Impact of cation type and concentration in injected brine on oil recovery in sandstone reservoirs

This work contributes to the understandings of the impacts of double layer expansion on oil recovery during waterflooding. Zeta potential results showed that Na+ changes the electrical charge at both oil/brine and rock/brine interfaces to highly negative, which results in higher repulsive forces between the two interfaces, and hence wettability alteration. Moreover, waterflood experiments with NaCl solutions improved oil recovery significantly compared to CaCl2 and MgCl2. These results showed that there seems to be a correlation between zeta-potential and oil recovery which implies that double-layer expansion could be a primary mechanism of oil recovery by low salinity waterflood. This study demonstrates that cation type has a significant impact on oil recovery, and it could be more dominant than the effect of total salinity of the injected brines. These findings can help in screening the brines that have higher potentials for oil recovery improvement.