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 highrank 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.& COPY; 2022 Southwest Petroleum University. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).