Abstract
The importance of heavy oils as energy resource is continuously increasing, thanks to the development of enhanced oil recovery methods, such as thermal recovery. Radiofrequency reservoir heating through a downhole antenna system can be an effective alternative to steam injection methods, giving advantages such as good energy distribution, greater independence from reservoir properties, equipment compactness, high efficiency and possibility to focus the energy on the oil bed. In this paper we present a numerical study of a new electromagnetic heating method, which combines a radiating antenna with a well-reservoir interface structure, called tight shell. The study was conducted adopting dielectric and physical parameters measured on real oil sand samples and heating requirements relative to an actual oil sand reservoir. The study aims to evaluate the optimal operating irradiation frequency, as well as the effectiveness of the tight shell interface. Results show that, with a proper system design, a considerable volume of reservoir can be uniformly heated by a single downhole antenna. Frequencies in the 10-20 MHz range give the best results, and the use of a tight shell made of a low-loss dielectric material surrounding the irradiating element proves extremely efficient in lowering peak temperatures at the radiating well, preserving well completion and extending the heated volume. The use of a tight shell makes also the method much less sensitive to possible dishomogeneities in the dielectric properties of the reservoir material.
