Page 279 - Formation Damage during Improved Oil Recovery Fundamentals and Applications
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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
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