Method and apparatus for measuring mud resistivity

• US 7,091,722 B2
• Filed: 09/29/2004
• Issued: 08/15/2006
• Est. Priority Date: 09/29/2004
• Status: Expired due to Fees

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: Sebline, Nicolas, Homan, Dean M., Omeragic, Dzevat, Wang, Hanming
• Primary Examiner(s): LEDYNH, BOT L
• Application Number:
  US10/711,657
• Publication Number:
  US 20060066313A1
• Time in Patent Office: 685 Days
• Field of Search: 324/324, 324/339, 324/346, 324/369
• US Class Current: 324/339
• CPC Class Codes: G01V 3/28 using induction coils

Abstract

A sensor for measuring mud resistivity in a borehole includes a transmitter having a magnetic moment in a first direction; and a receiver having a magnetic moment in a second direction, wherein the first direction and the second direction are substantially different, wherein the transmitter and the receiver are disposed in an insulating collar of a downhole tool, and wherein the transmitter is disposed at a selected distance no more than 10 inches from the receiver along a longitudinal axis of the downhole tool.

Claims

1. A sensor for measuring mud resistivity in a borehole, comprising:

a transmitter having a magnetic moment in a first direction; and

a receiver having a magnetic moment in a second direction,

wherein the first direction and the second direction are substantially different,

wherein the transmitter and the receiver are disposed in an insulating collar of a downhole tool, and

wherein the transmitter is disposed at a selected distance no more than 10 inches from the receiver along a longitudinal axis of the downhole tool.

2. The sensor of claim 1, wherein the first direction is substantially orthogonal to the second direction.

3. The sensor of claim 1, wherein at least one of the transmitter and receiver is on a printed circuit board.

4. The sensor of claim 1, wherein the selected distance is no more than 5 inches.

5. The sensor of claim 1, wherein the selected distance is no more than 2 inches.

6. The sensor of claim 1, wherein the selected distance is about 1 inch.

7. The sensor of claim 1, wherein one of the first direction and the second direction is substantially perpendicular to the longitudinal axis of the downhole tool.

8. The sensor of claim 1, wherein one of the first direction and the second direction is substantially parallel to the longitudinal axis of the downhole tool.

9. The sensor of claim 1, wherein at least one antenna of the transmitter and the receiver comprises a tilted antenna.

10. The sensor of claim 1, wherein the transmitter and the receiver are in a module configured to be placed in a cavity in the insulating collar of the downhole tool.

11. The sensor of claim 1, wherein the downhole tool is one selected from a wireline tool, measurement-while-drilling tool, logging-while-tripping tool, and a logging-while-drilling tool.

12. A sensor for measuring mud resistivity in a borehole, comprising:

a transmitter having a magnetic moment in a first direction; and

a receiver having a magnetic moment in a second direction,

wherein the first direction and the second direction are substantially different,

wherein the transmitter and the receiver are disposed in an insulating collar of a downhole tool, and

wherein the transmitter and the receiver, when projected onto a plane substantially perpendicular to a longitudinal axis of the downhole tool, are separated from each other by an azimuthal angle of less than 90 degrees.

13. The sensor of claim 12, wherein the azimuthal angle is no more than 45 degrees.

14. The sensor of claim 12, wherein the azimuthal angle is no more than 30 degrees.

15. The sensor of claim 12, wherein the first direction is substantially orthogonal to the second direction.

16. The sensor of claim 12, wherein at least one antenna of the transmitter and the receiver comprises a tilted antenna.

17. The sensor of claim 12, wherein at least one of the transmitter and receiver is on a printed circuit board.

18. The sensor of claim 12, wherein one of the first direction and the second direction is substantially perpendicular to the longitudinal axis of the downhole tool.

19. The sensor of claim 12, wherein one of the first direction and the second direction is substantially parallel to the longitudinal axis of the downhole tool.

20. The sensor of claim 12, wherein the transmitter and the receiver are in a module configured to be placed in a cavity in the insulating collar of the downhole tool.

21. The sensor of claim 12, wherein the downhole tool is one selected from a wireline tool, measurement-while-drilling tool, logging-while-tripping tool, and a logging-while-drilling tool.

22. A downhole tool comprising a mud resistivity sensor disposed in an insulating portion of the downhole tool, wherein the mud resistivity sensor comprises:

a transmitter having a magnetic moment in a first direction; and

a receiver having a magnetic moment in a second direction,

wherein the first direction and the second direction are substantially different,

wherein the transmitter is disposed at a selected distance no more than 10 inches from the receiver along a longitudinal axis of the downhole tool.

23. A downhole tool comprising at least one mud resistivity sensor disposed in an insulating portion of a lowermost section of the downhole tool, wherein the mud resistivity sensor comprises:

a transmitter having a magnetic moment in a first direction; and

a receiver having a magnetic moment in a second direction,

wherein the first direction and the second direction are substantially different, and

wherein the transmitter is disposed at a selected distance no more than 10 inches from the receiver along a longitudinal axis of the downhole tool.

24. The downhole tool of claim 23, wherein the at least one mud resistivity sensor comprises two mud resistivity sensors, wherein the two mud resistivity sensors are disposed at a substantially identical location along a longitudinal axis of the downhole tool.

25. A method for measuring mud resistivity in a wellbore, comprising:

energizing a transmitter to induce a magnetic field, wherein the transmitter has a magnetic moment in a first direction;

acquiring a voltage measurement using a receiver at a selected location,

wherein the receiver has a magnetic moment in a second direction that is substantially different from the first direction, and wherein the selected location is no more than 10 inches away from the transmitter; and

deriving a mud conductivity from the voltage measurement.

26. The method of claim 25, wherein the transmitter is energized by passing an alternate current having a frequency of at least 400 KHz.

27. The method of claim 25, wherein the selected location is no more than 5 inches from the transmitter.

28. The method of claim 25, wherein the selected location is no more than 2 inches from the transmitter.

29. The method of claim 25, wherein the first direction is substantially orthogonal to the second direction.