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<p>Injection of CO<sub>2</sub> into deep coal seams promotes coalbed methane production and achieves dual goals of emission reduction and energy exploitation. Under conditions of high pressure, high temperature, and high humidity in deep formations, CO<sub>2</sub> may exist in the form of supercritical CO<sub>2</sub> (scCO<sub>2</sub>) and undergoes geophysical and chemical reactions of scCO<sub>2</sub>–H<sub>2</sub>O–coal under the coupling effect of temperature and pressure, thereby affecting coal structure. To reveal the effect of scCO<sub>2</sub> on the dissolution of coal minerals and the changes of pore and fracture structure under hydrothermal conditions, an experimental platform for CO<sub>2</sub>–H<sub>2</sub>O–coal reaction kinetics simulation was developed. Subsequently, with coal samples from Ulanhada mining area as the research object, water–rock reaction experiments were performed at 50&#xa0;℃ under 10 MPa. Coal structures were characterized at multiple scales through mercury intrusion, CO<sub>2</sub> adsorption, liquid N<sub>2</sub> adsorption, and high-resolution 3D X-ray microscopy imaging system (3D-XRM) experiments. Finally, the influence of dissolution on the spatial distribution of coal fractures was explored by a comparative analysis of the characteristic values of fracture changes based on 3D reconstruction. The research results revealed that changes of coal pores mainly result from the extraction and swelling of scCO<sub>2</sub>, manifested as a decrease in volume of micropores, an increase in volume of macropores, and an insignificant change in volume of mesopores. The volume of micropores ultimately declines by 13.04%, while that of macropores rose by 75.29%. The acidic medium formed by scCO<sub>2</sub> and H<sub>2</sub>O is soluble and can dissolve minerals to a certain extent, thus altering the spatial structure characteristics of coal fractures. Its internal spatial topological structure changes from being simple to being complex and then to being simple again. In the fluid system of scCO<sub>2</sub>–H<sub>2</sub>O–coal under the coupling effect of temperature and pressure, thermal stress induces the generation of secondary cracks in coal to some extent, and these cracks serve as seepage channels for chemical dissolution of the scCO<sub>2</sub>-generated acidic medium. The research results can theoretically support CO<sub>2</sub> coal seam storage and coalbed methane development.</p>

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Influence of scCO2–H2O Medium on the Pore and Fracture Structure of Coal at the Time Scale

  • 期刊论文

  • 发表日期：

    2026年1月9日

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  • Zhenyong Zhang,
  • Baiquan Lin,
  • Tong Liu,
  • Ting Liu

摘要

Injection of CO2 into deep coal seams promotes coalbed methane production and achieves dual goals of emission reduction and energy exploitation. Under conditions of high pressure, high temperature, and high humidity in deep formations, CO2 may exist in the form of supercritical CO2 (scCO2) and undergoes geophysical and chemical reactions of scCO2–H2O–coal under the coupling effect of temperature and pressure, thereby affecting coal structure. To reveal the effect of scCO2 on the dissolution of coal minerals and the changes of pore and fracture structure under hydrothermal conditions, an experimental platform for CO2–H2O–coal reaction kinetics simulation was developed. Subsequently, with coal samples from Ulanhada mining area as the research object, water–rock reaction experiments were performed at 50 ℃ under 10 MPa. Coal structures were characterized at multiple scales through mercury intrusion, CO2 adsorption, liquid N2 adsorption, and high-resolution 3D X-ray microscopy imaging system (3D-XRM) experiments. Finally, the influence of dissolution on the spatial distribution of coal fractures was explored by a comparative analysis of the characteristic values of fracture changes based on 3D reconstruction. The research results revealed that changes of coal pores mainly result from the extraction and swelling of scCO2, manifested as a decrease in volume of micropores, an increase in volume of macropores, and an insignificant change in volume of mesopores. The volume of micropores ultimately declines by 13.04%, while that of macropores rose by 75.29%. The acidic medium formed by scCO2 and H2O is soluble and can dissolve minerals to a certain extent, thus altering the spatial structure characteristics of coal fractures. Its internal spatial topological structure changes from being simple to being complex and then to being simple again. In the fluid system of scCO2–H2O–coal under the coupling effect of temperature and pressure, thermal stress induces the generation of secondary cracks in coal to some extent, and these cracks serve as seepage channels for chemical dissolution of the scCO2-generated acidic medium. The research results can theoretically support CO2 coal seam storage and coalbed methane development.