Prediction of zyxw Mass Diffusivity of zyx C02 into Bitumen ANIL K. MEHROTRA, ANJU GARG and WILLIAM Y. SVRCEK Department of Chemical and Petroleum Engineering, The University of Calgary, Calgary, Alberta, T2N IN4 The infinite dilution and mutual diffusion coefficients for the CO,/bitumen system were predicted using existing cor- relations. Out of seven semi-empirical correlations tested, the Umesi-Danner correlation was found to be best suited for the prediction of gas-liquid infinite dilution diffusion coefficient. For the mutual diffusion coefficient, Teja's method based on the generalized corresponding states principle was successfully used. The predictions are compared with the limited COz/bitumen diffusivity data available in the literature. On a prkdit zyxwvutsrqpo h partir de correlations existantes les coefficients de diffusion mutuelle et le coefficient de diffusion a dilution infinie du systkme CO, /bitume. Sur les sept correlations semi-empiriques testies, c'est la correlation d'Umesi- Danner qui s'est avkree la plus appropriee pour prkdire le coefficient de diffusion zyxw B diffusion B dilution infinie d'un systeme gaz-liquide. La rnethode de Taja basee sur le principe des Ctats correspondants generalis6 a pu &tre appliquke avec succes dans le cas du coefficient de diffusion mutuelle. Ces predictions sont comparees aux quelques rksultats existants sur la diffusivitk du systeme CO,/bitume. Keywords: prediction, diffusion coefficient, mass diffusivity, carbon dioxide, bitumen. itumen is a highly viscous, dense fluid which is B composed of a multitude of hydrocarbons. The uncer- tainty of its exact chemical structure coupled with its viscous nature makes the design of processes for the recovery of bitumen a complicated task. Thus, the implementation of a viscosity-reduction procedure such as dissolving gases in bitumen is essential. Regardless of whether the gases are injected directly into the reservoir formation in order to serve as an aid for enhanced oil recovery or the injection is done at the surface, an important design parameter is the diffusivity of gases into bitumen. Very limited data for the mass diffusivity of C 0 2 into bitumen are available in the literature. Clearly, there is a need for more experimental data. From a practical view- point, it is also important to develop a predictive method for the mass diffusivity of gases into bitumen. This was achieved in this study by the prediction of infinite dilution diffusion coefficients followed by the prediction of a mutual diffusion coefficient for the COz/bitumen system. Seven correlative/predictive methods for the infinite dilution coefficient were evaluated in this study. The most accurate predictive method for gas-liquid or liquid-liquid systems was determined by testing these seven methods on a total of nine different gas-liquid and liquid-liquid systems. The most satisfactory values of the infinite dilution coefficient were then used to predict the mutual diffusion coefficient for the C02/bitumen system using a corresponding states method. The available literature on the mass diffusivity of gas- liquid and liquid-liquid systems is extensive. However, the paucity of literature specifically related to the diffusion of gases into bitumen necessitated a review of the existing theories and/or correlations for mass diffusivity zyxwvuts . Essentially, four approaches or theories to diffusion have been proposed in the literature. These include the hydrodynamic theory, the kinectic theory, the statistical-mechanical and the irrever- sible thermodynamic approaches. Due to its simplicity, the most popular approach in terms of practical application has involved the hydrodynamic theory. One of the limitations in searching for an effective method for the prediction of mass diffusivity of COz into bitumen is that only a very small set of data from one experimental procedure are available. Schmidt et al. (1982) reported, Table 1, the dependence of C 0 2 diffusivity in Athabasca bitumen on the mole fraction of COz at four separate temperature and pressure conditions. However, no infinite dilution experimental data are available for the C02/bitumen system. METHODS FOR MUTUAL DIFFUSION COEFFICIENT The following four predictive procedures for calculating the mutual diffusion coefficient in concentrated binary solutions were selected from the literature: zyx (1) The Wilke (1949) equation: (2) 7;he Caldwell and Babb (1956) equation: DAm = xAD~A + xBD~~ , . . . . . . . . . . . . . . . . . (3) The Lefler and Cullinan (1970) equation: ... .... zy (4) The Teja (I 985) generalized corresponding procedure: tmDU = xi,$iiD5 + xjtjD$ . . . . . . . . . . . . . . . . where a26 THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING. VOLUME 65, OCTOBER 1987