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 Morrow  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 place . However, several laboratory studies and field tests have confirmed its potential also in carbonate reservoir enhanced oil recovery. There are two main advantages compared to other enhanced oil recovery methods; (1) low cost and (2) less impact on the environment .
Wettability alteration plays an important role
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 can be used to study wettability alteration
To study the wettability alteration caused by low salinity water, contact angle measurements have been utilized . In the study of Ding et. al. , 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 the smart water flooding happens at reservoir conditions, it is important to take that into account when contact angles are measured. To hear how temperature and pressure can also be considered in contact angle measurements, please watch the webinar by Prof. Xu.