Analysis of influencing factors on gas drainage effect of coal seam boreholes

In order to reveal the influencing factors of gas drainage, a fluid-solid coupling model of coalbed methane considering the adsorbed and free gas is established in this paper.The COMSOL numerical simulation software is used to analyze the gas drainage effect and the variation of the effective radius of gas drainage under the conditions of different initial in-situ stress, initial permeability and borehole diameter.The research results show that the initial in-situ stress, initial permeability and borehole diameter will all affect the gas drainage effect, but they have different effects on the gas drainage effect.The effective radius of drainage is most sensitive to the change of initial permeability, followed by the borehole diameter and the initial in-situ stress.The gas drainage effect does not change significantly with the increase of the borehole diameter within a certain range.However, the gas drainage effect is significantly improved beyond this range.Therefore, selecting an appropriate borehole diameter is very important to improve the gas drainage effect.