Petroleum Geology and Hydrocarbon Potential of a Syn-Rift Basin Infill in the Diourbel-Thies Area, Onshore Senegal

Abstract

Pre-rift basin infill on both Atlantic coniugate margin contain important prolific petroleum systems which have been discovered and developed mostly in the Southern Atlantic region (i.e. Gabon). A recent re-examination of onshore Senagal seismic and well data, provided the opportunity to re-evaluate the petroleum geology of the area (Senegal-Mauritanian Basin, SMB) where hydrocarbons could be accumulated in deeply seated syn-rift basins (4-5 km deep), lying underneath the gently westward dipping passive margin stratigrahic units. The stratigraphic succession of the SMB lyes on a Upper Proterozoic to Paleozoic metamorhpic substratum and consists of a syn-rift (Permian to Triassic) and post-rift (Middle Jurassic to Paleozoic) megasequences. The post-rif megasequence is relatively well-known and it consists of Cretaceous siliciclastic marine sediments, followed by Tertiary marine shales and carbonates. On the other hand, the syn-rift sequence has not yet been penetrated, thus it has been inferred mostly considering the stratigraphic record of the nearest southern (Casamance sub-basin) and northern basins (Mauritania sub-basin). In these domains the syn-rift unit consists of a thick Jurassic to Triassic evaporitic sequence (nearly 2000 m), overlying Triassic clastic rocks, which can include organic rich-lacustrine deposits (potential source rocks). In this work the syn-rift depositional sequence occurring in the SMB is characterized by integrating 2D seismic, gravimetry data and well-logs. The interpretation of the geometry of the stratigraphic units and faults, and their relationship with the regional tectonic events, allows us to suggest different geological scenarios for the area. In order to estimate the hydrocarbon potential of the area, the distribution of evaporite and lacustrine deposits in the syn-rift grabens has been proposed. The latter could be potential source rocks whereas the presence of evaporite could favour the formation of traps and enhance favourable thermal gradients for source rock maturation. Finally, the different tectonic-stratigraphic models were analysed to determine the petroleum generation, migration and accumulation history (g-m-a). Thermal modelling was applied, in order to estimate the timing of the potential source rock maturation and hydrocarbons expulsion, the migration paths and the potential formed reservoirs for the different scenarios.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018