Study On The Effective Radius Of Drilling Gas Extraction Based On Flow-Solid Coupling Model

Pre-drainage of coal seam gas effectively reduces the incidence of gas accidents in coal mines.The research on effective radius of coal seam gas drainage has definite engineering guiding significance for reasonably arranging drainage boreholes and controlling coal seam gas.Taking a working face in No.3 coal seam of Shanxi Jinmei Group Qinxiu Coal Industry Co.,Ltd..Y coal mine as the research object,this paper adopts the approach of combining theoretical analysis,software numerical simulation and actual working conditions on the spot,a coupling mathematical model of coal and rock mass deformation and fluid-solid was established for gas pre-drainage from coal seam by borehole along Seam No.3 in Y coal mine.COMSOL Multiphysics is used to simulate and solve the mathematical model in order to study the effective radius of coal seam gas extraction.Based on the COMSOL numerical simulation results and field measured data,the theoretical guidance is provided for the hole spacing and hole arrangement in the gas extraction engineering of No.3 coal seam.The conclusion is as follows:(1)On the basis of collecting and arranging the basic general situation and gas parameters of No.3 coal seam in Y coal mine,seven boreholes are arranged along the working face of No.3 coal seam,the test results show that the influence radius of coal seam gas drainage is 1 m,1.5 m,2 m and 2.5 m respectively on the 3rd,6th,10 th and15th day.(2)According to the dynamic change equation of porosity and permeability,combining with the deformation control equation of coal and rock mass,mass conservation principle and gas state equation,the control equation of gas movement in coal seam is obtained,construction of coupling control model of coal and rock mass deformation-seepage.The influence radius of coal seam gas extraction is simulated by using COMSOL software,and compared with the field test results,the correctness of the numerical model simulation is obtained,it provides a theoretical basis for the effective radius of coal seam gas drainage.(3)The research results show that after 30,60,90,120,150,180,210 days,the effective radius of gas drainage in coal seam is studied by using the validated numerical model,the effective radius of gas drainage is 0.68 m,1.01 m,1.21 m,1.38 m,1.51 m,1.62 m and 1.72 m respectively.(4)When other conditions are invariable,the distance between two boreholes is 2.5m,2.75 m,3 m,3.25 m and 3.5 m,the number of days needed to reach the standard of gas drainage is 78 days,101 days,133 days,163 days and 218 days respectively.(5)When the spacing of drill holes is 2.5 m,2.75 m,3 m,3.25 m and 3.5 m,the number of days needed to reach the standard of gas drainage in the middle zone of the borehole is 71,94,119,151 and 199 days respectively.28 figures,16 tables,and 80 references.