Natural gas hydrate, a potential energy resource, is attracting worldwide attention. In this study, we propose a new method of hydrate dissociation which uses seawater and electrostatic fields (SE method) cooperatively. The hydrate molecular dissociation mechanism of gas hydrate is a key issue in studying the kinetic properties of gas hydrate using the SE method. Therefore, molecular dynamics simulations were used to investigate the thermodynamic properties and structural changes of methane hydrate (MH) in multiple kinds of salt solutions under an electrostatic field. The results show that the electric field can drive cations into the MH phase to form a series of random semiopen cages, which are essentially temporary and metastable. The variation in free energy indicates that it is more difficult for divalent cations to enter the hydrate phase than monovalent cations, meaning that the hydrate structures formed with divalent cations are more unstable. Then, the ion current occurred in the hydrate phase (called ion migration in this study), which greatly accelerated hydrate dissociation. In contrast, the promotion effect of cations with the same charge on MH dissociation is as follows: Sr 2+ > K + ≈ Na + > Ca 2+ ≈ Mg 2+ . In general, the presence of common marine cations enhanced the promotion effect of the electric field on gas hydrate dissociation.

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In this study, nonequilibrium molecular dynamics simulations (NEMDs) were used to investigate the thermodynamic properties and structural changes of methane hydrate (MH) in the NaCl solution at different temperatures (270−290 K, 40 bar) and electric field intensities (0−0.07 V/Å). The dissociation rate of hydrate increases exponentially with the increasing electric field. Compared to pure water, the presence of salt ions in solution enhances the inhibitory effect of electric field on methane hydrates significantly. This is because the intensive electric field can drive the Na + and Cl − ions into the methane hydrate layer to randomly replace some water molecules and subsequently form temporary and unstable cage structures. Some typical hydrate structures containing ions were observed and found that the ions exist as part of the cage, causing the distortion of the hydrogen-bond network. These structures are unstable and the ions can migrate easily from the cage, leading to the breakdown of the structures. Generally, the movement of ions in the hydrate is leaping and jumping rapidly from a metastable position to another. With the intensification of ion migration, nearby hydrates break down and form a flow channel in the middle of the hydrate layer, enabling the ions to move freely through the channel. These results provide useful insights into the mechanism of inhibition of methane hydrates using an electric field.