Basin Analysis and Petroleum Systems Modeling of the Lokichar Basin (Kenya)
Résumé
A first wave of exploration of the Cenozoic half graben basins of the East African Rift System in the early 1990's resulted in the acquisition of 2D seismic in the Turkana area (northern Kenya) and the drilling of well Loperot-1 in the eastern part of the Lokichar Basin. The well turned out to be a commercial failure, and a second dry hole further north marked the end of the exploration activities. Recently, exploration has been revived in East Africa and revealed major discoveries in the vicinity of Loperot-1 and in particular along the western bounding fault of the Lokichar Basin. This play is currently drilled out, and first appraisal wells will reveal the commerciality of the discoveries. We will present a regional synthesis, seismic interpretation and derived isopach maps, and a series of structural restoration sequences and petroleum systems models. Using this information, we first review the failure of Loperot-1. This wildcat well encountered the organic-rich and oil-mature Lokhone and Loperot shale members and good reservoir facies in the Auwerwer and Lokhone sandstones, with oil shows. However, late tectonic activity of the trap-bounding fault is interpreted to have a destructive impact on the modeled pre-existing oil accumulation. Based on a serious of 2D and 3D petroleum systems models, we will then discuss the elements (source, reservoir and seal rocks) and dynamic processes (trap formation, charge and preservation) of the petroleum systems to discuss the success of the recent drilling activities in the Lokichar Basin. Finally, we will point out potential areas for future exploration. The analysis of the unconformities and the orientation of spatial trends in the isopach maps suggest 3 distinct periods of tectonic activity, from which only the most recent can be accurately dated (starting approximately Late Oligocene). The directional trend of the deepest identifiable basin fill is interpreted to be aligned with the extensional direction of the Cretaceous Central African Rift System (NW to SE). This suggests that the Lokichar Basin might have been formed already during Cretaceous as part of the Central African Rift System, which hosts major oil reserves in the neighboring Soudan. Sandstones of Cretaceous age are observed in the Lapur Range in the northern Turkana area, and similar sediments might be present below the Cenozoic basin.