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Abstract
Heavy-oil and bitumen recovery from difficult geological media such as deep, heterogeneous and high shale content sands and carbonates, and oilshale reservoirs requires techniques other than conventional thermal and miscible injection methods. Materials in oil reservoirs (formation water, crude oil, oil-water emulsions, bitumen and their components like resins, asphaltenes, and paraffin) are non-magnetic dielectric materials with low electrical conductivity. If the electromagnetic field can be created to change these properties, electro-thermo controlled hydrodynamics could improve the displacement and recovery of heavyoil/ bitumen.

This paper deals with the recovery improvement of heavy-oil/bitumen by Radio-Frequency (RF) Electromagnetic (EM) radiation. The RF-EM fields in the form of waves can penetrate deeply enough - from fractions of a meter to several hundred meters - into oil and gas containing reservoirs to generate heat and eventually improve recovery mainly due to the reduction of oil viscosity. The recovery mechanisms and the dynamics of the RF-EM heating process were analyzed for several field scale applications in Russia. In the Yultimirovskaya tar sand deposits, RF-EM energy was transmitted from the RF-EM generator, located at the surface, into the formation by a coaxial system of the well pipes. Another field example analyzed was the RF-EM stimulation process in several wells of the Mordovo-Karmalskaya tar sands performed in the 1980s. It was observed that the formation was heated to the temperature which was sufficient for injection of oxidant (air) to initiate fire flooding.

Then, a mathematical model of this process was presented with a sample exercise. Some data needed for this exercise were obtained from the field tests evaluated.

Field tests proved the efficiency of the RF-EM stimulation of heavy oil / bitumen deposits with low water cut values (in operating production wells with water cut <30% on early field development stages). Numerical simulations suggest that bottomhole temperature and heat/mass transfer effects in the reservoir can be controlled by setting the output performance of the RF generator and by the difference between the reservoir and bottom-hole pressure.

Introduction
Applying radio-frequency electromagnetic energy (RF-EM) into heavy-oil reservoirs is an unconventional stimulation method. The RF-EM radiation generates a volume source of heat in the reservoir rock. Due to dielectric absorption in the medium, the EM energy transforms into thermal energy, and the resulting heat reduces the viscosity of the reservoir fluids.

Results of RF-EM treatment experiments were well documented in numerous studies (Chakma and Jha, 1992; Kasevich et al., 1994; Nigmatulin et al., 2001; Ovalles et al., 2002). Theoretical aspects of heavy-oil production were covered by Abernethy (1976), Islam et al. (1991), Sahni et al. (2000), Sayakhov et al. (2002), and Carrizales et al. (2008). Several other studies investigated the heat and mass transfer processes in heavy oil reservoirs stimulated by EM radiation (Sayakhov et al., 1998; Kovaleva and Khaydar, 2004; Kovaleva et al., 2004; Davletbaev et al., 2008 and 2009). A number of other investigations proposed analytical models of lab experiments (Hiebert et al., 1986; Ovalles et al., 2002).