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Asphaltene plugging is a known cause of near-wellbore formation damage. Deposited asphaltenes can reduce effective hydrocarbon mobility by (1) blocking the pore throats; (2) adsorbing onto the rock, thereby altering the formation wettability from water-wet to oil-wet; and (3) increasing hydrocarbon viscosity by nucleating water-in-oil emulsions. Asphaltene flocculation and deposition can be avoided in some, but not all, cases. Some formation damage resulting from asphaltene plugging is permanent and hence must be prevented rather than treated. Prevention of asphaltene-induced formation damage should be started in the early stages of drilling and well completion, once the oil is known to be asphaltenic. This paper presents a systematic approach to successful diagnosis, prevention, and mitigation of asphaltene problems during recovery of asphaltenic oils. A mechanism of asphaltene flocculation and deposition is proposed and analyzed, and the previously defined concept of asphaltene deposition envelope is further refined. Diagnostic technology is presented that can test the compatibility of drilling and completion fluids with any asphaltenic oil. Important issues that need to be considered in the design of treatments for asphaltene removal are discussed. Finally, the paper presents a methodology for restoring unfavorable wettability changes caused by asphaltene deposition.

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The need to understand the nature of asphaltenes and asphalts & their role in the production, transportation and processing of crude oil is well recognized internationally, as manifested by the current activities•in the petroleum industry towards exploration, drilling, production and processing of heavier oils (higher in asphaltene content). Asphaltene deposition during oil production and processing ranks as one of the costliest technical problems the petroleum industry currently faces. In the present report, a c9lloidal model has been developed, capable of predicting the onset of flocculation of colloidal asphaltene in oil mixtures, due to either changes in composition (i.e., solvent addition) or electrical phenomena (i.e., streaming potential generation due to flow of asphaltenes containing oil• in conduits or porous media). For oil mixtures, from which flocculation is caused simply by flow, the model can make predictions as to the velocity ranges where colloidal asphaltene flocculation can be avoided. This could have a significant _impact on allowed reservoir drawdown rates, well spacing and tubing design.

Small angle X-ray scattering was used to determine the effect of pressure on the extent of asphaltene aggregation for a system under near-critical conditions. A mixture containing 60 vol % Crude Oil A in n-pentane was studied at 110 °C, at pressures ranging from 25 to 400 bar. As the pressure of the nearcritical solution is isothermally decreased, these results indicate (1) an increase in the extent of asphaltene aggregation and/or (2) increased attractive interactions among aggregates. Information derived from different regions of the X-ray scattering curve indicate increasing aggregation with decreasing pressure. From these experimental results, together with theoretical interpretation, we infer that as the pressure is reduced, increased aggregation of asphaltenes results which may contribute to formation damage in hydrocarbon reservoirs, and to fouling in hydrotreatment and cracking catalysts.