Interfacial Tension Characteristics of Alkyl Carboxymethyl Betaine Surfactant Dispersed at the Crude Oil/Formation Water Interface

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Abstract
This work aims to investigate the interfacial tension characteristics of alkyl carboxymethyl betaines dispersed at the crude oil/formation water interface. Four alkyl dimethyl carboxymethyl betaines and one alkyl diethyl carboxymethyl betaine were synthesized, then the effects of surfactant molecular structure, crude oil component, and inorganic salt composition of formation water on interfacial tensions were studied systematically. The results show that the synthesized octadecyl diethyl carboxymethyl betaine has the highest interfacial activity and exhibits superior anti-dilution performance. In the presence of polyacrylamide, this betaine also displays good anti-adsorption capability. With respect to crude oil components, the resin component, especially the petroleum acid and alkali components, play important roles in tension reduction. For formation water, its alkaline inorganic salts are crucial to obtain an ultra-low interfacial tension by its saponification effect on petroleum acid. The octadecyl diethyl carboxymethyl betaine also exhibits good temperature and salt resistance, but poor tolerance toward divalent cations owing to the consumption of alkaline inorganic salts. Moreover, it is found that there exists synergism between octadecyl diethyl carboxymethyl betaine and dodecylbenzene sulfonate which can further reduce the interfacial tension. The above findings are conducive to the selection of betaine surfactants in chemical flooding.
Funding Information
  • National Science & Technology Major Project of China (2025ZD1405400)
  • Science & Technology Major Project of PetroChina Company Limited (2023ZZ17YJ04)

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