Prediction of oxygen solubility in pure water and brines up to high temperatures and pressures

A thermodynamic model is presented to calculate the oxygen solubility in pure water (273–600 K, 0–200 bar) and natural brines containing Na+, K+, Ca2+, Mg2+, Cl−, SO42−, over a wide range of temperature, pressure and ionic strength with or close to experimental accuracy. This model is based on an accurate equation of state to calculate vapor phase chemical potential and a specific particle interaction model for liquid phase chemical potential. With this approach, the model can not only reproduce the existing experimental data, but also extrapolate beyond the data range from simple aqueous salt system to complicated brine systems including seawater. Compared with previous models, this model covers much wider temperature and pressure space in variable composition brine systems. A program for this model can be downloaded from the website: http://www.geochem-model.org.