Influence of Individual Ions on Oil/Brine/Rock Interfacial Interactions and Oil-Water Flow Behaviors in Porous Media

The low salinity effect (LSE) in enhanced oil recovery (EOR) is widely accepted. However, its underlying mechanisms remain unclear due in part to the complex interactions at the oil/brine/rock interface. The chemistry of brine largely depends on the ionic composition. Thus, in this work, attention was placed on the roles of individual ions and salinity in LSE through direct measurements of oil/brine/rock interfacial behaviors, oil displacement efficiencies, and oil-water relative permeability in sandstone porous media. The results showed that the oil/water interfacial tensions (IFTs) were weakly dependent on ion and the lowest IFTs were generated at the salinities of 0.2-0.5 wt %. In contrast, the interfacial dilational modulus varied significantly with ion types and salinities due to the adsorption of polar components at the oil/water interface. Moreover, wettability alteration of the sandstone surface was found to be associated with the divalent ions in our work. As a result of the viscoelastic interfaces, the breakage of oil column into oil droplets or ganglia was delayed, which subsequently led to the improvement of the oil water relative permeability and oil displacement efficiencies. Based on the analysis, it was concluded that HCO3-, Mg2+, and SO42- were potential-determining ions (PDIs) in LSE. The results of the tests, to our knowledge, are the first that particularly emphasize the roles of individual ions at the interfaces and oil water flow patterns in porous media.