Experiment on the deformation of the meso-structure of coal during the methane adsorption and desorption

The changes of microstructure of coal sample with a diameter of 8. 5 mm are observed by SEM and CT scan- ning during methane adsorption and desorption under different pressures. The study shows that coal is a kind of natural non-homogeneous rock consisting of coal matrix and a small amount of clay minerals. In the process of methane adsorp- tion and desorption,the structure deformation of coal can be divided into expansion deformation ( density decrease) and extrusion deformation (density increase). Under a low adsorption pressure,the regions containing clay minerals expend rapidly,which has a strong extrusion effect on the adjacent matrix of coal,and leads to significant deformation. With pressure increase,expansion deformation is enhanced and extrusion deformation is weakened. The coal matrix re- gions without clay mineral have a low degree of deformation,which can be approximated to homogeneous deformation. After desorption,the recovery abilities of different coal regions are related to the degree of non-uniform. The stronger the non-homogeneity,the worse the ability of deformation recovery.