Research on determination method of effective drainage radius of gas drainage borehole

In order to solve the problems of complex process and lower accuracy in current determination method of effective drainage radius of gas drainage borehole, a determination method of effective drainage radius was put forward, which is based on the law of negative exponential attenuation of gas flow in boreholes and taking the index of gas extraction standard on working face as criterion.The calculation formula of effective drainage radius of boreholes in terms of drainage rate was derived. The initial gas drainage volume and gas emission attenuation coefficient of hundreds of meters borehole are obtained by measuring the attenuation law of gas flow in the coal seam, combined with the criterion of gas extraction standard on working face, the effective drainage radius of borehole corresponding to different drainage time of coal seam is determined according to the drainage rate: when the gas emission amount of the working face mainly comes from the adjacent strata and surrounding rock, the absolute gas emission of working face is taken as the criterion to determine the gas drainage rate of the working face, and then the effective drainage radius is calculated; when the gas emission amount of the working face mainly comes from the coal seam, the effective drainage radius is calculated with the design drainage rate and the desorption gas quantity as the index; when the outburst coal seam is mined, the original gas pressure of the working face is greater than 0.74 MPa or the original gas content is greater than 8 m3/t, the gas drainage rate is calculated by measuring the original gas pressure or the original gas content, and then the effective drainage radius is calculated. The field test results verify the correctness of the method.