Free Volume Estimates of Thermodynamic and Transport Properties of Heavy Oils with CO₂


Carbon dioxide is to be used to displace crude oil in reservoirs by effecting miscibility. Even where no miscibility is reached, as in heavy oils, there are still some advantages. When CO2 dissolves in oil, it increases the volume of oil and squeezes it out of narrow capillaries. Further, the viscosity of oil also decreases at times by an order of magnitude. To quantify the process it is necessary to know the CO2 solubility, the swelling produced, and the changes in viscosity and diffusivity with the CO2 content. There is no available theory that unifies both thermodynamic and transport data in a single model with the exception of the free volume theory which applies when the free volume is low. In addition, most models require a molecular weight of oil, where only a weighted average is available and it is questionable if this weighting will work for oils from different sources, or to different physical properties. We start with the density-pressure-temperature data without CO2 for heavy oil available in the literature to establish the correlations using the free volume theory and thereby predict the remaining viscosity data. We then interpret the data on swelling by CO2 which leads us to the volume fraction of CO2. The viscosity data leads us to the free volumes of CO2 in oil and allows us to calculate the diffusivities of CO2.In all, the energy of solubilization from Henry's law constants, theory of interfacial tension and the diffusivity at infinite dilution using Stokes-Einstein theory are the only instances where we had to go outside the free volume theory. It is also suggested that the predictions are independent of oil type as long as the oil is sufficiently heavy and the properties are correctly scaled.


Chemical and Biochemical Engineering

Second Department

Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

CO2; Enhanced Oil Recovery; Heavy Oil; High Pressures; Thermodynamic Properties; Transport Properties; Free-Volume Theory; Henry's Law Constant; Infinite Dilution; Transport Data; Viscosity Data; Weighted Averages

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version


File Type





© 2012 Elsevier, All rights reserved.

Publication Date

01 Oct 2012