Impact of Pressure and Added Diluents on Rheological Properties of Heavy Oils

• Author / Creator

  Mortazavi Manesh, Sepideh

• The rheological properties of heavy oil and bitumen depend on factors such as temperature, pressure, diluent type and diluent composition, as well as sample shear and thermal histories and shear conditions during measurements. Each of these factors can affect the value of apparent viscosity significantly. Uncertainties in the available literature data arise when one or more of these factors have not been considered and have not been reported. Heavy oil and bitumen exhibit non-Newtonian rheological behaviors at lower temperatures. Methods for detecting and quantifying non-Newtonian behaviors are developed, presented and explored in this work using a well-characterized heavy crude oil. The methods and results presented for Maya crude oil provide a reliable database for rheological model development and evaluation, and a template for assessing the rheological behavior of other heavy crude oils. The thixotropic behavior of Maya crude oil was explored systematically using a stress-controlled rheometer. Thixotropy affects the efficiency and length scale of mixing during blending operations, and flow behaviors in pipes and pipelines following flow disruption where it affects the pressure required to reinitiate flow. Maya crude oil is shown to be a shear thinning fluid below 313 K. The thixotropic behaviors are explored using transient stress techniques (hysteresis loops, step-wise change in shear rate, start-up experiments). The magnitude of the thixotropy effect is larger at lower temperatures. Relationships are identified between rest times and other thixotropic parameters such as hysteresis loop area and stress decay in start-up experiments. Stress growth, which occurs as a result of a step-down in shear rate, is shown to correlate with temperature. The interrelation between rheological behavior of Maya crude oil and its phase behavior is discussed. The effect of pressure on the non-Newtonian rheological properties of Maya crude oil is also investigated over broad ranges of temperature from (258 to 333) K and at pressures up to 150 bar. At fixed temperature, the magnitude of the non-Newtonian behaviors of Maya crude oil appears to increase with increasing the pressure and shear thinning is shown to persist to higher pressures below 313 K. Boundaries of the non-Newtonian region with respect to temperature, pressure and viscosity are identified and discussed. The thixotropic behavior of Maya crude oil is also shown to persist at higher pressure and the recovery of the moduli at rest appears to be faster at elevated pressures than at atmospheric pressure. Understanding the rheological properties of mixtures of heavy oil or bitumen and diluents, specifically at low temperatures, is key in designing different processes employed in production or transportation of these resources reliably and efficiently. The effect of diluents (n-heptane, toluene and toluene + butanone (50/50 vol. %)) on the non-Newtonian behavior of Maya crude oil including shear thinning and thixotropy at temperatures from (258 to 333) K are discussed. Toluene + butanone (50/50 vol.%) addition to Maya crude oil induces the greatest reduction in shear thinning behavior irrespective of temperature. Thixotropic properties of mixtures of Maya crude oil and diluent were studied through start-up experiments. It was shown that toluene + butanone (50/50 vol.%) is the best diluent in moderating the thixotropic effect, while n-heptane showed the most pronounced thixotropic effect. It was shown that toluene + butanone (50/50 vol. %) is more promising in decreasing oil viscosity in comparison to two other diluents tested. Less of this diluent is required to decrease the viscosity to a certain value, which confirms its potential application to be used in the industry as a diluent.

• Subjects / Keywords

  • Rheology
  • Non-Newtonian
  • Heavy Oil
  • Viscosity
  • Bitumen

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R38P5VJ14

• 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.