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Conduction and Dielectric Relaxation Mechanisms in Athabasca Oil Sands with Application to Electrical Heating Tinu Abraham, Artin Afacan, Priyesh Dhandharia, and Thomas Thundat Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b00954 • Publication Date (Web): 20 Jun 2016 Downloaded from http://pubs.acs.org on June 30, 2016
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Energy & Fuels
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Conduction and Dielectric Relaxation Mechanisms
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in Athabasca Oil Sands with Application to
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Electrical Heating
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Tinu Abraham*, Artin Afacan, Priyesh Dhandharia, Thomas Thundat**
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Department of Chemical and Materials Engineering, University of Alberta, Alberta,
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Canada T6G 2V4
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ABSTRACT
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Six oil sands with increasing water and clay content were investigated for their electrical
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relaxation mechanisms using broadband dielectric spectroscopy with frequency (1 Hz to 1 MHz)
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and temperature (20 to 200 °C) to identify suitable operational strategies for electrical heating.
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Oil sands having least water and clay content showed conduction relaxation mechanism
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following Jonscher’s law due to Maxwell-Wagner (MW) polarizations at bound water interfaces
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between bitumen and silica grains. MW polarizations due to free water interfaces between 1 kHz
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and 1 MHz was observed for oil sands having pendular connected water channels between sand
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grains. Poor oil sands with water entrapped in fine clusters had dominant dc conduction
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mechanism. Additionally, all oil sands displayed dipole relaxations due to bitumen molecules
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between 100 kHz and 1 MHz. Electrical properties increased as temperatures were increased
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from 20 to 120 ℃, while further increase from 120 to 200℃ resulted in reduction of these
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properties and dominance of ac conduction, causing all oil sands to behave the same irrespective
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of their grade.
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KEYWORDS Conduction relaxation, oil sands, dielectric relaxation, electrical heating, dielectric
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heating, dipole relaxation, electromagnetic heating
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INTRODUCTION
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The oil sands of Alberta are the world’s third largest oil reserves having 166 billion bbls of
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extractable oil in the form of bitumen1. The high viscosity of bitumen found to be approximately
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106 cP at reservoir temperature has proved to be the greatest obstacle that this industry faces for
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extracting this resource2. While, thermal recovery methods utilizing hot water and steam are
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usually considered most effective for lowering viscosity of bitumen, they are also considered
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inefficient in some cases, due to low reservoir injectivity, steam leakage to thief zones,
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overburden heat loss in thin pay zones as well as prohibitive heat losses in the reservoir3. These
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thermal methods are also incompatible for use in intermediate in situ reservoirs which are too
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shallow to withstand steam pressures3,4. Furthermore, water based thermal technologies result in
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a host of produced water treatment problems, cause hydrogeological environmental damage and
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contribute towards the greenhouse effect3. Electrical heating is a relatively new technique in
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enhanced oil recovery and is envisioned to be the much-needed innovation5–8 for the oil sands
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industry to overcome or reduce the disadvantages of current thermal recovery methods.
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Electrical heating has the ability to heat targeted parts of oil sands reservoirs, resulting in lower
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heat losses causing more effective heating than with thermal methods3. Heat is generated from
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within the oil sands volumetrically due to electrical conduction and polarization mechanisms
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rather than through surface based thermal conduction or convection mechanisms aided by hot
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water or steam3. While there are several studies of pilot and field scale implementation of
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electrical heating for enhanced oil recovery3,7,9–14 , there are very few fundamental studies
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published about the conduction and polarization behavior of oil sands5,15, resulting in the slow
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progress of its commercialization. Lack of research in this field has resulted in certain
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operational disadvantages in electrical heating methods such as over dependence on water in oil
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sands while carrying out electrical heating, over-heating of regions around electrodes, excessive
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consumption of electric current when carrying out joule heating, reduction of electromagnetic
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radiation intensity with increasing distance from the electrodes8,16.
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The conversion of electrical energy to heat is due to electrical conduction and polarization
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mechanisms in oil sands. These mechanisms arise as a function of its composition and the
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manner in which different components are thereby arranged. Oil sands typically is a
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heterogeneous mixture consisting of coarse sand grains (> 44 µm) of quartz minerals, fine
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mineral solids (11%
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bitumen) having increasing water and clay content and one is poor grade (
