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250 Rouzbeh G. Moghanloo et al.
6.2.3.1 Coloidal model
In this model, the surrounding adsorbed resins have lower molecular
weight. The resins stabilize the asphaltenes by adsorbing on to their sur-
face and their partitioning between the surface and surroundings deter-
mines the asphaltene solubility (Seifried, 2016).
6.2.3.2 Thermodynamic model
In this approach, resins are not taken into account and precipitation can
be reversed. Reducing the asphaltene solubility can lead to phase separa-
tion. At thermodynamic equilibrium, each component’s chemical poten-
tial value becomes equal in both phases (Wang and Buckley, 2001).
EoS model and the activity coefficients model (ACM) are used for the
thermodynamic model approach. EoS models are used to relate pressure
to temperature to predict phase behavior of hydrocarbons and asphaltenes.
Whereas EoS assumes that all asphaltenes in the crude oil have the same
size and molecular weight, ACM assume that precipitated asphaltenes do
not affect the vapor liquid equilibrium (VLE), and are used to predict the
activity coefficient γ in a mixture.
Furthermore, an example based on group-contribution is the predic-
tive model UNIFAC-FV (Oishi and Prausnitz, 1978), which was specifi-
cally derived for polymer solvent mixtures. These models have limitations
in the region of critical temperature and pressure. Tabibi et al. (2004) use
the concept of perturbation theory to modify the Soave-Redlich-Kwong
(SRK) EoS. This essentially was an asphaltene phase behavior predicting
model, accurate for heavy oils.
6.2.4 Asphaltene deposition
Asphaltene deposition is the process whereby there is attachment of asphal-
tene aggregates onto a surface. Depending on the interaction between the
surface and asphaltenes they may adsorb on the surface (Alian et al., 2011).
Asphaltene deposition studies are mainly performed using microfluidics
(more specifically capillary flow), Taylor-Couette (TC) cells or core flood-
ing experiments through a porous media. Microfluidic studies provide
researchers the chance to study phenomena such as colloidal dynamics at
very low Reynolds numbers, where the small dimension of the capillary or
the microfluidic device offers the suitable length scale (Saha and Mitra,
2012). Furthermore, the Taylor Couette device has the advantage of study-
ing deposition at reservoir temperature and pressure conditions. Finally,
core flood experiments use surface chemical techniques such as scanning