Abstract: In view of the unvaried nature of current oil displacement systems and uncertainty about the action of rhamnolipids in oil displacement and oil field development, the mechanisms and performance of rhamnolipids in oil displacement were investigated in the present study. Fermentation broths consisting primarily of two types of biosurfactants, viz. mono-rhamnolipids and di-rhamnolipids, were obtained via indoor fermentation, and the interfacial performance, wettability, oil washing efficiency, and oil displacement efficiency of the fermentation broths were assessed. The rhamnolipid fermentation broths were highly resistant to heat and salt, and the interfacial tensions between the 1% fermentation broths and crude oil were 0.2~0.5 mN/m. Assessments of the wettability and oil washing efficiency of the fermentation broths showed that di-rhamnolipids resulted in a greater improvement in wettability and achieved an oil washing efficiency of 90.1%, an increase of 15% compared to that of the mono-rhamnolipids. It was found that rhamnolipids could reduce the work of adhesion between crude oil and the substrate from 30.2 mN/m to a minimum of 0.059 8 mN/m (achieved with di-rhamnolipids), and that this was a key factor in the enhancement of oil washing efficiency by the fermentation broths. Assessment of oil displacement efficiency revealed that the di-rhamnolipid fermentation broth increased the oil displacement efficiency by 12.3% based on a water-oil displacement efficiency of 42.16%, thereby exhibiting great potential for field applications.

Key words: rhamnolipids, fermentation broth, wettability, work of adhesion, oil displacement efficiency