Mechanical caliper system for a logging while drilling (LWD) borehole caliper

• US 9,217,323 B2
• Filed: 03/14/2013
• Issued: 12/22/2015
• Est. Priority Date: 09/24/2012
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: Clark, Brian Oliver
• Primary Examiner(s): GAY, JENNIFER HAWKINS
• Application Number:
  US13/802,778
• Publication Number:
  US 20140083771A1
• Time in Patent Office: 1,013 Days
• US Class Current: 1/1
• CPC Class Codes: E21B 10/32 with expansible cutting tools
• CPC Class Codes: E21B 47/08 Measuring diameters or related dimensions at the borehole
• CPC Class Codes: E21B 47/13 by electromagnetic energy, e.g. radio frequency

Abstract

A logging while drilling (LWD) caliper includes a drill collar, at least one movable pad, a hinge coupler, a power transmitter and a power receiver. The hinge coupler couples the movable pad to the drill collar in such a way that the movable pad can move between an open position and a closed position. The power transmitter is coupled to the drill collar in such a way that the power transmitter receives power from the drill collar. The power receiver is coupled to the movable pad in such a way that the power receiver provides power to the movable pad. Also, the power transmitter is coupled to the drill collar and the power receiver is coupled to the movable pad is such a way that power is transmitted from the power transmitter to the power receiver.

Claims

1. A method comprising:

providing a first coil within a drill collar;

providing a second coil in the moveable member;

coupling the first and second coils with a coupling coefficient, k, wherein, k=M/√

{square root over (L₁L₂)}≦

0.9, M is a mutual inductance between the first and second coils, L₁ is a first self-inductance of the first coil, and L₂ is a second self-inductance of the second coil; and

resonantly tuning the first coil at a first frequency, f₁, with a first capacitance, C₁, and the second coil at a second frequency, f₂, with a second capacitance, C₂, wherein f₁ is approximately equal to f₂,

2. The method as recited in claim 1, further comprising:

approximately matching a source impedance of the first coil, R_S, with a load impedance of the second coil, R₁, wherein R_S≈

R₁√

{square root over (1+k²Q₁Q₂)}.

3. The method as recited in claim 1, further comprising:

approximately matching a load impedance of the second coil, R₁, with a source impedance of the first coil, R_S, wherein R_L≈

R₂√

{square root over (1+k²Q₁Q₂)}.

4. The method as recited in claim 1, wherein the moveable member measures a borehole diameter.

5. The method as recited in claim 1, wherein the moveable member includes at least one of an electromagnetic measurement sensor, a nuclear measurement sensor, and an acoustic measurement sensor.

6. The method as recited in claim 1, wherein the moveable member is a moveable caliper arm or a moveable pad.

7. The method as recited in claim 1, wherein the moveable member is an under-reamer arm.

8. The method as recited in claim 1, wherein the first coil is coupled to the drill collar and the second coil is coupled to the movable member so that power is transmitted from the first coil to the second coil as a function of a distance between the movable member and the drill collar.

9. The method as recited in claim 1, wherein the moveable member comprises a plurality of movable members each coupled to the drill collar, wherein each of the plurality of movable members has a second coil coupled thereto and each second coil has a corresponding first coil coupled to the drill collar, and wherein each first coil transmits power to a corresponding second coil whereby the corresponding movable member moves between an open position and a closed position.

10. The method as recited in claim 1, further comprising monitoring the position of the movable member relative to the drill collar.

11. A logging while drilling apparatus, comprising:

a drill collar;

a moveable member coupled to the drill collar;

a first coil coupled within the drill collar;

a second coil coupled within the moveable member;

wherein the first and second coils are coupled with a coupling coefficient, k, wherein, k=M/√

{square root over (L₁L₂)}≦

0.9, M is a mutual inductance between the first and second coils, L₁ is a first self-inductance of the first coil, and L₂ is a second self-inductance of the second coil, and

wherein the first coil is resonantly tuned at a first frequency, f₁, with a first capacitance, C₁,

wherein the second coil is resonantly tuned at a second frequency, f₂, with a second capacitance, C₂, wherein f₁ is approximately equal to f₂,

12. The apparatus as recited in claim 11, wherein a source impedance of the first coil, R_S is approximately matched with a load impedance of the second coil, R₁, wherein R_S≈

R₁√

{square root over (1+k²Q₁Q₂)}.

13. The apparatus as recited in claim 11, wherein a load impedance of the second coil, R₁, is approximately matched with a source impedance of the first coil, R_S, wherein R_L≈

R₂√

{square root over (1+k²Q₁Q₂)}.

14. The apparatus as recited in claim 11, wherein the moveable member measures a borehole diameter.

15. The apparatus as recited in claim 11, wherein the moveable member includes at least one of an electromagnetic measurement sensor, a nuclear measurement sensor, and an acoustic measurement sensor.

16. The apparatus as recited in claim 11, wherein the moveable member is a caliper arm.

17. The apparatus as recited in claim 11, wherein the moveable member is an under-reamer blade.

18. The apparatus as recited in claim 11, wherein the moveable member is a moveable pad.

19. The apparatus as recited in claim 11, wherein the moveable member is coupled to the drill collar in such a way that the movable member is urged in the open position.

20. The apparatus as recited in claim 11, wherein the first coil comprises a multi-turn coil wrapped on a ferrite core, wherein the second coil comprises a multi-turn coil wrapped on a ferrite core, and wherein the first coil is coupled to the drill collar and the second coil is coupled to the movable member such that magnetic poles of the first coil and the magnetic poles of the second coil are aligned with an axis of the drill collar.

21. The apparatus as recited in claim 11, wherein the moveable member comprises a plurality of movable members each coupled to the drill collar, wherein each of the plurality of movable members has a second coil coupled thereto and each second coil has a corresponding first coil coupled to the drill collar, and wherein each first coil transmits power to a corresponding second coil whereby the corresponding movable member moves between an open position and a closed position.