Hydraulic Flushing Of Pressure Relief And Permeability Enhancement Effect For Coal Research

Hydraulic flushing technology has been popularized and applied in many coal mines because of its remarkable pressure relief and permeability enhancement effect and its superior prevention and control effect of coal and gas outburst.By changing the stress state,pressure relief area,water content and the number of fractures of the coal around the drainage borehole,this technology improves the permeability of the coal,increases the permeability of the coal around the borehole,improves the gas drainage efficiency and effectively reduces the time and cost of gas drainage.This paper comprehensively analyzes the effect of hydraulic flushing technology on coal seam pressure relief and permeability enhancement by using the research methods of theoretical analysis,laboratory experiment,numerical simulation and field investigation.The main conclusions are as follows:1)Hydraulic flushing technology has a significant effect on coal seam permeability transformation.It increases the number of fractures in the coal body and provides a channel easy for gas migration;The gas pressure and in-situ stress acting on the coal body are changed,so that the stress concentration of the coal body around the borehole moves to the depth of the coal seam,the pressure of the coal body in a certain range around the borehole is relieved,the pressure relief range of the borehole is expanded,and the permeability is increased.2)At the initial stage of coal loading,the permeability decreases significantly.After loading to a certain load,the decline rate of permeability slows down to the minimum;After continuous loading,the coal body will suffer plastic damage and the permeability will "surge";Unloading is carried out after the permeability reaches the minimum value,and the coal permeability will gradually recover at a slow speed,but it cannot recover to the initial permeability of the coal.2)Using COMSOL multiphysics simulation software,the model of 4310 fully mechanized top coal caving face in Changping Coal Mine is established.The pressure relief and permeability enhancement effect,gas drainage effect and influence range of hydraulic flushing measures in Changping Coal Mine are simulated.The simulation results show that the pressure relief range of ordinary boreholes is small,and the drainage effect and drilling control range are limited;After the implementation of hydraulic flushing measures,with the increase of the amount of coal washed out,the pressure relief range of the coal around the borehole is significantly increased,and the extraction effect is significantly improved.The effective influence radius under different extraction times is increased by 4.02 ～ 6.40 times.Combined with the actual field production of the coal mine,it is determined that the reasonable coal flushing amount of 4310 fully mechanized top coal caving face in Changping Coal Mine is 1t /M and the extraction time is 3 months.4)The investigation results of pressure relief and permeability enhancement effect of hydraulic flushing in 4310 fully mechanized top coal caving face of Changping Coal Mine show that the effective influence radius of hydraulic flushing borehole after 60 days of drainage is in the range of 6 ～ 8m,the total drainage volume is 11.52 times higher than that of ordinary borehole,the coal seam permeability coefficient is 66.1times higher,and the gas flow attenuation coefficient of hydraulic flushing borehole is only 1 / 2 of that of ordinary borehole.