Salt SpheresInorganic Structures Isolated from Petroleum-Based Emulsions

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.