| Coal seam gas injection displacement is a new technology for controlling coal seam gas,but the related research on this technology is not sufficient.This thesis adopts a combination of theoretical analysis,numerical simulation,and on-site measurement to study the application effect of gas injection displacement technology in Sima Coal Industry.Through theoretical analysis,the mechanism of coal seam gas injection displacement and suitable gas injection sources are identified.The influence of gas injection time on coal seams was studied through numerical simulation;We studied the effects of gas injection pressure,negative pressure of extraction,distance between injection holes and drainage(drainage)holes,and gas injection methods on coal seam gas,and conducted on-site experiments in Sima Coal Industry to compare the results of the two.Using COMSOL software to establish a mathematical model for nitrogen injection displacement,simulate the effects of gas injection time,pressure,method,negative pressure of extraction,and hole spacing on the displacement effect.The results show that when injecting gas into a single hole,the greater the nitrogen injection pressure,the greater the range of nitrogen injection displacement effect within the same injection time;When the injection pressure is constant,the influence range of nitrogen also increases with the increase of injection time;The displacement effect is best when continuous gas injection is used,with a gas injection pressure of 1.6MPa and a spacing of 3m between holes.After 10 days of gas injection,the maximum gas content in the coal seam decreased by 42.3%,but at the same time,the gas content in the same position of the coal seam was only 0.11～0.18m3/t lower than the gas injection pressure of0.8MPa.Therefore,it is advisable to choose a gas injection pressure of 0.8MPa.When continuous gas injection is used,with a gas injection pressure of 0.8MPa and a negative pressure of 15 k Pa applied to the gas producing hole for extraction,the maximum gas content in the coal seam decreases by 49.5% after 10 days of gas injection.Compared with the numerical simulation results without applying negative pressure under the same conditions,the gas content decreases faster and the displacement effect is more obvious within the same time period.According to the numerical simulation results,the gas injection pressure for the downhole test was selected to be 0.8MPa.The test results showed that the maximum mixed flow rates at test points 1,2,and 4 were 20.8 times,5.83 times,and 4.8 times higher than before the gas injection,respectively;The maximum pure gas content is 5.2times,3.24 times,and 4.04 times higher than before gas injection.The maximum mixed flow rate of each gas producing pore at test point 2-1 during gas injection is 6.1 times,5.13 times,and 5.91 times that before gas injection,respectively;The maximum pure gas content is 2.67 times,2.84 times,and 2.5 times higher than before gas injection.During the period of continuous gas injection and the application of 15 k Pa negative pressure to the gas producing pores,the mixed flow rate and gas purity of each gas producing pore significantly increased at test points 2 to 2.After stabilization,the mixed flow rate increased by more than 66 times compared to before gas injection,and the gas purity also increased by more than 20 times compared to before gas injection.Analysis shows that the closer the distance between the injection and production pores,the better the displacement effect.The continuous gas injection displacement effect is significantly better than the cyclic gas injection,and the displacement effect is significantly improved after applying negative pressure for pumping.After the injection was stopped,the mixed flow rate,gas purity,and gas concentration of each gas producing pore all recovered,but they did not return to the values before the gas injection.The reason may be that the gas injection displacement of coal seam gas has a certain fracturing effect on the coal seam.After displacement,the gas content within the displacement range of all three test points decreased to 4.5m 3/ Below t,good displacement effects were achieved.Meanwhile,research has shown that the conclusions of theoretical analysis,numerical simulation,and on-site experiments have good consistency.This thesis has 70 figures,14 tables,and 113 references. |
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