Heavy oil is a significant global resource but is challenging to recover and process due to its high intrinsic viscosity. One method to reduce its viscosity is to add solvent. Mixing heavy oil and solvent sounds simple in principle but can lead to surprisingly complex results. Multiple phases may form and the viscosity of these phases can span five orders of magnitude. Hence, it is vital to accurately measure and predict the phase behavior and properties of these mixtures in order to appropriately design and operate solvent-based heavy oil processes.
The purposes of this presentation are to: 1) illustrate the potential outcomes when solvent is added to heavy oil; 2) highlight the current strengths and limitations in modeling these outcomes. In particular, two aspects of these mixtures are considered: phase behavior and viscosity. First, the phase behavior of mixtures of heavy oil and light n-alkanes is reviewed, including vapor-liquid boundaries, liquid-liquid boundaries, and asphaltene-rich phase yields over a wide range of pressures, temperatures, and compositions. The nature of the heavy liquid phase (from dispersed glassy particulates to a viscous liquid) is examined and the kinetics of the phase change is discussed. The performance of equations of state in modeling the phase behavior for mixtures of heavy oil and solvent is assessed. Second, the effect of solvent addition on heavy oil viscosity is shown and different approaches for predicting the viscosity of these mixtures are examined. The data and modeling approaches shown in this presentation are the product a decade of research and have application in many industrial processes including in situ recovery processes, oil sands froth treatment, solvent deasphalting, and flow assurance. The current status of heavy oil/solvent processes is reviewed with a focus on the role of phase behavior and properties in selected applications is discussed.
The one takeaway idea is that phase behavior can be complex; it can make your project if understood and break it if not.