Conduction and Dielectric Relaxation Mechanisms in Oil Sands Influencing Electrical Heating

  • Author / Creator
    Abraham, Tinu M
  • Electrical heating has been proposed in the past as an alternative to conventional water based thermal methods for reducing viscosity of bitumen in oil sands reservoirs. This could reduce or even eliminate water use and associated problems like inefficient heat transfer in the reservoir, poor bitumen recovery as well as produced water treatment issues in the oil sands processing plant. However, four decades since its initial ideation, electrical heating of oil sands is still not commercialized. The reasons are rooted in a lack of understanding about the dynamic electrical heat generation mechanisms in oil sands. This has led to over-dependence of electrical heating on water, resulting in non-uniform and discontinuous heating of the reservoir, as well as overheating of electrodes leading to failure during field trials. This research study therefore gave importance to understanding the dynamic electrical heat generation mechanisms in heterogeneous oil sands as a function of their composition, microstructural arrangement and heating temperatures. The first approach was to determine conduction and dielectric relaxation mechanism in oil sands using impedance spectroscopy studies conducted between 1Hz and 1 MHz and at temperatures between 20 and 200°C. These studies revealed an array of conduction and polarization mechanisms. When water content of oil sands was high (>5%) present as connected water channels, dc conduction was the dominant mechanism via which electrical energy was dissipated as heat. On the other hand when it was low (<5%), water was assumed to be present in isolation at the interface between bitumen and silica grains resulting in interfacial or Maxwell Wagner (MW) polarizations which showed dielectric relaxations between 1 kHz and 1 MHz. Oil sands with least water content (<1%) showed a dominance of conduction relaxations via charge hopping mechanisms following Jonscher’s law owing to the presence of silica grains having conduction through grain and grain boundaries. They also showed dominance of dipole relaxations in bitumen between 100 kHz and 1 MHz. These bitumen relaxations were present in all oil sands irrespective of their water content but were revealed only in cases where water was low. Temperature based studies revealed that beyond 120°C all oil sands behaved similarly, revealing a dominance of conduction relaxations due to silica and dipole relaxations due to bitumen, irrespective of the initial water and clay contents making them low loss heterogeneous dielectrics. Results from the second research approach linking heating patterns to the dynamic electrical behaviour of oil sands shed light on important operational strategies that could be implemented while carrying out electrical heating. A resonant autotransformer was used for electrically heating, probing and controlling the heating iii process via capacitive heating configuration. The studies revealed that joule or ohmic heating could be most suitable for high water content (>5%) oil sands having dominance of dc conduction. Frequency tuned capacitive heating would be useful for oil sands showing a dominant loss peak due to MW polarizations (1 to 5% water). Whereas capacitive or dielectric heating set at the relaxation frequency of bitumen molecules would be most suitable for oil sands with least water content (<1%). Pure capacitive heating could also be most suitable beyond 120°C for all oil sands as they showed similar electrical behavior therefore suggesting that as temperature changes, operational strategies should be varied to catch up with changing electrical behaviour of oil sands. This research study therefore sheds new light on the electrical heat generation mechanisms which could influence efficient electrical heating of oil sands. These findings are expected to improve oil sands extraction process, resulting in cost reduction coupled with reduced impact on environment due to reduction in water usage, and carbon emissions.

  • Subjects / Keywords
  • Graduation date
    Fall 2016
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • 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.