Assessment of Petroleum Source Rocks of Yola Basin, North-Eastern Nigeria: From the Viewpoint of Bulk Geochemistry and Organic Petrography

The Yola Basin is a hydrocarbon exploration frontier basin in Nigeria where to date; minimal subsurface data is available for adequate assessment of its petroleum source rocks. The Bima Formation is the oldest lithogenetic unit in the basin followed by Yolde, Dukul, Jessu, Sekuliye formations, Numanha Shales and Lamja Formation. Source rock geochemical characterisation was conducted on the Cretaceous sequences of Yola Basin with the aim to determine the organic matter type, richness, thermal maturity and hydrocarbon generation potential. The organic matters within the shales of Bima Formation have reached peak oil window to high thermal maturity stage of oil generation. They possess fair source generative potential based on the present-day kerogen Types I, Type III and Type IV, showing minor oil and major gas prospect. The shales of Yolde, Dukul, Jessu, Sekuliye formations and Numanha Shales have reached peak-oil window to mature stage of oil generation and possess fair source rock generative potential based on their present-day kerogens Type II-III, Type III and Type IV and are likely to generate mainly gas although, minor oil could be expected owing to the presence of small amount of Type II kerogens. The Lamja Formation shales and coals are at early to peak oil generation window and possess poor to very good source generative potential based on the present-day Type III and Type II-III kerogens, expected to generate major gas and liquid components of hydrocarbons. The high thermal maturity has effect on the original nature of the organic matter and any oil-prone organic matter if present would have been cracked into thermogenic gas probably due to the intense thermal event attributed by the Tertiary volcanic intrusion known to be present in the basin.