Experimental investigation of gas seepage characteristics in coal seams under gas-water-stress function

Seepage experiences were conducted on coal samples with diverse levels of moisture content, gas pressure, and effective stress to investigate how gas seepage in a coal seam is affected by the interaction of gas, water, and stress. The results of the study revealed the intricate relationship between these factors and their impact on the permeability and seepage behavior of coal. The findings indicate that, with increasing gas pressure, the permeability of coal specimens containing different levels of moisture varies distinctly. When coal samples have low moisture content, their permeability displays a pattern of "increase - decrease - increase" as gas pressure increases. However, with the further increase of moisture content, the "increase-decrease" trend of permeability with the increase of gas pressure disappears. The relationship between permeability and effective stress can be modeled using either a quadratic or logarithmic function. On the other hand, the connection between permeability and moisture content, can be represented by a quadratic or exponential function. At low levels of moisture content, gas pressure has the most pronounced effect on permeability of coal samples, followed by moisture content and effective stress. Conversely, at high levels of moisture content, the most influential factor is moisture content, followed by gas pressure and effective stress. Finally, a model of permeability has been developed that takes into account the collective impacts of gas pressure, moisture content, and effective stress. The research outcomes can establish a basis for optimizing gas recovery from coal seams.