Mechanical Response Characteristics and Mechanism of Coal-Rock with CO2 Injection in Deep Coal Seam: A Review

To reveal the mechanical response characteristics and mechanisms of coal-rock with CO2 injection, the influencing factors of mechanical properties of coal-rock with CO2 injection, the transformation effect of CO2 on the macro molecular-pore-fracture structure of coal-rock and the statistical model, theoretical model and intelligence prediction model of mechanical parameters of coal-rock with CO2 injection were reviewed. Results show that mechanical properties of coal-rock with CO2 injection are controlled by the coal rank, the CO2 pressure, the moisture, the confining pressure and the time. The increase of CO2 injection pressure, the addition of water and the extension of time can further reduce the mechanical properties of coal-rock with CO2 injection, while the confining pressure can ameliorate the weakening effect of mechanical property to a certain extent. The CO2 aqueous solution recombines the macro molecular structure of coal-rock by the swelling, extraction and plasticization effects, reforms the pore structure of coal-rock by the micro crystalline structure change, chemical corrosion and non-uniform deformation effects, damages the fracture structure by the chemical corrosion, swelling stress and chemical-stress coupling effects, which all weaken the mechanical properties of coal-rock in varying degrees. Among the prediction models of mechanical parameters of coal-rock with CO2 injection, the Langmuir-like model, the extended exponential model and the modified cohesion model have clear physical significance, while the intelligence prediction model has higher prediction accuracy, and the prediction accuracy can reach more than 99%. This study lays a theoretical foundation for scientifically evaluating the CO2-ECBM safety and promoting the efficient injection of CO2 into deep coal seams. © 2022, Editorial Department of Earth Science. All right reserved.