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

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.

Automated summary

This study examined the differences between CO2 and N2 as gas injection sources in coal seam methane replacement. The results showed that CO2 injection had a greater and longer-lasting temperature rise effect, promoting the desorption of methane. The adsorbability of the injection source gas had a significant impact on displacement rate and injection-placement ratio, while the injection ratio only affected CO2 injection. Enhancing gas injection method and process improved the displacement efficiency of N2 injection, while increasing injection volume and time improved CO2 injection.