Measurement and modeling of the phase behavior of solvent diluted bitumens
Creators: name: Agrawal, Pawan
Publisher: name: University of Calgary
Year: 2012

description: Bibliography: p. 108-117
description: The design of solvent-based and solvent assisted heavy oil recovery processes requires accurate predictions of phase behaviour as straightforward as saturation pressures and as potentially complex as vapour-liquid-liquid equilibria and asphaltene precipitation. Among the various methods of predicting the phase behaviour of crude oils, the equation of state (EoS) is the most commonly used. To use an EoS, the amounts, critical properties, acentric factor, molecular weight and binary interaction parameters of the constituent components are required to characterize the fluid. For conventional oils, techniques such as distillation are used to obtain a normal boiling point curve which can be divided into pseudo-components. The boiling point curve is extrapolated over the relatively small heavy residue fraction and then correlations are used to determine the properties of each pseudo-component. However, for heavy oils, only about 30 to 50% of the oil can be distilled even with vacuum distillation. Hence, there is a need for a methodology to characterize the large residue fraction of heavy oils for EoS models. The objective of this thesis is to adapt a heavy oil characterization method for an equation of state model for not only conventional vapour-liquid and liquid-liquid equilibria but also asphaltene precipitation for mixtures of heavy oil and solvents. Literature data on saturation pressures and liquid-liquid phase boundaries were collected for pseudo­binaries of bitumen and carbon dioxide, methane, ethane, and propane. Saturation pressures and the onset of asphaltene precipitation were measured for a pseudo-binary of bitumen and n-pentane. Saturation pressures were measured in a Jefri PVT cell at temperatures from 20 to 180°C. The onset of precipitation was determined at 20 and 180°C by titrating the bitumen with n-pentane and periodically circulating the mixture past a high pressure microscope. Saturation pressures were also measured for a live bitumen diluted with a multi-component solvent also at temperatures from 20 to 180°C. The data were modeled with the Advanced Peng-Robinson equation of state. The maltene fraction of the bitumen was characterized into pseudo-components based on extrapolated distillation data. The asphaltenes were characterized based on a Gamma distribution of the molecular weights of self-associated asphaltenes. The APR EoS was tuned to fit the saturation pressure and asphaltene onset data of the pseudo-binaries by adjusting the binary interaction parameter between the solvent and the bitumen pseudo-components. A temperature dependent binary interaction parameter correlation was developed for the interaction parameters. The model with temperature dependent binary interaction parameters fit the saturation pressures, liquid-liquid boundaries, asphaltene onset over a wide range of temperatures. The model predicted saturation pressures of live oil and live oil diluted with condensate solvent generally within experimental error. The model also predicted the asphaltene onset in propane diluted bitumen although the asphaltene yield at higher dilution was underestimated. The model extends the capability for modeling the phase behaviour of solvent based heavy oil processes to a broad range of operating conditions.