A geological mapping project report of the Albertine graben area, Ntoroko district, Western Uganda
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This report discusses the findings and interpretation of the geologic field mapping exercise done by fourth year students of B.Sc. in petroleum Geoscience and Production. The study was carried out on, Semliki basin, which is one of the most prospecting basins for petroleum exploration in Uganda and available data shows the presence of a petroleum system. The field exercise was carried out in this area (Kibuku) with a major aim of collecting and interpreting stratigraphic, petrographic, sedimentologic and structural data; which are very important in hydrocarbon exploration. To achieve this aim, surface geological and structural data were collected through thorough study of the basement rocks and sediments. Seismic, Gravity and Aeromagnetic data were provided to by the Department of geology and petroleum studies, Makerere University in form of images for interpretation. The study began with analysis of the basement rocks along foothills of the Northern Rwenzori block while identifying the structures and measuring their trends. This was a step by step strategy starting from older basement rocks to younger sediments (establishing the contact at UTM 0192485E, 0102062N) in the Semliki plain. Logging was then carried out on the sedimentary lithologies and discussions held at the established stations. The data obtained was analysed, presented in groups and interpreted. The basement lithology comprised; altered granites, granitic gneisses, schist and amphibolite while the lithology of sediments comprised inter-fingered fluvial and lacustrine sediments with Mt Rwenzori and the escarpment as the provenance. The major sedimentary environments are fluvial, deltaic and lacustrine. Semliki basin has a complete petroleum system as evidenced by the Semliki seismic section, facies and the interpreted Turaco 1 and 2 well log data that showed presence of hydrocarbons at depth with significant temperature and pressure. The thick well sorted sands of Kisegi formation are believed to be the reservoir rock in the study area due to the high-quality sands with good permeability and large lateral extent. The cap rocks are the clays and shales as well as gypsum. The sediments are very young (Miocene in age) and shallow implying little possibility of hydrocarbons forming in the area. However, the presence of the Sempaya hot spring can play a very big role in providing the necessary temperature required to generate hydrocarbons from the organic matter in the shale. The hydrocarbons can then migrate to the reservoir and trapped by the sealing faults hence accumulation. This justifies the hydrocarbon potential of the study area.