Magnetic damper

Abstract

A device may include a housing, wherein the housing has a longitudinal axis. A device may include a magnet rotationally fixed to the housing. A device may include a rotational mass supported in the housing and rotatable relative to the housing around a rotational axis with a magnetic field of the magnet penetrating the rotational mass, the rotational mass including an electrically conductive material that produces an eddy current when translated relative to the magnetic field.

Description

MAGNETIC DAMPERBACKGROUND

[0001] During drilling of a borehole, the drill string and components of the drill string are exposed to rotational inertia and episodes of shock and vibration during drilling. The transmission and propagation of the shock and vibration through the drill string can damage components.SUMMARY

[0002] In some aspects, the techniques described herein relate to a downhole tool including: a housing, wherein the housing has a longitudinal axis; a magnet rotationally fixed to the housing; and a rotational mass supported in the housing and rotatable relative to the housing around a rotational axis with a magnetic field of the magnet penetrating the rotational mass, the rotational mass including an electrically conductive material that produces an eddy current when translated relative to the magnetic field.

[0003] In some aspects, the techniques described herein relate to a downhole tool including: a housing, wherein the housing has a longitudinal axis; a magnet rotationally fixed to the housing; a rotational mass supported in the housing and rotatable relative to the housing around a rotational axis with a magnetic field of the magnet penetrating the rotational mass, the rotational mass including an electrically conductive material that produces an eddy current when translated relative to the magnetic field; and a means for moving the magnet in a radial direction relative to the rotational axis of the rotational mass.

[0004] In some aspects, the techniques described herein relate to a downhole tool including: a housing, wherein the housing has a longitudinal axis; a magnet rotationally fixed to the housing; a rotational mass supported in the housing and rotatable relative to the housing around a rotational axis with a magnetic field of the magnet penetrating the rotational mass, the rotational mass including an electrically conductive material that produces an eddy current when translated relative to the magnetic field; a means for changing the magnetic field; at least one sensor; and a controller in data communication with the sensor and the means for changing the magnetic field, wherein the controller instructs the means for changing the magnetic field at least partially in response to a signal received from the sensor.

[0005] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] In order to describe the manner in which the above-recited and other features of the disclosure can be obtained, a more particular description will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. For better understanding, the like elements have been designated by like reference numbers throughout the various accompanying figures. While some of the drawings may be schematic or exaggerated representations of concepts, non-schematic drawings should be considered as being to scale for some embodiments of the present disclosure, but not to scale for other embodiments contemplated herein. Understanding that the drawings depict some example embodiments, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0007] FIG. 1 is a side schematic view of a drilling system, according to some embodiments of the present disclosure;

[0008] FIG. 2-1 and 2-2 illustrate torsional shock and vibration in a drill string, according to some embodiments of the present disclosure;

[0009] FIG. 3-1 and 3-2 are cross-sectional views of a viscous grease damper, according to some embodiments of the present disclosure;

[0010] FIG. 4 is a schematic illustration of eddy current generation in a magnetic damper, according to some embodiments of the present disclosure;

[0011] FIG. 5 is a side cross-sectional view of a magnetic damper with axially positioned magnets, according to some embodiments of the present disclosure;

[0012] FIG. 6 is a side cross-sectional view of a magnetic damper with radially positioned magnets, according to some embodiments of the present disclosure;

[0013] FIG. 7-1 and FIG. 7-2 are side cross-sectional views of a magnetic damper with actively movable magnets, according to some embodiments of the present disclosure;

[0014] FIG. 8 is a side cross-sectional view of a magnetic damper with passively movable magnets, according to some embodiments of the present disclosure; and

[0015] FIG. 9 is a side cross-sectional view of a magnetic damper with selectively actuatable electromagnets, according to some embodiments of the present disclosure.DETAILED DESCRIPTION

[0016] Embodiments of the present disclosure generally relate to devices, systems, and methods for limiting propagation of shock and vibration through a drilling assembly, drill string, or bottomhole assembly in a downhole environment. More particularly, the present disclosure relates to damping, absorbing, or otherwise reducing oscillations in a drill string. In some embodiments, a drill string includes a plurality of components coupled together to form a long assembly. In some embodiments, the drill string is rotated in the downhole environment to remove material from a target material, such as surrounding geological formation, a borehole casing, or another downhole tool. In some examples, the drill string can further contact and experience friction with the walls of the borehole or casing. The contact with the target material and / or contact with the borehole walls can apply torque to different longitudinal portions of the drill string, which can induce torsional oscillations along the drill string. In some embodiments, the torsional shock, vibration, oscillations, or combinations thereof can damage downhole components.

[0017] The rotational energy imparted by the torques applied to the drill string can be damped, absorbed, or otherwise reduced by a rotational damper positioned in the drill string at one or more locations. A portion of the rotational damper is rotatable relative to the rest of the drill string around a rotational axis. In some embodiments, the rotational axis of the rotational damper is coaxial with the rotational axis of the drill string. In a conventional rotational damper, a rotational mass of the rotational damper is rotatable relative to a housing and connected to the housing by a viscous grease that transmits a portion of the rotational energy to the rotational mass by fluidic drag of the viscous grease between the housing and the rotational mass. The viscous grease transmits rotational energy based at least partially on the viscosity of the grease in a chamber of the housing, surface features of an outer surface of the rotational mass contacting the grease, the inner surface of the housing proximate the chamber contacting the grease, or combinations thereof.

[0018] The transfer of rotational energy from the housing to the rotational mass and / or from the rotational mass to the housing can damp sudden changes in relative rotational speed of the drillstring relative to the rotational mass. For example, the transfer of rotational energy between the rotational mass and the housing can accelerate the housing and slow the rotational mass during a sudden relative decrease in the rotational speed of the housing (e.g., sticking). In other examples, the transfer of rotational energy between rotational mass and housing can accelerate the rotational mass and slow the housing during sudden relative increases in the rotational speed of the housing (e.g., slipping). In some conventional dampers, the viscous grease can render the damper difficult to assemble and / or service. The viscosity of the grease can change with temperature, degrading the performance of the damper during periods of high demand for the damper.

[0019] In some embodiments according to the present disclosure, a damper includes one or more magnets fixed relative to a housing and positioned proximate a rotational mass. The magnets produce a magnetic field through which an electrically conductive material of the rotational mass moves. As the electrically conductive material moves through the magnetic field of the magnets, an electrical eddy current is generated in the electrically conductive material, and the electrical eddy current produces a resultant force on the electrically conductive material in the magnetic field to resist the movement of the electrically conductive material through the magnetic field. The magnitude of the electrical eddy currents generated in the electrically conductive material is proportionate to the speed of the electrically conductive material through the magnetic field, and the resultant force is proportionate to the magnitude of the electrical eddy currents. In some embodiments, a greater differential rotational speed of the housing relative to the electrically conductive material of the rotational mass creates a proportionately larger force therebetween to damp the shock, vibration, oscillations, or combinations thereof of the housing and drill string connected thereto.

[0020] FIG. 1 illustrates an embodiment of a drilling system and downhole environment. FIG. 1 shows one example of a drilling system 100 for drilling an earth formation 101 to form a wellbore 102. The drilling system 100 includes a drill rig 103 used to turn a drilling assembly 104 which extends downward into the wellbore 102. The drilling assembly 104 may include a drill string 105 and a bottomhole assembly (BHA) 106 attached to the downhole end of drill string 105. Where the drilling system 100 is used for drilling formation, a drill bit 110 can be included at the downhole end of the BHA 106.

[0021] The drill string 105 may include several joints of drill pipe 108 connected end-to-end through tool joints 109. The drill string 105 transmits drilling fluid through a central bore and cantransmit rotational power from the drill rig 103 to the BHA 106. In some embodiments, the drill string 105 may further include additional components such as subs, pup joints, etc. The drill pipe 108 provides a hydraulic passage through which drilling fluid 111 is pumped from the surface. The drilling fluid 111 discharges through selected-size nozzles, jets, or other orifices in the bit 110 for the purposes of cooling the bit 110 and cutting structures thereon, for lifting cuttings out of the wellbore 102 as it is being drilled, and for preventing the collapse of the wellbore 102. The drilling fluid 111 carries drill solids including drill fines, drill cuttings, and other swarf from the wellbore 102 to the surface. The drill solids can include components from the earth formation 101, the drilling assembly 104 itself, from other man-made components (e.g., plugs, losttools / components, etc.), or combinations thereof.

[0022] The BHA 106 may include the bit 110 or other components. An example BHA 106 may include additional or other components (e.g., coupled between to the drill string 105 and / or the bit 110). Examples of additional BHA components include drill collars, stabilizers, measurement- while-drilling (MWD) tools, logging-while-drilling (LWD) tools, downhole motors, underreamers, directional steering tools, section mills, hydraulic disconnects, jars, vibration or dampening tools, other components, or combinations of the foregoing.

[0023] In general, the drilling system 100 may include other drilling components and accessories, such as special valves (e.g., kelly cocks, blowout preventers, safety valves, centrifuges, shaker tables, and rheometers). Additional components included in the drilling system 100 may be considered a part of the surface system (e.g., drill rig 103, drilling assembly 104, drill string 105, or a part of the BHA 106, depending on their locations and / or use in the drilling system 100).

[0024] The bit 110 in the BHA 106 may be any type of bit suitable for degrading downhole materials. For instance, the bit 110 may be a drill bit suitable for drilling the earth formation 101. Example types of drill bits used for drilling earth formations are fixed-cutter or drag bits, roller cone bits, impregnated bits, or coring bits. In other embodiments, the bit 110 may be a mill used for removing metal, composite, elastomer, other materials downhole, or combinations thereof. For instance, the bit 110 may be used with a whipstock to mill into casing 107 lining the wellbore 102. The bit 110 may also be a junk mill used to mill away tools, plugs, cement, other materials within the wellbore 102, or combinations thereof. Swarf or other cuttings formed by use of a mill may be lifted to surface by the drilling fluid 111 or may be allowed to fall downhole. The conditions ofthe equipment of the drilling system 100, the formation 101, the wellbore 102, the drilling fluid 111, or other part of the wellsite can change during operations.

[0025] FIG. 2-1 and FIG. 2-2 schematically illustrate a torsional oscillation of a portion of a drill string 205. FIG. 2-1 illustrates a rotating drill string 205 sticking in a downhole environment. In a steady state, a first longitudinal portion 212-1 of the drill string 205 at a first longitudinal location on the drill string 205 is rotating at a first rotational speed 214-1 and a second longitudinal portion 212-2 of the drill string 205 at a second longitudinal location on the drill string 205 is rotating at the same first rotational speed. When the second longitudinal portion 212-2 of the drill string 205 sticks or otherwise slows in the rotational direction to a second rotational speed 214-2, torsional energy can build in the drill string 205 (e.g., as a torsional spring) as the first longitudinal portion 212-1 of the drill string 205 continues rotating at the first rotational speed 214-1.

[0026] FIG. 2-2 illustrates the second longitudinal portion 212-2 of the drill string 205 slipping and the torsional energy stored in the torsional spring of the drill string 205 releasing. The torsional energy accelerates the second longitudinal portion 212-2 of the drill string 205 to a third rotational speed 214-3 greater than the first rotational speed, and the second longitudinal portion 212-2 can oscillate as the first longitudinal portion 212-1 and the second longitudinal portion 212-2 of the drill string 205 equilibrate back to a steady state. In some embodiments, sudden acceleration of portions of the drill string, deceleration of portions of the drill string, oscillation of portions of the drill string, and vibrations associated therewith can damage components of the drill string. In some embodiments, the sudden acceleration of portions of the drill string, deceleration of portions of the drill string, oscillation of portions of the drill string, and vibrations associated therewith can create challenges in steering or controlling the drill string in the downhole environment. A rotational damper can damp the sudden acceleration of portions of the drill string, deceleration of portions of the drill string, oscillation of portions of the drill string, and vibrations associated therewith to improve performance, control, and operational lifetime of a drill string and components thereof.

[0027] FIG. 3-1 is a cross-sectional view of an embodiment of a conventional rotational damper 316 that transfers rotational energy by a viscous grease 318. The rotational damper 316 includes a rotational mass 320 positioned in a housing 322. The housing 322 is connected to the drill string 305 to rotate with the adjacent components of the drill string while the rotational mass 320 is rotatable relative to the housing 322 around a rotational axis 324. In some embodiments, the rotational axis 324 of the damper 316 is coaxial with a rotational axis 324 of the drill string 305.The viscous grease 318 is packed into a chamber 326 of the housing 322 surrounding the rotational mass 320. The viscous grease 316 contacts an outer surface of the rotational mass 320 and an inner surface of the housing 322. The fluidic drag of the viscous grease 316 between the outer surface of the rotational mass 320 and the inner surface of the housing 322 transfers a portion of the rotational energy between the housing 322 and the rotational mass 320 when there is a difference in rotational speed between the housing 322 and the rotational mass 320.

[0028] For example, in a steady state, the rotational mass 320 and the housing 322 will rotate at a substantially equal rotational speed (e.g., angular velocity) around the rotational axis 324 of the damper 316. As illustrated in FIG. 3-2, upon acceleration (positive acceleration or negative acceleration, i.e., deceleration) of the housing 322 relative to the rotational mass 320, the viscous grease 318 transfers rotational energy between the housing 322 and the rotational mass 320 to damp the acceleration of the housing 322, deceleration of the housing 322, oscillation 328 of the housing 322, and vibrations associated therewith. In some embodiments, the viscous grease 318 transfers the rotational energy through shear flow and / or turbulent flow of the viscous grease 318. However, the viscosity of the viscous grease 318 changes with temperature. As the operating conditions expose the viscous grease 318 to higher temperatures, the viscosity decreases as the viscous grease 318 heats during operation. Therefore, the damping performance of the damper 316 can decrease during periods of high demand. Additionally, temperatures during maintenance and / or assembly of the damper 316 are lower than during operation, and the viscous grease 318 with desirable viscosity during operation can exhibit high viscosities making maintenance and / or assembly difficult. In some embodiments, a magnetic damper can limit and / or prevent the degradation in performance during operation and allow for easier assembly and / or maintenance.

[0029] FIG. 4 is a schematic illustration of eddy current generation in a solid disk rotational mass 420. In some embodiments, a magnet 430 includes a pair of magnets positioned on opposite sides of the rotational mass 420. For example, the magnet 430 includes a first magnet 430-1 with a north pole oriented toward a first side 432-1 of the rotational mass 420 and a second magnet 430- 2 with a south pole oriented toward an opposite second side 432-2 of the rotational mass 420. The first magnet 430-1 and second magnet 430-2, therefore, produce a magnetic field 434 oriented through the rotational mass 420. In some embodiments, at least a portion of the magnetic field 434 exhibits magnetic field lines that are substantially perpendicular to the first surface 432-1 and / or second surface 432-2 of the rotational mass 420. In at least one embodiment, at least aportion of the magnetic field 434 exhibits magnetic field lines that are substantially normal to the first surface 432-1 and second surface 432-2 of the rotational mass 420.

[0030] In some embodiments, the rotational mass 420 is made and / or includes an electrically conductive material. When the electrically conductive material of the rotational mass 420 moves relative to the magnetic field 434 (e.g., when the magnets 430-1, 430-2 and rotational mass 420 move relative to one another) eddy currents 436 are generated in the electrically conductive material. Eddy currents are loops of electric current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a magnetic field. Eddy currents flow in closed loops within conductors, in a plane perpendicular to the magnetic field. For example, the eddy currents 436 flow in closed loops in the plane of the rotational mass 420. As the eddy currents 436 flow in the rotational mass 420 moving relative to the magnets 430-1, 430-2, the movement of the eddy currents 436 relative to the magnetic field 434 produces a resultant force 438 (e.g., Lorentz force) therebetween that acts opposite the direction of rotation and proportionately to the rotational speed, transferring rotational energy between the rotational mass 420 and the magnet(s) 430-1, 430-2 fixed to the housing.

[0031] In some embodiments, the electrically conductive material of the rotational mass 420 is or includes a substantially non-magnetic material. For example, the electrically conductive material may be aluminum, gold, palladium, silver, copper, titanium, lead, tin, or zinc. In some embodiments, it is desirable for the rotational mass 420 to have a greater rotational inertia and, hence, a greater mass. For example, a gold rotational mass has a greater mass than an aluminum rotational mass of equal dimensions. The gold rotational mass has a greater rotational inertia than the aluminum rotational mass at an equal rotational speed. In some embodiments, the electrical and inertia properties of the rotational mass can be adjusted by changing dimensions and / or location of the electrically conductive material in the rotational mass.

[0032] FIG. 4 illustrates an embodiment of a rotational mass 420 with a solid disk of electrically conductive material. However, the mass of the rotational mass 420 can be changed by increasing an axial thickness (e.g., longitudinal dimension) of the rotational mass 420. A solid disk of electrically conductive material with a greater axial thickness has a greater mass and may exhibit greater amplitude eddy currents than a solid disk with a lesser axial thickness. In some embodiments, the rotational mass includes electrically conductive material and non-electrically conductive material to increase the mass of the rotational mass while the electrical response to themagnetic field remains the same. Tn a particular example, a rotational mass includes an aluminum electrically conductive material coupled to a tungsten carbide non-electrically conductive material to increase the mass of the rotational mass while the aluminum portion provides the electrical response to the magnetic field.

[0033] In some embodiments, the rotational mass includes a solid disk of electrically conductive material coupled to a solid disk of non-electrically conductive material. For example, the solid disk of electrically conductive material may be axially bonded to a solid disk of non-electrically conductive material in axial layers. In another example, the rotational mass includes a plurality of solid disks of electrically conductive material axially stacked in the rotational mass. In some embodiments, the rotational mass includes an annular ring of electrically conductive material coupled to a solid disk of non-electrically conductive material radially within the annular ring. In some embodiments, the rotational mass includes an annular ring of non-electrically conductive material coupled to a solid disk of electrically conductive material radially within the annular ring. In some examples, the rotational mass includes a plurality of annular rings of electrically conductive material axially stacked in the rotational mass with a non-conductive material radially within the annular rings.

[0034] In some embodiments, the rotational mass includes at least one angular sector of electrically conductive material and at least one angular sector of non-electrically conductive material. For example, the rotational mass may include 60° angular sectors of alternating electrically conductive material and non-electrically conductive material. In other examples, the rotational mass includes 45° angular sectors of alternating electrically conductive material and non-electrically conductive material. In yet other examples, the rotational mass includes 90° angular sectors of alternating electrically conductive material and non-electrically conductive material. In some embodiments, the electrically conductive material and the non-electrically conductive material are positioned in the rotational mass such that the rotational mass is rotationally balanced around the rotational axis.

[0035] FIG. 5 is a cross-sectional view of an embodiment of a magnetic damper 516 according to the present disclosure. The magnetic damper 516 includes a housing 522 that is fixed and / or coupled to other components of the drill string 505. For example, the housing 522 of the magnetic damper 516 may be coupled in line with a drill pipe, drill collar, bit, mill, or other components of the drill string such as described in relation to FIG. 1. In some embodiments, the housing 522 ofthe magnetic damper 516 is coupled within a housing of another downhole component, such as a directional steering device. In some embodiments, the housing 522 of the magnetic damper 516 is integrally formed with the housing of another downhole component.

[0036] In some embodiments, the magnetic field 534 is generated between a first magnet 530-1 and second magnet 530-2 of each magnet pair of the damper 516 through the rotational mass 520. The magnetic field 534 passes through the rotational mass 520 to induce the eddy currents in the electrically conductive material of the rotational mass 520. In some embodiments, the rotational mass 520 is rotatable relative to the housing 522 by an axle 540 aligned with the rotational axis 524. In some embodiments, the rotational mass 520 is rotatable relative to the housing 522 by race bearings, thrust bearings, a bearing surface, or other mechanism that limits and / or prevents friction therebetween.

[0037] In some embodiments, the magnetic damper 516 transfers rotational energy between the rotational mass 520 and the housing 522. In some embodiments, a fluid 542 positioned in the chamber 526 of the magnetic damper 516 provides additional transfer of rotational energy. The eddy currents and resultant Lorentz force provides an energy transfer that is proportionate to the relative motion of the rotational mass 520 and the magnets 530-1, 530-2 coupled to the housing 522. In some embodiments, small degrees of relative motion produce little to no electrical current in the electrically conductive material, and a fluid may transfer rotational energy more efficiently at low relative rotational speeds.

[0038] For example, the fluid 542 in the chamber 526 may be any non-conductive fluid, such as an oil or a grease. In some embodiments, the fluid 542 in the chamber 526 may be a viscous grease, such as that described in relation to FIG. 3-1 and FIG. 3-2. The chamber 526 containing the fluid 542 is, in some embodiments, a sealed chamber with a substantially non-compressible fluid therein, such that the chamber (and magnetic damper) is pressure-compensated. In some embodiments, the chamber 526 is open and the fluid 542 therein is a drilling mud or other fluid of the drill string or downhole environment (such as the drilling mud 111 described in relation to FIG. 1). While an open chamber may allow contaminants or foreign particles into the chamber, the chamber naturally pressure-equalizes with the downhole environment.

[0039] FIG. 4 and FIG. 5 describe embodiments of magnetic dampers with at least one pair of magnets providing a magnetic field through the rotational mass with a first magnet and a second magnet on opposite sides of the rotational mass In some embodiments, the magnet(s) arepositioned in other locations to provide a magnetic field that passed through the electrically conductive material of the rotational mass.

[0040] FIG. 6 is a cross-sectional view of another embodiment of a magnetic damper 616 according to the present disclosure. In some embodiments, the magnet 630 is positioned radially outside the rotational mass 620. The magnetic field lines pass through the electrically conductive material 644. In some embodiments, the magnet 630 is positioned radially outside at least a portion of the electrically conductive material 644 of the rotational mass 620 with the magnetic dipole oriented axially relative to the rotational axis 624. The magnetic field lines pass through the electrically conductive material 644 of the rotational mass 620 in a substantially perpendicular direction to a plane of the rotational mass 620. In some embodiments, such as an annular ring of electrically conductive material 644 (which optionally includes a non-electrically conductive material 646 radially within the annular ring of electrically conductive material 644), the magnetic dipole is oriented radially relative to the rotational axis 620 such that the magnetic field lines pass through the radially outermost surface 648 of the rotational mass 620 in a substantially perpendicular direction. In such an example, the eddy currents are generated in a radially outermost surface 648 (e.g., edge) of the rotational mass 620 in a plane concentric to the rotational axis 624 of the rotational mass 620.

[0041] While the magnets described in relation to FIG. 5 and FIG. 6 allow for eddy current generation in the rotational mass, the resultant Lorentz force generated is proportionate to the translational speed of the rotational mass at the radius of the magnetic field. In some embodiments, the magnetic field is movable or changeable to alter the magnitude of the resultant Lorentz force independently of the rotational speed of the rotational mass. In some embodiments, a magnetic damper includes a means for moving a magnetic field in a radial direction relative to the electrically conductive material of the rotational mass. The means for moving the magnetic field may include an active movement mechanism to move the magnet(s), a passive movement mechanism to passively move the magnet(s), a plurality of electromagnets to selectively position the magnetic field, or other means for moving the magnetic field.

[0042] In some embodiments, the magnetic field of the magnetic damper is movable in a radially direction relative to the rotational axis of the damper to change the translational speed of the electrically conductive material for a given rotational speed. For example, the radially outermost edge of the rotational mass is moving at a higher translational speed than a portion proximate therotational axis for a given rotational speed. For example, a magnetic field located proximate to the radially outermost edge of the rotational mass will induce an eddy current with a greater magnitude than a magnetic field located radially proximate the rotational axis. Similarly, the higher translational speed of the rotational mass proximate to the radially outermost edge of the rotational mass will induce a resultant Lorentz force with a greater magnitude than radially proximate the rotational axis for a given magnitude eddy current in the rotational mass.

[0043] In some embodiments, the magnetic field is movable relative to the rotational mass by actively moving the magnets in a radial direction. FIG. 7-1 and 7-2 are cross-sectional views of an embodiment of a magnetic damper 716 with actively radially movable magnets 730. In some embodiments, the magnets 730 are actively movable by an active movement mechanism 750, such as a piston-and-cylinder (hydraulic or gas), an electric motor, shape memory alloy springs, or other mechanisms that allow a controller 752 to move a magnet 730 in a radial direction relative to the rotational axis 724. For example, the controller 752 may include or be in communication with an accelerometer, gyroscope, or other sensor 754 to determine a rotational speed of the housing 722, the rotational mass 720, or a relative rotational speed between the housing 722 and the rotational mass 720. In some examples, the controller 752 actuates the active movement mechanism 750 based at least partially on a measurement of the sensor(s) 754. In other examples, the controller 752 receives instructions to move the magnet(s) 730 from a control service of the drill string or drilling rig based on other measurements or properties of the drill string and / or downhole environment. For example, the controller 752 may receive instructions to move the magnet(s) 730 based at least partially on the composition of the surrounding geologic formation and / or geometry of the borehole.

[0044] In some embodiments, the magnetic field is movable relative to the rotational mass by passively moving the magnets in a radial direction. FIG. 8 is a cross-sectional view of an embodiment of a magnetic damper 816 with passively radially movable magnets 830. In some embodiments, a passive movement mechanism 856 includes a movement mechanism that adjusts the radial position of a magnet 830 based at least partially on the rotational speed of the housing 822. For example, an increase in rotational speed 858 of the housing 822 (to which the magnet 830 is rotationally fixed) may generate an increase in a radially outward component 860 of the inertia of the magnet 830 (e.g., centrifugal force) as the magnet 830 moves around the rotational axis 824. In some embodiments, a radial biasing element of the passive movement mechanism856 applies a radially inward biasing force to the magnet 830 to urge the magnet 830 toward the rotational axis 824.

[0045] In at least one example, as the rotational speed 858 of the housing 822 and magnet 830 increases, the radially outward component 860 of the inertia of the magnet 830 causes the magnet 830 to move radially outward in a channel 862 of the housing 822 relative to the rotational axis 824 against the radial biasing element of the passive movement mechanism 856. As the rotational speed of the housing 822 decreases, the radially outward component 860 of the inertia of the magnet 830 decreases, and the radial biasing element of the passive movement mechanism 856 applies the radially inward biasing force to move the magnet 830 radially inward toward the rotational axis 824.

[0046] In some embodiments, the magnet 830 moves radially outward as a rotational speed 858 of the housing 822 increases. In some embodiments, a sudden increase in the rotational speed 858 of the housing 822 can cause the magnetic field 834 to move radially outward and produce a greater resultant Lorentz force between the rotational mass 820 and the housing 822. In some embodiments, the housing 822 and rotational mass 820 rotate with a substantially equal rotational speed 858 during steady state for the drill string. The magnet(s) 830 move radially outward during a steady state with a greater rotational speed 858 and inward in a steady state with a lesser rotational speed 858. The same relative change in rotational speed 858, therefore, produces a larger damper response at higher rotational speeds 858 as the magnet 830 is radially farther from the rotational axis 824 during the higher rotational speed 858 steady state.

[0047] In some embodiments, the magnetic field is movable relative to the rotational mass by selectively activating electromagnetics of a series of electromagnets positioned in a radial direction. FIG. 9 is a cross-sectional view of an embodiment of a magnetic damper 916 with electromagnetics to selectively control a magnetic field 934. In some embodiments, a controller 952 is in electrical communication with the electromagnet(s) 930. The controller 952 may adjust or instruct the electromagnet 930 to adjust a current applied to the electromagnet 930 to change the magnitude of the magnetic field 934 generated by each electromagnet 930.

[0048] In some embodiments, the controller 952 may increase or decrease the amperage of the current applied to the electromagnet(s) 930 to change the strength of the magnetic field 934 applied to the electrically conductive material 944 in the rotational mass 920. In some embodiments, the controller 952 may selectively enable or disable an electromagnet 930 in a radial series ofelectromagnets 930 to move the magnetic field 934 radially relative to the rotational axis 924. For example, in a power-constrained environment or tool, the controller 952 may have a limit to the available electrical power and changing the electromagnet 930 to which the electrical current is applied may change the resultant Lorentz force between the rotational mass 920 and the housing 922. In some embodiments, the controller 952 may selectively enable, disable, or change the magnitude of the magnetic field 934 of each electromagnet 930 in a radial series of electromagnets 930 to adjust the position and strength of the magnetic field(s) 934 applied to the electrically conductive material 944 in the rotational mass 930.INDUSTRIAL APPLICABILITY

[0049] The present disclosure relates generally to the reduction of shock and vibration in a drill string or a component of a drill string by use of magnetic damper including magnets and rotational mass that is rotationally independent of the magnets. In some embodiments, a magnet includes a pair of magnets positioned on opposite sides of a rotational mass. For example, the magnet includes a first magnet with a north pole oriented toward a first side of the rotational mass and a second magnet with a south pole oriented toward an opposite second side of the rotational mass. The first magnet and second magnet, therefore, produce a magnetic field oriented through the rotational mass. In some embodiments, at least a portion of the magnetic field exhibits magnetic field lines that are substantially perpendicular to the first surface and / or second surface of the rotational mass. In at least one embodiment, at least a portion of the magnetic field exhibits magnetic field lines that are substantially normal to the first surface and second surface of the rotational mass.

[0050] In some embodiments, the rotational mass is made and / or includes an electrically conductive material. When the electrically conductive material of the rotational mass moves relative to the magnetic field (e.g., when the magnets and rotational mass move relative to one another) eddy currents are generated in the electrically conductive material. Eddy currents are loops of electric current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a magnetic field. Eddy currents flow in closed loops within conductors, in a plane perpendicular to the magnetic field. For example, the eddy currents flow in closed loops in the plane of the rotational mass. As the eddy currents flow in the rotational mass moving relative to the magnets, themovement of the eddy currents relative to the magnetic field produces a resultant force (e g., Lorentz force) therebetween that acts opposite the direction of rotation and proportionately to the rotational speed, transferring rotational energy between the rotational mass and the magnet(s) fixed to the housing.

[0051] In some embodiments, the electrically conductive material of the rotational mass is or includes a substantially non-magnetic material. For example, the electrically conductive material may be aluminum, gold, palladium, silver, copper, titanium, lead, tin, or zinc. In some embodiments, it is desirable for the rotational mass to have a greater rotational inertia and, hence, a greater mass. For example, a gold rotational mass has a greater mass than an aluminum rotational mass of equal dimensions. The gold rotational mass has a greater rotational inertia than the aluminum rotational mass at an equal rotational speed. In some embodiments, the electrical and inertia properties of the rotational mass can be adjusted by changing dimensions and / or location of the electrically conductive material in the rotational mass.

[0052] In some embodiments, the rotational mass is of uniform thickness. However, the mass of the rotational mass can be changed by increasing an axial thickness (e.g., longitudinal dimension) of the rotational mass. A solid disk of electrically conductive material with a greater axial thickness has a greater mass and may exhibit greater amplitude eddy currents than a solid disk with a lesser axial thickness. In some embodiments, the rotational mass includes electrically conductive material and non-electrically conductive material to increase the mass of the rotational mass while the electrical response to the magnetic field remains the same. In a particular example, a rotational mass includes an aluminum electrically conductive material coupled to a tungsten carbide non-electrically conductive material to increase the mass of the rotational mass while the aluminum portion provides the electrical response to the magnetic field.

[0053] In some embodiments, the rotational mass includes a solid disk of electrically conductive material coupled to a solid disk of non-electrically conductive material. For example, the solid disk of electrically conductive material may be axially bonded to a solid disk of non-electrically conductive material in axial layers. In another example, the rotational mass includes a plurality of solid disks of electrically conductive material axially stacked in the rotational mass. In some embodiments, the rotational mass includes an annular ring of electrically conductive material coupled to a solid disk of non-electrically conductive material radially within the annular ring. In some embodiments, the rotational mass includes an annular ring of non-electrically conductivematerial coupled to a solid disk of electrically conductive material radially within the annular ring. In some examples, the rotational mass includes a plurality of annular rings of electrically conductive material axially stacked in the rotational mass with a non-conductive material radially within the annular rings.

[0054] In some embodiments, the rotational mass includes at least one angular sector of electrically conductive material and at least one angular sector of non-electrically conductive material. For example, the rotational mass may include 60° angular sectors of alternating electrically conductive material and non-electrically conductive material. In other examples, the rotational mass includes 45° angular sectors of alternating electrically conductive material and non-electrically conductive material. In yet other examples, the rotational mass includes 90° angular sectors of alternating electrically conductive material and non-electrically conductive material. In some embodiments, the electrically conductive material and the non-electrically conductive material are positioned in the rotational mass such that the rotational mass is rotationally balanced around the rotational axis.

[0055] In some embodiments, a magnetic damper includes a housing that is fixed and / or coupled to other components of the drill string. For example, the housing of the magnetic damper may be coupled in line with a drill pipe, drill collar, bit, mill, or other components of the drill string such as described herein. In some embodiments, the housing of the magnetic damper is coupled within a housing of another downhole component, such as a directional steering device. In some embodiments, the housing of the magnetic damper is integrally formed with the housing of another downhole component.

[0056] In some embodiments, the magnetic field is generated between a first magnet and second magnet of each magnet pair of the damper through the rotational mass. The magnetic field passes through the rotational mass to induce the eddy currents in the electrically conductive material of the rotational mass. In some embodiments, the rotational mass is rotatable relative to the housing by an axle aligned with the rotational axis. In some embodiments, the rotational mass is rotatable relative to the housing by race bearings, thrust bearings, a bearing surface, or other mechanism that limits and / or prevents friction therebetween.

[0057] In some embodiments, the magnetic damper transfers rotational energy between the rotational mass and the housing. In some embodiments, a fluid positioned in the chamber of the magnetic damper provides additional transfer of rotational energy. The eddy currents and resultantLorentz force provides an energy transfer that is proportionate to the relative motion of the rotational mass and the magnets coupled to the housing. In some embodiments, small degrees of relative motion produce little to no electrical current in the electrically conductive material, and a fluid may transfer rotational energy more efficiently at low relative rotational speeds.

[0058] For example, the fluid in the chamber may be any non-conductive fluid, such as an oil or a grease. In some embodiments, the fluid in the chamber may be a viscous grease. The chamber containing the fluid is, in some embodiments, a sealed chamber with a substantially non- compressible fluid therein, such that the chamber (and magnetic damper) is pressure-compensated. In some embodiments, the chamber is open and the fluid therebetween is a drilling mud or other fluid of the drill string or downhole environment. While an open chamber may allow contaminants or foreign particles into the chamber, the chamber would naturally pressure-equalize with the downhole environment.

[0059] In some embodiments, a magnet is positioned radially outside the rotational mass. The magnetic field lines pass through the electrically conductive material. In some embodiments, the magnet is positioned radially outside at least a portion of the electrically conductive material of the rotational mass with the magnetic dipole oriented axially relative to the rotational axis. The magnetic field lines pass through the electrically conductive material of the rotational mass in a substantially perpendicular direction to a plane of the rotational mass. In some embodiments, such as an annular ring of electrically conductive material, the magnetic dipole is oriented radially relative to the rotational axis such that the magnetic field lines pass through the radially outermost surface of the rotational mass in a substantially perpendicular direction. In such an example, the eddy currents are generated in a radially outermost surface (e.g., edge) of the rotational mass in a plane concentric to the rotational axis of the rotational mass.

[0060] In some embodiments, the magnetic field is movable or changeable to alter the magnitude of the resultant Lorentz force independently of the rotational speed of the rotational mass. In some embodiments, a magnetic damper includes a means for moving a magnetic field in a radial direction relative to the electrically conductive material of the rotational mass. The means for moving the magnetic field may include an active movement mechanism to move the magnet(s), a passive movement mechanism to passively move the magnet(s), a plurality of electromagnets to selectively position the magnetic field, or other means for moving the magnetic field.

[0061] Tn some embodiments, the magnetic field of the magnetic damper is movable in a radially direction relative to the rotational axis of the damper to change the translational speed of the electrically conductive material for a given rotational speed. For example, the radially outermost edge of the rotational mass is moving at a higher translational speed than a portion proximate the rotational axis for a given rotational speed. For example, a magnetic field located proximate to the radially outermost edge of the rotational mass will induce an eddy current with a greater magnitude than a magnetic field located radially proximate the rotational axis. Similarly, the higher translational speed of the rotational mass proximate to the radially outermost edge of the rotational mass will induce a resultant Lorentz force with a greater magnitude than radially proximate the rotational axis for a given magnitude eddy current in the rotational mass.

[0062] In some embodiments, the magnetic field is movable relative to the rotational mass by actively moving the magnets in a radial direction. In some embodiments, the magnets are actively movable by an active movement mechanism, such as a piston-and-cylinder (hydraulic or gas), an electric motor, shape memory alloy springs, or other mechanisms that allow a controller to move a magnet in a radial direction relative to the rotational axis. For example, the controller may include or be in communication with an accelerometer, gyroscope, or other sensor to determine a rotational speed of the housing, the rotational mass, or a relative rotational speed between the housing and the rotational mass. In some examples, the controller may actuate the active movement mechanism based at least partially on a measurement of the sensor(s). In other examples, the controller may receive instructions to move the magnet(s) from a control service of the drill string or drilling rig based on other measurements or properties of the drill string and / or downhole environment. For example, the controller may receive instructions to move the magnet(s) based at least partially on the composition of the surrounding geologic formation and / or geometry of the borehole.

[0063] In some embodiments, the magnetic field is movable relative to the rotational mass by passively moving the magnets in a radial direction. In some embodiments, a passive movement mechanism includes a movement mechanism that adjusts the radial position of a magnet based at least partially on the rotational speed of the housing. For example, an increase in rotational speed of the housing (to which the magnet is rotationally fixed) may generate an increase in a radially outward component of the inertia of the magnet (e.g., centrifugal force) as the magnet moves around the rotational axis. In some embodiments, a radial biasing element of the passivemovement mechanism applies a radially -inward biasing force to the magnet to urge the magnet toward the rotational axis.

[0064] In at least one example, as the rotational speed of the housing and magnet increases, the radially outward component of the inertia of the magnet causes the magnet to move radially outward in a channel of the housing relative to the rotational axis against the radial biasing element. As the rotational speed of the housing decreases, the radially outward component of the inertia of the magnet decreases, and the radial biasing element applies the radially -inward biasing force to move the magnet radially-inward.

[0065] In some embodiments, the magnet moves radially outward as a rotational speed of the housing increases. In some embodiments, a sudden increase in the rotational speed of the housing can cause the magnetic field to move radially outward and produce a greater resultant Lorentz force between the rotational mass and the housing. In some embodiments, the housing and rotational mass rotate with a substantially equal rotational speed during steady state for the drill string. The magnet(s) move outward during a steady state with a greater rotational speed and inward in a steady state with a lesser rotational speed. The same relative change in rotational speed, therefore, may produce a larger damper response at higher rotational speeds as the magnet is radially farther from the rotational axis during the higher rotational speed steady state.

[0066] In some embodiments, the magnetic field is movable relative to the rotational mass by selectively activating electromagnetics of a series of electromagnets positioned in a radial direction. In some embodiments, a controller is in electrical communication with the electromagnet(s). The controller may adjust or instruct the electromagnet to adjust a current applied to the electromagnet to change the magnitude of the magnetic field generated by each electromagnet.

[0067] In some embodiments, the controller may increase or decrease the amperage of the current applied to the electromagnet(s) to change the strength of the magnetic field applied to the electrically conductive material in the rotational mass. In some embodiments, the controller may selectively enable or disable an electromagnet in a radial series of electromagnets to move the magnetic field radially relative to the rotational axis. For example, in a power-constrained environment or tool, the controller may have a limit to the available electrical power, and changing the electromagnet to which the electrical current is applied may change the resultant Lorentz force between the rotational mass and the housing. In some embodiments, the controller may selectivelyenable, disable, or change the magnitude of the magnetic field of each electromagnet in a radial series of electromagnets to adjust the position and strength of the magnetic field(s) applied to the electrically conductive material in the rotational mass.

[0068] It should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein, to the extent such features are not described as being mutually exclusive. Numbers, percentages, ratios, or other values stated herein are intended to include that value, and also other values that are “about”, “substantially”, or “approximately” the stated value, as would be appreciated by one of ordinary skill in the art encompassed by embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within 5%, within 1%, within 0.1%, or within 0.01% of a stated value.

[0069] The terms “approximately,” “about,” and “substantially” as used herein represent an amount close to the stated amount that is within standard manufacturing or process tolerances, or which still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” and “substantially” may refer to an amount that is within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of a stated amount. Further, it should be understood that any directions or reference frames in the preceding description are merely relative directions or movements. For example, any references to “up” and “down” or “above” or “below” are merely descriptive of the relative position or movement of the related elements.

[0070] A person having ordinary skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations may be made to embodiments disclosed herein without departing from the spirit and scope of the present disclosure. Equivalent constructions, including functional “means-plus-function” clauses are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in thesame manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words ‘means for’ appear together with an associated function. Each addition, deletion, and modification to the embodiments that falls within the meaning and scope of the claims is to be embraced by the claims. The described embodiments are therefore to be considered as illustrative and not restrictive, and the scope of the disclosure is indicated by the appended claims rather than by the foregoing description.

Claims

CLAIMSWhat is claimed is:

1. A downhole tool comprising: a housing, wherein the housing has a longitudinal axis; a magnet rotationally fixed to the housing; and a rotational mass supported in the housing and rotatable relative to the housing around a rotational axis with a magnetic field of the magnet penetrating the rotational mass, the rotational mass including an electrically conductive material that produces an eddy current when translated relative to the magnetic field.

2. The downhole tool of claim 1, wherein the rotational mass is positioned in a sealed chamber in the housing and the sealed chamber is pressure compensated.

3. The downhole tool of claim 1, wherein the rotational mass is immersed in a fluid.

4. The downhole tool of claim 3, wherein the fluid is a viscous grease.

5. The downhole tool of claim 1, wherein the rotational mass is positioned in an unsealed chamber in the housing.

6. The downhole tool of claim 1, wherein the magnet includes a first magnet positioned on a first axial side of the rotational mass and a second magnet positioned on a second axial side of the rotational mass opposite the first side.

7. The downhole tool of claim 1, wherein the magnet is positioned radially outside of the rotational mass relative to a rotational axis of the rotational mass.

8. The downhole tool of claim 7, wherein the magnet is oriented with a magnetic dipole in an axial direction relative to the rotational axis.

9. The downhole tool of claim 7, wherein the magnet is oriented with a magnetic dipole in a radial direction relative to the rotational axis.

10. The downhole tool of claim 1, wherein the rotational mass is a solid disc.

11. The downhole tool of claim 1, wherein the rotational mass is an annulus.

12. The downhole tool of claim 1, wherein the rotational mass further includes a non- electrically conductive material coupled to the electrically conductive material.

13. The downhole tool of claim 1, wherein the magnet further includes a plurality of electromagnets selectively activatable to change the magnetic field.

14. A downhole tool comprising: a housing, wherein the housing has a longitudinal axis; a magnet rotationally fixed to the housing; a rotational mass supported in the housing and rotatable relative to the housing around a rotational axis with a magnetic field of the magnet penetrating the rotational mass, the rotational mass including an electrically conductive material that produces an eddy current when translated relative to the magnetic field; and a means for moving the magnet in a radial direction relative to the rotational axis of the rotational mass.

15. The downhole tool of claim 14, wherein the means for moving includes an active movement device selectively actuated to move the magnet.

16. The downhole tool of claim 15, wherein the active movement device includes a piston- and-cylinder.

17. The downhole tool of claim 14, wherein the means for moving includes a passive movement device.

18. The downhole tool of claim 17, wherein the passive movement device includes a spring.

19. A downhole tool comprising: a housing, wherein the housing has a longitudinal axis; a magnet rotationally fixed to the housing; a rotational mass supported in the housing and rotatable relative to the housing around a rotational axis with a magnetic field of the magnet penetrating the rotational mass, the rotational mass including an electrically conductive material that produces an eddy current when translated relative to the magnetic field; a means for changing the magnetic field; at least one sensor; and a controller in data communication with the sensor and the means for changing the magnetic field, wherein the controller instructs the means for changing the magnetic field at least partially in response to a signal received from the sensor.

20. The downhole tool of claim 19, wherein the sensor is an angular rotation sensor, and the controller instructs the means for changing the magnetic field at least partially in response to a signal received from the angular rotation sensor.

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