Investigating the Impact of Crude Oil Solubility on Water-in-Oil Emulsion Stability and Its Relation to Molecular Composition of Crude Oil at the Oil–Water Interface

Abstract

Substantial work in the literature has been devoted to studying emulsion stability caused by specific fractions of crude oil, such as asphaltenes or naphthenic acids. However, emulsion stability issues occur in the field with whole crude oil present and not just fractions. Understanding how all molecules in whole crude oils behave when the solubility parameter is varied could help to answer the question of what makes an emulsion stable from a molecular perspective. This work attempts to address solubility and the molecules that lead to emulsion stability from the whole crude oil perspective. Investigating the specific solubility class of molecules for emulsion stability limits understanding of interactions between different solubility classes, whether competitive or synergistic. In this work, emulsion stability and the composition of the interfacially active crude oil molecules are studied in parallel. Emulsion stability tests were performed with solutions containing different amounts of asphaltenes and having varied solubility parameter (by changing the heptane/toluene ratio). Heavy water extractions were also carried out to isolate crude oil molecules found at the water–crude oil interface. The separation of molecules is not related specifically to a solubility class or other chemical fractionation method. The separation is based on the molecular capability to form a stable emulsion and adhere to the water–oil interface. Crude oils separated from different heptol ratios exhibit both physical and chemical differences between one another, and compositions are compared to both whole crude oil and n -heptane asphaltenes.