Source rock properties and pore structural features of distinct thermally mature Permian shales from South Rewa and Jharia basins, India

Abstract

Source-rock properties and pore structural properties of Permian shales (Barakar Formation) were evaluated from two Indian basins, with contrasting thermal maturities. South Rewa basin shales were marked by lower thermal maturities, while higher thermal maturities were shown for the shales from the Jharia basin. However, one sample from the South Rewa basin showed unreliably high Rock-Eval Tmax. Examination of the S2 curve showed very low flame ionization detector (FID) value, and thereby indicating the unreliability of the Tmax. However, the Rock-Eval oxidation temperature-peak (S4Tpeak) was observed to show reliable maturity estimate for the sample. The results presented establish the reliability of S4Tpeak as a maturity proxy for shales marked by unreliable pyrolysis signatures. Fractal analysis of low pressure N2 gas adsorption data and pore size distribution trends revealed presence of complex porous structures within the Jharia basin shales, while showing less complicated simpler structures within the South Rewa shales. While two fractal dimensions were observed to be present in the thermally mature Jharia shales, the differences in slopes of the two fractal segments showed minimal variation for the South Rewa shales, indicating the influence of thermal maturity levels on fractal properties.