Evaluation of correlations for estimating the viscosities of hydrocarbon fluids

Ali, J.K., 1991. Evaluation of correlations for estimating the viscosities of hydrocarbon fluids. J. Pet. Sci. Eng., 5: 351-369. A critical evaluation is presented for two types of correlations used in estimating the viscosities of hydrocarbon fluids; a residual viscosity correlation due to Lohrenz et al. (LBC) and a correlation based on the extended principle of corresponding states (CS) due to Pedersen et al.* More than 100 experimental data for mixtures ranging from simple binary fluids to reservoir fluids form the basis of the study. Experimentally determined phase compositions and phase densities were used as input data. This is important since the correlations are therefore evaluated independently of any models for estimation of phase densities or compositions. The results indicate that both correlations can represent the data with average errors of less than 15%. However, the LBC correlation is very sensitive to the liquid density where a 5% error can result in an error up to 50% in the estimated viscosity. If an equation-of-state is to be used to provide the volume data it is recommended that a volume-translated Peng-Robinson equation of state or the Schmidt-Wenzel equation-of-state be used. The Pedersen et al. correlation is found to combine the accuracy of the Transport Properties Prediction program TRAPP with the simplicity of the LBC correlation and is recommended for liquid and gas viscosity estimation.