A report of the geologic and geophysics field work of Semliki Basin in the Albertine Graben, Ntoroko District, Western Uganda

Abstract

Semliki basin which was the study area is part of the Albertine graben in the East African rift system (EARS) where Uganda discovered her commercial oil reserves. The study area is found in the southern part of the Albertine graben in Uganda; onshore south of Lake Albert, it is bounded by an escarpment to the east and south and River Semliki to the west. The aim of this study was to enable us apply the geological, geophysical and other knowledge we have acquired during the course of the program to understand the geology and analyze the petroleum system of the area practically. While carrying out the field work studies, environments of deposition as well as the depositional processes that took place in the area through the critical analysis of the stratigraphy and structures of the sediments were studies. Vast structural and stratigraphic data collected were then analyzed to make conclusions about the petroleum potential of Semliki basin. Many different facies types were identified in the area, as well as their significance in the formation of good reservoir rocks and seals. The basin was affected by intensive tectonic activity, that led to the formation of vast types of structures with in the basement and sediments that were observed. Examples of these structures include faults and folds. Sedimentary structures such as faults, folds (anticlines) would be good structural traps for petroleum. The presence of hot springs with in the area indicated the presence of high enough thermal gradients for oil maturation. According to the Turaco well geophysical logs that were interpreted, the sediments were thick enough and are comprised of alternating layers of thick sand stones over lain by clays. These geophysical logs also showed the presence of hydrocarbons due to the cross overs observed between the neutron porosity and density logs. It was concluded that the study area has a good petroleum system with potential seals, traps, source rocks and reservoir rocks.