Project report of study area: Semiliki basin (Albertine Graben)

Abstract

As Students pursuing a Bachelor’s degree in Petroleum Geoscience and Production, it is required of us to do fieldwork and excursion study in the Semliki basin under the guidance of our lecturers. The Kibuku area is located in the southern part of the Albertine graben (Ntoroko district) western Uganda. Semliki area lies onshore south of Lake Albert; it is bounded by the escarpment to the east and south and by rivers Lamia and Semliki to the west. It covers approximately 1200km². This study is aimed at application of accumulated geological, geophysical knowledge acquired during the course of the program to understand the geology, scrutinize and analyze the petroleum system of the area of interest inclusive of the study of prevailing environments of deposition and the depositional processes that took place in the area. A vast amount of structural and stratigraphic data was collected and then analyzed to make conclusions about the petroleum potential of Semliki basin. The materials used in the field include Jacob’s staff, geological compass, topographic maps, hoes, and spades among others. Methods used include structural measurements, grain size analysis, degree of metamorphism analysis, degree of sorting analysis. The study area comprised of fluvial, deltaic and lacustrine sediments. The fluvial deposits include sand, conglomerates and thin layers of clays whereas the lacustrine deposits comprised of thick clay layers, mudstones and silt sediments. 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 we observed, examples of these structures include faults, joints, folds, veins and banding. Sedimentary structures observed included cross bedding, and unconformities. Faults, plunging folds would be good structural seals. The surface manifestation of Sempaya Hot spring is evident for the early maturation of the organic matter to expel Oil in the young sediments of Albertine Graben. Geophysics of the Semliki basin was analyzed. Gravity anomaly interpretation indicates that sedimentary sections overlie the pre-Cambrian rift floor. Magnetic intensity anomaly interpretation indicates that the areas in the northern part of the map with high magnetic signatures reflect dense pre-Cambrian basement formations (metamorphic or igneous) while areas with low magnetic signatures towards the southern part indicate sides of young sediments accumulation. Seismic interpretation indicates presence of roll over anticlines, transverse anticlinal structures, positive flower structures and dip slip faults. Sedimentology, stratigraphy and tectonics are applied to develop a full understanding of the rocks and the sediments that fill Semliki sedimentary basin and use this information to interpret the geologic history and evaluate the economic importance of these rocks (Boggs, 1995). Conclusions were drawn supporting the notion that the study area had a good (working) petroleum system basing on the presence required system components that is source rocks reservoir rocks, seals, traps and migration pathways