Shale, Patti Formation, Enagi Formation, Organic Matter, Hydrogen Index

Abstract

This study focuses on the sedimentology and organic geochemistry of the shale sequence in the Bida Basin, Nigeria: Implications for potential petroleum source rocks. Outcrop samples from the Patti Formation (Ahoko) in the southern part of the basin and subsurface samples from the Enagi Formation (Gulu and Kudu) in the northern part were analyzed. Sedimentological analysis of the Ahoko section revealed a sequence of shales, siltstones, and ironstones, indicative of fluctuating depositional conditions similar to the Gulu and Kudu sections characterized by sandstones, claystones, and shales interbeds. The Total Organic Carbon (TOC) values range from 0.70 to 2.61 wt% in Ahoko, 3.14 to 6.52 wt% in Gulu, and 0.67 to 54.19 wt% in Kudu, suggesting fair to good, good to very good and good to excellent source rocks respectively. Hydrogen Index (HI) values indicate predominantly gas-prone kerogen in Ahoko (25 to 82 mg HC/g TOC), and oil and gas prone in Gulu (125 to 165 mg HC/g TOC) and Kudu (108 to 402 mg HC/g TOC) source rocks suggestive of a higher potential for liquid hydrocarbon generation in the northern Bida Basin. Thermal maturity (Tmax) values suggest that the shales are mostly immature, with some Kudu samples approaching the oil window (386°C to 430°C). The findings suggest that the Kudu shales have the most promising hydrocarbon source rock potential, followed by Gulu, while Ahoko shales have the least potential. Ultimately, this research underscores the strategic importance of the Kudu shale as a potential primary source rock and a key driver for future petroleum exploration and development within the Bida Basin and other inland basins in Nigeria and West Africa.