Geochemical and organo-petrographic characterization for hydrocarbon generation from Barakar Formation in Auranga Basin, India

Abstract

Keeping in pace with global studies of shale gas/oil, the authors had selected fifty-one (41 shales and 10 coal) core samples of Barakar Formation (lower Sakmarian–Kungurian) from four boreholes of Auranga basin, to understand hydrocarbon generation potential. The Rock-Eval pyrolysis along with total organic carbon content (TOC), organo-petrographic, vitrinite reflectance, Fourier Transform infrared spectroscopy (FTIR), X-ray fluorescence (XRF) analyses were carried. These studies indicate that all the samples (coal and shale) have fair to excellent hydrocarbon generation in respect of TOC and S2 (under Rock-Eval pyrolysis). Further, the thermal maturity (Tmax) of shales and coals are placed in ranges from 409 to 468 and 420–426°C respectively. However, vitrinite grains having reflectance>0.60% (↑Vt60%) may indicate the onset of thermogenic oil generation could possible in the majority of the samples. The presence of alginite, sporinite, resinite, liptodetrinite and suberinite along with perhydrous vitrinite and inertinite macerals is observed. The linear relationship of total maceral content (TMC) with TOC may help in their determination empirically. Multiple regression analysis denote maceral reactivity in the generation of S2. In addition, A-factor (aliphatic/aromatic peak intensity) and C-factor (carbonyl/aromatic peak intensity) under FTIR spectra, suggest dominance of kerogen type III, IV and II/III. The geochemical indices like CIA (chemical index of alteration), CIW (chemical index of weathering) and ICV (index of compositional variation) indicate strong to intermediate weathering, under passive continental margin depositional environment supporting luxurious vegetation and organic matter preservation.