顺层钻孔注液态CO2驱替煤层CH4技术的参数优化与工程试验OA

To improve the drainage efficiency of outburst and low-permeability coal seam gas,this study takes the liquid CO2 displa-cing coal seam CH4 technology as the core,and explores the influence of CO2 injection pressure parameters and borehole spacing on gas drainage effect through the combination of numerical simulation and field test.Based on the geological conditions of the out-burst coal seam in Jixian Coal Mine,a fluid-solid coupling model was established,and the dynamic evolution laws of coal seam gas pressure under different pressure injection pressures(2-7 MPa)and borehole spacings(5 m,8 m,12 m)of liquid CO2 were analyzed.Based on this,the optimal process parameters of the field test were optimized and determined.The results show that the influence of liquid CO2 injection pressure on the effective drainage radius shows obvious stage characteristics,and the effective drainage radius is significantly expanded with the increase of pressure:when the injection pressure is 2-3 MPa,the effective extraction radius is 5.0-8.0 m;when the pressure increases to 4-5 MPa,the radius increases to 8-13 m,when it is further increased to 6-7 MPa,the radius can reach 13-20 m.The pressure change in the process of gas drainage can be divided into three stages:in 0-100 d,the CH4 pressure drop rate under 6-7 MPa injection pressure is higher than the average value of 0.004 5,and the displacement effect is better than that un-der low pressure conditions;in 100-200 d,5-7 MPa pressure still maintains a high pressure drop rate;after 200 days,the pressure drop rate was significantly slowed down due to the large amount of CH4 drainage in the early stage.The study results show that the optimal injection pressure is 5-7 MPa.The drainage effect of 5 m spacing is better than that of 8 m and 12 m.It is suggested that the 5 m spacing should be preferred in the project.In the field application,after injecting 8.2 m3 liquid CO2 into a single hole,the volume fraction of gas drainage increased to 3.57 times of the original,the extraction purity reached 6.96 times of the original,and the active period of drainage lasted for more than 85 days.