What is smart water flooding?
Smart water flooding is an enhanced oil recovery (EOR) method where the composition and salinity of the injected brine are adjusted to improve oil recovery, often by changing the wettability of the reservoir rock. Waterflooding has long been used as a secondary recovery method both in carbonate and sandstone reservoirs. However, in the mid‑’90s the pioneering work by Yildiz and Morrow1 showed that changing the brine composition can influence the oil recovery. Since then, the injection of so‑called smart water with the correct salt composition and salinity has gained a lot of interest. Several groups have studied the mechanisms by which the improved oil recovery is achieved.
At first, the research was mainly concentrated on sandstone reservoirs where extra oil recovered from low salinity flooding varied in the range of 5–30 % of original oil in place2. However, several laboratory studies and field tests have confirmed its potential also in carbonate reservoir enhanced oil recovery.
There are two main advantages of smart water flooding compared to other enhanced oil recovery methods:
-
low cost and
-
less impact on the environment3.
How smart water flooding alters reservoir wettability
The underlying mechanism for low salinity flooding is not completely understood but it is related to complex crude oil/brine/rock interactions mostly between injected water and rock surface. For wettability alteration, the activation energy or energy barrier for the chemical reactions needed for wettability improvement to take place is crucial. Reservoir temperature plays an important role because activation energy is dependent on the temperature. Higher than 100 °C temperatures have shown to be more efficient.
Contact angle measurements for smart water flooding studies
To study the wettability alteration caused by low salinity water, contact angle measurements have been utilized3. In the study of Ding et al.3, the contact angles of different brine solutions were measured on the rock surface. To mimic the oil‑wet state of the reservoir rock, the surface was aged in mineral oil. The water contact angle after the aging period was measured to range from 121° to 130°. To conduct the measurements with different brine solutions, the rock was immersed into mineral oil and the brine contact angles were measured through the oil phase.
As smart water flooding happens at reservoir conditions, it is important to take that into account when contact angles are measured. Contact angle measurements can be carried out at elevated temperatures and high pressures using suitable high‑pressure cells and temperature‑controlled stages, which makes it possible to study wettability alteration under reservoir‑like conditions.
FAQ: Smart water flooding in enhanced oil recovery
What is smart water flooding?
Smart water flooding is a form of water flooding where the composition and salinity of the injected brine are modified to improve oil recovery. By adjusting specific ions in the brine, the rock–oil–brine interactions can be influenced and the wettability of the reservoir rock can be changed.
How does smart water flooding differ from conventional water flooding?
In conventional water flooding, formation water or seawater is usually injected without major changes to its composition. In smart water flooding, the total salinity and the concentration of selected ions are tuned to activate additional mechanisms, such as wettability alteration, which can lead to extra oil recovery compared to conventional water flooding.
Is smart water flooding applicable to carbonate reservoirs?
Smart water flooding was first studied mainly in sandstone reservoirs, where additional oil recoveries of 5–30 % of original oil in place have been reported2. Later laboratory studies and field tests have shown that carefully designed low salinity or smart water injections can also improve oil recovery in carbonate reservoirs, which are often mixed‑wet or oil‑wet.
How are contact angle measurements used in smart water flooding studies?
Contact angle measurements are used to follow changes in wettability caused by different brine compositions. By measuring brine contact angles on oil‑aged rock surfaces, it is possible to see how smart water formulations affect the wetting behavior of the rock. When these measurements are carried out at elevated temperatures and pressures, they can better mimic reservoir conditions and provide more relevant information for EOR design.
Learn more: Measuring wettability and interfacial tension for EOR optimization
If you would like to hear more about how temperature and pressure can be taken into account in contact angle and interfacial tension measurements for EOR studies, you are welcome to join our free webinar “Measuring wettability and interfacial tension for EOR optimization”.
In this 60‑minute session on May 12, 2026, Susanna Laurén from Biolin Scientific walks through how wettability and interfacial tension are measured under relevant conditions and shows examples of how laboratory results can be used in enhanced oil recovery optimization.
