Influences of roof pressure law on gas drainage concentration in high level boreholes and optimization of extraction drilling parameters

Through the field measurement, theoretical analysis and Fluent numerical simulation, the working resistance of the support of the 12B801 fully mechanized top coal caving face and the change of gas extraction concentration in the high level hole in a Xinjiang mine are studied.The results show that the pressure of the top plate presents a large and small periodic change law, the large period average pressure step distance about 65.0 m, the small period average pressure step distance about 15.5 m, and the large and small period pressure directly affects the gas extraction concentration in the high borehole; using the law of large and small cycle pressure, the parameters of the original design are optimized, and the Fluent simulation shows that the gas concentration in the upper corner of the working face can be reduced by more than 45% after the drilling optimization optimized.The maximum gas concentration in the upper corner of the working face is only 0.24%, which proves that the optimization of the extraction drilling is reasonable.