Hydrocarbon-generation potential and thermal-maturity of few Indian coals: inferences from organo-petrography and Rock-Eval

Abstract

In this work, hydrocarbon-generation potential and thermal-maturity of few Indian coals from two Indian basins have been studied. Samples from Jharia basin were observed to be more mature showing higher vitrinite reflectance, Rock-Eval Tmax, and lower volatile matter (VM) yield, hydrogen index (HI). The baked-coal (Jhama) showed least HI, VM, and highest Tmax, indicating the thermal-influence of igneous intrusions. Liptinite concentration was observed to be directly controlled by the maturity indices. The most-mature coal, beyond ‘third coalification jump’ was marked by absence of liptinites, while the least-mature sample, placed near ‘first coalification jump’ was marked by highest liptinite content, S1 and S2. All these indicate the influence of maturity on hydrocarbon-generation and organic-composition of coals. Strangely, the petrographically determined original HI (HIO) was observed to be lower than present-day HI values. Negative fraction-of-conversion (f) was observed in the coal samples, erroneously implying that no kerogen-conversion or hydrocarbon-generation has taken place from the samples. This could possibly be caused due to presence of sub-microscopic hydrogen-rich organic-materials, not identifiable under microscope.