Effect of Asphaltenes on the Stability of Water in Crude Oil Emulsions

The presence of asphaltene, especially in heavy crude oil, causes difficulties in the de-watering/desalting process, which is the initial step of crude oil pretreatment. This study investigates the effect of asphaltenes on the stability of crude oil emulsions using a simulated oil system composed of toluene and n-heptane. It was found that asphaltenes behave like conventional surfactants, adsorbing at the oil-water interface and reducing interfacial tension. The critical aggregation concentration (CAC) of W/O emulsions formed from a toluene and n-heptane mixture (7:3 volume ratio) was found to be 0.05 g/L. When the asphaltene concentration was greater than CAC, the asphaltene aggregated into clusters, forming a viscoelastic interface film that enhanced the strength of the emulsion droplets. At an asphaltene concentration of 0.01 g/L, the storage modulus (G ') and loss modulus (G '') were 1.12 Pa<middle dot>s and 8.94 Pa<middle dot>s, respectively. The storage modulus G ' was less than the loss modulus G '', indicating that the viscoelastic nature of the emulsion, and both the G ' and G '' of the emulsions increased with the increasing asphaltene concentration. When the concentration reached 11 g/L, G ' and G '' were 1033 Pa<middle dot>s and 416 Pa<middle dot>s, respectively, with G ' exceeding G '', indicating that the emulsion became more stable. Moreover, increasing the solvent aromaticity led to a rise in the CAC of asphaltene, which was favorable for breaking emulsions. The findings imply that reducing the asphaltene content at the interfaces of oil-water by adding an aromatic solvent or blending with light crude oil is a feasible way to break the emulsion and further dewater and desalt.