Smartwater Synergy With Chemical Enhanced Oil Recovery: Polymer Effects on Smartwater

Abstract

Summary The synergy between various enhanced-oil-recovery (EOR) processes has always been raised as a potential optimization route for achieving a more-economic and more-effective EOR application. In this study, we investigate the possible synergy between polymer and smartwater flooding for viscous-oil recovery in carbonates. Although the potential for such synergy has been suggested and researched in the literature, we investigate this possibility in a more-realistic framework: part of the development of an EOR portfolio for a slightly viscous Arabian heavy-oil reservoir. In this work, we study the possible synergy between smartwater and polymer flooding by performing rheological, electrokinetic potential (ζ-potential), contact-angle, interfacial tension (IFT), and recovery experiments. Rheological tests, as expected, demonstrated the possibility of achieving the same target viscosity at lower polymer concentrations. With smartwater, the polymer concentration required to achieve a target viscosity of 11 mPa·s was found to be one-third lower than that with normal high-salinity injection water. Electrokinetic-potential and contact-angle results demonstrated that polymer presence has negligible to slightly favorable effect on wettability alteration induced by smartwater. On synthetic calcite surfaces, polymer showed negligible effect, whereas on reservoir-rock surfaces, polymer resulted in further reduction in contact angles beyond that obtained with smartwater. Coreflooding experiments conducted at reservoir conditions with finite smartwater/polymer slugs—besides yielding comparable performance to surfactant/polymer flooding—demonstrated the enhanced performance of smartwater/polymer compared with either of these individual processes. A combined smartwater/polymer process was able to recover substantial additional oil—6.5 to 9.9% original-oil-in-core (OOIC)—above that obtained with either of the two processes when applied independently. Ultimate recoveries from the application of smartwater/polymer (70% OOIC) were quite comparable to, and actually slightly higher than, that of surfactant/polymer (67% OOIC). However, in terms of the remaining oil in core (ROIC) after polymer flooding, both processes (smartwater/polymer and surfactant/polymer) exhibited quite similar incremental recoveries of 20.6 and 20.5% OOIC, respectively. The results of this work clearly demonstrated the potential synergy between smartwater and polymer flooding—beyond that of the well-established polymer-viscosity enhancement—for a realistic scenario. The additive effect of smartwater was successfully shown to combine with polymer to increase oil recovery, in addition to lowering the polymer concentration. This favorable synergy will reduce chemical-consumption costs and improve recovery to enhance EOR-project economics.