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

Abstract

To scientifically explain the mechanism of increasing CBM production by CO₂ 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 CO₂-ECBM. The results indicate that there exists a limit to the magnitude of growth in CO₂-ECBM displacement efficiency driven by gas injection pressure. The pressure sensitivity, enhancing potential, and production enhancement ability of CO₂-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 CO₂-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 CO₂-ECBM production enhancement mechanism in different coal seams, providing new theoretical viewpoints for accurately assessing its application effect and production enhancement potential.