Experimental study of meso-structural deformation of coal during methane adsorption-desorption cycles

With a method combining SEM-EDS and micro-CT scan, meso-structural deformations of coal during three methane adsorption-desorption cycles were observed. The results indicated that irreversible damage in coal occurred and accumulated during methane adsorption-desorption cycles, with the deformation capacity of coal decreasing with an increasing number of cycles. Because of the inhomogeneous deformation behaviours and mechanics of different meso-structures in coal, the deformations of coal during methane adsorption are primarily caused by the swelling and extrusion stresses between different regions. The telocollinite in coal tends to exhibit swelling deformations, leading to the extrusion deformations of meso-fractures and cavity pores in telinite; the deformations of clay minerals are primarily influenced by the deformations of their adjacent coal matrix. Because of the lack of coordination of deformation and recovery capacities between the inner structures, the residual deformations in coal primarily exist in the regions with strong density inhomogeneity. With the new statistical method based on CT scan, the swelling and extrusion effects in coal were counted; the results can be used as an effective evaluation basis for the influences on both the mechanical strength and seepage capacity of coal during methane adsorption-desorption cycles.