Enhanced Oil Recovery by Low Salinity Water Flooding Based on Wettability Change
Low salinity water injection refers to the injection of water with low ion concentration into the reservoir.Usually,the salinity of the injected water is less than 5000 mg·L-1.A large number of laboratory experiments and a small amount of field tests have confirmed that low-salt water flooding can improve the recovery of sandstone and carbonate reservoirs.In this paper,the wetting angle test of rock slices was carried out,the results showed that low salinity brine could change the wettability of rock surface,which was not only related to the salinity of brine,but also related to the ionic composition of brine and the composition of crude oil.Core displacement experiments with different salinity brines showed that reducing the salinity of the injected water could improve the ultimate recovery of the core,and under the same salinity conditions,the ultimate recovery of the core could be further improved by optimizing the ion composition of the injected water,indicating that low salinity water flooding has great potential for oil production.During the displacement experiment,the pressure difference between the two ends of the core and the pH value of the fluid at the outlet end were the intuitive phenomena of the change of rock wettability.The double layer diffusion and multi ion exchange were the dominant mechanisms of the change of core wettability.
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