The effect of shear rate on aggregation and breakage of asphaltenes flocs: Experimental study and model-based analysis

Abstract

The study of the effect of shear stresses on the aggregation and breakage of asphaltene flocculation is one of the important issues that little research has been done on it. In this paper, the effect of shear rate on the behavior of asphaltene particles of samples including medium and heavy oil in the colloidal state before and after precipitation has been investigated using viscometric method. The physical and chemical properties of dispersed oil systems depend on the particles of asphaltene dispersed in the colloidal state that form complex structural units (CSUs). The size of CSU for two medium and heavy oils was estimated by the Manzhai et al. equation using viscosity data in terms of temperature (T) at different shear rates. By increasing the shear rates from 10 S−1 to 200 S−1, the CSU radius decreases from 155 to 46.1 nm and from 6.64 to 1.27 nm for Azadegan (representative of medium crude oil) and model (representative of heavy crude oil) samples, respectively. Using the generalized Pal–Rhodes equation, the viscosities of heavy oil samples containing different extracted asphaltene contents are predicted at different shear rates. The shape factor at shear rates of 10 and 300 was 6.106 and 4.356, respectively, which indicates that it is approaching the spherical state by increasing the shear rate. Finally, to calculate the effective volume fraction of asphaltene particles in the unsteady state, using the viscosity data of the toluene and crude oil solution and applying the Lobe equation, the viscosity of the background (free-asphaltene) was calculated. With the viscosity of the background and the viscosity data of heptane and crude oil, the amount of effective volume fraction of asphaltene particles was calculated by the Gillespie equation. These values are obtained for three modes: different shear rates, different volume ratios of heptane, and in the presence of two novel inhibitors of cocamide diethanolamine and dodecylbenzene sulfonic acid.