Experimental Study on the Effect of Pressure on the Replacement Process of CO2-CH4 Hydrate below the Freezing Point

The recovery of natural gas from CH4 hydrate deposits in permafrost environments through injection of CO2 is considered to be a suitable strategy for CH4 production and CO2 storage. To study the replacement characteristics of CO2-CH4 hydrate below the freezing point, the experiment was conducted in ice powder with particle size of 800 mu m at different injection pressures (3.6, 4.0, and 4.5 MPa) of CO2. The experimental results showed that the average replacement rate and efficiency increased with the increasing of injected pressure of CO2 gas. Also, the average replacement rate and efficiency reached up to 0.403 mmol/h and 13.20% when the injected pressure of CO2 was at 4.5 MPa. The results also indicated that, compared with the temperature conditions above the freezing point, the replacement rate of CO3-CH4 hydrate was slow below the freezing point. These results provide a theoretical guidance for gas production from methane hydrate using CO2-CH4 replacement method in permafrost region in the future.