Large-Scale Nonequilibrium Molecular Studies of Thermal Hydrate Dissociation

Theenergy content of methane hydrate reservoirs (MHRs) is at leasttwice that of conventional fossil fuels. So, there is considerableinterest in their commercial development by heating, among other dissociationmechanisms. However, a few researchers have highlighted the potentiallyuncontrollable release of methane from MHRs, which could occur becauseof global warming. Therefore, it is crucial to understand the kineticsof thermal hydrate dissociation to safely develop these resourcesand prevent the release of this greenhouse gas into the environment.Although there have been several molecular studies of thermal dissociation,most of these use small simulation domains that cannot capture thetransient nature of the process. To address this limitation, we performedcoarse-grained molecular dynamics (CGMD) simulations on a significantlylarger domain with a hundred times more hydrate unit cells than thoseused in previous studies. We monitored the kinetics of dissociationusing an image-processing algorithm and observed the dynamics of theprocess while maintaining a thermal gradient at the dissociation front.For the first time, we report the formation of an unstable secondarydissociation path that triggers gas bubbles within the solid hydrate.The kinetics of thermal dissociation appears to occur in three stages.In the first stage, the energy of the system increases until it exceedsthe activation energy, and dissociation is initiated. Consistent dissociationoccurs in the second stage, whereas the third stage involves the dissociationof the remaining hydrates across a nonplanar and heterogeneous interface.

Automated summary

The energy content of methane hydrate reservoirs is double that of conventional fossil fuels, making them a commercially attractive resource for development. However, there is concern regarding the potentially uncontrollable release of methane due to global warming. To address this concern, understanding the kinetics of thermal hydrate dissociation is crucial to safely harness these resources and prevent environmental methane emissions. Previous studies on thermal dissociation have often used small simulation domains, limiting the capture of transient processes. In this study, larger-scale coarse-grained molecular dynamics simulations were performed, revealing the formation of an unstable secondary dissociation path and providing insights into the three-stage kinetics of thermal dissociation.