Evaluation of source rock potential and hydrocarbon composition of oil sand and associated clay deposits from the Eastern Dahomey Basin, Nigeria

Abstract

Oil sands are classified as unconventional hydrocarbon plays and are being exploited to augment global energy needs. Nigeria has the largest conventional oil industry in Africa, but is also endowed with abundant oil sand deposits found within the Afowo Formation of the Eastern Dahomey Basin. In this study, outcrop samples of clay, oil sand, and bitumen seepage from a forestry reserve (J4) in Ogun State, South Western Nigeria were evaluated for organic matter maturity and hydrocarbon composition. Pyrolysis results for the clay indicate that the total organic carbon ranges from 5.95 to 18.46 wt % with a maturation temperature (Tmax) within the range of 417–426 °C. A complementary gas chromatography (GC) analysis of the free hydrocarbons in the clay reveals that both light and heavy hydrocarbon components are present. In contrast, oil sand and bitumen contain mostly heavy end hydrocarbon components with hydrocarbon chains C6–C12 missing, confirming oil biodegradation. This study demonstrates that these oil sands and clays represent viable exploration targets. With vast oil sand deposits in the Eastern Dahomey Basin, exploration and exploitation of this resource will open new frontiers to increase Nigeria's hydrocarbon production.