Delineation of sub-basalt sedimentary basins in hydrocarbon exploration in North Ethiopia

In Northern Ethiopia oil seepage could be traced flowing through fractured basalts at the Mechela river bed near Wereilu town. These rocks make up part of the huge volume of Ethiopia's Oligocene-Miocene Plateau basalts and associated rhyolites that cover most of the central and northern part of the country. They overlie the marine sedimentary formations of Triassic–Cretaceous age and constitute one of the largest visible flood basalts on the face of the earth.2-D and 3-D analyses of the gravity field have been performed to determine the structural pattern and subsurface density distributions beneath the thick volcanic sequences. The resulting images offer significant new insights into the structural pattern and geophysical characterization of the study area. A NW–SE elongated basin of significant dimension has been localized directly beneath the oil seep at Wereilu. The basin is a graben formed within and by the NW–SE trending structures of the Karroo rift system. A younger generation of faults in the NE–SW direction has affected the basin exerting significant control on the geometry and perhaps on the sedimentation pattern that might have played a major role in hydrocarbon accumulation and localization.The nature and thickness of the sub-volcanic sedimentary succession, attaining a significant thickness of more than 5 km, coupled with the overlying thick volcanic sequences providing the necessary thermal gradient for the maturation of the organic material create a favorable condition for the generation and accumulation of hydrocarbon deposit.