Study On Outburst Elimination Technique In Low Permeability Coalbed Using Zonal Gas Pre-drainage By Cross-measure Boreholes

As China's leading energy, coal is an effective guarantee of the rapid national economy with sustainable development. Meanwhile, the disasters caused by coal exploitation restrict the coal production and expanding economy. Particularly, coal and gas outburst is most harmful. Because of low permeability and high outburst risk in coalbed of China, the studies focus on outburst elimination technique with stress relief and gas pre-drainage. Mining protective layer of which has got some breakthrough progress, whereas in high outburst risk coalbed with no stress relief and outburst elimination, the technique using zonal gas pre-drainage by cross-measure boreholes is provided for further study.As a sub-topic of Eleventh Five-Year national science and technology support program, safty control technique and equipment development in deep mining, the paper studies three parts by theoretical analysis and practical application, as follows:(1) Outburst elimination mechanism&influence factors of zonal gas pre-drainage by cross-measure boreholesBased on the relation of permeability and effective stress, an understanding of permeability variation during gas pre-drainage is presented. The influence of coalbed feature during gas pre-drainage is theoretically analysed. And outburst elimination mechanism using zonal gas pre-drainage by cross-measure boreholes is induced by description of coal and gas outburst.(2) Numerical simulation&layout optimization of zonal gas pre-drainage by cross-measure boreholesThe numerical model and method of gas seepage are set up to analysed the distribution of gas pressure, the quantity, efficiency, effective period and radius of gas drainage. Due to permeability variation during gas pre-drainage, the effect influenced by subpressure is shown with practical work. Using gas pressure change to find effective radius of gas drainage is assumed lacking on field testing. Applying flow rate to survey effective radius is presented, and then the method of layout optimization is estabished. (3) Practical work of zonal gas pre-drainage by cross-measure boreholesThree examples of zonal gas pre-drainage by cross-measure boreholes are analysed as follows:The first one is roadway advancing safeguarding by zonal gas pre-drainage in the 62110 panel floor roadway of Xin zhuangzi coal mine. Effect of different location boreholes and permeability variation during gas pre-drainage are paid more attention on analysis. The outburst risk index and gas gush feature are analysed during roadway progress. The result proves that the effectiveness of zonal gas pre-drainage by cross-measure boreholes.The second one, after compareing zonal gas pre-drainage with gas drainage while excavation, shows that the advantage of former and emphasizes the idea of zonal measures to go ahead and partial measures to reinforce.The third one, a water hammer equipment of high pressure pulsating for improving permeability is applied to enhance the effect of gas pre-drainage in low permeability coalbed. The outcome of experiment shows that applying the equipment has more effective to crack propagation and gas drainage, moreover, the result of improving permeability is proved better.