Determination on Effective Drainage Radius of In-Seam Borehole Based on Gas Content Test and Numerical Simulation Calculation Method

In order to accurately and efficiently determine the effective drainage radius of the in-seam borehole, the advantages and disadvantages of the current effective drainage radius test methods are analyzed, and the method of combining the gas content field and numerical simulation calculation is proposed to accurately determine the effective drainage radius of the borehole, which is applied in the mine. The results show that the method combining gas content test and numerical simulation calculation has the advantages of a short measurement period and advanced means. The effective drainage radius of the borehole increases rapidly at the initial stage of gas drainage and then gradually slows, eventually reaching a limit value. The relationship between the effective drainage radius and drainage time follows a Langmuir function relationship. When the drainage time exceeds 300 days, the effect of the drainage time on the effective drainage radius becomes relatively small. The average error between the numerical simulation results of effective drainage radius and the field verification results of gas content is 2.2%, which validates the rationality of the constructed coal seam gas–solid coupling model. The research can provide theoretical references for accurately determining and reasonably laying out the effective drainage radius of the bedding borehole in the mining seam of the coal mine, which is of great practical significance for the safety production of the mine.