Synergetic effect of resins and asphaltenes on water/oil interfacial properties and emulsion stability

It is widely concerned that the adsorbed natural surface-active components at the interface between crude oil and produced water form a protective layer to prevent emulsion from instability. Asphaltenes and resins are considered to perform significant roles among these natural surface-active components in the crude oil. This study deals with the effect of the interactions between asphaltenes and resins on water/oil interfacial properties and emulsion stability. Firstly, the dynamic surface pressure of asphaltenes and resins are obtained with the shape analysis method of pendant droplet, respectively. A synergetic effect of asphaltenes and resins is confirmed by comparing the dynamic surface pressure of the binary system with that of the single system. The addition of resins enhances the interfacial affinity of asphaltenes at the beginning of the adsorption. Asphaltenes have stronger influence than resins in the long-term adsorption. Then, the dilational modulus is measured with the method of interfacial small-amplitude oscillation. The addition of resins reduces the dilational modulus, weakening the structural strength of interfacial layer. Conductivity experiments are carried out to determine the dispersed state of asphaltenes. Due to the synergetic effect of asphaltenes and resins, adding resins motivates the dispersal of asphaltenes, thus changing the turning point of conductivity to higher proportion of n-heptane. At last, emulsion stability experiments are performed to back up the synergetic effect occurred at the interface. The addition of resins increases the stability of emulsion at initial time. However, the emulsion stability is deteriorated when the resins are excessive. Similar to the adsorption phenomenon at the interface, resins have slighter impacts on emulsion stability in the long term. Asphaltenes still possess a dominated position in determining the emulsion stability.