Effect of Internal Gas Pressure on Gas Permeability of Coal in Unsteady-State Gas Flow. Study on gas permeability of coal by crack network model (2nd Report).

The purpose of this study is to prove the effect of internal pore pressure on unsteady-state gas flow in coal. Practically, the gas permeation model of coal which consists of the gas permeable and non-permeable crack network was proposed. Then the numerical simulations of gas permeation by this model were carried out by changing the parameters such as inlet pressure in the crack network, confining pressure against coal, closing probability of cracks, etc.The results of these simulations on fluctuations of unsteady-state gas flow were in agreements with the experiments of gas permeation of coal. From these considerations it was found that the above gas permeation model was accurate enough for practically. Moreover, the results of the simulations on unsteady-state gas flow in coal gave an explanation to the deviation from the Darcy's law in the relationsbetween gas flow and difference pressure.