A modification of Pedersen's model for saturated crude oil viscosities using standard black oil PVT data

This paper presents a modification of Pedersen's corresponding states compositional viscosity model that enables viscosity prediction for black oil systems when there are no compositional data available. This model can be easily implemented in any reservoir simulation software, it can be easily tuned, and it provides better estimates of oil viscosity than the existing correlations. Viscosity from 324 sets of differential liberation data consisting of 2343 observations covering a wide range of pressure, temperature, and oil density were used to develop the correlation which retains most of the functional form of Pedersen's model. These modifications include (1) use of n-decane as the reference fluid; (2) consider the oil mixture as a single pseudocomponent with molecular weight and critical properties correlated to its density; and (3) add a functional dependence to solution gas/oil ratio and gas-specific gravity. The average error over 2343 viscosity observations was 0.9%. The model was tested against a second data set consisting of 150 observations and the average error was 0.7%. The predictions were compared with those predicted from the correlations of Khan et al. [SPE 15720 (1987)] and of Petrosky [SPE 29468 (1995)] that are applicable to the experimental conditions of our data sets. These average errors for these correlations were -28 and 4.9%, respectively, for the first data set; and -60.8 and -1.4% for the second data set. (C) 2001 Elsevier Science B.V. All rights reserved.