Role of Acid Components and Asphaltenes in Wyoming Water-in-Crude Oil Emulsions

Two classes of stabilizing oil components in water-in-crude oil emulsions for three oils from the state of Wyoming are investigated in this paper. The associated contributions appear to be different for each crude oil. Given the molecular complexity of crude oils and their properties, more than one oil component is thought to contribute to emulsion stability and we speculate that stability is the outcome of competing materials adsorption on water-oil interfaces, in addition to interfacial and bulk rheology. The presence of emulsion-stabilizing acids and their complexes, presumed here to be naphthenic acids for at least one of the crude oils used here, is claimed to stabilize water-in-crude oil emulsions. The presence of acids is inferred from pH changes of the resolved water fraction obtained in centrifuge-bottle tests, as well as in partition tests. The oil wash test, in which oil obtained after emulsification is reused to generate new water-in-crude oil emulsions, is used here to elucidate the role of the water-insoluble fraction. The effect of di- and monovalent cations in solution on emulsion stability is compared for two oils. Results show that stability improves when the aqueous phase contains calcium ions only in contrast with solutions containing sodium ions exclusively at the same ionic strength.