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Research On The Deflection Amount Of Bedding Gas Drainage Borehole For Effective Outburst Prevention

Posted on:2015-05-02Degree:MasterType:Thesis
Country:ChinaCandidate:K LiFull Text:PDF
GTID:2271330479951576Subject:Mining engineering
Abstract/Summary:PDF Full Text Request
Along the coal seam gas extraction is an important measure of regional gas disaster control. But offset phenomenon of drilling into the roof or floor strata is often occurred in the drilling construction process. When the offset is too large, gas can not pass through the rock into the extraction borehole, gas extraction is not balanced, the local gas extraction blank tape come into being, which caused great hazards in mine production safety. By theoretical analysis and numerical simulation, taking the ji 15-32020 working face of Pingdingshan fifth coal mine as experimental site, this paper gave a scientific analysis and reasonable explanation to the phenomenon that outburst prevention measures in the area was still valid although the borehole occurred partially offset during the along the coal seam gas extraction. The result provided a theoretical evidence of reasonable and optimization borehole layout.Based on the law of gas flow in coal seam and the characteristics of stress distribution around borehole in coal and rock mass, this paper analyzed gas flow pattern and pressure-relief range around offset borehole. The results showed:gas migration around offset borehole in rock seam can be seen as a half radial-way steady flow, gas migration around offset borehole in coal seam can be seen as a radial-way steady flow, it is an effect way to improve the result of gas extraction by increasing the permeability of rock and coal; coefficient of horizontal pressure impact mainly the shape of pressure-relief range of borehole, all of them are in favor of expanding the pressure-relief range to reduce the intensity of coal and rock, increase the buried depth of borehole, borehole diameter and softening modulus. Taking the actual circumstances in the test area for instance, this paper analysed the pressure-relief range of offset borehole in the rock, the change of gas permeability and the effective radius of gas extraction through theoretical model calculation and RFPA numerical analysis. The results of numerical analysis showed:the actual pressure-relief range of offset borehole in test area should be between 0.357-0.525m, permeability coefficient of rock seam in pressure-relief range is raised to permeability coefficient of coal seam, gas pressure in the control region of extraction borehole can be reduced to within 0.445-0.579MPa after extracting for 300 days. By comparing the eliminate outburst result in test area, it indicated that the simulation results corresponded with the actual results, the deflection amount of bedding gas drainage borehole for effective outburst prevention in the test area is the pressure-relief range of offset borehole in rock seam. Through a comprehensive analysis, the deflection amount of bedding gas drainage borehole for effective outburst prevention is determined by magnitude and distribution of virgin rock stress, mechanical parameters of coal and rock mass and the diameter of borehole and affected by the gas parameter of coal seam, the permeability of coal seam and extraction time.
Keywords/Search Tags:offset borehole, gas extraction effect, pressure-relief range, permeability coefficient, numerical simulation
PDF Full Text Request
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