Low Salinity Waterflood in Combination with Surfactant/Polymer; Effect of Surfactant Slug Size

Abstract

In last years, there has been a growing interest in the effect of reducing salinity of injected water in oil recovery. Many studies have showed that low salinity waterflooding is a promising method that can lead to a significant reduction in residual oil saturation compared to traditional waterflooding. The mechanisms behind improved oil recovery by low salinity waterflooding are not fully understood, but many researchers have claimed wettability alteration. In this study, the effect of low salinity waterflooding on improving oil recovery is investigated in six Berea sandstone cores. In addition a combined low salinity and surfactant- polymer slugs injection were carried out in tertiary mode to determine and optimize its effectiveness in increasing oil production. The results of this study indicated that the performance of low salinity waterflooding was affected by wettability of the cores. Thus, investigating the potential of increasing oil recovery by low salinity waterflooding requires establishing initial reservoir wettability state (non-waterwet). The tertiary low salinity surfactant-polymer slugs injection showed an increased in oil recovery with increasing size of surfactant slug injected at constant surfactant concentration. The wettability of the cores had impact on the efficiency of the slugs injected on oil recovery. A low salinity polymer slug injected at the end with higher concentration resulted in producing additional oil from the cores. However the performance of this injection varied due to different residual oil saturation obtained after tertiary low salinity surfactant and polymer slugs injection.