Further Investigation of Downhole Heating by an Electric Cable

Abstract

Heat is an important component in heavy oil production. One method includes generation of electric current using solar panels or other methods and converting electricity into heat for surface or downhole applications via an electric cable. The heat can help removal of paraffin, wax or hydrate in the production tubing, removal of heat sensitive skins in and around perforations and reduction of oil viscosity in the reservoir zone. The objectives of this study are to present the results obtained from a finite element model study including the cable, well, and the reservoir. Reported results are in continuation of our previous study reported in SPE-185736-MS in 2017. The study uses a commercial finite element model. The model consists of the production tubing, cable, well and the porous media as the reservoir zone. The wellbore fluid is different gases or mostly water. The cable is attached to the production tubing's sides and immersed in well fluid in different lengths. The model solves the two-dimensional heat of conduction equation providing same temperature distributions obtained from other analytical methods. Following parameters are changed using a fixed cable heat density, W/m: well fluids, length of cable immersed, cable orientation, cable lengths, reservoir thermal conductivity and reservoir porosity. The finite element model runs are obtained for vertical well at different model mesh sizes. The best results were reported. In case of stagnant gas surrounding the electric cable, the sand face of the well heats up very quickly. However, transfer of heat up to many meters into the reservoir continues at a slower pace. Similar results are obtained for both vertical as well as horizontal wells. Thermal conductivity of the porous media and its specific heat and density plays an important role in heat transfer and distribution in the reservoir zone. If water is surrounding the cable and given its thermodynamic states of pressure and temperature is allowed to reach near boiling, the heat transfer to the reservoir naturally can be accelerated due to initiation of latent heat of vaporization and its transfer to the reservoir. This study will present all the new finite element runs obtained and the temperature distributions as a function of time and radial distances into the reservoir. Heat is always needed in production of heavy oils worldwide and specifically in California as steam injection faces its own operational challenges. The technology of electric heating needs to be understood and cables needed to be designed properly and effectively. If that happens many deeper and larger heavy oil zones can be produced more economically. Like other similar studies, this study will help design evolution needed for more rugged and robust and effective downhole heaters.

Waveguide Analysis of Radiofrequency Transmission in Well Tubulars for Electromagnetic Heating of Heavy Oil

“…Transmission lines (TLs) convey power from the RFG to feed-points of antennas [35]. The transmission process becomes a primary source for power degradation due to impedance mismatches, radiation, and heat losses [36], [37]. Guided waves travelling along a TL reflect due to impedance variation in the transmission path.…”