Experimental study on the key influencing factors of phase inversion and stability of heavy oil emulsion: Asphaltene, resin and petroleum acid

• The key influencing factors of emulsion phase change have been initially clarified. • The effects of asphaltenes, resins and petroleum acids on the stability of emulsions are discussed. • The effects of asphaltenes, resins and petroleum acid on interfacial tension and expansion modulus have been studied. This study investigates the effects of asphaltene, resin and petroleum acid on the phase inversion, stability and oil–water interface characteristics of emulsions. First, different ratios of asphaltene, resin, petroleum acid and formation water were emulsified and the emulsion viscosity was measured to obtain the phase inversion point. Through comparative analysis of phase inversion point data under different conditions, we showed that the synergy of asphaltene and resin was the key to the emulsion phase inversion and the best asphaltene to resin ratio was 1:3. Moreover, the addition of petroleum acid would accelerate the phase inversion. Then, the dynamic interfacial tension of oil and water was measured using the rotating drop method. The synergistic effect of asphaltene and resin would decrease the interfacial tension. However, excessive resin would compete with asphaltene for adsorption, which would increase the interfacial tension. The lowest interfacial value was observed when the mass concentration ratio of asphaltene to resin was. Thus, the addition of petroleum acid significantly reduced the interfacial tension of oil and water. Next, the hanging drop method was employed to measure the interfacial tension of oil and water and the expansion modulus was obtained using the oscillatory drop method. Experimental studies have shown that asphaltene influences the expansion modulus more than resin and the synergistic effect of asphaltene and resin increases the expansion modulus. However, the addition of petroleum acid would decrease the expansion modulus towing to the small molecular weight of petroleum acid. Finally, the emulsion stability was determined using the bottle test method. Experiments showed that the synergistic effect of asphaltene and resin would enhance the emulsion stability. However, the addition of asphaltene played a pivotal role in enhancing the emulsion stability. Further, the addition of petroleum acid would severely destroy the emulsion stability.