Wellbore motor having magnetic gear drive

A wellbore motor includes a means for converting flow of fluid in the wellbore into rotational energy. A magnetic gear member is operatively coupled at an input thereof to the means for converting. A wellbore rotary tool is coupled to an output of the magnetic gear member.

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the field of rotary tools used in drilling and completion of wellbores in the Earth. More specifically, the invention relates to rotary tools that make use of geared couplings between a driven input shaft and a driving output shaft.

2. Background Art

Drilling and completion of wellbores in the Earth, such as are used in the production of petroleum from subsurface reservoirs, includes the use of a number of types of rotary tools. A particularly important one of such rotary tools is the so-called “turbodrill.” A turbodrill is used in association with a drill string suspended from a drilling rig. The drill string is typically formed from lengths of steel pipe threaded together end to end and suspended from the rig by suitable hoisting equipment. Pumps force fluid called “drilling mud” through the interior of the drill string and out the bottom of the drill string through a drill bit, which performs the actual cutting of the rock formations. The exiting drilling mud cools the bit and lifts cuttings from the wellbore to the surface. When the drill string includes a turbodrill, the turbodrill itself is used to rotate the drill bit. The turbodrill includes one or more turbines disposed within a housing and ultimately rotationally coupled to the bit, such that the flow of drilling mud is converted to rotational energy to drive the drill bit.

Other applications for drilling mud flow-driven turbines include generation of electrical power to operate various formation characterization and/or drilling survey instruments known as measurement while drilling (“MWD”) instruments.

It is a characteristic of mud flow-driven turbines that they generate relatively low torque, but can rotate at relatively high speeds. In turbodrilling applications, it has been shown to be beneficial to provide a speed-reducing gear system between the turbine and the drill bit, such that the drill bit can be driven at relatively lower rotational speed, and at correspondingly higher torque. Uses for such “geared turbodrill” devices are described, for example, in R. Searle, et al., “Geared Turbodrilling Applications and Case Histories in the North Sea, Paper No. 90495, Society of Petroleum Engineers, Richardson, Tex. (2004).

Reduction gear systems when operated in wellbores using well fluid movement for a rotary power source have a number of limitations. First, it is necessary to provide a rotary seal between the turbine-driven shaft, which is necessarily exposed to the wellbore fluid, and the interior of the driven device. In a geared turbodrill, the device includes a planetary gear set. The interior of the device is usually filled with a lubricant, such as oil, that is subject to degradation when exposed to high temperatures (typical in wells drilled into the Earth). The fluid in the interior of the device must ordinarily be pressure compensated to be maintained at the same fluid pressure as the hydrostatic fluid pressure in the wellbore, or the rotary seal will be subjected to differential fluid pressure in excess of its capacity to exclude wellbore fluid from the interior of the device. Pressure compensation devices known in the art may be subject to delays in compensation, causing fluid penetration into the interior of the device or fluid leakage. To limit fluid intrusion caused by such delay, preferably, the pressure compensation device maintains a slightly higher fluid pressure inside the device than in the wellbore. The slight pressure differential has the effect of causing slow, but constant loss of the pressure compensating fluid. Thus, even under ideal conditions the typical rotating seal device has a finite time that it can be used in a wellbore before removal to replenish the compensating fluid.

In the case of rotary devices using gears to multiply or reduce output speed relative to input speed, loss of lubrication can lead to gear failure. Application of abrupt high torque has also been known to cause gear failure. While the strength of the gears could otherwise be increased by increasing the size of the gears, such remedy is limited in the case of wellbore tools because such tools are typically limited in diameter to that of the wellbore being drilled less an annular space to allow cuttings and return mud flow to the Earth's surface. In turbodrilling applications, as well as in wellbore drilling generally, such abrupt torque application is frequent, because of the highly variable mechanical properties of the Earth formations being drilled and the relatively low resolution control over the amount of axial force applied to the drill bit on the typical drilling rig.

Typical turbodrill reduction gear devices include planetary gear sets. Planetary gears are particularly suitable for wellbore applications because in wellbore applications the input and output shafts of the gear devices are typically coaxial. Planetary gears are generally limited to about 3¼ to 3½ to 1 input to output ratio because of the limitations of shaft and gear diameters, among other factors. To step up or step down the speed between input and output shafts more than would be feasible with a single planetary gear set would require coupling a plurality of such gear sets end to end. Such arrangement increases the overall length, weight, complexity and required lubrication reservoir capacity of the gear set.

There exists a need to have a wellbore rotary device that can include a gear unit, but does not require rotary seals or pressure compensation. There also exists a need for a rotary device for use in a wellbore that can have a wide range of gear reduction ratios without the need for compound gear sets.

SUMMARY OF THE INVENTION

One aspect of the invention is a wellbore tool that includes a means for converting flow of fluid in the wellbore into rotational energy. A magnetic gear member is operatively coupled at its input to the means for converting. A wellbore rotary implement, such as a drill bit, is coupled to an output of the magnetic gear member.

Another aspect of the invention is a magnetically geared wellbore drilling motor. A drilling motor according to this aspect of the invention includes a turbine for converting flow of drilling fluid in the wellbore into rotational energy. An input shaft is rotationally coupled to the turbine. The input shaft has at least one magnet on it. An output shaft is disposed rotatably about an exterior surface of the input shaft. The output shaft has on it a plurality of circumferentially spaced apart pole pieces formed from a ferromagnetic material. The motor also includes a magnet section having a plurality of magnets disposed circumferentially about an exterior of the output shaft. The magnet section has a magnet retainer with an external shape adapted to cooperate with an interior of a housing in which the magnet section is disposed, such that rotation between the magnet section and the housing is substantially prevented. The motor includes a driving device rotationally coupled to the output shaft and adapted to operate a rotary wellbore drilling tool. The driving device is rotationally coupled to the output shaft to substantially isolate axial force on the drilling tool from the output shaft. The driving device is arranged to transfer axial loading to the housing.

DETAILED DESCRIPTION

An aspect of the invention related to geared wellbore motors will first be explained in terms of a drilling motor that uses flow of drilling mud as an energy source. One implementation of a wellbore fluid-driven, geared motor according to the invention is shown inFIG. 1as it would be used in a drill string for drilling a wellbore into the Earth. The drill string11includes segments of drill pipe14threadedly coupled end to end and suspended at the upper end thereof by a top drive18. The top drive18is movably suspended within a derrick structure of a drilling rig16. The drilling rig16includes a drill line32spooled by a winch called a “drawworks”30to raise and lower the top drive18as required during drilling operations. The drill line32moves through a crown block30A and a traveling block30B having multiple sheaves thereon to raise and lower the top drive18. The top drive18includes an electric or hydraulic motor (not shown separately) to turn the drill string11as needed during drilling operations. The foregoing illustration of a drilling rig and its associated equipment is only to show a possible application of a geared motor according to the invention. Other devices for conveying the motor into a wellbore that may be used with the invention include coiled tubing, production tubing, casing or any other conveyance known in the art. Accordingly, the threaded drill pipe, drilling rig, top drive and associated equipment shown inFIG. 1are not limits on the scope of the invention.

The lowermost end of the drill string11includes a rotary wellbore tool, in this case a drill bit12. The drill bit12is rotated and advanced axially to gouge, cut and/or crush the Earth formations13to advance the drilling of the wellbore15. The drill bit12performs its well drilling action by being rotated by either or both the top drive18(through the drill string11) and a fluid driven, geared motor called a “drilling motor”, shown generally at10. The drilling motor10will be explained in more detail with reference toFIGS. 2 and 3. The drilling motor10in the present embodiment is threadedly coupled to the drill string11at its upper end, and includes a rotatable “bit box”10A at its lower end for threaded coupling to the drill bit12using a male threaded connection called a “pin end”, shown12A. The bit box10A is able to rotate relative to the remainder of the drilling motor10, as will be further explained below.

During drilling operations, the drill bit12is rotated, and some of the weight of the drill string11is applied to the drill bit12by rotating the drawworks30to selectively release the drill line32. Selective release of the drill line32causes the top drive18to move downwardly by gravity, such that a measured portion of the weight of the drill string11and top drive18are transferred to the drill bit12. As the drill bit12is axially urged into contact with the bottom of the wellbore15by such weight, and is rotated by the top drive18and/or the drilling motor10, a mud pump22lifts drilling fluid called “drilling mud”24from a storage tank26or surface pit and pumps the drilling mud24through a standpipe20in hydraulic communication with the top drive18. The drilling mud24is then forced through a central opening (not shown separately inFIG. 1) within the drill string11until it passes through the drilling motor10, and finally, through orifices (not shown) called “jets” in the bit12such that drill cuttings (not shown) are lifted from the bottom of the wellbore15and are returned to the Earth's surface. After the drill cuttings (not shown) are removed from the drilling mud24, the drilling mud24is returned to the tank26by a return line28.

The drilling motor10includes internal components, as will be explained below with reference toFIGS. 2 and 3, that convert some of the energy in the moving drilling mud24into rotational energy to rotate the drill bit12.

FIG. 2shows one embodiment of a drilling motor10according to the invention. The drilling motor10is generally contained with in a housing40that can be made from a high strength metal alloy. The housing40preferably has an external diameter similar to a drill string segment known as a “drill collar”, such that the bending and torsional stiffness of the housing40will be similar to the adjacent components of the drill string (11inFIG. 1). The housing40includes an upper threaded connection42adapted to threadedly engage a corresponding threaded connection on the adjacent part of the drill string (11inFIG. 1).

As explained above with reference toFIG. 1, the lowermost part of the drilling motor10includes a rotatably mounted, threaded coupling (called the “bit box”)10A for threaded engagement by internal threads54with a corresponding threaded coupling (12A inFIG. 1) on the drill bit (12inFIG. 1). An axial thrust bearing52is disposed between an upper shoulder10AA on the bit box10A and a lower shoulder40A on the housing40such that axial force from the weight of the drill string (11inFIG. 1) can be transferred through the housing40to the bit box10A while maintaining the ability of the bit box10A to freely rotate with respect to the housing40. The axial thrust bearing52is preferably a polycrystalline diamond compact (“PDC”) bearing such that maintaining separate lubrication and sealing arrangements for the bearing52is not necessary. PDC thrust bearings used in drilling motors are known in the art.

Inside the interior of the upper portion of the housing40is located a turbine46, which may include one or more rotor and stator stages, according to design techniques well known in the art, for converting the flow of drilling mud (24inFIG. 1) into rotational energy. The turbine46is rotationally coupled to an input shaft48of a magnetic gear member41. The magnetic gear member41in this embodiment reduces the input shaft speed and increases the torque applied to the input shaft, such that an output shaft50rotates at a selected fraction of the input shaft speed and provides a corresponding, inversely related output torque. Other applications for a wellbore motor may require that the input shaft speed is multiplied, rather than reduced. Accordingly, the ratio of input speed to output speed of the gear member41is not a limit on the scope of this invention.

Preferably, the turbine46is rotationally coupled to the input shaft48using splines or the like such that thrust load on the turbine46caused by movement of the drilling mud (24inFIG. 1) is not transferred to the input shaft48. Thrust load on the turbine46, caused by flow of mud against the turbine46, may be transferred from the turbine46to the housing40using an axial thrust bearing (not shown inFIG. 2) similar to the thrust bearing52above the bit box10A. While the present embodiment shows a turbine as the device used to convert wellbore fluid flow into rotational energy, it should be clearly understood that other devices known in the art, including vane type hydraulic motors, gear type hydraulic motors and other types of positive displacement motor can be used in other embodiments to convert fluid flow into rotational energy to operate the wellbore rotary tool through a magnetic gear member.

The magnetic gear member41also includes a magnet section44, that in the present embodiment is rotationally fixed to the housing40and is disposed externally to both the input shaft48and to a gear member output shaft50. The output shaft50is disposed radially generally between the input shaft48and the magnet section44, and is rotationally coupled to the bit box12A. Just as for the turbine coupling to the input shaft, the output shaft50is preferably rotationally coupled to the bit box12A such that substantially no axial force on the bit box12A is transferred to or from the output shaft50. Such coupling can be accomplished using splines or the like. Splines permit at least some degree of relative axial motion between the spline-coupled components, and thus can prevent transfer of axial loading between the coupled components. Although not shown inFIG. 2, the input shaft48is preferably rotatably supported within the output shaft50by a radial bearing, such as a journal bearing or sealed ball bearing. Correspondingly, the output shaft is preferably rotatably supported in the housing40by radial bearings, such as journal bearings.

FIG. 3is a cross section of the drilling motor10along line3-3′ inFIG. 2. The cross section is located longitudinally within the magnetic gear member41to show the relationship of and the operation of the components of the magnetic gear member41. The input shaft48may be made from high strength alloy, such as explained above with reference to the housing40. The input shaft48includes a plurality of circumferentially spaced apart, permanent magnets49oriented such that their poles are aligned radially with alternating polarity as shown inFIG. 3. The magnets49are preferably made from a high flux density, high coercivity, relatively heat insensitive material such as samarium-cobalt. The magnets49extend generally longitudinally along the input shaft48. The longitudinal dimensions of the magnets49(and corresponding components in the magnet section and output shaft) are selected such that the motor is capable of providing a selected amount of output torque to the output shaft50. The embodiment inFIG. 3includes two magnets49on the input shaft48. However, the number of magnets used on the input shaft48in other embodiments will be related to the desired gear ratio for the magnetic gear member41. The magnets49may be enclosed on their exterior by a thin walled erosion barrier48A made from titanium or similar material that is non-magnetic and is resistant to erosion from flow of fluid past the input shaft48. In other embodiments, the magnets49may be made from a single piece of magnetic material that is polarized to have alternating, radially oriented magnetic poles similar to the arrangement of magnets shown inFIG. 3. “A plurality of magnets” as used herein with respect to the magnet section44or the input shaft48is intended to include such arrangement of multipolar single element magnet material.

The output shaft50, as explained above is located radially between the input shaft48and the magnet section44. The output shaft50can be made from a high strength, non-magnetic alloy such as monel or an alloy sold under the trademark INCONEL, which is a registered trademark of Huntington Alloys Corporation, 3200 Riverside Drive, Huntington, W.Va. Alternatively, the output shaft50can be made from composite material such as fiber reinforced plastic. The output shaft50can include on its exterior surface, in suitably shaped channels or receptacles, pole pieces51disposed circumferentially around the output shaft50. The pole pieces51extend longitudinally for substantially the same length as the input shaft magnets49. The pole pieces51may be surrounded on their exterior by an erosion barrier50, similar to that as explained above for the input shaft magnets49. The pole pieces51are preferably made from a ferromagnetic material such as soft iron.

Disposed externally to the output shaft is the magnet section44. The magnet section44includes a plurality of circumferentially spaced apart magnets56. The magnets56extend longitudinally substantially the same length as the input shaft magnets49and the pole pieces51. The magnets56are oriented such that their dipole moment is substantially transverse to the longitudinal axis of the gear member41, and radially inward. The magnets56are arranged such that adjacent magnets have inverse magnetic polarity with respect to each other. In the present embodiment, the magnets56may be permanent magnets such as samarium-cobalt or neodymium-iron-boron. In other embodiments, and as will be explained below with reference toFIG. 4, one or more of the magnets56may be electromagnets, such that the gear ratio of the gear member41may be changed electrically while the motor (10inFIG. 1) is in the wellbore (15inFIG. 1). The magnets56are preferably disposed in a non-magnetic alloy retainer55, such as may be made from monel or INCONEL and are preferably enclosed on their radial outer ends by a flux enclosure55A such as may be made from ferrite or similar magnetically permeable material. The magnet retainer55may include keys55B or similar locking feature arranged to cooperate with the inner surface of the housing40to prevent rotation of the magnet retainer55, and to provide mud flow channels54for drilling mud to pass through after it moves past the turbine (46inFIG. 2). The magnet section44may include an erosion barrier44A substantially as explained above for the input shaft48and output shaft50.

In the present embodiment, the number of input shaft magnets49, the number of pole pieces51and the number of magnets56in the magnet section44may be selected to provide any reasonable speed ratio between the input shaft and the output shaft. While other embodiments may provide a different radial arrangement of input shaft, fixed magnet member and output shaft, the present arrangement can provide the advantage of simple mounting and bearing support for the rotating components of the motor10, while providing relatively large flow area for the drilling mud.

A perspective view of the present embodiment of the magnetic gear member is shown inFIG. 3A.

Another embodiment of a magnet section for a magnetic gear member is shown inFIG. 4. The magnet section44B inFIG. 4includes a plurality of magnets56arranged circumferentially as explained with reference toFIG. 3. In the embodiment ofFIG. 4, however, at least one of the magnets is an electromagnet56A, such as can be made from a soft iron core and having a wire coil wound therearound. The one or more electromagnets56A may be selectively operated by a controller60, which may be any microprocessor based controller, coupled to a switch62for each electromagnet. A power supply64provides electrical power to operate the controller and electromagnets56A. The controller60, in various embodiments, may be operated from any one of a number of control signal sources, including, without limitation, pressure signals transmitted through the drilling mud (24inFIG. 1) by modulating its pressure and/or flow rate, electromagnetic or acoustic telemetry, and the like, or in response to torque and/or speed sensors placed proximate to the drilling motor (10inFIG. 1). By selecting the number of electromagnets56A that are turned on, the effective number of magnets in the magnet section44B can be changed during operation of the magnetic gear member, thus changing the gear ratio.

Another implementation of a wellbore magnetically geared motor that can be used with a different rotary wellbore tool, in this case a wellbore completion valve, is shown in cross-section inFIG. 5. A casing140is disposed in a wellbore115drilled through a fluid-producing Earth formation115A. In the present implementation, the purpose of a completion valve is to controllably enable and disable fluid flow from the Earth formation115A into the casing140to be moved to the Earth's surface. The casing140in this embodiment may include one or more fluid flow ports141that enable fluid flow through the casing140. The casing140in this embodiment may be cemented or otherwise affixed in the wellbore115. In the present embodiment, a magnet section144of a magnetic gear unit is affixed to the interior of the casing140. The magnet section144may include a plurality of permanent and/or electromagnets, shown generally at156and arranged substantially as explained with reference toFIGS. 3 and 4.

A valve spool150is located with in the magnet section144and can rotate therein, and may include one or more port plugs161, arranged such that when the plugs161are rotationally positioned over corresponding ports141in the casing140, the plugs161stop the flow of fluid into the casing140. The valve spool150may be rotated, thus moving the plugs161to expose the ports141such that fluid flow into the interior of the casing140is enabled. The valve spool150in the present embodiment may be made in a manner similar to the output shaft of the gear member explained above with reference toFIG. 3, and may include a selected number of pole pieces151arranged circumferentially around the valve spool. The pole pieces151may be made from soft iron or similar ferromagnetic material, also as explained with reference toFIG. 3. In this embodiment, the output of the magnetic gear member is the same physical element as the valve spool150, however other implementations may have the valve spool located at a different longitudinal position along the wellbore and thus form a different physical element than the gear member output shaft.

An input shaft148is disposed within the radial interior of the output shaft, and includes one or more magnets149thereon. The input shaft148may be rotationally coupled to a turbine, such as shown inFIG. 2, or similar device to convert movement of fluid within the casing140into rotational energy to drive the input shaft148.

It will be appreciated that the combination of magnet section144, valve spool150and input shaft148are similar in operating principle to the gear member shown in and explained with reference toFIG. 3. In the present embodiment, however, rather than driving a drill bit, the valve spool150, which is functionally equivalent to the output shaft50inFIG. 3, drives the port plugs161to cover and uncover the ports141in the casing140. Thus, the embodiment shown inFIG. 5may be used to selectively open and close fluid flow from the formation115A. In other implementations, the magnets156in the magnet section144may be electromagnets, such that the gear member may be selectively activated and deactivated, substantially as explained with reference toFIG. 4. By providing selective activation and deactivation of the gear member, the movement of the valve spool150may be controlled even in the presence of continuous fluid movement within the casing140. In some embodiments, the polarity of the magnets156may be reversible, when electromagnets are used, such that the rotational direction of the valve spool may be reversed as well. Alternatively, the valve spool may be rotated in the same direction, the rotation being stopped when the ports141are covered or uncovered as the valve operator selects. The embodiment shown inFIG. 5has the valve spool, ports, output shaft, magnet section substantially axially collocated, however other embodiments may have the valve components (valve spool, port plugs and casing ports) axially spaced apart from the magnetic gear member.

Embodiments of a geared wellbore motor according to the various aspects of the invention can provide large gear ratio in a diametrically compact housing, can provide ability to resist torsional shock loading without breaking internal components, and can provide reduction (or speed multiplying) gearing without the need to seal a compartment within the motor from wellbore fluids to provide lubrication for mechanical gearing.