The characterization of water-in-crude-oil emulsions can be more challenging than resolving such emulsions. In production, achieving dry crude oil and clean water is a key requirement for uninterrupted operation. Minimizing the buildup of unresolved emulsion at the oil-water interface is another closely related element in the overall process of demulsification. Most oilfield emulsions are never completely resolved before being sent downstream for refining. For example, Karl Fisher measurements always show some water present in the oil phase. Investigations were performed to probe select features of unresolved emulsions. Using the American Society for Testing and Materials D4807-88 procedure, which involves diluting samples with hot toluene, emulsion solids were isolated and then studied using scanning electron microscopy and energy dispersive spectrometry. The characterization of the solids from several different oilfield emulsions revealed interesting structures that might be called "salt spheres" or "salt scaffolds". These skeletal structures appear to outline once existent water droplets. In one case study, partly flocculated or coalesced salt structures were identified. The occurrence of these more complex structures gives the impression that the demulsification process was frozen in time. In another study, a partially filled salt sphere was isolated. Such a structure would likely remain with the crude oil in downstream processing as undesaltable solids and cause corrosion in the high-temperature process vessels as well as contribute to the poisoning of catalyst beds. It is not clear whether these inorganic artifacts contributed to the stability of the original emulsion or resulted from the lab isolation method. Nonetheless, the existence of these intriguing structures provides indirect evidence regarding the importance of solids in stabilizing emulsions.

A number of factors are known to contribute to and enhance water-in-crude oil emulsion stability. Organic-based and naturally occurring materials (e.g., asphaltenes, resins, naphthenic acids, waxes, etc.) have received a great deal of attention regarding their role in stabilizing and, at times, destabilizing petroleum-based emulsions. While these materials are known to reside at the oil−water interface, inorganic constituents are likewise known to contribute to emulsion stability and have been shown to also reside at the oil−water interface. To study the inorganic components in unresolved oilfield emulsions, numerous field samples were subjected to the American Society for Testing and Materials D4807-88 procedure that involves a hot toluene filtration. This method effectively removes the organic phase and isolates the inorganic components that may have also played a role in emulsion stabilization. The residual inorganic residues were initially characterized by a combination of scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS). Following up on the initial report where several samples contained highly organized inorganic structures, called salt spheres or salt scaffolds, this study takes a closer look into their compositional makeup using enhanced EDS capability with the addition of digital compositional mapping (DCM). Salts with low solubility-product constants appear to outline once existent water-in-crude oil droplets and, thus, may have played a key role in emulsion stabilization. Sodium chloride crystals often dominate the interior of these structures, and it is this entity that upon further examination was found to be unstable with regard to prolonged exposure to humidity. In comparison to dry or treated sales oils, inorganic solid levels from the oil−water interface of two oilfield separators were found to be considerably higher, with one of the samples containing an abundance of well-defined salt spheres. By use of the DCM technique, the separator sample was shown to contain salt spheres with an outer coating of strontium sulfate.

Production of crude oil is generally accompanied by several other product phases, namely water, gas and solids. Pressure drops across chokes, concomitant gas evolution (due to pressure drops) and turbulence caused by various pipeline configurations can create difficult-to-resolve emulsions. Natural crude oil surfactants and solids exacerbate the problem further by migrating to the newly created oil-water interface and stabilizing the unwanted emulsions. Once the fluids arrive at the production facilities, a variety of vessels are employed to separate the oil, gas and water. Depending on the wettability of the solids, they will exit via one or both of the liquid phases. In a worse case scenario, the solids will accumulate at the oil-water interface.

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