ICE 2022


The Cretaceous sediments of eastern Dahomey (Benin) Basin are host to one of the largest bitumen deposits in the world. Understanding the hydrocarbon generative potentials of Cretaceous source rocks is key to future exploration success in the basin. This study integrates data from LECO TOC/ Rock Eval-2 pyrolysis of Cretaceous shale samples from four (4) shallow exploration boreholes (< 60 m), and two-dimensional (2-D) basin models constructed based on data from five (5) exploration wells (< 3,000 m) that penetrated sedimentary successions and Basement Complex rocks, were used to determine the maturity, timing, and distribution of hydrocarbon generation in eastern Dahomey (Benin) Basin. The reliability of the 2-D models was tested by comparing the generated models with hydrocarbon shows in each of the exploration wells and also with surface hydrocarbon occurrence on an exposed outcrop section. The analyzed shale samples from shallow intervals (< 60 m) have TOC content in the range of 0.24 and 2.50 wt. %, and can be considered as poor to excellent source rocks. The cross plots of HI vs. OI and S2 vs. TOC indicate that the analyzed shale samples at shallow depths contain type III and type IV kerogen with the potential to generate gas and/or condensate. However, the Rock-Eval pyrolysis Tmax and PI show that the shale samples are immature at the present shallow depths. The results of 2-D basin modeling indicate that Maastrichtian source rocks underwent two phases of hydrocarbon generation with the first early generation phase occurring during Eocene and a second, intense generation during Miocene. Liquid hydrocarbon generated and expelled from the deeply buried Maastrichtian shale must have migrated upwards along the sediment-basement interface and unconformity-bound surfaces. The simulated 2-D models presented conditions favourable for oil and gas accumulations in the basal conglomeratic sandstone. The occurrence of heavy oil in outcrop sections and boreholes, light oil in all the wells reflects the viability of the Cretaceous play in the eastern part of the Dahomey (Benin) Basin. Exploration success in the eastern Dahomey (Benin) Basin hinges on the identification of deeply buried Cretaceous source rocks that has sufficient burial depths.