Correlations For Properties of Bitumen Saturated With CO2 , CH4 And N2 , And Experiments With Combustion Gas Mixtures

Abstract

Abstract The solubility in bitumen of a synthetic combustion gas (SCG) mixture of target composition, '17% CO2, 1% CH, and 82% N2 was experimentally measured. Along with the viscosity and density measurements of gas-saturated bitumen, the compositions of dissolved and equilibrium gases were also determined. Correlations are presented that predict solubilities of pure CO2CH4 and N2 gases, and the viscosity of saturated bitumen as functions of pressure and temperature. The experiments with SCG mixtures reveal that the mixture solubility is somewhat lower than that predicted by pure component partial solubilities. Although individual gas solubilities are not additive, the composition of dissolved gas can be predicted within a reasonable accuracy using the pure component solubility data. Introduction The solubility of carbon dioxide, methane and nitrogen gases in Athabasca bitumen along with the viscosity and density data for gas-saturated bitumen were presented elsewhere(l). The need for suitable correlations for the prediction of viscosity and solubilities of gases in bitumen cannot be overemphasized. Such correlations will find extensive applications in numerical simulation of the extraction of tar-sands by in-situ techniques such as CO2-injection, fire-flooding, etc. The quantitative description of the bitumen viscosity behaviour is a rather complicated matter. Due to a great range in the properties and composition of tar-sands bitumen, it may be of interest to introduce a means of oil characterization. However, the complete analysis of bitumen is virtually impossible at the present time. Hence, bitumen may be characterized either by the viscosity of gas-free oil (the dead oil), reflecting the sum total contribution of all the components present, or by partial, analysis in terms of several real arid hypothetical components: Bishnoi et al.(2) presented a computational scheme based on the latter approach for the prediction of C02 and CH4 solubilities in bitumen. Their calculation procedure used the Peng-Robinson equation of state and a Chao-Seader correlative method. The bitumen was characterized by 5 "cuts" of hypothetical components with assigned molecular weights, densities, mole fractions and boiling points. Their computed predictions were remark a by close to the experimental results(3). Most of the heavy hydrocarbon viscosity correlative methods in the literature are based on dead oil viscosities. However, there is no literature on the correlation of gas-solubility data that may be suitable for a bitumen system. The empirical correlations for viscosity prediction reflect the effects of temperature and/ or pressure. These correlations also depend on the kind of gas which is dissolved in the hydrocarbon phase. (Figure in full paper) comparative basis by Tsturyants and Muradov(4). These authors investigated the effects of methane, ethane and propane under saturation conditions. At the same mole fraction of a dissolved gas, the highest viscosity decrease was caused by propane followed by ethane and then methane. The change in viscosity became more pronounced as the total molar concentration in gas (i.e. pressure) was increased. Tumasyn et al.(5) studied the effect of CO2 on oil viscosity. Their experiments clearly showed that oil viscosity decreases with the amount of carbon dioxide dissolved. Furthermore, the drop in oil viscosity was higher for the oils that had a high dead oil viscosity.