Research On Gas Drainage Of Crossing-Mesure By Expanding Borehole Diameter In Low Gas Permeability Coal Seams

Coal and gas outburst accidents often happen in the process of coal roadway driving in outburst coal seam of coal mine safety production,which causes a very big menace. Borehole area extraction is to eliminate the danger of coal.and gas outburst of major technical methods, and low permeability coal seam, the gas pumping effect is poor, often using layer antireflection technique. Based on the analysis of insufficient of common improve air permeability technology, we put forward a kind of simple operation and has universal application of the anti-reflection technology--borehole seam section reaming technique, its principle is the aperture extending through a corresponding increase in holes in coal body bare area, to increase the permeability coefficient, improve the effect of extraction.(1) through the theoretical analysis of gas in coal pore migration, determine the coal body around boreholes stress influence range, on the drill gas drainage and cutting hole reaming measures of eliminating outburst mechanism, introduces several kinds of influence factors of gas drainage effect, and their analysis of the relationship between.(2) by using two numerical simulation analysis software, through the FLAC3d software to simulate the stress distribution around the hole, observe with the diameter increases, coal body around boreholes destressing range is enlarged; through the FLUENT software to simulate different pumping negative pressure, the hole diameter, pumping time around the borehole pressure relief range changes, research shows that, according to the actual geological conditions determine coal seam extraction.(3) the anti-reflection technology has been tested in Li Zuizi coal mine of Huainan Mining Group,in order to tunneling shield machine32329in32327bottom drainage roadway, research shows that:the seam section of the borehole diameter by113mm is extended to260mm, borehole gas drainage radius increased from2m to3m, reducing the amount of borehole layout. The cutting hole and drainage investigation shows, cutting hole after extraction of pure decreased from1.72m3/h to2.26m3/h,which is1.3times the original, concentration increases from7.84%to9.89%, which is1.26times of that of the original, by increasing the unit time extraction scalar shorten regional preliminary drainage of gas in time to solve the problem, production to succeed.(4) through the experiments in Gubei Coal Mine show that:the average quantity of coal cutting hole drilling out113kg/m, increased59.81kg/m more than theory coal quantity; cutting hole drilling and borehole drainage study compared with display drainage flow, long time, extraction of high concentration, large quantity of spare gas characteristics; during1、2#expand borehole drilling pressurization, investigation radius2m examines hole adopting the net flow increased31.94～171.48%, investigation radius2.5m drilling drainage net flow increased19.44～138.24%. Show positive pressure drilling influence radius of2.5m, the effect of positive pressure antireflection is good.Through theoretical analysis, numerical simulations and experiments show that:by using the borehole seam section reaming strengthening antireflection technique, increases the drilling of coal body around the exposed area, effectively removing stress and gas pressure, drilling of coal body around to produce stress damage and fracture, raise coal permeability coefficient, increasing the effective drainage radius, thereby improving the coal seam gas drainage and extraction rate, shorten the time of gas pre drainage. At the same time, because this technique mainly adopts mechanical operation, simple and convenient operation, improves production efficiency, and achieved good economic benefit; in addition, it also reduces the coal and gas outburst danger, so as to solve the high gassy outburst coal seam roadway excavation and disallowed gas concentration in coal faces and gas outburst problem, help roadway quick tunneling, has realized the low permeability outburst coal seam working face balance of "excavating, mining,pumping ",which is a very valuable technology.