Modeling on gas hydrate phase equilibrium at high concentration of alcohols

Abstract

As the major interest in flow assurance of oil and natural gas production, the concentrations of injected alcohols are commonly high exceeding mass fraction of 30 %. In this work, the non-ideality of aqueous phase is represented by the activity coefficient model, in which the water and inhibitor molecules are regarded as associating compounds, and the differences in size and shape between them are properly considered. Coupled with the Chen-Guo hydrate model, the proposed model has been extended to represent the hydrate phase equilibrium of pure gas and gas mixtures in aqueous alcohol solutions with concentrations up to 50 wt%. Moreover, the hydrate lattice parameter was reoptimized to extend the Chen-Guo hydrate model to systems below 273.15 K, when high-concentration of alcohols is present. The predictions of the proposed model have been compared with the experimental data, with the average relative deviations in pressure and temperature of 3.991 % and 0.108 %, respectively, verifying the reliability of this model. Compared with other thermodynamic models or correlations, the proposed model in this work is equivalent to or outperformed those in predicting hydrate formation conditions, especially at high alcohol concentrations.