Deposition of complex and heavy organic compounds which exist in petroleum crude can cause a number of severe problems. To prevent deposition inside the reservior, in the well head, and inside the transmission lines it is necessary to be able to predict the onset and amount of deposition due to various factors. In the present paper the mechanism of organic deposition is modeled based on statistical mechanics of polydisperse polymer solutions joined with the kinetic theory of aggregation and its predictive capability is discussed. Utilization of statistical mechanics of polydisperse polymer solutions joined with kinetic theory of aggregation enables us to develop a realistic model which is able to predict, both, reversible and irreversible heavy organic depositions. The present model is capable of describing several reversible and irreversible situations, such as the phenomena of organic deposition, growing mechanism of heavy organic aggregates, the size distributions of precipitated organics, and the solubility of heavy organics in a crude oil under the influence of miscible solvents. As an example the present model is applied for heavy organics deposition prediction of a particular crude oil for which experimental multi-phase behavior data are available. It is shown that the prediction results of the present model are in very good agreement with the experimental data.
Organic deposition during petroleum and heavy oil production and processing is a very serious problem in many areas throughout the world. The economic implications of this problem are tremendous considering the fact that a problem workover cost each time could get as high as a million dollars. For example in a heavy crude production field formation of asphaltic sludges after shutting in a well temporarily and/or after stimulation treatment by acid has resulted in partial or complete plugging of the well [1,2]. The downtime, cleaning, and maintenance costs are a sizable factor in the economics of producing a heavy crude field prone to organic deposition. Considering the trend of the oil industry towards the utilization of heavier asphaltic crudes and the increased utilization of miscible flooding techniques for recovering and transportation of oil, the role of organic deposition in the economic development of petroleum production will be important and crucial.
The parameters that govern precipitation of heavy organic substances appear to be compositions of crude and injection (or blending) fluid, pressure and temperature. With alterations in these parameters the nature of heavy organic substances which precipitate will vary. Also, it is a proven fact that the precipitation of asphaltene is generally followed with polymerization, or flocculation, of the resulting precipitate, which produces an insoluble material in the petroleum fluid which will also contain other heavy organics and mineral depsotis [3–7].
Over the last six decades a number of investigators have researched the nature of heavy organics and mechanism of the organics deposition. There has been extensive progress made in the past several years in the formulation of accurate vapor liquid phase behavior prediction of complex petroleum fluids , statistical mechanics of polydisperse polymer solutions  and kinetic theory of aggregation and precipitation .