Geochemical Characteristics of Carbonaceous Shales from the Surkha Lignite Mine, Saurashtra Basin, India: Implications for Gas Potential
Sanyasi Rao. Marrapu1, Devleena Mani1, Kalpana. M. S.1, Patil. D. J.1, Dayal. A. M.1
Citation : Sanyasi Rao. Marrapu,et.al, Geochemical Characteristics of Carbonaceous Shales from the Surkha Lignite Mine, Saurashtra Basin, India: Implications for Gas Potential International Journal of Petroleum and Petrochemical Engineering 2016, 2(3) : 4-16
The carbonaceous shales collected from the Surkha lignite deposits of Saurashtra basin, Gujarat have been studied to decipher the source and quality of kerogen present in it. The pyrolysis and bulk carbon isotope ratio signatures have been determined using Rock Eval6 and EA-IRMS, respectively. Total Organic Carbon (TOC) content of thirty-five shale and lignite samples collected from the open cast lignite mine ranges between 0.4 and 52.4 %. The S1 and S2 values vary from 0.1to 14.9 mg HC/g rock and 0.1 to 363.8 mg HC/g rock, respectively. Rock Eval thermal maturity indicator, Tmax values, varies between 404°C and 433°C respectively. The hydrogen index (HI) ranges between 5 and 695 mg HC/g TOC, whereas the oxygen Index (OI) values ranges between 15 and 307 mg CO2/g TOC. Organic matter (OM) is typified predominately by Type III kerogen, with partial contribution from Type IV kerogen. The Tmax and calculated Rock Eval VRo% (< 0.6) suggests immature stage for hydrocarbon generation. Rock Eval parameters, S1, S2, and TOC correlate well with each other and suggest the well preserved and unaltered nature of organic components. Bulk carbon isotope ratios (δ13C) range between -22.7 to -26.5% and indicate the contribution of OM from terrestrial land plants. Major element composition determined using XRF technique indicates it to be Fe-shale, with mineral matrix rich in smectite and illites. With shale gas and shale oil emerging as alternate source of energy in recent times, this study provides useful insights on the kerogen properties of the Surkha shales.