PETROLEUM GEOLOGY AND EXPLORATION POTENTIAL OF SOUTH LOKICHAR BASIN IN EAST AFRICAN RIFT SYSTEM

The East African Rift System (EARS) is a Cenozoic intercontinental rift basin group consisting of two main rifts: the Western Branch and Eastern Branch. Exploration risk in EARS was considerable high in the past decades. However, since 2012, several oil discoveries have been found in South Lokichar Basin in the Eastern Branch. Scholars began to rethink the previous conclusions. Through integrated studies of seismic, well and other geological data from the South Lokichar Basin, its petroleum geological features and reservoir-forming mechanisms revealed, exploration potential evaluated and prospecting direction predicted. The Basin has a small-scale, mono-faulted structural characteristics, faulting in the west and overlapping in the east, and has been filled with a fluvial-(fan) delta-lacustrine depositional system since Oligocene. Based on the analysis of samples of wells and outcrops, it was determined that both the Miocene Lokhone shale and the Oligocene Loperot shale are high quality source rocks with mid-high maturity, the Miocene Lower Auwerwer fan delta sand is a good reservoir, and it forms a good combination with the overlying regional mudstone. In the western steep slope zone of the basin, structural traps were developed and large-scale oil fields formed with the reserve accounting for 99% of the whole basin. In the eastern gentle slope of the basin, however, poor containment condition led to only small-scale oil discoveries. In the northeastern area of the basin, fault-block traps are developed, which makes it a favorable exploration zone. Recent data from wells has confirmed that this area has similar petroleum accumulation conditions with the western steep slope zone.