Experimental study on the influence of gas pressure on CH4 adsorption-desorption-seepage and deformation characteristics of coal in the whole process under triaxial stress

• The timeliness characteristics of CH 4 adsorption-desorption-seepage and coal deformation were analyzed. • The influence of gas pressure on CH 4 adsorption-desorption-seepage and coal deformation was clarified. • The quantitative relationship between CH 4 adsorption-desorption-seepage and coal deformation was discussed. • A whole-process strain model of coal for CH 4 adsorption-desorption-seepage was established. CH 4 adsorption-desorption-seepage characteristics of coal is an important indicator to measure the gas extraction capacity of coal seam. The deformation of coal caused by CH 4 adsorption-desorption-seepage is an important factor affecting the extraction ability of CH 4 . Synchronous test experiments of CH 4 adsorption-desorption-seepage and whole-process coal deformation under different gas pressures were carried out by using the self-developed comprehensive test experimental system of gas-solid coupling for coal measure gas. The timeliness characteristics of CH 4 adsorption-desorption-seepage and coal deformation were analyzed. The influence of gas pressure on CH 4 adsorption-desorption-seepage and coal deformation was clarified. The quantitative relationship between CH 4 adsorption-desorption-seepage and coal deformation was discussed. A whole-process strain model of coal for CH 4 adsorption-desorption-seepage was established. The results showed that increasing gas pressure could promote CH 4 adsorption-desorption-seepage of coal. The higher the gas pressure was, the greater the capacity of CH 4 adsorption-desorption-seepage in coal was. Increasing gas pressure could promote the expansion/contraction deformation caused by CH 4 adsorption-desorption-seepage in coal. The higher the gas pressure was, the stronger the deformation ability of CH 4 adsorption-desorption-seepage in coal was. The expansion or contraction deformation caused by CH 4 adsorption-desorption-seepage in coal was simultaneously affected by coal bedding structure and external stress. The axial/circumferential strain caused by CH 4 adsorption-desorption-seepage in coal showed exponential function, quadratic function, and exponential function growth relationship with adsorption capacity, desorption capacity, and seepage capacity of CH 4 , respectively. The stress in the process of CH 4 adsorption-desorption-seepage in coal covered the expansion stress of adsorbed CH 4 to coal matrix, the compression stress of free CH 4 to coal matrix, and the expansion stress of free CH 4 to coal microporous fracture. Considering three kinds of deformation effects by CH 4 in two states, the whole process strain model of CH 4 adsorption-desorption-seepage in coal was established, which could effectively reflect the deformation timeliness characteristics of the whole process of CH 4 adsorption-desorption-seepage in coal. This research provides some theoretical support for the efficient extraction of coal seam gas.