| With the gradual increase of coal mining depth in China,the frequency of gas overrun and other gas disasters at the working face has increased dramatically,which has seriously threatened the mine production safety.The use of high level drilling to extract gas from the overburden fissures in the mining area is an effective way to manage the gas overburden at the working face,however,the precise determination of the layout of high level gas extraction drilling is the key to determine the gas management effect of this method.Therefore,in this paper,the optimal arrangement of high gas extraction boreholes in high gas working face is studied for the problem of gas overlimit in the test mine 1311 working face(buried depth 700-750 m),and the following main conclusions are obtained.:(1)Based on the results of "key layer theory" and "O-ring theory of mining fissures",the process of overburden destruction in the mining area is explained,and the height of collapse zone of 1311 working face is 25 m.Based on the results of key layer identification of overburden at the working face,it is determined that the height of the coal(rock)seam is 81.95 m(706.7 m-624.75 m=81.95 m)above the coal roof.After the unloading,the development height of the air-conducting fracture zone of the overburden of 1311 working face is 81.95 m above the coal bed roof(706.7 m-624.75m=81.95 m);(2)Studied the changing law of the width range of the mining fissure "O" circle formed after the collapse of the overburden of 1311 working face,and determined that the width of the mining fissure "O" circle of the overburden of 1311 working face is from 35 m to 57 m,with an average width of 46 m.Moreover,with the increase of the working face width,the width of the mining fissure "O" circle of the overburden shows a changing trend of gradually increasing and then tending to be flat and stable.;(3)By simulating and analyzing the distribution law of gas concentration in the mining area under different extraction pressure,the best extraction negative pressure of extraction drill hole is 25 Kpa by using the research method of single-factor variation,and by studying different drilling arrangement layer,it is determined that the gas extraction effect is good when the best arrangement layer is 50 m from the height of coal roof,and the maximum value of gas extraction concentration of drilling hole is 17%.The concentration of gas in the upper corner is from 0.33% to 0.48%,and the gas extraction concentration is higher when the high gas extraction drill hole is near the side of 13111 auxiliary air inlet road,and gradually starts to decrease when it is located in the side of the middle compaction zone of the mining area;(4)According to the geological conditions of the working face,the industrial experiments of gas extraction in the extraction area by high level drill holes were carried out in combination with the best arrangement of layers of high level gas extraction drill holes.The actual measurement results show that the maximum gas extraction volume of high level drill hole in 1311 working face is 45757.4 m~3/d,the minimum gas extraction volume is 8646.4 m~3/d,and the extraction concentration is stable at about 20%after the larger extraction concentration at the initial stage;the minimum gas concentration in the corner corner of 1311 working face is 0.12%,and the maximum gas concentration value is basically stable between 0.5% and 0.7%.The effect of gas management is remarkable.The paper has 54 figures,19 tables,and 82 references. |
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