Delineation of petroleum plays in the Semliki Basin, Albertine Graben Western Uganda, from trap-type perspective

Abstract

Prospects evaluation in the Semliki basin demonstrated working petroleum system, but no viable targets have been discovered. This work was aimed to identify and group the prospective hydrocarbon resource areas of the basin into petroleum plays as a basis for future hydrocarbon exploration and prospects evaluation strategy. The petroleum plays of the Semliki basin were delineated from seismic dataset together with well dataset and corroborated with geological field observations of surface exposed structures on outcrops in Kibuku area of the basin. The seismic dataset analysis included structural interpretation and seismic attributes analysis. The traps identified included; structural traps such as positive flower structures, rollover folds, inversion anticline, horst block/ drape fold, and tilted fault blocks; and stratigraphic traps such as pinch-out and unconformity. Time structure maps and depth structural maps for Nyaburogo and Kisegi horizons were generated. Five plays were delineated based on the tectonic settings, trap type and geometry investigated from structural closures of depth structural maps, and stratigraphic features observed from instantaneous phase attribute. These include; 1) Tilted fault play, 2) Fault-related anticlinal play, 3) Positive flower structural play 4) Pinch-out play, and 5) Unconformity play. Each play possesses unique distribution, seismic characteristics, structural configuration and sealing integrity. The depth structural maps were further visualized to investigate the hydrocarbon charge risks of these plays based on hydrocarbon kitchen areas/depocentres and migration pathways. The basin’s depocentres that are favorable centers for hydrocarbon generation are located in the southwest and in the northwest of the basin. The results revealed geographic relationship between the plays and the adjacent depocentres. Multiple faults mapped in the area are potential migration pathways for both vertical and lateral hydrocarbon migration from the kitchen areas towards structurally up-dip areas. Also the unconformable contact between the underlying Kisegi reservoir and the Kasande source rock above the reservoir favors down-dip migration of hydrocarbons in the basin.