Study on the Differences between Various Gas Injection Sources in the Process of Coal Seam Methane Replacement by Gas Injection

[Image: see text] To study the differences between various gas injection sources in the process of coal seam methane replacement, experimental research was conducted to study the influences of different gas injection sources and gas injection ratios on coal seam methane replacement by considering the strong adsorption gas CO(2) and the weak adsorption gas N(2). The experimental results show that the temperature rise effect of the CO(2) injection gas is greater and lasts longer than that of the N(2) injection gas in the process of coal seam methane replacement by gas injection, and the temperature rise can promote the desorption of adsorbed methane well. However, due to the different effects of gas compressibility, the increase in gas pressure caused by injecting N(2) under the same conditions is higher than that of CO(2); due to the strong adsorption of CO(2), the gas pressure after injecting CO(2) continues to decrease slowly. From the displacement effect, the adsorbability of the injection source gas has a significant effect on the displacement rate and injection-placement ratio, while the injection ratio has a significant effect on CO(2) displacement but not on N(2) injection. From the experimental results, for N(2) injection, the effects of coal seam methane replacement by gas injection can be enhanced by improving the gas injection method and process; for CO(2) injection, the effects of coal seam methane replacement by gas injection can be improved by the following two aspects: gas injection volume and gas injection time.