Predicting the Thermo-Kinetics of sII Structure with Parameter-Free Hydrate Phase Description: Validation and Derivative-Free Optimization

This work aims at developing the theoretical framework of sII hydrate structure, taking its kinetic and thermodynamic aspects relevant to formation dynamics. To make it rigorous and versatile for various applications in the hydrate domain, fundamental issues are addressed with practical relevance, including a wide range of guest gas species and their compositions, presence of salt ions in water, porous particles with variable size and shape, and porosity and permeability associated with an underground reservoir, among others. Along with fractional order kinetics and changeable reaction surface, the phase equilibrium among coexisting hydrate–vapor–liquid makes the hydrate dynamics complex and highly parametric with infinite solution sets. Estimating the thermodynamic equilibrium for vapor and liquid phases is at the matured state. For the rest of the hydrate phase, a recently proposed parameter-free model is adopted for the first time for the dedicated sII structure. Converging to an optimal parameter set specific to hydrate kinetics is one of the major concerns, for which a robust derivative-free global optimization method, namely, simplicial homology global optimization, is strategized. Finally, this proposed thermo-kinetic model framework is tested with a large variety of experimental data sets under reservoir mimicking conditions, including single to multicomponent guests, pure and saline water, and porous media.