Abstract

The focus of this work is the behavior of gas viscosity and gas density for hydrocarbon gas mixtures. The viscosity of hydro-carbon 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 pre-sents 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 operations.

In this work we created an extensive database of measured gas viscosity and gas density (>5000 points for gas viscosity and >8000 points for gas density). This database was used to evaluate existing models for gas viscosity and gas density. In this work we provide new models for gas density and gas viscosity, as well as optimization of existing models using this database.

The objectives of this research are:

  • To create a large-scale database of measured gas viscosity and gas density data which contains all of the in-formation required 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, validated, and presented graphically.

For this study, we created a large-scale database of gas properties using existing sources available in the literature. Our data-base includes: composition, viscosity, density, temperature, pressure, pseudoreduced properties and the gas compressibility factor. We use this database to evaluate the applicability of the existing models used to estimate hydrocarbon gas viscosity and gas density (or more specifically, the z-factor). Finally, we provide new models and calculation procedures for estimating hydrocarbon gas viscosity and we also provide new optimizations of the existing equations-of-state (EOS) typically used 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. National Institute of Standards and Technology1 (NIST). SUPERTRAPwas 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 up to 1,340.33 deg F and pressures up to 44,100 psia. As the SUPERTRAPalgorithm requires the composition for a particular sample, this method would not be generally suitable for applications where only the mixture gas gravity and compositions of any contaminants are known.

Carr, et al. Correlation:

Carr, et al.2 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 the desired temperature and pressure using a second correlation. The gas viscosity can be estimated using graphical correlations or using equations derived from these figures.

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. National Institute of Standards and Technology1 (NIST). SUPERTRAPwas 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 up to 1,340.33 deg F and pressures up to 44,100 psia. As the SUPERTRAPalgorithm requires the composition for a particular sample, this method would not be generally suitable for applications where only the mixture gas gravity and compositions of any contaminants are known.

Carr, et al. Correlation:

Carr, et al.2 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 the desired temperature and pressure using a second correlation. The gas viscosity can be estimated using graphical correlations or using equations derived from these figures.

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. National Institute of Standards and Technology1 (NIST). SUPERTRAPwas 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 up to 1,340.33 deg F and pressures up to 44,100 psia. As the SUPERTRAPalgorithm requires the composition for a particular sample, this method would not be generally suitable for applications where only the mixture gas gravity and compositions of any contaminants are known.

Carr, et al. Correlation:

Carr, et al.2 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 the desired temperature and pressure using a second correlation. The gas viscosity can be estimated using graphical correlations or using equations derived from these figures.

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