Improved/enhanced oil recovery by tuning the ionic composition of the injection water is currently deemed as new emerging recovery method. In the recent years, extensive research on oil/brine/rock systems has shown that injection low salinity brines in sandstone reservoirs has a significant impact on the amount of oil recovered. Although, the potential for carbonates has not been thoroughly investigated, some reported studies have excluded carbonates from this effect.

Based on the research work in the last years, we demonstrated in a previous reports (137634; SPEREE Journal, vol. 14(5), pp. 578-593, SPE 143550, SPE 141082) that substantial oil recovery beyond conventional waterflooding from carbonates can be achieved by optimizing the salinity and ionic composition of field injection brine. Also, research confirmed that the main cause for the substantial increase in oil recovery is wettability alteration of carbonate rock surface.

This paper highlights extensive and a broad range of laboratory studies including wettability, surface chemistry, and zeta potential studies to define the role of water ions in the induced wettability alteration, which is crucial in determining the optimum composition of injection water for future field applications.

The rock surface chemistry studies identified the potential mechanisms for wettability alteration triggered by injecting chemistry-optimized field injection water. The contact angle results confirmed that a sufficient reduction in the ionic strength of field injection water is required to trigger the effect of wettability alteration. Zeta potential measurements successfully addressed the impact of multivalent ions on rock surface charges. All evidence gathered during this research work indicates that interplay of water ions is important factor in this new recovery method.

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