Phase equilibrium of gas hydrates is altered in porous media as compared to bulk systems. Inside porous media, the thermodynamic potential of chemical components changes due to molecular interactions with pore walls and due to the energy required to maintain capillary equilibrium. A pore-freezing model was developed that can be used to predict gas hydrate equilibrium for pure CH4, CO2 and mixed CH4-CO2 systems in saline pore waters for any given pore size distribution. The important feature of this model is that it takes into consideration salting out phenomena, i.e. increase in salt concentration due to gas hydrate and ice formation. It also gives the gas hydrate saturation in porous medium. A new EOS developed for prediction of bulk gas hydrate equilibrium conditions, based on van der Waals – Platteeuw model, is used in the pore freezing model and can also be used to calculate heats of formation of these hydrates for a given pore size and pressure. The results obtained from the model are compared with experimental results.

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