Probing the Interaction Mechanisms among Asphaltenes, Fine Solids, Water-Oil Emulsions and Pipeline Surfaces in Oil Sands Production

• Author / Creator

  Gong, Lu

• Fouling problem has been one of the most challenging problems in oil industries. Asphaltenes, fine solids, and water-oil emulsions have been regarded as the major components in the fouling phenomena during oil production. Investigating the interactions between foulants (e.g., asphaltenes, fine solids, and water-oil emulsions) and substrate surfaces is of both fundamental and practical importance in understanding the fouling mechanisms and developing efficient antifouling strategies. In this thesis, the atomic force microscope (AFM) colloidal and drop probe techniques have been employed to directly quantify the surface interactions among asphaltenes, silica particles, water-oil emulsions and selected substrates. The commonly used iron substrate and remarkable electroless nickel-phosphorus (EN) coating have been included.
  The interaction forces between silica or asphaltene-coated silica particles and iron or EN substrate in aqueous solutions were measured using the AFM colloidal probe technique. The effects of salinity, pH and divalent ions (i.e. Ca2+) were investigated. The obtained force profiles were analyzed using the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. It was noticed that the attractive van der Waals (VDW) force between the particle and the substrate contributed to the attachment of particles, which finally led to the fouling phenomena, whereas the repulsive electric double layer (EDL) force played the important role in the antifouling property. The high salinity in the solutions could significantly compress the electric double layer and minimize the strength of the EDL repulsion. Basic pH could deprotonate the surface chemical groups and result in more negative surface potentials, thus strengthening the repulsive EDL force. The presence of Ca2+ ions could weaken the EDL repulsion because of the high positive charge density of divalent ions and the strong electric screening effect. Meanwhile, the asphaltene-coated silica particle was detected to have stronger adhesion with iron and EN substrates than silica particle due to the functional groups of asphaltenes. The adhesion between silica or asphaltene-coated silica particle and EN coating was much weaker than that with iron substrate, which suggested the easier removal of asphaltenes from EN surface.
  The interaction forces between water-oil emulsions and iron or EN substrates were investigated using the AFM drop probe technique. In oil-in-water emulsion case, the interaction forces between toluene drops with asphaltenes adsorbed at the interface and iron or EN substrate in aqueous solutions were investigated under effects of asphaltene concentration, salinity, pH and divalent ions. The measured force profiles were theoretically analyzed using the model combining Reynolds lubrication theory and augmented Young-Laplace equation. The results showed that the attractive VDW force played an important role in the fouling phenomena, while the repulsive EDL force prevented the contact between toluene drop and substrate surface, hence contributing to the antifouling property. Besides, the high salinity, acidic pH and presence of Ca2+ ions in aqueous solutions were demonstrated to weaken the EDL repulsion and promote the contact of oil drops on substrate surface. Compared with iron substrate, the surface potential of EN coating in aqueous solution was more negative and thus led to stronger EDL repulsion with oil drops, indicating the difficult contact of oil drops on EN coating surface.
  In water-in-oil emulsion case, the interaction forces between water drops with interfacial asphaltenes and iron or EN substrates in organic media were investigated, and the effects of asphaltenes, aging time, solvent type, loading force and contact time were explored. The measured results showed that more interfacially adsorbed asphaltenes, better solvent type, longer aging time, increased loading force and prolonged contact time could result in a stronger adhesion, which was due to the aggregation and the conformational change of interfacial asphaltenes. Moreover, it was noticed that the adhesion between water drops and EN substrate was much weaker than that with iron substrate, suggesting the easier removal of asphaltenes from EN coating surface.
  This work sheds useful insights into the interaction mechanisms between various foulants (e.g., asphaltenes, fine solids, and water-oil emulsions) and different substrates as well as the fundamental understandings of fouling problems, with the implications for the development of novel efficient antifouling coatings in oil industries.

• Subjects / Keywords

  • Surface interactions
  • AFM force measurements
  • Fouling problems
  • Antifouling coatings

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-rcsx-ra67

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.