A set of three-phase equilibrium data from the literature for heavy oil was used to characterize the Peng-Robinson equation of state (PREOS). The tuned PREOS was then used to match other sets of similar data in the literature and it was also used to predict three-phase vapor-liquid equilibrium constants (kvalues) for use in simulation and process understanding. Results of this study show that:
the PREOS when properly tuned can match most literature data within 5 %accuracy,
the k-values generated for methane (C1) and carbon dioxide (CO2) by the PREOS are different from the existing- correlations which are currellt~v used in thermal simulators.
the water concentration in the equilibrium calculation consists of free water only i.e. the amount of water excluding the amount of water in the emulsion.
the k-values of C1 and CO2 are weak function of feed composition if the water concentration is greater than 0, otherwise they are strong function of feed compositions,
it is very important to observe the loci of the first dell' point locus and water saturation curve in a pressure temperature (P-T) diagram in deriving the k-values, and
the amount of water in the vapor phase deviates increasing from the ideal equation with pressure.
Since there is lack of study on the effect of emulsification on the three phase equilibrium for heavy oil, therefore to obtain the equilibrium constants (k-values) the existing thermal simulators use correlations for hydrocarbon and noncondensible gas components and the ideal equation for water component These k-values are function of temperature and pressure only. This is based on these assumptions (a) no mutual solubility between bitumen and water. (b) methane insoluble in water. (c) no CO2 in the oil composition. (d) no steam distillation on bitumen and (e) no emulsion formation. According to the latest literature data(l–8) and some field and lab observation these assumptions are no longer valid. Since it has been known that there is some mutual solubility among methane bitumen and water. Furthermore. it is observed that (a) steam distillation plays a very important role in oil recovery. (b) CO2 is generated in-situ(9) and (c) the flowing phase in the reservoir is emulsion/foam(1.4).
Emulsification is believed to be initiated by the presence of natural emulsifying agents which are present in oil. The insitu formation of emulsion in porous media(1–4) has been documented. There are many studies of emulsion rehology(4–5). but there is lack of study on the three phase equilibrium due to the emulsification.
The most recent study(6–8) on three phase equilibrium ignored this important phenomena even some of their data indicated the effect of emulsification. Therefore a study on the three phase equilibrium due to formation of emulsion is embarked to a better understanding of this physical phenomenon. This study is also prompted by the current simulator cannot match field gas-oil ratio.
The formation of emulsion results in reducing the amount of water content as feed concentration in three phase equilibrium calculation. Ignoring this fact, will lead to obtain incorrect k-Yalues since k-values is a function of feed concentration. The incorrect k-Yalues can result in many problems.
