Shukla, Priyanka and Mendhe, Vinod Atmaram and Kamble, Alka D. and Kumari, Sangam and Singh, Vikram Partap (2025) Influence of Petrographic, Geochemical, and Pore-Associated Matrix Characteristics on CH4 and CO2 Sorption of Coal and Shale from Early Permian-Gondwana Deposits, India. ACS Omega, 10 (28). pp. 30060-30086. ISSN ACS

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Abstract

CO2 storage in various geological formations presents a feasible option for reducing greenhouse gas emissions (GHG) in the atmosphere. The most viable and technoeconomic method involves injecting CO2 into deep, unmineable coal seams and shale beds to enhance CH4 recovery. CO2 exhibits a greater affinity with coal, shale, and associated siliciclastic-organic rich rock compared to CH4. However, detailed information about the coal and shale reservoirs is crucial prior to the CO2 injection and enhanced CH4 recovery. This study aims to evaluate the petrographic, geochemical (proximate, ultimate), and pore-matrix characteristics of coal and shale samples to assess the enhanced CH4 recovery through CO2 injection. Pore distribution studies, conducted through micropetrography, Field Emission Scanning Electron Microscopy photographs, and low-pressure BET sorption isotherms, categorized the pore structures of coal and shale into three types: cylindrical, slit, and wedge-shaped. These pore structures, particularly the end-opening of the pores, were found to be suitable for gas storage and release. Clays intermixed with organic matter formed pores, which created suitable adsorption sites for CH4 and CO2. The studied coal exhibited higher CH4 diffusivity and gas saturation compared to shale, favoring CH4 recovery with CO2 injection. The dominating collotelinite maceral has a positive relation with the Langmuir volume (VL) of CH4 and CO2 favoring greater sorption in coal/shale. Conversely, the semifusinite and sporinite macerals influence gas accumulation and diffusivity. The CH4 diffusivity of coal seam ranges from 2.355 × 10–3 to 4.019 × 10–3 min–1 (avg. 3.197 × 10–3 min–1), while shale diffusivity ranges from 1.185 × 10–3 to 2.371 × 10–3 min–1 (avg. 1.531 × 10–3 min–1). The higher diffusivity in coal is supported by the pore distribution and cleat intensity. The sorption ratio of CH4 and CO2, which is directly proportional to in situ gas, indicates an increase in CH4 diffusion and CO2 adsorption. Increasing vitrinite reflectance (VRo) values indicate improved maturity of coal and shale, associated with changes in macromolecular structures and pore-matrix systems suitable for CO2 storage.

Item Type:	Article
Subjects:	Methane Emission and Degasification
Divisions:	UNSPECIFIED
Depositing User:	Mr. B. R. Panduranga
Date Deposited:	30 Jan 2026 04:30
Last Modified:	30 Jan 2026 04:30
URI:	https://cimfr.csircentral.net/id/eprint/2932

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