Waterflooding has been used for many decades as a way of recovering more oil. Historically, the salinity of the injection water has not been regarded as a key variable in determining the amount of oil recovered. Crude oil/water/rock chemical interactions can lead to large variations in the microscopic displacement efficiency of waterflood. There is increasing evidence, as reported in the literature, that injecting low salinity brines has a significant impact on the amount of oil displaced, but the exact mechanism by which this occurs is an unsettled issue. The main objective of this paper is to determine the effects, advantages, and practicalities of using low salinity waterflood to displace more oil in both carbonates and clastic formations. Another objective is to understand the main mechanisms in low salinity waterflood, and to determine the effects of salinity level on oil recovery.

An extensive literature review is assembled about fluid/rock interactions, wettability alteration, clay hydration, and multi-component ion exchange (MIE), and waterflood experiments using coreflood setup. Seawater injection in carbonate formations has important effect on oil recovery, especially in fractures. The recovery mechanism is completely different in carbonate than in sandstone formations, due to different rock mineralogy, brine concentration and chemistry. Salt content in connate water also plays a role in increasing oil recovery, especially when decreasing the brine salinity. The effect of high, medium, and low salinity brines on lowering the oil-water interfacial tension and/or alter the wettability characteristics of the reservoir rock is discussed. The effects of various salinity brines on reservoir rocks during waterflooding are necessary to recover more oil and that at the end will increase oil recovery.

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