Compared with other electrical heating processes, RF heating has the advantages of volumetric heating, therefore it has great development potential in extracting heavy oil resources. Because the EM waves used to heat reservoir are mainly derived from RF antennas, it is necessary to determine the multi-antennas layout in the horizontal wellbore to maximize the thermal energy dissipation in a single reservoir layer with uneven thickness, and minimize the extra heat loss in non-reservoir.
In this work, the combination of three antenna arrays is considered during RF heating process, and the effects of their distance and operating parameters (voltage, and frequency) on heating patterns are analyzed. In addition, in order to achieve the purpose of heating reservoir at the expense of the least amount of electrical energy, the heating efficiencies of the antenna arrays with equal and different spacing are compared. At last the mathematical model used to describe RF heating process is solved by COMSOL to obtain the reservoir temperature profiles.
Simulation results indicates that the frequency and voltage applied to each dipole antenna have a contribution to the heating pattern, including heating range and direction. With the increasing antenna array spacing, the heating range expands, but the maximum reservoir temperature declines. In addition, the temperature distributions in the perpendicular bisectors of any two adjacent antennas trend to gradually diminish with the increasing spacing. Gradually increasing antenna spacing will also weaken the temperature accumulation effect at the center of the reservoir. When the single reservoir layer with different thicknesses is heated, the maximum heating efficiency is 0.73 in the condition of the antenna configuration with the same spacing. Whereas, the efficiency is up to 0.88 if the optimized spacing is adopted. Results indicate that the heating mode can be governed by optimizing the heating distance, as well as selecting the appropriate operating parameters.
The determination of RF heating pattern can provide the solutions for the placement of multiple antennas in horizontal boreholes. Ultimately, the extra energy waste is avoided and the maximum heating efficiency is accomplished.