In this section, the mechanisms of the heavy organic deposition according to Mansoori (1997) are described. Mansoori (1997) states that organic deposition during petroleum production and transportation may occur by one or several of the following four mechanisms:


1. Polydispersivity effect. As depicted in this article by Mansoori (1997), a stable state of a polydispersed oil mixture can be attained for a certain proper ratio of the polar to nonpolar and the light to heavy constituents in the crude oil at given temperature and pressure conditions. Thus, when the composition, temperature, or pressure are varied, the system may become unstable and undergo several processes. Mansoori (1997) depicts the formation of micelle-type aggregates of asphaltene when polar miscible compounds are added into the system. Mansoori (1997) describes the separation of the asphaltenes as a solid aggregate phase when more paraffinic hydrocarbons are added into the system.


2. Steric colloidal effects. At high concentrations, asphaltenes tend to associate in the form of large particles, as depicted by Mansoori (1997). In the presence of some peptizing agents, such as resins, these particles can adsorb the peptizing agents and become suspended in the oil.



3. Aggregation effect. When the concentration of the peptizing agent is low and its adsorbed quantity is not sufficient to occupy the particle surface completely, several particles can combine to form bigger particles as depicted by Mansoori (1997). This phenomenon is called flocculation. When the particles become

sufficiently large and heavy, they tend to deposit out of the solution as depicted in this article by Mansoori (1997).


4. Electrokinetic effect. As explained by Mansoori (1997), during the flow of oil through porous media and pipes, a "streaming current" and a potential difference are generated because of the migration


of the charged particles of the asphaltene colloids. The asphaltene particles are positively charged but the oil phase is negatively charged, as depicted in this article by Mansoori (1997). Therefore, the negative upstream and positive downstream potentials are generated along the pipe to resist the flow of the colloidal particles, as


depicted in this article by Mansoori (1997). This, in turn, induces a back diffusion of the colloidal asphaltene particles. Mansoori (1997) points out that the deposition of the polar, asphaltene by the electrokinetic effect and the non-polar paraffins by the dynamic pour point crystallization effect, could occur simultaneously when the oil contains both asphaltenes and paraffins.

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