Abstract
Nonionic–anionic surfactants are expected to be applied in chemical flooding due to their important properties such as ultralow IFT values, good salt tolerance, and no chromatographic separation in porous media. In this study, a new type of nonionic–anionic–hydrophobic group structure surfactant N, N-dihydroxyethylalkylamide carboxylate (EAMC) was synthesized. The synergistic effects between petroleum sulfonate (KPS) and EAMC in reducing interfacial tension (IFT) and emulsification properties were studied. The influences of salt, alkali and Ca2+ on the IFTs of surfactant solutions were also investigated. One-dimensional core flooding experiments were used to characterize the enhanced oil recovery capability of the KPS and EAMC mixed system. The experimental results show that both EAMC and KPS have high interfacial activity and can reduce IFTs to about 0.01 mN/m order of magnitude against decane at optimized concentrations. The area occupied by the hydrophilic group of EAMC on the interface is smaller than that of its own hydrophobic group. The interfacial film formed by EAMC alone is relatively loose. The IFTs of KPS containing different structure petroleum sulfonates is affected by the difference in the adsorption rate of petroleum sulfonates on the interface, which shows that both the dynamic and equilibrium interfacial tensions can have the lowest values. However, the IFTs of the EAMC solutions against crude oil can be reduced to ultralow values because the mixed tight adsorption film is formed by EAMC and crude oil fraction molecules with synergistic effect. On the other hand, the KPS molecule has a hydrophobic part with large size and no synergism with crude oil fractions can be observed in the solutions containing only KPS. The combination of EAMC and KPS shows synergistic effect, namely ultralow IFT values, good emulsification properties, high alkali tolerance, and good salt and Ca2+ tolerance during a wide percentage range of EAMC. The best formula of EAMC and KPS system can be applied for EOR after polymer flooding. The studies in this paper are helpful for the design and application of a chemical flooding formula with nonionic–anionic–hydrophobic group structure surfactants.
Highlights
After the traditional primary and secondary methods of oil recovery, there are still two-thirds of crude oil left in an oilfield reservoir [1,2]
Alkali flooding is an effective way to enhance oil recovery, especially for crude oil reservoirs containing petroleum acids, because the reaction of the alkaline solution with the organic acids in the crude oil and the generation of surfaceactive species, called in-situ surfactant, at the interface result in a remarkable decrease in interfacial tension (IFT) [7,8,9,10]
The reduction of IFT depends on the replacement of molecules of water and oil at the interface by molecules of surfactant
Summary
After the traditional primary and secondary methods of oil recovery, there are still two-thirds of crude oil left in an oilfield reservoir [1,2]. Development of tertiary oil recovery methods employing a chemical substance, such as a surfactant, polymer or alkali, to enhance oil recovery (EOR) will be a significant and promising area of work for energy production over the decades [3]. The efficiency of oil recovery would be greatly enhanced if the IFT value between the displacing aqueous and crude oil attained an ultralow value (
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