Modeling and Analysis on Coal Permeability Considering the Mineral Dissolution Caused by Flue Gas in Fractures

Permeability enhancement by injecting acidified flue gas to dissolve minerals within coal fractures offers a novel approach to solve the problem of gas drainage from deep, strongly adsorbent, and low-permeability coal seams. However, the dynamic response mechanisms of the internal expansion coefficient, fracture bulk modulus, and permeability during mineral dissolution in coal fractures remain unclear. To address this problem, we constructed a permeability model that considers the dynamic changes of the internal expansion coefficient and fracture bulk modulus during mineral dissolution based on the “matrix-rock bridge-fracture” physical model of coal. Then, the permeability changes of mineral-containing coal under a constant gas pressure, a constant effective stress, and a constant confining pressure at different reaction times were tested and analyzed using the self-built CO2–H2O–Coal interaction and permeability test system. Based on the fitting results between the constructed permeability model and the experimental data, we delved into the dynamic evolution patterns of the internal expansion coefficient and the fracture bulk modulus during mineral dissolution in coal fractures. Ultimately, the separate and coupling influences of key parameters of the model (soluble mineral content variation, initial fracture porosity, Langmuir strain constant, Langmuir pressure constant, and average molar volume of soluble minerals) on the coal permeability were clarified by utilizing local and global sensitivity analysis of the verified permeability model. This study can provide a theoretical reference for engineering permeability enhancement by mineral dissolution using flue gas.