Effect of Combined Low Salinity and Surfactant Injection on Oil Recovery in Aged Bentheimer Sandstones at Different Temperatures
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A moderate increase in crude oil recovery by reduction in salinity of the injection brine has been observed for numerous laboratory core flood experiments. The underlying mechanisms behind increased recovery by low salinity injection are not fully understood and are suggested to relate to complex crude oil/rock/brine interactions. Recent studies have also shown a positive effect by combining injection of low salinity brine and surfactant flooding. In this study, core experiments were conducted in four aged Bentheimer cores; two experiments were performed at 23°C and two experiments at 90°C. During low salinity and low salinity surfactant injection pH of the effluent was measured. In addition, density, viscosity and interfacial tension of the fluids injected were analysed. The results show a marginal potential of enhanced oil recovery by low salinity injection (less than 2 %OOIP). No fines or pH variation were observed during low salinity injection. The low potential of low salinity was suggested to be related to the small clay content and insufficient wettability alteration in the Bentheimer sandstone cores. Combination of low salinity and surfactant injection resulted in significant increase in oil recovery (additional 26% OOIP). The effect of temperature gave lower recovery at 90°C. A reduction in pH was also observed, suggesting hydrolysis of the surfactant at elevated temperature. Despite the insignificant response to low salinity brine, a combination with a surfactant may be more beneficial both to increase oil recovery and to be more economically than low salinity brine and surfactant flooding alone.