Organic richness and organic matter quality studies of source rocks in Imiegba and environs, Benin Flank, South-Western Anambra Basin, Nigeria

Abstract

The hydrocarbon potential of the Upper Cretaceous units (Maastrichtian Mamu Formation) exposed at Imiegba and environs of the Benin Flank, Western Anambra Basin was assessed by Total Organic Carbon (TOC) and Rock-Eval Pyrolysis Analyses. The investigated sections of the Mamu Formation consist of dark grey to black carbonaceous and coaly shales, brownish to grey siltstone, whitish claystones and milky white to reddish brown sandstones. The organic richness assessment based on free hydrocarbons generated before pyrolysis (S1), hydrocarbons resulting from kerogen conversion (S2) and Total Organic Carbon content (TOC) indicates poor to excellent source rocks in the sections studied and can therefore be considered as potential source rocks. Quality and Type of Organic Matter was evaluated using hydrogen and oxygen indices and plot of HI against Tmax which show that they are predominantly Type III kerogen (gas prone). This means that the organic matter is immature and predominantly terrestrial. Part of the study area, Imiegba is therefore considered to be of good petroleum potential particularly gaseous hydrocarbon.

Keywords: Organic Richness, Kerogen, Organic Matter, Source Rock