Nanopore Heterogeneity and Accessibility in Oil and Gas Bearing Cretaceous KG (Raghampuram) Shale, KG Basin, India: An Advanced Multi-analytical Study

Abstract

This study investigated the impact of pore accessibility and complexity on gas storage, transport, and recovery potential in the little-studied thermally mature Raghampuram shale samples collected from 2930 to 2987 m depth of Krishna–Godavari basin, India. Our findings reveal that sample nature (powdered, chipped, or cores) and assessment methods significantly influence pore accessibility evaluation, highlighting a research gap in the interpretation of irregularity, complexity, and heterogeneity of shale pore structure using unreliable monofractal theories. Employing a multiscale methodology involving low-pressure N₂ and CO₂ sorption, synchrotron small-angle scattering, and He-pycnometry techniques, we estimated accessibility in powder and core samples. Powder samples displayed a pore accessibility range of 36.07–106.94%, which was a substantial increase (154.54–423.07%) compared to that of solid core samples (1.61–4.16%). Total organic carbon was found to influence closed pore formation, while clay, carbonate, and quartz + K-feldspar contributed to open pores. Multifractal analyses comparing pore heterogeneity and complexity between accessible and inaccessible pores demonstrated higher heterogeneity and complexity in the latter, with accessible pores exhibiting simpler characteristics. Pore size distributions of both accessible and total pores (includes both accessible and inaccessible pores) exhibited multifractal behavior. Our findings emphasize the significance of evaluating pore accessibility and heterogeneity in shale-gas analysis, providing fresh insights into the interlinked elements of pore structure, composition, and gas recovery potential, thus advancing reservoir characterization understanding.