Thin liquid films in improved oil recovery from low-salinity brine

a r t i c l e i n f o Keywords: Low-salinity Waterflood LSW Brine Double-layer Sandstone Carbonate Film Low-salinity waterflooding is a relatively new method for improved oil recovery that has generated much interest. It is generally believed that low-salinity brine alters the wettability of oil reservoir rocks towards a wetting state that is optimal for recovery. The mechanism(s) by which the wettability alteration occurs is currently an unsettled issue. This paper reviews recent studies on wettability alteration mechanisms that affect the interactions between the brine/oil and brine/rock interfaces of thin brine films that wet the surface of reservoir rocks. Of these mechanisms, we pay particular attention to double-layer expansion, which is closely tied to an increase in the thickness and stability of the thin brine films. Our review examines studies on both sandstones and carbonate rocks. We conclude that the thin-brine-film mechanisms provide a good qualitative, though incomplete, picture of this very complicated problem. We give suggestions for future studies that may help provide a more quantitative and complete understanding of low-salinity waterflooding. Despite society's best efforts towards developing renewable energy sources, more than 70% of the global energy consumption in the coming decades is expected to come from fossil fuels [1]. To meet this high demand, the petroleum research community has continually strived to develop innovative methods for improved oil recovery. One such method that has gained much attention in the past two decades is low-salinity waterflooding (LSW). The improved recovery from LSW is referred to in the literature as the low-salinity effect (LSE). LSW has attracted great interest partly because of its deceptively simple nature. As its name implies, LSW involves the injection of only low-salinity brine. No additional chemicals, which may be costly to the operation, are necessary to observe the LSE, although there have been recent efforts to couple LSW with polymer flooding [2]. Improved recovery has been observed for both secondary-mode LSW, which involves injection of brine into rock saturated with oil, and tertiary-mode LSW, which involves injection of low-salinity brine after the rock has already been flooded in secondary mode with brine of a different composition. Studies on LSW date back to at least the 1940s, although most of the modern work on this topic began in the 1990s [3,4]. Since then, the number of papers on LSW has rapidly increased, especially in the past several years. Based on these studies, …