A Four-Phase Chemical/Gas Model in an Implicit-Pressure/Explicit-Concentration Reservoir Simulator

Abstract

Summary This study describes a general four-phase model developed for gas/oil/water/microemulsion (ME) coexisting at local equilibrium. The original framework of a chemical reservoir simulator is used to implement the model. This model represents a new method to couple the black-oil model with surfactant-phase behavior [i.e., the Hand (1939) rule]. The Hand (1939) rule is used to capture the equilibrium among surfactant, oil, and water species as a function of salinity and species concentrations for oil/water/ME phases. The interphase-mass transfer between gas/oil in the presence of the ME phase is calculated at the equilibrium between phases. For this purpose, a new volume-balance equation is derived to consider the pressure equation for compressible and real mixing in such a model. Hence, the pressure equation is derived by extending the black-oil model to a pseudocompositional model for a wide range of components (water, oil, surfactant, polymer, anion, cation, alcohol, and gas). Mass-balance equations are then solved for the components to calculate the concentration. Finally, we implemented the coupled surfactant and black-oil phase-behavior models and the fluid-flow formulations in an implicit-pressure/explicit-concentration (IMPEC) chemical-flooding simulator: UTCHEM (2011) four-phase. The results were verified against existing reservoir simulators for two different three-phase test cases comprising gas/oil/water and oil/water/ME. Then, the performance of the model in the presence of four phases was tested and validated against coreflood experimental data. The results showed that the new phase behavior and the fluid-flow equations are consistent with three-phase reservoir simulators for the case studies. In addition, the findings of this work can be used to model and capture the mechanisms behind processes such as micellar slug foam and alkaline and surfactant flooding into saturated (gas cap) reservoirs as well as alternating or coinjection of surfactant and gas processes. Modeling of such processes is far from satisfactory in existing phase behavior and fluid-flow simulators.