Influence of the Aggregation State of Asphaltenes on Structural Properties of the Model Oil/Brine Interface

Abstract

With the continuous exploitation of heavy oil resources, the stability of heavy oil emulsions and further its demulsification technology are receiving more and more attention. One of the most important elements that affect the stability of heavy oil emulsion is asphaltenes. Under this background, the effect of the aggregation state of asphaltenes on the structure-related properties of the model oil/brine water interface is investigated in this study, and further the relation between the structural properties of the interface and the macroscopic stability of the emulsion is studied. It is observed through the dynamic light scattering experiment that there is an abrupt increase in the particle size of the asphaltene aggregates at the concentration of 100 ppm, indicating the enhancement of the aggregation degree above this concentration. The higher level of aggregation changes the adsorption kinetics of the asphaltenes at the interface, causing a slower descending rate of the diffusion coefficient. Meanwhile, although the interfacial viscoelastic experiment demonstrates that the interfacial dilational modulus is increased with the addition of asphaltenes, the rising trend becomes gentle and the loss angle hardly changes at the concentrations above 100 ppm, indicating that the cross-linked structure in the interfacial film changes slightly with the addition of asphaltenes. In addition, it is found through the interface contraction experiment that no crumpling appears at the interfacial film at concentrations below 100 ppm. At the concentrations above 100 ppm, the crumpling of the interfacial film is observed. However, the contraction and expansion processes are reversible. Finally, it is proven with a bottle test method that there is a positive correlation between the macroscopic stability of the emulsion and the interfacial dilational modulus.