Interpretation of structural domains beneath Lake Edward- George basin, Southern Uganda from seismic data

Abstract

The recent oil and gas discoveries in Uganda particularly in the Albertine Graben have made the country one of the economically potential hydrocarbon provinces in the world thus causing an increased exploration of new areas for which structures are looked for during exploration activities. Exploratory works by Petroleum Exploration and Productions Department and Dominion Uganda Limited to delineate the structures in the Lake Edward-George basin were carried out by interpretation of gravity and magnetic data. Despite the existence of structures, structural domains beneath the Lake Edward-George basin are not known yet they are crucial for understanding seismic data and locating drilling areas. Structural domains are pertinent in the structural modelling of a basin and commonly form trapping and accumulation of hydrocarbons if a mature source rock exists. The study aimed at interpreting the structural domains beneath the Lake Edward-Geoge basin from 2D seismic data using petrel software to identifying structures, structural domains, structural fairways, and presenting their hydrocarbon potential. A seismic well tie was performed to create a time-depth relationship to allow well data which is measured in units of depth be compared to seismic data which is measured in units of time. Horizons and fault interpretations were carried out to identify the structures. Structural maps were generated to characterize and define the structural domains and identify the prospective structural fairways as well as present their hydrocarbon potential. The seismic interpretation results identified structures such as faults, positive flower structures, folds, rollover anticlines, and wedge structures. The faults showed some evidence of relative movement of the reflectors on the seismic section due to change in acoustic impedance while the fold showed pop-up reflectors on the seismic section due to tectonic forces. Some of the identified structures such as rollover anticlines and folds form hydrocarbon traps. The fault interpretation revealed that the Lake Edward George basin is NE-SW trending structure controlled by major normal faults with NE-SW, and commonly normal faults of NNE-SSW trend and anticlinal dip closure in the southeast along the rift boundary. Two zones presented structural domains namely extension and compressional structural. Extensional domains were characterized by tensile forces and rotational anastomosing faulting while compressional domains are characterized by compressional stress and elongated folds. These domains contribute to the geometry of the traps and the hydrocarbon accumulation. Six areas presented structural fairways in the Lake Edward-George basin namely areas where prospects A, B, and C, and lead 1, 2, and 3. Prospect C and lead 3 are likely to have hydrocarbon potential.