Experimental study on influence of stress environment on coal-rock adsorption deformation and permeability

Abstract

In the process of injecting CO2 to enhance coalbed methane development, the change of coal reservoir permeability is affected by the coupling of effective stress change, coal matrix swell/shrinkage caused by gas adsorption/desorption, and gas slippage effect. Therefore, the steady-state method is used to conduct CH4 and CO2 seepage experiments to study the influence of coal adsorption strain and gas slippage effect on the CH4 and CO2 seepage process under different stress environments. The results show that the maximum adsorption strain produced by coal adsorbing CO2 under the same stress environment is 1.01 to 2.39 times of CH4, making the permeability of CH4 in coal always higher than CO2 . At the same time, as the buried depth increases, the external stress increases, the adsorbed strain decreases. In a low-stress environment, the permeability changes in a V shape with the decrease of the gas pressure, with the external stress increases, the permeability and the gas pressure are negatively related. In addition, the increase of external stress will strengthen the influence of gas slippage effect, making it dominate the evolution of permeability earlier.

Keywords

• steady state method
• adsorption strain
• gas slippage effect
• stress environment
• coal and rock permeability