Geochemical Evaluation of the Permian Ecca Shale in Eastern Cape Province, South Africa: Implications for Shale Gas Potential

Shale gas has been the exploration focus for future energy supply in South Africa in recent time. Specifically, the Permian black shales of the Prince Albert, Whitehill, Collingham, Ripon and Fort Brown Formations are considered to be most prospective rocks for shale gas exploration. In this study, outcrop and core samples from the Ecca Group were analyzed to assess their total organic carbon (TOC), organic matter type, thermal maturity and hydrocarbon generation potential. These rocks have TOC ranging from 0.11 to 7.35 wt%. The genetic potential values vary from 0.09 to 0.53 mg HC/g, suggesting poor hydrocarbon generative potential. Most of the samples have Hydrogen Index (HI) values of less than 50 mg HC/g TOC, thus suggesting Type-IV kerogen. Tmax values range from 318°C to 601°C, perhaps indicating immature to over-maturity of the samples. The vitrinite reflectance values range from 2.22% to 3.93%, indicating over-maturity of samples. Binary plots of HI against Oxygen Index (OI), and HI versus Tmax show that the shales are of Type II and mixed Type II–III kerogen. Based on the geochemical data, the potential source rocks are inferred as immature to over-matured and having present-day potential to produce gas.