Turbine speed control system for downhole tool

Patent metadata

Field	Value
Publication number	US-9551186-B2
Application number	US-201314025726-A
Country	US
Kind code	B2
Filing date	Sep 12, 2013
Priority date	Sep 13, 2012
Publication date	Jan 24, 2017
Grant date	Jan 24, 2017

Abstract

Systems, methods, and devices are provided to generate a stable supply of electrical power in a drill string. In one example, a downhole turbine generator includes a turbine, a speed governor, and an alternator. The turbine may transform hydraulic power of a first fluid medium into rotational power of a rotating shaft. The speed governor may reduce the rotational power of the rotating shaft in a variable amount that depends on the speed of the rotating shaft. Specifically, weighted arms may shear a second fluid medium more when the speed is higher and less when the speed is lower. The shearing of the second fluid medium may generate a countervailing torque on the rotating shaft to reduce the rotational power of the rotating shaft. The alternator then may produce a generally stable supply of electrical power from the rotational power of the rotating shaft.

First claim

What is claimed is:

1. A downhole turbine generator comprising:
a turbine to transform hydraulic power of a first fluid medium passing through the turbine into rotational power of a rotating shaft
a speed governor to reduce the rotational power of the rotating shaft by a variable amount depending on a speed of the rotating shaft, wherein the speed governor comprises weighted arms that shear a second fluid medium to a greater degree when the speed of the rotating shaft is higher and shear the second fluid medium to a lesser degree when the speed of the rotating shaft is lower, wherein the shearing of the second fluid medium generates a countervailing torque on the rotating shaft that reduces the rotational power of the rotating shaft; and
an alternator configured to produce electrical power from the rotational power of the rotating shaft,

wherein at least a part of each weighted arm of the speed governor is configured to shear the second fluid medium by extending farther away from the rotating shaft and further into the second fluid medium when the speed of the rotating shaft is higher.

2. The downhole turbine generator of claim 1 , wherein the first fluid medium comprises drilling fluid.

3. The downhole turbine generator of claim 1 , wherein each weighted arm of the speed governor comprises a rotatable member that rotates around a respective arm axis, wherein a center of mass of each rotatable member is configured to move away from the rotating shaft owing at least in part to a centripetal force exerted by the rotating shaft and wherein the center of mass of each rotatable member is configured to move toward the rotating shaft owing at least in part to the shearing of the second fluid medium.

4. The downhole turbine generator of claim 1 , wherein each weighted arm of the speed governor comprises a rotatable member that rotates around a respective arm axis, wherein a center of mass of each rotatable member is configured to move away from the rotating shaft owing at least in part to a centripetal force exerted by the rotating shaft and wherein the center of mass of each rotatable member is configured to move toward the rotating shaft owing at least in part to a torsion device that provides a torque around the respective arm axis.

5. The downhole turbine generator of claim 1 , wherein the speed governor comprises at least two weighted arms.

6. The downhole turbine generator of claim 1 , wherein the speed governor comprises at least three weighted arms.

7. The downhole turbine generator of claim 1 , comprising a housing that contains the second fluid medium and at least the speed governor, wherein the housing separates the speed governor and the second fluid medium from the first fluid medium.

8. The downhole turbine generator of claim 7 , wherein the housing is configured to permit heat transfer from the second fluid medium to the first fluid medium to dissipate heat generated by the shearing of the second fluid medium.

9. A rotational speed governor for a downhole turbine generator, the rotational speed governor comprising:
a housing containing a fluid medium;
a rotatable shaft at least partially disposed within the housing, wherein the rotatable shaft is configured to rotate along a first axis;
a first member attached to the rotatable shaft, wherein the first member extends radially from the rotatable shaft;
a first weighted arm coupled to the first member, wherein the first weighted arm is configured to be at least partially rotatable around a second axis, wherein the second axis is parallel to the first axis and the second axis is configured to revolve around the first axis when the rotatable shaft rotates;
wherein a rotation of the rotatable shaft is configured to cause a centripetal force that causes the first weighted arm to at least partially rotate around the second axis, thereby extending into, and shearing, a volume of the fluid medium, wherein the shearing of the fluid medium by the first weighted arm results in a countervailing torque on the rotatable shaft that reduces a rotational power of the rotatable shaft to a greater degree when the rotation of the rotatable shaft is higher and that reduces a rotational power of the rotatable shaft to a lesser degree when the rotation of the rotatable shaft is lower.

10. The speed governor of claim 9 , comprising:
a second member substantially identical to the first member, wherein the second member is attached to the opposite side of the rotatable shaft from the first member; and
a second weighted arm substantially identical to the first weighted arm, wherein the second weighted arm is coupled to the second member and configured to operate in substantially the same way as the first weighted arm.

11. The speed governor of claim 9 , comprising:
at least two additional members substantially identical to the first member, wherein the at least two additional members are attached to the rotatable shaft along a plane perpendicular to the first axis, wherein the first member and the at least two additional members are attached to the rotatable shaft approximately equal distances apart from one another; and
at least two weighted arms substantially identical to the first weighted arm, wherein the at least two weighted arms are respectively coupled to the at least two additional members and are configured to operate in substantially the same way as the first weighted arm.

12. The speed governor of claim 9 , comprising a torsion spring attached to the first member and the first weighted arm, wherein the torsion spring is configured to apply a torque that at least partially counteracts the centripetal force on the first weighted arm.

13. The speed governor of claim 9 , wherein the first weighted arm is unequally balanced around the second axis.

14. A drill string used for drilling a borehole through a rock formation, the drill string comprising:
a downhole tool configured to measure a characteristic of the rock formation; and
a turbine generator according to claim 4 configured to generate electrical power to power the downhole tool, wherein the turbine generator is configured to:
convert hydraulic power of drilling fluid pumped through the drill string into rotational mechanical power of a rotating shaft;
maintain a speed of the rotating shaft within a range of acceptable speeds despite changes in a flow rate of the drilling fluid, wherein the speed of the rotating shaft is maintained by causing a fluid medium other than the drilling fluid to shear and produce a countervailing torque on the rotating shaft that is higher when the speed of the rotating shaft is higher and that is lower when the speed of the rotating shaft is lower; and
convert the rotational mechanical power of the rotating shaft into the electrical power.

15. The drill string of claim 14 , wherein the turbine generator comprises a housing, within which is wholly contained a rotor speed governor that is configured to maintain the speed of the rotating shaft within a range of acceptable speeds.

16. A method for drilling a borehole comprising:
pumping drilling fluid into a drill string, thereby supplying hydraulic power to a turbine generator of the drill string, wherein the turbine generator is according to claim 1 , wherein the speed governor wholly internal to the turbine generator is configured to cause the turbine generator to generate electrical power within a range of acceptable output voltages despite changes in drilling fluid flow rate;
operating a downhole tool of the drill string using the electrical power generated by the turbine generator of the drill string.

Assignees

• Schlumberger Technology Corp

Inventors

• Amsellem Olivier

Classifications

• F16D51/40

  all extending in the same direction from their pivots · CPC title

• F16D57/02

  with blades or like members braked by the fluid · CPC title

• F16D2127/002

  speed-responsive · CPC title

• E21B4/02 Primary

  Fluid rotary type drives · CPC title

• H02K7/1823

  structurally associated with turbines or similar engines · CPC title