Measurement and modeling of the phase behavior of solvent diluted bitumens

Abstract

The design of solvent-based and solvent assisted heavy oil recovery processes requires accurate predictions of phase behavior as straightforward as saturation pressures and as potentially complex as vapour–liquid–liquid equilibria and asphaltene precipitation. It is a challenge to predict this variety of phase behavior from a single fluid model. In this study, saturation pressures of dead and live Peace River bitumen were measured in a Jefri PVT cell at different concentrations of a multi-component solvent at temperatures from 20 to 180°C. Saturation pressures and the onset of asphaltene precipitation were also measured for the bitumen diluted with n-pentane. The onset of precipitation was determined by titrating the bitumen with pentane and periodically circulating the mixture past a high pressure microscope. Literature data including saturation pressures and liquid–liquid phase boundaries for pseudo-binaries of bitumen and carbon dioxide, methane, ethane, and propane were also evaluated.The data were modeled with the Advanced Peng–Robinson Equation-of-State (APR EoS). 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 fit the saturation pressures and onset of asphaltene precipitation over a wide range of temperatures. The model predicted liquid–liquid boundaries as well as the 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.