Modeling gas hydrate phase equilibria in laboratory and natural porous media

A method to predict hydrate phase behavior in laboratory-prepared and natur al porous media is presented. This model extends both the van der Waals and Platteeuw (vdWP) approach and our fugacity-based approach to porous media by accounting for the effects of both surface energy and pore size distribu tion. Our fugacity approach quantitatively predicts the equilibrium pressur e-temperature relation for hydrates in laboratory porous media above the no rmal freezing point of water without any empirical corrections to the surfa ce contact parameters, as have previously been required with the vdWP model . A pore size distribution model that depends on the soil type and pressure is developed and then used to predict methane hydrate formation in natural porous environments. The maximum depth of ocean hydrates using our fugacit y-based model with the pore size correction is calculated for seven drillin g sites. Our predictions for the hydrate depth have an average deviation of 4.9% compared to the experimental data, which is less than the 11.6% AAD u sing the common approach of assuming that the phase behavior in the pores i s identical to that in the bulk.