Assessment of CO2 geological storage capacity based on adsorption isothermal experiments at various temperatures: A case study of No. 3 coal in the Qinshui Basin

Carbon dioxide (CO₂) capture, utilization, and storage (CCUS) is an important pathway for China to achieve its “2060 carbon neutrality” strategy. Geological sequestration of CO₂ in deep coals is one of the methods of CCUS. Here, the No. 3 anthracite in the Qinshui Basin was studied using the superposition of each CO₂ geological storage category to construct models for theoretical CO₂ geological storage capacity (TCGSC) assessment, and CO₂ adsorption capacity variation with depth. CO₂ geological storage potential of No. 3 anthracite coal was assessed by integrating the adsorption capacity with the static storage and dissolution capacities. The results show that (1) CO₂ adsorption capacities of XJ and SH coals initially increased with depth, peaked at 47.7 cm³/g and 41.5 cm³/g around 1000 m, and later decreased with depth. (2) four assessment areas and their geological model parameters were established based on CO₂ phase variation and spatial distribution of coal thickness, (3) the abundance of CO₂ geological storage capacity (ACGSC), which averages 40 cm³/g, shows an analogous circularity-sharp distribution, with the high abundance area influenced by depth and coal rank, and (4) the TCGSC and the effective CO₂ geological storage capacity (ECGSC) are 9.72 Gt and 6.54 Gt; the gas subcritical area accounted for 76.41% of the total TCGSC. Although adsorption-related storage capacity accounted for more than 90% of total TCGSC, its proportion, however, decreased with depth. Future CO₂-ECBM project should focus on high-rank coals in gas subcritical and gas-like supercritical areas. Such research will provide significant reference for assessment of CO₂ geological storage capacity in deep coals.