Robust Chemical Flood Design for Maximum Recovery Using Updated FluidProperty Models

State-of-the-art chemical flooding simulators typically use nonpredictive phase behavior and propertymodels to design a surfactant flood. For example, a variation of the black-oil model is often used to representphase behavior in several commercial simulators. We examine the available methods including more recentphysics-based models such as the HLD-NAC equation-of-state and their effects on overall recovery, frontspeeds, and breakthrough times. We implement the HLD-NAC EoS model in UTCHEM to examine theimpact of changing salinity and other variables on the phase behavior and the recovery process. A novelpredictive viscosity model is also implemented for the first time in UTCHEM to give a more accurateprediction of viscosity. We isolate the impact of salinity and other gradients on recovery in a one-dimensionalhomogeneous reservoir. Results show that the composition path can enter the Winsor II+ region for certain changes in variablegradients. When the two-phase region is entered, the trailing injected fluid surpasses the chemical slug andcontacts the oil bank directly. The microemulsion phase saturation is then decreased to immobile valuesso that surfactant is now immobile and oil recovery is significantly decreased. We further show that thepresence of polymer-both in the buffer and the chemical slug-has little effect on the appearance ofthe arrested microemulsion and oil bank. Polymer does partially offset the negative effects by providingconformance control immediately after the microemulsion phase is trapped. The salinity gradient should bedesigned so that the composition path avoids the II+ lobe in its entirety, giving a robust and mobile slug withor without polymer. We propose a limit in injection salinity under which the II+ lobe can be avoided. Wealso show that the less accurate viscosity model overestimates recovery in a two-dimensional simulationof the chemical flood.