Microscopic study on the memory effect of methane hydrate in the presence of silica nanoparticles: Ⅰ. Dissociation mechanism & guest supersaturated hypothesis

•Evolution mechanism of methane molecules during hydrate dissociation.•Capture of dissociation configurations in different methane supersaturated states.•Hydrate-like orderly arrangement of methane induce reformation of hydrate cluster.•Dissolved methane is more conducive to hydrate reformation than nanobubbles.•Silica nanoparticles flowing in the solution inhibit reformation of hydrate cluster. As a key issue emerged in the exploitation of combustible ice resources, the memory effect inducing hydrate reformation in sand-containing dissociated-water system is still ambiguous. Among them, methane hydrate dissociation kinetics and guest supersaturated hypothesis for methane hydrate reformation are the primary issues to be addressed. A molecular dynamics simulation system where methane hydrate interacts with surface-hydroxylated silica nanoparticles was established to simulate dissociation process, which is necessary to construct hydrate reformation systems for further microscopic study on hydrate memory effect. The transportation mechanism of methane during hydrate dissociation in sand-containing aqueous system was elucidated. Based on this, hydrate-dissociated systems with methane supersaturated were captured, and molecular dynamics simulations were carried out to further study hydrate reformation mechanism regarding the guest supersaturated hypothesis. By analyzing the distribution and transportation of methane, hydrate clusters, and silica nanoparticles, it can be concluded that the hydrate-like orderly arrangement of methane that are dissolved in the solution or on the surface of nanobubbles are necessary to trigger hydrate memory effect by inducing the reformation of hydrate clusters, while the silica nanoparticles can inhibit the reformation of hydrate clusters by disturbing the arrangement of methane molecules and water molecules. Thence, the microscopic analysis indicated that supersaturated guest molecules is vital to the occurrence of hydrate memory effect and its effect varies between the supersaturated states.