Hydrocarbon generation and kinetics: A case study of Permian shales, India

Abstract

Reconstructing hydrocarbon generation history for predicting the onset of oil/gas generation is an important step for petroleum system modeling, and for the purpose, source rock kinetic analysis is required. For evaluating the controlling factors that influence shale rock kinetics, Lower Permian Barren Measures Formation shales from two Damodar Valley sub-basins, India are evaluated in terms of their source rock properties and kinetics. Rock-Eval open-system programmed-pyrolysis is applied at heating-rates of 5, 15 and 25 °C/min to determine the shales’ reaction kinetics. The results substantiate the importance of petrographic composition in controlling the shale source rock potentiality and reaction kinetics. North Karanpura Basin shales are shown to have liquid hydrocarbon generation potential, owing to their richness in type I-II kerogen. In contrast, the Raniganj Basin shales are richer in type III-IV kerogen and gas prone. The shales are grouped in distinct clusters on an E versus LnA (activation energy versus pre-exponential factor) kinetic distribution. The type I-II kerogen-bearing samples display the highest reactivity, while the type III-IV kerogen-bearing shales, and those with higher thermal maturity levels, display lower reactivity. The least reactivity is associated with a heat-altered shale from the Raniganj Basin, which also displays the highest Rock-Eval S2 Tmax, S4 Tpeak, and lowest HI (hydrogen index) value. This indicates the significant impact of igneous intrusions by removing hydrocarbons from shales and lowering their residual reactivity. The dominance of type I-II kerogen and presence of framboidal pyrite in the North Karanpura Basin shales also indicates some marine influence during their deposition.