Equilibrium calculations for coexisting liquid phases

Modeling of reservoir processes in gas miscible flooding may require that phase equilibrium between multiple liquid fluid phases are taken into consideration. Under certain conditions 2 hydrocarbon-liquid phases may form. Therefore, it may become desirable to account for mass transfer between the hydrocarbon and the aqueous phases. This work describes a refined successive substitution method for calculating multiphase flash equilibrium. The phase behavior is assumed to be described by an equation of state. The solution procedure proceeds in a stepwise manner and additional phases are introduced via a special testing scheme based on phase fugacities. This avoids trivial solutions and insures continuity across phase boundaries. The method has been tested on various 3- and 4-phase systems, and examples of application show that the method performs well. 11 references.