Low Salinity Oil Recovery - an Experimental Investigation

The idea of injecting low salinity water into a petroleum reservoir is not novel and was often used in the 70’s prior to the injection of surfactant. Yet, recently it was shown that simply injecting sufficiently low salinity water improves oil recovery (LoSalTM). Many possible mechanisms concerning Low salinity waterflood have been proposed in the literature. This paper describes an experimental investigation into some of the factors controlling the increased oil recovery observed when low salinity brine is injected into oil saturated reservoir core samples. Extensive chemical analyses were performed on the effluent showing the extent of interaction between the injected brine, the oil and the rock matrix. Introduction: It has been 10 years since Yildiz and Morrow [1] pushed forward the research started by Jadhunandan [2-4] and published their paper on the influence of brine composition on oil recovery which showed that changes in injection brine composition can improve recovery. Since then Tang & Morrow [5] progressed the research on the impact of brine salinity on oil recovery, followed by other researchers such as Webb et al. and McGuire et al. [3], which carried out an extensive research programme on low salinity injection (LoSalTM). This programme included numerous core floods at ambient and reservoir condition (Temperature and Pressure, with live fluid) both in secondary and tertiary mode, single well tracer tests and log inject log, which resulted in a series of publications [6-8] and the registration of the LoSal EOR process trademark. Numerous hypotheses have been devised to explain the increase in oil production associated with low salinity water injection, including increasing pH leading to In-situ saponification and interfacial tension reduction, emulsion formation, clay migration, and wettability alteration. In this paper the fines migration and pH increase mechanism are reviewed and discussed in the light of new data obtained during ambient and reservoir condition low salinity floods. Also a new mechanism based on the extended DLVO theory and cation exchange is discussed. * Corresponding author, [email protected]