Further Investigations into the Nature of Salt Spheres and Inorganic Structures at the Crude Oil−Water Interface

• Published in: Energy & fuels 2010-04, Vol.24 (4), p.2376-2382
• Main Authors: Cloud, Richard W, Marsh, Samuel C, Linares-Samaniego, Sandra, Poindexter, Michael K
• Format: Article
• Language: English
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/ef901063e

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.