Corresponding States Method For Calculating Bitumen Viscosity

Abstract

Abstract A method based on the extended principle of corresponding states is presented for calculating the viscosity of Alberta bitumen's. Bitumen's from four regions in Alberta, namely Athabasca, Peace River, Marguerite Lake and Wabasca, are examined in this study. The bitumens are modelled as mixtures of two, three and four pseudocomponenis. The Kesler-Lee correlations and the method of Riedel are used to estimate the critical properties and acentric factor of each bitumen pseudocomponent. Using PSU No. 625 (1,2,3.4,5,6,7,8-octahrydrophenanthrene) as the reference fluid and the shape factors of Leach et al. as modified by Johnson, the calculated bitumen viscosities compare satisfactorily with the published viscosity data over a wide range of temperatures. The calculated viscosities are within about 10% of the data over a wide viscosity range of 0.5 to 271 Pa.s. Introduction An obstacle to the economic recovery and processing of heavy oils and bitumen's is their high viscosity. To facilitate the recovery of heavy oils or bitumen's, a viscosity reduction process such as gas-miscible flood, steam stimulation or in-situ combustion, is necessary. In addition, adequate process equipment design requires a knowledge of the viscosity of heavy oils or bitumen. Due to the time and costs involved in obtaining experimental data, a method to predict the viscosity of heavy oils and bitumen's is required. Viscosity data for gas-free and gas-saturated bitumens have been presented in the literature. Jacobs et al.(1) and Svrcek and Mehrotra(2) provided the viscosity data for gas-saturated Athabasca bitumen. The viscosity, density and gas-solubility data for Marguerite Lake, Peace River, Wabasca and Athabasca bitumens were provided by Mehrotra and Svrcek(2–7). The effect of temperature on the viscosity of gas-free bitumens has also been shown in these investigations(1–7). Based on the above experimental viscosity data, viscosity correlations have been presented in the literature. Correlations for the viscosity and gas-solubility of Athabasca bitumen were developed by Mehrotra and Svrcek(1). Khan et al. (8) provided modified Eyring and Hildebrand equations that correlated the viscosity of gas-free Athabasca bitumen. Two other empirical orrelations were also proposed for the effect of temperature on the viscosity of Athabasca bitumen(8), Sarkar(9) developed a graphical method for correlating the viscosity of gas-saturated bitumens. Johnson(10) presented a method based on the extended principle of corresponding states for the prediction of Athabasca bitumen viscosity. It was shown that the use of methane as the reference fluid gave inadequate viscosity predictions for Athabasca bitumen, However, an aromatic-naphthenic compound (1,2,3,4,5,6,7 ,8-octahydrophenanthrene) as the reference fluid gave viscosity predictions that were within 6% of the gas free bitumen viscosity data of Jacobs(11). This approach also gave satisfactory predictions for the viscosity of gas-saturated Athabasca bitumen(10). It should be noted that this method docs not require any viscosity data, hence the method is truly predictive. The bitumen viscosity predictions in Johnson's method were obtained by characterizing the bitumen as a mixture of pseudo (or hypothetical) components, This type of characterization approach has also been shown to give satisfactory prediction of vapour-liquid and vapour-liquid-liquid equilibrium for bitumen/gas systems as well as the surface tension of Athabasca bitumen(12,13).