No abstract

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.

The application of low salinity water and ion management of the injected water affects the oil recovery in carbonate formations. Different forced and spontaneous imbibition experiments have been practiced on the carbonate core samples to show the performance of this smart water injection. Various experimental and modeling approaches have been applied by different researchers to optimize the smart waterflooding process. To achieve more practical conditions, the injection time of the smart water should be reduced to control the preparation cost on the field scale. In this paper, we present findings from different modeling/experimental studies to improve the performance of smart water flooding in carbonate formations by the idea of shock/soaking. Different researches showed that the presence of active ions such as Mg2+ and SO42- in the injection water alters the wettability of carbonates to more water-wet state and also reduces the IFT between the oil and the injected brine. Hence, spiking active ions concentration in the low salinity water improves oil recovery from carbonate formation. In this work, the optimized smart brine was used for injection with novel injection scheme. The optimized brine was set to be injected as the shock slug between two slugs of high salinity water. This smart water shock flooding was designed to reduce the pore volume of low salinity water flooding. The effect of the slug on relative permeability curves was modeled and analyzed in the core and sector scales. Also we experimentally studied the effect of soaking time after the shock on wettability alteration and improvement in recovery by re-injection of high salinity normal brine. Characterization tests such as contact angle measurement confirmed the effect of shock/soaking on alteration of governing mechanisms such as multi-ion exchange which leads to wettability alteration in the process. Our core flooding experiments showed that the shock injection at the best design can improve the tertiary recovery up to 7.8%. Also, modeling at the reservoir sector shows noticeable incremental oil recovery during the shock injection and high salinity water injection after it. Our modeling/experimental studies clearly illuminated a new approach to improve the performance of low salinity water flooding in an efficient and cheaper way. By this approach, higher oil recovery can be achieved by the application of less amount of diluted water which is beneficial for the oil industry.

No abstract

No abstract