Balanced-line RF electrode system for use in RF ground heating to recover oil from oil shale

Abstract

An in-situ method of extracting oil from a hydrocarbon bearing layer such as oil-shale or tar sands lying beneath a surface layer comprises applying a radiofrequency excitation signal to the hydrocarbon bearing layer through a system of electrodes. The electrodes are inserted into a matrix of holes drilled through the surface layer and into the hydrocarbon bearing layer. A coaxial line extending through the surface layer is connected to the electrodes extending into the hydrocarbon bearing layer. The electrodes have a length that is an integral number of quarter wavelengths of the radiofrequency energy. A matching network connected between the coaxial cable and a respective one of the electrodes maximizes the power flow into each electrode. The electrodes are excited uniformly in rows and as a "balanced-line" RF array where adjacent rows of electrodes are 180.degree. out of phase. This method does not produce substantial heating of the surface layer or the region surrounding the producing layer, and concentrates most of its power in the hydrocarbon bearing layer.

Dependencies are inferred from the claim text.