Assessing thermodynamic consistency of gas hydrates phase equilibrium data for inhibited systems

Abstract

Phase equilibrium properties of gas hydrates in the presence of thermodynamic hydrate inhibitors (THIs) like alcohols, glycols, and salts are essential in developing thermodynamic prediction models to identify their physicochemical features and phase behavior for gas production from hydrates and operation of oil/gas production systems. Though a significant amount of experimental data are available in the literature and models have been developed based on those data, a reliable method to assess the thermodynamic consistency of the data has not been established. Here, we provide a rigorous method to assess the thermodynamic consistency of hydrate phase equilibrium data in inhibited systems. Fundamental thermodynamic relations are used to derive the assessment criteria for thermodynamic consistency, including the heat of dissociation for solid hydrate phase and the activity for liquid water. The quantitative assessment of CH4 hydrate + THIs, including salts, glycols, methanol, and amino acids are performed for demonstration, and guidelines on how to assess the thermodynamic consistency are provided.