Hydrocarbon Generation, Migration and Accumulation Analysis in the Semliki Basin, Albertine Graben, Western Uganda

Abstract

Early petroleum exploration efforts in the Semliki basin discovered gas condensate with high concentration of CO2 gas in its reservoirs, setting scientific challenges to understand these accumulations. Being a frontier basin located directly adjacent to a trend of high potential hydrocarbon production fields, it would be expected that the Semliki basin shares some of its neighbouring region's hydrocarbon successes. However, despite the presence of all the petroleum system elements and similarity of geologic history between Semliki basin and the productive areas directly north in the Albertine Graben, there are significant differences in the types of hydrocarbons in their reservoirs. Therefore, a 3D basin modelling study of the Turaco area was carried out for the purpose of understanding generation, migration and accumulation of hydrocarbons in the Semliki basin.

In this study, seismic interpretation was performed using 3D & 2D seismic data and well data using Petrel software to understand the structural setting of the Semliki basin. PetroMod software version 2018 was used for 3D petroleum system modelling by integrating geophysical, geochemical and geological data in order to understand the petroleum system of the study area. Reconstruction of burial and thermal maturation history revealed that the Kasande source rock is in the early maturity stage with respect to hydrocarbon generation and the highest extent of kerogen transformation is exhibited by its deeply buried parts (North and West).

Generation and expulsion from the Kasande source rock began in Late Miocene, with hydrocarbons migrating both laterally and vertically accumulating in the basin highs and faulted areas in the Kisegi and Kakara reservoir rocks. Modeling results showed that traps were formed before hydrocarbon generation and expulsion (Mid Miocene), and this good timing enabled hydrocarbon accumulation. Based on the findings of this study, it is certain that Semliki basin has early mature hydrocarbons trapped in neighboring unexplored areas. Therefore, the Semliki basin remains an under evaluated area despite general lack of encouragement from drilling results in the past years. This study is important because it has established a detailed understanding of the processes responsible for hydrocarbon accumulation in the Semliki basin, hence, providing useful insights into its hydrocarbon potential.