Chemical dissolution of minerals in anthracite after supercritical carbon dioxide immersion: Considering mechanical damage and enhanced porosity

Carbon dioxide injection into in-situ coal seams can effectively enhance coalbed methane recovery and promote carbon sequestration, increasing energy production while reducing greenhouse gas emissions. CO2 is prone to exist in a supercritical state in deep coal seams, so it is of great significance to quantitatively describe the mechanical properties damage of coal caused by supercritical carbon dioxide (SC–CO2). Based on the non-equilibrium thermodynamic framework, a nonlinear model of SC–CO2–coal interaction is developed using the special forms of Helmholtz free energy and energy dissipation. Two damage variables are employed to quantify the irreversible degradation induced by chemical reactions and mechanical loads, respectively. The results indicate that the long-term effect of SC-CO2 can increase the porosity of anthracite by approximately 5.49%, but reduce the elastic modulus and strength by about 58% and 56% respectively. The experimental data confirms that the damage model facilitates an analysis of the interplay among SC-CO2 absorption, porosity, elastic modulus and tensile strength of anthracite. The degradation of anthracite mechanical properties is time-dependent, which means that the risk of coal-rock dynamic disasters increases with the passage of CO2 injection time. This work is expected to study the complex multi-field coupling mechanism of SC-CO2 on in-situ coal seams, providing a theoretical basis for guiding CO2 geological sequestration and CO2 enhanced coalbed methane recovery.