Brine composition and waterflood recovery for selected crude oil/brine/rock systems

For many years, it has been strongly recommended that injection of low salinity brines be avoided because the brine salinity plays an important role in stabilizing the clay particles at the rock surfaces. In general, decrease in the brine salinity tends to decrease clay particle stability. However, the results presented in this thesis show that decrease in brine salinity can result in a large increase in waterflood recovery.; Three kinds crude oil samples, one refined oil sample, three synthetic reservoir brines, and six kinds rocks including a target reservoir sandstone were used for this study. Results showed consistent increase in waterflood recovery with decrease in salinity of injection brine, or connate brine, or both was obtained for a variety of different crude oil/brine/rock systems. Even at residual oil saturation, switching the injection brine to dilute brine can cause an increase in oil recovery by waterflooding.; Change in rock properties with injection of dilute brine were also studied. The effect of mobile clay particles on wetting and waterflood recovery with injection of dilute brine was also investigated. Observed increase in effluent pH indicates that cation exchange occurs between the injected dilute brine and clay. The presence of mobile clay particles appears to play a key role in the increased oil recovery through increase in microscopic displacement efficiency.; The presence of polar components in crude oil, clay particles which are potential mobile, and initial water saturation are also shown to be essential to increase in oil recovery with decrease in brine salinity for both spontaneous imbibition and waterflooding. Using refined oil as the oil phase rather than crude oil; stabilizing the clay particles by firing and acidizing sandstone; or using sandstone initially 100% saturated with crude oil; all cause the oil recovery to be no longer sensitive to decrease in brine salinity. Possible mechanisms for how change in brine composition affect wettability and oil recovery by waterflooding are discussed.