Compliant rolling element retainer

A drill bit is provided that includes a bit body having one or more blades extending therefrom, a plurality of cutters secured to the one or more blades, and a rolling element assembly positioned within a cavity defined on the bit body. The rolling element assembly includes a rolling element rotatable within the cavity about a rotational axis, and a compliant retainer extendable within a retainer slot defined in the cavity to secure the rolling element within the cavity. The compliant retainer and the cavity cooperatively encircle more than 180° but less than 360° of a circumference of the rolling element while leaving a full axial width of the rolling element exposed. The compliant retainer is compressible responsive to forces from the rolling element to absorb vibrations and/or automatically adjust depth of cut.

TECHNICAL FIELD

The present description relates in general to wellbore drilling, and more particularly, for example and without limitation, to a compliant rolling element retainer for a rolling element of a drill bit for wellbore drilling.

BACKGROUND OF THE DISCLOSURE

In conventional wellbore drilling in the oil and gas industry, a drill bit is mounted on the end of a drill string, which may be lengthened by adding segments of drill pipe as the well is progressively drilled to the desired depth. At the surface of the well site, a rotary drive (referred to as a “top drive”) may be provided to rotate the entire drill string, including the drill bit at the end, to drill through the subterranean formation. Alternatively, the drill bit may be rotated using a downhole mud motor without having to rotate the drill string. When drilling, drilling fluid is pumped through the drill string and discharged from the drill bit to remove cuttings and debris. The mud motor, if present in the drill string, may be selectively powered using the circulating drilling fluid.

One common type of drill bit used to drill wellbores is a “fixed cutter” bit, wherein the cutters are secured to the bit body at fixed positions. This type of bit is sometimes referred to as a “drag bit” since the cutters in one respect drag rather than roll in contact with the formation during drilling. The bit body may be formed from a high strength material, such as tungsten carbide, steel, or a composite/matrix material. A plurality of cutters (also referred to as cutter elements, cutting elements, or inserts) are attached at selected locations about the bit body. The cutters may include a substrate or support stud made of a carbide (e.g., tungsten carbide), and an ultra-hard cutting surface layer or “table” made of a polycrystalline diamond material or a polycrystalline boron nitride material deposited onto or otherwise bonded to the substrate. Such cutters are commonly referred to as polycrystalline diamond compact (“PDC”) cutters.

In fixed cutter drill bits, PDC cutters are rigidly secured to the bit body, such as by being brazed within corresponding cutter pockets defined on blades that extend from the bit body. Some of the PDC cutters are strategically positioned along the leading edges of the blades to engage the formation during drilling. In use, high forces are exerted on the PDC cutters, particularly in the forward-to-rear direction. Over time, the working surface or cutting edge of each cutter that continuously contacts the formation eventually wears down and/or fails.

DETAILED DESCRIPTION

The present disclosure relates to earth-penetrating drill bits and, more particularly, to rolling-type depth-of-cut control elements that can be used in drill bits.

Various aspects of the disclosure provide rolling element assemblies that can be secured within corresponding cavities provided on a drill bit. Each rolling element assembly includes a cylindrical rolling element strategically positioned and secured to the drill bit so that the rolling element is able to engage the formation during drilling. In response to drill bit rotation, and depending on the selected positioning and/or orientation of the rolling element with respect to the body of the drill bit, the rolling element may roll against the underlying formation, cut against the formation, or both roll against and cut the formation. The rolling elements of the presently disclosed rolling element assemblies are retained within corresponding cavities on the bit body using a compliant arcuate retainer received within a retainer slot defined in the cavity.

It has been discovered that vibrations during drilling (e.g., drilling using particular combinations of motors and/or bottom hole assemblies (BHAs)) can be transferred from a cylindrical rolling element through an arcuate retainer for the cylindrical rolling element to a securing element for the arcuate retainer. The securing element may be a pin, nail, screw, weld, or other attachment structure that secures the arcuate retainer in the retainer slot. These transferred vibrations can cause the securing element to disengage and/or otherwise release the retainer, which can lead to failure of the rolling element.

In accordance with various aspects of the subject disclosure, a retainer for a cylindrical rolling element of a rolling element assembly is provided. The retainer may be an arcuate structure having a base structure with one or more cavities therein. The cavities increase the compliancy of one or more portions of the retainer or of the entire retainer. The one or more cavities may be filled with compliant material such as an elastomeric material (e.g., a polymer or metallic resilient material). Vibrations on the cylindrical rolling element are dampened by the one or more cavities. In this way, vibrations at the securing element are reduced and/or eliminated, which can increase the lifetime of the rolling element and can prevent rolling element failures that can increase the time and expense of a drilling operation.

Moreover, providing a compliant retainer can allow self-adjustment of the depth-of-cut (DOC) by allowing the position of the cylindrical rolling element to move relative to the bit face by compression or decompression of the compliant retainer.

Rolling element assemblies described herein can be configured as rolling depth of cut control (DOCC) elements that roll along the formation as the drill bit rotates. In a rolling DOCC element configuration, a rolling element may be oriented so that a full axial span of the rolling element bears against the formation. Rolling DOCC elements may exhibit enhanced wear resilience and allow for additional weight-on-bit without negatively affecting torque-on-bit. The compliant retainer can allow small adjustments in the depth-of-cut, responsive to changing loads on the rolling DOCC elements (e.g., due to changing weight-on-bit and/or changing formations during drilling). This may allow a well operator to minimize damage to the drill bit, thereby reducing trips and non-productive time, and decreasing or increasing the aggressiveness of the drill bit without sacrificing its efficiency.

In some example implementations, the rolling element assemblies described herein can be configured as rolling cutting elements. In yet other example implementations, the rolling element assemblies described herein may operate as a hybrid between a rolling cutting element and a rolling DOCC element (e.g., by orienting the rotational axis of the rolling element on a plane that does not pass through the longitudinal axis of the drill bit or through the longitudinal axis of the drill bit). Rolling cutting elements and/or rolling hybrid DOCC cutting elements may exhibit enhanced wear resilience and allow for additional weight-on-bit without negatively affecting torque-on-bit.

FIG. 1Ais an isometric view of an exemplary drill bit100, in accordance with aspects of the present disclosure. In the example ofFIG. 1A, drill bit100is depicted as a fixed cutter drill bit having rolling element assemblies118(denoted118aand118b) that include compliant retainers (not explicitly shown). Fixed cutter drill bit100may be implemented as a crystalline diamond compact (PDC) drill bit, a drag bit, a matrix drill bit, and/or a steel body drill bit (as examples). However, it should also be appreciated that rolling element assemblies118that include compliant retainers as described herein can be provided in other types of drill bits operable to form a wellbore including, but not limited to, roller cone drill bits, reamers, or other rock removing tools.

Drill bit100has a bit body102that includes radially and longitudinally extending blades104having leading faces106. Bit body102may be made of steel or a matrix of a harder material, such as tungsten carbide. Bit body102rotates about a longitudinal drill bit axis107to drill into an underlying subterranean formation under an applied weight-on-bit. Corresponding junk slots112are defined between circumferentially adjacent blades104, and a plurality of nozzles or ports114can be arranged within junk slots112for ejecting drilling fluid that cools drill bit100and otherwise flushes away cuttings and debris generated while drilling.

Bit body102further includes a plurality of cutters116secured within a corresponding plurality of cutter pockets sized and shaped to receive cutters116. Each cutter116, in this example, comprises a fixed cutter secured within its corresponding cutter pocket via brazing, threading, shrink-fitting, press-fitting, snap rings, or any combination thereof. Fixed cutters116are held in blades104and respective cutter pockets at predetermined angular orientations and radial locations to present fixed cutters116with a desired back rake angle against the formation being penetrated. As the drill string is rotated, fixed cutters116are driven through the rock by the combined forces of the weight-on-bit and the torque experienced at drill bit100. During drilling, fixed cutters116may experience a variety of forces, such as drag forces, axial forces, reactive moment forces, or the like, due to the interaction with the underlying formation being drilled as drill bit100rotates.

Each fixed cutter116may include a generally cylindrical substrate made of an extremely hard material, such as tungsten carbide, and a cutting face secured to the substrate. The cutting face may include one or more layers of an ultra-hard material, such as polycrystalline diamond, polycrystalline cubic boron nitride, impregnated diamond, etc., which generally forms a cutting edge and the working surface for each fixed cutter116. The working surface is typically flat or planar, but may also exhibit a curved exposed surface that meets the side surface at a cutting edge.

Generally, each fixed cutter116may be manufactured using tungsten carbide as the substrate. While a cylindrical tungsten carbide “blank” can be used as the substrate, which is sufficiently long to act as a mounting stud for the cutting face, the substrate may equally comprise an intermediate layer bonded at another interface to another metallic mounting stud. To form the cutting face, the substrate may be placed adjacent a layer of ultra-hard material particles, such as diamond or cubic boron nitride particles, and the combination is subjected to high temperature at a pressure where the ultra-hard material particles are thermodynamically stable. This results in recrystallization and formation of a polycrystalline ultra-hard material layer, such as a polycrystalline diamond or polycrystalline cubic boron nitride layer, directly onto the upper surface of the substrate. When using polycrystalline diamond as the ultra-hard material, fixed cutter116may be referred to as a polycrystalline diamond compact cutter or a “PDC cutter,” and drill bits made using such PDC fixed cutters116are generally known as PDC bits.

As illustrated inFIG. 1A, drill bit100may further include a plurality of rolling element assemblies118, shown as rolling element assemblies118aand118b. The orientation of a rotational axis of each rolling element assembly118with respect to a tangent to an outer surface of blade104may dictate whether the particular rolling element assembly118operates as a rolling DOCC element, a rolling cutting element, or a hybrid of both. As mentioned above, rolling DOCC elements may prove advantageous in allowing for additional weight-on-bit (WOB) to enhance directional drilling applications without over engagement of the fixed cutters116. Effective DOCC also limits fluctuations in torque and minimizes stick-slip, which can cause damage to fixed cutters116.

FIG. 1Bis an enlarged portion of drill bit100indicated by the dashed box shown inFIG. 1A. As shown inFIG. 1B, each rolling element assembly118is located in blade104and includes a rolling element122. Exposed portions of rolling elements122are illustrated in solid linetype, while portions of rolling elements122that are seated within corresponding housings or pockets of the rolling element assemblies118are illustrated in dashed linetype.

Each rolling element122has a rotational axis A, a Z-axis that is perpendicular to the blade profile, and a Y-axis that is orthogonal to both the rotational and Z-axes. As shown, the exposed portion of each of rolling elements122is constant with respect to the position along the rotational axis of the rolling element, in either the DOCC or the cutter orientation.

If, for example, the rotational axis A of a rolling element122is substantially parallel to a tangent to outer surface119of the blade profile, that rolling element assembly118bmay generally operate as a rolling DOCC element. Said differently, if the rotational axis A of the rolling element122passes through or lies on a plane that passes through the longitudinal axis107(FIG. 1A) of the drill bit100(FIG. 1A), then the rolling element assembly118bmay substantially operate as a rolling DOCC element. If, however, the rotational axis A of a rolling element122is substantially perpendicular to leading face106of the blade104, then that rolling element assembly118amay substantially operate as a rolling cutting element. Said differently, if the rotational axis A of a rolling element122is perpendicular to or lies on a plane that is perpendicular to a plane passing through the longitudinal axis107(FIG. 1A) of the drill bit100(FIG. 1A), then the rolling element assembly118amay substantially operate as a rolling cutting element.

Accordingly, as depicted inFIG. 1B, rolling element assembly118amay be positioned to operate as a rolling cutting element and rolling element assembly118bmay be positioned to operate as a rolling DOCC element. Rolling element assemblies118may also be provided in which the rotational axis A of the rolling element122lies on a plane that does not pass through the longitudinal axis107(FIG. 1A) of the drill bit100(FIG. 1A) nor is the plane perpendicular to the longitudinal axis107, that rolling element assembly118operating as a hybrid rolling DOCC and cutting element.

Traditional load-bearing type cutting elements for DOCC can unfavorably affect torque-on-bit (TOB) by simply dragging, sliding, etc. along the formation, whereas a rolling DOCC element, such as rolling element assemblies118b, may reduce the amount of torque needed to drill a formation because it rolls to reduce friction losses typical with load bearing DOCC elements. A rolling DOCC element will also have reduced wear as compared to a traditional bearing element. As will be appreciated, however, one or more of rolling element assemblies118bcan also be used as rolling cutting elements, which may increase cutter effectiveness since heat may be distributed more evenly over the entire cutting edge and minimize the formation of localized wear flats on the rolling cutting element.

Referring again toFIG. 1A, rolling element assemblies118bmay be placed in the cone region of drill bit100and otherwise positioned so that rolling element assemblies118btrack in the path of adjacent fixed cutters116(e.g., the rolling element assemblies are placed in a secondary row behind the primary row of fixed cutters116on blade104). However, since the second rolling element assemblies118bare able to roll, they can be placed in positions other than the cone without affecting TOB.

Strategic placement of rolling element assemblies118aand118bmay further allow the rolling element assemblies to be used as either primary and/or secondary rolling cutting elements as well as rolling DOCC elements, without departing from the scope of the disclosure. For instance, in some implementations, one or more rolling element assemblies118aor118bmay be located in a kerf forming region120located between adjacent fixed cutters116. During operation, kerf forming region120results in the formation of kerfs on the underlying formation being drilled. One or more of rolling element assemblies118aand118bmay be located on the bit body102such that they will engage and otherwise extend across one or multiple formed kerfs during drilling operations. In this example, rolling element assemblies118aand/or118bmay also function as prefracture elements that roll on top of or otherwise crush the kerf(s) formed on the underlying formation between adjacent fixed cutters116. In other cases, one or more of rolling element assemblies118aand118bmay be positioned on the bit body102such that they will proceed between adjacent formed kerfs during drilling operations. In yet other examples, one or more of rolling element assemblies118aand/or118bmay be located at or adjacent the apex of drill bit100(e.g., at or near longitudinal axis107). In such examples, drill bit100may fracture the underlying formation more efficiently.

Rolling element assemblies118aand118bmay be positioned on a respective blade104such that rolling element assemblies118aand118bextend orthogonally from the outer surface119(FIG. 1B) of the respective blade104. One or more of rolling element assemblies118aand/or118bmay be positioned at a predetermined angular orientation (three degrees of freedom) offset from normal to the profile of the outer surface119of the respective blade104. As a result, rolling element assemblies118aand/or118bmay exhibit an altered or desired back rake angle, side rake angle, or a combination of both. As will be appreciated, the desired back rake and side rake angles may be adjusted and otherwise optimized with respect to primary fixed cutters116and/or surface119(FIG. 1B) of the blade104on which the rolling element assemblies118aand/or118bare disposed.

FIG. 2is an isometric view of one example of a rolling element assembly200, according to aspects of the disclosure. Rolling element assembly200may be, for example, implemented in drill bit100ofFIGS. 1A-1B. For example, rolling assembly200may be an implementation of any of rolling element assemblies118aor118bofFIG. 1A or 1B. As illustrated inFIG. 2, rolling element assembly200may be positioned within a cavity202defined in blade104of drill bit100. While cavity202is shown as being defined in blade104, it will be appreciated that the principles of the present disclosure are equally applicable to cavity202being defined in other locations of drill bit100, without departing from the scope of the disclosure.

Blade104is depicted inFIG. 2in phantom to allow the component parts of rolling element assembly200to be viewed. Moreover, only a portion of blade104is represented inFIG. 2and depicted in the general shape of a cube. In some scenarios, drill bit100is made of a matrix material, and cavity202may be formed by selectively placing displacement materials (e.g., consolidated sand or graphite) at the location where cavity202is to be formed. In other examples, drill bit100has a steel body drill bit, and conventional machining techniques may be employed to machine cavity202to desired dimensions at the desired location.

Rolling element assembly200includes a rolling element204that comprises a generally cylindrical or disk-shaped structure having a first axial end208aand a second axial end208bthat is opposite the first axial end208a. The distance between first and second axial ends208aand208bis referred to herein as the axial width210of the rolling element204. As shown in the example ofFIG. 2, at each position on rolling element204between first and second axial ends208aand208b(e.g., at each position along the axial width of rolling element204), the same amount of rolling element204is exposed above the surface of blade104. However, it should be appreciated that, in some implementations, the axis of rolling element204may be non-parallel to the profile of blade104such that one end of rolling element204is exposed more or less than the other end, depending on the desired bottom hole pattern and configuration.

Rolling element204includes a substrate212and opposing diamond tables214aand214barranged at first and second axial ends208aand208b, respectively, and otherwise coupled to opposing axial ends of substrate212. Substrate212may be formed of a variety of hard or ultra-hard materials including, but not limited to, steel, steel alloys, tungsten carbide, cemented carbide, any derivatives thereof, and any combinations thereof. Suitable cemented carbides may contain varying proportions of titanium carbide (TiC), tantalum carbide (TaC), and niobium carbide (NbC). Additionally, various binding metals may be included in substrate212, such as cobalt, nickel, iron, metal alloys, or mixtures thereof. In substrate212, the metal carbide grains are supported within a metallic binder, such as cobalt. In other cases, substrate212may be formed of a sintered tungsten carbide composite structure or a diamond ultra-hard material, such as polycrystalline diamond (PCD) or thermally stable polycrystalline diamond (TSP).

Diamond tables214aand214bmay be made of a variety of ultra-hard materials including, but not limited to, polycrystalline diamond (PCD), thermally stable polycrystalline diamond (TSP), cubic boron nitride, impregnated diamond, nanocrystalline diamond, ultra-nanocrystalline diamond, and zirconia. These hard and/or ultra-hard materials may be suitable for use as bearing surfaces, as herein described.

Rolling element204may include one or more cylindrical bearing portions. More particularly, in the example ofFIG. 2, the entire rolling element204is cylindrical and made of hard, wear-resistant materials, and thus any portion of rolling element204may be considered as a cylindrical bearing portion to the extent it slidingly engages a bearing surface of cavity202or another component of rolling element assembly200when rolling, such as would be expected during drilling operations. In some examples, one or both of diamond tables214aand214bmay be considered cylindrical bearing portions for rolling element204. In other implementations, one or both of diamond tables214aand214bmay be omitted from rolling element204and substrate212may alternatively be considered as a cylindrical bearing portion. In yet other examples, the entire cylindrical or disk-shaped rolling element204may be considered as a cylindrical bearing portion and may be made of any of the hard or ultra-hard materials mentioned herein, without departing from the scope of the disclosure. In the example ofFIG. 2, the bearing surface of rolling element204is a smoothly contiguous surface that is free of grooves or protrusions thereon, to help facilitate smooth rotation of that bearing surface against the bearing surface of cavity202. The bearing surface of cavity202is similarly smoothly contiguous and free of protrusions or grooves.

It should be noted that the features of rolling element204are shown for illustrative purposes only and may or may not be drawn to scale. For example, the thickness or axial extent of both diamond tables214aand214bmay or may not be the same. In at least one example, one of diamond tables214aand214bmay be thicker than the other. Moreover, in some examples, one of diamond tables214aor214bmay be omitted from rolling element204altogether. In yet other examples, substrate212may be omitted and rolling element204may instead be made entirely of the material of diamond tables214aand214b.

Rolling element assembly200also includes a retainer206configured to help secure or retain rolling element204in cavity202(e.g., during use). More particularly, cavity202provides and otherwise defines an opening216large enough to receive rolling element204. When seated within cavity202, an arcuate portion of rolling element204extends out of cavity202to expose the full axial width210of that portion of rolling element204.

Retainer206is a compliant retainer that includes one or more compliant portions or that has an overall compliancy. Compliant retainer206may subsequently be inserted into cavity202so that cavity202and retainer206cooperatively retain rolling element204within cavity202. Cooperatively retaining rolling element204within cavity202is accomplished as portions of cavity202and retainer206jointly encircle more than 180° of the circumference of rolling element204, but less than 360°, so that the full axial width210of a portion of rolling element204remains exposed for external contact with a formation during drilling operations.

Retainer206may be provided with compliancy at one or more locations thereon by providing one or more internal voids or cavities therein. The internal cavities may be evacuated, air-filled, gas-filled, or filled with a compliant material such as an elastomer or a low modulus metal capable of withstanding downhole conditions. One or more materials having differing moduli of elasticity may be used to form the base structure of retainer206and to fill one or more cavities in the base structure to provide a retainer having a desired compliancy at one or more locations thereon. The amount of the arcuate portion of rolling element204that extends out of cavity202to expose the full axial width210that portion may vary based on the compressive state of retainer206(e.g., due to varying amounts of compression of compliant retainer206).

During drilling operations, rolling element204is able to rotate within cavity202about a rotational axis A of rolling element204. As rolling element204rotates about the rotational axis A, the arcuate portion of rolling element204extending out of cavity202and otherwise exposed through opening216engages (e.g., cuts, rolls against, or both) the underlying formation. This rotation allows the full axial width210of rolling element204, across the entire outer circumferential surface, to progressively be used to engage the formation as rolling element204rotates during use. In configurations in which the amount of rolling element204that is exposed is constant across the axial width, the wear on the outer surface of rolling element204is uniform across the axial width.

FIG. 3is a side view of rolling element assembly200as installed within the cavity202defined in blade104. Again, blade104is depicted inFIG. 3in phantom to allow the component parts of rolling element assembly200to be viewed, and only a portion of blade104is represented inFIG. 2and depicted in the general shape of a cube. Retainer206is shown inFIGS. 2 and 3receiving rolling element204to rotatably secure the rolling element about rotational axis A of the rolling element.

As illustrated, cavity202includes a retainer slot302configured to receive and seat retainer206. More specifically, cavity202may provide a first arcuate portion304athat extends from one side of opening216and a second arcuate portion304bthat extends from the opposing side of opening216. The first arcuate portion304ahas a first radius R1and second arcuate portion304bhas a second radius R2that is greater than first radius R1End wall306provides a transition between first and second arcuate portions304aand304b. With a larger second radius R2, second arcuate portion304bis sized to accommodate retainer206within cavity202. Accordingly, retainer slot302is defined, at least in part, by second arcuate portion304band end wall306.

Retainer206includes an inner arcuate surface308aand an outer arcuate surface308bopposite inner arcuate surface308a. When retainer206is disposed within retainer slot302, outer arcuate surface308bwill be disposed against or otherwise adjacent second arcuate portion304band inner arcuate surface308awill be disposed against or otherwise adjacent the outer circumferential surface of rolling element204. Moreover, compliant retainer206is sized such that the curvature of first arcuate portion304awill transition smoothly to the curvature of inner arcuate surface308a, at least when retainer206is uncompressed, to enable rolling element204to bear against a continuously (uniformly) curved surface at all angular locations within cavity202during operation. In the example ofFIG. 3, arcuate surface308ais smoothly contiguous (e.g., free of protrusions or grooves) to provide a uniform surface for rotation of rolling element204against surface308a.

As shown inFIG. 3, retainer206has a radial thickness defined by an interior thickness WI(e.g., the distance between surfaces308aand308bat an inner edge of retainer206that is configured to be disposed adjacent to end wall306), an outer thickness WO(e.g., the distance between surfaces308aand308bat an outer edge310that is configured to be disposed parallel to the outer surface blade104), and a central thickness WC(e.g., the distance between surfaces308aand308bat a location between the inner and outer edges).

In an uncompressed configuration in which retainer206is free of external forces, inner thickness WI, outer thickness WO, and central thickness WImay be the same. However, a force FCon surface308aof retainer206(e.g., a force provided by the surface of rolling element204) may compress one or more portions of retainer206. For example, in operation, a force FRprovided on rolling element204by the formation can cause rolling element204to press into surface308awith force FC. As described in further detail hereinafter (see, e.g.,FIGS. 5-11and the associated description), one or more interior cavities may be arranged within retainer206to provide the desired compliancy at the desired locations.

Retainer206may be secured within cavity202(e.g., retainer slot302) using a variety securing features or attachment structures such as, but not limited to, brazes, welds, an industrial adhesive, a press-fit, a shrink-fit, one or more mechanical fasteners (e.g., screws, bolts, snap rings, pins, a ball bearing retention mechanism, a locking wire, etc.), or any combination thereof. In at least one example, as illustrated inFIG. 3, a set screw312(shown in dashed lines inFIG. 3) or the like may be used to secure retainer206within retainer slot302. In the illustrated example, set screw312may be extended through a hole314adefined in blade104, such as a trailing face of blade104, and threaded into a correspondingly aligned hole314bdefined in retainer206. It will be appreciated, however, that set screw312may be used to secure retainer206within retainer slot302via alternately defined holes provided in other locations, without departing from the scope of the disclosure.

If care is not taken, vibrations of rolling element204can be transferred to screw312or other attachment structures. These vibrations can cause screw312to back out of hole314bor can cause other securing elements or attachment structures to become unsecured or to break down (e.g., in the case of a weld, braze, or other securement material). Compliant retainer206is arranged to absorb some or all of these vibrations (e.g., at desired frequencies) to prevent the vibrations from being transferred to screw312.

Rolling element assembly200may be arranged on blade104such that rolling element204will rotate about the rotational axis A in a first direction320during operation. As rolling element204engages an underlying subterranean formation and rotates about the rotational axis A, weight on bit (WOB) force F1and friction force F2will act on rolling element204. WOB force F1is the weight force applied to rolling element204in the direction of advancement of drill bit100(FIGS. 1A-1B). Friction force F2is a drag force assumed by rolling element204and applied in the direction opposite rotation of drill bit100. Based on the respective magnitudes of WOB force F1and friction force F2, a resultant force FRwill be assumed by rolling element204. The magnitude of the resultant force FRmay be determined as follows:
FR2=F12+F22Equation (1)

The resultant force FRvector will be directed at an angle θ offset from the WOB force F1. The angle θ may be determined as follows:

If the direction of the resultant force FRvector intersects retainer206as positioned within retainer slot302, then retainer206helps retains rolling element204in cavity202and acts as a bearing element that assumes at least a portion FCof the resultant force FRof rolling element204during drilling operations

In the example ofFIG. 3, an arc length L of retainer206is long enough that the resultant force FRvector will intersect retainer206, which allows retainer206to operate as a retaining structure and a bearing element that receives force FCfrom rolling element204. Moreover, because of the arcuate shape of the retainer206, the maximum arc length L may be limited to the size of opening216.

Accordingly, compliant retainer206not only helps secure rolling element204in cavity202, but can also serve as a compliant bearing surface that supports and guides rolling element204, may assume most (if not all) of the load exerted on rolling element204, absorbs vibrations from rolling element204, and/or allows variations in the position of rolling element204in cavity202responsive to the force FRon rolling element204. In contrast, first arcuate surface304amay see only minimal loads under normal operation conditions. Given the design of rolling element assembly200, the force exerted on retainer206during operation may be primarily compressive in nature. Surface308aof retainer206may be made of a hard or ultra-hard material to help reduce the amount of friction and wear between rolling element204and retainer206as rolling element204bears and slides against inner arcuate surface308a.

However, as noted above, at least some portions of retainer206may be compliant or compressible portions such that force FCon surface308aof retainer206(e.g., a force provided by the surface of rolling element204) can compress one or more portions of retainer206. For example, in operation, force FRon rolling element204by the formation can cause rolling element204to press into surface308awith force Fc. Force Fccan cause deformation of retainer206such that central thickness Weis reduced (e.g., by movement of surface308atoward surface308bdue to pressure from204responsive to weight on bit (WOB) force F1and friction force F2acting on rolling element204). In this way, changes in the force FRcause compression or extension of compliant retainer206such that compliant retainer206absorbs vibrations and/or allows automatic adjustment of the DOC.

Outer thickness WOand/or inner thickness WIof retainer206can also be reduced by a compressive force exerted by rolling element204. However to avoid wear at the interface between edge wall306and surface304a, in some implementations, compliant retainer206may have an inner edge wall at the inner edge portion thereof that is rigid and incompressible or relatively less compliant that other portions of retainer206(e.g., such that inner thickness W1does not decrease when thicknesses WOand/or WCare reduced by compression).

The example ofFIG. 3also shows how retainer206may include an extraction feature316used to help extract retainer206from cavity202when desired. Extraction feature316may comprise any negative or positive alteration in the geometrical shape of retainer206that provides a location where retainer206may be gripped or otherwise engaged to pry (rotate) retainer206out of retainer slot302. When it is desired to remove retainer206from cavity202, a user may access and engage extraction feature316with a rigid contrivance (e.g., a pick, a screwdriver, a rigid rod, etc.) and pry (rotate) compliant retainer206out of retainer slot302. In at least one example, as illustrated, an access groove318may be defined in the upper surface of blade104to provide a location where a user can access extraction feature316and gain leverage over compliant retainer206to pry it out of cavity202. In the example ofFIG. 3, access groove318is formed in the upper surface of blade104adjacent outer arcuate surface308bof retainer206. In other examples, access groove318can be formed in the upper surface of blade104adjacent one or both of the sidewalls of retainer206. In implementations in which retainer206is brazed into cavity202, the braze may first be melted prior to extracting retainer206.

It should be noted that, although rolling element assembly200has been described as retaining one rolling element204, rolling element assembly200(or any of the rolling element assemblies described herein) may include two or more rolling elements204, without departing from the scope of the disclosure. In multiple rolling element implementations, the multiple rolling elements204may be retained within cavity202using a single retainer206or each rolling element204may be supported by an individual retainer206.

FIGS. 4A and 4Bshow exterior features of compliant retainer206.FIGS. 5-10show cross-sectional views of compliant retainer206so that various configurations of the compliant features of retainer206can be seen.FIG. 11shows an exemplary compressed configuration for retainer206.

FIGS. 4A and 4Bare isometric and end views, respectively, of an example implementation of compliant retainer206. As illustrated inFIG. 4A, retainer206may include a generally arcuate base structure402having a first end404a, a second end404b, inner arcuate surface308a, outer arcuate surface308b, a first sidewall406a, and a second sidewall406b. The inner and outer arcuate surfaces308aand308bextend between the first and second ends404aand404b. Second end404bmay be configured to engage or come into close contact with end wall306(FIG. 3) when the retainer206is inserted into the retainer slot302(FIG. 3). The first and second sidewalls406aand406bextend radially between the inner and outer arcuate surfaces308aand308bon each axial end of the retainer206.

In some examples, as shown inFIG. 4B, some or all of the base structure402of the retainer206may exhibit a polygonally symmetric cross-sectional shape. As used herein, the term “polygonally-symmetric” refers to a cross-sectional shape that is polygonal and symmetric on both axial sides of the shape. In the example ofFIGS. 4A and 4B, retainer206exhibits a generally dovetail cross-sectional outer shape. More particularly, inner arcuate surface308amay, in an uncompressed configuration, exhibit a first width W1and outer arcuate surface308bmay exhibit a second width W2greater than the first width W1. Accordingly, sidewalls406aand406bmay taper inward as extending radially from outer arcuate surface308bto inner arcuate surface308a. In examples in which retainer206is brazed into retainer slot302(FIG. 3), the tapered sidewalls406aand406bmay prove advantageous in helping prevent retainer206from shifting out of retainer slot302during the brazing process. It will be appreciated, however, that other polygonally-symmetric cross-sectional shapes may also be employed, such as a T-shaped base structure402, without departing from the scope of the disclosure. Moreover, some or all of base structure402of retainer206may alternatively exhibit rounded features or polygonally asymmetric cross-sectional shape, as discussed in more detail below.

In some examples, transition corners408between second end404band the first and second sidewalls406aand406band of retainer206may be chamfered or radiused. Chamfered or radiused transition corners408may help with ease of installation of the retainer into retainer slot302(FIG. 3). In other examples, however, transition corners408may be angled, such as including a 90° (or substantially 90°) transition between second end404band first and second sidewalls406aand406bof retainer206, without departing from the scope of the disclosure.

FIG. 5shows a cross-sectional side view of rolling element assembly200. As shown inFIG. 4, compliant retainer206may be provided with a base structure500(e.g., an implementation of base structure402) having an internal cavity502. Under a compressive force from rolling element204, a portion of rigid base structure500can be pressed into cavity502, responsive to a force on the inner arcuate surface, to provide compliancy for the compliant retainer by a reduction in size or other deformation of the cavity.

Base structure500of retainer206can be formed from any combination of the hard or ultra-hard materials described above for the substrate212and the diamond tables214aand214b. More specifically, base structure500may include one or more materials such as, but not limited to, steel, a steel alloy, tungsten carbide, a sintered tungsten carbide composite structure, cemented carbide, polycrystalline diamond (PCD), thermally stable polycrystalline diamond (TSP), cubic boron nitride, impregnated diamond, nanocrystalline diamond, ultra-nanocrystalline diamond, zirconia, any derivatives thereof, and any combinations thereof. Alternatively, or in addition thereto, the retainer206may be made of an engineering metal, a coated material (i.e., using processes such as chemical vapor deposition, plasma vapor deposition, etc.), or other hard or abrasion-resistant materials. Base structure500may be formed from a hard material with an ultra-hard material on the bearing surface thereof (e.g., to form a hard faced region). The materials for base structure500are selected to provide a tough ductile material with a hard faced region, to provide the desired bearing resistance while still allowing the toughness of the retainer substrate.

A base structure500formed from or having an inner surface formed from a hard or ultra-hard material may help reduce the amount of friction and wear between rolling element204and retainer206as rolling element204bears and slides against inner arcuate surface308a. Hard or ultra-hard materials of base structure500may reduce or eliminate the need for lubrication between retainer206and rolling element204. Inner arcuate surface308amay be polished so as to further reduce friction between the opposing surfaces, if desired. Inner arcuate surface308amay be polished, for example, to a surface finish of about 40 micro-inches or better.

As rolling element204rotates in first direction320, element204urges retainer206to remain secured in cavity202. More particularly, friction generated between the outer circumference of rolling element204and inner arcuate surface308aof retainer206will continuously provide a force that urges retainer206against end wall306and otherwise deeper into cavity202.

In the example ofFIG. 5, cavity502is filled with an elastomeric material504. Elastomeric material504can be a polymer material or a relatively more elastic metal (e.g., a low modulus metal capable of withstanding downhole conditions) than that of base structure500. However, it should be appreciated that providing elastomeric material504in cavity502is merely illustrative. In some implementations, cavity502may be an air-filled cavity, a cavity filled with another desired gas or fluid, or can be an evacuated cavity.

Retainer206, having an internal cavity502in a base structure500, may be formed in a molding, casting, investment casting, additive manufacturing (e.g., 3-dimensional (3D) printing) or other suitable manufacturing process. Base structure500may be a monolithic base structure or may be formed from multiple pieces (e.g., two interfacing pieces, each having a recess that, together, form an interior cavity when the two interfacing pieces are attached together).

In the example ofFIG. 5, base structure500is provided with a single internal cavity502that extends, equidistant from inner and outer surfaces308aand308bin a circumferential direction between edges404aand404b, with a portion of base structure500separating cavity502from each of outer surfaces308aand308band edges404aand404b. In the example ofFIG. 5, cavity502has a constant width and a constant thickness progressing along the length in a direction between edges404aand404b. However, it should be appreciated that the single, constant-width, constant-thickness, centered cavity502ofFIG. 5is merely illustrative and that other arrangements are contemplated (e.g., multiple cavities, varying width cavities, varying thickness cavities, varying length cavities, and/or varying location cavities).

For example,FIG. 6shows an example in which base structure500includes multiple cavities502. Some or all of cavities502may be filled with elastomeric material504. In one example, each of cavities502is filled with a common material504. In other examples, some of cavities502may be free of material504and/or some of cavities502are provided with a different elastomeric material (e.g., to provide varying degrees of compressibility at various locations on retainer206.

In the examples ofFIGS. 5 and 6, material504substantially fills the cavity(ies) in which it is disposed. However,FIG. 7shows another example in which voids700are provided at various locations within material504in cavity502. The shapes and positions of voids700can be arranged to provide a desired (e.g., varying) compressibility at various locations on retainer206.

In the examples ofFIGS. 5-7, cavity502is a closed cavity that is entirely encapsulated by base structure500. However, as shown inFIG. 8, cavity502can extend to one or more of edges404aor404b. In the example ofFIG. 8, cavity502extends to outer edge404aof retainer206and includes a taper portion802that tapers in the direction of inner edge404b. In this example, the apex of tapered portion802is separated from inner edge402bby a portion of base structure500. In this way, retainer206may be arranged to be compressible at the location of center thickness WCand have a compressible outer edge800, while inner edge404ais substantially incompressible so that inner thickness W1does not change, even in the presence of force FCon retainer206.

In the example ofFIG. 8, compliant retainer206may be increasingly compressible at locations that are circumferentially further from inner edge404bso that outer thickness WOis reduced more than central thickness WC, which is reduced more than inner thickness W1which may be the thickness of an incompressible inner edge wall at edge404a(e.g., incompressible relative to other portions of retainer206). In this configuration, increased forces FRfrom the formation on rolling element204cause rolling element204to be moved into cavity202and also laterally within opening216, reducing the size of opening216. As shown inFIG. 8, a tapered cavity502and/or a cavity extending to the edge of base structure500can be filled with elastomeric material504, if desired.

As noted above, base structure500and cavity(ies)502can be formed from any of various manufacturing processes including, for example, an additive manufacturing process (e.g., a 3D printing process). Forming retainer206using additive processes such as 3D printing processes can facilitate more complex shapes for cavity502. For example,FIG. 9shows a configuration of retainer206in which cavity502is an undulating cavity having a substantially constant thickness progressing circumferentially between edges404aand404b, but with a varying distance from inner and outer arcuate surfaces308aand308b.

In this way, a compressible retainer206can be provided with a desired spring constant and/or other resiliency features such as a location-dependent compressibility and/or a formation-specific compressibility. A location-dependent compressibility can include a compressibility at each location on surface308athat is tuned to a desired spring constant (e.g., a location-dependent spring constant) for that location (e.g., to control where vibrations are primarily absorbed and transferred within retainer206and/or to control the motion of rolling element204into cavity202due to the compression of retainer206). A formation-specific compressibility may be a compressibility (e.g., an overall compressibility or a location-dependent compressibility) that is tuned to the particular formation to be drilled or to a particular wellbore drilling environment.

In the example ofFIG. 9, cavity502is a single contiguous undulating closed cavity with regular undulations progressing in a direction between edges404aand404b. However, it should be appreciated that other arrangements of cavity502can be provided, including but not limited to undulations progressing between sidewalls406aand406b, irregular undulations, broken undulations (e.g., in a discontinuous set of cavities), or non-undulating cavities shaped to provide a desired overall and/or location-dependent compliancy for retainer206. As shown inFIG. 9, a shaped cavity such as an undulating cavity can be filled with elastomeric material504, if desired.

In the examples ofFIGS. 5-9, base structure500is a contiguous base structure with one or more internal cavities. However, as shown inFIG. 10, in some implementations, compliant retainer206can be formed from an inner rigid structure500′ and an outer rigid structure500″ with a compliant structure502′ disposed between inner rigid structure500′ and outer rigid structure500″. Inner rigid structure500′ and outer rigid structure500″ can be formed from the same material or different materials such as any of the materials described above in connection with base structure500. Compliant structure502′ may be formed from any of the elastomeric or resilient materials described above in connection with elastomeric material504.

In the example ofFIG. 10, the inner surface of inner rigid member500′ forms inner arcuate surface308aof retainer206and the outer surface of outer rigid member500″ forms the outer surface308bof retainer206. In this example, compliant member502′ extends from outer edge404ato inner edge404bof retainer206.

For illustrative purposes, the compliancy of retainer206is reflected in the side-view example ofFIG. 11in which center thickness WChas been reduced to a reduced center thickness WC. In the example ofFIG. 11, outer thickness WOand inner thickness W1are unchanged and inner surface308aof retainer206has deformed and moved toward outer surface308bresponsive to the force being applied by rolling element204. However, it should be appreciated that, depending on the direction and magnitude of the force applied by rolling element204, and the arrangement of compliancy features (e.g., cavities and/or elastomeric materials) within retainer206, any or all of thicknesses WO, WI, or WCmay be compressed by the force from rolling element204.

In some implementations, one or more depressions (not shown) may be defined in inner arcuate surface308aof retainer206to retain and otherwise receive a hardfacing material, which may prove advantageous in increasing the abrasion, erosion, and/or corrosion resistance of the inner arcuate surface308aof the retainer206.

One suitable hardfacing material comprises sintered tungsten carbide particles in a steel alloy matrix. The tungsten carbide particles may include grains of monotungsten carbide, ditungsten carbide and/or macrocrystalline tungsten carbide. Spherical cast tungsten carbide may typically be formed with no binding material. Examples of binding materials used to form tungsten carbide particles may include, but are not limited to, cobalt, nickel, boron, molybdenum, niobium, chromium, iron and alloys of these elements. Other hard constituent materials include cast or sintered carbides consisting of chromium, molybdenum, niobium, tantalum, titanium, vanadium and alloys and mixtures thereof.

In some implementations, one or more material recesses (not shown) may be defined or otherwise provided on outer arcuate surface308bof retainer206. The outer surface recesses may be used to retain a locking material (e.g., braze paste, solder, etc.) used to secure retainer206within cavity202(see, e.g.,FIGS. 2 and 3).

Although rolling element204described above in connection with, for example,FIGS. 2 and 3includes a constant diameter progressing axially thereacross, in some implementations, rolling element204may exhibit a variable diameter between the axial ends and along the axial width thereof. More specifically, the outer surface of the rolling element may be curved, rounded, or otherwise arcuate while maintaining a smooth contiguous profile across the axial width (e.g., free of circumferential or axial protrusions or grooves) such that the exposed portion of the rolling element is constant at least at first and second axial ends208aand208b. Compliant retainer206may have, in an uncompressed configuration, an arcuate, smooth, contiguous surface308athat conforms and is complementary to any of these cylindrical profiles for rolling element204.

Various examples of aspects of the disclosure are described below as clauses for convenience. These are provided as examples, and do not limit the subject technology.

Clause A. A drill bit, comprising: a bit body including one or more blades; a plurality of cutters secured to the one or more blades; a rolling element; and a retainer within a cavity in the bit body, the retainer receiving the rolling element to rotatably secure the rolling element about a rotational axis of the rolling element, wherein the retainer has an inner arcuate surface that abuts the rolling element, and wherein the retainer has a compliant portion that is compressible responsive to a force from the rolling element on the inner arcuate surface.

Clause B. A rolling element assembly, comprising: a rolling element rotatable about a rotational axis of the rolling element when the rolling element is positioned within a cavity in a bit body of a drill bit; and a compliant retainer extendable within the cavity to receive and rotatably secure the rolling element within the cavity, wherein the compliant retainer comprises an inner arcuate surface, and wherein the compliant retainer is compressible responsive to a force from the rolling element on the inner arcuate surface.

Clause C. A compliant retainer for a rolling element assembly that is configured to be positioned within a cavity in a bit body of a drill bit, the compliant retainer comprising: a rigid base structure formed from a rigid material and having an inner arcuate surface that is complementary to a rolling element of the rolling element assembly; and a cavity formed in the rigid base structure such that a portion of the rigid base structure can be pressed into the cavity, responsive to a force on the inner arcuate surface, to provide compliancy for the compliant retainer.

The claims are not intended to be limited to the aspects described herein, but are to be accorded the full scope consistent with the language of the claims and to encompass all legal equivalents. Notwithstanding, none of the claims are intended to embrace subject matter that fails to satisfy the requirements of the applicable patent law, nor should they be interpreted in such a way.