Molecular origins of crude oil interfacial activity part 3: Characterization of the complex fluid rag layer formed at crude oil-water interfaces

Rag layers formed at crude oil-water interfaces are micro-heterogeneous complex fluids. The continuous phase of the complex fluid rag layer is the crude oil. Dispersed in this continuous crude oil phase are water, solids, and a second dense oil phase. Water-in-oil emulsions, solids-in-oil dispersions, oil-in-oil dispersions, and oil-in-water-in-oil multiple emulsions coexist in the continuous oil phase of the complex fluid rag layer. Higher concentrations of sulfur, nitrogen, metals, and Conradson carbon (CCR) in the complex fluid rag layer compared to the bulk crude oil indicate that the most surface-active of the asphaltene phases separates into the rag layer. A higher concentration of naphthenic acids in the complex fluid rag layer compared to the bulk crude oil indicates the preferential partitioning of the most surface-active naphthenic acids in the complex fluid rag layer. Asphaltenes and naphthenic acids stabilize the water and solids in the crude oil continuous phase of the rag layer to result in a complex fluid rag layer.