1、Numeric Analysis of Hydraulic Fracturing Technique in Preventing Outburst and the Control TechniqueZhao xue-bing Wei wei Ni mao-longXuzhou mining Group Co Ltd Xu zhou,china,221006Abstract: To give full play to the technique of hydraulic fracturing in removing the danger of coal and gas outburst by o
2、verall relieving the stress, the FLAC3D software was used to analyze the stress distribution after the hydraulic fracturing, and the relation of spatiotemporal coupling of hydraulic fracturing and controlled blasting techniques was theoretically analyzed. The result shows that the technique of hydra
3、ulic fracturing should generate high pore pressure and distribute in chaos while relieving the ground stress, which results new hidden danger. The controlled blasting technique used before the hydraulic fracturing should generate crannies which lead the fracturing direction and relieve the stress ov
4、erall. By analyzing an outburst example of a mine, the spatiotemporal coupling relationship of hydraulic fracturing and controlled blasting techniques directly affects the stress relieving effect. Finally, a number of proposals to avoid incidents were post out to improve the safety use of the hydrau
5、lic fracturing technique.Keywords: controlled blasting; hydraulic fracturing; spatiotemporal coupling; overall relieving the stress; coal and gas outburst, pore pressureCoal and gas outburst is affected by ground stress and gas pressure 1, and for a long time it is one of the main problem to highlig
6、ht the safety production of a mine. Scholars at home and abroad have done a great deal of research works about relieving coals stress, and have played a significant role in preventing outburst 2,5. However, with the deepening of the depth of coal mining, the increasing stress reduce the permeability
7、 of coal, conventional methods cant be effectively removed the stress and gas pressure, coal and gas outburst occur from time to time in complex geological condition region 6, 7. Hydraulic fracturing technology is an effective method to preventing outburst by injecting high.pressure water into the r
8、ock and fracture the coal and rock to release stress and increase the coal.rock permeability. Because the fracturing direction is uncontrollable 8, new high pore pressure will be generated at another places while relieving the stress and distribute in chaos, which has a bad effect on safety producti
9、on and restricts the extent use. To control fracturing, this paper gave a detailed analysis of the overall relieving stress mechanism of spatiotemporal coupling of controlled blasting and hydraulic fracturing techniques, and made a number of recommendations with the view to make a good use of the te
10、chniques to reduce the similar incidents and serve in the coal mine safety production.1. Hydraulic Fracturing Technique and the DeficiencyHigh pressure water can fracture and expand crannies around a hole to relief the ground stress around, but at the same time high pore pressure and addition stress
11、 concentration will formed at some other place, which was proved in China Pigmies Sheena Group. Because the fracturing direction is uncontrollable and difficult to detect at present, most of the cases the fracturing direction is unclear. The coal and mine outburst maybe occur when the coal mine get
12、into the high pore pressure region without realization.Its very difficult to get clear of the stress distribution after hydraulic fracturing through laboratory or field test, and the repeatability is also weak, while the numeric simulation technique, as a new method, can overcome these shortcomings.
13、 Three conditions of one crack, two cracks or three cracks as show in figure 1 were simulated separately. In the figure, “c.i” means crack number i, crack 1 goes along the roadway, crack 2 and 3 goes start with the injection hole and vertical to the roadway, but the crack 3 is upper to crack 2. And
14、the nij means the node number j in condition i, and high pressure water was injected into the injection hole. Fig. 1 Crack distribution （a） one crack （b） two cracks （c） three cracks1.1 Numeric Simulation AnalysisTo enable the calculation more close to reality, the model of 504020 m was built accordi
15、ng to the outburst location of a mine. The coal seam is 3.5 m thick, 700 m deep, with an inclination of 22. The fluid.solid coupling mode of FLAC3D was used to analyze the stress distribution after hydraulic fracturing 9. The upper face was applied 18 MPa pressure, and norm to others was fixed. The
16、model was shown as figure 2:Fig. 2 Numeric analysis model1.1.1 Bringing no main crack after hydraulic fracturingWhen no main crack formed after hydraulic fracturing, the high pore pressure shown in figure 3 will be generated.Fig. 3 The stress distribution when no main crack formedFigure 3 shows that although no main crack formed after hydraulic fracturing, the high pressure water had already been injected into the coal, which generated 9
