Probing Interfacial Water-in-Crude Oil Emulsion Stability Controls Using Electrorheology

The stability of water-in-oil emulsions is controlled by several interfacial mechanisms that include the oil film rheology between approaching drops and the resistance to rupture of drop interfaces or a combination of these two interfacial controls. Film drainage is mainly a function of the continuous phase rheology. Temperature is regulated to control the viscosity of the continuous phase and, hence, determine its effect on emulsion stability through film drainage, in contrast with interracial resistance to rupture. In this study, one crude oil is used to formulate water-in-oil emulsions. Oil-water interfacial tensions are measured to gauge other interfacial changes with temperature. The influence of cation type in the aqueous phase, which have been determined to affect emulsion stability, is examined by comparing the stability of emulsions made with either purely monovalent or divalent aqueous solutions with the same overall ionic strength. Divalent cations in water contribute to form stronger emulsions than those produced with purely monovalent aqueous phase. The critical field value, used as proxy of emulsion stability, approaches a plateau value for NaCl emulsions and slowly decreases for CaCl2, at sufficiently high temperature (50 degrees C), which is interpreted here to reflect the intrinsic drop-coating film resistance to coalescence. Interfacial tension does not vary significantly with either aqueous phase composition or temperature. From the comparison with previous results using a less asphaltic oil, it is speculated that the drop coating film is composed of a fraction of asphaltenes, for the crude oil studied here.