(251f) Viscosity of Several Hydrocarbons At Temperatures to 533 K and Pressures to 276 Mpa

Modeling fluid flow in petroleum reservoirs and production wells requires reliable predictions of the phase behavior, density, and viscosity of brine and hydrocarbon mixtures. This study focuses on the accurate prediction of hydrocarbon viscosity at the high-temperature, high-pressure (HTHP) conditions associated with ultradeep formations. Because reservoir compositional simulators typically model crude oil, condensate, and natural gas as a mixture of components, this study focuses on model hydrocarbons. Viscosity experiments are performed with a high-temperature, high-pressure, windowed, rolling ball viscometer constructed from Inconel 718 and using Inconel 718 balls. Pyrex 7740 tubes and balls can also be used with this viscometer for the measurement of extremely low-viscosity fluids, such as methane and propane. The viscometer has been calibrated with n-octane at different temperatures and pressures to 276 MPa. Experimental viscosity results for n-pentane, n-decane, n-hexadecane, and n-octadecane are reported at pressures to ~ 276 MPa and temperatures to ~ 533 K. The frictional theory of viscosity (F-theory) and the free volume theory of viscosity (FV theory) are used to predict the viscosity. F-theory under-predicts the viscosity by as much as 20% at pressures near 276 MPa, but this problem is greatly diminished by including a correction term which is a function of system temperature, boiling temperature, critical temperature, critical pressure, and repulsive pressure. For n-alkanes, viscosity predictions from the corrected F-theory are comparable with those obtained from FV theory. When coupled to density predictions made using an accurate equation of state (EoS), FV theory typically gives mean absolute percentage deviations (MAPDs) from experimental viscosity values of less than 3%. Three EoSs are considered for density predictions: the perturbed-chain statistical associating fluid theory (PC-SAFT) EoS, the HTHP volume translated Peng-Robinson (HTHP-VT-PR) EoS, and the HTHP volume translated Soave-Redlich-Kwong (HTHP-VT-SRK) EoS. Coupling the PC-SAFT densities to FV theory results in the most accurate viscosity predictions at HTHP conditions.