“Three zones”microseismic monitoring and analysis of gas drainage effect of overlying strata in gob of high dip high gas seam

In order to clarify the development of mining-induced fractures in overburden of high-dip and high-gas coal seams and improve the effect of pressure relief gas extraction, microseismic monitoring technology was used to record the microseismic events of mining-induced overburden strata during the advance of (4-5) 06 working face in Liuhuanggou Coal Mine (xinjiang). Based on this, the development morphology and evolution trend of fractures in the overlying strata were analyzed,and the microseismic monitoring results were verified by empirical formulas, and the microseismic monitoring results were verified by empirical formulas, and the gas drainage parameters of high-level drilling sites were optimized based on the monitoring results and the gas extraction effect was tested.The results show that: the periodic pressure step of (4-5) 06 working face is about 15 m, and the height of mining-induced overburden fracture zone is about 60 m, and the overall shape of the fracture is asymmetrical ellipticwith its central symmetry and axial reversal. Based on this, the gas drainage drilling parameters of the high-level drilling field are optimized, and the three layers of high, medium and low drilling holes are designed. All of them are arranged in the area within the dominant gas migration channel zone near the side ofthe working face. By analyzing the data recorded by the on-site gas drainage monitoring device, it is found that the gas drainage concentration and drainage flow of the borehole at the high, middle and low levels of the high drilling field showa trend of first increasing and then decreasing. In addition, the gas extraction concentration in the middle drilling field is significantly higher than that in the other layers. After optimization, the gas drainage flow rate of the high-level drilling siteis 63—85 m3/min, and the drainage concentration of the drilling field is 6.22%—10.94%.The gas concentration in the downhole return airway and the upper corner are all lower than the threshold value of 1%, effectively ensuring the safe advancement of the working face. Practice shows that the microseismic monitoring technology can be effectively applied to the monitoring of the height development and morphological positioning of the fracture zone in high-dip and high-gas coal seams, which provides a basis for the design and optimization of gas extraction parameters in high-level drilling sites.