Impact mechanism of microscopic pore structure on sensitivity and ability of CO2-ECBM based on X-ray nano-CT

To scientifically explain the mechanism of increasing CBM production by CO 2 injection pressure from the microscopic scale, and effectively evaluate the CBM production enhancement potential, adopting the fluid intrusion method and ray non-destructive testing technique, this research reconstructed the real coal microscopic pore structure and carried out the microscopic scale numerical simulation of CO 2 -ECBM. The results indicate that there exists a limit to the magnitude of growth in CO 2 -ECBM displacement efficiency driven by gas injection pressure. The pressure sensitivity, enhancing potential, and production enhancement ability of CO 2 -ECBM change continually over time. In high metamorphic coal reservoirs, the disadvantages of the engineering cycle, absolute displacement efficiency, and CBM production-increasing ability are obvious, while pressure sensitivity and enhancing potential are higher in the middle and late stages. The differences exhibited by CO 2 -ECBM in different metamorphic coals are attributed to the pore structure quality. Specifically, high-quality pores have the characteristics of convenient passage, multiple paths, and higher pore surface areas. The findings can enrich the CO 2 -ECBM production enhancement mechanism in different coal seams, providing new theoretical viewpoints for accurately assessing its application effect and production enhancement potential. • The continuous process of CO 2 -ECBM in microscopic pore structure was simulated. • Evaluation indexes of CO 2 -ECBM were proposed from a microscopic perspective. • Impact mechanism of pore structure on sensitivity and ability of CO 2 -ECBM was revealed.