Measurements of zeta potential in intact carbonate samples with application to controlled salinity waterflooding

Laboratory experiments and field trials have shown that oil recovery from carbonate reservoirs can be increased by modifying the brine composition injected during recovery in a process termed controlled salinity water-flooding (CSW). However, CSW remains poorly understood and there is no method to predict the optimum CSW composition. This work demonstrates that improved oil recovery (IOR) during CSW is strongly correlated to changes in zeta potential at both the mineral-brine and oil-brine interfaces. We report experiments in which IOR during CSW occurs only when the change in brine composition induces a repulsive electrostatic force between these interfaces. The polarity of the zeta potential at both interfaces must be determined when designing the optimum CSW composition. Results show that the zeta potential at the oil-water interface may be positive at conditions relevant to carbonate reservoirs and this has a significant impact on the choice of optimum bring composition for CSW. We report new measurements of zeta potential in intact carbonates at reservoir conditions of temperature and brine composition to understand how the zeta potential changes during CSW.