Molecular Dynamics Investigation on the Coupled Effects of Temperature, Pressure, and Salinity on the Growth and...

In this study, molecular dynamics (MD) simulations were employed to investigate the coupled effects of the temperature, pressure, and salinity (NaCl concentration) on the nucleation and growth kinetics of H₂S hydrates. A liquid-solid two-phase system was constructed based on the sI-type H₂S hydrate unit cell, and the structural evolution under various thermodynamic and saline conditions was systematically simulated. Multiple indicators─including potential energy, radial distribution function (RDF), mean square displacement (MSD), molecular number density distribution, and F₄ order parameter─were used to comprehensively evaluate the crystallization rate and structural ordering of the hydrates. The results revealed that a low temperature (250 K) and high pressure (15 MPa) significantly promote the nucleation and growth of H₂S hydrates, enhancing the compactness and crystallinity of the system. In contrast, increasing NaCl concentration markedly inhibits the formation of ordered hydrate structures, with nearly no crystal formation observed under 13 wt % salinity. The F₄ order parameter analysis further confirmed the findings from RDF and MSD, indicating that a high pressure can partially mitigate the negative impact of ionic interference. This work provides valuable theoretical insights into the microscopic mechanisms of H₂S hydrate formation and the thermodynamic behavior under complex geological conditions.