Simulations of foam-assisted surfactant chemical EOR in fractured systems require simultaneous modeling of foam flow in fractures for mobility control and chemical EOR in matrix by diverted surfactant solution. Modeling of surfactant phase behavior as a function of salinity and representing microemulsion (ME) properties are challenging because commercial simulators lack the capability to explicitly model these complex chemical processes. In this paper, we develop and validate techniques for simultaneous modeling of foam flow and surfactant-oil-brine key characteristics, using the general framework of CMG-STARS commercial simulator. Laboratory surfactant-salinity phase behavior data is transferred into k-value based compositional model, where oil is also characterized by multi-components. Surfactant Winsor Type phase variations are tracked by a pseudocomponent based on combined surfactant-salinity criteria, an invention of this paper. The mobility control provided by foam is fulfilled by bubble model of low quality liquid foam with increased aqueous phase viscosity through bubble characteristics.
2D cross section models are constructed for the modeling of foam transport in fractures and surfactant EOR processes in matrix. The critical process physics of surfactant phase behavior is represented in detail, including k-value based component splitting between phases, viscosity variation of ME phases and the corresponding interfacial tension reduction. The results show that our developed methodologies correctly account for diversion of surfactant solution into matrix for intended chemical EOR processes and for mobility control by foam flow in the fractures. Investigation of phase viscosities, IFT and compositions show that the modeling of ME phases and representing their properties in various gridblocks of the simulation model and over different time intervals follow the underlying process mechanism. As such, the techniques developed provide a methodology for modeling foam-surfactant chemical EOR in naturally fractured reservoirs within the framework of available commercial simulators and along with their limited functionalities.