A field study report of the Semliki basin in the Albertine Graben, Western Uganda

Abstract

The field study is conducted for 12 days in the Kibuku area within the Semliki Basin in Western Uganda the area which lies onshore south of Lake Albert basin on the eastern side of the Albertine Graben which lies in the western branch of the East Africa rift system with the rift flanks rising to approximately a height of 400m above the Graben on the eastern side. It is bounded by an escarpment to the east and south and River Semliki to the west. These rift flanks are underlain by the Basement Complex rocks which have undergone intense metamorphism that led to the formation of vast types of structures. This report comprises a detailed compilation of findings from the field and is made up of seven chapters that give a detailed account of the objectives, materials and methods, lithology and stratigraphy, basin and facies analysis, structures, Geophysics of the Semliki basin and discussion of results which help in understanding of the petroleum play of the area. Many different facies types are identified in the area, as well as their significance in the formation of good reservoir rocks and seals. The sedimentary structures include faults and plunging folds (anticlines) that would be good structural traps for hydrocarbons. The presence of hot springs with in the area are indicative of the presence of high enough geothermal gradients for oil maturation. The geophysical logs that are interpreted imply that the sediments are thick enough and comprise of alternating layers of thick sand stones overlain by clays. Vast structural and stratigraphic data collected are then analyzed to make conclusions about the petroleum potential of Semliki basin where the 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 up to clays. It is structurally wedge shaped and majorly comprises faults, joints, laminations and bedding planes, cross beds, foliations, quartz veins, unconformities, and soft sediment deformation structures. It is concluded that the study area has a good working petroleum system evidenced by the abundance of excellent reservoirs, regionally mature source rocks, traps, intra formational and regional seals as well as hydrocarbon-migration pathways in the basin.