SmartWater flooding through tuning of injection water salinity and ionic composition is recently gaining good attention for enhanced oil recovery (EOR) in carbonates. The development of new hybrid recovery methods by capitalizing on the synergy with SmartWater can provide one potential optimization route for achieving more economic and effective EOR applications in the field.

In this experimental investigation, we evaluated the synergy of alkali with SmartWater through interfacial tension and contact angle measurements. These measurements were performed at reservoir conditions (2,500 psi and 70°C) using the crude oil and rock substrates from a carbonate reservoir. The high pH common alkali (NaOH) was used at dilute concentrations of 0.1 wt% in two different SmartWater recipes at a fixed low salinity (5,760 ppm TDS). The SmartWater recipes chosen include; 10-times reduced salinity seawater and low salinity water enriched with sulfates and without the divalent cations together with the seawater as baseline.

The contact angle results with high salinity seawater showed the strongly oil-wet behavior (140°) for a carbonate surface, which was favorably altered toward an intermediate-wet state (90°) with SmartWater recipes. The addition of alkali to 10-times reduced salinity seawater increased the contact angle to 152° due to alkali precipitate (formed by the reaction with divalent cations) preventing the interaction of key ions in the SmartWater with carbonate rock surface. A significant shift in the wettability toward a water - wet state (70°) was obtained by the addition of alkali to the SmartWater-enriched with sulfates to confirm the major role of pH on wettability alteration. In addition a reduction in the interfacial tension from 16.6 mN/m to about 7.2 mN/m was achieved by the addition of alkali to the SmartWater-enriched with sulfates in comparison to seawater, as a result of favorable alkali interactions with carboxylic acid groups present in the crude oil. The compounding of these beneficial wettability alteration and interfacial tension reduction effects observed with alkaline chemicals would further reduce capillary forces to mobilize relatively higher amounts of waterflood residual oil in carbonates.

This study is of practical significance as it successfully demonstrates the positive impact of combining SmartWater with alkaline chemicals for both wettability alteration and IFT reduction in carbonates at reservoir conditions. It also opens up a new avenue to exploit the use of synergistic alkaline based hybrid recovery processes for efficient and economical EOR applications in carbonate reservoirs.

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