Understanding Interaction Mechanism of Deformable Droplets in Oil Production

• Author / Creator

  Shi, Chen

• Interactions mechanisms of deformable air bubbles and liquid droplets play critical roles in many established and modern industrial processes. Understanding the interaction mechanisms of oil droplets and air bubbles is of fundamental and practical importance to solve many challenging issues, especially for oil industries. In this study, a state-of-art droplet probe atomic force microscopy (AFM) coupled with reflection interference contrast microscopy (RICM) was applied, for the first time in the world, to simultaneously quantify interaction forces and the spatiotemporal evolution of the thin water film between air bubbles and solid mica surfaces. The measured force results were analyzed using a theoretical model based on Reynolds lubrication theory and augmented Young-Laplace equation to elucidate the intrinsic interaction mechanisms. Stable films sustained by van der Waals force were always observed between air bubbles and hydrophilic mica surfaces, whereas bubbles were found to readily attach onto hydrophobized mica surfaces. An exponential equation was also developed to quantify the hydrophobic attraction involved in asymmetric systems involving deformable droplets and air bubbles. The validated AFM droplet probe technique and theoretical model were then applied to quantitatively study the interaction mechanisms of (1) oil droplets interacting in aqueous media in the presence or absence of asphaltenes, representing stabilization mechanism of oil-in-water emulsions (2) water droplets interaction in oil media with or without presence of asphaltenes, which represents the stabilization mechanism of water-in-oil emulsion, and (3) oil droplets interacting with solid surfaces in aqueous media, representing the bitumen and oil liberation processes. The force results between oil droplets in water revealed that the interaction between two pristine oil droplets in water could be described by the classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Adsorption of asphaltenes at oil/water interface was found to result in more negative surface potential of the oil droplets and also induced steric repulsion, both of which inhibited coalescence of oil droplets and contributed to the stability of O/W emulsion. Lower pH could lead to less negative surface potential, and divalent ions (Ca2+) could disrupt the protection of interfacial asphaltenes and induce oil droplets coalescence. For water droplets in oil, rapid coalescence was observed between bare water droplets, while interfacially adsorbed asphaltenes sterically inhibited droplet coalescence and induced interfacial adhesion. The adhesion increased with asphaltenes concentration but drastically decreased after the concentration exceeded ~ 100 mg/L. The addition of poor solvent (heptane) strengthened the interfacial adhesion at low asphaltenes concentration, while the opposite trend was observed for high asphaltenes concentration. Pure heptane was found to destabilize asphaltenes-coated water droplets. Droplet probe AFM was also applied to directly measure the interaction force between oil droplets (i.e. toluene and heptol) with the addition of asphaltenes and mica surfaces with varying hydrophobicity in aqueous media to understand the wetting mechanisms of the oil/water/solid system. For hydrophilic mica surfaces, asphaltenes adsorbed at oil/water interface strengthened electrical double layer repulsion and induced steric repulsion, stabilizing water films and inhibiting oil droplet attachment on the surfaces. For hydrophobized mica surfaces, the hydrophobic attraction overcame the steric hindrance of interfacial asphaltenes, leading to rapid attachment and strong adhesion of oil droplet on the surfaces. This study provides a novel technique to study the interaction mechanisms of deformable droplets and air bubbles, with the capacity of synchronous measurements of the interaction forces and the drainage dynamics of thin liquid films. Results obtained using this technique for the systems in oil production also provide fundamental insights into the interaction mechanisms of oil and water droplets in complex solution conditions, with valuable implication on the stabilization mechanism of O/W and W/O emulsions and the wetting mechanisms of oil/water/solid systems in presence of asphaltenes.  

• Subjects / Keywords

  • Asphaltenes
  • Drop
  • Emulsions
  • Surface Force
  • AFM

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3NK36H7B

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.