Chemical combination flooding technique (CCF) meets great technical challenges in High temperature, High salinity (HTHS) reservoir. The requirements on thermal stability, salt tolerance, solubility and interfacial activity of surfactant greatly narrow the selection scope of chemical agent. Conventional anionic surfactant heavy alkyl benzyl sulfonate (HABS), petroleum sulfonate (PS) or nonionic surfactant Ninol are not suitable due to drawbacks of solubility and stability.

A novel extended surfactant alkyl polyoxyethylene Ether Sulfate (AES) was developed for CCF in HTHS reservoir. Compatibility with reservoir conditions and other surfactants of prepared AES surfactant were tested. Interfacial activity and phase behavior of related formulations were studied. In addition, the wettability alteration capability of AES was also investigated.

The experimental results demonstrate surfactant AES has very strong salt tolerance capability, showing a clear solution at salinity as high as 200,000 mg/L. As a comparison, conventional surfactants HABS and PS have poor solubility under high salinity environment. The addition of AES in surfactant solution greatly improves solubility of anionic surfactants HABS and PS. At the same time, interfacial tension (IFT) of these combined formulations is also remarkably decreased to ultralow magnitude (10−3 mN/m or lower). Electrolyte screening in oil/water phase behavior test demonstrates gradual transfer of phase type from Winsor I, Winsor III to Winsor II with the increase of salt concentration from 0 to 200,000 mg/L. Contact angle of 0.20% AES solution on modified silicon film decreases with the increase of electrolyte content.

The developed extended sulfate surfactant shows unique advantages under HTHS reservoir. The combined AES and HABS formulation makes it possible for the application of conventional anionic surfactant in HTHS conditions.

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