Numerical Simulation for the Effect of Surface Borehole Extraction on Gas Migration and Spontaneous Combustion

The extraction through surface borehole led to the increase of air leakage, the change of gas and oxygen distribution in goaf, and affect the risk of spontaneous combustion. By means of numerical simulation, the width of oxidation zone and the distribution of gas concentration under different drilling and extraction conditions of different boreholes were simulated. The reaserch results showed that the gas concentration reduced on both sides of the golf and high concentration area moved backward, however, the width of spontaneous combustion oxidation zone increased at the same time. The gas concentration reduced and the width of oxidation zone increased with the growth of drainage gas flow. Through combined extraction by arranging the borehole close to working face and deep location of the goaf, a better distribution of oxidization zone and gas concentration was got. As under the condition of reasonable spacing of the holes and extraction flow, utilizing multiple borehole combined extraction can not only decline the gas concentration in golf, but also control the width of oxidation zone, which solved gas emission and spontaneous combustion in goaf effectively.