Improvement of the Expanded Fluid Viscosity Model for Crude Oils: Effects of the Plus-Fraction Characterization Method and Density

Abstract

The expanded fluid (EF) model is known for its capacity to calculate the viscosities of crude oil and its mixtures with solvents at high pressure and temperature using a cubic equation of state with a minimum amount of experimental data. The main drawback of the EF model is usually the requirement of a proper plus-fraction characterization and accurate density input data. In this study, the sensitivity of the EF model to the characterization method and the density of the oil was evaluated against viscosity data on reservoir fluids. The oil viscosity was calculated above and below the saturation pressure in order to compare the EF model with other viscosity models available in the literature. The results confirmed that the viscosity strongly depends on the quality of the density predictions as well as on a good description of the phase behavior below the saturation pressure. This demonstrates that proper characterization is needed in order to calculate the oil viscosity accurately. Furthermore, a new tuning method with minimum experimental data improved the viscosity prediction as a function of pressure.