Accurate identification and efficient drainage of relievedmethane in goaf of high outburst mine

It is of great significance to identify the enrichment zone of relieved methane in the goaf of high outburst mine and to layout the drainage boreholes in the enrichment zone for controlling the methane overrun in the high outburst coal face and extracting the methane in the goaf relief area. The scope of relieved methane enrichment zone in the goaf of high outburst mine was studied by physical similar simulation and theory analysis. Based on the theory of “three zones” and “elliptic paraboloid zone”, the discriminant method of gradually and accurately identifying relieved methane enrichment zone was put forward, and the differential sweep numerical modeling method of elliptic paraboloid zone was also innovated. Based on the RSM-BBD(Response Surface Methodology Box-Behnken Design)method, the experiment was designed, and the numerical simulation of methane extraction parameters was carried out by using Fluent software. The influences of single factor and interaction factor on the extraction effect were analyzed, and the regression model between the extraction parameters of each layer and the methane concentration in the upper corner was fitted to optimize the optimal drainage borehole parameters of each layer. Finally, according to the accurate identification of relieved methane enrichment area and the optimization results of drilling parameters in the enrichment area, the field drainage test of high position directional drilling was carried out.The results show that there are “relieved methane existing zone”, “elliptic paraboloid zone type active migration zone” and “relieved methane annular enrichment zone” in goaf. The influence degree of single factor on the drainage effect in the annular enrichment area with the same vertical distance is as follows: the drill diameter>drill horizontal distance>drainage negative pressure, and the interaction between the drainage negative pressure and the drill horizontal distance also has an obvious influence on the methane concentration in the upper corner. After optimizing the extraction parameters, the gas concentration in the return air and the total drainage pipe of the drilling field showed a downward trend during the drainage period of the test working face. The average gas concentration in the return air was 0.32%, and the average gas concentration in the total drainage pipe of high position directional drilling field was 12.95%.Methane in the coal face is effectively controlled.