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

Abstract

The geological and geophysical field study was undertaken at the end of the sixth semester, and lasted two weeks, from 21st July 2019 to 3rd August 2019, under the guidance of academic staff from the Department of Geology and Petroleum Studies, Makerere University. The study area was the Semliki Basin, located in Ntoroko District, Western Uganda, on the southern side of the Albertine Graben. The main objective of the field work was to acquire training on how to collect and interpret stratigraphic, petrographic, sedimentologic and structural data which are very important in hydrocarbon exploration. According to the log and facies analysis, the sediments of the basin were deposited in swampy, deltaic. fluvial and lacustrine environments. The sediments included sands, clays, silt and conglomerates, whose provenance was deduced to be the Rwenzori Mountains and the escarpment. The stratigraphic succession of the basin comprises of seven Formations namely: Kisegi, Kasande, Kakara, Oluka, Nyaburogo, Nyakabingo and Nyabusosi. Semliki Basin is structurally wedge shaped, the southern part of this basin has the highest elevation but the smallest thickness of accumulated sediments whereas the depocenter (5km thickness of sediments) is in the northern part of the Semliki basin. The basin was affected by intensive tectonic activity, that led to the formation of vast types of structures within the basement and sediments that were observed. Examples of these structures include faults, folds and joints. Sedimentary structures such as mud diapirs, faults, plunging 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. It was concluded that this basin has a high potential for hydrocarbon accumulation due to the presence of thick extensive sand beds that can act as reservoirs, organic rich thick clay beds that can be good source rocks, clay beds that can act as seals, faults and anticlinal folds that can provide good trapping mechanisms.