Efficient Methods for Calculations of Compressibility, Density, and Viscosity of Natural Gases

Abstract

This study presents two new methods for calculating the properties of natural gases. The first is an efficient empirical model to calculate compressibility and density of natural gases containing high amounts of heptane plus and non-hydrocarbon components. The model is derived from 2,400 measurements of compressibility and density of various gases presented in this study. Accuracy of the model is compared to various equations of state (EOS), corresponding state, and empirical methods. The study shows that the new model is simpler and more efficient than EOS. It eliminates the numerous computations involved in EOS calculations. The new method also eliminates the characterization of the heptane plus fraction and estimation of binary interaction parameters needed for EOS calculations. Experimentally measured densities of several gases have been used to study the validity of the proposed method. These measurements indicate that the new method successfully captures the physical trend of changing gas density as a function of pressure, temperature, and composition. The second method is a modification of the Lee-Gonzalez-Eakin gas viscosity correlation. The new method accounts for the presence of heptane plus, hydrogen sulfide, and carbon dioxide in natural gases. The proposed method is compared to other EOS-based viscosity models, corresponding state methods, and correlations. The comparison indicates the superiority of the new method over other methods used to calculate the viscosity of natural gases.