A Phase Equilibrium Model for Gas Hydrates Considering Pore-Size Distribution of Sediments

Abstract

The phase equilibrium condition for gas hydrates has been an important and difficult subject in gas hydrate-related research. In this paper, the mechanism of the effect of pore-size distribution on the phase equilibrium is first explored and the concept of effective pore radius is proposed. Using information on the pore-size distribution of sediments, a relationship between hydrate saturation and effective pore radius is developed. Combined with the van der Waals-Platteeuw model, this relationship was then used to develop a new phase equilibrium model for gas hydrates in sediments, which can properly account for the effect of pore-size distribution. In contrast to the traditional models, this new model does not represent a curve on the p-T plane but instead addresses the relationship between the temperature, pressure, and hydrate saturation. Such a feature allows the new model to take into account the effect of pore-size distribution on the phase equilibrium while treating the formation and/or dissolution processes of gas hydrates in pores more realistically. The simulated results were compared with the experimental data available in literature showing that the new model gives better results compared with the other traditional models. Given the temperature and the pore pressure, the hydrate saturation can be determined using the proposed model. Therefore, the new model can be used to estimate the amount of hydrate resources in the field.