The impact of brine salinity and its ionic composition on oil displacement efficiency has been investigated extensively in recent years due to the potential of enhanced oil recovery (EOR). Wettability alterations through relative interactions at the mineral surface have been the basis of proposed mechanisms. The ion specific interaction between fines and polar fractions of crude oil at the oil-water interface has been less explored.

In this study the relative affinity between different ions and the oil surface was determined. The experiments prove the importance of Ca2+, SO42−, and HPO42− ions in enhancing oil emulsion formation by increasing interactions between polar acids and brine solutions. The results propose the potential use of HPO42− ions in reservoirs having inactive mineral surfaces.

The relative oil affinity of different ions including K+, Na+, Mg2+, andCa2+ (cations), and Cl, SO42−, HPO42−, and HCO3 (anions), were studied through gas chromatographic analysis. Crude oil from the North Sea was doped with various fractions of organic acids to mimic different polar behavior. Increased brine concentration showed up to 15% upsurge of polar fractions on the oil-water emulsion formation. During emulsion formation the relative interactions at the oil-water interface are proved to follow the Hofmeister series: K+<Na+<Mg2+<Ca2+. Beyond CaCl2concentrations of 0.08mol/l no additionalacid participation in emulsion formation was observed. Among anions, SO42−and HPO42− showed optimum emulsion formation at 0.05mol/l. The amount of emulsion formation showed significant dependency on the type of acid doped in oil.

Experiments demonstrate that the brine solution can alter the micro forces at the oil-water interface, and this ion specific interaction leads to oil emulsion formation andthus reduces the interfacial viscoelasticity of the trapped oil. These resultsshow significant correlation between oil emulsion formation and increased oil recovery.

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