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

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 CO₂ and the weak adsorption gas N₂. The experimental results show that the temperature rise effect of the CO₂ injection gas is greater and lasts longer than that of the N₂ 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 N₂ under the same conditions is higher than that of CO₂; due to the strong adsorption of CO₂, the gas pressure after injecting CO₂ 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 CO₂ displacement but not on N₂ injection. From the experimental results, for N₂ injection, the effects of coal seam methane replacement by gas injection can be enhanced by improving the gas injection method and process; for CO₂ 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.