During smart water injection into carbonates, wettability alteration is subjected to be the main mechanism contributing to incremental oil recovery. Apart from the smart water composition, level of dilution, and the underlying mechanisms, "injection scheme" is of a great importance when developing a field scale flooding project. The pivotal target of this paper is to evaluate the efficiency of smart water injection by deploying tertiary smart water "shock slug" injection within the periods of water flooding.
At the first stage, genuine reservoir brine was 10 times diluted. Ion Chromatography analysis was utilized to optimize the composition by adding 2.65 g/ml of MgSO4.7H2O. Core samples were initially flooded by the original high salinity water to reach the residual oil saturation. Smart water shock slugs were chosen in various volumes including, .75, 1, 1.5, and 2 PV. Subsequently, smart water was injected for the selected shock slug sizes. At this stage the procedure was stopped for 12 hours in order to let the smart water interact with rock sample. Afterward the process was followed by the high salinity water injection. To have a comprehensive perspective of the procedure, production data was recorded at all stages of the injection. Also, the contact angle was measured under standard condition by generating a sessile drop of oil on the carbonate surface submerged in the brine environment. The pH of the injection fluids was also measured during contact angle and core flood tests. X-Ray Diffraction inspection was utilized to analyze the mineralogy of the core samples.
Evaluating the results of the contact angle measurements, it was obtained that smart water was capable of altering the wettability towards more water wet. pH of smart water was increased after it was kept in contact with the oil-aged rock for two weeks. Core flooding results indicated that the tertiary injection of the smart water as shock slug leads to a considerable amount of incremental oil recovery at tertiary mode and changes the wettability towards more water wet. This is mainly due to the effective ionic exchange which leads to the favorable wettability alteration during smart water injection.
This study showed that smaller sizes of smart water shock slug can increase the incremental recovery as effective as larger sizes of smart water shock slug in analogues situation. Hence, the asserted method can be a good alternative for conventional low salinity water flooding due to being less time-consuming and cost-effective.