Developing a water chemistry model in the CO2-mixed salts-H2O system to predict the corrosion of carbon steel in supercritical CO2-containing formation water

Abstract

In this work, a water chemistry model was developed by combining the activity coefficient-fugacity coefficient type solubility model and species equilibrium model to determine the mutual solubilities of CO2 and H2O, and the corresponding species concentrations in the CO2-mixed salts-H2O system (mainly contains Na+, Ca2+, Mg2+, K+, Cl-, and SO42-) with the temperature range of 15–250 °C, the pressure range of 1–600 bar and the salt molality range of 0–6 mol/kg. The computed solubilities of CO2 and H2O, and pH values show a good agreement with the experimental data in the literature, which indicates the high accuracy and accessibility of this water chemistry model. Based on this accurate water chemistry model, a comprehensive mechanistic model was established to predict the corrosion of carbon steel in supercritical CO2-containing formation water based on finite element method. The modeling corrosion rate agrees well with the measured corrosion rate.