Study on the Synergistic Effects between Petroleum Sulfonate and a Nonionic–Anionic Surfactant for Enhanced Oil Recovery

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.

Synthesis and Properties Evaluation of Sodium Fatty Alcohol Polyoxyethylene Ether Sulfonate

Sodium salts of fatty alcohol polyoxyethylene ether sulfonates with different length of hydrophobic chain (CnE3SO3, n +; 14, 16, 18) were synthesized from sodium isethionate, then the structure was verified by IR. The temperature resistance, calcium-tolerant stability and salt tolerance were evaluated by pyrogenetic decomposition, phase separation and middle phase emulsion respectively. In addition the mixture of CnE3SO3 and heavy alkylbenzene sulfonate (HABS) was studied. The results showed that: (1) CnE3SO3 was very stable at 150°C especially in neutral, weak acid and weak alkaline conditions; (2) CnE3SO3 performed a good salt tolerance and have a rank of C18E3SO3 > C16 E3SO3 > C14E3SO3; (3) the calcium-tolerant stability of CnE3SO3 reached 8700 mg/L, 9500 mg/L and 10000 mg/L respectively; (4) CnE3SO3 was very good for improving the salt tolerance of mixture of CnE3SO3 and HABS. C18E3SO3 was the best in mixtures of Daqing crude oil/water containing C18E3SO3 and HABS in a ratio of ω(C18E3SO3):ω(HABS) = 3:7 and showed the strongest synergistic effect. The interfacial tension in the system Daqing crude oil/water reached a minimum in the order of 10–3 mN/m and was always below 10–2 mN/m for cNaCl from 0 to 15000 mg/L.