Spatial evolution mechanism of coal structure damage and gas permeability under water-based ultrasonic treatment

This study investigates the spatial damage effect of water-based ultrasonic on the structure and the permeability of high-grade coal. Herein, anthracite from No.10 coal seam of Bangou Coal Mine in Shanxi Province as the research object and the following were drawn from the experimental research and the gas seepage simulation: (1) the matrix and minerals attached to the coal surface are shattered by bubbles, and some irregular pores and impact pits appear on the surface of the coal. (2) The internal pore structure of coal can be significantly improved in a relatively short period of time, while the fracture structure requires a longer action time. (3) Some large pores and fractures will achieve breakthroughs from none to some. The previously isolated seepage pores and fractures with larger pores are connected to each other and act for a long time, forming larger connected pore clusters and fractures. (4) As the action time prolongs, the permeability of coal increases by orders of magnitude. The growth rate is faster in the pore-making stage and the connected pore cluster formation stage, while the expansion stage is relatively slow.