부산대학교 도서관

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 oil/brine/rock interface. Since the chemistry of brine largely depends on the ionic composition. Thus, in this work, attention was placed on the roles of individual ion 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 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 droplet 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 emphasizes the roles of individual ion at the interfaces and oil water flow patterns in porous media.