Summary
The calculation of pressure drop resulting from the flow of oil through
porous media or pipes requires the evaluation of viscosity. This is the single
most important transport property necessary to calculate pressure drop
accurately. The basis for oil-viscosity calculations using a traditional
black-oil approach is the determination of dead- or gas-free-oil viscosity.
A total of 23 dead-oil-viscosity calculation methods have been identified
from the literature and evaluated in this paper. A large database consisting of
data from conventional pressure/volume/temperature (PVT) reports, crude-oil
assays, and the literature was compiled from more than 3,000 samples from
around the world. The number of actual viscosity measurements exceeded 9,800.
An evaluation of the correlations yielded unacceptable results largely because
of the failure of the methods to properly account for the physics of the
problem. In general, this results from the methods’ failure to properly account
for the change in viscosity with temperature and to address the chemical nature
of the oil. A significant improvement in results can be realized through the
use of the Watson characterization factor in addition to oil API gravity and
temperature in the correlation of viscosity. This work has identified the
character of the crude to have a significant effect on oil viscosity,
especially for oils with gravities less than 25°API.
Methods have been proposed in the literature that use the Watson
characterization factor; however, these have been largely ignored in the
upstream oil industry. Therefore, a new method has been developed that shows
significant improvement over existing methods. At reservoir conditions, a 2- to
13-fold reduction in average absolute error was noted when compared with the
error observed from traditional methods. At surface process conditions, this
improvement ranged 3- to 60-fold. In addition, an updated correlation for
Watson characterization has been developed. The ASTM density correction for
varying temperature has been examined. Revised coefficients were developed that
enhance the method’s accuracy for both oils and pure components and provide a
suitable means to convert kinematic viscosity to absolute viscosity.
The pdf file includes an associated discussion by Faruk Civan, SPE,
University of Oklahoma, and the authors' reply.
© 2009. Society of Petroleum Engineers
View full textPDF
(
4,203 KB
)
History
- Original manuscript received:
2 August 2007
- Meeting paper published:
11 November 2007
- Revised manuscript received:
31 December 2008
- Manuscript approved:
14 February 2009
- Published online:
17 December 2009
- Version of record:
31 December 2009
View Cart
