One of the major unsolved complex systems confronting the petroleum and natural gas industries at present is the untimely deposition of heavy organic compounds present in the oil. The production, transportation and processing of petroleum, bitumen, and other heavy-organic-containing hydrocarbons could be significantly affected by flocculation and deposition of  asphaltene, resin, paraffin / wax , diamondoid, organo-metallics, etc. in the reservoir rock tubulars, oil well, pumps, storage vessels, transfer pipelines, and refinery and upgrading equipment with devastating economic consequences.

Four different effects (mechanisms) are recognized for such depositions. One or more of these mechanisms would describe the organic depositions that may occur during oil production, transportation or processing.

The degree of dispersion of heavy organics in petroleum fluids depends upon the chemical composition of the petroleum. The ratio of polar or non-polar and light or heavy molecules and particles in petroleum are the factors primarily responsible for maintaining the stability of the polydisperse oil mixture.

Solubility Effect
Deposition of heavy organics can be explained by an upset in the polydisperse balance of oil composition. Any change in

• Temperature
• Pressure
• Composition (such as addition of a miscible solvent to oil) may destabilize the polydisperse oil. Then the heavy and/or polar fractions may separate from the oil mixture into steric colloids, micelles, another liquid phase or into a solid precipitate

Segments of the separated fractions which contain sulfur, nitrogen, and/or hydrogen bonds could start to flocculate and as a result produce the irreversible heavy organic deposits which may be insoluble in solvents.

Colloidal Effect
Some of the heavy organics (specially asphaltenes) will separate from the oil phase into an aggregate (large particles) and then will remain suspended in oil by some peptizing agents, like resins, which will be adsorbed on their surface and keeping them afloat.

Stability of such steric colloids is considered to be a function of concentration of the peptizing agent in the solution, the fraction of heavy organic particle surface sites occupied by the peptizing agent, and the equilibrium conditions between the peptizing agent in solution and on surface of heavy organic particles. The amount of peptizing agent adsorbed is primarily a function of its concentration in the oil. A concentration variation of a peptizing agent (such as resins) in oil will cause its adsorbed amount on surface of heavy organic particles to change. Migration of peptizing molecules (shown by arrows) from the surface of heavy organic particles could take place due to the change in their chemical-potential-balance between the bulk oil phase and the surface phase.

Aggregation Effect
The peptizing agent concentration in oil may drop to a point at which its adsorbed amount would not be high enough to cover the entire surface of heavy organic particles. This causes the potential for aggregation of heavy organic particles due to development of free active sites on their surfaces, and their eventual flocculation. This may then permit the heavy organic particles to come together (irreversible aggregation), grow in size, and flocculate. The nature and shape o f the resulting aggregates will determine their effect on the behavior of the petroleum fluids.

Various aggregating macromolecules follow different aggregation pattenrs.

Electrokinetic Effect
When a crude oil is flowing in a conduit (porous media, well, pipeline, etc.) there is an additional effect (electrokinetic effect) to be considered in the behavior of its heavy organic constituents. This is because of the development of electrical potential difference along the conduit due to the motion of charged particles. This electrical potential difference could then cause a change in charges of the colloidal particles further down in the pipe, the ultimate result of which is their untimely deposition and plugging of the conduit. The factors influencing this effect are the electrical and thermal characteristics of the conduit, flow regime, flowing oil properties, characteristics of the polar heavy organics and colloidal particles, and blending of the oil.