Influence of Sulfate Ions on the Combined Application of Modified Water and Polymer Flooding—Rheology and Oil Recovery

Abstract

Oil recovery using modified/smart water technology can be maximized by optimizing the composition of the injected water. Brine optimization is also believed to improve polymer flooding performance. This chapter assesses and defines the potential impact of combining low-salt-modified water with polymer flooding, based on the presence of sulfate in the injection water. Hence, we evaluated the influence of sodium sulfate on (1) polymer viscoelasticity, under the assumption that the phenomena exists, and (2) oil recovery and pressure response. Mainly, a comprehensive rheological evaluation and two-phase core flood experiments are the focus of this work. Composition of injection brine is optimized after having synthetic seawater as a base brine. Core-flood experiments were performed in a secondary, tertiary and a sort of post-tertiary (quaternary) mode to evaluate the feasibility of applying both processes (modified water and polymer flood). Obtained data was subsequently cross-analyzed and as an overall observation, sodium sulfate helped with improving polymer viscosity compared to sodium chloride or divalent cation presence. Moreover, optimized modified water, with the higher amount of sulfate ions, showed an additional oil recovery in both secondary and tertiary mode of about 5.0%. Additionally, polymer injection in tertiary mode, after modified-water injection, showed significant additional oil recovery.