Thermodynamics Model of Predicting Gas Hydrate in Porous Media Based on Reaction-Adsorption Two-Step Formation Mechanism

A thermodynamics model is improved to predict the hydrate water gas equilibria in micropores based on the reaction adsorption two-step formation mechanism by considering the effect of capillarity. The interfacial tension values between hydrate and water for different gas species are determined by the Gibbs Thomson relationship or generalized as a linear function of temperatures. The hydrate phase equilibrium conditions for carbon dioxide, methane, ethane, propane, and (6.7% methane + 2.1% ethane + 91.2% propane) gas mixtures in porous media with different pore diameters predicted by the thermodynamics model developed in this work are equivalent to or superior to those of the traditional van der Waals-Platteeuw type models if the interfacial tension values are fixed. The absolute average deviations for all porous media systems can be decreased to 5.08% after a linear relation of interfacial tension and temperatures are introduced. It was found that the interfacial tension values between hydrate and water are in the magnitude order of propane, ethane, carbon dioxide, and methane, which is related to hydrate structure type and the Occupancy of linked cavities for different gas species.