Double media seepage-stress coupling model for heterogeneous coal and rock

To simulate effects of fractures and heterogeneous coal' damage on gas drainage, coal is viewed as double media composed of continuous and fractured media. The heterogeniety of Young's modulus and strength of continuous coal is simulated with Weilbull distribution, and the crack(fractured media) is simulated with Desai thin element. Based on elastic damage theory of coal, coupling of stress and damage with permeability for coal is taken into account, and the seepage-stress coupling mathematical model is presented. Numerical code is developed in Coupling Analysis. Gas drainage progress for a gas well is also simulated with the model. The result shows that the change in effective stress induces the damage of some elements during gas drainage. In damage area, the maximum of gas permeability coefficient increases by 2.7 times. Due to confining pressure, the maximum of gas permeability coefficient in elastic area decreases by 95%. Results also show that the model can simulate the effect of stress, damage and heterogeneity of coal on gas permeability coefficient, and an effective method is provided to simulate gas drainage.