Preliminary assessment of source rock potential and Palynofacies analysis of maastrichtian dark shale, Sw Anambra Basin

Abstract

The source rock potential of Maastrichtian Dark Shale in the South Eastern flank of the Anambra Basin has been extensively studied, with very little or no research carried out in the South Western flank (Benin flank). To this end, outcrop samples of the Maastrichtian Dark Shale obtained from Auchi, Uzebba, Sobe, Agbanikaka and Ikabigbo, SW flank, were assessed using Rock-Eval Pyrolysis and Palynofacies analysis techniques. Results of this preliminary assessment show that organic richness ranges from good to excellent; plot of HI against Tmax shows that its source quality is predominantly of Type III (gas prone Kerogen). Kerogen analysis reveals Phytoclast palynofacies (vitrinite) as the most abundant palynofacies (over 75%), about 20% miospore and less than 5% dinocysts recorded. This also depicts dominant Type III (gas prone) kerogen and a Terrestrial – Transitional depositional environment for the shales. Thermal maturity based on Tmax and Spore colour index suggests largely immature to early mature kerogens. Although a low thermal maturity exists at the surface, this study reveals that the Maastrichtian Dark Shale in the SW Anambra Basin/Benin flank has good source potential (sufficient organic richness, mainly of gas prone type III kerogen) and compares favourably with published data from the SE. Furthermore, it is anticipated that the right thermal maturity required for hydrocarbon generation may be attained at depths or close to regional fractures, which is the case in the SE Anambra Basin.

 Keywords: Palynofacies, Pyrolysis, Black-shale, Kerogen, Anambra Basin, Maturity