Nanopore Characteristics of Barakar Formation Shales and Their Impact on the Gas Storage Potential of Korba and Raniganj Basins in India

Abstract

Lithologically diverse shales were collected from two different proliferous basins, namely, the Korba (SM) and Raniganj Basin (BK) in India, and were experimented with at an isothermal condition using CO₂ and N₂ as probe gases in the low-pressure gas adsorption method, demonstrating the disparity between shale pore attributes and surface roughness. The Korba Basin is one of the potential sites for gas storage and production in India and needs to be explored in terms of pore statistics. Literature reviews demonstrate that pore characteristics in shale changes with depth, organic matter, and mineral composition, which can elucidate the gas storage potential for anthropogenic CO₂ storage. Gas adsorption capacity and surface roughness are directly associated with the difference in organic and mineral compositions, which certainly affects the phase distribution of flow regimes in shale reservoirs. The result determines that micropore and mesopore attributes are in good correlation with the TOC and clay minerals, respectively. SM shale shows 30-37% higher micropore attributes and 17-19% lower mesopore attributes than those of BK shales. Furthermore, the siderite content shows a variance in the pore size distribution in BK shales. The fractal dimension (D_s) is evaluated based on the N₂ adsorption isotherm curve using the Frenkel-Halsey-Hill model. SM shales show a strong correlation with both micropores and mesopores at low relative pressure regimes, while BK shales depict their dominance with mesopores at the high relative pressure regime. Therefore, this research provides a preliminary attempt to determine the influence of changes in the depth, surface roughness, and organic and mineral compositions on shales. However, a complete extrapolation of other reservoir factors, viz., seam thickness, shale-water interaction, and permeability variation at reservoir conditions, is vital to unlocking the technical and environmental feasibility of CO₂ storage and gas production in these basins.