Viscosity model is an important component in enhanced oil recovery packages and, for pure bitumen, several accurate models are available. In this study a simple correlation presented in an earlier publication is extended to predict viscosity of bitumen-diluent mixtures, as well as the mass fraction required o reduce bitumen viscosity to pumping viscosity.
In developing the viscosity model, viscosities of pure bitumen anddiluent were used as the endpoints, and the diluent mass fraction was raised to a power of 'n ' (a viscosiv reduction parameter) to cater for the sharp drop in bitumen viscosity with increase in diluent mass fraction. The model was developed with 99 data points from three different bitumens and five diluents spanning a viscosity range of 10−1 to 106 cSt.
The model was used to recalculate the viscosity and mass fraction values, and results compared with similar Correlations by Cragoe and Chirinos. Best match was obtained with our correlation, with overall average absolute deviations of 12% and 5% for viscosity and mass fraction predictions respectively. Predictions on data not used in developing the model showed an excellent match between experimental and predicted values, with an overall average absolute deviation of below 10% for viscosities of mixtures at 25 °C, 60.3'C and 82.6'C.
In the recovery of bitumen, viscosity reduction becomes important both below and above the ground. The addition of a liquid diluent is thought to break down or weaken the intermolecular forces which create high viscosity in bitumen [I]. The effect is so dramatic that the addition of even 5% diluent can cause a viscosity reduction in excess of 80%; thus facilitating the in situ recovery and pipe line transportation of bitumen.
The knowledge of the bitumen-diluent viscosity is highly important since without it, calculations in upgrading process, in situ recovery, well simulation, heat transfer, fluid flow and a variety of other engineering problems would be difficult or impossible, to solve. This paper presents, the development of a simple correlation to predict the viscosity of binary mixtures of bitumen-diluent in any proportion.
The data used for the development of the correlation was obtained from Wallace et al.  and Wallace and Henry . The data consisted of a total of 99 points obtained from three bitumens and five diluents respectively listed in Tables I and 2.
Each ofthese bitumen samples was diluted at 30 °C to 5, 10,25, 50 and 75 weight percent diluent with each of the diluents. After mixing, the samples werere-weighed and any weight loss was attributed to solvent evaporation. The diluent weight fractions were adjusted accordingly and the viscosities of the mixtures measured. For a detailed account of experimental procedures, refer to Wallace and Henry .
Many correlations have been developed to predict the viscosity characteristics ofbitumen-diluent mixtures . While several have been successful in making these predictions, most are cumbersome to use. Conventional mixing rules for the mixture of pure substances are not generally applicable in the case of bitumen-solvent mixtures.