MSE-SRK: A Thermodynamic Model to Maximize the Accuracy of Predicting Phase Equilibria in Systems Containing Sour Gases, Electrolytes, and Hydrocarbons

摘要

To facilitate a better understanding of the susceptibility of metallic materials to corrosion, a comprehensive thermodynamic framework, referred to as the MSE-SRK model, has been developed for simulating mixtures containing H_2S, CO_2, CH_4, H_2O, hydrocarbons, and various salts that may exist in production environments. The MSE-SRK model is based on the previously developed Mixed-Solvent Electrolyte (MSE) framework, which provides a very accurate representation of electrolyte systems in both aqueous and mixed-solvent (e.g., glycol-containing) environments. The MSE-SRK framework combines an equation of state for standard-state properties of individual species, an excess Gibbs energy model to account for solution non-ideality in the aqueous electrolyte phase, and the Soave-Redlich-Kwong equation of state (SRK EOS) to calculate the properties of the gas phase. The MSE-SRK framework, however, provides a different treatment of the non-electrolyte-rich second liquid phase for liquid-liquid equilibria. MSE-SRK assumes the second (usually organic-rich) liquid phase to be non-ionic, and reproduces its properties using the SRK EOS. This allows the MSE-SRK framework to more easily reproduce the critical behavior of nonelectrolyte systems. The MSE-SRK framework has been parameterized using experimental phase equilibrium data for various binary and ternary subsystems containing H_2S, CO_2, CH_4 and higher hydrocarbons, N_2, H_2O, and various common salts, and has been validated for temperatures ranging from 0 to 300°C, pressures up to 3000 atm, and salt concentrations up to solid saturation. Owing to its ability to predict pH, activities and fugacities in complex ionic mixtures, and the effect of high pressure on multiphase equilibria, MSE-SRK can serve as a foundation for studying metal/environment interactions in upstream oil and gas environments.