(208e) A Molecular-Level Model for Predicting Properties of Electrolytes At High Pressure and Temperature

Predicting scaling and corrosion at conditions of high temperature, pressure, and TDS is essential for safe and successful operation of ultra-deepwater oil and gas production processes. However, experimental data and thermodynamic models for predicting scaling, corrosion, and stress cracking at these extreme conditions are scarce. The ability of a theoretical model to describe the fluid-phase properties of ionic species such as Na⁺, Ca²⁺, Ba²⁺, Fe²⁺, Fe³⁺, Cl^-, SO₄^2-, CO₃^2-, and S^2- at pressures and temperatures as high as 24,000 psi and 250^oC is key to the development of an accurate predictive tool. The current statistical associating fluid theory (SAFT) based equation of state models accounts for ionic interactions by incorporating Debye-Hückel theory or mean spherical approximation (MSA). These models treat ions as completely dissociated species and account for ion hydration by fitting association parameters from SAFT to experimental data at ambient conditions. At conditions of interest, the above assumptions do not hold well and hence there is a need for a model capable of accounting for ion hydration and ion-pair association at elevated temperature and pressure. A review of the current SAFT based models for electrolytes for prediction of equilibrium properties at ultra-deepwater conditions is presented. The authors also propose development of a new equation of state to account for  ion hydration and ion pair association through modification to Wertheim's  thermodynamic perturbation theory.