Bearings for downhole tools, downhole tools incorporating such bearings, and related methods

A bearing system configured for use on a downhole tool including a rolling cutter member having a plurality of cutting structures thereon comprises a first plurality of bearings disposed between a head washer and an at least substantially planar shaft washer, and a second plurality of bearings disposed between the at least substantially planar shaft washer and a rolling cutter washer. A downhole tool, such as an earth-boring rotary rolling cutter drill bit includes such a bearing system between a rolling cutter and a head of a bit body. Methods of forming such a downhole tool include the assembly of such a bearing system between a rolling cutter and a head of a bit body.

FIELD

Embodiments of the present disclosure relate generally to bearing systems for earth-boring tools employing at least two rows of thrust bearings in association with a rotatable component, earth-boring tools including such bearing systems, and to methods of making and using such bearing systems and earth-boring tools.

BACKGROUND

Roller cone drill bits for drilling earth formations conventionally have roller cones (which may also be characterized as rolling cutters), each cone mounted on a head or head on a distal end of a leg protruding from or secured to a bit. As the drill bit rotates to drill an earth formation under applied weight on bit (WOB), the roller cones are caused to rotate on their respective heads responsive to WOB and engagement with the formation. The outer surfaces of the cones include cutting structures, which are conventionally in the form of teeth formed integrally with the roller cones or inserts disposed in recesses formed in the outer surfaces of the roller cones. The cutting structures impact, gouge and crush the underlying earth formation material as the drill bit is rotated within the wellbore to form the borehole.

A bearing system is included between each cone and its associated head. The bearing system may include a thrust bearing and a radial bearing. The bearings of the bearing systems are located and configured to carry the load to which the roller cones are subjected while the bit is rotated under WOB, while allowing the roller cones to rotate on the heads. Specifically, the thrust bearing carries the axial component of the load applied parallel to the head, while the radial bearing carries the radial component of the load applied perpendicular to the head. The high loads present during drilling cause friction in the rotating components and generate heat, which may cause deterioration of the bearings. Bearing deterioration may cause bit failure, resulting in time-consuming and expensive removal and replacement of the bit from the borehole.

Bearing systems used in roller cone bits may be sealed bearings or open bearings. Sealed bearing systems conventionally include a lubricant reservoir for supplying lubricant, such as a bearing grease, to the bearing surfaces between the roller cones, the heads and the bearing elements. A pressure compensator may be used to equalize the lubricant pressure with the fluid pressure within the borehole to prevent pressurized borehole fluids from invading the lubricated volumes between the head, cone and bearings. Open bearing systems, by contrast, have no seals or bearing grease. Open bearing systems may use drilling fluid, such as a drilling mud, to both cool and lubricate the bearings.

Additionally, a small amount of clearance (on the order of a few thousandths of an inch) is conventionally provided between mating components of the cones and their corresponding heads due to manufacturing and assembly constraints. This clearance enables a small amount of movement or “play” between the cones and their corresponding heads in both the axial direction parallel to the longitudinal axis of the head and in the radial direction perpendicular to the longitudinal axis of the head. This play between the cones and heads may result in misalignment between the bearing system components during drilling, which may result in excessive wear of the misaligned bearing components.

Recently, new connection methods for connecting roller cones to corresponding heads of a bit body have been developed in which the cones are retained on their corresponding heads using tensioner bolts, such that the tensioner bolts apply forces urging the cones onto their heads to substantially eliminate play between the cones and the heads. Examples of such connection methods are disclosed in U.S. Pat. No. 8,950,515, issued Feb. 10, 2015 to Schroder, and in U.S. Pat. No. 8,955,622, issued Feb. 17, 2015 to Schroder, the disclosure of each of which is hereby incorporated herein in its entirety by this reference.

BRIEF SUMMARY

In accordance with some embodiments, the present disclosure includes a bearing system configured for use on a downhole tool including a rolling cutter member having a plurality of cutting structures. The bearing system includes a head washer, an at least substantially planar shaft washer, and a first plurality of bearings disposed between the head washer and the at least substantially planar shaft washer. The bearing system further includes a rolling cutter washer, and a second plurality of bearings disposed between the at least substantially planar shaft washer and the rolling cutter washer.

In additional embodiments, the present disclosure includes downhole tools including a tool body including at least one head, a rolling cutter mounted on the at least one head, and a bearing system disposed between the at least one head and the rolling cutter mounted on the at least one head. The bearing system includes a head washer, an at least substantially planar shaft washer, and a first plurality of bearings disposed between the head washer and the at least substantially planar shaft washer. The bearing system further includes a rolling cutter washer, and a second plurality of bearings disposed between the at least substantially planar shaft washer and the rolling cutter washer.

Further embodiments of the present disclosure include methods of forming an earth-boring tool configured for use in a subterranean formation. In accordance with such methods, a tensioner bolt may be inserted into a rolling cutter, a rolling cutter washer may be inserted into the rolling cutter, a plurality of bearings may be provided on the rolling cutter washer within the rolling cutter, and an at least substantially planar shaft washer may be inserted into the rolling cutter such that the bearings are disposed between the rolling cutter washer and the at least substantially planar shaft washer. A retaining member may be provided within the rolling cutter to retain the at least substantially planar shaft washer, the plurality of bearings, the rolling cutter washer, and the tensioner bolt within the rolling cutter. A head washer may be positioned over and around a head of a tool body of the earth-boring tool, and an additional plurality of bearings may be provided on the head washer. The rolling cutter may be positioned on the head such that the tensioner bolt extends through the head, and such that the additional plurality of bearings is disposed between the head washer and the at least substantially planar shaft washer retained within the rolling cutter. The tensioner bolt may be secured to the head to secure the roller cutter to the head, and the tensioner bolt may be tensioned to compress the additional plurality of bearings between the head washer and the at least substantially planar shaft washer, and to compress the plurality of bearings between the at least substantially planar shaft washer and the rolling cutter washer.

DETAILED DESCRIPTION

The illustrations presented herein are not meant to be actual views of any particular downhole tool, drill bit, bearing system, or other component, but are merely idealized representations that are employed to describe the disclosed embodiments. Thus, the drawings are not necessarily to scale and relative dimensions may have been exaggerated for the sake of clarity. Additionally, elements common between figures may retain the same or similar numerical designation.

The term “downhole tool,” as used herein, means includes any type of downhole tool employing a component rotatable with respect to another component with a bearing system as described herein therebetween, and includes, for example, earth-boring rotary drill bits including rolling cutters, Moineau-type “mud” motors, turbine motors, submersible pumps, coring bits, reamers, and other drilling bits and tools employing rotatable components, as known in the art.

FIG. 1illustrates an earth-boring tool configured for use in a subterranean formation in the form of an earth-boring rotary drill bit100. The drill bit100is a rolling cutter drill bit, and includes a tool body102having integral leg members104and rolling cutters106mounted on heads protruding from the distal ends of corresponding leg members104. As the drill bit100is rotated within a wellbore, the rolling cutters106rotate on the corresponding heads. As the rolling cutters106rotate, cutting structures108disposed on the rolling cutters106gouge, crush and scrape away formation material so as to drill the borehole in the subterranean formation. The cutting structures108illustrated inFIG. 1comprise inserts (e.g., cemented tungsten carbide and/or polycrystalline diamond inserts), although in other embodiments, the cutting structures108may comprise integral teeth formed on the rolling cutters106using machining processes. Hardfacing material may, optionally, be applied on the rolling cutters106.

In accordance with embodiments of the present disclosure, a bearing system as described herein with reference to any ofFIGS. 2 through 5is disposed between each of the rolling cutters106and the corresponding heads.

FIG. 2illustrates a bearing system110disposed between a rolling cutter106and a head105protruding from a leg104of the tool body102. The bearing system110is configured to bear forces acting between the head105and the rolling cutter106as the rolling cutter106rotates relative to the head105during use of the drill bit100within a subterranean formation. In further detail, the bearing system110includes a thrust bearing112and a radial bearing114. The thrust bearing112is located and configured for bearing forces acting between the rolling cutter106and the head105in directions generally parallel to the longitudinal axis ALof the head105(and the axis of rotation of the rolling cutter106), which is referred to herein as the “axial” direction. The radial bearing114is located and configured for bearing forces acting between the rolling cutter104and the head105in directions generally perpendicular to the longitudinal axis ALof the head105, which is referred to herein as the “radial” direction.

As shown inFIG. 2, the thrust bearing112includes a head washer120disposed on the head105, an at least substantially planar shaft washer122retained within the rolling cutter106and disposed around the head105, and a rolling cutter washer124retained within the rolling cutter106. The thrust bearing112further includes a first plurality of bearings126disposed between the head washer120and the shaft washer122, and a second plurality of bearings128disposed between the shaft washer122and the rolling cutter washer124.

The head washer120comprises an annular ring member that rests upon a shoulder103of the head105around an annular protrusion of the head105. The shaft washer122comprises an at least substantially planar annular ring member that also extends around the annular protrusion of the head105, but is not secured thereto. The upper and lower surfaces of the shaft washer122are at least substantially planar (i.e., flat). The rolling cutter washer124also comprises an annular ring member that extends around the annular protrusion of the head105.

In the embodiment ofFIG. 2, the first plurality of bearings126and the second plurality of bearings128comprise tapered rolling bearing elements, each bearing element126,128having the geometry of a truncated solid cone. The upper and lower surfaces of the shaft washer122may be at least substantially planar and oriented at least substantially perpendicular to the longitudinal axis ALof the head105, such that the upper surfaces of the first plurality of bearings126and the lower surfaces of the second plurality of bearings128are oriented at least substantially perpendicular to the longitudinal axis AL. The lower surfaces of the first plurality of bearings126and the upper surfaces of the second plurality of bearings128are oriented at an acute angle α to the longitudinal axis AL. As a non-limiting example, the acute angle α may be in a range extending from about 65° and about 85°, such as about 75°.

The upper surface of the head washer120may comprise an angled, frustoconically-shaped surface oriented at the angle α to the longitudinal axis ALso as to be complementary to the lower surfaces of the first plurality of bearings126. The head washer120may include an axially projecting lip that extends along at least a portion of a radially outer end surface of each of the first plurality of bearings126. The axially projecting lip and the angled, frustoconically-shaped surface of the head washer120prevent the first plurality of bearings126from sliding in the radial direction during operation of the drill bit100.

Similarly, the lower surface of the rolling cutter washer124may comprise an angled, frustoconically-shaped surface oriented at the angle α to the longitudinal axis ALso as to be complementary to the upper surfaces of the second plurality of bearings128. The rolling cutter washer124may include an axially projecting lip that extends along at least a portion of a radially outer end surface of each of the second plurality of bearings128. The axially projecting lip and the angled, frustoconically-shaped surface of the rolling cutter washer124prevent the second plurality of bearings128from sliding in the radial direction during operation of the drill bit100.

The configuration of the thrust bearing112may find particular utility in rolling cutters106having relatively small diameters of less than about 13.0 centimeters (about 5 inches). For example, in some non-limiting example embodiments, the head washer120, the shaft washer122, and the rolling cutter washer124may have maximum outer diameters of about 6.5 centimeters or less (about 2.5 inches or less).

The radial bearing114may have any suitable configuration. As a non-limiting example, the radial bearing114may be a journal bearing comprising an annular sleeve129that is coupled to the rolling cutter106within the central cavity107thereof. For example, the annular sleeve129may be secured to the rolling cutter106within the central cavity107using a shrink fit and/or a press fit. The annular sleeve129may comprise a relatively hard and wear-resistant metal, such as a steel alloy.

Optionally, at least a portion of the outer side surface of the head105that is located and configured to bear against the annular sleeve129may comprise a hardfacing material130that has a composition that is relatively harder and/or more wear-resistant relative to the bulk material of the head105, so as to extend the life of the radial bearing114. For example, as shown inFIG. 5, at least the radially outward, load-bearing side of the head105may be provided with such a hardfacing material130.

During operation, the interface between the annular sleeve129and the adjacent bearing surface of the head105may be lubricated with pressure compensated grease or oil. Optionally, one or more recesses may be formed in the radially inward, non-load-bearing side of the head105, as is shown inFIG. 2. Furthermore, a radial clearance of, for example, from about one micron (1.0 μm) to about three hundred microns (300 μm), and more particularly from about twenty-five microns (25.0 μm) to about one hundred fifty microns (150 μm), may be provided between the inner surface of the annular sleeve129and the adjacent outer surface of the head105so as to provide a film of lubricating fluid of corresponding dimensions therebetween during operation of the drill bit. It is desirable for purposes of assembly of the rolling cutter106onto the head105, as well as for proper operation of the radial bearing114, to allow for a relatively small amount of clearance and play in the radial direction between inner surface of the annular sleeve129and the adjacent outer surface of the head105.

One or more seals131may be employed to establish a fluid-tight seal between the rolling cutter106and the head105to prevent exposure of the bearing system110to fluids outside the drill bit100. As a non-limiting example, the drill bit100may include an energized metal-faced seal131as described in U.S. Pat. No. 7,413,037, issued Aug. 19, 2008, the entire contents of which are hereby incorporated herein in their entirety by this reference. As described therein, the energized metal-faced seal131may include a rigid seal ring132that engages a rearward end of the annular sleeve129of the radial bearing114, an elastomeric energizer ring134, which may be an O-ring or another cross-sectional shaped ring, and a secondary seal ring136. The seal131may be located between the base of the head105and an inner surface of the rolling cutter106proximate a rear surface138of the rolling cutter106.

The rolling cutter106may be retained on the head105using a retaining member140, a tensioner bolt142, and a nut150.

In particular, the retaining member140may secure an enlarged head144of the tensioner bolt142, the rolling cutter washer124, the second plurality of bearings128, and the shaft washer122within a central cavity107of the rolling cutter106. In some embodiments, the retaining member140may comprise a threaded annular ring member having a threaded outer side surface. Complementary threads may be formed on the inner side surface of the rolling cutter106within the central cavity107, such that the threaded annular ring member may be threaded to the rolling cutter106within the central cavity107. In this configuration, the enlarged head144of the tensioner bolt142, the rolling cutter washer124, the second plurality of bearings128, and the shaft washer122within the central cavity107of the rolling cutter106are secured between the blind end or bottom of the central cavity107(the upper end of the central cavity107from the perspective ofFIG. 2) and the retaining member140. In other embodiments, the retaining member140may be secured to the rolling cutter106within the central cavity107using a threadless connection. For example, the retaining member140may be secured to the rolling cutter106within the central cavity107using a shrink fit and/or a press fit.

As noted above, the head washer120may be positioned on a shoulder103of the head105. In some embodiments, the head washer120may be secured around an annular protrusion of the head105using a shrink fit and/or a press fit. In other embodiments, the head washer120may include threads on an inner side surface thereof, and complementary threads may be formed on an outer side surface of the annular protrusion of the head105, such that the head washer120may be threaded onto the annular protrusion of the head105until it bears against the shoulder103of the head105. After positioning the head washer120over and around the annular protrusion of the head105and on the shoulder103of the head105, the first plurality of bearings126may be positioned on the head washer120.

After inserting the tensioner bolt142, the rolling cutter washer124, the second plurality of bearings128, and the shaft washer122into the central cavity107and securing these components within the central cavity107of the rolling cutter106using the retaining member140, an elongated shaft146of the tensioner bolt142that extends from the enlarged head144may be inserted through a complementary hole of the head105, and the nut150may be threaded onto a threaded end148of the elongated shaft146. As the nut150is tightened on the threaded end148of the elongated shaft146of the tensioner bolt142, the elongated shaft146of the tensioner bolt142is placed in a state of tension, and the enlarged head144of the tensioner bolt142compresses the components of the thrust bearing112between the enlarged head144and the shoulder103of the head105.

The rolling cutter106may be secured to the head105generally, as described in the aforementioned U.S. Pat. Nos. 8,950,515 and 8,955,622. In addition, the thrust bearing112and/or the radial bearing114may be lubricated using grease or other lubricating fluid, and a pressure compensating system, as described in the aforementioned U.S. Pat. Nos. 8,950,515 and 8,955,622, may be used to ensure that the pressure of the grease or other lubricating fluid is maintained at substantial equal pressure to the fluid pressure outside the drill bit100.

A keyed interface may be provided between the enlarged head144of the tensioner bolt142and the rolling cutter washer124so as to prevent rotation of the rolling cutter washer124about the head105during operation of the drill bit100. The shaft washer124is fixed to the rolling cutter106by the retaining member140, such that the shaft washer124rotates with the rolling cutter106between the first plurality of bearings126and the second plurality of bearings128during operation of the drill bit100. Thus, during rotation of the rolling cutter106about the longitudinal axis ALof the head105, the head washer120and the rolling cutter washer124, and the tensioner bolt142are fixed in static position relative to the head105, while the shaft washer122and the retaining member140rotate with the rolling cutter106about the head105.

Due to the fact that the components of the thrust bearing112are compressed between the enlarged head144of the tensioner bolt142and the shoulder103of the head105, there may be little to no play between the rolling cutter106and the head105in the axial direction. As discussed above, however, a predetermined amount of clearance between the inner side surface of the annular sleeve129and the adjacent outer side surface of the head105in the radial bearing114may be required for assembly of the rolling cutter106with the head105, and/or for proper operation of the radial bearing114. As a non-limiting example, a clearance of from about one micron (1.0 μm) to about three hundred microns (300 μm), and more particularly from about twenty-five microns (25.0 μm) to about one hundred fifty microns (150 μm), may be provided between the inner side surface of the annular sleeve129and the adjacent outer side surface of the head105in the radial bearing114. In accordance with embodiments of the present disclosure, at least one component of the thrust bearing112may be capable of sliding radially relative to at least one other component of the thrust bearing112so as to accommodate the play in the radial bearing114in the radial direction, even though the thrust bearing112is in a state of compression with little to no play between the rolling cutter106and the head105in the axial direction.

For example, in the embodiment ofFIG. 2, the at least substantially planar shaft washer122may be capable of sliding radially relative to the first plurality of bearings126and the second plurality of bearings128so as to accommodate the play in the radial bearing114in the radial direction. A clearance gap may be provided between the inner side surface of the shaft washer122and the adjacent outer side surface of the head105that is equal to or greater than the predetermined amount of clearance between the inner side surface of the annular sleeve129and the adjacent outer side surface of the head105in the radial bearing114. As a non-limiting example, if the predetermined amount of clearance between the inner side surface of the annular sleeve129and the adjacent outer side surface of the head105in the radial bearing114is one hundred microns (100 μm), the clearance gap between the inner side surface of the shaft washer122and the adjacent outer side surface of the head105may be one hundred microns (100 μm) or more, one hundred fifty microns (150 μm) or more, or even two hundred fifty microns (250 μm) or more.

Furthermore, during operation of the drill bit100, when the net force acting on the rolling cutter106is oriented so as to urge the rolling cutter106in the axial direction onto the head105, such as during a normal drilling operation, the first plurality of bearings126may bear a higher compressive load than the second plurality of bearings128. When the net force acting on the rolling cutter106is oriented so as to urge the rolling cutter106in the axial direction off the head105, as may be encountered during a forward reaming operation or a backward reaming operation in which a previously drilled borehole is being enlarged by the drill bit100, the second plurality of bearings128may bear a higher compressive load than the first plurality of bearings128.

FIG. 3is a cross-sectional view of a portion of a drill bit160similar to that ofFIG. 2and having a rolling cutter106mounted on a corresponding head105of a leg104of bit body102(FIG. 1) of the drill bit160. The only difference between the drill bit160ofFIG. 3and the drill bit100ofFIGS. 1 and 2is the configuration of the thrust bearing of the bearing system110. In particular, the drill bit160includes a thrust bearing162having a head washer164, a shaft washer166, and a rolling cutter washer168. A first plurality of tapered roller bearings126, as described with reference toFIG. 2, may be disposed between the head washer164and the shaft washer166, and a second plurality of tapered roller bearings126, as previously described with reference toFIG. 2, may be disposed between the shaft washer166and the rolling cutter washer168.

In the embodiment ofFIG. 3, however, the head washer164has an at least substantially planar upper surface oriented perpendicular to the longitudinal axis AL, and the lower side surface of each of the first plurality of bearings126that rests upon the upper surface of the head washer164is oriented perpendicular to the longitudinal axis AL. Similarly, the rolling cutter washer168has an at least substantially planar lower surface oriented perpendicular to the longitudinal axis AL, and the upper side surface of each of the second plurality of bearings128that bears against the lower surface of the rolling cutter washer168is oriented perpendicular to the longitudinal axis AL.

In addition, in the embodiment ofFIG. 3, the shaft washer166is not substantially planar. The lower surface of the shaft washer166may comprise an angled, frustoconically-shaped surface oriented at the angle α to the longitudinal axis ALso as to be complementary to upper surfaces of the first plurality of bearings126. In addition, the lower surface of the shaft washer166has a downward axially projecting lip that extends along at least a portion of a radially outer end surface of each of the first plurality of bearings126. The downward axially projecting lip and the angled, frustoconically-shaped lower surface of the shaft washer166prevent the first plurality of bearings126from sliding in the radial direction relative to the shaft washer166during operation of the drill bit100. The upper surface of the shaft washer166may comprise an angled, frustoconically-shaped upper surface oriented at the angle α to the longitudinal axis ALso as to be complementary to lower surfaces of the second plurality of bearings128. In addition, the upper surface of the shaft washer166has an upward axially projecting lip that extends along at least a portion of a radially outer end surface of each of the second plurality of bearings128. The upward axially projecting lip and the angled, frustoconically-shaped upper surface of the shaft washer166prevent the second plurality of bearings128from sliding in the radial direction relative to the shaft washer166during operation of the drill bit160.

In this configuration, the non-planar shaft washer122, together with the first plurality of tapered roller bearings126and the second plurality of tapered roller bearings128, may be capable of sliding radially relative to the head washer164and the rolling cutter washer168so as to accommodate the play in the radial bearing114in the radial direction. A clearance gap may be provided between the inner side surface of the shaft washer166and the adjacent outer side surface of the head105that is equal to or greater than the predetermined amount of clearance between the inner side surface of the annular sleeve129and the adjacent outer side surface of the head105in the radial bearing114, as described above with reference toFIG. 2. The head washer164and the rolling cutter washer168may be fixed in position relative to the head105as previously described with reference toFIG. 2.

In additional embodiments, the head washer164may be integrally formed with, and comprise an integral portion of the head105. Similarly, in additional embodiments, the rolling cutter washer168may be integrally formed with, and comprise an integral portion of the tensioner bolt142.

FIG. 4is a cross-sectional view of a portion of a drill bit180similar to that ofFIGS. 2 and 3, and having a rolling cutter106mounted on a corresponding head105of a leg104of bit body102of the drill bit180. The difference between the drill bit180ofFIG. 4and the drill bits100ofFIGS. 1 and 2and the drill bit160ofFIG. 3is the configuration of the thrust bearing182of the bearing system110. In particular, the drill bit180includes a thrust bearing182having a head washer164as previously described with reference toFIG. 3, a shaft washer122as previously described with reference toFIG. 2, and a rolling cutter washer168as previously described with reference toFIG. 3. The thrust bearing182further includes a first plurality of cylindrical roller bearings184disposed between the head washer164and the shaft washer122, and a second plurality of cylindrical roller bearings186disposed between the shaft washer122and the rolling cutter washer168.

In the embodiment ofFIG. 4, the head washer164has an at least substantially planar upper surface and each of the first plurality of cylindrical roller bearings184have substantially planar lower surfaces that are oriented perpendicular to the longitudinal axis AL. Similarly, the rolling cutter washer168has an at least substantially planar lower surface and each of the second plurality of cylindrical roller bearings186have substantially planar upper surfaces that are oriented perpendicular to the longitudinal axis AL. Similarly, the shaft washer122has at least substantially planar upper and lower surfaces oriented perpendicular to the longitudinal axis AL, and the upper side surface of each of the first plurality of cylindrical roller bearings184and the lower side surface of each of the second plurality of cylindrical roller bearings186are oriented perpendicular to the longitudinal axis AL.

In this configuration, the planar shaft washer122, the first plurality of cylindrical roller bearings184, and the second plurality of cylindrical roller bearings184may be capable of sliding radially relative to head washer164and the rolling cutter washer168so as to accommodate the play in the radial bearing114in the radial direction. A clearance gap may be provided between the inner side surface of the shaft washer122and the adjacent outer side surface of the head105that is equal to or greater than the predetermined amount of clearance between the inner side surface of the annular sleeve129and the adjacent outer side surface of the head105in the radial bearing114, as described above with reference toFIG. 2. The head washer164and the rolling cutter washer168may be fixed in position relative to the head105as previously described with reference toFIG. 2. In addition, a clearance gap may be provided between the inner side surface of each of the first plurality of cylindrical roller bearings184and each of the second plurality of cylindrical roller bearings186, and the adjacent outer side surface of the head105that is equal to or greater than the predetermined amount of clearance between the inner side surface of the annular sleeve129and the adjacent outer side surface of the head105in the radial bearing114.

In additional embodiments, the head washer164may be integrally formed with, and comprise an integral portion of the head105. Similarly, in additional embodiments, the rolling cutter washer168may be integrally formed with, and comprise an integral portion of the tensioner bolt142.

FIG. 5is a cross-sectional view of a portion of a drill bit190similar to that ofFIGS. 2 and 3, and having a rolling cutter106mounted on a corresponding head105of a bit body102of the drill bit190. The difference between the drill bit190ofFIG. 5and the drill bits100,160,180previously described herein is the configuration of the thrust bearing192of the bearing system110. In particular, the drill bit190includes a thrust bearing192having a head washer164as previously described with reference toFIG. 3, a shaft washer122as previously described with reference toFIG. 2, and a rolling cutter washer168as previously described with reference toFIG. 3. The thrust bearing182further includes a first plurality of polycrystalline diamond compact (PDC) bearings194disposed between the head washer164and the shaft washer122, and a second plurality of PDC bearings200disposed between the shaft washer122and the rolling cutter washer168.

In the embodiment ofFIG. 5, the head washer164has an at least substantially planar upper surface, and the shaft washer122has an at least substantially planar lower surface. The first plurality of PDC bearings194includes a first set of non-rolling PDC bearing elements196each including a volume of polycrystalline diamond material, and an opposing second set of non-rolling PDC bearing elements198each including a volume of polycrystalline diamond material. The polycrystalline diamond material of the second set of PDC bearing elements198is located and configured to abut against and slide relative to the polycrystalline diamond material of the first set of PDC bearing elements196during operation of the bearing system110. The first set of PDC bearing elements196may be statically fixed to the head washer120and the head105, and the second set of PDC bearing elements198may be fixed to the shaft washer122and the rolling cutter106, such that the second set of PDC bearing elements198slide against and past the first set of PDC bearing elements196along the interface therebetween during rotation of the rolling cutter106relative to the head105. The interface between the first set of PDC bearings196and the second set of PDC bearings198is generally planar and oriented perpendicular to the longitudinal axis AL.

Similarly, the rolling cutter washer168has an at least substantially planar lower surface, and the shaft washer122has an at least substantially planar upper surface. The second plurality of PDC bearings200includes a first set of non-rolling PDC bearing elements202each including a volume of polycrystalline diamond material, and an opposing second set of non-rolling PDC bearing elements204each including a volume of polycrystalline diamond material. The polycrystalline diamond material of the second set of PDC bearing elements204is located and configured to abut against and slide relative to the polycrystalline diamond material of the first set of PDC bearing elements202during operation of the bearing system110. The first set of PDC bearing elements202may be statically fixed to the rolling cutter washer168and the head105, and the second set of PDC bearing elements204may be fixed to the shaft washer122and the rolling cutter106, such that the second set of PDC bearing elements204slide against and past the first set of PDC bearing elements202along the interface therebetween during rotation of the rolling cutter106relative to the head105. The interface between the first set of PDC bearing elements202and the second set of PDC bearing elements204is generally planar and oriented perpendicular to the longitudinal axis AL.

In this configuration, the planar shaft washer122, the second set of PDC bearing elements198of the first plurality of PDC bearings194, and the second set of PDC bearing elements204of the second plurality of PDC bearings200are capable of sliding radially relative to head washer164, the first set of PDC bearing elements196of the first plurality of PDC bearings194, the rolling cutter washer168, and the first set of PDC bearing elements202of the second plurality of PDC bearings200so as to accommodate the play in the radial bearing114in the radial direction. A clearance gap may be provided between the inner side surface of the shaft washer122and the adjacent outer side surface of the head105that is equal to or greater than the predetermined amount of clearance between the inner side surface of the annular sleeve129and the adjacent outer side surface of the head105in the radial bearing114, as described above with reference toFIG. 2. The head washer164and the rolling cutter washer168may be fixed in position relative to the head105as previously described with reference toFIG. 2. In addition, a clearance gap may be provided between the inner side surface of each of the second plurality of PDC bearings200and each of the second plurality of PDC bearings186, and the adjacent outer side surface of the head105that is equal to or greater than the predetermined amount of clearance between the inner side surface of the annular sleeve129and the adjacent outer side surface of the head105in the radial bearing114.

As previously mentioned, the bearing systems described herein may be employed in other types of downhole tools. As another non-limiting example of such a downhole tool,FIG. 6illustrates an earth-boring rotary hybrid drill bit210that includes rolling cutters106having cutting structures108thereon, as previously described with reference toFIGS. 1 and 2, as well as fixed cutting elements211mounted on stationary blades212. The blades212may be integral parts of a bit body214of the hybrid drill bit210. In addition, the heads105to which the rolling cutters106are respectively mounted also may be may be integral parts of the bit body214of the hybrid drill bit210. A bearing system110as previously described herein with reference to any ofFIGS. 2 through 5may be provided between each of the rolling cutters106and the corresponding head105to which it is respectively mounted.

Additional non-limiting example embodiments of the present disclosure are set forth below.

Embodiment 1: A bearing system configured for use on a downhole tool including a rolling cutter member, the rolling cutter member including a plurality of cutting structures, comprising: a head washer; an at least substantially planar shaft washer; a first plurality of bearings disposed between the head washer and the at least substantially planar shaft washer; a rolling cutter washer; and a second plurality of bearings disposed between the at least substantially planar shaft washer and the rolling cutter washer.

Embodiment 2: The bearing system of Embodiment 1, wherein at least one of the first plurality of bearings and the second plurality of bearings comprises rolling bearing elements.

Embodiment 3: The bearing system of Embodiment 2, wherein the rolling bearing elements comprise tapered rolling bearing elements.

Embodiment 4: The bearing system of Embodiment 2, wherein the rolling bearing elements comprise cylindrical rolling bearing elements.

Embodiment 5: The bearing system of Embodiment 1, wherein at least one of the first plurality of bearings and the second plurality of bearings comprises opposing sets of non-rolling bearing elements each including a volume of polycrystalline diamond material, the polycrystalline diamond material of a first set of the opposing sets configured to abut against and slide relative to the polycrystalline diamond material of a set of the opposing sets during operation of the bearing system.

Embodiment 6: The bearing system of any one of Embodiments 1 through 5, wherein the substantially planar shaft washer has an outer diameter of 6.5 centimeters or less.

Embodiment 7: An earth-boring tool configured for use in a subterranean formation, comprising: a tool body including at least one head; and a rolling cutter mounted on the at least one head; and a bearing system disposed between the at least one head and the rolling cutter mounted on the at least one head, the bearing system including: a head washer disposed on the at least one head; an at least substantially planar shaft washer retained within the rolling cutter and disposed around the at least one head; a first plurality of bearings disposed between the head washer and the at least substantially planar shaft washer; a rolling cutter washer retained within the rolling cutter; and a second plurality of bearings disposed between the at least substantially planar shaft washer and the rolling cutter washer.

Embodiment 8: The earth-boring tool of Embodiment 1, wherein the bearing system comprises a thrust bearing system, and wherein at least one component of the thrust bearing system is capable of sliding in a radial direction relative to at least one other component of the thrust bearing system so as to provide a selected degree of radial play between the rolling cutter and the at least one head.

Embodiment 9: The earth-boring tool of Embodiment 7 or Embodiment 8, wherein the earth-boring tool comprises a rolling cutter earth-boring rotary drill bit.

Embodiment 10: The earth-boring tool of Embodiment 7 or Embodiment 8, wherein the earth-boring tool comprises an earth-boring rotary hybrid drill bit.

Embodiment 11: The earth-boring tool of Embodiment 7 or Embodiment 8, wherein the earth-boring tool comprises a reamer configured to enlarge a diameter of a previously drilled wellbore.

Embodiment 12: The earth-boring tool of any one of Embodiments 7 through 11, wherein the at least substantially planar shaft washer is configured to slide in the radial direction relative to the first plurality of bearings and the second plurality of bearings.

Embodiment 13: The earth-boring tool of any one of Embodiments 7 through 12, wherein at least one of the first plurality of bearings and the second plurality of bearings comprises rolling bearing elements.

Embodiment 14: The earth-boring tool of Embodiment 13, wherein the rolling bearing elements comprise tapered rolling bearing elements.

Embodiment 15: The earth-boring tool of Embodiment 13, wherein the rolling bearing elements comprise cylindrical rolling bearing elements.

Embodiment 16: The earth-boring tool of any one of Embodiments 7 through 12, wherein at least one of the first plurality of bearings and the second plurality of bearings comprises opposing sets of non-rolling bearing elements each including a volume of polycrystalline diamond material, the polycrystalline diamond material of a first set of the opposing sets configured to abut against and slide relative to the polycrystalline diamond material of a set of the opposing sets during operation of the bearing system.

Embodiment 17: The earth-boring tool of any one of Embodiments 7 through 16, wherein the head washer is integrally formed with, and comprises an integral portion of the head.

Embodiment 18: A method of forming an earth-boring tool configured for use in a subterranean formation, comprising: inserting a tensioner bolt into a rolling cutter; inserting a rolling cutter washer into the rolling cutter; providing a plurality of bearings on the rolling cutter washer within the rolling cutter; inserting a substantially planar shaft washer into the rolling cutter such that bearings of the plurality of bearings are disposed between the rolling cutter washer and the at least substantially planar shaft washer; providing a retaining member within the rolling cutter to retain the at least substantially planar shaft washer, the plurality of bearings, the rolling cutter washer, and the tensioner bolt within the rolling cutter; positioning a head washer over and around a head of a tool body of the earth-boring tool; providing an additional plurality of bearings on the head washer; and positioning the rolling cutter on the head such that the tensioner bolt extends through the head, and such that the plurality of bearings is disposed between the head washer and the at least substantially planar shaft washer retained within the rolling cutter; and securing the tensioner bolt to the head to secure the rolling cutter to the head and tensioning the tensioner bolt to compress the additional plurality of bearings between the head washer and the at least substantially planar shaft washer, and to compress the plurality of bearings between the at least substantially planar shaft washer and the rolling cutter washer.

Embodiment 19: The method of Embodiment 18, further comprising selecting at least one of the plurality of bearings and the additional plurality of bearings to comprise rolling bearing elements.

Embodiment 20: The method of Embodiment 18, further comprising selecting the rolling bearing elements to comprise tapered rolling bearing elements.

Embodiment 21: The method of Embodiment 18, further comprising selecting the rolling bearing elements to comprise cylindrical rolling bearing elements.

While the present disclosure has been described herein with respect to certain embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Rather, many additions, deletions, and modifications to the embodiments described herein may be made without departing from the scope of the invention as hereinafter claimed, including legal equivalents. In addition, features from one embodiment may be combined with features of another embodiment while still being encompassed within the scope of the invention as contemplated by the inventor.