Downhole signal source

• US 20050264293A1
• Filed: 05/28/2004
• Published: 12/01/2005
• Est. Priority Date: 05/28/2004
• Status: Active Grant

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Gao, Li, Rodney, Paul F.
• Granted Patent: US 7,219,748 B2
• Time in Patent Office: Days
• US Class Current: 324/326
• CPC Class Codes: G01V 11/002 Details, e.g. power supply systems for logging instruments, transmitting or recording data, specially adapted for well logging, also if the prospecting method is irrelevant means for transmitting well survey signals E21B47/12; signal transmission systems in general G08C; transmission in general H04B

Abstract

A signaling apparatus comprises a magnet and a shield moveable relative to the magnet. The shield is moveable relative to the magnet between a first position in which the magnet is relatively exposed and a second position in which the magnet is relatively shielded. The apparatus can include a synchronization signal source, a downhole sensor signal source, and/or means for modulating the magnetic field in response to the signal from any source. A method of using the signaling apparatus to locate a bottomhole assembly includes moving the shield so as to modulate the magnetic field created by the magnet, sensing the modulation of the magnetic field, and determining the location of the bottomhole assembly using the information collected. The BHA can be located using phase shift or amplitude measurements. Receivers detecting the modulated magnetic field can be at or below the earth'"'"'s surface.

Claims

1. A downhole tool, comprising:

a magnet; and

a shield moveable relative to said magnet.

2. The tool according to claim 1 wherein said magnet comprises a permanent magnet and said magnetic shield is moveable relative to said magnet between a first position in which said magnet is relatively exposed and a second position in which said magnet is relatively shielded.

3. The tool according to claim 1 wherein said magnet comprises an electromagnet.

4. The tool according to claim 1, further including means for providing a synchronization signal and means for controlling movement of said shield in response to said signal so as to modulate the magnetic field created by said magnet.

5. The tool according to claim 4 wherein said means for controlling includes means for doubling the frequency of said synchronization signal.

6. The tool according to claim 1, further including a downhole sensor generating a signal and means for modulating the magnetic field created by said magnet in response to said signal from said downhole sensor.

7. The tool according to claim 1, further including a downhole sensor generating a sensor signal, said shield being moveable in response to said sensor signal so as to modulate the magnetic field created by said magnet.

8. A low frequency magnetic signaling device, comprising:

a permanent magnet; and

a magnetically permeable shield moveable relative to said magnet.

9. A method of locating a bottomhole assembly in a well, comprising:

a) providing a signaling device coupled to said bottomhole assembly, said signaling device comprising a magnet and a shield moveable relative to said magnet;

b) moving said shield so as to modulate the magnetic field created by said magnet;

c) sensing said modulation of the magnetic field; and

d) determining the location of the bottomhole assembly using information collected in step c).

10. The method according to claim 9, further including providing a synchronization signal and using said synchronization signal to control modulation by said shield of the magnetic field created by said magnet.

11. The tool according to claim 10, further including controlling said modulation in response to said synchronization signal.

12. The tool according to claim 11 wherein said controlling step includes doubling the frequency of said synchronization signal.

13. The method according to claim 11 wherein step c) includes detecting a phase shift between said synchronization signal and said modulated magnetic field.

14. The method according to claim 11 wherein step c) includes detecting amplitude variations in said modulated magnetic field.

15. The method according to claim 9, further including providing a plurality of receivers spaced apart from said bottomhole assembly, wherein step c) includes using said sensors to detect said modulation.

16. The method according to claim 15 wherein said receivers are located below the earth'"'"'s surface.

17. The method according to claim 15 wherein said receivers are located at the earth'"'"'s surface.

18. A method of locating a bottomhole assembly in a well, comprising:

a) providing a signaling device coupled to said bottomhole assembly, said signaling device comprising a magnet and a shield moveable relative to said magnet;

b) providing a synchronization signal

c) using said synchronization signal to control modulation of the magnetic field created by said magnet by moving said shield in response to said signal;

d) detecting said modulation of the magnetic field; and

e) determining the location of the bottomhole assembly using information collected in step d).

19. The tool according to claim 18 wherein step c) includes doubling the frequency of said synchronization signal.

20. The method according to claim 18 wherein step e) includes detecting a phase shift between said synchronization signal and said modulated magnetic field.

21. The method according to claim 18 wherein step e) includes detecting amplitude variations in said modulated magnetic field.

22. The method according to claim 18, further including providing a plurality of receivers spaced apart from said bottomhole assembly, wherein step e) includes using said receivers to detect said modulation.

23. The method according to claim 22 wherein said receivers are located below the earth'"'"'s surface.

24. The method according to claim 22 wherein said receivers are located at the earth'"'"'s surface.