Project for field study to the Albertine Graben, Western Uganda
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The Semliki basin is covered by sediments that represent the Middle Miocene to Recent, which are described from outcrop and well data, underlain by possible Jurassic or Permo-Triassic to early Tertiary sediments, which rest unconformably on the basement, described from Seismic Data. The report comprises a detailed compilation of findings from the Semliki basin field study in the Albertine area, Western Uganda. The materials and methodology used to achieve the main objective; collection and interpretation of stratigraphic, petrographic, sedimentologic and structural data, have been outlined and discussed in a single chapter and the study results and interpretations as well as discussions and conclusions about the petroleum system of the study area clearly presented in the succeeding chapters that is a clear differentiation of the lithology and stratigraphy of the basement rock and that of the overlying sediments, an integration of basin analysis concepts in interpretations, facies analysis elements and facies analysis interpretations from observed lithologic units, structures in the basement rock and sediments as well as geophysics of the basin. The Semliki basin is generally filled with Middle Miocene to recent age sediments exhibiting a fining upward sequence (characteristic of fluvial systems) from conglomerates (overlying the basement rock) to sands to silts to clays. It is structurally wedge shaped and majorly comprises faults, joints, laminations and bedding planes, cross beds, foliations, quartz veins, unconformities, soft sediment deformation structures among others. The southern part of this basin has the highest elevation but the smallest thickness of accumulated sediments whereas the depocentre (5km thickness of sediments) is in the northern part of the Semliki basin. The basin has a valid petroleum system evidenced by the abundance of excellent reservoirs, regionally mature source rocks, traps, intraformational and regional seals as well as hydrocarbon-migration pathways in the basin. The study has allowed a better understanding of the stratigraphic relationship of the different rock units that are exposed on outcrop, those encountered in the wells, plus a section interpreted from seismic data. In general, the depositional environment of the sediments in the Semliki Basin is Fluvial-Lacustrine/ Deltaic showing significant variations in Gamma ray character, which reflect water level changes and river interactions through the depositional period and the influence of rifting tectonics on sediment deposition through time and space.