A Simple Predictive Calculation for the Viscosity of Liquid Phase Reservoir Fluids With High Accuracy for CO2 Mixtures
- W.S. Fong (Chevron Petroleum Technology Co.) | S.I. Sandler (U. of Delaware) | A.S. Emanuel (Chevron Petroleum Technology Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- September 1996
- Document Type
- Journal Paper
- 243 - 250
- 1996. Society of Petroleum Engineers
- 5.2 Reservoir Fluid Dynamics, 4.6 Natural Gas, 5.2.2 Fluid Modeling, Equations of State, 5.4.2 Gas Injection Methods, 4.1.5 Processing Equipment, 5.4.6 Thermal Methods, 5.2.1 Phase Behavior and PVT Measurements, 5.4 Enhanced Recovery, 5.5 Reservoir Simulation
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A simple and accurate correlation has been developed for predicting the viscosity of CO2-reservoir oil mixtures from composition. The method is suitable for equation-of-state based reservoir simulations, and is useful for a wide range of oil viscosities from 0.2 to 400,000 cP. The correlation is based on a generalized power mixing rule and was developed with experimental viscosity data from 20 oil systems, ranging from volatile oils to heavy bitumens. The pressure-temperature range of the data was 14.7-7000 psi and 70-255 deg F. A Peng-Robinson equation of state characterization was developed for each of the oils to match PVT data. This PREOS characterization was then used in the viscosity correlation. Accurate predictions require an experimental value of CO2-free reservoir oil at reservoir temperature above bubble point pressure. For the oils and bitumens tested, this method predicts oil-solution gas-CO2 mixture viscosity with 12.5% average absolute deviation (AAD).
Accurate estimation of CO2-oil mixture viscosity is important in reservoir engineering studies of miscible and immiscible CO2 injection projects. The Lohrenz-Bray-Clark (LBC) correlation is commonly used. LBC correlation is a modification of the Jossi, Stiel and Thodos correlation for pure components, and is suitable for gases and light oils. For liquid phase viscosity, the LBC correlation was developed using a database of mixtures containing 4% or less CO2. The correlation has proven inaccurate for liquid phase Oil-CO2. Lansangan et al. reported an AAD of 40.5% for 9 oil systems tested (oil viscosity up to 4.4 cP) using the LBC correlation. For heavier oils, errors of greater than 100% AAD are common. For bitumens, the predictions can be in error by two orders of magnitude.
One contributing factor to those deviations is that small errors in EOS density predictions can cause large errors in the LBC correlation. Alternative correlations available in the literature are Simon and Graue's graphical method (1964), corresponding state methods of Ely and Hanley (1981); Pedersen et al. (1983), mixing rule method by Emanuel (1985), and improved LBC by Lansangan et al. (1990). Compared with other correlations, the correlation presented in this paper is simple, compatible with EOS description of other PVT properties, and covers a wider range of viscosities with good accuracy.
CORRELATION FOR PURE HYDROCARBONS
A new correlation developed by Orbey and Sandler (1993) is used here for pure components in a reservoir oil mixture. Their correlation is briefly outlined as follows:
Low Pressure Viscosity as a Function of Temperature
The reduced liquid viscosity , defined as viscosity at temperature T divided by its viscosity , at normal boiling temperature Tb, fits the following function:
This reduced expression is found to reproduce atmospheric pressure liquid propane viscosity well.
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