“Smart Water” as Wettability Modifier in Carbonate and Sandstone

Waterflooding has for a long time been regarded as a secondary oil recovery method. In the recent years,<br>extensive research on crude oil, brine, rock (COBR) systems has documented that the composition of the<br>injected water can change wetting properties of the reservoir during a waterflood in a favorable way to<br>improve oil recovery. Thus, injection of Smart Water with a correct composition and salinity can act as a<br>tertiary recovery method. Economically, it is, however, important to perform a water flood at an optimum<br>condition in a secondary process. Examples of Smart Water injection in carbonates and sandstones are:<br>Injection of seawater into high temperature chalk reservoirs<br>Low Salinity floods in sandstone reservoirs<br>The chemical mechanism behind the wettability alteration promoted by the injected water has been a topic<br>for discussion both in carbonates and especially in sandstones. In this paper, the suggested mechanisms for<br>the wettability modification in the two types of reservoir rocks are shortly reviewed with a special focus on<br>possible chemical similarities. The different chemical bonding mechanisms of polar components from the<br>crude oil onto the positively charged carbonate and the negatively charged quartz/clay indicates a different<br>chemical mechanism for wettability modification by Smart Water in the two cases.