Investigation of Modified Water Chemistry for Improved Oil Recovery: Application of DLVO Theory and Surface Complexation Model

Abstract

Abstract It is widely accepted that oil recovery during waterflooding can be improved by modifying the composition of the injected brine. A typical approach is diluting the formation water to a specific lower salinity. However, recent experimental studies report the adverse effect of formation water dilution on oil recovery for specific oil/brine/rock systems. The adverse effect depends on the interactions within the system and is more pronounced in carbonates. In this study, we investigated the effect of water composition on the performance of low salinity water injection by considering the complex interplay interaction of oil, brine, and rock system. We used a coupled in-house compositional simulator and geochemical (IPhreeqc) framework for this study. Using this simulator we were able to capture true physics of the modified salinity waterflooding process. First, employing PHREEQC, we developed a surface complexation model for oil and rock surfaces to calculate the zeta-potential at these two surfaces. Second, we considered a water film between oil and rock and used DLVO theory to calculate the attractive/repulsive forces between oil and rock surfaces. Furthermore, we used the augmented Young-Laplace equation to calculate the resulting contact angle of the system. Then, we defined an interpolating parameter as a function of the calculated contact angle to predict wettability alteration. Finally, the geochemistry model was implemented in UTCOMP-IPhreeqc to investigate the effect of modified salinity water injection on wettability alteration and enhanced oil recovery. In order to validate our approach, the results of our simulations were compared with a recently published coreflood experiment. Our results show that in carbonates, the charge of the oil/brine and rock/brine surfaces is a determining factor for the success of modified salinity waterflooding. Our contact angle calculations using DLVO theory and the augmented Young-Laplace equation accurately estimated the dynamic trend of contact angle during low salinity flood. Moreover, our zeta potential calculations based on surface complexation model reproduced the experimental data of oil/brine and brine/calcite zeta potential measurements. Modeling wettability alteration as a function of contact angle was sufficient to predict the low salinity effect in carbonates. Similar approach can be used to model low salinity effect in sandstones. We believe this is the first study that a comprehensive compositional reactive transport simulator is used to assess modified salinity waterflooding as a function of contact angle, employing DLVO theory and surface complexation model.