This study bridges a knowledge gap in oil recovery mechanisms by investigating the influence of water salinity and ion type on oil displacement within porous media, under dynamic flow conditions. Micromodel waterflooding experiments with MgCl2 and Na2SO4 brines at varying ionic strengths (i.e., 0.00832 and 0.832 M), revealed that the high salinity brines considerably boost oil recovery, compared to the low salinity ones. As an instance for MgCl2, the low salinity brine (0.00832 M) resulted in 23% final recovery (one third of which occurred after breakthrough time), while the high salinity one (0.832 M) resulted in 38.5% final recovery (half of which occurred after breakthrough time). High-salinity solutions not only suppressed fingering, observed with low-salinity brines; but also facilitated the formation of stable water-in-oil emulsions, as observed by microscopic images. These emulsions exhibited increased rigidity and elasticity of the interfacial layer, promoting broader fluid distribution within the porous media. Lowering interfacial tension (IFT) – as evidenced by 10–20 % reduction in IFT by increasing brine\\\'s salinity - as well as enhancing interfacial viscoelasticity and water-oil emulsion stability were also recognized as the main mechanisms which ultimately led to improved oil displacements at higher salinities.

Keywords