Vapor-liquid and liquid-liquid equilibrium data of mixtures of a Saskatchewan heavy oil and its constituent fractions with CO2 were correlated by the Peng-Robinson equation of state. An excellent fit of the data was obtained by using optimized interaction parameters. Two predictive methods from the literature gave only qualitative agreement with the data.

The phase behavior data were also interpreted using binary and ternary mixtures of CO2 with normal alkanes having the same molecular weights as the oil fractions. The ternary phase behavior of these CO2/n-alkane systems was consistent with the CO2/heavy oil data.

The errors in the density predictions of the Peng-Robinson equation ranged from 10–20%. The volume translation method of Peneloux et. al. improved the level of errors down 1.2%.

Equations proposed by Lederer and by Svreek and Mehrotra were combined to predict the viscosities of the various oil/CO2 mixtures within 8%.


Immiscible carbon dioxide flooding is increasingly being considered for enhanced oil recovery, especially from medium and heavy oil reservoirs. The physical mechanisms by which CO2, contacts and mobilizes the crude oils are oil swelling and viscosity reduction, which in turn influence the oil displacement process. CO2 besides being used as a miscible and immiscible flooding agent, is also used as a well stimulant during fracturing and acidizing and as an additive to the steam injection process.

The main objective of this work is to correlate the extensive phase behavior and physical property data measured by Kokal et. al. (1) The heavy crude oil selected in that companion work was from the Lone Rock field in western Saskatchewan. It had a viscosity of 2000 mPa.s and a density of 950 kg/m3 at room temperature. It was divided into three fractions: a pentane insoluble asphaltene/resin fraction and the de-asphalted oil (De-oil) which was further distilled into a light (F1) and heavy (F2) fraction. Phase behavior and physical property measurements were then made on mixtures of CO2 with the heavy oil, the De-oil, F1 and F2, The properties which were measured were the solubility's, gas-oil ratios, densities, swelling factors and viscosities of the mixtures saturated with CO2. No measurements were made of CO2 with the pentane-insoluble solid fraction.

The objective of this exercise is to use the fractions of the heavy oil as pseudo-components for equation of state (EOS) correlation purposes, since it is not practical to include all components of the heavy oil into an EOS. The oil is therefore divided into a limited number of pseudo-components at fractions. Since the fractions are "real ", the characterization of the heavy oil is based on experimental evidence.

The results of the correlation of the data of Kokal et. al.(1) are presented below. The phase behavior results are first described, followed by the density then the viscosity correlations. Finally, the conclusions drawn from this work are presented.

Phase Behavior

The phase behavior data of CO2/Lone Rock heavy oil exhibits vapor-liquid (V-L), liquid-liquid (L-L) and liquid-liquid-vapor (L-L-V) equilibrium.

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