Raw-coal CH4 diffusion experiment under the conditions of different temperatures, confining pressures and gas pressures

In this study, in order to investigate the impacts and control mechanisms of temperature, confining pressure, gas pressure and other factors on raw-coal CH4 diffusion characteristics, regular block samples are combined using the gas chromatography method for raw-coal CH4 diffusion experiments under different temperatures (18.0-48.0°C), confining pressures (8.0-21.0 MPa) and gas pressures (4.9-12.6 MPa). The experimental results show that the raw-coal CH4 diffusion rate is slower, and the diffusion coefficient is 10-8 orders of magnitude; in addition, the raw-coal CH4 diffusion coefficient exponentially decreases with the increase of confining pressure and gas pressure, and exponentially increases as the temperature rises. The analysis shows that the confining pressure increases, thereby leading to an increase in the effective stress, so that the coal pores and throat become contracted and deformed by the effect of the effective stress, then the coal porosity and diffusion coefficient decline; when the temperature increases, the movement energy of the gas molecules improve, causing the diffusion rate to accelerate and diffusion coefficient to increase; meanwhile, the gas pressure has two opposite effects, i.e. mechanics and adsorption, and the diffusion coefficient is ultimately controlled by the coal-particle adsorption-expansion volume strain, which will decrease with the increasing gas pressure. © 2014 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.