Shock/Soaking Injection Scheme to Improve Oil Recovery in Carbonate Formations by Low Salinity Water Flooding

Abstract

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.