Functional Molecules and the Stability of Water-in-Crude Oil Emulsions

Abstract

In the production and transportation of crude oil, undesirable water-in-oil emulsions may form. Undesirable water-in-oil emulsions may also form in hydraulic fracking when acid is added to the injection water. We investigate the role of acid–base interactions in the stability of water-in-oil emulsions. Asphaltenes and resins, referred to as functional molecules, constitute the polar fractions of crude oil. They contain heteroatoms such as N, O, and S, which lead to acidic and basic functionalities in petroleum fluids and contribute to the stability of water-in-oil emulsions. We have quantified the acidity and the basicity of nine petroleum fluids (light, medium, heavy, and extra-heavy crude oils) by measuring their total acid number (TAN), total base number (TBN), and hydroxyl number (HN). Except in extra heavy oils where the TAN and TBN are close, all the other oils are basic (i.e., TBN > TAN). We observe that all the light crude oils form stable emulsions with deionized (DI) water, while medium, heavy, ...