Surface Complexation Modeling of SmartWater Synergy with EOR in Carbonates

Abstract

Summary Injection water chemistry plays a major role in governing oil recovery from carbonate formations due to its strong effect on wettability. Various studies have shown that surface charge manipulation caused by tailored water chemistry is the main driver behind modifying carbonate reservoir wettability towards a water-wet state. Therefore, understanding the electrokinetics of brine/calcite and brine/crude oil interfaces is important for optimizing injection water compositions for different enhanced oil recovery (EOR) methods in carbonates. In this work, the physicochemical interactions of various EOR-based water solutions in carbonates are studied using a Surface Complexation Modeling (SCM) approach. First, the brine recipes of NaCl, Na2SO4 SmartWater, and high-salinity water are analyzed as a baseline for zeta-potential comparisons. Different EOR additives, such as surfactants, and dissolved CO2 are added to these brine recipes. The SCM results are compared with experimental zeta-potential measurements for calcite suspensions and crude-oil emulsions in various brine chemistries. The SCM results for EOR-solutions reasonably capture the experimental zeta-potential trends for both brine/calcite and crude oil/brine interfaces. In surfactant solutions, the anionic surfactants shift the zeta-potential values of brine/calcite and crude oil/brine interfaces toward more negative values for all considered brine recipes with the impact being more pronounced for SmartWater and high-salinity water. For the amphoteric surfactant, which includes both anionic and cationic hydrophilic ends, the surfactant effect is found to be in the opposite direction, where the surface charge has been altered toward a positive direction. For carbonated water, where CO2 is dissolved at high pressure, the magnitude of the zeta-potentials is found to be positive at the two interfaces due to the high activity of H+ surface reactions in both calcite and crude-oil surfaces. The novelty of this work is that it successfully validates the SCM results with experimental zeta potential data. Such validated models can be used to determine the physicochemical interaction of different EOR-based solutions in carbonates. These modeling results provide new insights on optimal SmartWater compositions that synergize with various EOR methods to yield enhanced wettability alteration and further improvement in oil recovery in carbonate reservoirs.