Study on borehole spacing for gas extraction via borehole-as-tunnel substitution under gas-oxygen-temperature multi-field coupling

LI Runzhi

doi:10.11799/ce202512012

Abstract：Current methods for determining borehole spacing in gas extraction using boreholes instead of roadways mainly rely on goaf gas migration simulations and field experience.They lack systematic multi-field coupling analysis and insufficiently consider risk factors beyond gas concentration.To address this issue,the 2-105 working face in Tenghui Coal Mine was selected as a test site for integrated simulation and field measurement.First,gas migration patterns in the goaf under different borehole spacings were simulated to establish a baseline spacing range.Subsequently,a comprehensive optimization was conducted by coupling the temperature field,oxygen concentration field,and airflow field in the goaf.Finally,field measurements were carried out to validate the simulation results.The study shows that the borehole spacing based solely on gas field simulation is 25 m.However,multi-field coupling analysis reveals that larger spacing increases air leakage and oxygen concentration,leading to the expansion of the spontaneous combustion zone and the migration of high-temperature areas.Therefore,a dynamic extraction strategy with a spacing of 20 m is proposed.Field measurements indicate that when boreholes are located 15～35 m from the working face,the gas concentration at the upper corner remains below 0.8％,with the maximum differences of 0.9％in oxygen concentration and 0.8 K in temperature,showing minor deviations from the simulation results and confirming the accuracy of the simulation.