Interfacial Properties of Asphaltenes at Oil/Water Interface

• Author / Creator

  Zhang, Shuo

• Asphaltenes are the heaviest components in crude oil. It is generally believed that asphaltenes adsorbed at oil/water interface can form a protective layer to stabilize the water-in-oil emulsions. Therefore, it is of both fundamental and practical importance to understand the adsorption kinetics of asphaltenes to the oil/water interface. In this work, the effects of asphaltene concentration and temperature on the dynamic interfacial tension (IFT) of oil/water interface were investigated using pendent drop shape method. The adsorption process showed three stages as a function of adsorption time. It was found that the reduction kinetics of interfacial tension in the initial state (Regime I) was diffusion-controlled, during which asphaltenes were adsorbed to the oil/water interface spontaneously. Diffusion coefficient was found to increase with increasing temperature and decreasing asphaltene concentration. While asphaltene concentration showed a dominant influence on the diffusion coefficient as compared with temperature. With increasing adsorption time, in the Regime II, the steric hindrance arisen from the adsorbed asphaltenes at oil/water interface tended to inhibit the further adsorption. Continuous adsorption of asphaltenes to the sublayer of the interface and reconfiguration of adsorbed asphaltenes might contribute to the continuous reduction of dynamic interfacial tension in Regime III. The experimental data was fitted with Gibbs adsorption model, which showed that elevated temperature had a negative impact on the maximum surface excess concentration of asphaltene. Calcium chloride is the main salinity present in low-salinity water flooding which is an efficient process for enhanced oil recovery (EOR). In this thesis, the effect of calcium chloride concentration on the interfacial tension and dilatational interfacial rheology was investigated and further validated by emulsion stability experiments. It was found that with increasing calcium chloride concentration both the dynamic interfacial tension and surface pressure increased. Diffusion coefficient and maximum interfacial excess concentration of asphaltenes were enhanced with the existence of calcium chloride in the aqueous phase. The results of dilatational interfacial rheology and compressibility studies have demonstrated that calcium chloride could induce the rearrangement of asphaltene molecules and form a more rigid film at the oil/water interface. The results of interfacial tension, dilatational interfacial rheology and emulsion stability tests further demonstrate that calcium chloride could significantly influence the stability of water-in-oil emulsions. Our results provide useful information regarding the adsorption kinetics and adsorption mechanism of asphaltenes at oil/water interface in oil production, as well as the correlation between interfacial properties and emulsion stability in the presence of asphaltenes, particularly under high temperature conditions and with calcium chloride.

• Subjects / Keywords

  • Calcium chloride
  • Asphaltenes
  • Temperature
  • Interfacial properties
  • Interfacial dilatational rheology
  • Interfacial tension

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3ZG6GM9V

• 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.