Unveiling the Effect of Salt on Methane Hydrate Dissociation Kinetics under Strong Thermal Perturbation

Hydrate dissociation kinetics is fundamental to understanding the hydrate dissociation process and has been commonly used to assess the gas release rate of marine methane hydrates, which is critical for evaluating both hydrate resource exploitation and ocean-atmosphere carbon cycling. Geothermal anomalies or thermal-assisted exploitation can cause a substantial temperature increase on the order of 50 °C within hydrate-bearing sediments, potentially intensifying or weakening the inhibitor effect of salt in seawater on hydrate dissociation with significant uncertainty. In this study, we employed molecular dynamics simulations to unveil the temperature-dependent effect of salt on methane hydrate dissociation kinetics under such strong thermal perturbation. The simulation results demonstrate that at high temperatures (>320 K), salt in seawater promotes hydrate dissociation primarily by directly disrupting the clathrate structure, which differs markedly from the observed mechanism of modulating dissolved methane concentration at low-to-moderate temperatures (268 to 290 K). During temperature elevation, the enhancement of salt on the hydrate dissociation rate reaches a peak of 71% at 325 K. However, beyond this temperature, hydrate dissociation accelerates further. The increased release of water and methane molecules outstrips the spontaneous mass transport driven by concentration gradients, resulting in salt-ion dilution near the hydrate boundary. Consequently, the promoting effect of salt on hydrate dissociation gradually diminishes with rising temperature, decreasing to 28.0% at 345 K. Based on these findings, we propose a method combining depressurization with intermittent hot brine injection to enhance the hydrate dissociation rate while reducing energy consumption.