Experimental and numerical investigation on the effect of moisture on coal permeability

Coalbed methane is a kind of clean energy source and also a kind of hazardous gas threatening the safety of coal mine production. Permeability is a key parameter to evaluate gas migration capability. However, the permeability is influenced by moisture content. Here, a series of seepage experiments were conducted to analyze the development tendency of flux and permeability to reveal the impact mechanism. Experimental results show that permeability tends to be a sharp drop with increasing moisture, but it had a slight fluctuation with relative gas pressure increasing under the constant mean effective stress. Considering the effect of moisture and gas sorption, a new gas–solid coupling model was developed based on experimental results and theoretical analysis and was implemented into FEM software for simulation. The numerical results of the new gas–solid coupling model were in good accordance with the experimental results and have a priority to cube law in precision. This study reveals that, on the one hand, the moisture can influence the adsorption-induced strain and, on the other hand, it can lead to a significant decrease in porosity due to pore volume occupation.