Coupled model of deformation and gas flow process with temperature and slippage effect

The effects of temperature, slippage effect and effective stress of coal on the coupled mechanism of deformation and gas glow are key issues to control coal and gas outburst and design the methane recovery engineering. Firstly, intact coal from Huaxing mine in Jilin Province is crushed and coal briquette specimen are made. Then the tri-axial coupled test setup of the deformation, gas flow and temperature developed by ourselves is adopted to investigate the effects of pore pressure, effective stress and temperature on the permeability of coal briquette specimen. The results show that: 1) Under the condition of low pore pressure, the permeability first reduces with pore pressure increasing, then at a threshold of pore pressure it rises with pore pressure increasing, which is called “slippage effect”. 2) The effective confining stress significantly influences the permeability. With increasing effective confining stress, the space of pores and cracks are compressed and the permeability reduces. 3) The temperature significantly influences the permeability and the permeability decreases with temperature increasing. The main reason is that the space of pores and cracks is compressed due to the temperature stress. Because of the constraint around, temperature compressive stress appears in internal coal samples. Coal pore and fracture space is compressed, and the sample permeability decreases. Besides, the viscosity of gas increases with temperature increasing. It decreases the trend of coal permeability . The temperature influence on coal permeability approximates to linear relationship. 4) The empirical permeability evolution equation with varying temperature, effective stress and slippage effects is presented. The coal is viewed as elastic medium, combined with effective stress principle and the empirical permeability equation, the coupled model of deformation and gas flow with varying temperature and slippage effects is built. Furthermore, the code based on the finite element method in MATLAB is developed. The effects of varying temperature and slippage effects on the deformation and gas flow are studied through a numerical case, and the results show that: 1) without the temperature and slippage effects the gas flow may be underestimated, and the temperature and slippage effects should be taken into account in the coupled analysis of the deformation and gas flow; 2) the effects of varying temperature, slippage effect and effective stress on gas flow can be reflected by the model in this paper, which provides a new method to predict gas flow