Coarse-Grained Molecular Dynamics Simulations of Hydrate Dissociation under Thermal Gradient

The amount of energy stored in gas hydrate reservoirs is more than twice that in conventional hydrocarbon resources, rendering their economical exploration crucial for the world’s future energy security. This study introduces the first large-scale simulation of the isobaric thermal dissociation of methane hydrates, the most abundant source of gas hydrate reservoirs, under a symmetric thermal gradient. Leveraging the monoatomic water (mW) model and Stillinger-Weber (SW) potential, we simulated a system encompassing a hundred-fold more sI unit cells than in previous research studies, thus enabling the observation of unique phenomena unattainable within smaller simulation domains. We repeated our simulations for two imposed boundary temperatures of 288 and 293 K at a fixed pressure of 100 atm. We used the template-matching algorithm to quantify the rate of dissociation. Our findings suggest that hydrate thermal dissociation transpires in three stages, with the initial stage demonstrating the lowest dissociation rate. Our large-scale simulations enabled the first-time observation of a secondary dissociation path at the third stage’s onset. The emergence of these secondary dissociation paths instigates the dissociation of hydrate clathrates within the solid hydrate, leading to the genesis of gas bubbles therein. Overall, the dissociation rate is principally controlled by the temperature at the crystal/liquid interface, the formation of gas bubbles at this interface, and the initiation of the secondary dissociation path.