Robust Chemical Flood Design for Maximum Recovery Using Updated Fluid Property Models

State-of-the-art chemical flooding simulators typically use nonpredictive phase behavior and property models to design a surfactant flood. For example, a variation of the black-oil model is often used to represent phase behavior in several commercial simulators. We examine the available methods including more recent physics-based models such as the HLD-NAC equation-of-state and their effects on overall recovery, front speeds, and breakthrough times. We implement the HLD-NAC EoS model in UTCHEM to examine the impact of changing salinity and other variables on the phase behavior and the recovery process. A novel predictive viscosity model is also implemented for the first time in UTCHEM to give a more accurate prediction of viscosity. We isolate the impact of salinity and other gradients on recovery in a one-dimensional homogeneous reservoir. Results show that the composition path can enter the Winsor II+ region for certain changes in variable gradients. When the two-phase region is entered, the trailing injected fluid surpasses the chemical slug and contacts the oil bank directly. The microemulsion phase saturation is then decreased to immobile values so that surfactant is now immobile and oil recovery is significantly decreased. We further show that the presence of polymer - both in the buffer and the chemical slug - has little effect on the appearance of the arrested microemulsion and oil bank. Polymer does partially offset the negative effects by providing conformance control immediately after the microemulsion phase is trapped. The salinity gradient should be designed so that the composition path avoids the II+ lobe in its entirety, giving a robust and mobile slug with or without polymer. We propose a limit in injection salinity under which the II+ lobe can be avoided. We also show that the less accurate viscosity model overestimates recovery in a two-dimensional simulation of the chemical flood.