Application of high-frequency alternating-current principles to develop practical induction well bore heaters for in-situ thermal ground remediation

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The Government of Canada lists 23,670 sites Canada-wide where contaminants in soil and water have been remediated or are in need of remediation. In Alberta alone, roughly 6.48 million liters of hydrocarbon liquids have leaked onto soil and water between 1990 and 2012. A few electrical and chemical methods are currently in use to remediate the contaminated soil in the vicinity of these hydrocarbon leaks. Electrical methods involve electro-thermal or electrical heating of contaminated soil and water using large electrodes inserted into the ground, which are driven using a large AC power source on the surface. Electro-thermal heating offers the advantage of desorbing hydrocarbon contaminants in soil without adding secondary chemical pollutants. Challenges with electro-thermal heating of contaminated soil come from power losses and limited heat penetration over distance in less permeable soil types. More recently inductive heaters fitted with coils that produce magnetic fields at AC frequencies much higher than 60 Hz to induce heat in the walls of surrounding steel wellbore pipe casings have also been developed by the industry partner (McMillan-McGee Corp.) for heating soil more effectively. Unlike conventional 60 Hz electrodes, characterizing and mitigating these losses at high frequencies is even more challenging since losses are expected to be due to not just coil conductor losses but also due to the interaction of the coil's electric and magnetic fields with the surrounding well-bore pipe, and to a lesser extent on the surrounding ground formation. For electro-thermal applications, some of these losses get converted to heat and assist with the electrical heating process but others inhibit electrical power transfer and transmission along the coils. McMillan-McGee and the University of Calgary have formed a research collaboration to study and characterize these high frequency electrical losses in McMillan-McGee's new higher frequency Electro-thermal inductive heaters. With power levels of between 10-80 kW sent down hole into the heaters during the electro-thermal remediation process characterizing and minimizing these losses becomes important for quicker decontamination of soil and saving more energy.