Thermodynamic Model for Quaternary Aqueous Ca2+, Na+, Cl-, SO42- System

Symmetric Electrolyte Non-Random Two Liquid model (eNRTL) is selected as the thermodynamic framework to model the quaternary aqueous Ca²⁺, Na⁺, Cl^-, SO4^2- electrolyte system. This is a part of a large effort to develop a comprehensive thermodynamic model for high salinity produced water in oil and gas production. Each binary system (electrolyte-water or electrolyte-electrolyte) needs three pairs of binary parameters which are directly correlated with excess Gibbs energy, excess enthalpy and excess heat capacity of the system concerned. These binary parameters are regressed with thermodynamic and phase equilibrium data including salt solubility data available in literature. Binary parameters are obtained for CaCl₂-water, CaSO₄-water, CaCl₂-CaSO₄, CaCl₂-NaCl, and CaSO₄- Na₂SO₄ binary systems. These binary parameters are integrated with the rest of the parameters readily available in literature. The model shows excellent agreement with literature data with temperature from 0°C - 200°C and electrolyte concentration up to saturation.  This model is being extended to cover K⁺, Mg²⁺, Ba²⁺, Sr²⁺ and HCO3^-.