Research On Numerical Simulation Of Borehole Gas Drainage Effective Radius And Borehole Optimization Based On THM Multi-field Coupling

Coal seam gas drainage is an important means to control mine gas disasters.Gas extraction can effectively prevent and control gas disasters,and the extracted gas can be used as clean energy.When designing coal seam gas drainage holes,the effective drainage radius is essential basic data.Although the research system on effective radius is relatively mature,at present,there is still a lack of research on the law of the influence of coal seam temperature on the effective radius,and the response law between the two is not yet clear.Based on this,in order to further explore the response law between the coal bed temperature and the effective drainage radius,at the same time,after considering the coal bed temperature,other drainage influencing factors have an effect on the effective drainage radius.Therefore,this paper uses a combination of theoretical analysis,numerical simulation and field testing to achieve the purpose of research.First,based on the determined THM multi-field coupling model of gas drainage,the response between coal seam initial temperature,drainage time,coal seam initial permeability,borehole diameter,drainage negative pressure and drainage effective radius was studied by COMSOL Multiphysics numerical simulation.Secondly,the gas pressure index method was used to conduct a field test study on the effective drainage radius of the test coal seam.Finally,based on the effective drainage radius,the reasonable drilling spacing of the test coal seam was determined through numerical simulation,and the parameters of the spacing between the holes were tested optimized design.The main research results obtained by the thesis are as follows:(1)According to the numerical simulation results of COMSOL Multiphysics,it is concluded that the high-temperature coal seam is not conducive to gas drainage.As the coal seam temperature increases,the effective radius of gas drainage in the borehole decreases,and when the coal seam temperature is low,the effective gas drainage radius and drainage The rate of decrease in the area that meets the standards is relatively slow.As the temperature of the coal seam rises,the effective gas drainage radius and the area where the standards meet the standards decrease faster;the extraction time is positively correlated with the effective radius of extraction;the greater the initial permeability of the coal The greater the effective radius of extraction;the larger the borehole diameter of extraction,the greater the effective radius of extraction;the negative pressure of extraction has almost no effect on the effective radius of extraction.(2)The effective radius of the borehole extraction radius obtained by numerical simulation is the same as the actual measured borehole extraction radius.The error of the results obtained by the two methods is small,which verifies the gas development based on the determined THM multi-field coupling model of gas extraction.The feasibility and correctness of the effective radius of drainage,the results of numerical simulation can provide theoretical guidance for the layout of on-site gas drainage holes.(3)Based on the effective radius of the drainage,numerical simulation was used to determine the reasonable hole spacing of the test coal seam to be 2.62?3.93 m.According to the optimized scheme,the conclusion that the three-eye hole layout is better than the rectangular hole layout in the pre-extraction of gas from the test coal seam was obtained through numerical simulation.