Properties of Crude Oil-in-Water and Water-in-Crude Oil Emulsions: A Critical Review

Water and crude oil emulsions can be produced during oilfield operations. Since most oilfields are in the secondary or tertiary recovery stages, the amount of produced water is not negligible. Furthermore, enhanced oil recovery makes use of surfactants injection (chemical substances that lower the surface tension of the liquid) and polymer flooding (polymers are large molecules, composed of repeating blocks bounded together, which are injected to decrease the water–oil mobility ratio), leading to increased emulsion problems. Knowledge of fluid petrochemical properties and behavior is fundamental for designing the production system, transport infrastructures, and refinery layout. Depending on the fluid composition, the flow rate, and the PVT conditions, different physical behaviors and flow patterns will occur. Even though significant effort has been carried out to take a broader view of liquid–liquid models, there is a wide range of correlations to consider with different crude oil compositions and diverse field conditions. In this work, a critical review was carried out to assess the main principles that affect an emulsion, how the flow patterns are influenced by the water fraction, which equations can be used to estimate the main physical properties, and last what are the methods or techniques for identifying or characterizing an emulsion. As a result, a strong background in this matter is offered, and future research directions are synthesized.