CO2 seepage behaviour in coal under different stress and water content conditions

Understanding CO2 seepage behaviour in coal beds is crucial for effective geological CO2 storage. This study explores CO2 seepage characteristics in coal samples under varying stress conditions (axial, confining and gas pressures) and water content through laboratory tests, theoretical analysis and mathematical modelling. Increasing axial and confining pressures compresses the original pores and cracks in the coal, leading to a gradual reduction in CO2 seepage. At low gas pressures values, the slip effect impacts permeability; however, as gas pressures increases from 3 to 4 MPa, the higher pressure reduces this effect, increasing CO2 permeability by c. 300%. The water content also significantly influences permeability, with dry samples showing the highest permeability and water-saturated samples the lowest. The direction of confining pressure, perpendicular to the seepage flow, obstructs gas seepage channels more effectively, making confining pressure the most strongly correlated factor with seepage discharge (correlation coefficient of 0.72). Based on the regression fitting and neural network analysis of experimental data, a permeability model (R2 = 0.92) was developed, providing accurate predictions of CO2 seepage behaviour in coal under various conditions and serving as a valuable numerical reference for similar studies.