Full aperture pore structure characteristics of coal fractured by CO2 phase transition fracturing technology

ZHAO Xiaoying; JIANG Zebiao; QUAN Xiping; KANG Xiangtao; CHEN Siliang

doi:10.11799/ce202512025

Abstract：In order to investigate the effect of CO2 phase transition fracturing on the full aperture pore structure of the coal,coal samples before and after CO2 fracturing were selected from Liupanshui Danyun Coal Mine and Dahebian Coal Mine in Guizhou,China,and the pore characteristics and fractal properties of the coal body before and after fracturing were analyzed by mercury intrusion porosimetry,low-temperature N2 adsorption test,low-pressure CO2 adsorption test,combining with the fractal theories.The results show that the pore structure of the original coal samples is mainly composed of slit pores formed by the accumulation of flake-shaped particles,and after the CO2 phase transition fracturing,the number of micropores in the coal decreases,while the number of mesopores and macropores increases,the pore structure develops,producing a large number of ink-bottle shaped semi-open/open pores,with the micropores developing into medium pores,the medium pores developing into large pores,and the large pores developing into larger pores.In terms of fractal characteristics,CO2 phase change fracturing has different effects on the structures of micropores,mesopores and macropores,with micropores increasing in fractal dimension,becoming more complex and non-homogeneous,macropores decreasing in fractal dimension,becoming simpler and less non-homogeneous,and mesopores in the low-pressure zone(P/P0≥0.5)decreasing in fractal dimension,becoming simpler and less non-homogeneous.The fractal dimension of mesopores in the high-pressure region(P/P0<0.5)does not show any obvious pattern.The results of engineering applications show that CO2 phase transition fracturing technology can significantly reduce the attenuation coefficient of gas flow,increase the permeability coefficient and permeability,reduce the gas content,and improve the efficiency of gas extraction.