Reservoir simulation and research activities of heavy oil production processes such as SAGD, VAPEX or the steam-solvent combined hybrid process require accurate values of equilibrium constants (K-values) at elevated temperatures. However, such data is rarely available in open literature either because of the temperature limitation of PVT equipment or difficulties in performing high temperature three phase vapor liquid equilibrium experiments.

In this paper, with the assistance of a state-of-the-art fully visual PVT cell specifically developed for heavy viscous oils and capable of performing fluid phase behavior studies at temperatures up to 250°C and effectively mix samples with viscosity up to 1,000 cP at test temperature, a heavy oil-solvent-steam equilibrium case study is presented. The heavy oil was mixed with solvent and water at specified weight ratio, temperature and pressure in the heavy oil PVT cell. After achieving equilibrium, the volumes of vapor, liquid and water phases were measured. The samples from each phase were drawn for compositional analysis using gas chromatography and K-values of the hydrocarbon components were examined. The component compositions from this experiment were utilized for equation of state (EoS) model turning. This case study shows that with proper care, the EoS can be characterized and used to match with experimental data for heavy oil.

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