Role of Physicochemical and Interfacial Properties on the Binary Coalescence of Crude Oil Drops in Synthetic Produced Water

An important aspect of efficient treatment of produced water is to promote the coalescence of dispersed oil drops. Therefore, a fundamental understanding of the relations between interfacial and physicochemical properties of crude oils and the coalescence process is essential, and elucidating these relationships was the aim of this investigation. Nine crude oils and fractions of two crude oils, where acids, bases, and asphaltenes were selectively extracted, were included in the studies. The dynamic interfacial tension and interfacial rheology of the oils were followed in synthetic produced water. The binary coalescence of oil drops was followed by a micropipette setup, and characteristic times for three phenomena occurring during the coalescence process were identified: the time of film thinning, the time for rupture of the thin film, and the apparent time of merger of the two drops. Decreasing the density of the crude oils and increasing the strength of the interfacial layer were determined to influence the coalescence process most significantly, by slowing it down. The elasticity and strength of the interfacial layers were primarily associated with the presence of asphaltenes at the interface. The strength of the interfacial layer decreased as the amount of aromatics and acidic components in the crude oil increased. In both cases, this was attributed to improved stability of the asphaltenes in the bulk of the crude oil