Structure and lithology-based reservoir characterization of the Lake Edward-George Basin, Western Uganda

Abstract

This research was conducted in the Lake Edward-George basin, Albertine Graben. It focused on the structural and lithological analysis aimed at understanding the hydrocarbon reservoir characteristics of the Lake Edward-George basin. The research utilized a combination of seismic datasets and well log interpretation techniques to unravel the geological complexities of the basin. In this research, examination of the basin's geological characteristics, employing a multi-disciplinary approach combining seismic interpretation, well log analysis, and reservoir delineation techniques were undertaken. Structural analysis using the 2D seismic data revealed a dominance of normal faults that strike NE-SW which is evidence of extensional tectonics, alongside compressional features such as reverse faults and positive flower structures. The basin geometry is tilted to the west, indicating typical example of a half graben. Through detailed seismic interpretation and fault mapping, fault networks were delineated. Lithological characterization further enhanced the understanding of the basin's hydrocarbon reservoir characteristics. Utilizing well log data from the Ngaji-1 Well, distinct lithological units comprising sandstone reservoirs intercalated with clay-rich strata, were observed. Advanced petro-physical analysis elucidates the porosity-permeability relationship within these reservoir units, providing insights into fluid flow behavior and reservoir connectivity. The integration of gamma ray, density, neutron, and resistivity logs enabled discerning of the lithological variations and quantification of key reservoir parameters such as volume of shale and total porosity. The study revealed seven (7) reservoir zones encountered in the Ngaji-1 Well with thickness of between 7 m to 28 m. The lowest average effective porosity of the reservoirs range is 15% and the highest average porosity of 37%. The lowest average permeability of the reservoir is 0.2 D as the highest average permeability is 28 D. Reservoir delineation efforts reveal heterogeneous distribution of the potential reservoirs, influenced by faulting and depositional facies changes. By correlating seismic reflections with well log data, detailed subsurface models revealed reservoir compartments. Notably, areas characterized by thicker sedimentary sequences away from the Ngaji-1 Well exhibit better reservoir qualities, emphasizing the importance of localized geological conditions that control reservoir quality.