Integrated Geochemical and Field Evaluation of the Fika Shale, Upper Benue Trough (NE Nigeria): Implications for Petroleum Source Rock Potential

Abstract

This study examines the Fika Shale in the Upper Benue Trough of north-eastern Nigeria to determine its petroleum source rock potential using a combination of field observations and laboratory analyses. Fifteen fresh shale samples were collected from the Pantami and Kundulun stream exposures and analyzed for Total Organic Carbon (TOC), Rock-Eval pyrolysis, and vitrinite reflectance. The TOC values (0.6–2.7 wt.%, average 1.67 wt.%) show that the shale contains fair to very good amounts of preserved organic matter. Rock-Eval results indicate Hydrogen Index values between 138 and 241 mg HC/g TOC, which point mainly to Type III kerogen with minor Type II/III influence in a few intervals. These kerogen types suggest that the shale can generate gas, with limited potential for mixed oil and gas. Most samples fall in the moderate source rock category based on their S2 and genetic potential values, although the Liji Shale and PT-7 intervals stand out as better developed source horizons. Vitrinite reflectance values (0.77–1.34 %Ro) and Tmax readings (426–435 °C) show that the formation lies within the oil window and is approaching early wet-gas maturity in its more evolved sections. Field evidence, such as dark coloration, fine laminations, scattered pyrite, and the absence of bioturbation, supports deposition under low-energy, oxygen-deficient marine conditions that aided organic matter preservation. Altogether, the results indicate that the Fika Shale is an important contributor to petroleum generation within the Upper Benue Trough and forms a meaningful part of the basin’s hydrocarbon system.