Abstract: In this paper, to analyze the influencing factors on time-varying characteristics of displacement coalbed methane by gas injection, the mathematical model of displacement coalbed methane technology by N2 injection was established, and the effects of the influencing factors, such as gas injection pressure, drainage negative pressure, gas injection time, et al, on the time-varying characteristics of displacement coalbed methane by gas injection have been simulated by using COMSOL multiphysics software, then the variation laws of the methane content and outburst elimination cycle under different conditions were studied. The results show that the greater the gas injection pressure is, the faster the methane content decreases, and the shorter the outburst elimination cycle is, while the reasonable gas injection pressure is 0.5 MPa. In addition, the influence of drainage negative pressure on the time-varying characteristics is not obvious, and the reasonable drainage negative pressure is 5-13 KPa. Moreover, the methane content decreases gradually with the increase of injection time, while the position near the gas injection borehole is the weak area in the displacement coalbed methane technology by gas injection. Furthermore, the field tests were carried out in Shigang Company. By comparing with the numerical results, the measured methane contents are always slightly smaller than that in simu-lation results under the same conditions. The reasons for this difference were also analyzed.

Key words: gas injection, time-varying characteristics, influencing factors, numerical simulation, gas injection pressure, drainage negative pressure