New insight into geochemical characterization of Paleogene coals from Jarain coalfield, Meghalaya, N-E India: Hydrocarbon potential and organic petrographic analysis

Abstract

In the present work, geochemical techniques such as Rock-Eval pyrolysis, TOC, Organic petrographic analysis, and statistical investigation have been performed to conclude hydrocarbon generation potential and thermal maturity of studied source rocks samples. Thermal maturity measurement of source rock samples has been assessed by calculated VRo and pyrolysis temperature Tmax (400–418 °C). The result demonstrates that samples are thermal immature in nature and cannot produce hydrocarbons at the commercial level. Modified Van Krevelen diagram (HI versus Tmax) and hydrogen indices (HI) plotted against OI. The study of samples demonstrates that Type II and mixed Type II-III kerogens exist in almost all investigated samples; the HI varies from 203 to 447 mg HC/g TOC and thus can be considered fair oil source and gas/oil source rock. The plot between HI vs Tmax also evaluated the above result. The result of HI vs Tmax is also confirmed by the hydrocarbon richness value (S2/S3), which indicates the emphatic possibility for oil and gas generation in all studied samples. The ternary diagram obtained from microscopic petrographic data typifies that coal forms in platform regions during the coalification process under alternating oxic and anoxic moor conditions. The finding of statistical techniques like Pearson's correlation and cluster analysis also demonstrated that the source rock has tremendous potential for producing hydrocarbons, with a negative correlation between TOC and HI and a decent association between S2 and HI.