Molecular dynamics-based analysis of the factors influencing the CO₂ replacement of methane hydrate

The benefits of large reserves, wide distribution, and high combustion energy density of natural gas hydrates are of great practical importance to alleviate the energy tension, enhance the existing energy system in China and reduce the greenhouse effect. The CO₂ replacement method is a critical way to develop natural gas hydrate, while traditional experimental methods are difficult to reveal the microscopic mechanism of the replacement system. An MD (molecular dynamics) technique was utilized in this work to simulate the process of carbon dioxide replacement of gas hydrates. This simulation investigates the effects of temperature, pressure, and CO₂ purity during the CO₂ replacement process. CO₂, different concentrations of CO₂/H₂O, and CO₂/NH₃ are used as the injected fluid. The simulation results show that the influence of temperature on the CO₂ replacement of natural gas hydrate is more significant than that of pressure. Within the temperature and pressure range specified in the simulation, H₂O inhibits the replacement of CO₂, owing to the inhibitory effect increasing as the concentration of H₂O increases; NH₃ promotes the process of CO₂ replacement under the temperature conditions of 250 K and 260 K, and the promotion effect becomes more significant as the concentration of NH₃ increases. However, adding NH₃ inhibits the CO₂ replacement process with hydrate when the temperature lifts to 270 K. These findings provide new ideas to improve the efficiency of the CO₂ replacement method and provide theoretical insight for the engineering exploitation of hydrates.