Viscosity prediction for natural gas processing applications

The Expanded Fluid (EF) viscosity correlation was used to model the viscosity of mixtures commonly encountered in natural gas processing. This correlation provides viscosity values as a function of fluid density and characterizes each pure compound with three fluid-specific parameters: c2, ρ s o and c3, when using experimental densities (Version 1) and two parameters, c2 and ρ s o , when using a cubic equation of state (Version 2). In particular, the original EF correlation for hydrocarbons was adapted for non-hydrocarbon components, including: carbon dioxide, hydrogen sulfide, nitrogen, helium, water, methanol, ethylene glycol, diethylene glycol and triethylene glycol. A temperature dependency was introduced for parameter c2 for components with significant hydrogen bonding such as water and methanol. For all other components, a fixed c2 was found to be adequate. Both versions of the correlation were fit to experimental data for the non-hydrocarbon components with overall average absolute relative deviation (AARD) below 6%. The viscosities of several sweet and sour natural gas mixtures were predicted with overall AARDs of 6.3% and 5.1% for Versions 1 and 2, respectively. The viscosities of aqueous solutions both of methanol and of glycols were also modeled. A binary interaction parameter was required to fit the data for all aqueous mixtures in Version 2 but only for mixtures of water and methanol in Version 1. The overall AARDs of the calculated viscosities of the aqueous solutions of methanol and glycols by Versions 1 and 2 were 6% and 8.7%, respectively.