Study On Crossing Hole Pre-drainage Gas Out Burst Prevention Of Cross-hole Uncovering Coal

Coal in China’s energy supply structure,has long occupied the core position.However,with the intensification of mining coal resources,coal and gas outburst accidents emerge one after another,and most of these accidents occur in the process of exposing coal in Shimen,which has caused huge casualties and economic losses to China’s coal mining enterprises.Therefore,it is particularly important to implement effective measures to eliminate outburst before uncovering coal.Aiming at the actual problem of coal and gas outburst risk when the +1168m rail transport stone gate of a coal mine in Ningxia exposed No.3 coal seam,this paper effectively eliminated the danger of coal and gas outburst and ensured the safety of coal exposed by rail transport stone gate by means of gas parameter measurement,theoretical analysis,numerical simulation and engineering practice.First of all,the measured the basic parameters of no.3 coal seam gas,coal and gas outburst is studied in theory,drilling,coal seam around the cause of the rule of stress and permeability changes,draw drilling drainage gas can be weakened by in-situ stress,reduce the pore gas pressure and increased the strength of coal body skeleton three aspects to the outburst prevention effect.Secondly,with the aid of Darcy seepage equation and Comsol-Multiphysics simulation software,the model of drilling gas extraction was established.According to the simulation results,the influence of different factors on the extraction effect was analyzed,and the following conclusions were drawn:(1)The larger the diameter of the drilling hole is,the larger the plastic zone around the drilling hole is,and the better the drainage effect is,but the improvement effect is limited.(2)The drainage time has the most obvious effect on the improvement of the drainage effect,but there is a limit of the extraction time,after which the gas extraction flow is very small.Increase extraction time on extraction effect at this time of ascension has little(3)improve the extraction pressure to the extraction effect of test area rather than(4)the choice of hole spacing is determined by the extraction time,arrangement of borehole spacing should consider not only the production safety,at the same time in pursuit of maximum economic value,should reasonable use of radius of gas pressure control.Finally,in the engineering practice,according to the simulation results and considering the actual situation of the field,it is determined that the diameter of the drainage hole is 75 mm,the extraction time is 90 days,the extraction negative pressure is 10 k Pa,and the spacing of the drilling holes is 4.5m.After the regional inspection and the working face inspection,the measured gas indexes are all lower than the critical value of the Detailed Rules for Prevention and Control of Coal and Gas Outburst,and the coal uncovering work of +1168m rail transport stone door can be carried out smoothly.