Bitumen, with its high asphaltene content, has a much higher viscosity than conventional crude oils. The high viscosity of bitumen represents the greatest obstacle to both efficient recoveries by conventional processes and transportation to the refinery for upgrading. To produce bitumen, its viscosity must be reduced using techniques such as solvent aided processes (SAP).
Solvent aided processes, such as LASER (Liquid addition to steam to enhance recovery), significantly reduce the viscosity of bitumen by adding a liquid solvent to the injected steam. This process increases the production rate and reduces the ratio of required steam to oil. To improve oil recovery prediction, it is essential to have accurate measurements the physical properties of the bitumen-solvent system at conditions similar to those encountered in situ and in transport. Measurements of the viscosity of complex bitumen-solvent systems can be used to develop an appropriate model for predicting the viscosity of diluted bitumen/solvent mixtures.
This study aimed to accurately measure the physical properties (viscosity and density) of bitumen diluted with liquid solvents (hexane and toluene) over a wide range of pressures (up to 10 MPa), temperatures (ambient to 345 K), and solvent mass compositions (0.05, 0.1, 0.2, 0.35, 0.5, 0.70, and 0.80) for several bitumen-solvent systems. In addition to density and viscosity measurements, the possibility of asphaltene formation at high solvent concentration was visually investigated. The viscosity and density of the raw bitumen, pure solvents (toluene and hexane), and toluene and hexane diluted bitumen were also measured. Additional solvent mixtures were prepared by mixing hexane with toluene in different mass fractions (0.25, 0.5, and 0.75). The physical properties of bitumen diluted with these mixtures were recorded. The experimental results for all bitumen/solvents mixtures were evaluated using prediction schemes and correlation models from the literature.
The experimental results showed that the viscosity and density of the solvent diluted bitumen decreased as the temperature and mass fraction of solvents was increased, and increased as the pressure was increased. Asphaltene precipitation was detected in hexane-diluted bitumen at 0.5 mass fraction of hexane and increased significantly when the mass fraction of hexane was increased to 0.7. The addition of aromatic solvent i.e. toluene to hexane delayed the critical concentration in case of bitumen/mixture (hexane 75 mass % + toluene 25 mass %) resulting in asphaltene precipitation at only ws= 0.80.