AAPG Annual Convention and Exhibition

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The Upper Cretaceous Post Rift Petroleum Systems of the West African Transform Margin and MSGBC Basin (Benin to Mauritania), Learnings From the Past, the Present and the Identification of Future Plays

Abstract

The West Africa Transform Margin the discovery of the material Jubilee Field in 2007 was the catalyst for intense exploration activity by many operators in the deep-water Upper Cretaceous clastic plays. The success rate along the Transform Margin since 2007 has been a 60% technical success yet the commercial success so far has been only 16%, with more than 20 unappraised discoveries due to both below and above ground events. A look back pre and post Jubilee, in all wells, at the post drill dry hole risks shows how these have evolved over time. A series of rift basins each with a unique structural and depositional history characterized by asymmetrical rifting and varying deep structural observations influenced the heat flow and the petroleum potential of both syn and post rift sequences. The post rift sequences are dominated by multiple stacked deep-water turbidite and shelf sand plays interbedded with marine source rocks notably Turonian in age. The Upper Cretaceous Turonian reservoir quality is controlled by many factors however new plays are also now being realized in the Cenomanian, Campanian and Maastrictian. The quality of discovered fluids is further controlled by maturation, migration, and reservoir transformation, whilst trap geometries and timing vary significantly along the margin and at different stratigraphic intervals. Multiple source rocks are present including both syn and post rift intervals albeit variable in quality and distribution whilst maturity is influenced by basin history and local heat flow. Local highs/arches provide short focused migration and material volumes. Top, seat and lateral seal assessment are critical pre-drill. The traps are variable and are often combined structural/stratigraphic traps. Interestingly, seismic attributes can play a key role, with some attributes e.g. Extended Elastic Impedance (EEI) proving more successful. A series of learning's have been developed from the historic Exploration activity, that when combined with a detailed understanding of the structural evolution and petroleum systems, regional play mapping, common risk segment maps and rigorous dry hole analysis can be used to polarize thoughts on the plays to chase and the portfolio to drill. Careful play based mapping has identified some 7 regional sweet spots with stacked plays. The talk will focus on the learning's, risk mitigation strategies and future plays in these sweet spots that can drive the future exploration success in these basins.