Electromagnetic Heating for Heavy-Oil and Bitumen Recovery: Experimental, Numerical, and Pilot Studies

Summary This study provides an extensive critical review of electromagnetic heating (EMH) methods [inductive heating (IH), low-frequency heating (LFH), and high-frequency heating (HFH)] to highlight their existing challenges in enhanced heavy-oil and oil sands recovery. In general, IH is considered to be less practicable than LFH and HFH. The resistance (ohmic or conduction) heating prevails in LFH while dielectric heating prevails in HFH. Thus, the effectiveness of LFH decreases if reservoir water is overheated to generate steam. Also, the intensity of the energy released and the temperature rise in LFH are not as significant as those in HFH. LFH also fails in penetrating the media with breaks, heterogeneities, and in partially saturated media (e.g., when some oil saturation has been produced). These challenges might somewhat be remedied by HFH at the expense of reducing the electromagnetic (EM) wave penetration depth. The advantages of HFH include remote heating through a desiccated reservoir region around the EM energy source, higher intensity of the energy released and greater temperature rise, and better EM wave penetration through partially saturated media with breaks and heterogeneities. The caveat, however, is that the practical application of HFH could be more expensive than LFH. Besides, the lower depth of EM wave penetration in HFH remains a challenge. During HFH, the temperature increase occurs as a result of the induced molecular rotation in the dielectric material, in particular if the material contains more polar compounds. The polar molecules follow the EM field. This increases the internal molecular friction within the material and generates heat, leading to the rise of temperature. Because the heat generated is a function of the stored (absorbed) energy in the reservoir, the dielectric constant or the real permittivity of the reservoir should be enhanced to enhance the performance of HFH. This ensures that the temperature has risen reasonably in a reasonable amount of time with a reasonable amount of electricity consumption. However, to generate a uniform rise in temperature on a large scale away from the wellbore, the imaginary permittivity of the material should be reasonably lowered, too, for maximizing the penetration of the EM wave (while the real permittivity is an indication of the degree of polarization, the imaginary permittivity is associated with dielectric losses). Lowering the imaginary permittivity away from the wellbore helps minimize the effects of steam condensation (condensate formation retards the EM wave propagation) or delay steam condensation because the reservoir temperature is reduced during the later stages of oil production. The thermal conductivity of the formation should also be enhanced, especially away from the wellbore to generate a more uniform rise in temperature. These three reservoir improvements (enhancing real permittivity, lowering imaginary permittivity, and enhancing thermal conductivity) in an attempt to enhance EMH underpin the rationale behind proposing future optimizations of EMH, and in particular, HFH.