Polymer flooding most commonly uses partially hydrolyzed polyacrylamides (HPAM) injected to increase the declining oil production from mature fields. Apart from the improved mobility ratio, also the viscoelasticity-associated flow effects yield additional oil recovery. Viscoelasticity is defined as the ability of particular polymer solutions to behave as a solid and liquid simultaneously if certain flow conditions, e.g., shear rates, are present. The viscoelasticity related flow phenomena as well as their recovery mechanisms are not fully understood and, hence, require additional and more advanced research. Whereas literature reasonably agreed on the presence of these viscoelastic flow effects in porous media, there is a significant lack and discord regarding the viscoelasticity effects in oil recovery. This work combines the information encountered in the literature, private reports and field applications. Self-gathered laboratory data is used in this work to support or refuse observations. An extensive review is generated by combining experimental observations and field applications with critical insights of the authors. The focus of the work is to understand and clarify the claims associated with polymer viscoelasticity in oil recovery by improvement of sweep efficiency, oil ganglia mobilization by flow instabilities, among others.

The injection of sulfonated-modified water could be an attractive application as it results in the formation of a mechanically rigid oil-water interface, and hence, possible higher oil recovery in combination with polymer. Therefore, detailed experimental investigation and fluid-flow analysis into porous media are required to understand the possible recovery mechanisms taking place. This paper evaluates the potential influence of low-salt/sulfate-modified water injection in oil recovery using a cross-analyzed approach of coupled microfluidics data and core flooding experiments. Fluid characterization was achieved by detailed rheological characterization focusing on steady shear and in-situ viscosity. Moreover, single and two-phase micromodels and core floods experiments helped to define the behavior of different fluids. Overall, coupling microfluidics, with core flooding experiments, confirmed that fluid-fluid interfacial interaction and wettability alteration are both the key recovery mechanisms for modified-water/low-salt. Finally, a combination of sulfate-modified/low-salinity water, with polymer flood can lead to ~6% extra oil, compared to the combination of polymer flood with synthetic seawater (SSW). The results present an excellent way to make use of micromodels and core experiments as a supporting tool for EOR processes evaluations, assessing fluid-fluid and rock-fluid interactions.

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.