Organic matter characteristics and gas generation potential of the Tertiary shales from NW Kutch, India

Abstract

Geochemical attributes of shale such as the TOC content, thermal maturity and kerogen properties provide useful insights on its gas generation potential. Here, the Tertiary shales interbedded within the lignite sequences of Naredi Formation in North Western Kutch Basin have been studied to understand the abundance, thermal maturity and quality of kerogen in the shale[U+05F3]s organic matter. The samples have been collected from the opencast mines of Matanomadh, Panandhro and drill site of Umarsar, where the Naredi Formation is exposed. Open system pyrolysis of the Tertiary shales was carried out using the Rock Eval 6 pyrolyser. The results show the S1 (free hydrocarbons) and S2 (hydrocarbons cracked from kerogen) values to range between 0 and 3.71mgHC/g rock and 0.02 and 91.13mgHC/g rock respectively. The Tmax (temperature at the highest yield of S2) ranges between 383 and 452°C. The Total Organic Carbon (TOC) content varies between 0.35% and 30.92% and the hydrogen index (HI) values lie between 3 and 358mgHC/g TOC.In general the shales, particularly the subsurface cores from Matanomadh and Umarsar indicate very good to excellent organic richness. Based on the hydrogen and oxygen indices, the organic matter is characterized by Type-II and Type-II/III kerogen. The variation of HI vs Tmax suggests immature stage for the generation of hydrocarbons. The shales interbedded within the Naredi Formation can have high potential for gas generation in areas where the formation is buried deeply and has attained sufficient thermally maturity to generate the gas.