3-D dynamic evolution analysis of coal-rock damaged field and gas seepage field during the gas extraction process

Abstract

Coal seam construction disturbances or gas depressurization and extraction can cause rupture damage of the surrounding coal and rock. The damage not only changes the structural property and mechanical behavior of the coal and rock, but also changes the physical parameters of the coal and rock. The gas migration not only changes the pore pressure, but also changes the effective stress and the adsorption and expansion deformation of coal seams, which resulted in the damage evolution and accumulation of coal and rock. The temperature change will not only affect the stress distribution of coal and rock, but also affect gas adsorption properties and diffusion capacity. In fact, the gas extraction is a multi-field coupling process of the coal-rock damaged field, temperature field and gas seepage field. In this paper, coal and rock is considered as a double medium of pore and crack. The damaged variable is defined in view of the damaged and failure characteristics of coal and rock. The damaged constitutive equations of coal and rock are established considering the effects of gas pressure and temperature. On this basis, the gas diffusion and seepage coupling equations in damaged coal and rock are derived. Based on the basic theory, the two development of the finite element source program is carried out by using the FORTRAN language. This program was developed to consider the temperature, gas seepage and deformation of coal and rock. Based on this program, the work process of gas drilling in coal mine is simulated and the dynamic evolution process of the damaged field of coal and rock and the permeability of the gas are quantitatively described. These achievements have extremely important theoretical guidance to guide the design of gas extraction in coal seams and improve the gas drainage rate.