this type development. stream, setting an industry record for the timeline from discovery to first oil for this type development.

The guiding principles underpinned the Phase 1 Development Plan and enabled the fast track delivery were: • Employ industry best-practices and proven technology for a deepwater FPSO scheme

The guiding• Phased principles development underpinned focussing the on Phasethe appraised 1 Development “core” portion Plan of theand Jubilee enabled Field the fast track The guiding principles underpinned the Phase 1 Development Plan and enabled the fast track delivery• Ongoingwere: data acquisition during the development drilling phase to optimize the plan on a continuous basis delivery were: • • EmployPhase industry 1 would bestbe used-practices to frame and future proven phases technology of development for a deepwater data obtained FPSO scheme and early performance • • Employ industry best-practices and proven technology for a deepwater FPSO scheme • PhasedFocus developmenton development focussing of the highon the confidence appraised reservoirs “core” portion first. of the Jubilee Field • Phased development focussing on the appraised “core” portion of the Jubilee Field • Ongoing data acquisition during the development drilling phase to optimize the plan on a continuous basis • Ongoing data acquisition during the development drilling phase to optimize the plan on a continuous basis • Phase 1 would be used to frame future phases of development data obtained and early performance • Phase 1 would be used to frame future phases of development data obtained and early performance • Focus on development of the high confidence reservoirs first. • Focus on development of the high confidence reservoirs first.

HGS – PESGB 17th Conference on Africa E&P 75 Consistent with the phased philosophy of development, between 2014 and 2015 a further ten wells were drilled, designed to increase production and recover additional reserves, targeting the previously undeveloped areas of the field and one additional stratigraphic zone.

In the February 2016, the project encountered a major challenge: an issue with the turret bearing of the Jubilee FPSO Kwame Nkrumah was identified. This resulted in the need to implement new operating and offtake procedures. The necessary phases of operations shut down during this period however presented a unique learning opportunity for the sub-surface and enabled a series of carefully planned interference tests within the reservoir. Consistent with the phased philosophy of development, between 2014 and 2015 a further ten wells Learningwere anddrilled, understanding designed to increase of the productiondynamic behaviourand recover and additional connectivity reserves within, targeting the reservoirthe previously has been undeveloped areas of the field and one additional stratigraphic zone. further supported by the acquisition of the first 4D survey in offshore Ghana in February 2017. With a strongIn thelithology February and 2016, weaker the projectfluid element encountered in the a majorreservoir challenge rock: physics, an issue thewith resultsthe turret of bearing the 4D of have shownthe a Jubilee dominant FPSO pressure Kwame Nkrumaheffect allowing was identified. pressure This baffles, resulted previously in the need inferred to implement through new reservoir modeloperating history andmatching offtake andprocedures. geological The necessaryunderstanding phases, to of be operations mapped shut directly. down during this period however presented a unique learning opportunity for the sub-surface and enabled a series of carefully planned interference tests within the reservoir.

Learning and understanding of the dynamic behaviour and connectivity within the reservoir has been further supported by the acquisition of the first 4D survey in offshore Ghana in February 2017. With a strong lithology and weaker fluid element in the reservoir rock physics, the results of the 4D have shown a dominant pressure effect allowing pressure baffles, previously inferred through reservoir model history matching and geological understanding, to be mapped directly.

Figure 3: Lithology & 4D difference between wells

Integration of dynamic reservoir behaviour, geophysical, geological data, and with field analogues has allowed detailed insights into the evolution, architecture , and flow behaviour of this turbidite fan Figure 3. Lithology and 4D difference between wells system. Figure 3: Lithology & 4D difference between wells

Figure 4. Detailed Conceptual Model of One part of Jubilee Reservoir Figure 4: Detailed Conceptual Model of One part of Jubilee Reservoir • Phased development focussing on the appraised “core” Learning and understanding of the dynamic behaviour and portion of the Jubilee Field connectivity within the reservoir has been further supported This talk will lead the audienceFigure 4: onDetailed a journey Conceptual from Model the of earlyOne part understanding of Jubilee Reservoir of the geology of Jubilee, • Ongoing data acquisition during the development drilling by the acquisition of the first 4D survey in offshore Ghana in sharing insights on the key learnings in the course ofFebruary the development, 2017. With a strong to the lithology latest and view weaker of fluidthe element phaseThis to optimize talk will the lead plan the on audience a continuous on basisa journey from the early understanding of the geology of Jubilee, Jubilee reservoir architecture, and the impact of thisin understanding the reservoir rock onphysics, the thenext results phase of the of 4D development have shown • drilling.Phasesharing 1 would insightsbe used toon frame the key future learnings phases of in development the course of the development, to the latest view of the Jubilee reservoir architecture, and the impact of this understandinga dominant pressure on the effect next allowing phase ofpressure development baffles, previously data obtained and early performance inferred through reservoir model history matching and drilling. • Focus on development of the high confidence reservoirs first. geological understanding, to be mapped directly.

Consistent with the phased philosophy of development, between Integration of dynamic reservoir behaviour, geophysical, 2014 and 2015 a further ten wells were drilled, designed to geological data, and with field analogues has allowed detailed increase production and recover additional reserves, targeting insights into the evolution, architecture, and flow behaviour of the previously undeveloped areas of the field and one additional this turbidite fan system. stratigraphic zone. This talk will lead the audience on a journey from the early In the February 2016, the project encountered a major challenge: understanding of the geology of Jubilee, sharing insights on an issue with the turret bearing of the Jubilee FPSO Kwame the key learnings in the course of the development, to the latest Nkrumah was identified. This resulted in the need to implement view of the Jubilee reservoir architecture, and the impact of this new operating and offtake procedures. The necessary phases of understanding on the next phase of development drilling. n operations shut down during this period however presented a unique learning opportunity for the sub-surface and enabled a series of carefully planned interference tests within the reservoir.

76 HGS – PESGB 17th Conference on Africa E&P Wednesday, September 12 | Theme 4 | 15:55 Keith Myers Jubilee to Liza: Lessons from a DecadeEdwige of Exploration Zanella, in Jamie the Central Collard, Atlantic Helen Doran Westwood Energy Keith Myers*, Edwige Zanella, Jamie Collard, Helen Doran; Westwood Energy The play opening the billion-barrel Jubilee oil discovery in Ghana in 2007 triggered a decade of exploration drilling chasing analogues in the deep water Central Atlantic margins, from Mauritania to Jubilee to CameroonLiza: in theLessons West Africa margin fromand from Guyana a toDecade NE Brazil in South Americaof (Figure 1). Many were enticed into the play but the rewards have been concentrated in only a few companies. So what Explorationlessons have beenin learned? the First Central and foremost, if you Atlantic want to repeat a success, then you need to first understand the geological factors that are needed for the success you are trying to replicate. The play opening the billion- barrel Jubilee oil discovery in Ghana in 2007 triggered a decade of exploration drilling chasing analogues in the deep water Central Atlantic margins, from Mauritania to Cameroon in the West Africa margin and from Guyana to NE Brazil in South America (Figure 1). Many were enticed into the play but the rewards have been concentrated in only a few companies. So what lessons have been learned? First and foremost, if you want to repeat a success, then you need to first understand the geological factors that are needed for the success you are trying to replicate.

Seventy-eight companies have spent Figure 11.: LateLate CretaceousCretaceous (80(80 Ma)Ma) Atlantic Atlantic Margin Margin showing showing the thelocation location of exploration of exploration wells wells and $11.4bn drilling 128 exploration commercialand commercial resources resources discovered discovered in the in Cretaceous the Cretaceous turbidite turbidite plays. plays. wells in 13 basins along the Atlantic margins in the hunt for the next Seventy-eight companies have spent $11.4bn drilling 128 exploration wells in 13 basins along the Atlantic margins in the hunt for the nextquickly Jubilee the from key 2007 geological to early elements2018. needed for success and the Jubilee from 2007 to early 2018. integration of geological and geophysical analysis. Sixty-one wells have been drilled at the frontier stage of exploration, prior to the first commercial Sixty-one wells have been drilled at the frontierdiscovery stage being of made in a basin. Frontier exploration delivered four commercial basin-opening discoveries at a commercial successLessons rate have (CSR) been of hard 7% and won technical for many, success but there rate is (TSR) plenty of of39%. A total exploration, prior to the first commercialof 6.5discovery bnbbl of being oil and made 41 tcf ofrunning gas have room been fordiscovered the industry. in the WestwoodTano, MSGBC, estimates Sergipe that-Alagoas 80% and in a basin. Frontier exploration deliveredSuriname four commercial-Guyana basins . Nineof of exploration the companies wells that have participated so far targeted in the frontierthe slope discoveries areas of captured basin-opening discoveries at a commercial74% success of the totalrate volume.(CSR) The companiesthe margins that (Figure drilled the3). Amost key frontier lesson explorationis that a large wells part didn’t of theget the most reward, however (Figure 2). of 7% and technical success rate (TSR) of 39%. A total of 6.5 commercial resources in the slope setting are located in areas bnbbl of oil and 41 tcf of gas have been discovered in the Tano, dominated by normal faulting with gentle slopes, where higher MSGBC, Sergipe-Alagoas and Suriname-Guyana basins. Nine quality deep water reservoir sands can be deposited and creating of the companies that participated in the frontier discoveries optimal conditions for hydrocarbon migration. Success rates captured 74% of the total volume. The companies that drilled are lower on steeper, narrow slopes where deep water sands are the most frontier exploration wells didn’t get the most reward, more confined and traps are smaller. however (Figure 2). Significant resources remain to be discovered on the margin The keys to unlocking commercial success in the Cretaceous slopes and industry attention is also focusing on frontier plays plays of the Central Atlantic margins lie in participating early on the ultra-deep-water basin floor settings that have a proven in the opening of a new province, being selective, learning high potential but have been tested by only a few wells to date. n

HGS – PESGB 17th Conference on Africa E&P 77 Keith Myers is President, Research at Westwood Global Energy, responsible for research across the business. Keith joined BP in 1987, having graduated with a geology PhD at Imperial College. Following a variety of technical roles, he became Senior Commercial Advisor leading several major business negotiations for new business access. He also led strategy for BP’s business in West Africa in the Strategic Alliance with Statoil. After leaving BP in 2000, Keith was an advisor to numerous energy companies on strategy and partnership issues. Keith founded Richmond Energy Partners in 2006 to provide independent advice to investors in smaller oil and gas companies. REP advised some of the largest funds and institutions investing in the sector and provided exploration strategy and benchmarking services for the global exploration industry. REP launched Wildcat, the online global exploration intelligence service in 2014 and REP became part of Westwood Global Energy Group in 2015. Keith takes a keen interest in the oil sector governance and serves as a member of the advisory group for the Natural Resource Governance Institute.

Biographical Sketch West Africa in the Strategic Alliance with Statoil. After leaving Keith Myers is President, BP in 2000, Keith was an advisor to numerous energy companies Research at Westwood Global on strategy and partnership issues. Keith founded Richmond Energy, responsible for research Energy Partners in 2006 to provide independent advice to across the business. Keith investors in smaller oil and gas companies. REP advised some joined BP in 1987, having of the largest funds and institutions investing in the sector and graduated with a geology PhD provided exploration strategy and benchmarking services for at Imperial College. Following the global exploration industry. REP launched Wildcat, the a variety of technical roles, he online global exploration intelligence service in 2014 and REP became Senior Commercial became part of Westwood Global Energy Group in 2015. Keith Advisor leading several major takes a keen interest in the oil sector governance and serves business negotiations for new as a member of the advisory group for the Natural Resource business access. He also led Governance Institute. strategy for BP’s business in

Figure 2. Gross frontier wells drilled by company in the Cretaceous turbidite plays of the Central Atlantic versus net resources discovered resources from 2007 to 1Q 2018. Figure 2: Gross frontier wells drilled by company in the Cretaceous turbidite plays of the Central Atlantic versus net resources discovered resources from 2007 to 1Q 2018.

The keys to unlocking commercial success in the Cretaceous plays of the Central Atlantic margins lie in participating early in the opening of a new province, being selective, learning quickly the key geological elements needed for success and the integration of geological and geophysical analysis.

Lessons have been hard won for many, but there is plenty of running room for the industry. Westwood estimates that 80% of exploration wells have so far targeted the slope areas of the margins (Figure 3). A key lesson is that a large part of the commercial resources in the slope setting are located in areas dominated by normal faulting with gentle slopes, where higher quality deep water reservoir sands can be deposited and creating optimal conditions for hydrocarbon migration. Success rates are lower on steeper, narrow slopes where deep water sands are more confined and traps are smaller.

Significant resources remain to be discovered on the margin slopes and industry attention is also focusing Figure 3 Wells in the study area divided into their positions on the depositional system. Only 12 on frontier plays on the ultra-deep-water basin floor settings that have a proven high potential but have been testedpenetrations by only a few to date wells have to ventureddate. onto the basin floor yet those wells account for >50% of the total discovered resources and have the highest success rates.

Figure 3: Wells in the study area divided into their positions on the depositional system. Only 12 penetrations to date have ventured onto the basin floor yet those wells account for >50% of the total discovered resources and have the highest success rates. 78 HGS – PESGB 17th Conference on Africa E&P

Notes

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HGS – PESGB 17th Conference on Africa E&P 79 Notes

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80 HGS – PESGB 17th Conference on Africa E&P The 17th HGS-PESGB Conference Est. 1964

PES .org.uk on African E&P pesgb

Professional Poster Presentations Abstracts

September 10-13, 2018 Norris Convention Centre, Houston Texas Matt Morris, Ping Lu Anadarko Petroleum Corporation Matt Morris is a Geophysical Advisor in Anadarko’s Advanced Analytics and Emerging Technologies team. He holds a Masters degree in Geophysics from The University of Texas Using Generative Adversarial Networksat Austin and a B.S to Improvec. in Geophysics from Missouri University of Science & Tech. In his 15 years with Anadarko, Matt’s worked exploration and development projects across the US Deep Learning Fault PredictionLower 48, the NetworksGulf of Mexico, and most recently in offshore Mozambique.

The field of Deep Learning (DL) is arguably one of the most redshift of the signal toward lower-frequencies less than 35Hz, important innovations in artificial intelligence in recent times. and a significant boostIn recent years, Matt has served on Anadarko’s r in frequencies greater than 35Hz. Since isk and economic consistency teams that It allows for computational solutions to problems that aren’t this is not a spectral enhancementoversee a global portfolio of conventional and unconventional exploration prospects. In technique, no new thin-beds this easily characterized by a mathematical model or deterministic are introduced to the image.role, Matt provided oversight for r isk and uncertainty assessment, and developed a suite of algorithm. It also allows for automated solutions to problems Bayesian and frequentist statistical tools to aid in the assessment of exploration portfolios. that have inherently subjective solutions. Both of these criteria Last, the super-sampledToday, he’s data is then deployedcurrently working into our alongside petrotechnical professionals and data scientists to are endemic in the earth sciences, so novel solutions to these conventional DL training and prediction process to detect faults. challenges should be welcomed. By introducing a pre-processingintegrate m sharpeningachine learning techniques into step, the predicted Anadarko’s seismic interpretation workflows. faults become less blurry, more compact, and more amenable to Here, we demonstrate a recent refinement to Anadarko’s seismic- programmatic attempts to segment them into discrete features. n based Deep Learning fault identification process that improves the continuity and compactness of predicted fault planes in Biographical Sketch areas where faults intersect one another. Historically, these zones Matt Morris is a Geophysical of intersection were characterized by a cloud of intermediate Advisor in Anadarko’s probability values. To remediate this “blurring” problem and Advanced Analytics and enhance confidence of inferences, we demonstrate a pre- Emerging Technologies team. processing technique in the image domain that “sharpens” the He holds a Masters degree seismic image prior to training and prediction. in Geophysics from The University of Texas at Austin This sharpening solution consists of two neural networks. A and a B.Sc. in Geophysics feature extraction network is used for extracting both local and from Missouri University global features from an unrelated high-quality “donor” seismic of Science & Tech. In his 15 survey. Then, the dataset of interest is sent through the donor years with Anadarko, Matt’s reconstruction network where a generator architecture creates worked exploration and plausible-looking images at a denser-sampling rate with high development projects across the perceptual quality. US Lower 48, the Gulf of Mexico, and most recently in offshore Mozambique. In the study presented here, we create our sharpening network using a high-quality, South-American deepwater 3D survey as a In recent years, Matt has served on Anadarko’s risk and donor. The resulting generator architecture is then applied to our economic consistency teams that oversee a global portfolio dataset of interest—a 3D survey in the Gulf of Mexico. Similar to of conventional and unconventional exploration prospects. a 5D-interpolation, the super-sampled version of the GoM data In this role, Matt provided oversight for risk and uncertainty contains three times the Inline and Crossline trace density, and assessment, and developed a suite of Bayesian and frequentist the traces themselves are up-sampled by a factor of three. statistical tools to aid in the assessment of exploration portfolios. Today, he’s currently working alongside petrotechnical The super-sampled data yields a grossly similar frequency professionals and data scientists to integrate machine learning response to its parent with two notable differences: a subtle techniques into Anadarko’s seismic interpretation workflows.

82 HGS – PESGB 17th Conference on AfricaReturn E&P completed to Richard Sech and Jackson Bi

South Gabon’s Pre-Salt Revelation

Neil Hodgson*, Karyna Rodriguez, and David Eastwell; Spectrum Geo Ltd, Woking, United Kingdom

INTRODUCTION

To date, successful exploration for oil in the pre-salt play of South Gabon has primarily focussed on the Early Cretaceous Gamba sandstone play. On the shelf, the shallow water discovery creaming curve in the Gamba play had begun to plateau as explorers reached the interpretaional limitations of the inadequate imaging of available seismic resulting from complex post-salt geology. However, recent developments in 3D seismic acquisition and processing has allowed a new level of imaging to be achieved in the pre-salt, offering to unlock the remainingNeil Hodgson potential, Karyna of the Rodriguez, Gamba play and and David revealing Eastwell a new Spectrum Geo Ltd, Woking, United Kingdom system of traps and plays never before deliberately targetted; the intra syn-rift play.

PRE-AND POST-SALTSouth PROSPECTIVITY Gabon’s Pre-Salt Revelation

A reviewand applicationof legacy dataof source and andhistorical reciever operations de-ghosting records with an allowed understandinginterpretation-driven of the geological pre-stack and depth geophysical migration, comphas resultedlexities in an unprecedented image in the prospective pre- and post-salt previouslysections faced [2]. by operators in Gabon, specifically the challenge of resolving the pre-salt section due to velocity heterogeniity in the post- salt AlbianDuring “Madiela” the break-up carbonate of the Gondwana,. Integration deposition of a pre of-acqu the syn-isition survey designrift study, section efficient comprised operations fluvial-lacustrine management deltaic [1] sand, the sequences use of long (the Dentale and Kissenda Formations), in addition to two offsetmain streamers anoxic lacustrineand application source rocksof source (Kissenda and recieverand Melania de- ghosting with aFormations).n interpretation These-driven sequences pre- stackare characterised depth migration, by listric has resulted in an unprecedentedfault extensional image geometries. in the Upon prospective break-up, pre the- and first post marine-salt sections [2]. transgression eroded the upper part of the syn-rift section creating a low relief monocline upon which the transgressive Duringshoreface the break Gamba-up of sandstone the Gondwana was deposited., deposition of the syn-rift section comprisedAs the fluvialMadiela-lacustrine platform carbonatedeltaic sand developed, sequences it loaded (the the Dentale and Kissendagently Formation gravitationallys), in extending addition Ezangato two mainsalt, quickly anoxic creating lacustrine source rocksa (Kissendaheterogeneous and pop-interpod Melania Formations geometry) .( FigureThese 2sequences). In turn, are characterisedas the carbonate by list ricplatform fault extensional was drowned geometries. by prograding Upon clastic break -up, the sequences from the west, these too loaded the salt, changing first marine transgression eroded the upper part of the syn-rift section the geometries of the grounding pods and creating and infilling creatingturtle a backlow relief structures. monocline Reactive upon fall andwhich dissolution the transgressive of salt created shoreface Gambawide sandstone salt welds betweenwas deposited. isolated thin salt diapirs. This post-salt fabric is very heterogeneous in velocity, and this has led to the Figure 1.Simplified 1.Simplified stratigraphic stratigraphic column column of South of South Gabon’smajority Salt Basin. of seismic, both 3D and 2D, being unable to image the Gabon’s Salt Basin. pre-salt syn-rift sequence. IntroductionAs the Madiela platform carbonate developed, it loaded the gently gravitationally extending Ezanga salt, quickly creating a This has now been addressed using the power of modern To date, successful exploration for oil in the pre-salt play of heterogeneous pop-interpod geometry (Figure 2). In turn, multipleas the carbonate elimination platform strategies was and drowned careful velicity by prograding building clastic South Gabon has primarily focussed on the Early Cretaceous sequences from the west, these too loaded the salt, changingcontrol the on geometries pre-stack depth of the migration. grounding For pods the first and time creating the syn- and Gamba sandstone play. On the shelf, the shallow water discovery infilling turtle back structures. Reactive fall and dissolutionrift of saltis imaged, created revealing wide salt both welds Dentale betwe targetsen isolatedand intriguingly thin salt the diapirs. creaming curve in the Gamba play had begun to plateau pre-Dentale structures with no expression at Gamba level. These as explorersThis post reached-salt fabric the interpretaional is very heterogeneous limitations ofin thevelocity, and this has led to the majority of seismic, both 3D and 2D, being are particularly exciting as the lower syn-rift play has recently inadequateunable imagingto image of theavailable pre-salt seismic syn -resultingrift sequence. from complex been the target of very rewarding exploration offshore Congo to post-salt geology. However, recent developments in 3D seismic the south. The overlying Gamba sandstone sequence is seen to acquisition and processing has allowed a new level of imaging This has now been addressed using the power of modern varymultiple in thickness, elimination creating strategies extra volume and careful potential velicity in places building and control to be achieved in the pre-salt, offering to unlock the remaining on pre-stack depth migration. For the first time the syn-rift theis imaged potential, revealing for stratigraphic both Dentale traps in others.targets and intriguingly the pre- potential of the Gamba play and revealing a new system of Dentale structures with no expression at Gamba level. These are particularly exciting as the lower syn-rift play has recently traps and plays never before deliberately targetted; the intra been the target of very rewarding exploration offshore CongoThe toshallow the south. water TheMadiela overlying carbonate Gamba platform sandstone has high sequence porosity is syn-rift play. and reservoir potential generally at the platform margin edge. seen to vary in thickness, creating extra volume potential inWhilst places several and wellsthe potential in the area for have stratigraphic hydrocarbon traps shows in others.in the Pre-and Post-Salt Prospectivity Madiela Fm, we are now able to identify the platform margin A review of legacy data and historical operations records edge, identify karstified textures and de-risk the the petroleum allowed understanding of the geological and geophysical system at this interval. Indeed, the fidelity of the imaging of complexities previously faced by operators in Gabon, specifically the post-salt clastic systems (Cap Lopez Fm to Ewongue Fm) the challenge of resolving the pre-salt section due to velocity have revealed a new play system in the north of the area where heterogeniity in the post-salt Albian “Madiela” carbonate. pre-salt oil appears to be able to migrate into post salt. Multiple Integration of a pre-acquisition survey design study, efficient shoreface and channel sands ranging from 5-70m thick can be operations management [1], the use of long offset streamers

HGS – PESGB 17th Conference on Africa E&P 83

Figure 2. New 3D seismic PSTM sections demostrating pre- and post salt-targets in the shallow water South Gabon. FigureInset map 2. New shows 3D 3D seismic seismic PSTM location. sections demostrating pre- and post salt-targets in the shallow water South Gabon. Inset map shows 3D seismic location. identified from both seismic and well data which can be mapped attribute analysis. The new 3D in South Gabon is indeed a in combinationThe shallow structural/ water Madiela stratigraphic carbonate traps. platform has high porosityrevelation, and reservoir coincident potential with news generally of significant at the platform liquid margindiscovery edge. Whilst several wells in the area have hydrocarbon showsin the in pre-saltthe Madiela adjacent Fm, towe the are 3D now area. able It’s to time identify to re-appraise the platform Conclusion this exciting oil prone basin. n margin edge, identify karstified textures and de-risk the the petroleum system at this interval. Indeed, the fidelity of the To create a new creaming curve of discovery in South Gabon, requiresimaging either new of the technology post-salt (3Dclastic processing), systems ( Capnew geologicalLopez Fm to EwongueReferences Fm) have revealed a new play system in the north of plays (intrathe area syn-rift where plays) pre -saltor fresh oil appears access to to acreage. be able In to Southmigrate into[1] post Esestime, salt. Multiple P., Arti, shoreface L., Cvetkovic, and cha M.,nnel Rodriguez, sands ranging K., and from Gabon 5-in70m open thick acreage can webe haveidentified all three: from new both technology seismic and well dataHodgson, which can N., be (2017). mapped 3D in shallow combination water seismicstructural/ survey stratigraphic planning appliedtraps. in processing the 3D seismic has revealed for the first to deliver sub-salt imaging in South Gabon. First Break, 35, time significant intra- syn-rift tilted fault block structures, 85-89. heterogeneousCONCL GambaUSION distribution, undrilled Madiela structures with karstification textures and platform margin geometries [2] Esestime, P., Nicholls, H., Rodriguez., K., Hodgson, N. and (FigureTo 2), create and detailed a new wellcreaming correlation curve andof discovery reservoir in South Gabon,Arti, requires L., (2018). either Shallow new technology water Gabon (3D 3D:processing), Focused newprocessing mappinggeological are revealing plays undrilled (intra syn post-salt-rift plays) traps or freshas well access as an to acreage.images In Spre-outh and Gabon post-salt in open prospectivity. acreage we First have Break, all three 36, :55-60. new understandingtechnology of reservoir applied indisctribution processing usingthe 3D advanced seismic hasseismic reve aled for the first time significant intra- syn-rift tilted fault block structures, heterogeneous Gamba distribution, undrilled Madiela structures with karstification textures and platform margin geometries (Figure 2), and detailed well correlation and reservoir mapping are revealing undrilled post-salt traps as well as an understanding of reservoir disctribution using advanced seismic attribute analysis. The new 3D in South Gabon is indeed a revelation, coincident with news of significant liquid discovery in the pre-salt adjacent to the 3D area. It’s time to re- appraise this exciting oil prone basin.

REFERENCES

[1] Esestime, P., Arti, L., Cvetkovic, M., Rodriguez, K., and Hodgson, N., (2017). 3D shallow water seismic survey planning to deliver sub-salt imaging in South Gabon. First Break, 35, 85-89.

84 [2] Esestime, P., Nicholls, H., Rodriguez., K., Hodgson, N. and Arti, L., (2018). ShallowHGS – waterPESGB Gabon 17th Conference 3D: Focused on Africa E&P processing images pre- and post-salt prospectivity. First Break, 36, 55-60. Mik Isernia, Paul Endresen Bluware Ana Krueger University of Houston Data-driven Transformation in Geology, Geophysics and Engineering

The recent industry downturn has provided an opportunity to among many other things, in the ability to interactively handle unlock innovation to enable the industry to better compete in seismic data at full scale. the future and survive future down trends or other challenges. It is all about the data, and how it transforms into information Retaining all the data and information at every transformational as it flows from acquisition, to imaging, to attribute generation, step, and propagating the inherent uncertainty through the to reservoir modeling, dynamic simulation, and eventually to whole workflow, dramatically changes the way we work. decision making. Enabling this with a core technology optimized for random access and smart transformation of data makes new workflows Tangible technologies are the foundation to the success of that previously were regarded as impossible, possible. digitalization, from seismic processing, to interpretation, new Connecting workflows with smart data movement through reservoir simulators, analytics, and machine learning. Removing services with REST API’s, HPC, and cloudification transforms the limitations that plague traditional software enables us to the way workflows can be connected together, added to, and imagine workflows that were not conceivable before. One of enhanced. Eliminating the import and export of data saves those technologies is the modern Graphics Processing Unit time and money. Carrying multiple realizations of models (GPU). Modern GPUs have incredible potential to revolutionize through the workflow allows a deeper exploration of solutions the industry if they are combined with modern software to the challenges being tackled. Cloud data storage opens the architectures. Retrofitting old software with modern technology way for faster iteration on larger problems, problems which only delivers limited improvements, and this is the reason why cannot be solved in an acceptable time scale using data stored E&P’s have barely exploited the GPU potential. When we think in a traditional data management system. With the extreme about GPUs, the first thing that comes to mind that exemplify amounts of data being collected, Deep Learning will have an the best exploitation of the GPU power is the world of 3D unprecedented role to play in understanding and interpreting Gaming. We will cover the reasons why 3D Games have been the data, ultimately providing better decisions faster, and at a able to fully take advantage of GPUs, and show very tangible lower cost. n examples on the same approach applied to E&P, resulting,

HGS – PESGB 17th Conference on Africa E&P 85 Walter W. Wornardt PhD Micro-Strat, Inc., Houston, Texas Is Namibia Really An Oil Province? Is Namibia Really An Oil Province? Dr. Walter W. Wornardt Jr., Micro-Strat, Inc., Houston, Texas Dr. Marico Mello, a geochemist with HRT (a Brazilian company, Namibia, long neglected as an oil province, seems South America), stated he was determined to locate and to be in the perfect place for large oil discoveries. find oil in Namibia. He said that an overall understanding of After all Namibia is situated on the southwestern the geology of Namibia was needed, especially the detailed side of Africa and was originally tied to South chronostratigraphy, and identification and age of mature source America in the area of the oil rich country of Brazil. Is Namibia Really an Oil Province? rocks in many of the previous wells drilled in Namibia. After drilling thirteen wells, no commercial Walter W. Wornardt Ph.D., Micro-Strat Inc., Houston, Texas quantities of oil have been found in Namibia. We were assigned this project using eight of the previously Namibia is an under explored gas and potential oil Namibia, long neglected as an oil drilled wells in Namibia. This included wells drilled by Chevron province. Only thirteen wells have been drilledprovince, seems to be in the perfect place in the Orange Basin to the South, Shell in the Central area along the 1200km coastline. Most of these wellsfor large oil discoveries. After all Namibia Leuderitz Basin, Norsk Hydro, and the National Petroleum have source rocks and potential reservoirs, butis situated on the southwestern side of Africa and was originally tied to South Company of Namibia (NAMCOR, private co.) in the northern may not have a major seal, the key to a successful America in the area of the oil rich country Walvis Basin (Figure 2). oil discovery. of Brazil. After drilling thirteen wells, no commercial quantities of oil have been Our analysis of these eight wells included high resolution Dr. Marico Mello, a geochemist with HRT found (a in Namibia. Namibia is an under explored gas and potential oil province. biostratigraphy using calcareous nannofossils, planktonic Brazilian company, South America), stated he was determinedFigure 1. to locate and find oil in Namibia. He said Only thirteen wells have been drilled along foraminifera, benthic foraminifera, dinoflagellates and other that an overall understanding of the geology of Namibia was needed, especially the chronostratigraphy of the 1200km coastline. Many of these wells palynomorphs, paleobathymetry, and numerical age-dated the previous wells drilled in Namibia. We werehave assigned sourceNamibia, rocks this long andproject neglected potential using as reservoirs, an eightoil province, of the seems previously to be in Figure drilled 1 marker species correlated to the global cycle chart of Hardenbol wells in Namibia. This included wells drilled bybut Chevron maythe not perfect have in theaplace major Orange for seal, large the oilBasin key discoveries. to to a the After South, all NamibiaShell inis the 1998, et al., plus available geochemical information. These Central area Leuderitz Basin, Norsk Hydro, andsuccessful the Nationalsituated oil discovery.on Petroleum the southwestern These Company wells side are of Africaof Namibia and was (poriginallyrivate co.) located in the leases in (Figure 1). in the northern Walvis Basin. tied to South America in the area of the oil rich country of detailed biostratigraphic analysis and age-datable marker species related to the global cycle chart provide a regional Dr. MaricoBrazil. Mello, After adrilling geochemist thirteen with wells, HRT no (acommercial Brazilian quantitiescompany, of South America), stated he Our analysis of these eight wells included highwas resolution determinedoil have beenbiostratigraphy to locatefound inand Namibia. find with oil Namibiain calcareousNamibia. is an He under saidnannofossils, explored that an overall chronostratigraphic understanding of frameworkthe in Walvis Basin and Orange planktonic foraminifera, benthic foraminifera, dinoflagellatesgeologygas of and Namibia potential and was otheroil needed, province. palynomorph especially Only thirteen thes, detailedwells paleobathymetry have chronostratigraphy, been , Basin. andThe identificationdetailed chronostratigraphy is necessary to construct and age of mature source rocks in many of the previous wells drilled in Namibia. and numerical age-dated marker species correlated todrilled the globalalong the cycle 1200km chart coastline. of Hardenbol Many of these 1998, wells et have al., plus accurate time structure and seismic facies map and to ensure all geochemical information available. We weresource assigned rocks and this potential project reservoirs, using eight but of may the not previously have a major drilled wellsthat reservoir in Namibia. facies Thiswill be properly correlated regionally. includedseal, wells the keydrilled to a by successful Chevron oil in discovery. the Orange These Basin wells to arethe located South, Shell in the Central area Leuderitz Basin, Norsk Hydro, and the National Petroleum Company of Namibia (NAMCOR, These data provided HRT with an understanding of inthe the stratigraphic leases in (Figure position 1). of potential sandy reservoir These data provided HRT with an understanding of the private co.) in the northern Walvis Basin (Figure 2). stratigraphic position of potential sandy reservoir facies, facies, potential source rocks, detailed age and type of source rocks present in each well, plus the ability to correlate the same age rock including source rocks. Unconformities with missing stratigraphic sections potential source rocks, detailed age and type were identified. Changes in age versus paleobathymetry were identified and correlated to the major of source rocks present in each well, plus maximum flooding surface condensed section on the global cycle, to provide further clues to find and trace the ability to correlate the same age rock the source rocks in various basins in Namibia. These data were used by HRT in preparation for drilling the and same source rocks. Unconformities Wingat-1 well. with missing stratigraphic sections were identified and age-dated with the amount Pre-drilled expectations for the HRT Wingat-1, block 1911-07 in the Walvis Basin, northern Namibia were of time missing. Changes in age versus to test a seismic amplitude anomaly on a 3-D seismic well-defined elongated combination trap with 4-way paleobathymetry were identified and structural closure, to test the resource potential of the carbonate platform of Albian age at a depth of about correlated to the major maximum flooding 4000 meters. surface condensed section on the global cycle chart, to provide further clues to find, The Wingat-1 spudded March 25, 2004, in 1034 meters of water in the Walvis Basin, offshore Namibia. We correlate, and trace the source rocks in can confirm published information about the Wingat-1. The original total depth of the well was 4127 meters. various basins in Namibia. These data were We provided detailed biostratigraphic paleobathymetric, TAI, kerogen type, maturity, and generation used by HRT in preparation for drilling the information to HRT before they reached their initial TD depth of 4127 meters. With positive results below Wingat-1, Murombe-1 and Moosehead- 1500 meters the HRT consortium and Dr. Marico Mello decided to drill ahead. Like a true wildcatter, he 1wells (Figure 3 and 4). decided to drill to 5000 meters to test the presence of turbidite reservoirs and sample the mother source rocks in the Barremian shales. We were informed that the well had reached TD and to complete our report Wingat-1 on the well. Pre-drilled expectations for the HRT Figure Figure2. Namibia 2. Nambia Basins. basins. Wingat-1, (Figures 3 and 4) in the Walvis In May, 2004, it was announced that commercial amounts of top-quality oil were found in the Wingat-1 well 86 HGS – PESGB 17th Conference on Africa E&P in the Walvis Basin, Northern Namibia. Commercial quantities of oil were not available. Live oil was Our analysis of these eight wells included high resolution biostratigraphy using calcareous nannofossils, planktonic foraminifera, benthic foraminifera, dinoflagellates and other palynomorphs, paleobathymetry, and numerical age-dated marker species correlated to the global cycle chart of Hardenbol 1998, et al., plus available geochemical information. These detailed biostratigraphic analysis and age-datable marker species related to the global cycle chart provide a regional chronostratigraphic framework in Walvis Basin and Orange Basin. The detailed chronostratigraphy is necessary to construct accurate time structure and seismic facies map and to ensure that reservoir facies will be properly correlated regionally. These data provided HRT with an understanding of the stratigraphic position of potential sandy reservoir facies, potential source rocks, detailed age and type of source rocks present in each well, plus the ability to correlate the same age rock and same source rocks. Unconformities with missing stratigraphic sections were identified and age-dated with the amount of time Basin,missing. northern Changes Namibia inwere age to testversus a seismic paleobathymetry amplitude wereThe identifiedWingat-1 spudded and correlated March 25, 2004,to the located major in Block anomalymaximum on 3-D flooding seismic, surface a well-defined condensed elongated section combination on the global2212/07-1, cycle in 1034 chart, meters to provide of water furtherin the Walvis clue Basin,s offshore trapto find, with 4-waycorrelate, structural and closure, trace tothe test source the resource rocks potential in various Namibia. basins We in can Namibia. confirm mostThese of the data published were information ofused a carbonate by HRT platform in preparationwith a series of forprograding drilling carbonates the Wingat of about-1, Murombe the Wingat-1.-1 The and original Moosehead total depth-1wells of the well was Albian(Figure age 3 at and a depth 4). of about 4,100 meters. 4127 meters. We provided detailed biostratigraphy, marker species with numerical ages, paleobathymetry interpretations on a sample by sample basis, TAI, kerogen type, maturity, and oil generation information to HRT down to their initial TD depth of 4127 meters and total depth of 5000 meters. The carbonate reservoir was encountered as predicted but with much less porosity than anticipated. With increasing concentrations of hydrocarbon shows below 1500 meters the HRT consortium and Dr. Marico Mello decided to drill ahead. Like a true wildcatter, Marcio decided to drill to 5000 meters to test the presence of turbidite reservoirs and sample the mother source rocks in the Barremian FigureFigure 3. 3.Location Location Map ofMap HRT’s of Wingat-1,HRT's Wingat Murombe-1,-1, Murombe and the Moosehead-1,-1, and the Offshore Moosehead Africa -1, Offshoreshales. Africa We were informed that the well had reached TD and to complete our report on the well.

In May, 2004, it was announced that non- commercial amounts of high-quality oil were found in the Wingat-1 well in the Walvis Basin, Northern Namibia. Although this was the first live oil to be found in Namibia it was not found in commercial quantities. It seemed to be all there; the seal, the trap, sands, Aptian source rocks in the oil window that had generated light oil (38-42 gravity), a confirmed source potential; what was missing, the trap? In addition, there was minimum contamination and no water bearing zones Figure 4. 4.Location Location Map Mapof Wells of inWells Offshore in Offshore Namibia (Compliments Namibia (Compliments of ION basinSPAN, of ION2015). basinSPAN,identified. 2015). These results

HGS – PESGB 17th Conference on Africa E&P 87 Wingat-1 Pre-drilled expectations for the HRT Wingat-1, (Figures 3 and 4) in the Walvis Basin, northern Namibia were to test a seismic amplitude anomaly on 3-D seismic, a well-defined elongated combination trap with 4-way structural closure, to test the resource potential of a carbonate platform with a series of prograding carbonates of Albian age at a depth of about 4,100 meters.

The Wingat-1 spudded March 25, 2004, located in Block 2212/07-1, in 1034 meters of water in the Walvis Basin, offshore Namibia. We can confirm most of the published information about the Wingat-1. The original total depth of the well was 4127 meters. We provided detailed biostratigraphy, marker species with numerical ages, paleobathymetry interpretations on a sample by sample basis, TAI, kerogen type, maturity, and oil generation information to HRT down to their initial TD depth of 4127 meters and total depth of 5000 meters. The carbonate reservoir was encountered as predicted but with much less porosity than anticipated. With increasing concentrations of hydrocarbon shows below 1500 meters the HRT consortium and Dr. Marico Mello decided to drill ahead. Like a true wildcatter, Marcio decided to drill to 5000 meters to test the presence of turbidite reservoirs and sample the mother source rocks in the Barremian shales. We were informed that the well had reached TD and to complete our report on the well.

In May, 2004, it was announced that non-commercial amounts of high-quality oil were found in the Wingat-1 well in the Walvis Basin, Northern Namibia. Although this was the first live oil to be found in Namibia it was not found in commercial quantities. It seemed to be all there; the seal, the trap, sands, Aptian source rocks in the oil window that had generated light oil (38-42 gravity), a confirmed source potential; what was missing, the trap? In addition, there was minimum contamination and no water bearing zones identified. These results demonstrated the occurrence of several thin-bedded sandy reservoir facies saturated with 38-42 gravity light oil associated with two Aptian mature oil generating source rocks and an active petroleum system present in the Walvis Basin.

A major contribution from the Wingate-1 is the discovery of several high quality source rocks, in the oil generation window, rich in organic carbon, coupled with the IFA formation testing, of the recovered light oil from the same shale reservoirs penetrated in the Wingat-1. These source rocks generated liquid hydrocarbons of excellent quality at several depths. This seems to confirm the source potential for the immediate area and the Walvis Basin, and a new beginning of exploration in Namibia. The Wingat-1 well was plugged and abandoned in 2004, (Figure 5).

Further post drilling results from the Wingat-1 showed the presence of a number of systems in the Wingat-1: early Barremian Lacustrine to paralic, fluvial sediments; late Barremian to Aptian with mature shales as mature source rocks in the oil window, with the OAE1a, a major ocean anoxic event, that are associated with several thin sandy beds with light oil in the Aptian, (Figure 4).

deepwater fan system with a potential lowstand basin floor fan a thick sand with high porosity and permeability associated with lava flows. After our detailed analysis of cuttings samples, we dated the sediments in the well as Aptian/Barremian to lower Miocene, from 124.61Ma to 17.54 Ma, deposited in paleowater depth of shallow marine to middle Bathyal. Post drilling interpretation found the “basin floor fan” anomaly was related to lava flows with a fan like geometry, with intercalated carbonates (Figure 6). Although wet, this Baobob channel sand has an effective porosity of 17% and total porosity of 20%.

FigureFigure 5. 5. Regional Regional Tie-line Tie through-line through Wingat-1 Wingat and Murombe-1-1 and Muromb (Complimentse-1 (Compliments of AZINAM Namibia). of AZINAM Namibia).

Early Aptian to early Albian, restricted marine to increasing marine with calcareous shales and shallow to deeper marine sands. Followed by upper Albian to late Cenomanian deep marine sands and shales at the Cenomanian-Turonian unconformity, the OAE2 major ocean anoxic event at the CenomanianTuronian boundary. After completing the biostratigraphic analysis of the Wingat-1, we identified and recognized twelve age datable third order sequence boundaries and eleven age datable maximum flooding surfaces in 3360 meters from the Barremian to Eocene, in paleowater depth from transitional to middle bathyal (1500-3000 feet). The maximum flooding surfaces and their condensed sections are very important because they can be major seals, chronostratigraphic age datable mapping surfaces, defined by age datable nannofossil and foraminiferal abundance peaks associated with age datable marker species, as time lines that correlate to continuous reflectors on seismic. Murombe-1 with the established existence of mature source rock in the oil window and generated light oil of 38-42 gravity associated with recovered from oil in thin sandstones associated with this mature shale in the Wingat-1 confirming the source potential of the Walvis Basin in Namibia, HRT moved ahead with great anticipation to drill the next well, The Murombe - 1 Figurewell,Figure (Figures 6. 6. Enlarged Enlarged 3 seismic & 4).seismic section section showing showing the Wingat-1 the and Wingat the Murombe-1-1 and the wells Murombe in Walvis-1 Basin. wells (Compliments in Walvis Basin.of ION basinSPAN,(Compliments 2015) of ION basinSPAN, 2015) When these same source rocks and sands are located in similar situations the chance of demonstratedfinding the commercial occurrence of quantitiesseveral thin-bedded of oil is sandy much greaterBarremian than before to Aptian the with Wingat mature-1. shales as mature source rocks reservoir HRT'sfacies saturated second with objective 38-42 gravity in lightthe oilMurombe associated-1 wellin wasthe oil interpreted window, with asthe OAE1a,Santonian a major-age ocean sands anoxic in event, a with two Aptianconfined mature channel oil generating complex source with rocks high and amplitudean active that reflectors are associated and withlowstand several thinchannel sandy likebeds geometry.with light oil in petroleumSubsequentlyPost system drilling present weassessment in the analyzed Walvis Basin. ofthe this Murombe prospect-1 showedwell, thelocated Aptian,that Santonianin (Figure Block 4 ).2713/16-Age sands-1, the were second part of a low twstando wells lower drilled slope by HRT meandering in the Walvis channel Basin, turbidite located sand 15 kilometerschannel complex west of inthe deepwater. Wingat-1 well,The well A majordrilled contributionpenetrated to a total from a thickdepth the Wingate-1 water of 5729 wet is meters.the 35 discovery meter The ofnet Murombe sandHRT’s within-1 secondwas adrilled objectivethick to240 intest the meter an Murombe-1 anomaly, gross well section, a was interpreted with several highaverage quality porositysource rocks, of in18% the oilin generationa confined window, channel ascomplex. Santonian-age The sands sands in awere confined wet channeland considered complex with a rich in organicdry hole. carbon, The coupled associated with the IFAmature formation source testing, rocks highcould amplitude provide reflectors oil to theand lowstandlowstand channel sands like ingeometry. this of the recoveredchannel light system. oil from theThis same seems shale reservoirs to show that thePost late drilling Cretaceous assessment inof thisthe prospect Walvis showed Basin thatcan Santonian- also penetratedyield in the well Wingat-1. developed These highsource quality rocks generatedturbidite liquid sands Age (Figure sands 7).were part of a low stand lower slope meandering hydrocarbons of excellent quality at several depths. This seems channel turbidite sand channel complex in deepwater. The well to confirm the source potential for the immediate area and the penetrated a thick water wet 35 meter net sand within a thick Walvis Basin, and a new beginning of exploration in Namibia. 240 meter gross section, with average porosity of 18% in a The Wingat-1 well was plugged and abandoned in 2004, confined channel complex. The sands were wet and considered (Figure 5). a dry hole. The associated mature source rocks could provide oil to the lowstand sands in this channel system. This seems to show Further post drilling results from the Wingat-1 showed that the late Cretaceous in the Walvis Basin can also yield well the presence of a number of systems in the Wingat-1: early developed high quality turbidite sands (Figure 7). Barremian Lacustrine to paralic, fluvial sediments; late

88 HGS – PESGB 17th Conference on Africa E&P

Figure 7. Prospects in the Murombe-1 well Walvis Basin, Namibia After completing the biostratigraphic analysis of the Murombe-1 well, we identified and recognized a similar number of the same age datable maximum flooding surfaces as recognized the Wingat-1 well. We dated the sediments in this well to 3360 meters as Barremian to Eocene, in paleowater depth from transitional to middle bathyal (1500-3000 feet). The maximum flooding surfaces and their condensed sections are very important because they can be major seals and points of accurate correlation on logs and seismic. Figure 6 shows the location and stratigraphic position of the potential reservoirs of the Wingat-1 and Murombe-1 wells, in the Walvis Basin, offshore Namibia. Figure 7 shows the prospects drilled in the Murombe-1 after Namcor.

Moosehead-1 After completing the Murombe-1 well, we analyzed the third and final in the HRT series of wells in Namibia, the Moosehead-1 well, drilled in the Orange Basin, (Figures 3 & 4 ) South of the Wingat-1 and Murombe-1 in the Walvis Basin. The well was drilled in 1716 meters of water in offshore Namibia, to a total depth of 4170 meters. The original objective of this well was to test the equivalent age reservoir as in Brazil, the ‘pre-salt’ reservoirs; Barremian age carbonate reservoirs in a large 4-way dip closure. The Moosehead-1 results were somewhat similar to the FigureFigureWingat 8. Pre-drill Pre--drill1, interpretation without interpretation oil. of The the of Moosehead-1well the penetrated Moosehead Prospect, 100- 1Walvis Prospect,meters Basin. of (after Walviscarbonates, Namcor) Basin. but (after with Namcor) less porosity than was expected. Two or more potential source rocks were encountered with wet gas shows Moosehead-1(Figures 8 & 9). recognized a similar number of the same age datable maximum After completing the Murombe-1 well, we analyzed the flooding surfaces as recognized in the Wingat-1 and Murombe-1 third and final in the HRT series of wells in Namibia, the well. We dated the sediments in this well to 3360 meters as Moosehead-1 well, drilled in the Orange Basin, (Figures 3 and Barremian to Eocene, in paleowater depth from transitional 4) South of the Wingat-1 and Murombe-1 in the Walvis Basin. to middle bathyal (1500-3000 feet). The maximum flooding The well was drilled in 1716 meters of water in offshore Namibia, surfaces and their condensed sections are very important to a total depth of 4170 meters. The original objective of this well because they can be major seals and points of accurate was to test the equivalent age reservoir as in Brazil, the ‘pre-salt’ correlation on logs and seismic. Figures 4 & 6 shows the location reservoirs; Barremian age carbonate reservoirs in a large 4-way and stratigraphic position of the potential reservoirs of the dip closure. The Moosehead-1 results were somewhat similar Wingat-1 and Murombe-1 wells, in the Walvis Basin, offshore to the Wingat-1, without oil. The well penetrated 100 meters Namibia. of carbonates, but with less porosity than was expected. Two or more potential source rocks were encountered with wet gas The source rock and presence of a petroleum system in the shows (Figures 8 and 9). Walvis Basin is now fact. The established existence of thick restricted marine Aptian mature source rock in the oil window After completing the biostratigraphic analysis of the in the Murombe-1 and Wingat-1 and the DSDP 351 well Moosehead-1 in the Orange Basin, 2713/16-1, we identified and offshore is also fact. The recovery of the light oil 38-42 gravity Figure 8. Pre-drill interpretation of the Moosehead-1 Prospect, Walvis Basin. (after Namcor) HGS – PESGB 17th Conference on Africa E&P 89 in thin sandstones associated with Aptian mature shales in the much greater than before the Wingat-1 and Murombe-1 wells Wingat-1 is fact. These facts confirm an increased potential for were completed. It looks like a bright future for Namibia with well-developed oil reservoirs in the Walvis Basin in Namibia. all the potential reservoir sands, especially in the Walvis Basin When these same source rocks and sands are located in similar (Figure 10). n situations the chance of finding commercial quantities of oil is

Figure 9. ION basinSPAN seismic line through Moosehead-1, Orange Basin (Compliments of ION basinSPAN) Figure 9. ION basinSPAN seismic line through Moosehead-1, Orange Basin (Compliments of ION basinSPAN)

After completing the biostratigraphic analysis of the Moosehead-1 in the Orange Basin, 2713/16-1, we identified and recognized a similar number of the same age datable maximum flooding surfaces as recognized in the Wingat-1 and Murombe-1 well. We dated the sediments in this well to 3360 meters as Barremian to Eocene, in paleowater depth from transitional to middle bathyal (1500-3000 feet). The maximum flooding surfaces and their condensed sections are very important because they can be major seals and points of accurate correlation on logs and seismic. Figures 4 & 6 shows the location and stratigraphic position of the potential reservoirs of the Wingat-1 and Murombe-1 wells, in the Walvis Basin, offshore Namibia.

The source rock and presence of a petroleum system in the Walvis Basin is now fact. The established existence of thick restricted marine Aptian mature source rock in the oil window in the Murombe-1 and Wingat-1 and the DSDP 351 well offshore is also fact. The recovery of the light oil 38-42 gravity in thin sandstones associated with Aptian mature shales in the Wingat-1 is fact. These facts confirm an increased potential for well-developed oil reservoirs in the Walvis Basin in Namibia. When these same source rocks and sands are located in similar situations the chance of finding commercial quantities of oil is much greater than before the Wingat-1 and Murombe-1 wells were completed. It looks like a bright future for Namibia with all the potential reservoir sands, especially in the Walvis Basin (Figure 10).

Figure 10. Summary of occurrences of reservoir sands in Namibia (after Namcor) Figure 10. Summary of occurrences of reservoir sands in Namibia (after Namcor)

References 90 Azinam Namibia, Exploring Offshore Namibia, Brochure withHGS –Regional PESGB 17th Tie Conference-line Through on Africa WingatE&P and Murombe to Pel 34 3D.

HRT America Inc, High Resolution Biostratigraphy and Visual Source Rock Analysis of the HRT Murombe 01 Well, Block 2212/06-01 in Offshore Namibia, Africa, MICRO-STRAT INC., Houston, Texas, 2014.

Galp, Exploration and Production, Press Release, Wingat-1 Exploration Well Results, Galp Energie, May 2013.

HRT America Inc, High Resolution Biostratigraphy and Visual Source Rock Analysis of the HRT Wingat-01 Well, Block 2212/07-01 in Offshore Namibia, Africa, MICRO-STRAT INC., Houston, Texas, 2014.

HRT America Inc, High Resolution Biostratigraphy and Visual Source Rock Analysis of the HRT Moosehead-01 Well, Block 2713/16-01 in Offshore Namibia, Africa, MICRO-STRAT INC., Houston, Texas, 2014.

Hodgson, Neil, Spectrum Geo Ltd., Deepwater Turbidites Offshore Namibia Shown to Provide High-Quality Reservoir Sands, Geology & Geophysics, Offshore, April, 2017, pp. 30-31. Offshore Energy Today, Press Release, HRT Announces Sub-Commercial Oil Discovery Offshore Namibia, May, 2013, pp.1-3.

Offshore Energy Today, Press Release, Dry Well for HRT Offshore Namibia, September, 2013, pp. 1-3. Biographical Sketch References Biographical Sketch Azinam Namibia, Exploring Offshore Namibia, Brochure with Walter W Wornardt PhD Walter W Wornardt Ph.D. is President, MICRO-STRAT, Inc, Houston, Regional Tie-line Through Wingat and Murombe to Pel 34 3D. is President, MICRO- STRAT, Inc, Houston, Texas. Texas. Professional Geologist, Seismic Sequence Stratigrapher, and HRT America Inc, High Resolution Biostratigraphy and Visual Professional Geologist, Seismic Micropaleontologist. Born in Milwaukee, B.S. and M.S. Geology Source Rock Analysis of the HRT Murombe 01 Well, Block Sequence Stratigrapher, 2212/06-01 in Offshore Namibia, Africa, MICRO-STRAT INC., and Micropaleontologist. University of Wisconsin, Madison. Ph.D. Paleontology University of Houston, Texas, 2014. Born in Milwaukee, B.S. and California, Berkeley. Worked with Chevron; Esso Production M.S. Geology University of Galp, Exploration and Production, Press Release, Wingat-1 Wisconsin, Madison. Ph.D. Research, Houston, Unocal Research, California, Chairman of Exploration Well Results, Galp Energie, May 2013. Paleontology University of Geology - University Redlands, California. 1983-present, MICRO- California, Berkeley. Worked HRT America Inc, High Resolution Biostratigraphy and Visual with Chevron; Esso Production STRAT, Inc, Houston, TX and 8+ Cairo, Egypt. With Peter R Vail, Source Rock Analysis of the HRT Wingat-01 Well, Block Research, Houston, Unocal Ph.D. 1988, initiated well-log seismic sequence stratigraphic analysis, 2212/07-01 in Offshore Namibia, Africa, MICRO-STRAT INC., Research, California, Chairman of Geology - University Houston, Texas, 2014. Redlands, California. 1983-present,taught MICRO-STRAT, 41 courses Inc, worldwide; projects in Africa, South America and Far East. 2008 -present, 7 Houston, TX and 8+ Cairo, Egypt. With Peter R Vail, Ph.D. 1988, HRT America Inc, High Resolution Biostratigraphy and Visual initiated well-log seismic sequenceyears stratigraphic in unconventionals: analysis, taught Eagle Ford, Eaglebine, Haynesville, Niobrara, Utica, West Texas, Source Rock Analysis of the HRT Moosehead-01 Well, Block 41 courses worldwide; projectsPoland in Africa, South, and America Saudi and Arabia. Registered Geologist in state(s) CA-076 and TX-5638. Member of 2713/16-01 in Offshore Namibia, Africa, MICRO-STRAT INC., Far East. 2008 -present, 7 years in unconventionals: Eagle Ford, Houston, Texas, 2014. Eaglebine, Haynesville, Niobrara,AAPG, Utica, West SEG, Texas, Poland,and andHGS . Saudi Arabia. Registered Geologist in state(s) CA-076 and TX- Hodgson, Neil, Spectrum Geo Ltd., Deepwater Turbidites 5638. Member of AAPG, SEG, and HGS. Offshore Namibia Shown to Provide High-Quality Reservoir Sands, Geology & Geophysics, Offshore, April, 2017, pp. 30-31.

Offshore Energy Today, Press Release, HRT Announces Sub- Commercial Oil Discovery Offshore Namibia, May, 2013, pp.1-3.

Offshore Energy Today, Press Release, Dry Well for HRT Offshore Namibia, September, 2013, pp. 1-3.

McDermitt, Ken, Gilbert, Elizabeth, Gillbard, Clark, Nicole, From Basalt to Skeletons – the 200 million Year History of the Namibian Margin on Covered by New Seismic Data, ION PSTM Data from The NamibiaSPAN Survey, First break, Special Topic Fb, Geology and Basins, vol. 33, December, 2015, p. 77- 85.

Negonga, Martin, Acreage Portfolio of Namibian Sedimentary Basins, National Petroleum Corporation of Namibia (PTY) LTD, Presented at AAPG Annual Convention, International Pavilion Theatre, Houston, April 14 2014.

Petroleum S&P Global, Pratts, Press Release, HRT suffers Namibian Setback as Murombe-1 Exploration Well Comes Up Dry, London (Pratts) July 2013.

HGS – PESGB 17th Conference on Africa E&P 91 Syed Dabeer and Dr. Umar Ngala Petro-Vision Energy Services, London, UK The Influence of Shale Ridges on Reservoir Development and Implications for Exploration A Case Study from Onshore Niger Delta, Nigeria

Nigeria is the largest oil and gas producer in West Africa. Nearly help of seismic interpretation. The visual blending of seismic all the country’s production is coming from Agbada-Akata attributes was used to qualitatively interpret the top of shale petroleum system of the Niger Delta (Michele et al. 1999). The ridges. The fault pattern from many interpreted horizons source rock for this petroleum system is in the marine shales of was overlaid on the map of shale ridges to understand the Akata and Agbada Formations. The hydrocarbon reservoirs are relationship between faults and shale ridges. It was observed that within the paralic sequence of Agbada Formation (Short and major structure-building faults are located on the basinward side Stäuble. 1967 and Evamy et al. 1978). The age of reservoirs in of shale ridges. It was interpreted that the shale ridges provided the zone of interest is Middle to Late Miocene. The study area the weak zones for the initiation of structure-building faults. is located in the Eastern Niger Delta where eight commercial Based on structure-building faults and shale ridges, the study fields have been discovered. All the fields were discovered using area was divided into three megastructures. Each megastructure 2D seismic data, mostly in the 1960’s and 1970’s. Over 100 wells contains one megasequence. The influence of shale ridges on have been drilled in the block and most of the wells pre-date the the tectonostratigraphic evolution of the study area is shown in 3D seismic data used in the current study. The “G” field is the Figure 1. largest and started producing in the 1970s. It has 500+ MMSTB cumulative oil and about 1Tcf cumulative gas production. The The reservoirs in the Niger Delta are generally believed to be “B” field is the smallest and started producing in the 1990’s. It localised in extent. It was observed that this is not always true. has about 3 MMSTB cumulative oil and 3 Bscf cumulative Gas The reservoirs in a few fields were found to be quite extensive. production. All fields have multiple reservoirs and still have Few reservoirs could be correlated across four fields or extended unproduced resources. 40 Km across (limited by the extent of 3D seismic). The extent of an individual reservoir is controlled by the presence of shale Three unsuccessful exploration wells have also been drilled in ridges in all directions. If a shale ridge is present between two this block. The presence and the quality of reservoir have been fields then it was not possible to correlate the reservoirs across poor in all unsuccessful wells and considered as a major risk. those two fields. On the other hand, if there is no shale ridge This paper investigated the controls on reservoir development present between fields then the reservoirs can be extended to and hence the reasons for the inferior quality of the reservoirs in larger distances. It was observed that the dry wells, Well-1 and the dry wells. Well-2, were located just landward of the top of shale ridge or structure-building fault (Figure-1). The paralic sequence of A shale ridge is a depositional feature. It is formed of under- Agbada Formation was very shaly in both the wells. The Agbada compacted sediments and located at the distal edge of a Formation in well F-13 contained more sand and was located depocenter or megasequence. The shale ridges influence the on the seaward side of a shale ridge. All successful exploration tectonostratigraphic development and deposition of Agbada wells were drilled on the basinward side of a shale ridge and reservoirs in Niger Delta. Faults are initiated when high density encountered good reservoirs. This was interpreted to be the sands of subsequent megasequences are deposited on top of a result of variable subsidence. The basinward side of a shale ridge shale ridge (Evamy et al. 1978). Shale ridges mark the boundary would see higher subsidence due to growth along a structure- of an individual depocenter, and considered as top of the Akata building fault and hence coarser facies would be focussed there. Formation. It is not possible to map the top of a shale ridge as On the other hand, the distal end of a megasequence experiences no single event marks its top. A paralic sandy event (in Agbada less subsidence and would receive finer sediments while Formation) changes into shaly marine sediments (of Akata sedimentation is ongoing in a megasequence. Based on this Formation) on top of a shale ridge. observation, the areas just landward of the top of shale ridges are considered to have a much higher risk of reservoir as compared An excellent quality merged 3D seismic survey (around 1000 to the wells located on the basinward side. Km2) was used to do a detailed interpretation of 39 reservoirs from 7 fields. The interpretation was extended to neighbouring The integration of seismic interpretation, well logs, and fields. The well logs were correlated, where possible, with the petrophysics strongly suggest that shale ridges are one of the

92 HGS – PESGB 17th Conference on Africa E&P are considered to have a much higher risk of reservoir as compared to the wells located on the basinward side.

The integration of seismic interpretation, well logs, and petrophysics strongly suggest that shale ridges are one of the strongest influences on the development of reservoirs in the study area. The top of a shale ridge may be a good structural location but it is not a favourable for encountering a good reservoir in the Niger Delta.

Well-1 & 2 D Mega Structure N (f) Today S G Mega Structure F-13 F1 F2

(e) G Reservoir-2 Time Rd~Rs

(d) G Reservoir-1 Time Rd>Rs

(b) D Reservoir-1 Time Rd~Rs

(a) Start of Agbada S (Basinward) Rd>Rs N (Landward)

Shale Ridge F1

Figure-1: (a) Figureto (f) Tectonostratigraphic1. (a) to (f) Tectonostratigraphic development development of the ofarea the ofarea interest. of interest. The The delta delta showed showed progradation when rate ofprogradation deposition (Rd)when surpassesrate of deposition rate of(Rd) subsidence surpasses rate (Rs) of andsubsidence aggradation (Rs) and when aggradation Rate of deposition (Rd) is equal to rate of subsidence (Rs). The structure-building fault, like F2, is located toward the basinward when Rate of deposition (Rd) is equal to rate of subsidence (Rs). The structure-building fault, side of a shale ridge. like F2, is located toward the basinward side of a shale ridge. References: strongestEvamy, influences B.D., on Harembourethe development, J., of Kamerling,reservoirs in the P., Knaap,Biographical W.A., Molloy, Sketch F.A. and Rowlands, P.H. 1978. study area.Hydrocarbon The top of habitat a shale ridgeof Tertiary may be Niger a good Delta. structural AAPG Bulletin,Syed Dabeer 62, 1-39. has an MSc in location but it is not a favourable for encountering a good petroleum geoscience from reservoirMichele in the NigerL. W. Delta.Tuttle, n Ronald R. Charpentier and MichaelRoyal E. Brownfield. Holloway University The Niger Delta Petroleum System: Niger Delta Province, Nigeria, Cameroon, and Equatorialand Guinea, a bachelor’s Africa. degree in References Short, K. C. and Stäuble, A. J. 1967, Outline of Geologygeophysics. of Niger HeDelta. worked AAPG in Bull, 51, 761-779. Evamy, B.D., Haremboure, J., Kamerling, P., Knaap, W.A., Molloy, various exploration and F.A. and Rowlands, P.H. 1978. Hydrocarbon habitat of Tertiary reservoir geoscience roles in Niger Delta. AAPG Bulletin, 62, 1-39. Eni and Schlumberger from 2001 to 2013. He is presently Michele L. W. Tuttle, Ronald R. Charpentier and Michael E. working in Petro-Vision and Brownfield. The Niger Delta Petroleum System: Niger Delta based in London, UK. He has Province, Nigeria, Cameroon, and Equatorial Guinea, Africa. worked in a variety of projects in West Africa, Pakistan, Short, K. C. and Stäuble, A. J. 1967, Outline of Geology of Niger Northern Europe and the Gulf of Mexico. His areas of expertise Delta. AAPG Bull, 51, 761-779. are exploration geoscience, reservoir characterization and production geology. His current interests are the identification of the new plays in frontier basins and application of geoscience techniques to reduce the prospect risk.

HGS – PESGB 17th Conference on Africa E&P 93 Sadat Sembatya Makerere University, Kampala, Uganda Evolution of East African Rift System (EARS)

The East African Rift System (EARS) is a Tertiary intra- resulted in earthquakes and volcanic activity. Consequently, continental rift system which developed along the Precambrian there was down thrusting of the hanging wall to form graben orogenic belt of the African craton and is comprised of linked structures. intra-continental rift basins. The ongoing extension along the rift zone reaches about 5-10mm per year (Skobelev et al 2005), The evolution of the Eastern Rift (Kenya Rift) directly adjoining 3500km long and 50-150km wide. the Afar triple junction began at 30Ma BP with initial fracturing in the Afar region and the Ethiopian plateau, which was followed The system is comprised of some 30 discrete basins, mainly by first volcanism in the Kenya Rift at 20Ma BP (Chorowicz; half-grabens, which differ substantially in their structural style, Ebinger 1989; Morley 2002). For the Western Rift branch, fills, and geological history. There are two dominant trends; the however, thermal updoming and first distributed faulting did eastern and western branches. The Eastern branch, initiated in not begin earlier than in Early Miocene time, and volcanism early Eocene/Oligocene (~30 Ma), with lakes i.e. L. Turkana, is commenced in the middle Miocene (dated 12.6 Ma in the more volcanic while the Western branch, initiated during the northern Virunga province; Bellon and Pouclet 1980; Calais et al. Late Miocene (10 Ma), contains lakes e.g. Lake Albert, Malawi, 2006; Chorowicz 2005; Ebinger 1989). and Tanganyika, and is less volcanic. Evaluation of the rift basins for hydrocarbon potential shows At a large scale, the topography of the EARS is characterized variations in prospectivity is a result of tectonic control and by the Afar and Kenya/east African domes which are separated sedimentation styles. Widespread lacustrine source rocks with by the Turkana depression (~600m). The Afar dome elevation good TOC quality have been encountered in drilled wells and is approximately 1500m while the Kenya/East African dome surface formations, i.e. Ngorora formation in the central Kenyan is approximately 1200m. Both domes have diameters of about rift (Amoco data). Oils from lacustrine sources are commonly 1000km and are associated with negative gravity anomalies. waxy, have lower sulfur content, and tend to be higher quality Away from these areas, the topography ranges from 300-900m. refining oils than marine sourced oils, and similar occurrences are noted in the Lokichar basin, Albertine graben, among others. The EARS was formed by impingement of a thermal plume on Reservoir units are sandstones and normal faults form the major the lithosphere, which resulted in crustal thinning and uplift. structural traps. n These culminated in fracturing of the brittle crust, and faulting

94 HGS – PESGB 17th Conference on Africa E&P Magenta McDougall African Petroleum The Next Phase of Exploration in Sierra Leone: A Closer Look at the Basinward Cretaceous Plays in the Search for Improved Reservoir Quality

The exploration pendulum has veered to the negative side Is the answer to target younger and shallower reservoirs or after disappointing drilling results along the West African better reservoir facies downdip? How does onshore geology Transform Margin (WATM). Industry common belief states that affect reservoir quality in the basin? How do tectonics and uplift reservoir quality is ‘non-commercial’ throughout Liberia and impact sediment source areas and the resultant reservoir? How Sierra Leone, but thorough geological work suggests something does burial diagenesis vary for different reservoir compositions? different. Integrating key well results, reservoir provenance, and An investigation into these controls brings a more balanced tectonostratigraphic framework provides strong evidence that perception of reservoir variability within the Cretaceous from there is abundant high quality reservoir in Sierra Leone in the the Albian to the Campanian. The next phase of Sierra Leone Upper Cretaceous. As more wells are drilled along the WATM, exploration will target the best quality reservoir to achieve simplistic rule of thumb methods for screening acreage do not commercial flowrates and true Biographicalvalue creation. n Sketch apply. Where the younger, cleaner sands have been penetrated, charge and trap risk have been high, with shows but no Biographical Sketch Magenta McDougall is a geoscientist with a keen interest in commercial hydrocarbons. By looking at more distal lowstand Magenta McDougall is a reservoir quality along the West African Transform Margin. Her systems, there is evidence for proximal hydrocarbon migration geoscientist with a keen interest and apparent amplitude anomalies. in reservoir quality along work in the region began in 2014 with her MSc thesis- exploring the West African Transform the controls on reservoir quality in Cretaceous fan systems Older and deeper reservoirs should not be discounted as these Margin. Her work in the offshore Liberia. Since then she has worked on exploration and are often attractive targets from a charge and trap perspective. region began in 2014 with her Structural and stratigraphic trapping mechanisms set up MSc thesis – exploring the appraisal assets in Cote d’Ivoire, Tanzania, and Sierra Leone. from syn-rift faulting provide robust closures for syn-rift and controls on reservoir quality Prior to working on African assets, Magenta worked on North Sea younger sediments. Differing combinations of sorting, grain in Cretaceous fan systems exploration. Magenta hold an MSc from Imperial College London size, provenance, and burial diagenesis lead to different reservoir offshore Liberia. Since then she and a BSc from Royal Holloway, University of London. quality outcomes. Existing wells have generally been drilled has worked on exploration and in up-dip positions, located a reasonable column height down appraisal assets in Cote d’Ivoire, from the interpreted reservoir pinch-out. In these locations, Tanzania, and Sierra Leone. bypass, poor sorting, and cementation have often resulted in Prior to working on African assets, Magenta worked on North poor reservoir quality in the up-dip areas. As exploration to date Sea exploration. Magenta hold an MSc from Imperial College has been in shelfal/slope positions, there is little data from these London and a BSc from Royal Holloway, University of London. basin floor reservoirs in this region. New depositional and burial diagenesis models indicate that provenance, abrasive processes during sediment transport, and reservoir temperature history are the key controls on reservoir quality. Sierra Leone straddles a transform system creating a wider shelf to the north-west of the country. Previous wells have been drilled on a narrow shelf in shallower water. By looking at channels leading from the wider shelf with longer sediment residence time, in addition to re- working of older sediments, a compelling reservoir quality story emerges which has not been explored to date.

HGS – PESGB 17th Conference on Africa E&P 95 Neil Hodgson and Karyna Rodriguez Spectrum Geo Ltd, Woking, United Kingdom An Atlas of Character: A Model For the Control of Passive Margin Development

Introduction representing final syn-rift sedimentation whilst sub-areal flood As the long offset and long record length 2D seismic library basalts of pre-early drift are erupting) to clastic-poor outboard acquired over the world’s continental passive margins increases, produced during drift and early oceanic crust formation. so the key physical characteristics, and the variations therein, of Magma poor margins apparently display no flood basalts and these margins are being revealed. Three key characteristics are; outboard of the final continental crust fragments either transit 1) The nature of the continental crust to oceanic crust transition: into oceanic crust directly or exhumed mantle then oceanic abrupt continental margins to hyper-extended margins, and the crust. The amount of subaerial and submarine magmatism is asymmetry of the conjugates, 2) Magmatism: magma rich with clearly a function of relative sea level; we propose a model for Seaward Dipping Reflectors (SDRs) to magma poor margins, undulations along-rift in a syn-rift setting [1]. and 3) Stability of the passive margin fill through time. Each of these endmember series display localized variation on the Stability of Clastic to Passive Margin Basins basin and margin scale and indeed some are observed as part of The variation in stability of margins as expressed by continuums, others are binary distributions. gravitationally driven structures – mass transport systems, megaslides, conformable prograding clastic sequences, and lobe This presentation will take the form of a review of a number of switching varies conspicuously between adjacent basins and modern 2D long offset seismic lines from Africa passive margins through time in a given basin. This can be considered a result illustrating these characteristics and making observations of local sedimentary or tectonic processes, but when taken in the about the associations of these characteristics. The number whole a pattern of behavior is observed that allows such periodic of basins illustrated comprises an atlas of African passive and individual behavior to be seen as an expression of a global margins, comprising lines extending from the shelf and the model [2]. The consequences of the global model are discussed in continental crust, out to the oceanic crust, offering a chance to terms of dynamic topography, plate tectonics, and global sea level. compare and contrast the influence of these key characteristics on each margin, and observe the degree of variation between Conclusion them. For each of the three key characteristics a model will be To conclude, a simple model of global dynamic topography is presented that offers an explanation for why that characteristic introduced that provides a mechanism for both the formation endmember, and continuum set if appropriate, has developed. In of, and the variation in, all of the three key characteristics on conclusion we argue that one model can satisfy the observations passive margins. The simple model provides a global solution on all the characteristics. to several issues in continental rifting understanding: the continental margin architecture issue (abrupt-hyperextension), Nature of Continental to Oceanic Transition the asymmetry issue, and the magmatism issue. A further Abrupt continental margins have narrow zones of transition consequence of this model is that firstly, the generally carried separating oceanic crust from thick (>30km) continental crust, model for tectonic plate movement is compromised, and a and are often associated with SDRs, whilst hyper-extended control on coastal onlap that is specific to each basin is proposed. margins display fragments of extension and shear thinned Consequently, Global Sea Level (GSL) curves constructed on the continental crust drawn out far from the shelf and are not basis of coastal onlap may therefore represent a collation of local associated with SDRs [1]. Indeed, the latter margins often relative sea level observations, yet statistically the actual GSL display a zone of exhumed mantle between the final continental may only be observable in a minority of basins. n crust fragments and oceanic crust. We propose a model where variation in abruptness of a margin along-rift relates to variation Conferences in heat from mantle during rifting. This model suggests that [1] Hodgson, N., and Rodriguez, K., 2017. Shelf stability and asymmetric conjugate margins are to be expected. Mantle Convection on Africa’s Passive Margins (Part 1). First Break, 35 (3), 93-97. Magmatism Magma rich margins display wide zones of SDRs comprising [2] Hodgson, N., and Rodriguez, K., 2018. Toward the global largely flood basalts but varying from clastic-rich (often inboard tectonic model: A new hope (part 2). First Break, 36 (2), 77-80.

96 HGS – PESGB 17th Conference on Africa E&P David Connolly dGB Earth Sciences USA LLC ([email protected]) Visualization of Vertical Hydrocarbon Migration Pathways in Seismic Data: theToward success rate wasthe above Quantification 90%. We have applied this modelof Seal on a worldwide and basisCharge and gotten Risk similar results (Connolly et al, 2013). We also extended the classification to analyze charge risk, by looking at the morphologyfor ofAfrican chimneys immediately Exploration below the objective Plays reservoir.

This vertical hydrocarbon migration is often directly detected in the seismic record as zones of vertically chaotic, low energy data response called gas chimneys, blowout pipes, gas clouds, or mud volcanoes based on their morphology, rock properties, and flow mechanism. We will describe these features as “chimneys”, although they can be very widespread. They are associated with both oil and gas migration. Because of their diffuse character, these “chimneys” are often difficult to visualize in three dimensions. Thus, a method has been developed to detect these features using a supervised neural network. The result is a “chimney” probability volume. However, not all chimneys detected by this method will represent true hydrocarbon migration. Therefore, the neural network results must be validated by a set of criteria. Based on these criteria, reliable chimneys can be extracted from 3D seismic data as 3D geo-bodies. These chimney geo-bodies, which represent vertical hydrocarbon migration pathways, can then be superimposed on detected reservoir geo-bodies, which indicate possible lateral migration pathways and traps. The results can be used to assess hydrocarbon charge efficiency or risk, and top seal risk for Figure 1. Chimney Atlas for Africa. Stars are proprietary studies. identified traps. The amount of these chimneys directly below Figure 1. Chimney Atlas for Africa. Stars are proprietary studies. Well symbols indicate entries in Well symbols indicate entries in Atlas. Basin symbol indicates the reservoir geo-body provide an assessment of the charge risk, Aareastlas with. Basin published symbol studies. indicates areas with published studies.while the morphology of the chimneys above a reservoir provide an assessment of the top seal risk. ToA survey improve of major the exploration quantification companies suggests of top that seal seal and charge risk assessment, a Chimney Atlas (https://dgbes.com/chimney_atlas)and charge provide the majority of risk in today’s is beingconventional compiled How over can known this risk beoil quantified? and gas Adiscoveries study of 100 traps. The in the Atlasexploration also portfolio. includes Seal dry is a holes,major cause which of failure tested along valid the structuresNorwegian with North effective Sea was reservoir. undertaken Thus,(Heggland, the 2013) well to assess failedWest Africa either Transform from a margin, lack of and charge charge isor also seal. a significant We will showtop exa seal mplesfailure, sincefrom charge Africa, was which not a significant are currently risk in the area. risk. Traditional tools for assessing top seal such as capillary in the Atlas (Figure 1). One example from West AfricaAll traps is a contained commercial effective ga reservoirs,s field (Figureand were 2well). imaged.A pressure measurements of the sealing shales are often not Thus seal was considered the major risk. Traps, associated with Seismic section near the crest of the drilled structural anticline showed a subtle broad diffuse gas available over the structure being drilled. Shales with excellent chimneys, were divided into three classes: Class A had a leaking cloudcapillary (yellow) pressures, oversuch as the we mainobserve reservoir in offshore interval Nigeria, can(Connolly fault atet the al., crest 2013) of the. Thistrap (based trap onis faultclassified related chimneysas a over “Gasstill be Clveryoud leaky. Trap” Cross-fault (Class leakage C), indicating can be assessed a high with probability the ofcrest) effective and often seal contained underlying minor volumesthe gas of cloud. hydrocarbons; ChimneysAllen Diagrams related and Smear to underlying Gouge Ratio thrustsassessment. may However, provide chargeClass B intohad leakage the reservoir. on the flank These of the arestructure; classified Class C had asthe inputs“Direct (borehole Charge breakout Trap s”and. pressureExcess data) pressure needed foris theassociated hydrocarbons with both both thein the overlying reservoir and and in theunderlying cap rock (based on assessment of up-fault leakage along critically stressed faults, are chimneys. While current chimney studies have focuseda diffuse on thegas cloud offshore over the basins, structure). the A successtechnology rate for drilled not available in frontier settings. Basin models are an important traps with no chimneys was 46%. The success rate for traps with can also be applied to onshore seismic data. Studies from the Anza Graben of onshore Kenya tool for assessing hydrocarbon charge, but are often poorly associated chimneys was 78%. If the trap classification was used, (Baranovaconstrained. Improving et al., the 2012) quantification and the of Orientethese risks Basincan of avoiding Ecuador the demonstrateClass A traps, the thesuccess potential rate was above of the 90%. We technologyhave a significant in bothimpact rift on andthe expected foreland value basins. for exploration have applied this model on a worldwide basis and gotten similar opportunities. results (Connolly et al, 2013). We also extended the classification Additional case studies of drilled structures from Africato needanalyze to charge be included risk, by looking in the at theChimney morphology Atlas of chimneys, toMost improve of the hydrocarbons the quantification producing basins of chargealong the andAfrican seal riskimmediately in this below part the of objective the world reservoir.. Dry holes or disappointingMargin are dominated wells by are vertical especially hydrocarbon important migration. to include in the Atlas, since the current entries in the HGS – PESGB 17th Conference on Africa E&P 97 Atlas are generally over known discoveries or undrilled prospects. Figure 3 shows a 3D image of high probability chimneys over a drilled trap in the continental slope of offshore, Nigeria. The structure was drilled and encountered a thick permeable reservoir, which was water wet. The To improve the quantification of top seal and charge risk the overlying and underlying chimneys. While current chimney chimneyassessment, a results Chimney show Atlas (https://dgbes.com/chimney_atlas) fault related leakage, which studies shows have pock focused marked on the offshore morphology basins, the in technology a can bathymetryis being compiled map over of known the sea oil and floor. gas discoveries.We interpret The this trapalso as bea applied“Fault toLeak onshore Trap” seismic (Class data. StudiesA). While from the Anza Atlas also includes dry holes, which tested valid structures Graben of onshore Kenya (Baranova et al., 2012) and the Oriente this trap was breached, we have evaluated Fault Leak Traps which contain economic quantities with effective reservoir. Thus, the well failed either from a lack Basin of Ecuador demonstrate the potential of the technology in of hydrocarbons (oil). Thus, additional case studies from this class of trap are especially important. of charge or seal. We will show examples from Africa, which both rift and foreland basins. Theare currently benefits in theof Atlasdry hole (Figure evaluations 1). One example were from clearly West shown in the HGS “Deepwater Gulf of Mexico DryAfrica Hole is a commercial Seminar” gas(2000 field & (Figure 2004). 2). ASimilar Seismic investigations section Additional of both drycase holesstudies and of drilled discoveries structures should from Africa need to significantlynear the crest of improve the drilled exploration structural anticline success, showed both a subtle in the coastalbe included and in interior the Chimney basins Atlas, of toAfrica. improve the quantification broad diffuse gas cloud (yellow) over the main reservoir interval of charge and seal risk in this part of the world. Dry holes or (Connolly et al., 2013). This trap is classified as a “Gas Cloud disappointing wells are especially important to include in the Trap” (Class C), indicating a high probability of effective seal Atlas, since the current entries in the Atlas are generally over underlying the gas cloud. Chimneys related to underlying thrusts known discoveries or undrilled prospects. Figure 3 shows a 3D may provide charge into the reservoir. These are classified as image of high probability chimneys over a drilled trap in the

“Direct Charge Traps”. Excess pressure is associated with both continental slope of offshore, Nigeria. The structure was drilled and encountered a thick permeable reservoir, which was water wet. The chimney results show fault related leakage, which shows pock marked morphology in a bathymetry map of the sea floor. We interpret this trap as a “Fault Leak Trap” (Class A). While this trap was breached, we have evaluated Fault Leak Traps which contain economic quantities of hydrocarbons (oil). Thus, additional case studies from this class of trap are especially important. The benefits of dry hole evaluations were clearly shown in the HGS “Deepwater Gulf of Mexico Dry Hole Seminar” (2000 & 2004). Similar investigations of both dry holes and discoveries should significantly improve exploration success, both in the coastal and interior basins of Africa. n

References Connolly, D., Aminzadeh, F., Brouwer, F., and Nielsen, S., 2013, Detection of Subsurface Hydrocarbon Seepage in Seismic Data: Implications for Charge, Seal, Overpressure, and Gas-hydrate Assessment, in F. Aminzadeh, T. Berge, & D. Connolly, eds., Hydrocarbon Seepage: From Source to Surface, SEG AAPG Geophysical Developments no. 16, p. 199-220.

Heggland, R., 2013, Hydrocarbon Trap Classification Based on Associated Gas Figure 2. Seismic section through gas field uninterpreted (upper) and with chimney Chimneys, in F. Aminzadeh, T. Berge, & probability overlain (lower). Results show subtle broad diffuse gas cloud over main reservoir D. Connolly, eds., Hydrocarbon Seepage: interval, indicating an effective seal Chimneys related to underlying thrusts, may provide From Source to Surface, SEG AAPG charge into the reservoir. Excess pressure is associated with chimneys (from Connolly et al., Geophysical Developments no. 16, p. 2013) 221-230.

98 HGS – PESGB 17th Conference on Africa E&P Figure 2. Seismic section through gas field uninterpreted (upper) and with chimney probability overlain (lower). Results show subtle broad diffuse gas cloud over main reservoir interval, indicating an effective seal Chimneys related to underlying thrusts, may provide charge into the reservoir. Excess pressure is associated with chimneys (from Connolly et al., 2013)

Figure 3. 3D image of drilled Fault Leak Trap Continental Slope Nigeria (left) with bathymetry map overlain (right) (Heggland,Figure 3. 2013). 3D image of drilled Fault Leak Trap Continental Slope Nigeria (left) with bathymetry map overlain (right) (Heggland, 2013). Aminzadeh, F. and Berge, T. [2013]. Determining Migration Acknowledgments Path fromReferences a Seismically Derived Gas Chimney: A South Africa We would like to thank Marathon Oil for permission to publish Case History. In: Aminzadeh, F., Berge, T. and Connolly, D. (Eds.) the seismic examples from West Africa. We would also like to Hydrocarbon Seepage: From Source to Surface. SEG/AAPG. Aminzadeh, F. and Berge, T. [2013]. Determiningrecognize Migration Roar Heggland, Path Paul from Meldahl, a Seismically and others at DerivedEquinor (formerly Statoil) for the development of the Chimney detection Baranova,Gas V., A.Chimney: Mustaqeem, A F. SouthKaranja, Africaand D. Mburu, Case Neural History. In:technology. Aminzadeh, F., Berge, T. and Connolly, D. Network(Eds.) Application Hydrocarbon for Frontier Exploration: Seepage: East From / Central Source to Surface. SEG/AAPG. African Rift Example, Geoconvention 2012. Biographical Sketch Baranova, V., A. Mustaqeem, F. Karanja, andDavid D. Mburu, Connolly Neural is a Senior Network Application for Frontier Connolly,Exploration: D., Aminzadeh, East F., Brouwer, / Central F. and African Nielsen, S. Rift [2013]. Example, Advisor Geoconvention for dGB Earth Science. 2012. Detection of Subsurface Hydrocarbon Seepage in Seismic Data: He has over 40 years of Implications for Charge, Seal, Overpressure and Gas-hydrate Connolly, D., Aminzadeh, F., Brouwer, F. andindustry Nielsen, experience S. [2013]. in various Detection of Subsurface Assessment. In: Aminzadeh, F., Berge, T. and Connolly, D. (Eds.) aspects of petroleum geology HydrocarbonHydrocarbon Seepage: From Seepage Source to inSurface. Seismic SEG/AAPG. Data: Implicationsand geophysics. for Charge,He worked Seal,for Overpressure and Gas- hydrate Assessment. In: Aminzadeh, F., Berge,Getty T. / Texacoand Connolly, as a Petroleum D. (Eds.) Hydrocarbon Connolly,Seepage: D., Kemper, From J. and Thomas, Source I. to[2014]. Surfa Usingce. gas SEG/AAPG. Geoscientist in a variety of chimney detection to assess hydrocarbon charge and top seal international and national effectivenessConnolly, - offshore, D., Kemper,Namibia. 76th J. andEAGE Thomas,Conference & I. [2014].exploration Using assignments. gas chimney detection to assess Exhibition, Amsterdam. hydrocarbon charge and top seal effectivenessHe has- offshore, been with dGBNamibia. since 76th EAGE Conference & 2001. He is co-editor for the Heggland,Exhibition, R. [2013]. Hydrocarbon Amsterdam. Trap Classification Based on SEG/AAPG Geophysical Associated Gas Chimneys. In: Aminzadeh, F., Berge, T. and Developments #16, Hydrocarbon Seepage: From Source to Surface. Connolly,Heggland, D. (Eds.) Hydrocarbon R. [2013]. Seepage: Hydrocarbon From Source Trap to ClassificationHis poster Using Based gas chimney on Associated detection to assess Gas hydrocarbon Chimneys. In: Surface.Aminzadeh, SEG/AAPG. F., Berge, T. and Connolly, D. (Eds.)charge andHydrocarbon top seal effectiveness Seepage: – offshore, From Namibia Source, presented to Surface. SEG/AAPG. at the 2014 EAGE Convention, won the Cagniard Award in 2015 for the best poster. He graduated from Washington & Lee Acknowledgments University with a BA in Geology.

HGS – PESGB 17th Conference on Africa E&P 99 Neil Hodgson, Karyna Rodriguez Spectrum Geo Ltd, Woking, United Kingdom, Jonathan Watson Bridgeporth, Milton Keynes, United Kingdom JMA – The Hidden Treasure Below the Basalt

Introduction Jurassic section prognosis. After 840m of basalt were drilled the Despite the huge exploration successes of the last 10 years in East well was at TD’d. However, re-interpretation of this legacy dataset Africa, exploration efforts offshore Seychelles and Mauritius in suggested a thick Mesozoic section was barely half a kilometre the Indian Ocean have been stagnant since the last exploration away. This section is the prize for future exploration. over 30 years ago. This is curious as all the wells drilled in the 1980’s offshore Seychelles encountered oil shows. Plate reconstruction based on magnetic data suggests that the Mascarene Plateau continental crust fragment is surrounded The Seychelles and Mauritius Governments share the by oceanic crust. To the south the conjugate margin is East administration of the Joint Management Area (JMA), located Madagascar, and to the north the conjugate margin is the west between the two island groups over the Mascarene Plateau. In coast of India. Oceanic crust here would have formed after this extra-ordinary setting, surrounded by oceanic crust, lies Madagascar-India continental fragments rifted and during the a fragment of Gondwana. An integration of remote sensing early part of India’s movement north, i.e. Late Cretaceous in age. datasets, legacy 2D seismic, together with sea surface oil slick However, the basalts encountered by the Saya De Malha well-1 analysis, and a regional geological and conjugate margin were alkaine, titanium rich basalts dated ca 30 ma, i.e. plume evaluation suggest a working petroleum system ready to be related rather than oceanic crust. revealed with modern seismic data. A Frontier Hydrocarbon System Model Regional Geology The model developed is that the Mascarene Plateau crust The Mascarene Plateau is a relatively shallow water part of the comprises the syn-rift section attached to West India at the Indian Ocean, ranging in water depth from shoals to 1000m. time of separation from East Madagascar. This rift may have OceanicCretaceous Crust is and expected Jurassic to beshallow greater marine than 60 syn million-rift sediments, years as wellreactivated as in the an pre older-rift KarooKaroo grabensequence or fabric. provide As source India moved rock, in age,and such reservoir that thermal potential cooling exists shouldin pre- riftallow Karoo the sediments,crust to be syn-riftnorth shallow it travelled marine coarseover a -deepgrained mantle clastics, plume, shelf the andhot-spot channel that in equilibriumsands, deepwater in more Cretaceous than 4 km ofto water.Recent This turbidites, suggests and that Cretaceous created to Recent the Deccan carbonate Trapp buildvolcanism-ups. of Northern India. As the the crust under the plateau is less dense than oceanic crust, and west Indian margin travelled over the plume, the heat source indeedThe lowkey gravityquestion measurements is how thick areimply the that basalts instead on ofthe oceanic Mascarene effectivelyPlateau? A studymelted byoff Bridgeporth the extended was and commissioned thinned crust, tocausing crust,examine there is variations a thick buoyant from a continentalcentral case crustal of a 1. fragment5km thick below basalt/volcanic a ridge jumpunit. Basefrom bsouthasalt oftopology the Mascarene was adjusted Plateau as to was north, the thegeometry JMA [1]. of the basement (continental upper crust) to match thefreezing observed a remnant gravity response. syn-rift and pre-rift block into oceanic crust. The plume volcanics continued to be erupted over the Mascarene TheThe only modelling well drilled of a in line the over JMA, the Saya Mascarene De Malha-1, Plateau drilled, with 2424m well calibrationplateau laying from downthe Seychelles a 1.5km thick, involved unit. Ita isnumber these volcanics of possible of limestonesscenarios. beforeThe initial encountering modelling basalt. of a line This fro mwas the a veryJMA differentover the Sayathat werede Malha intercepted-1 well byused the the Saya pref Deerred Malha scenario well. As taken both platesfrom outcomethe Seychelles to that prognosis, line. Although which alternativehad expected models to encounter were tested, a thincontinued (1.5km) to basalt move layernorth provides over the mantlethe optimum plume, modelling the hot spot a “Seychelles” type stratigraphy, with Tertiary, Cretaceous, and trail continues to its current location under the island of Reunion. solution.

Figure 1: Geologic model for the Mascarene Plateau calibrated with gravity Figure 1: Geologic modelmodelling for the and Mascarene well data Plateau from the calibrated Seychelles with gravity modelling and well data from the Seychelles

CONCLUSION 100 HGS – PESGB 17th Conference on Africa E&P The Mascarene Plateau in the Indian Ocean offers a unique potential for an unexplored oil prone hydrocarbon system in moderate to shallow water depths, reminding us that even in perhaps the most unlikely of places, hydrocarbon systems await discovery.

REFERENCES

[1] Torsvik, T.H., Amundsen, H., E. H., Hartz, Corfu, F., Kusznir, N., Gaina, C., Doubrovine, P.V., Steinberger, B., Ashwal, L.D., and Jamtveit, B, 2013. A Precambrian microcontinent in the Indian Ocean. Nature Geoscience, 6, 223–227. doi:10.1038/ngeo1736. The continental crust under the Mascarene Plateau is expected The modelling of a line over the Mascarene Plateau, with well to have similar geology to the Cretaceous, Jurassic, and Karoo calibration from the Seychelles, involved a number of possible sequence in the Seychelles. These rocks are oil prone yet suffer scenarios. The initial modelling of a line from the JMA over the from shallow burial and lack of top seal. Under the Basalts and Saya de Malha-1 well used the preferred scenario taken from the Tertiary sequence of the Mascarene Plateau it is expected that the Seychelles line. Although alternative models were tested, a thin various source rocks observed in Seychelles will currently be in (1.5km) basalt layer provides the optimum modelling solution. the oil window. Notably a high confidence oil slick was seen on a satellite data review, interpreted as live evidence for a working oil Conclusion system in the JMA. The Mascarene Plateau in the Indian Ocean offers a unique potential for an unexplored oil prone hydrocarbon system in Cretaceous and Jurassic shallow marine syn-rift sediments, as moderate to shallow water depths, reminding us that even in well as in the pre-rift Karoo sequence provide source rock, and perhaps the most unlikely of places, hydrocarbon systems await reservoir potential exists in pre-rift Karoo sediments, syn-rift discovery. n shallow marine coarse-grained clastics, shelf and channel sands, deepwater Cretaceous to Recent turbidites, and Cretaceous to References Recent carbonate build-ups. [1] Torsvik, T.H., Amundsen, H., E. H., Hartz, Corfu, F., Kusznir, N., Gaina, C., Doubrovine, P.V., Steinberger, B., Ashwal, L.D., and The key question is how thick are the basalts on the Mascarene Jamtveit, B, 2013. A Precambrian microcontinent in the Indian Plateau? A study by Bridgeporth was commissioned to examine Ocean. Nature Geoscience, 6, 223–227. doi:10.1038/ngeo1736. variations from a central case of a 1.5km thick basalt/volcanic unit. Base basalt topology was adjusted as was the geometry of the basement (continental upper crust) to match the observed gravity response.

HGS – PESGB 17th Conference on Africa E&P 101 Hidden Boundary Fault at East African Rift Basin Revealed with FALCON© Airborne Gravity Gradiometry Data Janine Weber*, Ivonne Montiel Araujo, Rao Yalamanchili, CGG Multi-Physics, Houston, Texas and Sindi Maduhu, TPDC, Dar Es Salaam, Tanzania

We present the results of an integrated interpretation of high-resolution airborne gravity gradient and magnetic data survey. The potential field’s data were integrated with geological data over the region of Lake Eyasi rift valley in northern Tanzania. The Tanzania Petroleum Development Corporation (TPDC) was interested in evaluating the petroleum potential of the area where little subsurface information is available. Janine Weber, Ivonne MontielThe principal Araujo, interpretationRao Yalamanchili objective was improved understanding of subsurface geology with relevance to CGG Multi-Physics, Houston,hydrocarbon Texas exploration, but the region may also be of interest for helium exploration. The interpretation Sindi Maduhu, TPDC, Darfirst Es Salaam, focused Tanzania on the structural framework of the main rift-bounding faults, intra-basinal faults, crossing structures, and locations of shallow intrusions. Estimated depth-to-basement was based on magnetic profile data analysis. Inversion of an airborne gravity gradient (AGG) data with the constraint of magnetic Hiddenbasement Boundary was used to model Fault high-density at basement. East African Rift CGG Multi-Physics flew an AGG and magnetic© survey in December of 2015, over the Eyasi rift valley Basin Revealed(Figure 1). The with survey area FALCON straddles the portion ofAirborne the East African Rift Gravity System (EARS) where the Eastern Arm of the rift diverges into several small rifts with different orientations. Accordingly, this area is referred to as the “TanzanianGradiometry Divergence Zone”. ExtensionData associated with the divergence results from tectonic plate motion, creating narrow rift valleys that occur adjacent to major faults. The rift valleys are floored by We present the results Basementbasement rocks and in the are filled with a of an integrated westerncombination part of the of sediments and interpretation of high- surveyvolcanics area are both of the as clastics and as resolution airborne Archaeanflows. In Tanzanianareas with dense volcanic gravity gradient and craton,activity, while younger basement volcanic cones magnetic data survey. rockshave in intrudedthe eastern into and through sediment-filled basins. Basement The potential field’s data part of the survey are rocks in the western part of the were integrated with ofsurvey the Proterozoic area are of the Archaean geological data over the MozambiqueTanzanian craton,Mobile while basement region of the Lake Eyasi Belt.rocks The in Tanzanian the eastern part of the rift valley in northern cratonsurvey comprises are ofmostly the Proterozoic Tanzania. The Tanzania gneisses,Mozambique schists, and Mobile Belt. The Petroleum Development quartzitesTanzanian that craton have comprises mostly Corporation (TPDC) experiencedgneisses, several schists, and quartzites that have experienced several was interested deformation phases. deformation phases. in evaluating the The occurrence of petroleum potential of the area where little Neogene volcanics subsurface information to the east at Crater Figure 1: Survey location is available. The Highlands and of Figure 1: Survey location principal interpretation The occurrence of Neogene volcanics to the east at Crater Highlands Tertiaryand of kimberliteTertiary kimberlite intrusions objective was an improved understandingin the vicinity of implies the subsurface that the thermalintrusions history in could the vicinity support implies development that the thermal of young history hydrocarbons. The very geology with relevance to hydrocarbonsame conditions exploration, that but are the good for couldhydrocarbons support development could also of trap young helium hydrocarbons. gases originating The in the Archaean region may also be of interestbasement for helium exploration. and mobilized The by Tertiaryvery same volcanism conditions and that rifting. are good Major for hydrocarbons rift-bounding could faults occur along the interpretation first focused southeaston the structural rift margin, framework but ofare buriedalso beneath trap helium lake gases deposits. originating in the Archaean basement the main rift-bounding faults, intra-basinal faults, crossing and mobilized by Tertiary volcanism and rifting. Major rift- structures, and locations of shallow intrusions. Estimated bounding faults occur along the southeast rift margin, but are depth-to-basement was based on magnetic profile data analysis. buried beneath lake deposits. Inversion of an airborne gravity gradient (AGG) data with the constraint of magnetic basement was used to model high- The area is defined by narrow rift grabens that have developed density basement. in the crystalline basement. The Eyasi rift structure is narrower than the surrounding rifts (the Manyara and Natron rifts) CGG Multi-Physics flew an AGG and magnetic survey in because it is primarily developed within the strong Archaean December of 2015, over the Eyasi rift valley (Figure 1). The crust. The Manyara and Natron structures are half-grabens and survey area straddles the portion of the East African Rift System are broader than the Eyasi rift because of the influence of the (EARS) where the Eastern Arm of the rift diverges into several weaker basement east of Eyasi. Within the Eyasi rift, crossing small rifts with different orientations. Accordingly, this area structures compartmentalize the main graben. The western and is referred to as the “Tanzanian Divergence Zone”. Extension central sub-basins of the Eyasi Basin have the best chances for associated with the divergence results from tectonic plate thick sediments, extensive reservoir facies, and proximity to a motion, creating narrow rift valleys that occur adjacent to major hydrocarbon kitchen. faults. The rift valleys are floored by basement and are filled with a combination of sediments and volcanics both as clastics and The north-western bounding fault of the Eyasi graben has as flows. In areas with dense volcanic activity, younger volcanic topographic expression and a strong gravity signature. In cones have intruded into and through sediment-filled basins. contrast, the south-eastern bounding fault is completely buried

102 HGS – PESGB 17th Conference on Africa E&P Eyasi Rift Basin, Tanzania: Integrated interpretation

Figure 2: Central Eyasi rift valley with an overlay of the airborne gravity gradiometry data, and major interpreted structures (faults and dikes).

The area is defined by narrow rift grabens that have developed in the crystalline basement. The Eyasi rift structure is narrower than the surrounding rifts (the Manyara and Natron rifts) because it is primarily developed within the strong Archaean crust. The Manyara and Natron structures are half-grabens and are broader than the Eyasi rift because of the influence of the weaker basement east of Eyasi. Within the Eyasi rift, crossing structures compartmentalize the main graben. The western and central sub- basins of the Eyasi Basin have best chances for thick sediments, extensive reservoir facies, and proximity to a hydrocarbon kitchen.

The north-western bounding fault of the Eyasi graben has topographic expression and a strong gravity signature. In contrast, the south-eastern bounding fault is completely buried by young sediments, though it produces a strong linear anomaly in both the gravity and magnetic data (Figures 2 and 3). Because the south-eastern fault is buried, the Eyasi basin has often been described as a half-graben – consequently, basin depth has been assumed to be relatively shallow. The depth to magnetic basement was estimated Eyasi Rift Basin, Tanzania: Integratedto be just interpretation over 5200m in the central Eyasi sub-basin, which is sufficiently deep to contain thick sediments that could include organic-rich lake deposits. Figure 2: Central Eyasi rift valley with an overlay of the airborne gravity gradiometry data, and Figure 3. Central Eyasi rift valley with an overlay major interpreted structures (faults and dikes). of the major interpreted structures (faults and dikes) on horizontal gradient of reduced-to-the- pole magnetic data

The area is defined by narrow rift grabens that have developed in the crystalline basement. The Eyasi rift structure is narrower than the Acknowledgements surrounding rifts (the Manyara and Natron rifts) because it is primarily developed within the The authors wish to thank the management of strong Archaean crust. The Manyara and Natron Tanzania Development Petroleum Corporation structures are half-grabens and are broader than (TPDC) and CGG for granting permission to the Eyasi rift because of the influence of the publish this abstract. weaker basement east of Eyasi. Within the Eyasi rift, crossing structures compartmentalize the main graben. The western and central sub- basins of the Eyasi Basin have best chances for thickFigure sediments, 2: Central Eyasi extensive rift valley reservoir with an overlayfacies, of andthe airborneproximity toFigure a hydrocarbon 3. Central Eyasi kitchen. rift valley with an overlay of the major gravity gradiometry data, and major interpreted structures (faults interpreted structures (faults and dikes) on horizontal gradient of Theand dikes).north-western bounding fault of the Eyasi graben hasreduced-to-the-pole topographic expression magnetic data and a strong gravity signature. In contrast, the south-eastern bounding fault is completely buried by youngBiographical sediments, though it Sketch producesby young sediments, a strong though linear it anomaly produces ain strong both linear the gravity anomaly and Biographical magnetic data Sketch (Figures 2 and 3). Because the southin both-eastern the gravity fault and ismagnetic buried, data the (Figures Eyasi basin2 and 3). has Because often beenS.V. (Rao)described Yalamanchili as a half is -graben – consequently, basinthe south-eastern depth has fault been is buried, assumed the Eyasi to be basin relatively has often shallow. been TheVice depthPresident to ofmagnetic interpretation basement was estimated S.V. (Rao) Yalamanchili is Vice President of interpretation in CGG Multi- todescribed be just as over a half-graben 5200m in– consequently,the central basinEyasi depth sub- hasbasin , whichin CGGis sufficiently Multi-Physics. deep He to contain thick sediments Physics. He holds a M.Sc. (Tech) and a Ph.D. in Geophysics from Andhra thatbeen couldassumed include to be relatively organic shallow.-rich lake The deposits depth to. magnetic holds a MSc (Tech) and a PhD basement was estimated to be just over 5200m in the central in Geophysics from Andhra University, India and a Post graduate diploma in mining exploration Figure 3. Central Eyasi rift valley with an overlay Eyasi sub-basin, which is sufficiently deep to contain thick University, India and a Post of the major interpreted structures (faults and Geophysics from ITC, The Netherlands. He has over 40 years of teaching, sediments that could include organic-rich lake deposits. n graduatedikes) on diploma horizontal in mining gradient of reduced-to-the- research, and industry experience. He came to the USA in 1983 and explorationpole magnetic Geophysics data from Acknowledgements ITC, The Netherlands. He worked for several geophysical companies, (Aero Service, Geonex, PGS, The authors wish to thank the management of Tanzania has over 40 years of teaching, Development Petroleum Corporation (TPDC) and CGG for research, and industry AOA, Fugro), at various capacities from Geophysicist to Principal Advising granting permission to publish this abstract. experience. He came to the Geophysicist over the years. He was the recipient of a Gold medal and USA in 1983 and worked Young Scientist’s Award for the year 1978 by the Association of forAcknowledgements several geophysical companies, (Aero Service, Geonex, PGS, AOA, Fugro), at various capacitiesExploration from Geophysicist Geophysicists, to India. He has broad geographic experience in hydrocarbon PrincipalThe authors Advising wish Geophysicist to thankexploration overthe themanagement years. He was withof the an integrated interpretation of Gravity, Magnetic, and Seismic data. His recipientTanzania of a Development Gold medal and Petroleum Young Scientist’s Corporation Award for the year(TPDC) 1978 by and the Association CGG for grantingofprofessional Exploration permission Geophysicists, membershipsto India. include SEG, AAPG, GSH, and HGS. Hepublish has broad this geographicabstract. experience in hydrocarbon exploration with an integrated interpretation of Gravity, Magnetic, and Seismic data. His professional memberships include SEG, AAPG, GSH, and HGS.

HGS – PESGB 17th Conference on Africa E&P 103 Kemi Taiwo ND Western Limited, Victoria Island, Lagos, Nigeria Olusanmi O. Emmanuel Acetop Energy, Houston, Texas, USA Olajide Aworanti, Temitayo Ologun, and Uzezi Olorunmola ND Western Limited, Victoria Island, Lagos, Nigeria Enhancing Gas Production in Nigeria’s Marginal Fields: A Case Study of Ughelli-X Field

The X-East field is located in the Greater Ughelli Depobelt, finding new gas to supply both the NAG I and NAGII plants. onshore Niger Delta Basin. The field contains an estimated reserve of 1.2 Tcf of gas and has been delivering non-associated The 1997 and 1999 vintage 3D seismic data over the X-East field gas through its Non–Associated Gas (NAG I) plant to the Ughelli were merged, reinterpreted, reprocessed, and then re-interpreted Power station since gas production started in the field in 1966. again to resolve the limitations around poor resolution of faults A total of eighteen wells have been drilled in the X-East field and amplitude events, and to map new horizons and new gas- comprising nine oil wells, five gas wells, and four abandoned bearing sand bodies identified from gamma ray (GR) logs. By wells. Out of the five gas wells, only three are active producers integrating the improved seismic interpretation products with while the rest have been shut in due to problems ranging from updated fieldwide electrical log correlations, two additional gas crude fouling to water production. To ensure and maintain the reservoirs: Q3000X sand and Q53000X sand, with total gross supply of gas to the NAG I plant and to satisfy the gas design rock volume of about 70000ac-ft and 96000ac-ft respectively, capacity of 150MMscf/d for NAG II, it was imperative that gas were mapped across the field. The application of improved production optimization efforts be carried out in the field while formation evaluation workflows that accounted for the presence additional gas wells are drilled to assess new gas reservoirs to feed of shaly sands and clay laminations within the target zones and the NAG II plant. Therefore, a dual-headed workflow involving reservoirs also resulted in proper delineation of the individual geoscience data reprocessing and reinterpretation to identify flow units across the field. The field development plan was thus new gas accumulations on the one side, and recompletion and updated to optimally guide the recompletion efforts in the workover operations to optimize gas production on the other, existing wells and to locate additional gas development wells. was adopted by the team to meet both the short-term objective of increasing gas supply to NAG I, and the long-term objective of Based on the updated field development plan, successful workover operations were carried out for the shut-in wells in the field. Essentially, the approach involved pulling out the existing tubing and fishing out the packer before running and interpreting Reservoir Saturation Test (RST) logs. The RST logs helped to determine the present fluid contacts and fluid types while also identifying new gas producing reservoir zones and bypassed pay zones within the wells. Based on the results of the RST logs, newly identified reservoir zones, and bypassed pay zones such as the Q7000, were then perforated and the wells were recompleted as new gas producers. Production results from recently

Figure 1: Location of the X-East Field (Ejadewe, 2012) Figure 1: Location of the X-East Field (Ejadewe, 2012) 104 HGS – PESGB 17th Conference on Africa E&P

Data and Methods Essentially, the dataset comprised 1997 and 1999 vintage 3D seismic data covering about 24Km2, 2D seismic lines, electrical wireline logs including Gamma Ray, Resistivity, Neutron, and Density logs, and well deviation data from eighteen wells as well as checkshot data from one well. Table 1 below shows a summary of the data available for this work.

Table 1: Database

Data Type Number Coverage Data Format 3D Seismic 5 X-East Field SEG-Y (PSTM 15.30DEG, 25.40DEG, 35.50DEG, 45.60DEG and FULL) 2D Lines 5 Part of X-East Field SEGY (0034-69-02-0009, 0034-75-02-0059, 0034-81- 04-0170, 0034-86-04-0122 and 0034-87-02-0214) Well Header 17 X-East field ASCII

Well Logs 17 X-East field LAS Well Deviation 17 X-East field ASCII

Checkshot 1 X-East, X-W-002 ASCII completed wells suggests that the Q3000X sand and Q53000X Introduction sand are important gas producers, and future wells have been The tertiary Niger Delta is one of the part of the prolific Gulf planned to target both reservoirs in a structurally optimal of Guinea province of West Africa. It has only one identified position. This is to ensure a sustained sweep of gas reserves petroleum system (Kulke, 1995) with multiple depobelts. Our while leaving as little as possible as attic reserves. study area, X-East field is within the Ughelli depobelt which is some 25km Southeast of Warri, Delta State, Nigeria (Figure 1). Since the adoption of the discussed workflow, gas supply to the The field was discovered in 1959. X-East structure is generally NAG I plant has been ensured and maintained. Once the workover a 4-way dip closed anticline with minor fault dependence. The operations and the proposed infill gas wells have been completed, field contains an estimated reserve of 1.4 Tcf of gas and has been gas production in the field is predicted to increase to about delivering non-associated gas through her Non–Associated Gas 202MMscf/d, up from around 78MMscf/d before the adoption of (NAG I) plant to the Ughelli Power station since gas production Thethe availablecurrent workflow. electrical wirelineThe results logs suggest were interpretedthat these workflowsand correlated can startedacross inthe the field field to properlyin 1966. mapA total of eighteen wells have been existingbe applied gas to-bearing other marginal reservoirs fields and in identify the Niger new Delta.ones (Figure 2). Improveddrilled formation in the X–East evaluation field comprising nine oil wells, five gas wells and four abandoned wells. Out of the five gas wells, only workflows that accounted for the presence of shaly sands and clay laminations within the target zones three are active producers while the rest have been shut andData reservoirs Type was Numberalso used to helpCoverage delineate the individualData Format flow units across the field. The 1997 and 3D Seismic 5 X-East Field SEG-Y (PSTM in due to problems ranging from crude fouling to water 1999 vintage 3D seismic data over the X-East field were merged, reinterpreted, reprocessed, and then re- 15.30DEG, 25.40DEG, production. To ensure and maintain the supply of gas interpreted again to resolve the limitations around35.50DEG, poor resolution 45.60DEG of faults andto amplitude the NAG eventsI plant ,and and to to satisfy the gas design capacity map new horizons and new gas-bearing sand bodiesand FULL)identified from GR logs andof 150MMscf/d Neutron-Density for NAG cross- II, it was imperative that gas 2D Lines 5 Part of X-East SEGY (0034-69-02- plots. production optimization efforts be carried out in the Field 0009, 0034-75-02-0059, field while additional gas wells are drilled to assess new 0034-81-04-0170, gas reservoirs to feed the NAG II plant. Results and Discussion 0034-86-04-0122 and 0034-87-02-0214) The reprocessed seismic data quality is good and seismic interpretation over the field revealed the X- Well Header 17 X-East field ASCII In order to optimize and enhance production from East field as a simple rollover anticlinal structure separated from the X-West fieldmatured by a saddle“locked-in” (Figure reserves 2). It and to also identify further development opportunities within the X-East is boundedWell Logs to the North17 by a majorX-East synthetic field boundaryLAS fault trending NW-SE, and the field is situated at field, a dual-headed workflow involving geoscience theWell maximum Deviation curvature17 of this fault.X-East Most field of the reservoirsASCII of the X-East field are correlatable to those in data reprocessing and reinterpretation to identify new the X-West field. Seismic interpretation and well logs analysis indicate that thesegas reservoirsaccumulations are not on the one side and recompletion Checkshot 1 X-East, X-W-002 ASCII always in communication and often have different fluid contacts (Figure 3). and workover operations to optimize gas production Table 1. Database on the other, was adopted by our team to meet both the short-term objective 385000 387500 390000 392500 395000 of increasing gas supply to -9769 -10200 NAG I and the long-term

-9754 170000 -9800 objective of finding new -10200 -9498 -10000 170000 -9600 gas to supply both the -10000 -10001 -10200 NAG I and NAGII plants. LIMIT OF 3D SEISMIC DATA

-9800 -10000 Data and Methods -9800

-9729 Essentially, the dataset -10000 -9770 167500 -10400 -9735 -9694 -10200 -11912 -11882 comprised 1997 and 1999 -9800 167500 -9713 -12023 -9703 -9741 vintage 3D seismic data -10000 -9882 -10000 covering about 24Km2, -9778 2D seismic lines, electrical

-9800 -10600

-9786 -10200 wireline logs including -9855

165000 Gamma Ray, Resistivity, -10400

-10000

165000 Neutron, and Density logs, and well deviation data -10200 from eighteen wells as well 385000 387500 390000 392500 395000

-10000 Elev ation depth [ft] -9500 -9550 as checkshot data from -9600 0 250 500 750 10001250m -9650 -9700 -9750 -9800 -10600 1:25000 -9850 one well. Table 1 shows -10400 -9900 -9950 -10000 -10050 -10100 -10150 a summary of the data -10200 -10400 -10250 -10200 -10300 -10350 -10400 -10450 available for this work. -10500 -10550 -10200 -10600 -10650 FigureFigure 2 2:: Top Top StructureStructure MapMap ofof thethe XX-East-East field. HGS – PESGB 17th Conference on Africa E&P 105

Figure 3: 3NE-SW: NE- SWCorrelation Correlation of sand bodiesof sand across bodies the X-East across field theshowing X-East several field reservoirs showing with differentseveral fluidreservoirs contacts. with Thedifferent available fluid electrical contacts. wireline logs were interpreted and indicate that these reservoirs are not always in communication correlated across the field to properly map existing gas-bearing and often have different fluid contacts (Figure 3). reservoirs and identify new ones (Figure 2). Improved formation evaluationThe integration workflows of thatthe accountedimproved for 3Dthe seismicpresence ofinterpretation The integrationwith updated of the fieldwide improved 3Delectrical seismic interpretation log correlations shaly sands and clay laminations within the target zones and with updated fieldwide electrical log correlations led to the reservoirsled to the was mapping also used toof helptwo delineate additional the individual gas reservoirs: flow Q3000Xmapping sandof two andadditional Q53000X gas reservoirs: sand, Q3000Xwith total sand gross and unitsrock acrossvolume the field.of about The 70000ac1997 and 1999-ft andvintage 96000ac 3D seismic-ft resdata pectively.Q53000X sand, The with areal total extent gross rockof a volume previously of about identified 70000ac- over the X-East field were merged, reinterpreted, reprocessed, ft and 96000ac-ft respectively. The areal extent of a previously andreservoir then re-interpreted was equally again better to resolve delineated the limitations based around on the reprocessedidentified reservoir seismic was equally data. betterThis delineatedis rather basedimportant on pooras they resolution became of faults key and inputs amplitude for aevents, more and robust to map field new developmentthe reprocessed plan seismic with data. proper This identification is rather important of infillas they well horizons and new gas-bearing sand bodies identified from GR became key inputs for a more robust field development plan logslocations and Neutron-Density that enhance cross-plots.d the production optimization effortwith proper of the identification team. of infill well locations that enhanced the production optimization effort of the team. ResultsThe application and Discussion of improved formation evaluation workflows that accounted for the presence of shaly The reprocessed seismic data quality is good and seismic The application of improved formation evaluation workflows interpretationsands and clayover thelaminations field revealed within the X-the East target field aszones a andthat reservoirs accounted foralso the resultedpresence of in shaly proper sands delineation and clay of simplethe individual rollover anticlinal flow units structure across separated the field. from theThe X-West field developmentlaminations withinplan was the target thus zones updated and reservoirs to optimally also resulted guide field by a saddle (Figure 2). It is bounded to the North by a in proper delineation of the individual flow units across the majorthe recompletion synthetic boundary efforts fault in trending the existing NW-SE, wells and the, and field to locatefield. additionalThe field development gas development plan was thus wells. updated to optimally is situated at the maximum curvature of this fault. Most of guide the recompletion efforts in the existing wells, and to the reservoirs of the X-East field are correlatable to those in locate additional gas development wells. the X-West field. Seismic interpretation and well logs analysis

106 HGS – PESGB 17th Conference on Africa E&P Conclusion References Following the application of the discussed workflow, gas supply Ejedawe, J. 2012. Nigeria Potential Waiting to be Tapped. to the NAG I plant has been ensured and maintained. Once the American Association of Petroleum Geologists, (AAPG) workover operations and the proposed infill gas wells have been Explorer May 2012. completed, gas production in the field is projected to increase by an additional 120MMscf/d, bringing total production to an Kulke, H. 1995. Nigeria. In Regional Petroleum Geology of the estimated volume of 202MMscf/d post workflow optimization. World. Part II: Africa, America, Australia and Antarctica, H. These impressive results/outlook suggest that reprocessing and Kulke, editor. Gebrüder Borntraeger, Berlin, Germany, pp. 143- reinterpreting vintage seismic data is of immense benefit to 172 production optimization in mature fields in the Niger Delta basin, Nigeria. We recommend that the discussed workflow Weber, K. J. and Daukoru, E. M., (1975). Petroleum Geology of should be applied to other marginal fields in the Niger Delta to the Niger Delta. In 9th World petroleum congress proceedings arrest production decline and enhance gas recovery. n 2, pp. 209-221

HGS – PESGB 17th Conference on Africa E&P 107 Cape Fold Belt Fractured Basement Play Fairway

Neil Hodgson*, Karyna Rodriguez, and Hannah Kearns; Spectrum Geo Ltd, Woking, United Kingdom

INTRODUCTION

In the lexicon of hydrocarbon exploration, “basement” is a pejorative term for the deepest stratigraphy that is considered unprospective. This can comprise tight sediments, metamorphic rocks, or igneous bodies, but it is usually, by definition, the last place we go looking for Oil and Gas. Yet the South African Ga-A-1 well was the first well drilled offshore in the Pletmos sub-basin in 1968 and discovered gas in fractured basement – a quartzite – of the Table Mountain Group (TMG) Formation. New understanding provided by modern and reprocessed seismic data, complemented by outcrop studies and potential field data analysis, has enabled the identification of this play fairway along the regional Cape Fold Belt (CFB) trend, onto the West African margin and across to its conjugate in Argentina.

Prolific fractured basement reservoirs have been recognized globally for decades from Vietnam’s Southern Margin (Bach Ho Field, discovered in 1975) to the recent Atlantic Margin discovery of the Lancaster field [2], yet the complexity of understanding and de-risking the potential resource ahead of the drill bit have provided obstacles to chasing this play. Recently the application of modern seismic technology apears to be able to resolve some of these issues, and when combined with the re-appraisal of legacy “basement” drilling, suggests that significant volumes of undiscovered hydrocarbons hidden by a failure to identify and intersect an active fracture system can now be hunted down.

CAPE FOLD BELT FRACTURED BASEMENT PLAY FAIRWAY

TheNeil fractured Hodgson quartzite, Karynas comprisingRodriguez, theand Ga Hannah-A discovery Kearns reservoir are charged from an adjacent Jurassic lacustrine source Spectrum Geo Ltd, Woking, United Kingdom from the Southern Pletmos sub-basin and Superior Graben (Figure 1). A structural closure at basement level can have upside from back-fill of the fracture system following Hurricane Energy’s Lancaster model, in addition to a down-dip oil leg to a gas Capecap. Fold Belt Fractured Basement Play Fairway

FigureFigure 1.1. 2D2D seismic seismic section section over over the Ga-Athe Ga gas-A field gas infield the inPletmos the Pletmos sub-basin, sub offshore-basin, offshorSouth Africae South and Africaschematic and geological schematic cross geologicalsection across cross the Pletmossection sub-basinacross the illustrating Pletmos structural sub-basin style illustrating and source structural kitchens chargingstyle and the source fractured kitchens quartzitic charging basement the offractured the quarTabletzitic Mountain basement Group. of the Table Mountain Group. Introduction Cape Fold Belt Fractured Basement Play Fairway 2D seismic data reprocessed in 2016 were analysed and integrated with satellite-derived gravity anomaly data, to identify In the lexicon of hydrocarbon exploration, “basement” is a The fractured quartzites comprising the Ga-A discovery similarpejorative basement term for highs the deepest and map stratigraphy the fractured that is quartziteconsidered basement reservoir play fairwayare charged in the from Pletmos an adjacent and Jurassicother remaining lacustrine sub source- basinsunprospective. (Bredasdorp, This can Gamtoo, comprise Algoa tight, andsediments, Southern metamorphic Outeniqua) fromwithin the the Southern Outeniqua Pletmos Basin. sub-basin Regional and seismicSuperior data Graben is an essentialrocks, or igneoustool for bodies,initial identification but it is usually, of bythis definition, highly attractive the last play,(Figure together 1). Awith structural a good closure regional at basementgeological level understand can have ing, whichplace wecan go be looking gained for by Oil integrating and Gas. Yet all the availa Southble African data from onshoreupside geology, from back-fill wells, andof the potential fracture fieldsystem data. following Hurricane Ga-A-1 well was the first well drilled offshore in the Pletmos Energy’s Lancaster model, in addition to a down-dip oil leg Thesub-basin occurrence in 1968 of and fractured discovered basement gas in fractured potential basement within the – a C apeto F aold gas B cap.elt leads to the intriguing question of whether both quartzite – of the Table Mountain Group (TMG) Formation. playsNew understandingcontinue along provided the entirety by modern of the and fold reprocessed belt. Using recently2D rep seismicrocessed data seismic reprocessed reflection in 2016 data, were a analysed revised andplate reconstructionseismic data, complemented for the region by has outcrop been studies proposed and potential[1] which identifieintegrateds a direct with continuation satellite-derived of the gravity Cape anomaly Fold Belt data, offshore to into field data analysis, has enabled the identification of this play identify similar basement highs and map the fractured quartzite fairway along the regional Cape Fold Belt (CFB) trend, onto the basement play fairway in the Pletmos and other remaining sub- West African margin and across to its conjugate in Argentina. basins (Bredasdorp, Gamtoo, Algoa, and Southern Outeniqua) within the Outeniqua Basin. Regional seismic data is an essential Prolific fractured basement reservoirs have been recognized tool for initial identification of this highly attractive play, globally for decades from Vietnam’s Southern Margin (Bach together with a good regional geological understanding, which Ho Field, discovered in 1975) to the recent Atlantic Margin can be gained by integrating all available data from onshore discovery of the Lancaster field [2], yet the complexity of geology, wells, and potential field data. understanding and de-risking the potential resource ahead of the drill bit have provided obstacles to chasing this play. Recently The occurrence of fractured basement potential within the the application of modern seismic technology apears to be able Cape Fold Belt leads to the intriguing question of whether to resolve some of these issues, and when combined with the re- both plays continue along the entirety of the fold belt. Using appraisal of legacy “basement” drilling, suggests that significant recently reprocessed seismic reflection data, a revised plate volumes of undiscovered hydrocarbons hidden by a failure reconstruction for the region has been proposed [1] which to identify and intersect an active fracture system can now be identifies a direct continuation of the Cape Fold Belt offshore hunted down. into the southern portion of the Orange Basin. The restoration also suggests the continuation of the Cape Fold Belt westwards into the conjugate Argentinian Colorado Basin (Figure 2), suggesting the development of a fractured basement play along the northern Argentinian margin.

108 HGS – PESGB 17th Conference on Africa E&P the southern portion of the Orange Basin. The restoration also suggests the continuation of the Cape Fold Belt westwards into the conjugate Argentinian Colorado Basin (Figure 2), suggesting the development of a fractured basement play along the northern Argentinian margin.

Figure 2. Reconstruction of the southern South Atlantic at 140 Ma. This reveals Figure 2. Reconstruction theof the continuity southern of the South South Atlantic African at Cape 140 Fold Ma. Belt This (blue) reveals into the Argentiniancontinuity of the South African Cape Fold Belt (blue) into the ArgentinianColorado Basin Colorado and predicts Basin the and potential predicts for thefractured potential basement for fractured plays in bothbasement the plays in both the Orange and Colorado Basins [1]. Orange and Colorado Basins [1]. Conclusion References The fractured basement play is an overlooked play which has [1] Paton, D.A, Mortimer, E.J., Hodgson, N., and van der Spuy, CONCLUSIONbeen proven on a global arena, where it is associated with large D., 2017. The missing piece of the South Atlantic jigsaw: when resources and significant upside potential. The re-discovery continental break-up ignores crustal heterogeneity. Petroleum of this play offshore South Africa in both its southern and Geoscience of the West Africa Margin, Geological Society The fractured basement play is an overlooked play which has been proven on a global arena, where it is associated with western margins is possible from a platform that integrates all London, Special Publications, 438, 195-228. largeavailable resources data from and onshore significant geology, upside wells, potential. seismic, andThe potential re-discovery of this play offshore South Africa in both its southern and westernfield data. margins Such iswork possible has resulted from ina platformthe identification that integrates of the all available[2] Hurricane data Energyfrom onshore presentation, geology, 2017. wells, seismic, and potentialcontinuation field data.of the Suchpre-Atlantic work has opening resulted Cape in Fold the Belt identification and of the continuation of the pre-Atlantic opening Cape Fold Belt andpotential potential fractured fractured basement basement play fairway play fairway in the Outeniquain the Outeniqua and Orange Basins of South Africa, and the conjugate and Orange Basins of South Africa, and the conjugate Colorado ColoradoBasin of Argentina.Basin of Argentina. n

REFERENCES

[1] Paton, D.A, Mortimer, E.J., Hodgson, N., and van der Spuy, D., 2017. The missing piece of the South Atlantic jigsaw: when continental break-up ignores crustal heterogeneity. Petroleum Geoscience of the West Africa Margin, Geological Society London, Special Publications, 438, 195-228.

[2] Hurricane Energy presentation, 2017.

HGS – PESGB 17th Conference on Africa E&P 109 Matt Tyrrell, Mark Martin, Avril Ashfield, Andrea Maioli PGS Blandine Biaou Société Béninoise des Hydrocarbures (Sobeh) The Underexplored Shelf-edge Plays of the West Africa Transform Margin and the Opportunity to De-risk these on Merged 3D Seismic and Well Datasets through Togo, Benin, and Western Nigeria

Introduction despite excellent 2D seismic data coverage, exploration of this For more than 40 years, Mesozoic and Tertiary paleo-shelf play has been limited by the prevalence of block-specific, rather edges have been identified by Africa oil explorers as offering than play-oriented, 3D seismic datasets. the opportunity for high-energy, shallow water reservoir facies, combined with structural trapping styles and sealing Shelf-edge and pro-platform plays are shown to continue transgressive muds, providing plays in shallow water parallel through the Transform Margin of West Africa and in Togo, to the present-day coast. In addition to this shelf-edge play, Benin, and NW Nigeria these plays are equally under-explored. pro-platform talus slope and mass-flow fan deposits, shed off In Nigeria, Mesozoic age clastic shelf-edge plays host the Aje and datasets. The presentation will show examples of the shelf edge and pro-platform play concept and Ogo Fields, the former also exhibiting an Upper Albian shallow the platform top or front and deposited to onlap the shelf edge, will show the results of the interpretation work conducted. A number of leads and prospects provide a secondary exploration target, typically within the same associatedmarine mixed with carbonate these plays,and clastic located shelf in edge. both In open eastern acreage Benin, and farm-in opportunities, will be presented license area. andthe shelfalexplained wells. drilled at the Seme North and Seme South fields encountered clastic, mixed clastic, and carbonate shallow marine In the North West Africa Atlantic Margin (NWAAM), shelf- facies of Cretaceous age whilst the shelf edge play that lies edge and pro-platform fan plays are to be found extensively, distally to these was the target for the Gbenonkpo-1 exploration running from Morocco in the north to Guinea Conakry in the well drilled by Hunt Oil in 2014. In the waters of western Benin Figure 1. Basemap showing the datasets.south and spanning The presentationsix countries. Exploratory will show drilling examples of these andof the Togo, shelf multiple edge leads inan stackedd pro Mesozoic-platform and Tertiaryplay concept shelf- and integrated multiclient well log, 2D and 3D seismic datasets used within willplays show was mostly the conducted results prior of the to the interpretation 2000’s and success work has conducted.edge plays are imagedA number but to date of areleads untested and by prospectsdrilling. been limited to the Cap Juby field, discovered by Esso in 1971, the study. associatedthe Pelican and Fregatewith these pro-platform plays, fields located discovered in inboth 2003 openUnderexplored acreage and Shelf-edge farm-in and opportunities, Pro-platform will be presented andby Total, explained and the SNE. (shelf edge) and FAN (pro-platform fan) Prospectivity in the West Africa Transform Margin fields discovered by Cairn Energy in 2014. It is noticeable that Recently collated and merged 2D and 3D PSTM seismic datasets these discoveries are some 30 years apart and it is believed that over Togo, Benin, and Nigeria now provide a single multiclient seismic footprint from the western border of Togo to the Niger Delta. This merged dataset, together with multiclient well data, provides for the first time a continuousFigure image 1. Basemapof the shelf-edge showing the integrated multiclient well log, 2D and 3D seismic datasets used withinFigure 2. Seismic dip section the study. showing the stacked shelf-edge and pro-platform fan plays. Note that this data is in two way time.

Figure 1. Basemap showing the integrated multiclient well log, 2D Figure 2. Seismic dip section showing the stacked shelf-edge and and 3D seismic datasets used within the study. pro-platform fan plays. Note that this data is in two way time. Figure 2. Seismic dip section Figure 3. RMS amplitude display showing the stacked shelf-edge fromand MC3D data showing the paleo- 110 HGS – PESGB 17th Conference on Africa E&P shelf edge (purple outline) together pro-platform fan plays. Note thatwith this a lead location (green outline). data is in two way time.

Figure 3. RMS amplitude display from MC3D data showing the paleo- shelf edge (purple outline) together with a lead location (green outline).

datasets. The presentation will show examples of the shelf edge and pro-platform play concept and will show the results of the interpretation work conducted. A number of leads and prospects associated with these plays, located in both open acreage and farm-in opportunities, will be presented and explained.

Figure 1. Basemap showing the integrated multiclient well log, 2D and 3D seismic datasets used within the study.

Figure 2. Seismic dip section showing the stacked shelf-edge and pro-platform fan plays. Note that this data is in two way time.

Figure 3. RMS amplitude display from MC3D data showing the paleo- shelf edge (purple outline) together with a lead location (green outline).

Figure 3. RMS amplitude display from MC3D data showing the paleo-shelf edge (purple outline) together with a lead location (green outline). and pro-platform plays across three countries and some ten results of the interpretation work conducted. A number of blocks of which six are open acreage (Figure 1). The opportunity leads and prospects associated with these plays, located in both thus presents itself for oil companies to interpret, explore, and open acreage and farm-in opportunities, will be presented and de-risk this multi-country play and high-grade available acreage explained. n and farm-in opportunities. Furthermore, the availability of field tapes or raw data for many individual surveys provides Biographical Sketch the opportunity for the data footprint over the shelf-edge to Matt Tyrrell attained an MSc be depth migrated or depth converted, adding confidence to in Petroleum Geoscience from closures and volumes. Oxford Brookes University before joining Fugro-Aperia Interpretation work conducted by PGS across these three as an engineer, then Aceca as a countries has identified considerable shelf-edge and pro- Geologist focused on North Sea platform play prospectivity within four shelfal sequences; stratigraphy. He joined TGS in Albian-Cenomanian, Turonian, Santonian-Campanian, 2006 where he was responsible and Maastrichtian (Figure 2). A number of leads have been for geoscience interpretation identified, mapped, and risked (Figure 3). The application of a in Canada and Brazil, before sequence stratigraphic framework has helped to predict facies joining the TGS Africa group distribution at the paleo-shelf and sequence constrained facies as Lead Geologist where he maps show where the best shelf-edge reservoir qualities and pro- worked on new ventures and platform fan deposits may be. Basin modelling work indicates interpretation projects focused on East and West Africa. Matt that charge is low risk whilst rock physics work based upon joined PGS in 2015 as Principal Geologist for Africa where he multiclient well data has been used to constrain litho-fluid facies works on geoscience and business development tasks in West and to model the elastic properties’ behaviour to further de-risk Africa, with a focus on Cote d’Ivoire, Benin, Congo, and Angola. the identified leads. Matt is a principal geoscientist and project developer with over Conclusions 18 years of industry experience. Responsible for delivering There is significant overlooked shelf-edge and pro-platform exploration opportunities to clients through an understanding prospectivity through Togo, Benin, and Nigeria, and de-risking of geoscience, project development, business development, and of identified leads is now possible through integrated seismic both client and Ministry relationships. He is responsible for and well datasets. The presentation will show examples of the developing, scoping, and delivering integrated geoscience studies shelf edge and pro-platform play concept and will show the that provide our clients with exploration opportunities

HGS – PESGB 17th Conference on Africa E&P 111

Emma Tyrrell InPeter the Elliot, overlying and Matt Cretaceous Lofgran to Tertiary sedimentary wedge, hydrocarbons from the Akata Shale can be demonstratedElephant Oil Ltd, Tonbridge, to have migratedKent, UK up-dip and onshore, within both Cretaceous and Tertiary clastics. Traps are formed where Albian clastics drape over Devonian rift structures or where they are onlapped by TuronianHydrocarbon sandstones. Additionally, Potential intraformational of the permeability Onshore barriers Dahomey likely trap hydrocarbons during their up-dip migration. Embayment of Benin; Exploration of Devonian, The next phase of interpretation and exploration of this prospective onshore region of the West Africa TransformJurassic, margin will Cretaceous,require the acquisition and of additional Tertiary 2D seismic Plays data Usingcovering the main rift structures and basins identified by gravity and magnetic data. Once acquired, the integration of the new seismicIntegrated with the gravity Seismic and magnetic and data , Highwill greatly Resolution enhance the understanding Airborne of the petroleum systems and allow the Gravityplanning of the and first exploration Magnetic wells dueData in 2020.

barrels in place within Lower Cretaceous and Devonian clastics, sourced from Devonian source rocks, whilst the nearby Sèmè FieldFigure in Benin 1. contains A map ultimate of the recoverable West Africa reserves Transform of c.80 Margin, millionshowing barrels withinthe onshore Turonian extension and Albian clastics. of Cretaceous Immediately and Tertiary acrosssedimentary the maritime basinsfrontier inpresent- Nigerian daywaters. Bloc lies thek AjeB in Field, Benin is reportedly with 200 million barrels of oil and multi-TCF gas reservesoutlined recoverable in black from, the at Turonianthe centre sandstones, of the whilstDahomey the nearbyEmbayment. Ogo Field contains (Brownfield oil within an& Albian Charpentier, clastic reservoir. 2006).

Within the conjugate margin; the onshore Potiguar Basin of Brazil, exploration success has been prolific with approximately 1200 wells drilled and over 100 oil fields discovered. This success suggests that the remaining potential within the Dahomey Embayment may be considerable. Figure 1. A map of the West Africa Transform Margin, showing the onshore extension of Cretaceous and Tertiary sedimentary Recent studies by Elephant Oil over Block B, Onshore Benin, basins present-day. Block B in Benin is outlined in black, at the have focused on an integration of a sparse onshore and offshore centre of the Dahomey Embayment. (Brownfield & Charpentier, 2D seismic dataset with a high resolution airborne gravity 2006). gradiometer and magnetic survey flown in 2013.

The West African Transform Margin is characterised by a Stratigraphic Interpretation: number of Mesozoic sedimentary wedges, where Cretaceous Extrapolation of the known geological stratigraphy from the to Tertiary sequences are present onshore; the Niger Delta, shallow offshore waters suggests that in the onshore, Jurassic, the Dahomey Embayment (Benin, Togo and Ghana), and the Albian, mid-Cretaceous, and Tertiary sediments overstep Ivory Coast & Tano Basins. In many locations, these Mesozoic Devonian failed rift basins with clastic fills. These Devonian sedimentary wedges are additionally underpinned by Paleozoic basins are then onlapped by Cretaceous to Tertiary fluvial failed rift basins associated with earlier intracontinental deltaic sediments of the Agbada and Benin Formations. extensional phases. Interpretation of the seismic facies, supported by evidence Figure 2. Onshore to offshore seismic from their outcrop further north, have allowed facies mapping The profilesDahomey Embaymentshowing isthe the structural least explored and of the West and hint at interbedded sandstones and mudstones, deposited Africastratigraphic Transform margin interpretation. onshore sedimentary wedges. Just during transgressive phases, with intra-formational seals for eleven onshore exploration wells have been drilled to date; hydrocarbons migrating onshore and up-dip. three in Ghana and eight in Nigeria of which five encountered hydrocarbons. A water well drilled onshore Benin in 1932 Structural Interpretation: at Sazue reported gas, analysed as C1, C2 and C3, strongly Interpretation of airborne gravity data together with 2D seismic indicating the presence of thermogenic gas. data enables formation thickness and depth-to-basement to be modelled to permit an extrapolation of the Devonian, Jurassic, The offshore section of the Dahomey Embayment however has and Cretaceous structures, basins, and sediment thicknesses witnessed considerable exploration success within a number across the block. Several large horst structures are mapped, of stratigraphic intervals. The Lomé field has some 80 million providing targets for additional seismic and subsequent

112 HGS – PESGB 17th Conference on Africa E&P

Figure 3. Examples of paleo-facies maps for the Devonian rift and Turonian post-rift reservoir intervals.

In the overlying Cretaceous to Tertiary sedimentary wedge, hydrocarbons from the Akata Shale can be demonstrated to have migrated up-dip and onshore, within both Cretaceous and Tertiary clastics. Traps

are formed where Albian clastics drape over Devonian rift structures or where they are onlapped by InTuronian the overlying sandstones. Cretaceous Additionally, to Tertiary intraformational sedimentary wedge, permeability hydrocarbons barriers from likely the trap Akata hydrocarbons Shale can be during demonstratedtheir up-dip migration. to have migrated up-dip and onshore, within both Cretaceous and Tertiary clastics. Traps are formed where Albian clastics drape over Devonian rift structures or where they are onlapped by TuronianThe next sandstones.phase of interpretation Additionally, and intraformational exploration ofpermeability this prospective barriers onshore likely trap region hydrocarbons of the West during Africa theirTransform up-dip marginmigration. will require the acquisition of additional 2D seismic data covering the main rift structures and basins identified by gravity and magnetic data. Once acquired, the integration of the new Theseismic next with phase the of gravity interpretation and magnetic and exploration data, will of greatly this prospective enhance onshorethe understanding region of the of Westthe petroleum Africa Transformsystems and margin allow will the require planning the acquisitionof the first explorationof additional wells2D seismic due in data 2020. covering the main rift structures and basins identified by gravity and magnetic data. Once acquired, the integration of the new exploration drilling. To the west of the block, the data reveals have migrated up-dip and onshore, within both Cretaceous seismic with the gravity and magnetic data, will greatly enhance the understanding of the petroleum a large transform basin of likely Albian age that at present day and Tertiary clastics. Traps are formed where Albian clastics systemsaccommodates and Lake allow Ahémé. the At planning its widest partof the this transformfirst exploration drape wells over Devoniandue in 2020. rift structures or where they are onlapped basin measures 12 kilometres and extends 50 kilometres along byFigure Turonian 1. sandstones.A map of Additionally, the West Africaintraformational Transform Margin, its axis, whilst modelling of the gravity gradiometer data permeabilityshowing the barriers onshore likely trapextension hydrocarbons of Cretaceous during their and Tertiary suggests that the basin is up to 2.7 kilometres deep. up-dipsedimentary migration. basins present-day. Block B in Benin is Figure 1. A map of the West Africa Transform Margin, outlined in black, at the centre of the Dahomey showing the onshore extension of Cretaceous and Tertiary Onshore Dahomey Petroleum Systems: TheEmbayment. next phase of (Brownfield interpretation and& Charpentier,exploration of this 2006). All the elements for a fully-functioning petroleum system are sedimentaryprospective onshorebasins regionpresent- of theday West. Bloc Africak B Transform in Benin is shown to be present in the Onshore Dahomey Embayment. outlinedmargin willin black require, at the the acquisition centre of of theadditional Dahomey 2D seismic data The earliest rift structures are believed to be Devonian, with a Embayment.covering the main(Brownfield rift structures & Charpentier, and basins identified 2006). by gravity high likelihood of the working petroleum system encountered and magnetic data. Once acquired, the integration of the new offshore Togo extending into the onshore. seismic with the gravity and magnetic data, will greatly enhance the understanding of the petroleum systems and allow the In the overlying Cretaceous to Tertiary sedimentary wedge, planning of the first exploration wells due in 2020. n hydrocarbons from the Akata Shale can be demonstrated to

Figure 2. Onshore to offshore seismic profiles showing the structural and Figure 2. Onshore to offshore seismic profilesstratigraphic showing interpretation. the structural and stratigraphic interpretation.

Figure 2. Onshore to offshore seismic profiles showing the structural and stratigraphic interpretation.

Figure 3. Examples of paleo-facies maps for the Devonian rift and Turonian post-rift reservoir intervals. Figure 3.3. Examples Examples of of paleo paleo-facies-facies maps maps for for thethe DevonianDevonian rift rift and and Turonian Turonian post post-rift-rift HGSreservoirreservoir – PESGB 17th intervals.intervals. Conference on Africa E&P 113 Conjugate Margin Chronostratigraphy--Comparison of Cretaceous-Tertiary Petroleum Systems in Namibia and Uruguay

Katie-Joe McDonough1,2, *Kyle Reuber2, Brian W. Horn2, Kenneth G. McDermott2, Elisabeth C. Gillbard2, Friso Brouwer3

Katie-Joe McDonough 1 KJM Consulting, Pine, CO, USA, 2 ION E&P Advisors, Houston, TX, USA, 3 I^3 GEO, Denver, CO, USA KJM Consulting, Pine, CO, USA and ION E&P Advisors, Houston, TX, USA Kyle Reuber, Brian W. Horn, Kenneth G. McDermott, Elisabeth C. Gillbard ION E&P Advisors, Houston, TX,Significant USA offshore areas along the eastern and western margins of the southern South Atlantic remain underexplored. Offshore Brazil, Uruguay, and Argentina host multiple underexplored basins south of the Friso Brouwer salt provinces, and the conjugate Namibian margin has indications of a potential hydrocarbon exploration I^3 GEO, Denver, CO, USA province. Offshore basins containing Early Cretaceous through Tertiary sediment fill along the South Atlantic margins contain several significant discoveries in recent years in near-shore shelf carbonates to deep-water siliciclastic reservoirs. The Kudu gas field in offshore Namibia contains an estimated 1.3 TCF shallow marine reservoirs charged by an Aptian marine source. Similarly the 2010 Sea Lion discovery on Conjugatethe Falkland Margin Plateau targeted Chronostratigraphy fans charged by thick, high TOC Early Cretaceous lacustrine – shale. These recent discoveries reveal functioning petroleum systems on both (volcanic) margins and suggest a potential for future discoveries (Fig. 1). These conjugate margins shared similar geological histories until ComparisonEarly ofCretaceous Cretaceous-Tertiary rifting initiated their separation. Post-rifting, the margins Petroleum show synchronous, symmetrical evolution and development of the sedimentary section suggesting tectonic controls on Systemsvariable sedimentation in Namibia episodes between theand margins . Uruguay

Significant offshore areas along the eastern and western margins 95 Ma GPlates of the southern South Atlantic Reconstruction remain underexplored. Offshore Brazil, Uruguay, and Argentina host multiple underexplored basins south of the salt provinces, and the conjugate Namibian margin has indications of a potential hydrocarbon exploration province. Offshore basins containing Early Cretaceous through Tertiary sediment fill along the South Atlantic margins contain several significant discoveries in recent years in near-shore shelf carbonates to deep-water siliciclastic reservoirs. The Kudu gas field in offshore Namibia Well (Source Rock Present) contains an estimated 1.3 TCF Well (Dry Hole) shallow marine reservoirs charged Figure 1. Early Cretaceous (95 Ma) plate reconstruction showing locations of ION seismic profiles by an Aptian marine source. Figurealong 1.the Early offshore Cretaceous margins (95 ofMa) South plate Atlantic reconstruction and West showing Africa. locations Seismic of profiles ION seismic in red profiles were usedalong in Similarly the 2010 Sea Lion the offshore margins of South Atlantic and West Africa. Seismic profiles in red were used in this study, andthis straddled study, and the straddled Atlantic conjugate the Atlantic margin conjugate during Cretaceousmargin during time. Cretaceous time. discovery on the Falkland Plateau targeted fans charged by thick, margins of the South Atlantic enable comparison of basin-fill high TOC Early Cretaceous lacustrine shale. These recent chronostratigraphy on each margin (Figure 2), by establishing discoveries reveal functioning petroleum systems on both geochronology in the basins which form above the juncture (volcanic) margins and suggest a potential for future discoveries of continental and oceanic crust. The zone composed of SDR (Figure 1). These conjugate margins shared similar geological packages links the crustal processes driving magmatic rifting/ histories until Early Cretaceous rifting initiated their separation. stretching of the continental crust which lead to the formation Post-rifting, the margins show synchronous, symmetrical of oceanic crust, to sedimentation (including extrusive volcanic) evolution and development of the sedimentary section patterns observed along the rifted margins. Therefore the SDR suggesting tectonic controls on variable sedimentation episodes packages are included at the end of the syn-rift fill sediments between the margins. which fill early mini-grabens overlying continental crust.

We develop a detailed chronostratigraphic correlation of the Initially we generate HorizonCubes on 2D seismic profiles sedimentary section on the conjugate margins of Uruguay from each margin. A HorizonCube comprises a set of high- and Namibia through the geo-chronologic timing of syn- and resolution tracked horizons which includes virtually all stratal post-rift fill sequences including the enigmatic seaward-dipping surfaces present in the seismic data. We previously generated reflector (SDR) series. Long-offset 2D seismic profiles from both HorizonCubes in the sedimentary section which excluded SDRs

114 HGS – PESGB 17th Conference on Africa E&P Nam

Uru

Well (Source Rock Present)GPlates 5.0 Figure 2. Seismic profiles depicting offshore margins of Uruguay and Namibia.

Figure 3. HorizonCube and accompanying Wheeler (chronostratigraphic) diagram from Uruguayan and Namibian margins. Note synchroneity of major transgressive/regressive cycles across the conjugate margin. as synchronous with late syn-rift fill. However, in our model covers roughly twice the lateral extent as on the Uruguayan side the emplacement of the non-extrusive magmatic material that suggesting a potentially shallower gradient on the Namibian underlies the SDRs is typically thought to be coevally formed volcanic margin during rifting. This is interpreted to be the result at the paleo-volcanic spreading center. As this lower zone is of basement gradient changes that persisted into the sediment typically void of layered material, a lower bounding limit of section and drove subsidence variations through time. SDRs is currently included in generation of the HorizonCube (Figure 3). We found that stratigraphic evolution on the conjugate margins was synchronous and geometries mirror each other The horizons generated within the HorizonCube are for the Cretaceous as well as the Tertiary section (Figure 3). then flattened to create a chronostratigraphic “Wheeler”- Key regional transgressive-regressive packages are similarly style representation of sedimentation, including syn-rift timed on both sides of the mid-Atlantic. For example, the volcaniclastic SDRs along each profile. This flattening was Albian transgressive package produces coeval source rocks on done for HorizonCubes generated on each seismic line. The both sides. Late Cretaceous fill on the Uruguayan side may be flattened representation shows spatial variation in deposition limited to slope base and lowstand fan reservoirs, whereas the through time. Thus, we were able to compare evolution of both Namibian side appears to contain significant aggradational sedimentary basins from the conjugate margins across the south deepwater deposition. Lateral extents and inferred volumes Atlantic (Figure 3). This type of geochronological representation of the stratigraphic systems vary between the margins, with of the seismic data permits comparative analysis of evolution of greater depositional dip extent existing on the Namibian margin. stratigraphy in relation to the SDR series and magmatic crust. Stratigraphic evolution identified from the chronostratigraphic diagrams also records margin-specific events that appear to be Wheeler diagram scrutiny also permits predicting the formation related to local tectonic events, sediment budget, and margin and timing of key petroleum system elements across the southern architecture. These variables strongly influenced the depositional South Atlantic. One difference between the margins was the settings and facies over time. lateral extent of the coeval SDR packages. The Namibian margin

HGS – PESGB 17th Conference on Africa E&P 115 Fig. 3. HorizonCube and accompanying Wheeler (chronostratigraphic) diagram from Uruguayan and Namibian margins. Note synchroneity of major transgressive/regressive cycles across the conjugate margin.

These observations have important ramifications for understanding petroleum systems on both margins. Our comparison predicts that Uruguay has a potential post-Cretaceous play which may also exist in Namibia, and the Cenomanian-Turonian may be a viable source interval on both margins. Further interrogation of the details of HorizonCubes permits seismic facies analysis of stratal and geobody architecture. This further supports the prediction that viable petroleum system components of reservoir (Fig. 4) and source exist on both margins. Thus a detailed interrogation of conjugate margin chronostratigraphy permits more accurate discernment of depositional history and development of accurate play identification models within a regional framework.

Figure 4. Example from Uruguay showing HorizonCube revealing high-resolution stratal geometries and seismic facies. a) Detailed Fig.analysis 4. Example located in from the black Uruguay square showingon the upper HorizonCube image. Mounded revealing geometries high alternate-resolution with subparallel, stratal geometries infill stratal geometriesand seismicwhich stackfacies. compensatorily. a) Detailed These analysis suggest located alternating in theincision black and square construction on the systems, upper possibly image. channel-fan Mounded reservoirs. geometries The upper alternateset of images with b) subparallel, show the mounded infill stratalfacies, light geometries yellow in the which left images, stack withcompensatorily. the partial HorizonCube These suggestoverlay showing alternating the internal incisiongeometries and and construction outline of the systems, geobody on possibly the right image. channel The- fanlower reservoirs. set of images The c) show upper the infillset offacies, images shown b) in show brown thein left image. moundedThe right facies, image shows light subparallelyellow in naturethe left and images, laterally-building with the geometries, partial HorizonCube enlarged in inset. overlay showing the internal geometries and outline of the geobody on the right image. The lower set of images c) show the infill facies, shown in brown in left image. The right image shows subparallel nature and laterally-building geometries, enlarged in inset.

116 HGS – PESGB 17th Conference on Africa E&P These observations have important ramifications for Friso Brouwer is geophysical understanding petroleum systems on both margins. Our consultant and owner of I^3 comparison predicts that Uruguay has a potential post- GEO in Denver. Friso has 15 Cretaceous play which may also exist in Namibia, and the years industry experience, Cenomanian-Turonian may be a viable source interval on both involving both technical and margins. Further interrogation of the details of HorizonCubes managerial roles. His expertise permits seismic facies analysis of stratal and geobody covers both regular seismic architecture. This further supports the prediction that viable interpretation and application petroleum system components of reservoir (Figure 4) and source of specialized geophysical exist on both margins. Thus a detailed interrogation of conjugate techniques. Friso has worked margin chronostratigraphy permits more accurate discernment offshore, onshore and of depositional history and development of accurate play unconventional areas, both in identification models within a Biographicalregional framework. n Sketchthe US and internationally. His Biographical Sketch collaboration with ION Geophysical E & P Advisors is focused Biographical Sketch on enhancingKatie the-Joe interpretation McDonough, of the ION’s SPAN PhD. lines using is a geolophysicist specializing in multi- Katie-Joe McDonough, PhD Katiethe specialized-Joe McDonough, sequence stratigraphic PhD. interpretation is a geolophysicist tools for specializing in multi- dataset, integrated sequence stratigraphic and seismic interpretation. is a geolophysicist specializing dataset,seismic data. integrated sequence stratigraphic and seismic interpretation. in multi-dataset, integrated Katie-Joe’s areas of focus include multi-scale applications of stratigraphy sequence stratigraphic and Katie-Joe’s areas of focus include multi-scale applications of stratigraphy seismic interpretation. Katie- to basinto basin analysis, analysis, exploration exploration play assessment, play assessment,and reservoir-scale and reservoir-scale Joe’s areas of focus include development. She works worldwide continental to deep marine strata in multi-scale applications development. She works worldwide continental to deep marine strata in conventional and unconventional plays. Katie-Joe collaborated with of stratigraphy to basin conventional and unconventional plays. Katie-Joe collaborated with analysis, exploration play colleagues at ION E&P Advisors to generate and publish the initial assessment, and reservoir- versioncolleagues of this work, at which ION garneredE&P Advisors the 2017 toJules generate Braunstein and award publish for the initial scale development. She works worldwide continental to deep bestversion presentation of thisas poster work, at whichACE 2017. garnered Katie-Joe the currently 2017 alsoJules Braunstein award for marine strata in conventional serves as an industry mentor to YPs and graduate students. and unconventional plays. Katie-Joe collaborated with colleagues best presentation as poster at ACE 2017. Katie-Joe currently also at ION E&P Advisors to generate and publish the initial version serves as an industry mentor to YPs and graduate students. of this work, which garnered the 2017 Jules Braunstein award for best presentation as poster at ACE 2017. Katie-Joe currently also Kyle Reuber, PhD. is a geologist for ION’s E & P Advisors Team based serves as an industry mentor to YPs and graduate students. in Houston. His primary area of focus is Latin America and the Kyle Reuber, PhD is a geologist for ION’s E & P Advisors Team Caribbean.Kyle Reuber, His current PhD. role isis multi a geologist-faceted and for broad ION’s in scope. E & P Kyle Advisors Team based based in Houston. His primary area of focus is Latin America has indesigned Houston. SPAN Hisprograms primary in locations area of such focus as Panama, is Latin Argentina, America and the and the Caribbean. His current and West Africa. His interpretation projects integrate the regional 2D - role is multi-faceted and broad Caribbean. His current role is multi-faceted and broad in scope. Kyle in scope. Kyle has designed SPAN and available reprocessed vintage datasets. Kyle’s project SPAN programs in locations has designed SPAN programs in locations such as Panama, Argentina, such as Panama, Argentina, and management background also assists in his roles as the lead interpreter for multiple basin West Africa. His interpretation projects integrate the regional modeling studies along the Atlanticand West margins Africa. using Histhe ION interpretation data. projects integrate the regional 2D - 2D -SPAN and available reprocessed vintage datasets. SPAN and available reprocessed vintage datasets. Kyle’s project Kyle’s project management backgroundBrian also Horn, assists PhD. in his roles as the lead interpreter for multiplemanagement basin modeling studies background along also assists in his roles as the lead interpreter for multiple basin the Atlantic margins using the ION data. modeling studies along the Atlantic margins using the ION data.

Brian Horn, PhD. Friso Brouwer HGS – PESGB 17th Conference on Africa E&P 117

Friso Brouwer

Simon Greenfield, Dr. Peter Cox Core Laboratories UK Regional Reservoir Quality Trends in Cretaceous Sandstone Reservoirs in the Transform Margin Basins of Ghana

Cretaceous sandstones form major exploration targets across the Shelf edge locations in close proximity to the Romanche fracture Tano, Saltpond, and Accra-Keta basins in the transform margin zone in the Saltpond Basin, and to a much lesser degree in the of Ghana. Although there have been world class discoveries in Tano basin, were affected by the circulation of hot fluids that the Upper Cretaceous succession of the Tano Basin, large tracts were related to periods of high heat flow (Nemčok et al. 2015) of the margin remain relatively under explored. There is an that occurred following cessation of rifting and appear to have industry imperative to increase our understanding of the factors resulted in the precipitation of late carbonates and in some cases, controlling reservoir quality in these basins. quartz overgrowths that occlude high volumes of the remnant post compactional porosity. Lower Cretaceous sandstones from Our approach to this regional reservoir evaluation was to extract the Accra-Keta basin have much better reservoir quality. They maximum geological value from a large archive of legacy rock are interpreted to have been sourced from the Neoproterozoic samples (core, sidewall core (SWC), and cuttings) that has been Voltaian Basin and are far more compositionally mature, created by multiple exploration and appraisal drilling campaigns. containing far higher proportions of mechanically and Detailed petrographic descriptions have been performed chemically stable quartz, and are thus more resistive to both on over 700 thin sections describing detrital and authigenic compaction and diagenetic alteration. Furthermore, these mineralogy, the degree of compaction, and characterisation of sediments do not appear to have been significantly impacted by pore systems. Reservoir quality has been assessed by combining hydrothermal fluids. this observational data with an extensive legacy database of core analysis data, geothermal gradient data, and density A major shift in sandstone composition is recorded in the Upper porosity analysis. The objective of the study was to compare and Cretaceous succession of the Tano Basin, and it reflects the contrast the regional distribution of reservoir quality taking into transition to Syn-Transform and later (Uppermost Santonian – consideration sedimentary facies, sediment provenance, burial Maastrichtian) passive margin tectonic settings. Feldspar depth, and temperatures. and rock fragment abundances show a marked decrease in abundance when compared with the underlying Lower Lower Cretaceous (Berriasian - Albian) sandstones represent Cretaceous sediments, and show a progressive maturation the main rift sequence across the three studied basins. Reservoir through the Upper Cretaceous. Compositions are generally quality is strongly impacted by provenance. The principle subarkosic to sublithic during the Mid Cenomanian – Mid depositional environments at this time comprise basin margin Turonian, subarkosic to quartz arenites during the Late alluvial fans, braid delta fronts, and delta front slope fan lobes Turonian – Earliest Santonian, and are predominantly super- in deeper water sections of the basin. Reservoir quality is mature quartz arenites from the Late Santonian onwards. generally poor in the Tano and Saltpond basins except on High geothermal gradients result in the early onset of quartz structural highs and in some areas close to the present day overgrowth cementation at relatively shallow depths, around shoreline and onshore. Here, sandstone compositions are 1.5km burial. In some cases this had the positive effect of early generally both compositionally and texturally immature with shut-down of mechanical compaction. Super mature quartz sediment composition strongly influenced by the immediate arenites are generally more prone to strong quartz cementation hinterland geology. Sandstones are rich in feldspar; ductile due to the higher surface areas available for precipitation mica-rich foliated metamorphics and coarsely crystalline compared with coarse grained/poorly sorted quartz arenites plutonic rock fragments. The sediment load has been sourced and subarkoses. Good to excellent reservoir quality is hosted by from Paleoproterozoic terranes dominated by metamorphic moderately buried Mid Turonian to Earliest Santonian, coarse and plutonic lithologies, indicating that provenance is key to grained sandstones predominantly deposited in slope channel/ predicting reservoir quality at this time. Due to the high content stacked channel sequences. Microquartz is an important factor of brittle and ductile grains, the sandstones are prone to strong that precludes quartz cementation in sandstone deposited in mechanical compaction. Cenomanian – Late Turonian times. Its distribution may be stratigraphically controlled. n

118 HGS – PESGB 17th Conference on Africa E&P Rowan Edwards, Michael King and Gregor Duval CGG Using Broadband 3D Seismic to Validate and Upgrade Satellite Seepage Data, Gabon

CGG have recently combined their latest 3D Broadband Seismic tectonics in hydrocarbon migration within the basin, both as a survey from their MCNV (Multi Client new Ventures) group source of large structures connecting reservoirs to the shallow with satellite seepage data from their NPA Satellite Mapping subsurface, and as a method of forming small scale seabed faults Group. By combining NPA’s sea surface oil slick data derived related to localised doming. n from SAR (synthetic-aperture radar) imagery and 3D broadband seismic data acquired off the SW coast of Gabon, and using a Biographical Sktech previously developed oil slicks to seismic workflow, links can be I obtained my BSc in geology made between sea surface slicks with features on the seabed and before taking a role as a within the subsurface which are potentially related to seepage. mudlogger with Geoservcies. After working on a variety of The project aim was to both high grade and validate the seepage projects from deep water west data, as well as create hotspot maps which describe the quality of the Shetlands to onshore and frequency of these seepage related features, for example North Africa I returned to DHI’s, possible migration pathways, fluid escape features, or university to undertake an seabed features. By combining these maps with the sea-surface MSc in petroleum geoscience slicks, areas of potential hydrocarbon generation, migration, and at Royal Holloway. My thesis escape are able to be identified. was on 2D analogue modelling of rift systems, this led on to Additionally, by integrating the results of the seep to seismic my current role with NPA workflow with bathymetry and interpreted channels, a model Satellite Mapping where I have been for 5 years. My role involves can be built up of both active and inactive hydrocarbon onshore mapping projects, primarily in SE Asia and Africa, as seepage, as well as the potential migration pathways of these well as seismic interpretation, and working closely with offshore hydrocarbons through a combination of channels and shallow interpreters on our Seep to Seismic projects. faults. Inferences can also be made about the role of salt

HGS – PESGB 17th Conference on Africa E&P 119 Notes

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120 HGS – PESGB 17th Conference on Africa E&P The 17th HGS-PESGB Conference Est. 1964

PES .org.uk on African E&P pesgb

Student Poster Presentations Abstracts

September 10-13, 2018 Norris Convention Centre, Houston Texas Malik Muhammad Alam CBTH Project and Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas Comparing Controls on the Formation of 27 Passive Margin Fold-Belts from the Margins of the Gulf of Mexico, South Atlantic and Africa

I have compiled map information on 27 passive margin fold fold-belts with about ¾ of past production in the shallower- belts (PMFB) in the Gulf of Mexico, African, and Atlantic water, normal fault breakaway zone and ¼ of past production in margins, and haveComparing grouped controls them according on the formation to whether of their 27 p assive themargin deeper-water, fold-belts fold from and the thrust margins belt. ofn the Gulf of Mexico, South Atlantic and Africa basal detachment is composed of salt or shale (Figure 1). Biographical Sketch 46% of the 27,Malik PMFB Muhammad are controlled Alam, by CBTH salt detachments, Project and Department16% Biographical of Earth and Atmospheric Sketch Sciences, University of by shale detachments,Houston, and Houston, 38% by Texas other lithologies. In the Malik Muhammad Alam is Malik Muhammad Alam is a second year Geology MS student at the Gulf of Mexico,I hav salt-detachede compiled mapPMFB’s information include theon 27following passive margin afold second belts year(PMFB) Geology in the MS Gulf of Mexico, African, seven examples:and Atwater, Atlantic Keathley-Walker, margins, and have Timbalier, grouped themPerdido, according student to whether at the their University basal detachment of is composed University of Houston, working with Dr. Paul Mann as part of the Conjugate Campeche, Marbella,of salt or and shale Catemaco. (Fig. 1). Along46% of the the South 26 PMFB Atlantic’s are controlledHouston, by salt working detachments, with Dr. 16% by shale detachments, and 38% by other lithologies. In the Gulf ofPaul Mexico, Mann salt as -partdetached, of the PMFB’s include the Basin, Tectonics, and Hydrocarbons (CBTH) Consortium. His research margin of Southfollowing America, 7 examples: salt-detached Atwater, PMFB’s Keathley include-Walker, Timbalier, Perdido, Campeche, Marbella, and Jequitinhonha,Catemaco. Campos, andAlong Santos. the South Most Atlantic of the African margin ofPMFB’s South America,Conjugate salt- Basin,detached Tectonics, PMFB’s includes analyzing the CHIRP data from Houston Ship-channel area, as well are mostly controlledinclude Jequitinhonha,by salt detachments Campos (Aaiun,, and MSGBC,Santos. Most of theand African Hydrocarbons PMFB’s are (CBTH) mostly controlled by salt Lower Congo,detachments Kwanza, Benguela, (Aaiun, and MSGBC, Majunga); Lower only Congo, the Niger Kwanza, BenguelaConsortium., and His Majunga) research. O nly the Niger delta is controlled by shale detachments. The dip of both salt and shale detachments varies from 2° to 20° and as the Passive Margin Fold Belts in the Gulf of Mexico, South America, and delta is controlledthe width by shale of the detachments. up-dip, normal The fault, dip breakawayof both salt zone rangesincludes from analyzing 3 to 7 km. the Tectonic CHIRP- related over- and shale detachmentssteepening varies occurs from in the2° toMexican 20° and Ridges the width in the of western data Gulf from of Mexico. Houston Deltaic Ship--related progradation and the African Margins. He expects to graduate in May 2019. the up-dip, normalover- steepeningfault, breakaway occurs zone in the ranges Niger from delta. 3 Productiveto 7 km. petroleumchannel area,systems as well are as found the in 100% of the twenty-six-passive margin fold-belts with about 3/4 of past production in the shallower-water, normal Tectonic-relatedfault over-steepening breakaway zone occurs and 1/4 in theof past Mexican production Ridges in the deeperPassive- water,Margin fold Fold and Belts thrust in belt.the in the western Gulf of Mexico. Deltaic-related progradation and Gulf of Mexico, South America, over-steepening occurs in the Niger delta. Productive petroleum and the African Margins. He expects to graduate in May 2019. systems are found in 100% of the twenty-seven-passive margin

Figure 1: Locations of the Passive Margin Deepwater Fold-thrust Belts on the Gulf of Mexico, Atlantic Margin of SouthFigure America 1: Locations and of the African Passive MarginMargin. Deepwater Yellow Fold dots-Thrust signifies Belts on the the Gulf Salt of Mexico, Detachment Atlantic Margin Fold-thrust of South Ame beltsrica andand African Maroon Margin. Yellow Dots signifies the Salt Detachment Fold-Thrust belts and Maroon Dots signifies the Shale Detachment Fold-trust Belts. dots signifies the Shale Detachment Fold-thrust Belts.

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Figure 2: Marked Fold-Belts of Gulf of Mexico and South-American Margins

Figure 2: Marked Fold-Belts of Gulf of Mexico and South-American Margins Figure 2: Marked Fold-Belts of Gulf of Mexico and South-American Margins

Figure 3: Marked Fold-Belts of African Margins Figure 3: Marked Fold-Belts of African Margins

Figure 3: Marked Fold-Belts of African Margins

HGS – PESGB 17th Conference on Africa E&P 123 Nikola Bjelica University of Houston, Houston, Texas

Compilation of Widespread, Cretaceous OAE1, OAE2, and OAE3 Black Shale Horizons Documented in Wells from the Gulf of Mexico, Caribbean, and Atlantic Passive Margins

Oceanic anoxic events (OAEs) represent intervals in the Earth’s I have compiled the extent and thickness of OAE’s on Gulf of past where portions of oceans were depleted of oxygen at water Mexico, Caribbean, and Atlantic margins using published well depths ranging from 300-5500 meters. OAE events are caused data. This data shows that OAE1 can vary in thickness up to by increased tectonic activity that led to massive volcanic 200m with a TOC value up to 5% in the Gulf of Mexico whereas eruptions and deposition of carbon-rich, black shale in marine in the Atlantic is in range of 50-1700m with TOC values ranging environments. There are eight documented Cretaceous anoxic from 1-20%. OAE2 thickness in the Gulf of Mexico is up to 50m events that include: with TOC values in the range of 2-3% and in Atlantic margins of South America and Africa thicknesses range from 50-500m with 1. OAE1a Selli event of 124.2-123.4 Ma age related to Aptian TOC values 2-10%. OAE3 thicknesses are up to 100m with TOC volcanic activity of the Ontong Java oceanic plateau in the values in the range of 4-5%. n western Pacific Ocean. Biographical Sketch 2. OAE1b consists of the Jacob sub-event of Aptian age (113.6- 113.2 Ma), Paquier event of Albian age (112-111.6 Ma) and I am an undergraduate Geology Urbino event of Albian age (110.9-110.6 Ma); all three of these major at the University of sub-events are related to volcanic eruptions of the Albian Houston. I joined the CBTH Kerguelen Plateau eruptions in the Indian Ocean. research group in May 2018 and since then I have assisted 3. OAE1c Tollebuc event of Albian age (103.7-103.4 Ma) was in managing the GIS database related to volcanism during Albian South America-Africa for stratigraphy and wells, breakup. and analyzing compilation of 4. OAE1d Breistroffer event of (100.6-100.2 Ma) related to widespread Oceanic Anoxic volcanism related to Albian rifting of South America and Events (OAEs) black shale Africa. horizons documented in wells from the Gulf of Mexico, 5. OAE2 Bonarelli event of Cenomanian age (93.8-93.5 Ma) Caribbean and Atlantic passive produced by Turonian Caribbean Plateau eruptions in the margins. Caribbean Sea. 6. OAE3 event of Coniacian age (87.3-84.6 Ma) produced by Coniacian-Santonian volcanic eruptions related to the Caribbean oceanic plateau.

124 HGS – PESGB 17th Conference on Africa E&P Naila Dowla, Dale Bird, Michael Murphy University of Houston, Houston, Texas 3-D Crustal Model of Northwest Africa

Our understanding of the Central Atlantic conjugate continental rift basins bounded by high to moderately dipping reactivated margins is skewed; the North American side has been heavily normal faults. The thinning of the crust, in conjunction with studied, but the northwest African side has not. In particular, interpreted Triassic rift basins,Biographical suggests that the AfricanSketch margin most studies reject or minimize the extensional deformation of did indeed undergo crustal extension and deformation continental crust along the African margin. To examine possible during rifting. n th African deformation, we constructed a six-layer 3-D crustal Naila Dowla is a 5 year Geology Ph.D. candidate and teaching model of northwest Africa and performed a gravity structural Biographical Sketch inversion to estimate its crustal structure. The African margin Naila Dowla is a 5th year assistant at the University of Houston, with an expected graduation crustal thickness beneath the Mauritanides mountain belt Geology PhD candidate date of spring 2019. Her dissertation research focuses on extensional varies little along strike, ranging from 35 to 40 km. East of the and teaching assistant at the Mauritanides, its thickness varies little between 33 and 36 km, University of Houston, with an tectonics and the effects of rifting on crustal geometries, as well as similar to previously published West African Craton studies. expected graduation date of Westward, the thickness is variable, inconsistently thinning to spring 2019. Her dissertation the possible influences of pre-existing structures, using potential 15 km over 500 km. This shifts the limit of extension 400 km research focuses on extensional eastward of previously interpreted crustal extension limits. We tectonics and the effects of fields, specifically for the conjugate margins of the Central Atlantic. observe crustal thickness fluctuating between 25 to 15 km. rifting on crustal geometries, as Naila’s undergraduate studies include a B.S. in Physics from the The largest region of thinned crust follows the western well as the possible influences Mauritanides foothills, trending NNW and possibly represents of pre-existing structures, using University of Texas at Austin in 2011, and a post-baccalaureate B.S. in a foreland basin associated with Paleozoic compressional events potential fields, specifically culminating in the collision of Gondwana with Laurentia and for the conjugate margins of Geophysics from the University of Houston in 2014. She has held the closing of the Rheic ocean. The NNW-SSE trends diminish the Central Atlantic. Naila’s undergraduate studies include a BS numerous officer positions for the AAPG student chapter at the southward at the expense of smaller NE-SW trending highs in Physics from the University of Texas at Austin in 2011, and and lows. These features are parallel to eastern North America a post-baccalaureate BS in GeophysicsUniversity from the of University Houston, of such as treasurer, vice president, and president, and is an organizer for normal-fault bounded Triassic rift basins when the Central Houston in 2014. She has held numerous officer positions for Atlantic is reconstructed to 185 Ma, the estimated time of the AAPG student chapter atthe the University Houston of Houston, AA suchPG as Student Expo. oceanic crust formation. Because the orientation is comparable treasurer, vice president, and president, and is an organizer for to those rifts east of central portion of the Appalachians, we the Houston AAPG Student Expo. interpret these crustal thickness highs and lows to be Triassic

HGS – PESGB 17th Conference on Africa E&P 125 Marie-Nelsy Kouassi, Paul Mann, Joel Saylor, Kurt Sundell University of Houston, Houston, Texas New Insights into the Assembly and Breakup of Pangea from a Mega-Regional Compilation of 8,672 Detrital Zircon Ages from the Circum-Gulf of Mexico, Northern South America, and West Africa

We present a regional compilation of 8,672, published detrital This shift in provenance from a dominantly Gondwanan zircon ages to better constrain the linkages between the provenance to a mixed Laurentian and Gondwanan provenance Suwannee and the Maya terranes on the West African side of records the collision of Laurentia and Gondwana to form Gondwana, and the linkage between the Oaxaquia and the Pangea. The early Mesozoic breakup of Pangea left the Mixteca terranes on the South American side of Gondwana. Suwannee, Maya, Mixteca, and Oaxaquia terranes attached to Previous work has shown a variety of options on the spatial and the southern margin of Laurentia and enabled new and more temporal positioning of these terranes from the early Paleozoic complex, clastic sediment pathways. n to early Mesozoic. The compiled, detrital zircons ages consist of grains from Paleozoic and Mesozoic clastic rocks that blanketed Biographical Sketch Marie-Nelsy Kouassi is a first year Geophysics the area of pre-Iapetus rifting between the early Paleozoic peri- Marie-Nelsy Kouassi is a first Gondwana terranes and Gondwana and subsequently during year Geophysics PhD student Ph.D. student at the University of Houston, working with the early Mesozoic along the Gulf of Mexico and Atlantic rifted at the University of Houston, margins of Pangea supercontinent. The age distributions of the working with Dr. Paul Mann as Dr. Paul Mann as part of the Conjugate Basins, detrital zircons for each terrane and cratonic area were compared part of the Conjugate Basins, using stacked probability density plots. Zircon populations of Tectonics and Hydrocarbons Tectonics and Hydrocarbons (CBTH) Consortium. She all terranes were compared using the K-S test D value displayed (CBTH) Consortium. She received her BSc degree in Geophysics in May 2017 on multi-dimensional scaling plots. Abundant, Grenville age received her BSc degree in Geophysics in May 2017 from populations from Paleozoic strata from the Maya, Mixteca from the University of Houston. As a senior, she and Oaxaquia terranes show strong linkages and common the University of Houston. As clastic source areas with coeval Colombian Eastern Cordillera a senior, she completed a thesis completed a thesis involving the use of a large detrital (Colombia) terranes and the Sunsas province of the Amazonian involving the use of a large craton. In contrast, detrital zircon of the Suwannee terrane of detrital zircons age compilation zircons age compilation to correlate terranes in eastern Florida closely matches West African terranes as both regions to correlate terranes in eastern and southern Mexico and eastern shared Pan-African and TransAmazonian-Eburnean source U.S. to their potential sourcesand in West southern Africa and Mexico South and America. eastern U.S. to their potential sources in West Africa and South areas during the early Paleozoic. Similarities of these closely- Her PhD research focuses on the 3D velocity model building America. Her Ph.D. research focuses on the 3D velocity model building and depth migration of linked, Paleozoic terranes decline by post-orogenic, introduction and depth migration of 2D seismic data in subsalt environment of zircons related to reactivation of North American cratonic in the central U.S. deepwater2D Gulf seismic of Mexico data in inorder subsalt to improve environment in the central U.S. deepwater Gulf of Mexico in order to basement and orogenic-related magmatic activity. the resolution for seismic attributes extraction and structural interpretation. She expects toimprove graduate the in 2021.resolution for seismic attributes extraction and structural interpretation. She expects

to graduate in 2021.

126 HGS – PESGB 17th Conference on Africa E&P T.Q. Pham, C. Ebinger, S. Oliva Earth & Environmental Science, Tulane University, New Orleans, LA K. Peterson Earth & Environmental Science, University of Rochester, Rochester, NY P. Chindandali Malawi Geological Survey, Zomba, Malawi D. Shillington LDEO, New York Geometry and Kinematics of Seismically Active Border and Transfer Fault Systems in the Malawi Rift, Africa

Although the deep, wide basins of the Western Rift, Africa have earthquakes occurred at depths of 25-35 km along projections served as models for the formation and evolution of half- of the North basin border fault, indicating that the border fault graben basins, little is known of the geometry and kinematics of is still active. In the Central basin, the border fault is largely the border fault systems, nor of their depth extent. Using a new inactive, as well as the zone underlain by a Permo-Triassic local earthquake database from the 8/2013 through 10/2015 rift basin. Except for a few swarms of earthquakes beneath SEGMeNT (Study of Extension and maGmatism in Malawi Rungwe volcano, the volcanic province is largely inactive. After aNd Tanzania) seismic array, which comprised 57 onshore and developing a new local magnitude scaling, we determined 32 lake-bottom seismometers, we examine the kinematics and magnitudes of 1160 earthquakes that are well located within extension direction of the northern two basins of the Malawi the SEGMeNT array: 0.7 < ML < 5.1. The b-value is 0.88 ± 0.04, rift, including the Rungwe volcanic province. We also evaluate and magnitude of completeness is ML 1.9. The focal mechanism the geometry and kinematics of the intra-basin and border solutions are primarily dip-slip normal faults with steeply faults using nodal planes of 62 well-determined first motion dipping (> 45º dips) nodal planes, with some strike-slip and focal mechanisms, along-axis variations in seismogenic layer oblique reverse faults. Extension direction from stress inversion thickness, and existing constraints on crustal thickness. We and Kostrov summation of declustered local focal mechanisms located earthquakes using a new regional 1D velocity model, and Global CMTs indicates a N56 ± 28/15ºE and N70ºE and we use double-difference methods to relocate several opening direction, respectively. Representative cross-sections clusters of earthquakes. The spatial distribution of earthquakes illustrate the distribution of active strain across these archetypal shows that the regions with the highest levels of seismicity are half-graben basins, and enable comparisons with time-averaged intrabasinal faults in the North basin, including the Karonga deformation. n region that experienced damaging earthquakes in 2009. Some

HGS – PESGB 17th Conference on Africa E&P 127 Geraldine Tijerina University of Houston – Department of Earth and Atmospheric Sciences Constraints on Central Atlantic Rifting Based on a Compilation of Low-Temperature Thermochronology Ages from Rifted, Conjugate Margins of the East Coast of the USA and

Northwestern Africa

North America Formation Formation of Pangea/Collision between Gondwanan & Laurasia Opening Opening of Central the Atlantic/Pangea Breaks up Rifting Rifting and drifting related Acadian Orogeny Taconic Orogeny

The Appalachian orogeny was the result of progressive, to the present as the result of the collision between northern northeast-to-southwest closure of Gondwana (Africa and South Africa and Spain. The major phase of uplift in the High Atlas America) and Laurasia (North America), and assembly of the Mountains occurred during the Alpine phase of deformation in Pangean supercontinent from the Ordovician through Permian the Oligocene-Miocene (30-20 Ma). time: 1) the Taconic orogeny of the northern Appalachian orogeny involved volcanic arc-continent convergence from I used previous literature to compile Low-Temperature Middle Ordovician into Early Silurian time (470-443 Ma); 2) thermochronology (LTT) data from both the eastern US the Acadian orogeny represented terminal collision of the North and northwest African margins which include apatite fission American and African plates during the late Devonian and Early track (AFT), zircon fission track (ZFT), and helium methods Mississippian (375-359 Ma) and also had a more profound effect (U-Th/He). A total of 440 samples were compiled on the on the northern Appalachians; 3) progressive southwestward North American margin and a total of 227 data samples from and terminal suturing of the two continents during Late northwestern Africa. The DZ Stats software developed by Saylor Pennsylvanian to Permian time (299-252 Ma) led to widespread and Sundell (2016) was used to generate time-density plots compression in the southern Appalachians during the Alleghany shown as histograms, and the natural neighbor interpolation orogeny. During the Triassic and Jurassic, rifting extending the tool in ArcMap was used to generate interpolated age surfaces. Appalachian-Atlas Mountains with the eventual formation of Analysis of the resulting age-histograms from the North the modern Atlantic Ocean. The Anti-Atlas Mountains formed American margin reveals, with large LLT age populations for the during the Alleghenian orogeny and were later rifted during the Taconic orogeny in the northeastern USA during the Ordovician Triassic-Jurassic, Atlantic rift phase. The High Atlas Mountains (480-440 Ma), the Acadian Orogeny during the Devonian formed by inversion of these rifts from the early Cretaceous (398-359 Ma), and the terminal Alleghenian orogeny during the

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North America Formation Formation of Pangea/Collision between Gondwanan & Laurasia Opening Opening of Central the Atlantic/Pangea Breaks up Pennsylvania (325-260 Ma). A major exhumation phase of the Biographical Sketch Appalachians occurred in post-orogenic times from 200 to 150 Geraldine Tijerina is an Ma, and is believed to represent isostatic uplift and removal of undergraduate senior at Rifting Rifting and drifting related Acadian Orogeny Geraldine Tijerinathick, syn-collisionalis an undergraduate basins. Sample senior populations at thein northwest University the of UniversityHouston of- Houston-Taconic Orogeny Downtown whereAfrica show she exhumation is studying related to Geologydeformation of with the Anti- a concentrationDowntown where in she is Petroleum. SheAtlas is Mountains working and with Cenozoic Dr. collision Paul Mannduring the as Alleghany part of thestudying Conjugate Geology with a orogeny (325-260 Ma), and early Cretaceous rift inversion (145- concentration in Petroleum. Basins, Tectonics,100 Ma). andSamples Hydrocarbons from both margins (CBTH) show the shared Consortium Alleghany whereShe is working she iswith Dr. managing theorogeny GIS formed database during terminal, for thermochronology. continent-continent collision Geraldine Paul Mann is as the part of the Treasurer for between the AAPG Gondwana-UHD and Laurasia student around chapter 335 Ma andand the expects late Conjugate to graduate Basins, Tectonics, December of Triassic2019. – Early Jurassic rifting between the two margins in the and Hydrocarbons (CBTH) period of 236-199 Ma. n Consortium where she is managing the GIS database for thermochronology. Geraldine is the Treasurer for the AAPG-UHD student chapter and expects to graduate December of 2019.

HGS – PESGB 17th Conference on Africa E&P 129 JohnathanTorres University of Houston-Downtown, Natural Sciences Department, Houston TX, USA Stanislaw Nagy AGH University of Science and Technology, Department of Gas Engineering, Krakow, Poland SageMuttel, Dougles Syzdek, Janusz Grębowicz University of Houston-Downtown, Natural Sciences Department, Houston TX, USA Application of Raman Spectroscopy for Determination of Natural Gas Composition

Reservoir analysis plays a crucial role in both the characterization us in the exploration industry the simplicity of hydrocarbon and operations of hydrocarbon exploration. Raman spectroscopy determination. n (RS) uses scattering light to measure low frequency vibrational and rotational values and can hypothetically be used to Biographical Sketch determine in situ natural gas composition. Johnathan Torres graduated from University of Houston- RS displays specific gas intensity as a function of Raman shift Downtown where he or wavelength. Laser lights come into contact with variable received a bachelor’s of concentrations of natural gas components and produces a specific science in Geoscience with a amount of scattering light. The scattered light being produced is concentration in Petroleum ultimately being compared to the original beam, which allows for Geotechnology and a minor the spectrum to be created. Upon analysis, each sample’s individual in Applied Physics. Early in spectrum at a given temperature is compared to one another and his undergraduate career, he each peak is characterized by known natural gas values. embarked on his first research endeavor that analyzed Upon concluding the analysis, it was found that temperature core sediment from a local had little effect on the Raman shift value a given natural mitigation bank to determine gas exhibited. It became clear the frequency or Raman shift anomalies present since urban development and natural remained steady and the real effect was seen in the intensity disasters. Passionate about research he took on a field based of the spectrum. This change ranges anywhere from a couple study that focused on the lithostratigraphy and biostratigraphy Applicationhundred to of a Ramanvery slight Spectroscopy change in for intensity. Determination As well of as Natural a decrease Gas Composition of the Chinle Formation in central Utah. The study confirmed

JohnathanTorresin intensity a thinning1, Stanislaw in theNagy peak2, SageMuttel also seems1, Dougles to occur Syzdek in every1, Janusz Grębowiczhis interest1 in soft rock geology and encouraged Johnathan to sample. Overall the concentration of a certain gas does have an take on a laboratory setting study that focused on the thermal 1University of Houston-Downtown, Natural Sciences Department, Houston TX, USA 2impactAGH University on the ofshape Science of the and curve. Technology, It seems Department to depend of Gas mostly Engineering, on Krakow,analysis Poland of hydrocarbon bearing shale for retorting purposes. the molecular structure of each gas. This simplistic spectroscopy Johnathan’s involvement with UHD’s geological faculty landed Reservoir analysis plays a crucial role in both the characterization and operations of hydrocarbontechnique can exploration. easily be Raman used spectroscopyin individual (RS) determination uses scattering of light to measurehim alo studyw abroad research opportunity in central Poland. frequencynatural gas vibrational composition and rotational within values gaseous and mixtures.can hypothetically be used to determineWhile abroadin situ Johnathan spent his time in the geophysical lab natural gas composition. studying paleomagnetism on organic rich shale and in the RSPeak displays characterization specific gas intensity and the as description a function of ofRaman the relationship shift or wavelength. Lasergas engineeringlights come lab working with Raman spectroscopy on the intoof pressure contact with and variable temperature concentr onations Raman of natural shift gas is componentsthe core and produces a specific amount of scattering light. The scattered light being produced is ultimately beingdetermination compared to of natural gas composition. Upon completion of theimportance original beam, objective which allowswhen forconsidering the spectrum identifying to be created. both Upon in analysis,situ eachhis undergraduate sample’s degree, Johnathan landed a job in a geological individualand predetermined spectrum at a gaseous given temperature mixtures. is This compared serves to oneto remind another and each peak is characterized by known natural gas values. service company, where he works in both the XRD and XRF lab to determine mineralogy of various exploration wells across the country. Mr. Torres has since then enrolled in Rice University’s Subsurface Geoscience graduate program, where he continues his interest in research and learning industry applicable skills. Johnathan’s goal is to one day intergrade both geochemistry and geomechanical data to aid 3D geological modeling for Fig.1 Full Spectrum of 8 natural gas composites exploration and recovery processes. Figure 1. Full Spectrum of 8 natural gas composites Upon concluding the analysis, it was found that temperature had little effect on the Raman shift value130 a given natural gas exhibited. It became clear the frequency or Raman shift remained HGS – PESGB 17th Conference on Africa E&P steady and the real effect was seen in the intensity of the spectrum. This change ranges anywhere from a couple hundred to a very slight change in intensity. As well as a decrease in intensity a thinning in the peak also seems to occur in every sample. Overall the concentration of a certain gas does have an impact on the shape of the curve. It seems to depend mostly on the molecular structure of each gas. This simplistic spectroscopy technique can easily be used in individual determination of natural gas composition within gaseous mixtures.

Peak characterization and the description of the relationship of pressure and temperature on Raman shift is the core importance objective when considering identifying both in situ and predetermined gaseous mixtures. This serves to remind us in the exploration industry the simplicity of hydrocarbon determination Daniel Woodworth, Chengzu Wang Department of Earth, Environmental, and Planetary Science, Rice University, Houston, TX Nuhazein Mohamed Department of Earth, Environmental, and Planetary Science, Rice University, Houston, TX Geophysics Department, Al Neelain University, Khartoum, Sudan Richard G. Gordon Department of Earth, Environmental, and Planetary Science, Rice University, Houston, TX Is Africa Stationary? – A New Look at an Old Question

Introduction event. The initial rift development in the main Ethiopian Rift In a pioneering paper, Burke and Wilson (1972) proposed that area has been assigned ages of 18 to 11 Ma (Mohr, 1983; Wolde the Africa plate came to rest relative to the mantle and began to Gabriel et al., 1990; Ebinger et al., 1993). rise in association with widespread intraplate volcanism at ~30 Ma. Burke (1996) further developed this hypothesis, attributing Africa from ~15 Ma to Present: At 15 Ma, rifting propagated its above-average elevation to this cessation of motion, and southward from Afar into the main Ethiopian Rift, and the raising several intriguing questions: Why did the African Plate western rift initiated. It is possible that the development of these come to rest over the mantle circulation? How are rifting rifts and the new harrats of Arabia might have been related to episodes linked? Are these erupted rift volcanisms comparable the Bitlis collision. Formation of ocean floor in parts of the Red over the past 30 Myr? How is the development of the East Sea, transform offset on the Dead Sea system, propagation of African Rift System (EARS) related to the reconstruction of new ocean floor formation into the Afar region from the Gulf the Indian Plate and to the formation of the Central Indian of Aden, and southward propagation of rifting from Turkana and Carlsberg Ridges? Do the Red Sea and the Gulf of Aden to form the Gregory (Kenyan) Rift, constitute the most radical constitute part of the EARS? Understanding the evolution of changes in the EARS over the past 5 Ma. the African Plate over the past 30 Myr, integrated with different kinds of relevant data, will enable a comprehensive approach in Methods solving these queries. Our analysis focuses primarily on refining the absolute motion history of the African plates over the last 48 Myr using new Review of Africa from 65 Ma to Present global plate motion models. Koivisto et al. (2014) used a global Africa from 65 Ma to 30 Ma: This interval was marked by a plate circuit to relate rotations between the Pacific Plate and its relatively quiet tectonic state of Africa, with high global sea level underlying hotspots, which rely on the clear hotspot tracks on leaving Africa submerged since Late Cretaceous time (Sahagian, the Pacific Plate, to a global hotspot frame. For ages older than 1988), following Jurassic to Cretaceous rifting episodes. 48 Ma, this global frame fails, likely due to flaws in the plate From ~65 Ma to ~30 Ma, igneous activities, apart from those motion circuit, but since that age motion between hotspots has generated in Tristan and the Deccan Traps, were continuous been only 2-6 mm/yr—slow enough that the hotspots can be only in northern Carmeroon. A potential hotspot track can be considered to represent a global frame. found in southern Ethiopia between 45 and 35 Ma (Ebinger et al., 1993), possibly linked to activity at Lokitipi (Morley et al. However, these Pacific-based rotations suffer from the 1992). Its azimuth is roughly concentric with the Walvis Ridge uncertainty accumulated by rotating through the global plate trend, which might be considered a later manifestation of the motion circuit. Although they do provide useful constraints same plume (Burke, 1996). The collision with Eurasia along the on the motion of the African plates, it would also be desirable northern African Plate slowed at 65 Ma and accelerated at 35 Ma to have a set of more specifically targeted rotations. Wang et al. (Dewey et al., 1989). (in prep.) calculate a new set of current absolute plate motions, HS4-SKS-MORVEL, combining data from both hotspot trends Africa from ~30 Ma to ~15 Ma: Initial eruption in the main (e.g. Wang et al., 2017) and seismic anisotropy (e.g. Zheng et Ethiopian Rift was at ~30 Ma (Wolde Gabril et al., 1990), al., 2014). In combination with additional improvements in followed by rift-faulting episodes. Between 30 and 22 Ma, plate motion circuits, such as DeMets et al. (2016) and DeMets half-grabens developed south in Lokitipi and extended east and Merkouriev (2016), which provide highly detailed relative in Turkana (Morley et al., 1992). A change in the eruptive rotations between Nubia, North America, and the Pacific over composition in Kenya at ~16 Ma, from basalt to phonolite, is the last 20 Myr, we can attempt a detailed history of the absolute within the influential resolution of the Bitlis-Zagros collisional motion of the African plates (Figure 1).

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the Pacific Plate, to a global hotspot frame. For ages older than 48 Ma, this global frame fails, likely due to flaws in the plate motion circuit, but since that age motion between hotspots has been only 2-6 mm/yr—slow enough that the hotspots can be considered to represent a global frame.

However, these Pacific-based rotations suffer from the uncertainty accumulated by rotating through the global plate motion circuit. Although they do provide useful constraints on the motion of the African plates, it would also be desirable to have a set of more specifically targeted rotations. Wang et al. (in prep.) calculate a new set of current absolute plate motions, HS4-SKS-MORVEL, combining data from both hotspot trends (e.g. Wang et al., 2017) and seismic anisotropy (e.g. Zheng et al., 2014). In combination with additional improvements in plate motion circuits, such as DeMets et al. (2016) and DeMets and Merkouriev (2016), which provide highly detailed relative rotations between Nubia, North America, and the Pacific over the last 20 Myr, we can attempt a detailed history of the absolute motion of the African plates (Figure 1).

Figure 1. Major dated events that affect the African plate motion during the past 35 Ma [from Figure 7d & 7e DeMets et al. (2016)], whereFigure the 1. interval Major plate dated directions events (CW that from affect N) gradually the African increase plate and abruptly motion decrease during for the both past pairs 35 respectively Ma [from between Figure ~17 7d and & 207e Ma. DeMets et al. (2016)], where the interval plate directions (CW from N) gradually increase and abruptly decrease for both pairs respectively between ~17 and 20 Ma. Initial Findings and Discussion Biographical Sketch Biographical Sketch The rotations relative to the hotspots from Koivisto et al. (2014) Daniel Woodworth is a agree well with the hypothesis proposed by Burke (1996). From fifth-year PhD student in Daniel Woodworth is a fifth-year PhD student in the Department of Earth, 48-34Initial Ma, Findings these predict and steady Discussion motion of the African plates the Department of Earth, Environmental, and Planetary Sciences at Rice University in Houston, relative to the hotspots, with a notable slowdown between 34 Environmental, and Planetary Texas. His current research focuses primarily on reconstructing plate andThe 20 rotations Ma. For the relative past 20 Ma,to the the predictedhotspots motion from betweenKoivisto et al.Sciences (2014) at Riceagree University well with in the hypothesis proposed theby AfricanBurke plates(1996). and From the hotspots 48-34 is Ma,insignificant. these predict steadyHouston, motion Texas.of the His African current plates relative to the motion and true polar wander through analysis of the shape of marine hotspots, with a notable slowdown between 34 and 20research Ma. For focuses the pastprimarily 20 Ma,on the predicted motion magnetic anomaly profiles, equatorial sedimentation rates and sediment HS4-SKS-MORVELbetween the African provides plates an even and more the precisehotspots insight is insignificantreconstructing. plate motion facies, and secondarily on modelling strain rates distant from plate into current absolute motions. This model predicts slow but and true polar wander through HS4-SKS-MORVEL provides an even more precise insight into current absolute motions. This model boundaries and implementing improved methods of estimating spreading still significant motion between Nubia and Somalia and the analysis of the shape of marine hotspots,predicts with slow an butRMS still velocity significant of 11 mm/yr motion for the between former and Nubia magnetic and Som anomalyalia and profiles, the hotspots, with an RMS rates at mid-ocean ridges. 15velocity mm/yr offor 11the mm/yrlatter. Thus, for theboth former move slowly, and but15 aremm/yr not truly for theequatorial latter. sedimentationThus, both move slowly, but are not truly stationary—instationary— contrastin contrast to the to Antarctic the Antarctic and Eurasian and plates,Eurasian plates,rates and which sediment both facies, have motion so slow that it whichcannot both be have statistically motion so slowdistinguished that it cannot from be statistically no motion at andall. secondarily Figure 2 onsuggest modellings an strain even rates more distant nuanced from plate distinguishedapproach to from answering no motion the at all. question Figure 2 suggestsof the stationarityan even boundariesof Africa. and The implementing pole of rotation improved of methodsthe Nubia of estimating plate morerelative nuanced to the approach hotspots to answering actually the lies question on the of Nubiathe platespreading near 14°N rates on at mid-oceanthe seafloor ridges. west of the continent. stationarityThus at least of Africa. one The point pole on of the rotation Nubia of the plate Nubia is indeedplate stationary and nearby points move very slowly. As relativeone moves to the hotspotsaway from actually this lies point, on the in Nubia particular plate near to 14°Nthe southeastReferences, the speed of the Nubia plate lithosphere on the seafloor west of the continent. Thus at least one point on Burke, K and J.T. Wilson, (1972). Is the African plate stationary? the Nubia plate is indeed stationary and nearby points move Nature, 239, 387-390. very slowly. As one moves away from this point, in particular to the southeast, the speed of the Nubia plate lithosphere increases Burke K. (1996) The African Plate. S.Afr.J.Geol.,1996,99(4), 341-409 monotonically such that the Somalia plate and the eastern edge of the Nubia plate are clearly not stationary relative to the DeMets C. and S. Merkouriev (2016). High-resolution 2 hotspots and the deep mantle. reconstructions of Pacific–North America plate motion: 20Ma to present. Geophys.J.Int. 207, 741–773. doi:10.1093/gji/ggw305 These combined models provide insights into the past and present motion of the African plates, and an opportunity to Dewey, J.F., M.L. Helman, E. Turco, D.H.W. Hutton, and S.D. reexamine the Burke’s seminal hypothesis—and its implications Knott (1989). Kinematics of the western Mediterranean. In: for the history of Africa over the last 48. n Coward, M.P., Dietrich, D. & Park. R.G. (Eds.), Alpine Tectonics. Spec. Pub!. geol. Soc. Land., 45, 265-283.

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increases monotonically such that the Somalia plate and the eastern edge of the Nubia plate are clearly not stationary relative to the hotspots and the deep mantle.

These combined models provide insights into the past and present motion of the African plates, and an opportunity to reexamine the Burke's seminal hypothesis—and its implications for the history of Africa over the last 48

Figure 2. Global absolute plate motion from HS4-SKS-MORVEL (Wang et al., in prep.), calculated using hotspot trends and seismic Figure 2. Global absolute plate motion from HS4-SKS-MORVEL (Wang et al., in prep.), calculated using anisotropy. hotspot trends and seismic anisotropy. Duncan, R.A. (1981). Hot-spots in the southern oceans - an and F.M. Karanja (1992). Tectonic evolution of the northern absolute frame of reference for the motion for the Gondwana Kenyan Rift. J. geol. Soc. Land., 149, 333-348. continents. Tectonophysics, 74, 29-42. References Müller, R.D., J.Y. Royer, L.A. Lawver, (1993). Revised plate Ebinger C.J., T. Yemane, G. WoldeGabriel, J.L. Aronson, and R.C. motions relative to the hotspots from combined Atlantic and Burke, K and J.T. Wilson, (1972). Is the African plate stationary? Nature, 239, 387-390. Walter (1993). Late Eocene-Recent volcanism and faulting in the Indian Ocean hotspot tracks. Geology21 (3), 275–278. Burke K. (1996) The African Plate. S.Afr.J.Geol.,1996,99(4),341-409 southernDeMets main C. Ethiopianand S. Merkouriev rift. J. geol. Soc. (2016). Land., High150, 99-108.-resolution reconstructions of Pacific–North America plate O’Neill, C., D. Müller, B. Steinberger (2005). On the uncertainties motion: 20Ma to present. Geophys.J.Int. 207, 741–773. doi:10.1093/gji/ggw305 Koivisto, E.A., D.L. Andrews, and R.G. Gordon (2014), in hot spot recon-structions and the significance of moving hot Dewey, J.F., M.L. Helman, E. Turco, D.H.W. Hutton, and S.D. Knott (1989). Kinematics of the western Tests of fixity of the Indo-Atlantic hot spots relative to spot reference frames. Geochem. Geophys. Geosyst.6 (4), Q04003. Mediterranean. In: Coward, M.P., Dietrich, D. & Park. R.G. (Eds.), Alpine Tectonics. Spec. Pub!. geol. Pacific hot spots, J. Geophys. Res.Solid Earth, 119, 661-675, Soc. Land., 45, 265-283. Sahagian, D.L. (1988). Epeirogenic motions of Africa as inferred doi:10.1002/2013JB010413.Duncan, R.A. (1981). Hot-spots in the southern oceans - an absolute frame of reference for the motion from Cretaceous shoreline depostis. Tectonics, 7, 125-138. for the Gondwana continents. Tectonophysics, 74, 29-42. Morgan, W.J. (1981), Hot spot tracks and the opening of the Ebinger C.J., T. Yemane, G. WoldeGabriel, J.L. Aronson, and R.C. Walter (1993). Late Eocene-Recent Atlantic and Indian Oceans, in The Sea, The Oceanic Lithosphere, Wang C., Richard G. Gordon, Tuo Zhang, and Lin Zheng (2018). volcanism and faulting in the southern main Ethiopian rift. J. geol. Soc. Land., 150, 99-108. vol.7, edited by C. Emiliani, pp.443–487, Wiley, New York. Current Absolute Plate Velocities Inferred from Hotspot Tracks, Koivisto, E.A., D.L. Andrews, and R.G. Gordon (2014), Tests of fixity of the Indo-Atlantic hot spots and Comparison and Combination with Absolute Plate Velocity relative to Pacific hot spots, J. Geophys. Res.Solid Earth, 119, 661-675, doi:10.1002/2013JB010413. Morgan, W.J. (1983), Hot spot tracks and the early rifting of the from Orientation of Seismic Anisotropy. (In preparation) Morgan, W.J. (1981), Hot spot tracks and the opening of the Atlantic and Indian Oceans, in The Sea, The Atlantic, Tectonophysics, 94,123–139. Oceanic Lithosphere, vol.7, edited by C. Emiliani, pp.443–487, Wiley, New York. Wang C., Richard G. Gordon, and Tuo Zhang (2017). Bounds Morgan, W.J. (1983), Hot spot tracks and the early rifting of the Atlantic, Tectonophysics, 94,123–139. Morgan, W.J., and J. Phipps Morgan (2007), Plate velocities on geologically current rates of motion of groups of hot spots. Morgan, W.J., and J. Phipps Morgan (2007), Plate velocities in the hot spot reference frame, in Plates, in the hot spot reference frame, in Plates, Plumes, and Geophys. Res. Lett., 44, 6048-6056. Plumes, and Planetary Processes, vol.430, edited by G.R. Foulger and D.M. Jurdy, pp.6578, Planetary Processes, vol.430, edited by G.R. Foulger and Geol.Soc.of Am., Boulder,Colo., doi:10.1130/2007.2430(04). D.M. Jurdy, pp.6578, Geol.Soc.of Am., Boulder,Colo., Wolde Gabriel, G., J.L. Aronson, and R.C. Walter (1990). Geology, Mohr, P. (1983). Volcanotectonic aspects of Ethiopian rift evolution. Ancient Rifts and Troughs: Bull. doi:10.1130/2007.2430(04). geochronology, and rift basin development in the central sector Centres Rech. Explor.-Prod. Elf-Aquitaine, 7, 175-189. of the main Ethiopia rift. Bull. geol. Soc. Am., 102, 439-458. Mohr, P. (1983). Volcanotectonic aspects of Ethiopian rift evolution. Ancient Rifts and Troughs: Bull. Centres Rech. Zheng, L, Richard G. Gordon, and Corne Kreemer (2014). Explor.-Prod. Elf-Aquitaine, 7, 175-189. Absolute plate velocities from seismic anisotropy: Importance of correlated errors. J. Geophys. Res.: Solid Earth, 119, 7336-7352. Morley, C.K., W.A. Wescott, D.M. Stone, R.M. Harper, S.T. Wigger 3

HGS – PESGB 17th Conference on Africa E&P 133 Omar Zavala University of Houston – Department of Earth and Atmospheric Sciences Rift History of the South Atlantic Ocean from Subsidence Histories of Offshore Wells and Low-Temperature Thermochronology (AFT) Cooling Ages from the South American and West African Conjugate Margins

Previous studies have determined the variation in South Atlantic spreading rates from the time of its initial opening in the latest Jurassic (144 Ma) to the present. All previous plate models agree on the timing for abrupt variations in spreading rate: 1. maximum spreading rates up to 7 cm/yr occur from the time

of initial continental rifting from 150-120 Ma 2. to about 3 cm/yr. from 80-70 Ma; 3. rates remain constant before rising again to 6 mm/yr. in the Middle Eocene

4. then rates slow to a modern rate of 3.5 cm/yr (Colli et al., 2014). A simple, tectonic hypothesis is that periods of rapid spreading are expressed as widespread uplift of the passive margin and coastal areas that should be recorded both by the subsidence history of passive margin wells and the apatite fission track (AFT) cooling ages of near coastal rocks. To test this idea, I compiled burial-history plots of 26 passive margin wells on the two conjugate margins along with 1001 AFT ages from the South American coastal zone and 403 AFT ages from the West African coastal zone. Subsidence histories of the wells reveal the main rifting periods for the two conjugate margins and significant age differences for some conjugate, rift pairs (especially for the South Africa and southern South America conjugate margins). AFT ages for both conjugates were plotted as histograms using DZ Stats software developed by Saylor and Sundell (2016) and show a strong correlation with secular variations in spreading rates with denser clusters of cooling ages during periods of faster spreading (130-70 Ma). Andean orogenic events coincide with the high-density peaks of AFT ages in the late Cretaceous and in the Oligo-Miocene along the South American margin. The late Cretaceous peak of AFT ages on both margins may be a composite effect of continental rifting, the initial formation of oceanic crust, and the late Cretaceous, Peruvian, and Incaic orogenic events that affected the Andes. The lack of the younger age frequencies on the West African margin is consistent with the improbable transmission of compressive stress across the Mid-Atlantic spreading ridge.

To add, the lack of Oligo-Miocene low-temperature ages on the West African margin and the lack of uplift in offshore wells is also not supportive of the hypothesis that faster spreading uplifted both conjugate margins by equal amounts. n 134 HGS – PESGB 17th Conference on Africa E&P

Biographical Sktech completed his undergraduate senior research project on using Omar Zavala worked as subsidence histories of offshore wells and low-temperature an undergraduate research thermochronology ages from the South American and west assistant and GIS specialist African conjugate margins to study the rift history of the South for the Conjugate Basins, Atlantic Ocean. He currently works as a Field Geologist for RRC Tectonics, and Hydrocarbons Companies in Austin, Texas. (CBTH) project beginning in the spring semester of 2017. Omar graduated from the University of Houston with his Bachelor of Science degree in geophysics alongside a minor in mathematics. He

Omar worked as an undergraduate research assistant and GIS specialist for the Conjugate Basins, Tectonics, and Hydrocarbons (CBTH) project beginning in the spring semester of 2017. Omar graduated from the University of Houston with his Bachelor of Science degree in geophysics alongside a minor in mathematics. He completed his undergraduate senior research project on using subsidence histories of offshore wells and low-temperature thermochronology ages from the South American and west African conjugate margins to study the rift history of the South Atlantic Ocean. He currently works as a Field Geologist for RRC Companies in Austin, Texas.

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136 HGS – PESGB 17th Conference on Africa E&P Marcus P. Zinecker, Paul Mann Department of Earth and Atmospheric Sciences, University of Houston Plate Tectonic Framework for Petroleum Systems of Atlantic Conjugate Margins: Northwest Africa- Eastern USA and Northeast South America- Equatorial West Africa

The continental Guinea Plateau and nearby Guinea fracture South America and Africa plates before Equatorial Atlantic zone of offshore Guinea and Guinea-Bissau is a 100,000 km2 rifting commenced in the Late Aptian. Following Jurassic rifting submarine plateau which lies astride the boundary separating of North America from Gondwana, the Guinea Plateau and the older, (Triassic-Jurassic to recent Central Atlantic Ocean Demerara Rise formed a 15 to 30-km-thick passive margin. A to the north), from the younger, (Aptian-recent), Equatorial period of thermal subsidence created accommodation space Atlantic Ocean to the south. As a result of this location between for the deposition of a 2 to 7-km-thick carbonate sequence the two oceans, the Mesozoic tectonostratigraphy records west- of Late Jurassic-Early Cretaceous age, which thickens to the northwest rifting of the Central Atlantic during the Triassic and northwest. Rifting of Gondwana and the opening of the South early Jurassic and east-west rifting of the Equatorial Atlantic and Equatorial Atlantic began in the Early Cretaceous, starting in the Cretaceous. The Guinea Plateau can be reunited with with the South Atlantic and progressing northwards. Seafloor its conjugate, the 130,000 km2 submarine Blake Plateau along spreading finally initiated between the Demerara Rise and the southeastern margin of the USA by following the Guinea Guinea Plateau by the Early Albian. The depositional histories of Fracture Zone and the Cape Verde/Jacksonville Fracture the Demerara Rise and Guinea Plateau diverged following their Zone across the Central Atlantic. Early rifting of this part Early Albian separation. The Demerara Rise subsided quickly, of the Central Atlantic was accompanied by formation of accommodating deposition of thick marine shales, including Rhaetian-Hettangian (~204 MA to ~195 MA) salt basins along black shales from the OAE 1 and 2 events. Throughout the Late the Scotian/Moroccan and Carolina/Mauritania conjugate Cretaceous and Cenozoic, deltas and shorelines prograded and margins along with emplacement of thick, magmatic, seaward- retrograded onto the Demerara, creating interbedded, reservoir dipping reflectors (SDR’s) along both sides of the opening quality sands as well as shales. On the Guinea Plateau, a thin central Atlantic. Thinner SDR’s and volcanic rocks of similar layer of volcanic rocks was covered by predominately marine age were erupted during the rift phase of the northwestern shale deposition (including black shales from the Cenomanian- African margin. For most areas of both conjugate margins, Turonian OAE 2 event, followed by deltaic progradation in salt deposition ceased with the onset of seafloor spreading the Late Cretaceous, and finally carbonate deposition in the during the Sinemurian (193-190 Ma). Previous work has shown Cenozoic. n that Central Atlantic Magmatic Province (CAMP) volcanism Biographical Sketch took place over a 15 million year period, with two pulses of Biographical Sketch magmatism at 203 MA and 193 Ma. CAMP magmatic activity Marcus Zinecker is a first year Marcus Zinecker is a first year Geology PhD candidate at the University of and lithospheric weakening likely played a major role in Geology PhD candidate at the eventual continental breakup and the onset of seafloor spreading University of Houston, working Houston, working with Dr. Paul Mann as part of the Conjugate Basins, Tectonics, in the Central Atlantic. Rifting along the North American and with Dr. Paul Mann as part of and Hydrocarbons (CBTH) Consortium. He graduated Cum Laude with BS African margins was overall symmetrical, but early accretion the Conjugate Basins, Tectonics, rates of mid-ocean ridges were much higher to the west than and Hydrocarbons (CBTH) degrees in Geology and Geophysics in 2014 from the University of Houston. His to the east, resulting in significantly more oceanic crust on Consortium. He graduated PhD research includes the tectonostratigraphy and hydrocarbon potential of the North American Plate (56%) compared to its African Cum Laude with BS degrees counterpart (44%). in Geology and Geophysics offshore West Africa and its conjugate margins, as well as the effect of two- in 2014 from the University phase rifting on the subsidence history and hydrocarbon generation potential of South of the Guinea Fracture Zone, the Doldrums Fracture of Houston. His PhD research Zone connects the Guinea Plateau with its Equatorial Atlantic includes the tectonostratigraphy the southeast Gulf of Mexico. He expects to graduate in May of 2020. conjugate in northeastern South America, the Demerara Rise. and hydrocarbon potential This 60,000 km2 bathymetric high and area of continental and of offshore West Africa and its conjugate margins, as well as oceanic plateau crust is located offshore Suriname and French the effect of two-phase rifting on the subsidence history and Guiana in northeast South America. The Demerara Rise and hydrocarbon generation potential of the southeast Gulf of Guinea Plateau represent the final connection between the Mexico. He expects to graduate in May of 2020.

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Figure 1. Overview of the Central and Equatorial Atlantic ocean and fracture zones that serve as piercing points for the cojugate margins of the Guinea Plateau (GP), Blake Plateau (BP), and Demerara Rise (DR). Continent-ocean boundaries from [Brune et al., 2016], salt basin locations from [Biari et al., 2017], vertical gravity gradient from [Sandwell et al., 2014]. Land topograpahy is in meters.

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140 HGS – PESGB 17th Conference on Africa E&P The 17th HGS-PESGB Conference Est. 1964

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HGS Conference Committee

Al Danforth Advisor Ana Krueger Technical Committee, Session Chair - Oral Program Andrea Peoples Conference Co-Chair, Logistics Bill Dickson Session Chair - Oral Program BJ Davis Abstract Editor Bryan Cronin Abstract Review, Session Chair - Oral Program Brian Horn General Chairman, Session Chair - Oral Program Cheryl Desforges HGS Board President Ian Poyntz Advisor John Adamick Advisor John Jordan Speaker Gifts Ian Davison Session Chair, Oral Program Kyle Reuber Poster Session Luis Baez Session Chair - Oral Program Martin Cassidy Advisor Matthew Tyrrell Committee Nkechi Odumodu Judging

Onochie Okonkwo General Co-Chair, Judging, Session Chair - Oral Program Paul Haryott Technical Advisor Phil Towle Technical Program Chair Sam Loree Sponsorship, Booth Layout Sanmi Tunde Emmanuel Committee Stefania Gerbaudo Laronga Committee Thom Tucker Short Course Advisor Paul Harrgot Panel Discussion Moderator, Session Chair - Oral Program

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