A Semiliki basin field study report

Abstract

This report presents findings from fieldwork conducted in Uganda's Semliki Basin (Albertine Graben) from 30/06/2024 to 10/07/2024, analyzing stratigraphic, sedimentologic, and structural data critical for petroleum exploration. The basin, formed by tensional tectonics, contains Middle Miocene-Recent sediments overlying Jurassic/Permo-Triassic to Early Tertiary strata unconformably deposited on Precambrian basement (granite/gneiss/amphibolite). Lithologies include variably sorted sands (white/yellow), clays, polymictic/monomictic conglomerates, and siltstones showing cyclic fluvial-deltaic (coarsening/fining upward) and lacustrine (blocky) deposition. Paleocurrent analysis (Stereonet rose diagrams) suggests braided/meandering river systems, while gypsum/iron(III) minerals indicate semi-arid conditions. Stratigraphy comprises (ascending): Kisegi, Kasande, Kakara, Oluka, Nyaburogo, Nyakabingo, and Nyabusosi Formations. Structural analysis reveals NE-SW trending basement faults/joints (minor SE-NW trend) influencing sedimentary structures (cross-bedding, unconformities, mud cracks). Sempaya Hot Springs evidence active crustal thinning, providing sufficient thermal maturity (TTI) for hydrocarbon generation in Kasande Formation source rocks, with Kisegi Formation as reservoirs. Reservoir compartmentalization by thin clays/gypsum poses production challenges, while joints facilitate migration and normal faults create traps. The basin also shows significant geothermal potential.