Study of Permeability Evolution Model for Coal Containing Gas and Its Influencing Factors

In order to study the change rule of coal permeability during gas extraction, the porosity model and permeability evolution model of gas-containing coal with adsorption expansion stress were deduced and established. The model was verified by the experiment of coal containing gas permeability under the condition of triaxial stress, and the experimental results matched with the permeability model. Based on this model, on the condition of gap pressure unloading, the effects of coal elastic modulus, initial porosity, absorbability constant and adsorption expansion stress coefficient on permeability were studied. The results show that in the process of pressure relief, the lower the coal elastic modulus, the larger the change rate of permeability; the smaller the initial porosity, the larger the change rate of porosity, and thus the larger the permeability change rate; the influence of coal adsorption expansion stress coefficient on permeability is similar to Langmuir adsorption constant, the larger the value, the stronger the permeability caused by gas desorption and the slower the permeability decreases.