A field report on the basin and stratigraphic analysis of Semliki Basin in Western Uganda.
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Semliki Basin is one of Uganda’s most prospective basins for Oil and Gas exploration. It lies within Exploration Area 3 (EA 3) of Uganda’s licensed areas. It is a rift basin located within the western arm of the great East African Rift System (EARS) and forms its northernmost section. The deep end of the basin lies on the Congo side and the shallow end lies on the Ugandan side and this is where the Basement is exposed. Semliki Basin lithology has been classified into two i.e. the Basement lithology and the sedimentary lithology. The former is mainly composed of low-grade metamorphic rocks of the Buganda-Toro system of rocks which include but are not limited to granite gneisses and altered granites. The basin is overlain by a more than 6000m thick sedimentary succession as identified from studies done on Turaco-1 Well in 2001. The sedimentary succession is mainly made of cross-bedded coarse to fine sands, silts and clays. Based on lithological characteristics and age, the sedimentary succession in the Albertine Graben which Semliki Basin forms part, has been classified into seven different strata namely; Kasande Formation, Kakara Formation, Kisegi Formation, Oluka Formation, Nyabusozi Formation, Nyaburogo Formation, and Nyakabingo Formation (Lukaye, 2016).Semliki like other rift basins in the around, is characterized with typical rift basin structures such as rollover anticlines, faulted rollover anticlines, tilted fault blocks among others. The structures were traced from field observations as well as seismic data interpretations. Structural and stratigraphic data collected from the field showed that the basin area was a fluvial-lacustrine environment and sediment chronological dating also showed that these basin sediments were sourced from the nearby Rwenzori Mountains.Magnetic and Gravity data interpretations showed that the basin’s depocenter lies on the Congo and also the sediments were more argillaceous towards the Congo side as interpretated from litho-logs and seismic interpretation. Semliki Basin is still tectonically active as evidenced by the presence of Sempaya hot springs among many other hot springs along the basin margins. This also showed that the basin heat flow is quite high and has caused early maturity of the Cenozoic source rocks.It was therefore concluded from the study that Semliki Basin has a working petroleum play and it is highly prospective for hydrocarbon production.