Coreflooding Oil Displacements With Low Salinity Brine

Waterflooding is applied worldwide to improve oil recovery. Evidence of enhancement in waterflood efficiency by injecting low salinity brine has been observed in the laboratory and in the field. The technology is of considerable interest because of its simplicity and its low cost. In this work, laboratory corefloods were conducted to study the effect of low salinity waterflooding on oil recovery rate, residual oil saturation and relative permeability. Evidence of low salinity enhanced oil recovery was observed some of these corefloods. Improved oil recovery was generally accompanied by an increase in water-wetness, based on an observed decrease in end-point water relative permeability and an increase in end-point oil relative permeability. Injecting low salinity brine produced a persistent wettability alteration that eliminated oil recovery salinity dependence in subsequent floods. However, the sensitivity to salinity was restored by re-aging the core with the same oil. Tertiary low salinity recovery reported by other researchers was never observed. Low salinity waterflooding produced no oil recovery benefit in cores that were initially strongly water-wet. Based on these results, a working hypothesis is that injecting low salinity brine induces a wettability alteration from mixed-wet to water-wet in some cores and that this change improves the oil recovery. More experiments are needed both to identify the characteristics of the cores that are favorable for low salinity enhanced oil recovery and to better understand and quantify the mechanism.