For chemical enhanced oil recovery in high temperature, high salinity (HTHS) reservoirs, the development of surfactant faces great technical challenges. Conventional surfactants industrially applied such as heavy alkyl benzyl sulfonate, petroleum sulfonate, and polyoxyethylene ether are excluded due to poor properties in high salinity or high temperature conditions. Heat tolerant and salt resistant criteria dramatically narrow the screening window and make it very difficult to obtain a suitable surfactant candidate. On the other side, for reservoirs with low to medium salinity, it is not easy to find suitable surfactants either. Less of salts in solution needs surfactant having higher interfacial activity to attain ultralow interfacial tension (i.e. IFT, 10−3 mN/m magnitude).

In this study, two betaine surfactants, amidobetaine and etherbetaine were developed from long chain fatty acid and alcohol. Properties with respect to long term thermal stability, salt resistance, interfacial activity were evaluated. Besides, the synergistic effect of combined surfactants were also studied. After that, core flooding tests were conducted to evaluate the performance of the concerned betaine/polymer SP formulation.

The prepared betaine surfactants showed high interfacial activity with several crude oil, reaching ultralow IFT within surfactant concentration range of 0.05%-0.30%. For amidobetaine surfactant, excellent salt resistant property was observed at salinity as high as 200,000 mg/L. Sound stability of betaine solutions at high temperature, high salinity conditions were observed within 90 days aging test. In addition, the combined amidobetaine and conventional long-chain betaine/gemini surfactant demonstrated positive synergistic effect at low salinities. Moreover, amidobetaine surfactant showed remarkable viscosifying capability, displaying mobility control potential. Core flooding tests of binary amidobetaine/polymer formulation showed an average incremental oil recovery of around 17%.

The developed betaine surfactants provide good chemical candidates for CEOR in HTHS reservoirs.

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