Research On Influence Of Air Leakage Of Gas Drainage Borehole On Gas Extraction

Gas drainage is the main measure to control gas outburst in coal mine and use gas resources,however,air leakage of gas drainage borehole often lead to gas drainage failure.Therefore,it is necessary to study the influence of air leakage of gas drainage borehole on gas extraction.The research conclusion is of great significance to solve the gas extraction quality and to control the coal mine gas accident.This thesis is based on theoretical analysis and numerical simulation to establish the mathematical control equation of gas extraction,this equation considering the deformation of coal rock mass,the dynamic change of permeability and the seepage of coal seam gas and air.Using COMSOL numerical simulation software to simulate the physical process of gas extraction under the condition of air leakage,get distribution of air pressure in coal seam;study the gas extraction process of borehole under the conditions of different extraction time,depth of sealing hole,negative pressure of extraction,hole sealing quality and the development degree of roadway fracture,and analysis the variation of air leakage range,gas leakage and gas extraction and extraction concentration.The results show that:(1)the air in the tunnel is transported to the coal seam under the action of negative pressure,the air leakage pressure in the crack area of the roadway increases gradually with the time of extraction,and the air leakage pressure of undisturbed coal seam is close to zero;(2)under the condition that the sealing condition is constant,the influence range of the drilling leakage is gradually extended to the surrounding area,the leakage of the borehole gradually increases with the extraction time,the gas extraction and extraction concentration decrease with the time of extraction;(3)with the deepening of the sealing depth,the volume of gas extraction decreases gradually,but the reduction was small,the impact range of drilling leakage is also shrinking,the sealing depth is 10 m compared with the sealing depth of 8m,the leakage of borehole is reduced by about 1/3,and the concentration of gas extraction is increased by 10%~20%,in the engineering practice,it is necessary to consider the economic cost and the actual effect to determine the appropriate sealing depth to pass through the drainage area of the tunnel;(4)increasing the suction negative pressure not only increases the gas extraction but also increases the leakage of the borehole,and under the same sealing depth and other conditions,the concentration of gas extraction decreases with the increase of negative pressure,in engineering practice,it is necessary to reduce the negative pressure to improve the extraction effect when drilling leakage;(5)use the permeability to characterize the degree of fracture development and the quality of the sealing hole,with the increase of permeability in the fractured zone,the leakage of borehole is significantly increased,and the concentration of gas extraction is obviously decreased,in engineering practice,it should adopt the measures such as wall spray cement,grouting seal,powder plugging and so on,to reduce the permeability of the crack zone and improve the sealing quality,to achieve the purpose of improving gas extraction efficiency.