In Mobil's Joint Venture acreage offshore Nigeria, sands within the lower Pliocene Qua Iboe Shale are regressive-deltaic and upper-slope deposits. They filled an embayed area caused by tectonic collapse of a pre-existing deltaic shelf. Several major oil fields produce from these slope sands; over 100 wells and 10,000 ft of core provide ground-truth for our interpretations. The cores are classified in terms of lithology and the associated lab-measured reservoir properties, and these are correlated to a full well-log suite, allowing the quantification of rock properties in un-cored wells. Borehole data tied to 3D seismic allow definition of stratigraphic relations and the distribution of lithofacies regionally. Reservoir sand commonly occurs in straight to sinuous channels, solitary or nested in paleobathymetric lows. Reservoirs for 2 major oil fields are in a 3-km wide fairway of nested sinuous channel sands. This fairway formed during at least 4 cycles of incision and fill with an aggregate thickness of 800 feet. Lateral to the fairway, these cycles consist of silty shale and isolated channel sands overlain by condensed sections. The condensed sections are largely absent within the fairway due to erosion by subsequent cycles. Each cycle is correlated landward to a regressive-transgressive cycle of the delta that is 8 to 28 km north of the producing wells. Within the fairway, the early cycles are strongly erosional at base, and are back-filled with channelized pebbly coarse-grained sandstone, fining upward, flanked by silty shale. The youngest cycle is more weakly erosional, contains finegrained sand, and is an amalgamation of anastamosed channels.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah