Biomarkers and Geochemical Evaluation of Shale Units of the Maastrichtian Patti Formation, Bida Basin, Nigeria

O. A. Ehinola, O. O. Sonibare, and A. M. Falana
University of Ibadan, N/A, Nigeria

Nigeria's economy is a type that is crude oil dependent and most of the crude oil exported by Nigeria is sourced from the prolific Agbada Formation in the Tertiary Niger Delta. Apart from the social unrest, consequential to oil exploration and production activities, in the Niger Delta, the fear of depletion and political consideration are presently causing a shift of attention to other sedimentary basins among which is Bida Basin. Biomarkers and geochemical studies specifically Rock-Eval pyrolysis have been carried-out on shale samples of Patti Formation from the Bida Basin. This is to determine the hydrocarbon source rock characteristics, and hence, the hydrocarbon-generative potential. Most of the samples analysed have total organic carbon (TOC) values greater than 0.5 wt% indicative of low to fair amount of organic matter (OM) content. Also, hydrogen index (HI) of less than 100mgHC/grock for nearly all the samples suggest that the shales are organically poor to lean source rocks. The plots of HI against OI, HI against Tmax, HI against TOC, and S₂ against TOC suggest the prevalence of the Type III OM, which is land derived and gas prone. Kerogen thermal maturity (Tmax) shows that the OM is immature. The abundance of C₂₇-C₂₉ regular sterane in the rock extracts suggest that the OM is of mixed source, however, the relative abundance of C₂₉ with respect to those of C₂₈ indicates the dominance of terrestrial OM input. Biomarker maturity parameters of C₃₀ hopane, C₃₁ homohopane, ááC₂₉ and áâC₂₉ steranes show that the OM in the sediments is immature with respect to oil generation.