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Journal of Petroleum Science and Engineering 32 (2001) 217 – 230

Asphaltene flocculation and collapse from petroleum fluids
Valter Antonio M. Branco a, G. Ali Mansoori b,*, Luiza Cristina De Almeida Xavier a, Sang J. Park b, Hussain Manafi b

Petroleo Brasilerio S.A., Petrobras/CENPES/DIGER, Cidade Universitaria, Quadra 7, Ilma Fundao, Rio de Janeiro,RJ, 21910, Brazil b Thermodynamics Research Laboratory, Department of Chemical Engineering, University of Illinois at Chicago, 810 S. Clinton Street, Chicago, IL 60607-7000, USA

Abstract Deposition of complex and heavy organic compounds, which exist in petroleum crude and heavy oil, can cause a number of severe problems. To prevent deposition inside the reservoir, in the well head and inside thetransmission 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 asphaltene deposition, which is the major cause of most organic deposition cases, is modeled based on statistical mechanics of polydisperse polymer solutions joined with the kinetic theory of aggregation and its predictive capability isdiscussed. 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 ofheavy organic aggregates, the size distributions of precipitated organics and the solubility of heavy organics in a crude oil due to variations in oil pressure, temperature and composition. As an example, the present model is applied for heavy organics deposition prediction of two different Brazilian crude oils for which experimental data are available. It is shown that the prediction results ofthe present model are in good agreement with the experimental data. D 2001 Elsevier Science B.V. All rights reserved.
Keywords: Deposition; Oil; Compounds

1. Introduction Organic deposition during petroleum and heavy oil production and processing is a serious problem in many areas throughout the world. The economic implications of this problem are tremendous considering the fact that a problemworkover cost each time could get as high as a million dollars. For example, in a heavy crude production field, formation of asphaltic
Corresponding author. Tel.: +1-312-996-5592; fax: +1-312996-0808. E-mail address: (G.A. Mansoori).

sludge after shutting in a well temporarily and/or after stimulation treatment by acid has resulted in partial or complete plugging of thewell (Lichaa and Herrera, 1975; Escobedo et al., 1997). The downtime, cleaning and maintenance costs are a sizeable 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 asphaltenic 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.

0920-4105/01/$ - see front matter D 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 0 - 4 1 0 5 ( 0 1 ) 0 0 1 6 3 - 2


V.A.M. Branco et al. / Journal of Petroleum Science and Engineering 32 (2001) 217–230

Fig. 1. Average molecular structural models of thefractions of Athabasca tar – sand bitumen and petroleum bitumen. (a) Resin fraction, (b) asphaltene fraction of tar – sand bitumen; (c) asphaltene fraction of bitumen (Suzuki et al., 1982).

The major factor that govern precipitation of heavy organic substances appear to be due to asphaltene flocculation, which is initiated due to variations in compositions of crude and injection (or blending)...
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