Declining production from conventional resources in recent years has fueled increasing global interest in alternative resources, such as heavy oil and bitumen. The design and development of heavy oil and bitumen recovery processes, e.g. solvent-enhanced steam-assisted gravity drainage (ES-SAGD) and hybrid solvent, requires accurate predictions of phase equilibria and the mutual solubility of different solvents in bitumen. Despite the importance of accurate phase behaviour predictions, there is a lack of fundamental and mechanistic knowledge relevant to bitumen/solvent equilibrium properties.
This study provides a better understanding of the phase behaviour of bitumen/solvent systems. A phase behaviour model based on the Peng-Robinson equation of state was developed and validated with existing literature data. Then, available mixing rules for computing the co-volumes of polar and non-polar mixtures were incorporated into the developed model. In order to model the phase behaviour of bitumen/solvent mixtures, bitumen was first characterized to estimate its critical properties based on the boiling point distribution data. The boiling point distribution was modeled and extended using probability distribution functions. The phase behaviour of solvents (e.g. methane, ethane, and carbon dioxide) and Cold Lake bitumen systems were modeled using the developed model and the volume translation technique was applied to improve the saturated liquid densities.
The results show that the van der Waals mixing rule with two regression parameters successfully improves the accuracy of the solubility predictions to less than 4%. Incorporating the temperature dependency of the binary interaction coefficient makes the predictions even more accurate. A correlation incorporating the impact of temperature and component molecular weight on the calculation of saturated liquid densities was proposed for the translated volume values with a 0.6% deviation in density predictions.
The stepwise characterization scheme was developed in this study successfully define bitumen pseudo-components with least needed experimental data. The results also show the van der Waals mixing rule with two binary interaction coefficients predicts solvent solubility superior comparing to previous attempts.