A report on the geologic and stratigraphic logging project of Semlik Basin- Albertine Graben in Ntoroko District, Kibuku Area -Uganda

Abstract

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 (i.e.; collection and interpretation of stratigraphic, petrographic, sedimentologic and structural data) have been outlined and discussed. 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 i.e., 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 silt to clays. Similarly to the Mississippian basin; the low relief of Semliki basin, a constant large volume of fine grained sediment supply and prevalent fluvial processes have formed fluvially dominated lacustrine delta. Whereas, the black coaly shales (appendix 4) signify periods of plant and animal deposition.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 smallest thickness of accumulated sediments whereas the depocenter (5km thickness of sediments) is in the northern part of the Semliki basin. The sediments in the basin represent a petroleum play for hydrocarbon accumulations, in which the necessary elements of a valid petroleum system were identified as 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 low magnetic susceptibility has been interpreted as the probable areas of geothermal interest due to reduced magnetization as a result of thermal activities. The reduced velocity anomalies on seismic sections were interpreted as high temperature anomalies inferred to be hot actively degasing magmatic intrusions which could be the heat source for the hot springs. The sedimentary basin at Buranga is highly conductive due to the clay type minerals which are consolidated in the sediments.