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.