A practical method for the estimation of oil and water mutual solubilities

A simple model is proposed for the calculation of oil and water mutual solubilities as a function of temperature using the hydrocarbon specific gravity and Watson-K factor as correlating parameters. The model parameters were determined using a single consistent set of high quality solubility data collected at the water or hydrocarbon saturation pressures at temperatures from 273 K and 573 K but primarily from 298 K to 398 K. The hydrocarbon in water solubilities ranged over 11 orders of magnitude while the water in hydrocarbons solubilities ranged over 4 orders of magnitude. Hydrocarbon types ranged from low molecular weight paraffins such as n-pentane to heavy aromatics such as anthracene. The average absolute error in the estimated solubilities of water in hydrocarbons over 621 data points was 34% and approached the suggested underlying uncertainty in the reference data (30%). The average absolute error in the estimated solubilities of hydrocarbons in water over 964 data points was 88% and exceeded the suggested underlying uncertainty in the reference data (30%).The model can be extended to higher temperatures using a procedure based on activity coefficients or equations of state and is easily adapted to work with ill-defined hydrocarbon mixtures. Prediction and correlation of solubilities of water in kerosene, heavy oils, and bitumen were made at temperatures, pressures, and compositions far removed from the original data used for model construction. The correlation failed near the critical temperature of water because under these conditions, the properties hydrocarbon-rich phases in the mixtures on which the correlation is based (Type II and Type IIIa phase behaviour according to the van Konynenburg and Scott naming scheme) and those of water + heavy hydrocarbons (Type IIIb phase behaviour) diverge. A separate NRTL based correlation is presented for the mutual solubility of water + heavy oils at temperatures close to the critical temperature of water.