Predicting the Viscosity of Hydrocarbon Liquid Phases From Their Composition
Authors: Houpeurt A.H. , Thelliez M.B. 
Published: December 2007

When many pressure-temperature combinations are involved in predicting viscosities, it is desirable to be able to calculate them rather than to have to measure them. Here, a procedure similar to that used to determine the density of reservoir oils is proposed for predicting the viscosities of hydrocarbon liquid phases from their composition.

Introduction

Routine laboratory measurements of viscosities at high pressure and high temperature are always expensive and pressure and high temperature are always expensive and often inaccurate. When values are needed for many pressure-temperature combinations, it is obviously pressure-temperature combinations, it is obviously desirable to be able to calculate them instead of measuring them.

A few years ago, the ELF-ERAP group decided to elaborate on a method for determining, with appropriate accuracy, the viscosity of hydrocarbon liquid phases.

A procedure for predicting the viscosities of hydrocarbon liquid phases from their composition is proposed. It is similar to that used by Standing and proposed. It is similar to that used by Standing and Katz for determining the density of reservoir oils.

This work is based on 1,092 viscosity measurements made on 23 mixtures for 479 pressure-temperature combinations between 30 and 130 degrees C and between 50 and 500 atm.

These measurements were made with a specially designed capillary tube viscosimeter. The analysis of 289 measurements made on n-C, n-C, and n-C in the same range of pressures and temperatures showed a standard deviation of less than 0.0075.

Three conclusions were reached.The kinematic viscosity, v (p, T), of a C4+ at pressure p and temperature T may be calculated from its pressure p and temperature T may be calculated from its composition and the kinematic viscosities, v, of its components at p and T using the equationlog v (p, T) = xi log vi (p, T).The absolute viscosity of different values of C4+ at any pressure and temperature, mu (p, T), may be calculated from their "standard" viscosities, mu* (at 1 atm and 20 degrees C), using functions of p and T that appear to be independent of the nature of the C4+.The absolute viscosity, mu (p, T), of a liquid phase composed of a C4+ and light components (methane, ethane, propane, carbon dioxide, and nitrogen) depends only on the viscosity of that C4+ at p and T, and on the amount of each light component in the mixture.

A tentative correlation relating the standard viscosity of a C4+ to its average molecular mass is also presented.

Fig. 1 allows the determination of mu (p, T) from mu* and also contains the correlation mu*(M).

Fig. 2 is a new presentation of the results of Standing and Katz. It is a new determine the densities of a C4+ that are needed for calculating its kinematic viscosities.

Fig. 3 presents the networks for correcting the viscosity of a C4+ when it is mixed with known amounts of propane, ethane, methane, carbon dioxide, and nitrogen.

The procedure was experimentally checked using two mixtures for 16 pressure-temperature combinations. An average relative error of 0.0345 was observed, with a maximum deviation of 0.08, but only a limited number of heavy components were investigated.

Review of Literature

Refs. 1 through 4 present methods for determining the viscosity of oils. All are based on compilations of available data and are very empirical.

JPT

P. 223