Linear position sensor for downhole tools and method of use

• US 7,377,333 B1
• Filed: 03/07/2007
• Issued: 05/27/2008
• Est. Priority Date: 03/07/2007
• Status: Expired due to Fees

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Pathfinder Energy Services LLC (Schlumberger NV)
• Inventors: Sugiura, Junichi
• Primary Examiner(s): Bagnell; David J.
• Assistant Examiner(s): Andrish; Sean D
• Application Number:
  US11/714,966
• Time in Patent Office: 447 Days
• Field of Search: 175/73, 175/45, 166/66, 166/66.5, 166/61, 166/73, 166/76
• US Class Current: 175/45
• CPC Class Codes: E21B 17/1014 Flexible or expansible centering means, e.g. with pistons pressing against the wall of the well E21B17/1042 takes precedence
• CPC Class Codes: E21B 47/024 of devices in the borehole determining slope or direction of the borehole E21B47/022
• CPC Class Codes: E21B 7/06 Deflecting the direction of boreholes
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06

Abstract

Aspects of this invention include a downhole tool having first and second members disposed to translate substantially linearly with respect to one another. A magnet is deployed on the first member and a plurality of magnetic field sensors is deployed on the second member. The magnetic field sensors are spaced in a direction substantially parallel with a direction of translation between the first and second members. The tool typically further includes a controller disposed to determine a linear position of the first and second members with respect to one another from magnetic flux measurements made at the magnetic field sensors. Exemplary position sensor embodiments of the present invention are non-contact and therefore are not typically subject to mechanical wear. Embodiments of the invention therefore tend to advantageously provide for accurate and reliable linear position measurements.

Claims

1. A downhole tool comprising:

a downhole tool body;

first and second members disposed to translate substantially linearly with respect to one another;

at least one magnet deployed on the first member;

at least three magnetic field sensors deployed in a linear array on a circuit board, the circuit board deployed on the second member, the magnetic field sensors spaced in a direction substantially parallel with a direction of translation between the first and second members, at least three of the magnetic field sensors in sensory range of magnetic flux emanating from the magnet; and

a controller deployed on the circuit board along with the magnetic field sensors, the controller disposed to determine a linear position of the first and second members with respect to one another from magnetic flux measurements at the magnetic field sensors.

2. The downhole tool of claim 1, wherein the downhole tool is selected from the group consisting of wireline tools, measurement while drilling tools, logging while drilling tools, directional drilling tools, and rotary steerable tools.

3. The downhole tool of claim 1, wherein the magnet comprises a cylindrical magnet having a cylindrical axis substantially parallel with the direction of translation.

4. The downhole tool of claim 1, wherein the magnetic comprises first and second cylindrical magnets having cylindrical axes substantially parallel with the direction of translation, the first and second magnets deployed such that a magnetic pole on the first magnet is adjacent an opposing magnetic pole on the second magnet.

5. The downhole tool of claim 1, wherein the magnetic field sensors are deployed such that an axis of sensitivity of each of the sensors is substantially parallel with the direction of translation.

6. The downhole tool of claim 1, wherein the magnetic field sensors are deployed such that an axis of sensitivity of each of the sensors is substantially perpendicular to the direction of translation.

7. The downhole tool of claim 1, wherein the magnetic field sensors are selected from the group consisting of Hall-Effect sensors, magnetoresistive sensors, magnetometers, and reed switches.

38. The downhole tool of claim 1, wherein the circuit board is deployed in a sealed, pressure resistant housing.

8. A downhole steering tool configured to operate in a borehole, the steering tool comprising:

at least one blade deployed in a housing, the blade configured to displace between radially opposed retracted and extended positions in the housing;

a position sensor disposed to measure the position of the blade relative to the housing, the position sensor including a magnet assembly deployed on either the blade or the housing and a linear array of magnetic field sensors deployed on either the blade or the housing such that the linear array is substantially parallel with a direction of extension and retraction of the blade, the magnet assembly and linear array disposed to translate with respect to one another as the blade is retracted and extended in the housing, the linear array including at least three magnetic field sensors deployed along a line on a circuit board, at least three of the magnetic field sensors in sensory range of magnetic flux emanating from the magnet assembly, and

a controller deployed on the circuit board along with the magnetic field sensors, the controller disposed to determine an extension of the blade from magnetic flux measurements made by the magnetic field sensors.

9. The steering tool of claim 8, wherein the magnet assembly is deployed on the housing and the linear array is deployed on the blade.

10. The steering tool of claim 8, wherein the magnet assembly is deployed on the blade and the linear array is deployed in a sealed, pressure resistant housing which is fixed to said blade housing.

11. The steering tool of claim 8, wherein the magnetic field sensors are deployed on the array such that an axis of sensitivity of each of the sensors is substantially parallel with the direction of extension and retraction of the blade.

12. The steering tool of claim 8, wherein the magnetic field sensors are deployed on the array such that an axis of sensitivity of each of the sensors is substantially perpendicular to the direction of extension and retraction of the blade.

13. The steering tool of claim 8, wherein the magnet assembly comprises a cylindrical magnet having a cylindrical axis substantially parallel with the direction of extension and retraction of the blade.

14. The steering tool of claim 8, wherein the magnet assembly comprises first and second cylindrical magnets having cylindrical axes substantially parallel with the direction of extension and retraction of the blade, the first and second magnets deployed such that a magnetic pole on the first magnet is adjacent an opposing magnetic pole on the second magnet.

15. The steering tool of claim 8, wherein the controller is configured to determine the extension of the blade by determining at least one member of the group consisting of (i) a location in the linear array of a magnetic flux maximum and (ii) a location in the linear array of a magnetic flux null.

16. The steering tool of claim 15, wherein the controller is configured to locate the magnetic flux maximum by (i) selecting magnetic flux measurements made at three consecutive magnetic field sensors along the linear array and (ii) processing the three magnetic flux measurements according to the equation:

17. The steering tool of claim 15, wherein the controller determines the location of the magnetic flux null by (i) selecting first and second magnetic flux measurements made at adjacent magnetic field sensors having a magnetic flux null located therebetween and (ii) processing the first and second magnetic flux measurements according to the equation:

18. The steering tool of claim 8, wherein the magnetic sensors are selected from the group consisting of magnetoresistive sensors and Hall-Effect sensors.

19. A downhole tool comprising:

a downhole tool body;

a hydraulic fluid chamber deployed in the tool body and disposed to provide pressurized hydraulic fluid to at least one hydraulically actuated tool member, the hydraulic fluid chamber including a piston deployed in the chamber;

a position sensor disposed to measure a position of the piston in the chamber, the position sensor including a magnet assembly deployed on the piston and a linear array of magnetic field sensors deployed on the tool body such that the linear array is substantially parallel with a direction of motion of the piston in the chamber, the linear array including at least three magnetic field sensors deployed along a line on a circuit board, at least three of the magnetic field sensors in sensory range of magnetic flux emanating from the magnet assembly, and

a controller deployed on the circuit board along with the magnetic field sensors, the controller disposed to determine a fluid volume of the hydraulic chamber from magnetic flux measurements made by the magnetic field sensors.

20. The downhole tool of claim 19, wherein the magnetic field sensors are deployed on the array such that an axis of sensitivity of each of the sensors is substantially parallel with the direction of motion of the piston.

21. The downhole tool of claim 19, wherein the magnetic field sensors are deployed on the array such that an axis of sensitivity of each of the sensors is substantially perpendicular to the direction of motion of the piston.

22. The downhole tool of claim 19, wherein the magnet assembly produces a substantially radially symmetric flux about the piston.

23. The downhole tool of claim 19, wherein the magnet assembly comprises a cylindrical magnet having a cylindrical axis substantially parallel with the direction of motion of the piston.

24. The downhole tool of claim 19, wherein the magnetic comprises first and second cylindrical magnets having cylindrical axes substantially parallel with the direction of motion of the piston, the first and second magnets deployed such that a magnetic pole on the first magnet is adjacent an opposing magnetic pole on the second magnet.

25. The steering tool of claim 19, wherein the controller is configured to determine the fluid volume of the hydraulic chamber by determining at least one member of the group consisting of (i) a location in the linear array of a magnetic flux maximum and (ii) a location in the linear array of a magnetic flux null.

26. The steering tool of claim 25, wherein the controller is configured to locate the magnetic flux maximum by (i) selecting magnetic flux measurements made at three consecutive magnetic field sensors along the linear array and (ii) processing the three magnetic flux measurements according to the equation:

27. The steering tool of claim 25, wherein the controller determines the location of the magnetic flux null by (i) selecting first and second magnetic flux measurements made at adjacent magnetic field sensors having a magnetic flux null located therebetween and (ii) processing the first and second magnetic flux measurements according to the equation:

28. The downhole tool of claim 19, wherein:

the hydraulic fluid chamber comprises a piston pump, the piston actuated by a rotating shaft disposed to rotate with respect to the tool body; and

the tool further comprises a controller, the controller disposed to determine at least one of (i) a stroke volume of the pump, (ii) a rotation rate of the shaft with respect to the housing, and (iii) a rotational position of the shaft with respect to the house from magnetic flux measurements made by the magnetic field sensors in the linear array.

29. The downhole tool of claim 19, wherein the magnetic sensors are selected from the group consisting of magnetoresistive sensors and Hall-Effect sensors.

39. The downhole tool of claim 19, wherein the circuit board is deployed in a sealed, pressure resistant housing.

30. A directional drilling tool comprising:

a plurality of blades deployed in a housing, the blades configured to displace between radially opposed retracted and extended positions;

a hydraulic module deployed in the housing and disposed to extend the blades, the hydraulic module including a pressurized fluid chamber having a spring loaded piston;

each of the blades including a position sensor disposed to measure the position of a corresponding blade relative to the housing, each position sensor including a first magnet assembly deployed on either the corresponding blade or the housing and a first linear array of magnetic field sensors deployed on either the corresponding blade or the housing such that the first linear array is substantially parallel with a direction of extension and retraction of the blade, each of the first linear arrays including (i) at least three magnetic field sensors deployed along a line on a corresponding first circuit board and (ii) a first controller deployed on the first circuit board, the first controller disposed to determine an extension of the blade from magnetic flux measurements made by the magnetic field sensors in the first linear array, the magnet assembly and the first linear array disposed to translate with respect to one another as the blade is retracted and extended in the housing; and

a volume sensor disposed to measure a fluid volume of the pressurized fluid chamber, the volume sensor including a second magnet assembly deployed on the piston and a second linear array of magnetic field sensors deployed on the housing such that the second linear array is substantially parallel with a direction of motion of the piston in the pressurized fluid chamber, the second linear array including (i) at least three magnetic field sensors deployed along a line on a second circuit board and (ii) a second controller deployed on the second circuit board, the second controller disposed to determine a fluid volume of the pressurized fluid chamber from magnetic flux measurements made by the magnetic field sensors in the second linear array.

31. The directional drilling tool of claim 30, wherein the housing is disposed about a shaft, the shaft disposed to rotate relative to the housing.

32. The directional drilling tool of claim 30, wherein the controllers are configured to determine the corresponding blade extensions and the fluid volume by determining locations of magnetic flux nulls in the corresponding first and second linear arrays.

33. The directional drilling tool of claim 32, wherein the controller determines the location of each of the magnetic flux nulls by (i) selecting first and second magnetic flux measurements made at adjacent magnetic field sensors having a magnetic flux null located therebetween and (ii) processing the first and second magnetic flux measurements according to the equation:

40. The downhole tool of claim 30, wherein the first and second circuit boards are deployed in corresponding sealed, pressure resistant housings.

34. A method for determining a relative linear position between first and second members of a downhole tool, the method comprising:

(a) deploying a downhole tool in a borehole, the downhole tool including first and second members disposed to translate linearly with respect to one another, at least one magnet deployed on the first member, and a linear array of magnetic field sensors deployed on the second member such that the linear array is substantially parallel with a direction of translation between the first and second members, the linear array including at least three magnetic field sensors deployed along a line on a circuit board, the linear array further including a controller deployed on the circuit board;

(b) causing each of the magnetic field sensors to measure a magnetic flux; and

(c) locally processing the magnetic flux measurements with the controller to determine the relative linear position between the first and second members.

35. The method of claim 34, wherein (c) further comprises determining at least one member of the group consisting of (i) a location in the linear array of a magnetic flux maximum and (ii) a location in the linear array of a magnetic flux null.

36. The method of claim 35, wherein determining the location of the magnetic flux maximum in (c) further comprises:

(i) selecting magnetic flux measurements made at three consecutive magnetic field sensors along the linear array; and

(ii) processing the three magnetic flux measurements according to the equation;

37. The method of claim 35, wherein determining the location of the magnetic flux null in (c) further comprises:

(i) selecting first and second magnetic flux measurements made at adjacent magnetic field sensors having a magnetic flux null located therebetween; and

(ii) processing the first and second magnetic flux measurements according to the equation;