Research On Gas Migration Law In Goaf Under The Condition Of High Extraction Roadway And Directional Long Borehole In Fully Mechanized Face

Most of China’s coal seams have the characteristics of high gas content and low permeability,and the mining face is more prone to gas disaster accidents.According to the special geological and gas storage conditions of China’s coal mines,the pre drainage effect of coal seams is poor,so it is imperative to carry out pressure relief gas drainage in high outburst mines.Taking a high outburst mine in Heshun,Shanxi Province as the experimental prototype,using physical similarity simulation and numerical simulation,this paper determines the optimal layout horizon and optimal extraction parameters of collaborative extraction of high extraction roadway and directional long drilling,and applies the simulation results in the field.Through the physical similarity simulation experiment,the average pressure step distance of the overlying strata is 17.4m,the height of the caving zone is 22.4m,and the height of the fracture zone is 61.9m.The reasonable layout range of high pumping roadway and directional long drilling is determined.Combined with the results of physical similarity simulation experiment and field conditions,the Fluent numerical model is established.The simulation results show that the optimal layout and extraction parameters of high extraction roadway and directional long drilling are as follows:the horizontal distance of high extraction roadway is 25m,the vertical distance is 30m,and the extraction negative pressure is 3 kPa;The horizontal distance of directional long borehole is 10～20m,the vertical distance is 11～21m,and the negative pressure of pumping is 16 kPa.In the single extraction mode,the gas concentration curve of the working face has a micro-balance section of gas gushing and fresh air dilution gas capacity in the coal wall and goaf of the working face.Under the collaborative extraction mode,with the increase of borehole negative pressure,the pressure difference at the upper corner increases,which indirectly reduces the air leakage intensity in the lower comer area,and the change curve of gas concentration in the working face shows a monotonous increasing trend as a whole.The negative pressure of directional long drilling increases,and the span of the rapid lifting area on the return air side of the goaf increases significantly.According to the physical simulation experiment and numerical simulation results,optimize the theory and experimental results,arrange the extraction system,and carry out realtime observation of the extraction process.The monitoring results show that during the mining period of the working face,the net extraction volume of the high extraction roadway is 28.88 m3/min～80.39 m3/min,and the average net extraction volume is 64.8 m3/min;The net extraction volume of directional long borehole is 2.79 m3/min～23.59 m3/min,and the average net extraction volume is 9.7 m3/min.And the gas concentration in the working face,upper corner and return air roadway is kept within 0.8%,so as to realize the safe production of the working face.In this paper,through physical similarity simulation experiment,numerical simulation and other methods,the reasonable layout parameters and drainage parameters are determined,and the experimental results are verified on the spot,the three-dimensional drainage method is established,and the gas drainage effect is analyzed,so as to verify the rationality of the research results of this paper,provide a reference for the gas control of similar high outburst mines,and have a certain reference significance for the prevention and control of underground gas disasters.