Gas seepage characteristics and discharge radius of coal seam borehole

Borehole discharge radius is a critical technical parameter in mine gas control, and the gas seepage characteristics within boreholes play a pivotal role during advanced discharge boreholes. Based on this, finite element analysis software was employed to develop a coupled fluid-solid model for gas discharge in coal seam boreholes. This study explored the influence of discharge time, borehole aperture, and coal seam permeability on gas seepage characteristics and the discharge radius around the borehole. Field tests were conducted at Qidong Coal Mine to compare the gas discharge effects of various layout methods. The results demonstrate that gas pressure surrounding the borehole follows an elliptical distribution during gas discharge. As discharge time increases, gas pressure exhibits a decreasing trend. The discharge radius is positively correlated with discharge time, following a power function relationship. Under identical discharge durations, the discharge radius initially increases exponentially with borehole aperture but this effect diminishes in the later stages of discharge. Continuous borehole discharge indicates that coal seams with higher permeability experience a more rapid decline in gas pressure. In coal seams with higher permeability, shorter discharge durations can achieve comparable or even superior gas discharge effects. The discharge radius shows a linear relationship with coal seam permeability. On-site test data from Qidong Coal Mine were compared with numerical simulation results, confirming that the effective discharge radius is positively correlated with discharge time. Furthermore, the effective discharge radius rises as the borehole aperture expands, which aligns with the pattern of change in the gas discharge radius for coal seam boreholes. Longer spacing between borehole layouts requires extended periods to meet gas discharge safety standards. When gas discharge time is limited, the “triangle” borehole layout method demonstrates greater advantages. These research findings provide a solid theoretical foundation for localized outburst prevention measures on coal mining faces.