Fluid–Solid Coupling Characteristics of Gas-Bearing Coal Subjected to Hydraulic Slotting: An Experimental Investigation

Chinese coal seams are characterized by high gas content and low permeability. The permeability of coal seams should be improved to achieve maximum extraction of coalbed methane. This study explores how coal and gas behave when subjected to hydraulic slotting. A fluid–solid coupling experimental system of gas-bearing coal subjected to hydraulic slotting was first established. Then, the fluid–solid coupling property of gas-bearing coal subjected to hydraulic slotting was revealed using the established experimental system. Meanwhile, indicators used to describe the process of hydraulic slotting were derived, and the factors affecting the process of hydraulic slotting were analyzed using the aforementioned indicators. The research achievements indicate that the gas pressure response of the monitoring points in the coal sample shows different characteristics at different stages. Corresponding to the change trend of the gas pressure, the vertical and parallel strains demonstrate the five-stage change characteristics. With the increase of gas pressure, the final deformation amount before slotting gradually increases, and the gas diffusion parameter increases exponentially. With the increase of the slot radius, the gas diffusion parameter shows a similar change tendency with the ultimate deformation amount, i.e., it tends to become flat after a rapid increase. The research achievements can provide certain theoretical and practical references for the revelation of the enhanced coalbed methane recovery mechanism through hydraulic slotting and the rational selection of the key parameters in the field test, respectively.