Fine-scale Structural Stability of Carbon Dioxide Hydrate Pellets under Coarse-Scale Deformation Using Multi-Scale Coupled FEM-MD Simulations

In this study, we use a coupled finite element method (FEM)–molecular dynamics (MD) methodology to examine the complex deformation response at fine and coarse scales of carbon dioxide hydrate pellets. While previous studies in this area have focused on simple deformations of fine-scale structures using MD simulations, none have attempted to model the stability of hydrate pellets under complex deformations. To accurately represent the geometry of hydrate pellets, we employ FEM to model these cylindrical shapes and extract deformation gradients at each integration point. Subsequently, MD simulations are carried out to capture the detailed fine-scale response to the imposed deformation at each integration point. Further study of constrained expansion within a hydrate pellet uncovers differing responses depending on the location of the integration points. We observe higher peaks of von-Mises equivalent stress where a shear deformation mode is dominant. In all cases, the hydrate cage structure remains intact at an total equivalent strain of around 0.14, which is already beyond the critical point, where the stress of hydrate reaches its maximum value. This indicates that gas hydrate pellets are safe for carbon storage applications when not subjected to deformations above the critical point.