Effect of exposure time and crude oil composition on low-salinity water flooding

Rational and systematic approaches to the application of low-salinity water flooding have been slow to develop, due in part to a lack of understanding of the physics concerning oil/brine/rock interactions and uncertainty in assessments of wetting behavior of the rock. This paper provides insight into some of the factors controlling rock wettability during low-salinity water injection. A series of core flood experiments were performed on three crude oil samples with different resin and asphaltene concentrations. Three brine salinities of 122,000, 10,000, and 500 ppm were tested. Oil recovery, upstream pressure, and effluent pH were continuously monitored during the experiments. This study confirms that wettability alteration, during low-salinity water flooding, is sensitive to the heavy fractions of crude oil. Crude oils with a lower concentration of heavy ends are less responsive to low-salinity water injection. Additionally, this study indicates that the desorption of polar components is a time-dependent process, and sufficient exposure time between invaded low-salinity water and an in-situ oil/brine/rock system is required to ensure the complete transition from one wetting state to the next. These results add new experimental evidence to the literature that will assist in understanding the complex mechanism of wettability alteration in low-salinity water flooding. (C) 2016 Elsevier Ltd. All rights reserved.