Summary
The focus of this work is on the behavior of hydrocarbon-gas viscosity and
gas density. The viscosity of hydrocarbon gases is a function of pressure,
temperature, density, and molecular weight, while the gas density is a function
of pressure, temperature, and molecular weight. This work presents new
approaches for the prediction of gas viscosity and gas density for hydrocarbon
gases over practical ranges of pressure, temperature, and composition. These
correlations can be used for any hydrocarbon-gas production or transportation
opera-tions.
In this work, we created a large database of measured gas viscosity and gas
density. This database was used to evaluate existing models for gas viscosity
and gas density. We also provide new models for gas density and gas viscosity,
as well as optimization of existing models, using our new database.
The objectives of this research are as follows:
• To create a large-scale database of measured gas-viscosity and gas-density
data. This database will contain all the information necessary to establish the
applicability of various models for gas density and gas viscosity over a wide
range of pressures and temperatures.
• To evaluate a number of existing models for gas viscosity and gas
density.
• To develop new models for gas viscosity and gas density using our research
database; these models are proposed and validated.
For this study, we created a large database from existing sources available
in the literature. The properties in our database include composition,
viscosity, density, temperature, pressure, pseudoreduced properties, and the
gas compressibility factor. We use this database to evaluate the applicability
of existing models used to determine hydrocarbon-gas viscosity and
hydrocarbon-gas density (or, more specifically, the gas z-factor). Finally, we
developed new models and calculation approaches to estimate the hydrocarbon-gas
viscosity, and we also provide an optimization of the existing equations of
state (EOS) typically used for for the calculation of the gas z-factor.
Introduction
Hydrocarbon-Gas Viscosity. NIST—SUPERTRAP Algorithm. The
state-of-the-art mechanism for the estimation of gas viscosity is most likely
the computer program SUPERTRAP, developed at the U.S. Natl. Inst. of Standards
and Technology (NIST). SUPERTRAP was developed from pure-component and mixture
data and is stated to provide estimates within engineering accuracy from the
triple point of a given substance to temperatures of 1,340.33°F and pressures
of 44,100 psia. Because the SUPERTRAP algorithm requires the composition for a
particular sample, it generally would not be suitable for applications in which
only the mixture gas gravity and compositions of any contaminants are
known.
Carr et al. Correlation. Carr et al. developed a
two-step procedure to estimate hydrocarbon-gas viscosity. The first step is to
determine the gas viscosity at atmospheric conditions (i.e., a reference
condition). Once estimated, the viscosity at atmospheric pressure is then
adjusted to conditions at temperature and pressure using a second correlation.
The gas viscosity can be estimated with graphical correlations or using
equations derived from these figures.
Jossi et al. Correlation. Jossi et al. developed a
relationship for the viscosity of pure gases and gas mixtures; this correlation
includes pure components such as argon, nitrogen, oxygen, carbon dioxide,
sulfur dioxide, methane, ethane, propane, butane, and pentane. This “residual
viscosity” relationship can be used to predict gas viscosity with the “reduced”
density at a specific temperature and pressure, as well as the molecular
weight. The critical properties of the gas (i.e., the critical temperature and
critical pressure) are also required.
Our presumption is that the Jossi et al. correlation (or at least a
similar type of formulation) can be used for the prediction of viscosity for
pure hydrocarbon gases and hydrocarbon-gas mixtures. We will note that this
correlation is rarely used for hydrocarbon gases (other correlations are
preferred); however, we will consider the formulation given by Jossi et
al. as a potential model for the correlation of hydrocarbon-gas-viscosity
behavior.
© 2005. Society of Petroleum Engineers
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History
- Original manuscript received:
8 December 2003
- Revised manuscript received:
28 July 2005
- Manuscript approved:
13 September 2005
- Version of record:
15 December 2005
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