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

• US 5,236,039 A
• Filed: 06/17/1992
• Issued: 08/17/1993
• Est. Priority Date: 06/17/1992
• Status: Expired due to Term

• Current Assignee: General Electric Company, Shell Oil Company (Shell Plc)
• Original Assignee: General Electric Company
• Inventors: Hsu, Chia-Fu, Vinegar, Harold J., Mueller, Otward M., Edelstein, William A.
• Primary Examiner(s): Britts, Ramon S.
• Assistant Examiner(s): TSAY, FRANK
• Application Number:
  US07/899,839
• Time in Patent Office: 426 Days
• Field of Search: 166/50, 166/65.1, 166/248, 166/302
• US Class Current: 166/248
• CPC Class Codes: E21B 36/04 using electrical heaters
• CPC Class Codes: E21B 43/2401 by means of electricity
• CPC Class Codes: E21B 43/30 Specific pattern of wells, e.g. optimising the spacing of wells

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° 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.

Claims

1. A system for extracting oil in-situ from a hydrocarbon bearing layer below a surface layer comprising:

a) a master oscillator for producing a fundamental frequency;

b) a plurality of heating sources, each comprising;

radiofrequency (RF) producing means for providing a radiofrequency excitation signal based upon the fundamental frequency,

a coaxial line coupled to the RF producing means for passing the radiofrequency signal through said surface layer without substantial loss of power;

a conductive electrode located in the hydrocarbon bearing layer having a length related to the radiofrequency signal and adapted for radiating energy into said hydrocarbon bearing layer for causing shade oil to be extracted;

a plurality of matching elements, each matching element coupled, respectively, between each respective electrode and a respective coaxial line for maximizing radiation emitted by the electrodes when they receive the radiofrequency signal; and

c) a plurality of producer wells adapted for collecting the extracted shale oil.

2. The system for extracting oil as recited in claim 1 wherein the electrode has a length being an odd multiple of quarter wavelengths of a fundamental wavelength of the radiofrequency excitation signal.

3. The system for extracting oil as recited in claim 1 wherein the electrodes have a length d defined by:

space="preserve" listing-type="equation">d=(2n+1)(λ

/4)

where n is any positive whole integer, and λ

is a fundamental wavelength of the radiofrequency excitation signal.

4. The system for extracting oil as recited in claim 1 wherein the electrodes are arranged in rows being close to each other as compared to the radiofrequency excitation fundamental wavelength λ

, with the electrodes of each row having the same polarity of excitation, and alternate rows having opposite polarities so as to cause excitation of adjacent rows to be 180°

out of phase, thus forming a "balanced line" configuration.

5. The system for extracting oil as recited in claim 1 wherein the RF producing means comprises an RF amplifier.

6. A method of extracting oil from a hydrocarbon bearing layer beneath a surface layer comprising the steps of:

a) drilling a plurality of rows of holes through said surface layer and into said hydrocarbon bearing layer;

b) inserting electrodes coupled to shielded coaxial cables into the holes such that the electrodes extend into said hydrocarbon bearing layer and the coaxial cables extend above said surface layer;

c) passing a radiofrequency (RF) excitation signal through the coaxial cables such that RF radiation is transmitted from the electrodes into said hydrocarbon bearing layer to cause oil to be extracted from said hydrocarbon bearing layer, the RF excitation signal for each electrode in alternative rows having the same phase, and the RF excitation signal for electrodes in a row having a phase 180°

different from an adjacent row; and

d) collecting the oil which is extracted.

7. The method of extracting oil as recited in claim 6 wherein the step of collecting the oil comprises forcing the extracted oil through the drilled holes, acting as production wells.