Expanded fluid-based viscosity correlation for hydrocarbons using an equation of state

A previously developed correlation of viscosity to measured density was modified for use with densities calculated using a cubic equation of state. The correlation has two adjustable parameters per component, a compressed state density, ρso and an empirical parameter, c2, that scales the viscosity response to fluid expansion. The inputs to the correlation are the fluid density and molecular weight, pressure, and the low pressure gas viscosity. In this study, gas or liquid densities were determined using the Advanced Peng–Robinson equation of state and therefore the critical properties, acentric factor, and volume translation factor of the component are required as input instead of the density. The modified correlation fit experimental viscosities for 39 pure hydrocarbons including n-alkanes, branched alkanes, alkenes, cyclics, and aromatics comprising 8337 experimental liquid and fluid phase data points, over a broad range of temperatures and pressures with an average absolute error under 6.0%. The method was also tested against experimental binary viscosity data that include linear paraffins, branched paraffins, naphthenes and aromatics with an average absolute error under 6% at 25 °C without the use of a binary interaction parameter for the compressed state density. If adjustable interaction parameters are used then the average absolute error is under 1%. The method was also applied to as well as a sweet natural gas mixture with an average absolute error under 2% and to mixtures of heavy oil and n-decane as well as Cold Lake bitumen and toluene with average absolute errors under 16%. The method was implemented in a commercial simulator proving to be simple, consistent across the critical point, and very fast from a computational point of view, running approximately twice as fast as a corresponding states method.