Smart WaterFlooding for Carbonate Reservoirs: Salinity and Role of Ions

Abstract The salinity level of injection water in the past has not been considered as a key parameter in oil recovery from water-flooded reservoirs. In the recent years, extensive research on oil/brine/rock systems has shown that injection low salinity brines 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. Saudi Aramco through its upstream research arm (the Advanced Research Center) has initiated a strategic research program tagged "Smart WaterFlood" to explore the potential of increasing oil recovery by tuning the injection water properties. Based on the research work for the last three years, we demonstrated in a previous report (SPE 137634) 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 driving mechanism is wettability alteration of carbonate rock surface. This paper highlights extensive and a broad range of laboratory studies including wettability and surface chemistry 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 pointed out the potential mechanisms for wettability alteration triggered by injecting different salinity slugs of field injection water. The contact angle results indicated that a sufficient reduction in the ionic strength of field injection water is required to trigger the effect of wettability alteration. All evidence gathered during this research work indicate that what we deal with in this study is a new research trend, different from what have been addressed in the literature on low salinity waterflooding for sandstones, and seawater injection in chalks.