System And Method For Power Transmission In A Bottom Hole Assembly

• US 20140084696A1
• Filed: 03/13/2013
• Published: 03/27/2014
• Est. Priority Date: 09/24/2012
• Status: Abandoned Application

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Clark, Brian Oliver, Moriarty, Keith A., Gadot, Raphael
• Application Number:
  US13/798,080
• Publication Number:
  US 20140084696A1
• Time in Patent Office: Days
• US Class Current: 307/104
• CPC Class Codes: H04B 5/0031 for data transfer
• CPC Class Codes: H04B 5/0037 for power transfer
• CPC Class Codes: H04B 5/0093 with one coil at each side, e.g. with primary and secondary coils
• CPC Class Codes: H04B 5/266 One coil at each side, e.g. with primary and secondary coils
• CPC Class Codes: H04B 5/72 for local intradevice communication
• CPC Class Codes: H04B 5/79 for data transfer in combination with power transfer

Abstract

Various embodiments of methods and systems for wireless power and data communications transmissions to a sensor subassembly below a mud motor in a bottom hole assembly are disclosed. In a certain embodiment, a float valve is located above the motor. Power is supplied by a turbine or by batteries located in a subassembly above the float valve. Wires pass through the float valve and connect to an annular coil. Power is transmitted through the annular coil to an inductively coupled second, mandrel coil that is attached to the rotor. By leveraging resonantly tuned circuits and impedance matching techniques for the coils, power can be transmitted efficiently from one coil to the other despite relative movement and misalignment of the two coils.

Claims

1. A method for transmitting electrical power from a power source located above a positive displacement motor (“

PDM”

) in a bottom hole assembly of a drill string to a sensor subassembly located below the PDM in the drill string, the method comprising;

inductively coupling a pair of coils comprising a primary coil and a secondary coil, wherein;

the coils are located above the PDM;

the primary coil is an annular coil and the secondary coil is a mandrel coil extending from a rotor of the PDM;

the secondary coil is substantially positioned within a space defined by the primary coil;

the coils are loosely coupled such that;

k=M/√

{square root over (L₁L₂)}≦

0.9, wherein k is the coupling coefficient of the coils, M is the mutual inductance between the coils, and L₁ and L₂ are the self-inductances of the respective coils;

each coil is resonantly tuned with a capacitor such that;

f₁≈

f₂, wherein

2. The method of claim 1, further comprising approximately matching an impedance of the source, R_S, with an impedance of a load by setting:

R_S≈

R₁√

{square root over (1+k²Q₁Q₂)},

wherein R₁ is the series resistance of the primary coil, k is the coupling coefficient of the pair of coils, Q₁ is the quality factor associated with primary coil and Q₂ is the quality factor associated with the secondary coil.

3. The method of claim 1, further comprising approximately matching an impedance of a load, R_L, with an impedance of the source by setting:

R_L≈

R₂√

{square root over (1+k²Q₁Q₂)},

wherein R₂ is the series resistance of the secondary coil, k is the coupling coefficient of the pair of coils, Q₁ is the quality factor associated with primary coil and Q₂ is the quality factor associated with the secondary coil.

4. The method of claim 1, wherein the secondary coil comprises a wire wrapped on a core comprised of ferrite.

5. The method of claim 1, wherein the primary coil comprises a wire wrapped inside a cylinder comprised of ferrite.

6. The method of claim 1, wherein the power transferred from the primary coil to the inductively coupled secondary coil comprises data in the form of a modulated amplitude, phase or frequency of a current that drives the primary coil.

7. A method for transmitting electrical power from a power source located above a positive displacement motor (“

PDM”

) in a bottom hole assembly of a drill string to a sensor subassembly located below the PDM in the drill string, the method comprising;

inductively coupling a pair of coils comprising a primary coil and a secondary coil, wherein;

the coils are located above the PDM;

the primary coil is an annular coil and the secondary coil is a mandrel coil extending from a rotor of the PDM; and

the secondary coil is substantially positioned within a space defined by the primary coil;

providing power from the power source to the primary coil via a wired connection, wherein provision of the power to the primary coil causes power to be transmitted to the inductively coupled secondary coil; and

providing power from the secondary coil to the sensor subassembly via a wired connection that passes through the rotor of the PDM.

8. The method of claim 7, wherein the coupling coefficient, k, of the pair of coils is less than or equal to 0.9.

9. The method of claim 7, further comprising resonantly tuning the pair of coils with a capacitor such that the coils resonate at approximately the same frequency.

10. The method of claim 7, wherein a figure of merit, U, associated with the pair of coils is equal to or greater than 3.

11. The method of claim 7, wherein each of the pair of coils is associated with a high quality factor, Q, that is equal to or greater than 10.

12. The method of claim 7, further comprising approximately matching an impedance of the source, R_S, with an impedance of a load by setting:

R_S≈

R₁√

{square root over (1+k²Q₁Q₂)},

wherein R₁ is the series resistance of the primary coil, k is the coupling coefficient of the pair of coils, Q₁ is the quality factor associated with primary coil and Q₂ is the quality factor associated with the secondary coil.

13. The method of claim 7, further comprising approximately matching an impedance of a load, R_L, with an impedance of the source by setting:

R_L≈

R₂√

{square root over (1+k²Q₁Q₂)},

wherein R₂ is the series resistance of the secondary coil, k is the coupling coefficient of the pair of coils, Q₁ is the quality factor associated with primary coil and Q₂ is the quality factor associated with the secondary coil.

14. A system for transmitting electrical power from a power source located above a positive displacement motor (“

PDM”

) in a bottom hole assembly of a drill string to a sensor subassembly located below the PDM in the drill string, the system comprising;

an inductively coupled pair of coils comprising a primary coil and a secondary coil, wherein;

the coils are located above the PDM;

the primary coil is an annular coil and the secondary coil is a mandrel coil extending from a rotor of the PDM; and

the secondary coil is substantially positioned within a space defined by the primary coil;

a power source coupled to the primary coil via a wired connection and operable to provide power to the primary coil, wherein provision of the power to the primary coil causes power to be transmitted to the inductively coupled secondary coil; and

a wired connection through the rotor of the PDM operable to provide power from the secondary coil to the sensor subassembly.

15. The system of claim 14, wherein the coupling coefficient, k, of the pair of coils is less than or equal to 0.9.

16. The system of claim 14, wherein the pair of coils are resonantly tuned with a capacitor such that the coils resonate at approximately the same frequency.

17. The system of claim 14, wherein a figure of merit, U, associated with the pair of coils is equal to or greater than 3.

18. The system of claim 14, wherein each of the pair of coils is associated with a high quality factor, Q, that is equal to or greater than 10.

19. The system of claim 14, wherein the impedance of the source, R_S, is approximately matched with an impedance of a load by setting:

R_S≈

R₁√

{square root over (1+k²Q₁Q₂)},

wherein R₁ is the series resistance of the primary coil, k is the coupling coefficient of the pair of coils, Q₁ is the quality factor associated with primary coil and Q₂ is the quality factor associated with the secondary coil.

20. The system of claim 14, wherein the impedance of a load, R_L, is approximately matched with an impedance of the source by setting:

R_L≈

R₂√

{square root over (1+k²Q₁Q₂)},

wherein R₂ is the series resistance of the secondary coil, k is the coupling coefficient of the pair of coils, Q₁ is the quality factor associated with primary coil and Q₂ is the quality factor associated with the secondary coil.