A report on the field-study to the Albertine Graben Area, Western Uganda.
Nakalule, Kisaakye Phoebe
MetadataShow full item record
The area of study was Semliki basin located in the Southern part of the Albertine graben, Ntoroko district in Western Uganda. Semliki area lies onshore South of Lake Albert and it is bounded by the escarpment to the East and South and by rivers Lamia and Semliki to the West. It covers an area approximately 1200 km². The aim of this study was to enable us apply the geological, geophysical and other knowledge to understand the geology and analyze the petroleum system of the area, study the environments of deposition and the depositional processes/mechanisms that took place in the area. We collected vast structural and stratigraphic data, which were then analyzed to make conclusions about the petroleum potential of Semliki basin. The study area comprised of fluvial, deltaic and lacustrine sediments. Gravity, magnetic and seismic data acquired in the area show that the main structural elements in the Semliki Basin are faults, grabens and horsts formed as a result of tensional stress. It also shows that the basin is characterized by multi-stacked good quality reservoirs associated with growth and flower fault related structures. Areas of gravity lows generally have greater sedimentary thickness. The geology is such that alluvial fans and deltaic facies interfinger with lacustrine facies thereby providing excellent reservoir capabilities. Potential structures for hydrocarbon accumulation include normal faults, strata in alluvial fans, and fractured basement blocks. There are also several oil seeps in the basin. The basin was affected by intensive tectonic activity, that led to the formation of various types of structures with in the basement that propagate to the sediments such as faults, joints, folds, veins and banding. Sedimentary structures observed included cross bedding, unconformities, faults, a mud diaper and deformation bands. Mud diapirs, faults, plunging folds would be good structural seals. The presence of hot springs with in the area indicated the presence of high enough geothermal gradients for maturation of hydrocarbons. Sedimentology, stratigraphy and tectonics are applied to develop a full understanding of the rocks and the sediments that fill Semliki basin. This information was used to interpret the geologic history and evaluate the economic importance of these rocks. We concluded that the study area had a good petroleum system characterized with all the required system elements that is source rocks are of clastic facies, organic rich, oil-prone (type II kerogen), thermally mature (within peak oil generation) with good oil generative potential, reservoir rocks (thick sandstones), seals (shales and evaporites), both structural and stratigraphic traps (faults, diapirs) and migration pathways (cross beds, faults, and beds).