Kerogen typing using palynofacies analysis in Permian Barren Measures Formation in Raniganj sub–basin, East India

Abstract

The objective of the study is the simple assessment of kerogen type in Barren Measures Formation shale using palynofacies. The Barren Measures Formation sandwiched between the coal–rich formations consist of organic–rich black carbonaceous shales. These ̴ 1000 m thick, black shales are in the productive gas window having kerogen types III with excellent gas generation potential as proven in recent pyrolysis studies. In this study, the palynological analysis of the four core samples of the Barren Measures Formation shale was done. The analysis has revealed three types of kerogen assemblages, viz. palynomorphs, phytoclasts and amorphous organic matter. The palynomorph assemblage consists of spores and pollen; phytoclasts consist of secondary xylem wood macrophyte plant debris and amorphous organic matter is a higher plant decomposed product. Based on the application of published kerogen classification and correlation of Tyson (1995), the pure kerogen type in these shales is categorized as mixed type; type II (oil prone) and type III (gas prone). However, the gas–prone kerogen assemblage gets relatively dominant in the samples from greater depth in the studied borehole. Our results are analogous to the previously published outcomes of kerogen typing evaluated using Rock–Eval pyrolysis experiments.