(24d) Measurement and Modeling of Phase Equilibrium in Heavy Oil / Propane Systems

In order to model phase equilibrium of heavy oil with propane, several experimental measurements were undertaken using four samples from two different heavy crude oils, two as natural feeds and two as products of previous treatments.

The phase equilibrium experiments were performed in a high pressure PVT cell consisting of heavy oil/propane mixtures at a range of temperatures, pressures and solvent/oil ratios. The densities of the two resulting phases were measured at experimental conditions. The oil and the two phases resulting from the experiments (light and heavy) were further separated by SARA characterization (they were divided into Saturates, Aromatics, Resins and three asphaltenes fractions) and the mass, molecular weight, refractive index and densities of each of the six resulting SARA fractions were measured. These values were used in order to obtain critical properties of the fractions for phase equilibrium modeling with an equation of state (Peng-Robinson). About 70 equilibrium experiments were performed altogether.

An extensive modeling effort was also carried out using the Peng-Robinson equation of state, combined with an analysis of several correlations for critical properties, acentric factors and binary interaction parameters. The model gave results for oil yield, volume fraction of the phases as well as densities of the phases. Agreement was good in most cases, despite the complexity of the systems and the errors inherent in the various characterization methods.