Numerical simulation study on thermo-hydro-mechanical-chemical interaction mechanism during CO2 storage in deep coal seams

In order to study the effects of physical and chemical interactions between multiple gases, water and coal rock after CO2 injecting in coal seams on the CO2-injected enhanced coalbed methane recovery (CO2-ECBM) project, based on the dynamic characteristics of binary gas competitive adsorption, seepage diffusion, gas dissolution and mineral dissolution and precipitation, a thermo-hydro-mechanical-chemical coupling model of CO2-ECBM was established. CMG-GEM was used for numerical simulation study to analyze the effects of injection strategies and groundwater environment on gas adsorption capacity, permeability and dissolution and precipitation of inorganic mineral components under different coupling methods.The results show that the coupled thermo-hydro-mechanical-chemical model can describe the gas migration behavior in deep coal seams more accurately. After CO2 injection, competitive adsorption occurs, and the permeability around the injection well decreases rapidly, while the unaffected area increases slightly. Under the action of pressure, CO2 dissolves in water, increasing the acidity of groundwater. The dissolution and precipitation behavior of inorganic minerals in different groundwater environments is different, especially for carbonate minerals such as dolomite. Due to the inhibition of dissolution by Mg2+, pore blockage may be caused and displacement efficiency may be reduced.