| China is one of the countries with serious coal mine gas disasters in the world.guizhou because of its special characteristics of karst landform,unique distribution characteristics of coal seam and complex geological structure,most of the coal mine belongs to coal and gas outburst mine,the coal seams more for low permeability coal seam,and gas content,gas pressure,and in-situ stress higher series of unfavorable factors which causes the difficulty in mine gas extraction.At the same time,the mining depth of China’s coal mine is gradually deepening,the increase of ground stress,further reduce the permeability coefficient of coal seam,which leads to the effective influence range of ordinary drilling extraction is small,the pre-extraction drilling engineering quantity is large,the extraction efficiency is low,the conventional gas extraction method is difficult to play a role.Therefore,in order to expand the effective influence range of extraction drilling and improve the gas extraction effect of coal seam,it is particularly important to relieve pressure and improve permeability of lowpermeability coal seam.In view of this problem,this paper takes M9 coal seam of a mine in Guizhou as the research object to carry out the research and application of anti-permeability technology of high-pressure hydraulic slit.The research methods of theoretical analysis,numerical simulation and field engineering application are mainly carried out as follows:(1)Through the analysis of the impact dynamic characteristics of high pressure water jet,the structural characteristics,outlet velocity,flow rate and kinetic energy of water jet were analyzed theoretically,and the anti-reflection mechanism of high pressure hydraulic slit was revealed by analyzing the theory of water jet coal breaking.ANSYS/LS-DYNA and FLAC3 D numerical simulation software were used to establish the numerical simulation model of high pressure water jet impacting coal and high pressure hydraulic cutting.(2)The ANSYS/LS-DYNA software is used to simulate the process of high-pressure water jet impacting the coal body,analyze the process of the water jet impacting the coal body until a stable impact hole is formed,and measure the impact depth of the water jet.The results show that the water jet impacts the coal body to form impact holes.The depth of the coal increases with the increase of the water pressure.The depths of the water jets with three water pressures of 80 MPa,90 MPa and 100 MPa impacting the coal body are 0.63 m,0.84 m and 0.96 m,respectively.(3)On the basis of taking the depth of the water jet impacting the coal body as the radius of the high-pressure hydraulic kerf,the FLAC3 D software is used to carry out the numerical simulation calculation of the high-pressure hydraulic kerf,and analyze the results after the simulation of different parameters is completed.The influence of the change of body stress,the distribution of the plastic zone and the change of the displacement of the coal body.The analysis results show that with the increase of the water pressure and the radius of the slot,the farther the stress concentration point is from the center of the slot,the greater the reduction width of the stress,and the greater the plastic zone.The larger the width distribution is,the larger the displacement of the coal body and the larger the influence range will be.Through analysis,the reasonable slit parameters suitable for the mine are water pressure 90 MPa and slit radius0.8m.(4)Through the anti-reflection test of high pressure hydraulic slit in 1091 return air passage of a mine in Guizhou,a seam of about 0.89 m can be formed after the slit,and the pure amount of single hole extraction from slit hole is twice that of the comparison hole,and the extraction concentration is increased by 2-2.8 times,greatly improving the gas extraction efficiency of the hole.The experimental results show that the field application of anti-reflection technology of high pressure hydraulic slit achieves the expected purpose and can provide reference for gas extraction of coal seam with similar geological conditions in Guizhou. |
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