A model to predict the thermodynamic stability of abiotic methane-hydrogen binary hydrates in a marine serpentinization environment

Abiotic methane (CH4) and hydrogen (H-2), which are produced during marine serpentinization, provide abundant gas source for hydrate formation on ocean floor. However, previous models of CH4-H-2 hydrate formation have generally focused on pure water environments and have not considered the effects of salinity. In this study, the van der Waals-Platteeuw model, which considered the effects of salinity on the chemical potentials of CH4, H-2, and H2O, was applied in a marine serpentinization environment. The model uses an empirical formula and the Peng-Robinson equation of state to calculate the Langmuir constants and fugacity values, respectively, of CH4 and H-2, and it uses the Pitzer model to calculate the activity coefficients of H2O in the CH4-H-2-seawater system. The three-phase equilibrium temperature and pressure predicted by the model for CH4-H-2 hydrates in pure water demonstrated good agreement with experimental data. The model was then used to predict the three-phase equilibrium temperature and pressure for CH4-H-2 hydrates in a NaCl solutions, for which relevant experimental data are lacking. Thus, this study provides a theoretical basis for gas hydrate research and investigation in areas with marine serpentinization.