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

Abstract

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.

Influence of the Crude Oil and Water Compositions on the Quality of Synthetic Produced Water

“…The higher water-in-oil emulsion stability for the systems with the lighter crude oils was explained by the high saturate and low aromatic contents in these oils. This can facilitate increased interfacial activity, as well as the aggregation of asphaltenes, resulting in rigid interfacial layers that enhanced the emulsion stability 19,38,40 . It was also argued by other authors that wax particles, often found in light crude oils, can increase the emulsion stability 41 .…”

“…The interfacial activity of components in the crude oils will be affected by these parameters and can lead to increased emulsion stability and problems with separation [17][18] . It has been shown that the interfacial properties can influence the coalescence of oil droplets 19 and the stability of oilin-water emulsions [20][21] . Once in contact with an aqueous phase, water-soluble hydrocarbons in the crude oil will partition into the water phase [22][23][24] , adsorb at the gas-water interfaces and influence the oil removal efficiency by gas flotation [25][26] .…”

Microfluidic tools for studying coalescence of crude oil droplets in produced water

“…Several studies of the coalescence of model oil-in-water drops had been conducted [7][8][9] . Regarding the crude oil systems, the researchers have paid more attention to the coalescence of water drops in the continuous oil phase [10][11][12][13] , leaving the crude oil-in-water systems a relatively unexplored topic [14][15] . In addition, there are hardly any research tools that allow systematically investigating the coalescence of crude oil drops in water.…”

Microfluidic method for determining drop-drop coalescence and contact times in flow

“…Drainage and coalescence time are often used interchangeably, even though some authors divide the coalescence time into drainage and rupture times 8 . In dynamic conditions, however, the value of the rupture time is orders of magnitude lower and the difference between the drainage and coalescence time becomes negligible.…”