Viscosity reduction of extra-heavy oil using toluene in water emulsions

Surfactants are widely used to reduce the viscosity of heavy oil by emulsification, but emulsification of an extra-heavy oil is difficult and does not even occur in some cases. A diluent is effective in reducing the viscosity of extra-heavy oil, but substantial volumes are required. In this work, we combined the advantages of a surfactant solution and a diluent in the form of emulsions to emulsify extra-heavy oil. The toluene/water (T/W) emulsion was prepared with mixed (AES-DOA) surfactants formed from an anionic surfactant (AES, alkyl polyoxyethylene ether sodium sulfate) and a gemini-like surfactant (DOA, prepared by mixing oleic acid and Jeffamine D 230). Compared with using toluene or AES-DOA surfactant solution alone to achieve the desired extra-heavy oil viscosity (30 ± 10 mPa·s), the T/W emulsion decreased toluene and surfactant dosage from 56 to 3 wt% and from 12 to 2 mmol/L, respectively. The effect of toluene and AES-DOA mixed surfactant on emulsification was analyzed by measuring the viscosity of the resultant extra-heavy oil emulsions. The results suggest that the addition of toluene reduced the viscosity of extra-heavy oil (dispersed phase) and accordingly contributed to emulsify extra-heavy oil. The synergistic effect of the AES-DOA mixed surfactants was evaluated by measuring the interfacial tension and calculating interaction parameters (βm) of the mixed surfactants formed at different AES mole fractions. When the mole fraction of AES was 0.6 in the mixture, the mixed surfactant possessed the highest interfacial activity and the largest negative βm, confirming the strongest synergistic effect. As a result, the best emulsification efficiency was achieved at this mole fraction. Increasing toluene content and AES-DOA mixed surfactant concentration was found to increase the emulsion stability against coalescence. The results from this study demonstrate that T/W emulsions prepared using the AES-DOA mixed surfactants can overcome the difficulties in emulsifying the highly viscous extra-heavy oil.