Interfacial materials and naphthenic acids from Brazilian crude oils: Colloidal characterization and water-in-oil emulsions

Abstract

Different Brazilian crude oils form stable emulsions, although they have low asphaltenes content. The present study aimed to extract and characterize interfacial materials (IMs) from these oils to understand the factors driving this phenomenon. Polarized microscopy and small-angle X-ray scattering (SAXS) revealed that IMs can self-organize in certain conditions, and the formed aggregates could be related to the emulsification process. IMs promoted the formation of model emulsions of mineral oil and brine, but they were not enough to keep them stable. The original and residual oils from the extraction were also used to form emulsions with brine. SAXS, rheology, time-domain nuclear magnetic resonance (TD-NMR), and interfacial tension measurements allowed the comparison of these emulsions. Removal of IMs promoted self-organization of aggregates present in the oil, increasing the viscosity and stability of the emulsions. One of the crude oils had a significant content of naphthenic acids (NAs), which are known to behave as surfactants in some conditions. This fraction was also investigated, but it did not significantly affect the physicochemical properties of the emulsions in comparison with IMs. Hence, the aggregates formed by IMs combined with other components of the crude oils were probably responsible for the rheological properties affecting stability.