Calculation Of Gas Solubility In Wabasca Bitumen
Authors: Mehrotra Anil K. , Patience Gregory S. , Svrcek William Y. 
Published: March 2010

Calculations are described for the solubility of five gases, namely, N2, CO, CH4 CO2 and C2H6 in Wabasca bitumen at temperatures ranging from 23 °C to 110 °C. The gas solubilities were calculated using the Peng-Robinson equation of state, and these were compared with published data. The best results were obtained by modelling the bitumen as a mixture of three pseudocomponents which represent the distillable maltene, the undistillable maltene and the asphaltene fractions.

Introduction

In the past, we have published data for gas solubility, density and viscosity of Athabasca, Marguerite Lake, Peace River, Wabasca and Cold Lake bitumens(1–7). The gases whose effectson bitumen properties have been measured include N2, CO, CH4, CO2, CZH6, and mixtures containing two or more of these gases. Gas solubility and density data for Athabasca and Cold Lake bitumens were also reported by Fu et al.(8, 9).

To make the data useful in simulating oil sand or heavy oil reservoirs and/or processes, empirical correlations for gas solubility and viscosity of bitumens were provided(2–3). On the other hand, bitumen characterizations were developed(10–12) for the calculation of bitumen gas-solubility using the Peng-Robinson (P-R)(13) equation of state (EOS). In these studies, bitumens were subdivided into several pseudocomponents and the Kesler-Lee(14) correlations were shown to provide a satisfactory estimation of the critical properties and acentric factor for each bitumen pseudocomponent(7, 11, 12). Other gas solubility calculation methods(8, 9, 15, 16) were based on lumping the bitumen as one pseudocomponent. To match the calculated gas solubilities with the data, temperature-dependency for the binary interaction parameter was proposed.

The gas solubility results presented in this paper are based on the use of a three-pseudo-component ("3PC") characterization scheme that was developed for the calculation of the viscosity of gas-free Wabasca bitumen using the corresponding states method(17). For bitumen viscosity calculation, the use of a one-component characterization scheme has been shown to give unacceptable results(18). In recent studies(11, 12), we have attempted to demonstrate that the use of multicomponent bitumen characterization yields a better match of gas solubility data.

Furthermore, multicomponent bitumen characterizations would be needed for simulating some very interesting reservoir phenomena such as "fingering" and "distillation" effects. In surface facilities calculations, particularly separation simulations, one-component bitumen/heavy-oil characterizations would obviously be useless. Similarly, vapour-liquid-solid (V-L-S) multiphase equilibrium for bitumen-diluent systems can only be described with muiticomponent bitumen characterizations(19).

It is emphasized that the data for gas-bitumen phase equilibria of only the whole bitumens are presently available in the literature. That is, there are no reported data or properties for the fractions or ‘cuts’ of Alberta bitumens. Obviously, a more rigorous approach for predicting bitumen properties will be based on the characterization parameters and phase equilibrium data for each of the bitumen fractions.

Generally, the larger the number of pseudocomponents the better one would expect to model the heavy-oil/bitumen thermodynamic and transport properties. However, increasing the number of pseudocomponents that the heavy-oi