Temperature limited heaters using modulated DC power

• US 7,431,076 B2
• Filed: 04/22/2005
• Issued: 10/07/2008
• Est. Priority Date: 04/23/2004
• Status: Expired due to Fees

• Current Assignee: Shell Oil Company (Shell Plc)
• Original Assignee: Shell Oil Company (Shell Plc)
• Inventors: Vinegar, Harold J., Sandberg, Chester Ledlie
• Primary Examiner(s): KRECK, JOHN J
• Application Number:
  US11/112,713
• Publication Number:
  US 20050269089A1
• Time in Patent Office: 1,264 Days
• Field of Search: 166/60, 166/302, 392/301
• US Class Current: 166/60
• CPC Class Codes: E21B 36/04 using electrical heaters
• CPC Class Codes: E21B 43/12 Methods or apparatus for controlling the flow of the obtained fluid to or in wells E21B43/25 takes precedence; valve arrangements E21B34/00
• CPC Class Codes: E21B 43/122 Gas lift
• CPC Class Codes: E21B 43/24 using heat, e.g. steam injection
• CPC Class Codes: E21B 43/2401 by means of electricity
• CPC Class Codes: E21B 43/2405 in association with fracturing or crevice forming processes E21B43/247 takes precedence
• CPC Class Codes: E21B 43/38 in the well
• CPC Class Codes: H05B 3/141 Conductive ceramics, e.g. metal oxides, metal carbides, barium titanate, ferrites, zirconia, vitrous compounds

Abstract

The invention provides a system configured to heat at least a part of a subsurface formation. The system includes: an electrical power supply configured to provide modulated direct current (DC); and one or more electrical conductors configured to be electrically coupled to the electrical power supply and placed in an opening in the formation, wherein at least one of the electrical conductors has a heater section, the heater section comprising an electrically resistive ferromagnetic material configured to provide an electrically resistive heat output when electrical current is applied to the ferromagnetic material, and the heater section is configured to provide a reduced amount of heat near or above a selected temperature during use due to the decreasing electrical resistance of the heater section when the temperature of the ferromagnetic material is near or above the selected temperature, and the heater section has a turndown ratio of at least 1.1 to 1.

Claims

1. A system configured to heat at least a part of a subsurface formation, comprising:

an electrical power supply configured to provide modulated direct current (DC); and

a heater section comprising one or more electrical conductors electrically coupled to the electrical power supply and configured to be placed in an opening in the formation, at least one of the electrical conductors comprising ferromagnetic material;

wherein the heater section (a) provides a first heat output when electrical current is applied to the heater section below a selected temperature, (b) provides a second heat output approximately at and above the selected temperature during use, and (c) has a turndown ratio of at least 1.1 to 1; and

the system is configured to heat at least part of a subsurface formation.

2. The system of claim 1, wherein the heater section has a turndown ratio of at least 2 to 1.

3. The system of claim 1, wherein the electrical power supply is a variable frequency modulated DC electrical power supply.

4. The system of claim 1, wherein the electrical power supply is configured to provide square wave modulated DC.

5. The system of claim 1, wherein the electrical power supply is configured to provide modulated DC in a pre-shaped waveform and the pre-shaped waveform is shaped to at least partially compensate for phase shift and/or harmonic distortions in the electrical conductors.

6. The system of claim 1, wherein the second heat output is reduced compared to the first heat output.

7. The system of claim 1, wherein the second heat output is at most 90% of the first heat output.

8. The system of claim 1, wherein the heater section provides, when electrical current is applied to the heater section, the first heat output when the heater section is above 100°

C. and below the selected temperature, and the second heat output is reduced compared to the first heat output.

9. The system of claim 1, wherein the heater section automatically provides the second heat output above or near the selected temperature.

10. The system of claim 1, wherein at least a portion of the heater section is positionable proximate hydrocarbon material in the formation to raise a temperature of at least some of the hydrocarbon material to or above a pyrolysis temperature.

11. The system of claim 1, wherein the system is configured to exhibit an increase in operating temperature of at most 1.5°

C. at or near the selected temperature when a thermal load proximate the heater section decreases by about 1 watt per meter.

12. The system of claim 1, wherein the second heat output is at most 90% of the heat output at about 50°

C. below the selected temperature.

13. The system of claim 1, wherein the system comprises in addition a non-ferromagnetic material longitudinally coupled to the ferromagnetic material and the non-ferromagnetic material has a higher electrical conductivity than the ferromagnetic material.

14. The system of claim 1, wherein the selected temperature is within 25°

C., or approximately, the Curie temperature of the ferromagnetic material.

15. The system of claim 1, wherein an electrical resistance of at least a portion of the heater section decreases at and above the selected temperature such that the heater section provides the second heat output above the selected temperature.

16. The system of claim 1, wherein the electrical power supply is configured to provide a relatively constant amount of electrical current that remains within about 15% of a selected constant current value when a load of the electrical conductors changes.

17. The system of claim 1, wherein at least one of the electrical conductors has a length of at least 10 m.

18. A method for heating at least a part of a subsurface formation, comprising:

applying modulated direct current to a heater section to provide an electrically resistive heat output, the heater section comprising one or more electrical conductors electrically coupled to the electrical power supply and placed in an opening in the formation, at least one of the electrical conductors comprising ferromagnetic material;

providing a first heat output when electrical current is applied to the heater section below a selected temperature;

providing a second heat output approximately at and above the selected temperature during use, wherein the heater section has a turndown ratio of at least 1.1 to 1; and

allowing heat to transfer from the heater section to a part of the subsurface formation.

19. The method of claim 18, wherein the heater section has a turndown ratio of at least 2 to 1.

20. The method of claim 18, wherein the second heat output is lower than to the first heat output.

21. The method of claim 18, wherein the second heat output is at most 90% of the first heat output, the first heat output being at about 50°

C. below the selected temperature.

22. The method of claim 18, further comprising varying a frequency of the modulated electrical current.

23. The method of claim 18, wherein the electrical resistance of the heater section automatically decreases approximately at or above the selected temperature to provide the second heat output.

24. The method of claim 18, further comprising placing one or more of the electrical conductors in a wellbore in the formation.

25. The method of claim 18, wherein an electrical resistance of at least a portion of the heater section decreases above the selected temperature to provide the second heat output.

26. The method of claim 18, wherein the selected temperature is approximately the Curie temperature of the ferromagnetic material.

27. The method of claim 18, wherein the subsurface formation comprises a hydrocarbon containing formation.

28. The method of claim 18, wherein the subsurface formation comprises a hydrocarbon containing formation, and the method further comprises heating at least some hydrocarbons in the formation such that at least some of the hydrocarbons are pyrolyzed.

29. The method of claim 18, further comprising controlling a skin depth in the ferromagnetic material by controlling a modulation of the applied electrical current.

30. A method for heating at least a part of a subsurface formation, comprising:

applying modulated direct current to a heater section to provide an electrically resistive heat output, the heater section comprising one or more electrical conductors electrically coupled to the electrical power supply and placed in an opening in the formation, at least one of the electrical conductors comprising ferromagnetic material;

wherein the electrical current is applied to (a) provide a first heat output when the heater section below a selected temperature, and (b) provide a second heat output when the heater section is approximately at and above the selected temperature, the second heat output at most 90% of the first heat output; and

allowing heat to transfer from the heater section to a part of the subsurface formation.