Enhanced oil recovery by Smart Water injection in sandstone reservoirs

Extensive experimental research in recent decades has shown that oil recovery by waterflooding of oil-saturated sandstone core plugs is highly influenced by the composition of the water injected. It has been observed that injection brines with low salinity (LS) have shown beneficial effects on oil recovery, and it is believed that the extra oil is recovered because of wettability alteration toward more water-wet conditions. LS water is therefore a Smart Water in sandstones. In this chapter, Smart Water injection into sandstone reservoirs will be introduced and discussed—from a chemical point of view. Oil recovery by wettability alteration is dependent on initial wettability; thus factors and processes affecting the initial wettability of sandstone rocks are highlighted first. Then, Smart Water enhanced oil recovery effects are demonstrated in both outcrop and reservoir rocks, and it can be seen that capillary forces are important for displacing the oil from the heterogeneous porous media by Smart Water injection.