Abstract:

To enhance the low oil production rate in low-permeability reservoir development, the nanoemulsion based on rhamnolipid was prepared by diluting the microemulsion. The effects of the mass ratio of surfactant to cosurfactant （K_m）, temperature, and inorganic salts on the pseudo-ternary phase diagram and the droplet diameter were studied. Finally, the oil displacement efficiency of the nanoemulsion was evaluated. The results show that the area of the monophase microemulsion zone is first increased and then decreased with the increase of K_m. The area of the monophase microemulsion zone reaches a maximum at K_m=3. With the increase of temperature, the area of the monophase microemulsion zone is also first increased and then decreased. The maximum area of the monophase microemulsion zone is observed at 323.15 K. The area of the monophase microemulsion zone is increased with the concentrations of NaCl and CaCl₂. The addition of inorganic salts has reduced the critical micelle concentration of rhamnolipid and thus increased the miscibility of oil and water phases. When the mass fraction of water is lower than 80%, the droplet diameter is slightly increased with the increase of the storage time. In addition, the nanoemulsion shows excellent temperature and salt resistance. Core displacement experiment shows that nanoemulsion flooding can decrease the injection pressure of water flooding and can improve the recovery by 17%. Therefore, the nanoemulsion has the potential in enhancing oil recovery of low-permeability reservoirs.

Key words: nanoemulsion, rhamnolipid, enhanced oil recovery, pseudo-ternary phase diagram