Mechanisms for Enhanced Oil Recovery by Smart Water Injection

Nowadays, due to the development of industries, increasing energy demands, raising reservoir depletion rate, and providing the opportunity for future generations to use these valuable resources, enhanced oil recovery (EOR) is an utmost priority for the oil industry. Approximately, more than half of the discovered oil in the world are in carbonate reservoirs, which possess various complexities. The principal problem concerning this type of reservoirs is the high residual oil saturation, after primary oil recovery. One of the methods used to improve oil recovery is the spontaneous imbibition. Smart water injection to alter wettability state is one of the main parameters in EOR, particularly in such reservoirs with strongly oil-wet rocks. As stated by several scholars, carbonate rocks are initially oil-wet, and smart water injection leads to wettability alteration by changing the chemical properties of the injected water. Various mechanisms, such as oil-water interfacial tension (IFT) reduction, wettability alteration, rock dissolution, and double electric expansion are involved. Nevertheless, due to different chemical interactions during smart water injection, it is impossible to incorporate a single mechanism as the main mechanism for EOR. With this in view, we performed an integrated study on the effects of smart water injection, as well as the effective mechanisms during injection into carbonate reservoir rocks.