ABSTRACT: Petroleum Geology of the Southern Bida Basin, Nigeria

Sokari P. Braide

The Southern Bida basin is located in central Nigeria and is a major sedimentary area with a 3.5-km-thick sedimentary fill. However, it is the least understood of Nigeria's sedimentary basins because serious oil and gas exploration has not been undertaken in the basin. The surrounding Precambrian basement rocks experienced severe deformation during the Late Panafrican phase (600 ± 150 m.y.), and developed megashears that were reactivated during the Late Campanian-Maestrichtian. The ensuing wrench-fault tectonics formed the basin.

The sedimentary fill, which comprises the Lokoja Formation, are chiefly, if not wholly, nonmarine clastics. These have been characterized into facies that rapidly change from basin margin to basin axis, and have undergone only relatively mild tectonic distortion. Subsurface relations of the Lokoja Formation are postulated from outcrop study. The potential source rocks are most likely within the basinal axis fill and have not been deeply buried based on vitrinite reflectance of <0.65%. These findings, with the largely nonmarine depositional environment, suggest gas and condensate are the most likely hydrocarbons. Alluvial fans and deltaic facies that interfinger with lacustrine facies provide excellent reservoir capabilities. Potential traps for hydrocarbon accumulation were formed y a northwest-southeast-trending Campanian-Maestrichtian wrench system with associated northeast-southwest-oriented normal faults. The traps include strata in alluvial fans, fractured uplifted basement blocks, and arched strata over uplifted blocks. However, the size of hydrocarbon accumulations could be limited to some extent by a lack of effective hydrocarbon seal, because the dominant seals in the formation are unconformities.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990