Significance of Determining the Extraction Radius for Mine Safety and Efficient Resource Development.

Coalbed methane (CBM) extraction plays a dual role in ensuring the safety of coal mines and enriching clean energy resources. The extraction radius of CBM boreholes is influenced by multiple factors, but the interactions of the factors and their relationships with the extraction radius remain unclear. Therefore, the effective extraction radius under varying factors was simulated using COMSOL, and the major factors were determined through sensitivity analysis and response surface methodology. Further, the relationships between the main factors, their interaction effects, and the extraction radius were studied, and a calculation model was constructed. The results indicate the following. (1) The factors are ranked in a descending order of their influence on the effective extraction radius as follows: initial gas pressure, coal thickness, initial permeability, extraction time, borehole radius. Specially, the initial permeability and drainage time have comparable levels of impact. However, the negative pressure and vertical stress exhibit weak impacts. Notably, the effective extraction area always presents a vertically expanding oval-like shape, and the thinner the coal seam, the shorter the contours that appear in the coal seam, and the smaller the curvature of the contours. The intuitive manifestation in the coal seam is that the pressure contour gradually changes from an arc to a straight line. (2) Significant interactions exist between the initial gas pressure and the initial permeability, as well as between the initial gas pressure and extraction time. Moreover, these interactions manifest as the increased initial gas pressure significantly inhibiting the impacts of the initial permeability and extraction time on the extraction radius. (3) The effective extraction radius of the group coal in the same mine was calculated as 4.98 m using the established model, which closely aligns with the measured value of 5 m.