Study on numerical simulation of pulse water injection in coal seam based on flow-solid coupling

In order to study the humidification mechanism of coal seam pulse water injection technology and the influence law of pulse parameters on the mechanical characteristics of coal and the wetting effect of coal, the geometric model of pulse water injection was established based on fluid-solid coupling theory, and the pulse pressure function built in Rfpa software and Comsol Multiphysics 5.4 software were used for numerical simulation. The simulation results show that compared with the constant pressure, the effect of pulse alternating pressure on the "water wedge splitting" of coal seam is significantly enhanced. With the increase of pulse time, the pore pressure of coal shows a tendency of periodic fluctuation and rise. With the increase of pore pressure, the effective stress of coal decreases accordingly. There is a certain mathematical relationship between the pulse pressure and time and the wetting radius of coal, but the pulse angular frequency has little effect on the wetting effect. In pulse water injection, high pressure and low frequency pulse water injection method can be adopted and a certain injection time can be guaranteed, which can play a better humidification effect of coal.