Coupling model of gas seepage in low permeability coal seam considering start-up pressure gradient and its application

The low-velocity gas seepage in low permeability coal seam has the characteristic of non-darcy seepage. In order to reveal the seepage mechanism of non-darcy seepage phenomenon, the coupling law of gas seepage and coal and rock deformation with non-darcy seepage was studied. According to the characteristics of gas seepage in low-permeability coal seam and considering the non-darcy seepage law under the action of starting pressure gradient, the mechanism of free gas seepage, adsorption gas diffusion flow and coal and rock deformation were studied, and the seepage coupling model with starting pressure gradient was established, the model was used to carry out numerical simulation research on the pre-extraction borehole of this coal seam. The results show that the simulation results with considering starting pressure gradient are more consistent with the gas migration law in low-permeability coal seam. According to the simulation results, the borehole was arranged in the underground, and the gas extraction capacity of the pre-extraction borehole in the working face was 1.09 m³/t, the extraction effect was ideal.