SmartWater Synergy with Chemical EOR: Polymer Effects on SmartWater Spontaneous Imbibition

Abstract

Summary Synergy between EOR processes has the potential for achieving more effective application. Previously, we demonstrated Smart water's slight negative-impact on polymer and chase brine injectivity, positive impact on polymer retention, and negligible impact on polymer acceleration. We also demonstrated polymer's positive effects on Smart water's surface potentials, contact angles, and oil recoveries. Herein, we further investigate this synergy focusing on polymer's possible effects on SmartWater spontaneous imbibition. We also revisit singlephase displacement observations with regard to polymer injectivity and retention using bench-top experiments. The main experimental program consisted of spontaneous-imbibition and sorption measurements. A supplementary experimental program included polymer filterability and adsorption tests to provide additional insights on this synergistic SmartWater/Polymer process. Results showed the superiority of SmartWater as an imbibition fluid compared to the higher-salinity injection water. With polymer addition, the lower-salinity SmartWater upheld its superiority. Accounting for viscosity variations, sorption rates into powdered rock packs were actually very comparable with and without the polymer. In core plugs, and with both brines, polymer addition yielded further water imbibition above that obtained with polymer-free solutions. Still imbibition was much more effective with SmartWater even in the presence of the polymer. At the same polymer concentrations, polymer adsorptions onto the rock were comparable with both SmartWater and the higher-salinity injection water. However, at equivalent viscosities, polymer adsorption onto the rock was lower with SmartWater than with the higher-salinity injection water. These static adsorption results could provide an additional explanation to the substantially lower retention observed with the lower-salinity SmartWater in dynamic retention tests. At the same polymer concentration, the solutions in both brines exhibited comparable filtration ratios. However, for solutions of equivalent viscosities, the solution in the higher-salinity conventional injection water exhibited higher filtration ratio. This discrepancy with single-phase displacement results can be explained based on differences of the main mechanism contributing to permeability reduction (adsorption layer versus mechanical plugging). In conclusion, the favorable SmartWater/Polymer synergy extends to spontaneous imbibition. Polymer solutions, in both SmartWater and injection water yielded additional imbibition in tertiary mode. However, with injection water the additional imbibition after polymer addition is much smaller than with SmartWater.