| The coal mine production is serious threatened by coal and gas outburst,and therefore it is an urgent requirement for coal and gas outburst mines to eliminate outstanding dangers in a safe and economical way.However,it is difficult to drainage the gas due to the condition that more than 95%of the high-gas&outburst coal seams are low permeable seams.The high pressure water jet slitting technology that has been adopted in recently years can enhance the coal permeability effectively,and increase the gas drainage rate,decrease the risk of gas outburst.With the technique,good effect is achieved of pressure relief and enhanced permeability in the field practice,but there is still theoretical and technical problems in many aspects,like the defect of coal breaking mechanism study,the difficulty of slitting effect range confirmation,too much time&labor consuming in technique.In this paper,filed research,theoretical analysis,numerical simulation,laboratory experiments and filed application methods are used to conduct in deep research on the mechanism and application of high pressure water jet slitting enhanced permeability to low permeable soft coal seam.The details are as follows,(1)Based on the influencing factors of coal seam permeability and the basic theory of fluid dynamics,the destruction mechanism of coal under high pressure water jet is analyzed.Hereby,the analysis on the internal relationship between the damage mechanism of the coal body and the distribution of the stress field and the enhanced permeability process in the slotted area is adapted.(2)According to the theory of rock mechanics,elastoplastic mechanics,fracture mechanics and damage mechanics,the FLAC3D numerical calculation method is used to study the stress evolution law and damage range of the coal seam under different seam parameters.Then the synergistic enhanced permeability effects under the seam parameters are analyzed on the basis of the numerical results,and finally the optimized slit parameters are obtained.(3)The hydraulic cutting joint experimental platform was designed and constructed,and the experimental model of high-pressure water jet coal body impact destruction was studied.The cement-gypsum samples with different mechanical strengths were made by using similar materials to simulate the coal body.Under different test sample strengths and different water pressure conditions,the damage and damage characteristics of the slotted position were recorded by endoscope,and the vibration data were collected with the vibrometer.The law of shock vibration wave propagation is analyzed to study the damage law of high pressure water jet impacting coal under different conditions.(4)Based on the above research results,the high-pressure water jet slitting field application test was carried out in the mine,and the hydraulic slit nozzles with different parameters were customized.The nozzle geometry was optimize through investigation of the coal-breaking depth.The pump pressure were graduated.By examining the hole depth,the curve of pump pressure and hole depth is fitted,and the pumping parameters are optimized(5)Based on the test of the pressure change value of the pore gas and the descending ratio of the gas cutting hole before the gas drainage,the effective influence range of the hydraulic cutting joint is investigated on site,and the quantitative verification is carried out according to the gas emission amount and the extraction situation.The hydraulic slitting measures are effective in enhancing the extraction.Based on the above research,this paper has achieved the following results and innovations:(1)The Physical calculation model of hydraulic slittting was established.The dynamic expansion and stress field evolution law of coal damage under the condition of different cutting parameters were studied.The enhanced permeability effect under different conditions of water pressure,slit depth and slit width of different slits was analyzed.The hydraulic slitting seam pressure relief mechanism is fully revealed.Compared with similar researches,the synergistic enhanced permeability effect under double-hole and multi-slit conditions is a more important innovation.(2)A new platform for hydraulic slitting experiments was independently built.The damage range is recorded by endoscope.On the basis of the computer-assisted quantitative calculation and the combination of the vibration velocity waveform law of the coal surface,the macroscopic qualitative calibration of the high-pressure water jet damage to the coal body-microscopic quantitative comprehensive damage law was compressive revealed.(3)In order to solve the problem of large energy loss of water jet,the optimization of the structure and pumping parameters of the water jet nozzle improves the effect of anti-reflection and pressure relief,and improves the high-pressure water jet of the mine production to increase the seam of the soft coal seam.Thus,the on-site technological innovation was achieved.The research results of this paper have important theoretical and practical guiding significance for the on-site hydraulic slitting,pressure relief and permeability method,the design of water jet nozzle parameter structure,the implementation of kerf under different soft coal seam stress and gas pressure and the mechanism of enhanced permeability. |
PDF Full Text Request