Geological characteristics and exploration potential of Karoo clastic play, Ogaden Basin, Ethiopia

The Karoo clastic play is the most important gas play in the Ogaden Basin. The Bokh mudstones and the Calub and Adigrat sandstones worked as source rocks and reservoirs. Various traps developed in the Karoo clastic play, including faulted blocks, low-amplitude anticlines, lithologic pinchouts, channel sands and lens-shaped sand bodies. The distribution of regional paleo highs controlled the planar accumulation of hydrocarbon while trap formation timing determined the effectiveness of hydrocarbon charging. The traps which formed before the Late Cretaceous should be most efficient, for the Bokh source rocks had entered the gas window at that time. But in the following history, uplift took place in most parts of the Ogaden Basin, and the maturity of source rocks changed little. The Adigrat Formation has coarse sandstones in the northern basin and fine sandstones in the Bodle deep. The lower Adigrat Formation has better physical properties than the upper section. Structural traps are dominant in the lower part, while lithologic traps develop in the upper part. For the Bokh source rocks lay above the Calub reservoir, lateral migration was important for hydrocarbon accumulation. Intra-sag paleo highs are the most favorable, and the pinch outs in the basin slope also have a good potential. The Calub paleo high is a realistic exploration target since it is surrounded by the Bokh source rocks, where the Calub and Adigrat reservoirs were well developed. A widespread fracture system and various structural orientations also contribute to hydrocarbon migration and accumulation.