A Study On Parameters Optimization Of Injecting N₂ To Produce CBM

Duing to the complicated geological conditions and the low permeability of coal seam in China,it’s difficult to produce CBM.N₂-injection is one of the main methods to E-CBM,and there are few researches on intermittent N₂-injection to E-CBM.In this paper,the author studies the formation、occurrence and migration of CBM,the mechanism of N₂-injection displacement CH₄ through the way of literature research;indoor experiment are carried out with continuous and intermittent N₂-injection displacement CH₄,and the corresponding mathematical models are established;simulating the continuous and intermittent N₂-injection displacement CH₄ on different injection pressure,injection velocity,the amount of slug,intermittent time and optimizing the technological parameters by using the finite element method.Indoor experimental results show that when the pressure is increased from 2.5MPa to4.5MPa,the displacement efficiency is increased from 80.75% to 85.45%;when the injection velocity is increased from 400ml/min to 800ml/min,the displacement efficiency is increased from 49.67% to 52.21%;when the amount of slug is increased from 12 L to 38 L,the displacement efficiency is increased from 75.24% to 76.89%;when intermittent time is increased from 1h to 3h,the displacement efficiency is by the 76.03% to 72.55%.In numerical simulation,firstly,by simulating the injection pressure 、 injection velocity、 the amount of slug 、 intermittent time under laboratory condition verifies the accuracy of the model;secondly,by simulating the injection setting injection pressure 、 injection setting velocity 、the amount of slug、 intermittent time predicts the effects of injection pressure、 injection velocity 、the amount of slug 、 intermittent time on displacement efficiency.Simulation results show that when the pressure is greater than 10 MPa,the displacement efficiency tends to be stable for 87%,when the injection velocity is larger than 2200ml/min,the displacement efficiency tends to be stable for 54%,when the the amount of slug is 38 L,the maximum displacement efficiency is 73.51%,when the intermittent time is 1h,the maximum displacement efficiency is 73.47% under the same conditions so as to determine the optimal technological parameters of continuous and intermittent N₂-injection to E-CBM.The research results of this paper have a certain guiding role for the field test of E-CBM by N₂-injecting.