ABSTRACT
The diffusion coefficient is a key parameter to study the gas diffusion process in coalbed methane extraction and carbon dioxide geologic sequestration. First, a coupled thermal-diffused-mechanical model is developed, in which the effect of gas pressure and gas temperature on gas diffusion coefficient is considered. The effect of gas desorption induced coal matrix shrinkage on coal porosity and diffusion coefficient are also considered. Then, three sets of gas desorption-diffusion tests, isothermal desorption at 303.15 K, isothermal desorption at 323.15 K and gas desorption from 303.15 K under thermal insulation conditions (with gas adsorption equilibrium pressure of 0.4, 0.8 and 1.4 MPa), are carried out respectively to study the effect of thermal conditions on gas desorption and diffusion. Finally, the developed model is used to simulate gas desorption-diffusion process under thermal insulation conditions and back-calculate the diffusion coefficient. Comparison of measured and simulated results show that the developed model can replicate the whole desorption-diffusion process and back-calculate a consistent diffusion coefficient for different adsorption equilibrium pressure.
