Abstract
Petroleum exploration have been ongoing in the northern Benue Trough Nigeria, with little success in locating commercial oil pool. Clastic petroleum reservoir has been the main exploration target in the region, despite existence of other possible petroleum reservoir rock types. In this study, field, petrographic and geochemical evidences were presented to show the occurrences of oil in basement reservoir rocks (Precambrian Older Granite), clastic reservoir rocks (Cretaceous Bima Formation) and carbonate reservoir rock (Cretaceous Yolde
Formation) of the region. The studied oils which occurs as brittle solids and viscous fluids in the fractures and/or pore spaces of the studied rocks are believed to have been emplaced into fractures and pore spaces of the studied rocks as conventional light oils that have now been degraded to bitumen by biodegradation and water washing processes. TIC fragmentogram of the saturate fractions of the studied oils show the presence of unresolved complex mixture (UCM) humps, consistent with biodegraded oils. The sterane maturity parameters for the studied oils and their corresponding trisnorhopane thermal indicators (Ts:Tm ratio) are consistent with the thermal maturity values of petroleum source rocks within the oil window. Ternary plot of the relative amounts of C27, C28, and C29 regular steranes in the studied oils show marked resemblance for oils occurring in the Precambrian granitic rocks and the Bima Formation, suggesting the two oils originated from the same petroleum source rock. Oils occurring in the studied Yolde Formation is observed to have originated from a different
petroleum source rock, implying the existence of multiple petroleum source rocks in the Northern Benue Trough.