Role of asphaltenes in stabilisation of water in crude oil emulsions

Abstract

Even though asphaltenes do not have the well‐defined amphiphilic structure characteristic of surfactants, it has been shown that they can stabilise water‐in‐oil emulsions. We propose that this stabilisation occurs because asphaltene aggregation results in the formation of a network within the thin oil film separating approaching emulsified water droplets. This network changes the rheology of the film to non‐Newtonian, which prevents drainage of the film at thicknesses less than about 50–100 nm. The presence of the network also imparts steric stabilisation to the emulsion. The proposed stabilisation mechanism does not invoke any surfactant‐like behaviour of asphaltenes. Instead, it relies solely on their propensity to aggregate.

Effect of Asphaltene Aggregation on Rheological Properties of Diluted Athabasca Bitumen

“…We did not observe formation of precipitates for 40 wt.% solutions and apparent sediment was formed at the bottom of vials for 5 and 11 wt.% solutions. This observation agrees with previously reported value for critical S/B ratio in case of heptol (80:20) S/B ratio 11,18,21,27. As the initial precipitates formed in the solution at bitumen…”

“…11,18,21,27 Such non-Newtonian behavior of the film liquid was proposed to be a new mechanism for stabilization of water in oil emulsions. The experiments that showed such non-Newtonian behavior were performed for a similar system and concentrations as the system studied in this work.…”

Fractionation of Asphaltenes in Understanding Their Role in Petroleum Emulsion Stability and Fouling

“…It was reported that rather than whole asphaltenes, only a subfraction of asphaltenes is more likely the real contributor to the stabilization of W/O emulsions. 26,[80][81][82][83][84][85][86] The asphaltenes adsorbed onto clays have also been found to be different in composition from whole asphaltenes. 70,[75][76][77] Therefore, it is important to find ways to extract and study these particular species from asphaltenes, which are mainly responsible for the relevant issues of interest.…”

Asphaltene Subfractions Responsible for Stabilizing Water-in-Crude Oil Emulsions. Part 1: Interfacial Behaviors

“…It was suggested that the interfacial rigidity is due to the crosslinking of asphaltene aggregates. 3,13,14 Recently, Czarnecki et al [15][16][17] argued that the general belief that the whole asphaltene fraction is responsible for emulsion stabilization, and the wide use of SARA terminology 18 in the emulsion stability context are in fact impeding the progress in understanding petroleum emulsions stability. These authors suggested that "only a small fraction of asphaltenes are in fact involved in the emulsion stabilization".…”