Surface free energy of coal and its variation law with gas extraction

Abstract

In order to improve the effect of gas extraction and prevent coal and gas outburst, the structural characteristic of coal pore inner surface was discussed, the interface interaction between coal and gas was revealed from the perspective of surface free energy, and the expression between the coal surface free energy and the amount of gas adsorption was constructed. Using the OCG method, the surface free energy of the coal sample in Shaqu Coal Mine was determined to be 43.33 mJ/m2 under laboratory conditions. Through the hydraulic-mechanical-thermal coupled governing equations for gas extraction, the gas extraction process in Shaqu Coal Mine was numerically simulated. The results show that the inner surface of coal pore is in an asymmetrical force field, and the inner surface of coal pore has additional surface free energy compared to the inside of the coal phase, the greater the surface free energy of the coal pore inner surface, the stronger its adsorption capacity; the coal surface free energy continues to increase with the gas extraction operation, and the surface free energy is the highest in the area near the extraction borehole; before the gas extraction operation, effective technical measures to reduce the surface free energy of coal are helpful to improve the gas extraction effect.

Keywords

• gas absorption
• gas extraction
• surface free energy
• contact angle
• hydraulic-mechanical-thermal coupling