Zeta potential in oil-water-carbonate systems and its impact on oil recovery during controlled salinity water-flooding

Abstract

Laboratory experiments and field trials have shown that oil recovery from carbonate reservoirs can be increased by modifying the brine composition injected during recovery in a process termed controlled salinity water-flooding (CSW). However, CSW remains poorly understood and there is no method to predict the optimum CSW composition. This work demonstrates for the first time that improved oil recovery (IOR) during CSW is strongly correlated to changes in zeta potential at both the mineral-water and oil-water interfaces. We report experiments in which IOR during CSW occurs only when the change in brine composition induces a repulsive electrostatic force between the oil-brine and mineral-brine interfaces. The polarity of the zeta potential at both interfaces must be determined when designing the optimum CSW composition. A new experimental method is presented that allows this. Results also show for the first time that the zeta potential at the oil-water interface may be positive at conditions relevant to carbonate reservoirs. A key challenge for any model of CSW is to explain why IOR is not always observed. Here we suggest that failures using the conventional (dilution) approach to CSW may have been caused by a positively charged oil-water interface that had not been identified.

How much would silica nanoparticles enhance the performance of low-salinity water flooding?

“…In this mechanism, negatively charged nanoparticles diffuse around oil droplets lodged on the glass surface. Recalling that the water-oil interface beneath the oil droplet is of negative charge, except at the high pH and ionic strength relevant to the formation brines (Jackson et al 2016) and/or in highly acidic crude oil (Buckley 1999), as a result, repulsion between the interfaces leads to detachment of oil droplets from the surface by nanoparticles, and consequently, wettability changes the glass surface from oil wet toward water wet.…”

 Brine-Dependent Recovery Processes (Smart-Water/Low-Salinity-Water) in Carbonate and Sandstone Petroleum Reservoirs: Review of Laboratory-Field Studies, Interfacial Mechanisms and Modeling Attempts

“…Yousef, et al [183] demonstrated that ζ-potential of the rock-brine interface decreases as the brine salinity decreases and suggested that Ca 2+ ions leave the rock surface in form of mineral dissolution and enter the brine solution to re-establish chemical equilibrium. Jackson, et al [187] correlated improved oil recovery to ζpotential of rock-brine and oil-brine interfaces using a reservoir limestone core, different crude oil and brine solution. The authors concluded that the potential for improved oil recovery by low saline brine injection is increased when both interfaces possess the same polarity (ζ-potential sign), such that the electrostatic repulsive force generated between the interfaces stabilizes the water film on the rock surface.…”

A Surface Complexation Model of Alkaline-SmartWater Electrokinetic Interactions in Carbonates

“…However, the root causes of this wettability alteration effect, which takes place at the pore-level, remain poorly understood especially for carbonates [6]. This lack of fundamental understanding of root causes of wettability alteration has resulted in conflicting studies, where some studies have observed an increase in oil recovery while other cases have not shown an increment in oil recovery [7]. Various pore-scale mechanisms have been proposed to delineate the wettability alteration process in carbonates.…”