Geologic and stratigraphic logging report of Semiliki Basin, Albertine Graben
Chol, Awut Mellicine
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This report documents my field excursion experience in the Albertine graben for period of 10 days, from 15th March, 2021 to 24th March,2021, in the Kibuku area of Semiliki basin, South and East of Lake Albert basin with the aim applying the geological, geophysical and other relevant theoretical knowledge acquired during the course of the program to understand the geology, analyse the petroleum system and make conclusions based on field measurements and observations from the Semliki basin. The objectives were achieved through the use of software tools like Oasis Montaj, Sedlog, Techlog, well and seismic data. Semliki basin is structurally a half graben dominated by fluvial, deltaic and lacustrine sedimentary processes and deposits. The basin has sands, silts, clay and conglomerates as the four major lithologic units belonging to cross bedded sand facies, massive sand facies, clayey facies and conglomerate facies of middle Miocene to recent. The environments in the basin shifted over time from alluvial plain and fluvial channels, lacustrine, deltaic in semi-arid, humid and tropical climatic conditions. The basin is affected by intensive tectonic activity, that led to the formation of vast types of structures that include faults, joints, bedding, cross-bedding, laminations, unconformities, mud diapirs, and plunging folds among others. These structures exhibit a dominant NE – SW structural trend similar to the general structural trend of Albertine rift. The presence of oil seep in Kibuku confirms the presence of hydrocarbon in the subsurface. The well sorted sands of Kisegi, Kakara and Oluka formations are potential reservoir rocks; the huge clayey facies of Kasande formation are potential source rock and regional seal; and the intrasedimentary faults confirm the presence of a working petroleum system and contain hydrocarbon. Information from the field visit to sempaya hot spring indicate the presence of high enough geothermal gradients of over 67°C/km for the maturation and generation of hydrocarbons at shallow depths.Geophysical data of semliki basin and shallow, high resolution (150-200 Hz) seismic data from an intraslope salt withdrawal minibasin in the Gulf of Mexico were availed for interpretation. This data was later analysed by softwares such as Oasis montaj (Geosoft), sedlog, and Techlog64.