Effect of the Oscillating Electric Field on the Enhancement of CH4 Replacement in Hydrates by CO2: A Molecular Dynamics Study

Replacing CH4 from natural gas hydrates by CO2 is a promising option to produce CH4 and sequestrate CO2. However, the method is not efficient due to the mass transport blockage caused by the CO2 hydrates formed on the surface of the hydrate. To enhance CH4 recovery and CO2 sequestration, we proposed a method to improve the efficiency of CH4 replacement in hydrates by CO2 by applying an oscillating electric field. The effects of frequency, strength, and application time of the electric field on the dissociation of methane hydrates and CH4 replacement by CO2 were discussed. The results show that the presence of an electric field enhanced the dissociation of hydrates and increased the diffusivity of CH4 and CO2 molecules. More methane hydrates were dissociated by increasing the frequency, strength, or application time of the electric field. The carbon dioxide molecules continued to diffuse into the hydrate region after removing the electric field. Moreover, carbon dioxide hydrates were mainly formed in the residual cage structures after removing the electric field. Under the conditions of this work, the best efficiency of CH4 replacement in hydrates by CO2 was obtained when applying an electric field with a frequency of 10 GHz and an amplitude of 0.115 V/angstrom for 3 ns. This study helps us to understand the mechanism of how oscillating electric fields enhance the replacement of CH4 from natural gas hydrates by CO2 and is of applicable importance to boost CH4 recovery and CO2 sequestration.