Insight on the stability of methane hydrate in montmorillonite slits by molecular dynamics simulations

Abstract

The extent of interactions between clay surfaces and water molecules and their impact on hydrate stability in clay reservoirs have been a source of debate. This study employs molecular dynamics simulations to investigate the stability of methane hydrates in montmorillonite slits at various temperatures, focusing on the surface influence scale, bound water molecule distribution characteristics, and binding strength. The results reveal that hydrates in close proximity to the clay surface exhibit lower stability and higher decomposition susceptibility due to the hydrophilic nature of the surface, which leads to water molecule aggregation, driving methane molecules away during decomposition. Furthermore, we compare the charged and neutral tetrahedral layer surfaces of montmorillonite and find that the quasi-liquid layer on the neutral tetrahedral layer surface is thinner, with persisting semicage structures within the vacancies of the Si-O rings. These variations in surface influence range and binding strength can be attributed to intermolecular Coulomb interactions and charge redistribution at the interface. These research findings provide valuable molecular insights into the microscopic characteristics and behavior of hydrates within clay slits.