THRUST BEARINGS AND METHOD FOR COOLING THRUST

BEARINGS

BACKGROUND

Field of the Disclosure

[0001] Embodiments disclosed herein generally relate to turbodrills used in downhole drilling applications. Particularly, embodiments disclosed herein relate to apparatus and methods to provide more efficient cooling of thrust bearings in the turbodrill.

Background Art

[0002] Drilling motors are commonly used to provide rotational force to a drill bit when drilling earth formations. Drilling motors used for this purpose are typically driven by drilling fluids pumped from surface equipment through the drill string. This type of motor is commonly referred to as a mud motor. In use, the drilling fluid is forced through the mud motor, which extracts energy from the flow to provide rotational force to a drill bit located below the mud motor. There are two primary types of mud motors: positive displacement motors ("PDM") and turbodrills. The following disclosure focuses primarily on turbodrills; however, one of ordinary skill in the art will appreciate that thrust bearings disclosed herein may be similarly used in PDMs.

[0003] FIG. 1 shows a prior art turbodrill. A housing 45 includes an upper connection 40 to connect to the drill string. Turbodrill stages 80 are disposed within the housing 45 to rotate a shaft 50. At a lower end of the turbodrill, a drill bit 90 is attached to the shaft 50 by a lower connection (not shown). Radial bearings 70 are provided between the shaft 50 and the housing 45. Stabilizers 60 and 61 are disposed on the housing 45 to help keep the turbodrill centered within the wellbore.

[0004] While providing rotational force to the shaft 50, the turbodrill stages 80 also produce a downward axial force (thrust) from the drilling fluid. Upward axial force results from the reaction force of the drill bit 90. To transfer axial loads from the shaft 50 to the housing 45, thrust bearings 10 are provided.

[0005] In FIGS. 2A and 2B, a prior art thrust bearing 10 disclosed in U.S. Patent No.

4,468,138 is shown. The '138 Patent is incorporated herein by reference in its entirety. Cylindrical bearing pads 13 are disposed in recesses 14 formed on rings 11,

12. The bearing pads 13 are made of hardmetal studs with planar end faces made of a super hard material, such as polycrystalline diamond. A bearing pad made of this construction is known in the industry as a polycrystalline diamond compact ("PDC"). Other super hard materials may also be used. The rings 11, 12 fit in the annular space between the rotor and the housing (not shown). The ring 12 is attached to the housing and the ring 11 is attached to the rotor. During operation of the turbodrill, the rings 11, 12 rotate relative to each other and transfer axial forces between faces 17 of the bearing pads 13. The manner in which thrust bearings may be installed within the turbodrill are generally known within the art and not discussed in detail herein. U.S. Patent No. 6,629,571 discloses a turbodrill having a plurality of thrust bearings disposed therein. The '571 Patent is incorporated herein by reference in its entirety.

[0006] Thrust bearings are designed to allow the rotor and the housing to rotate freely with respect to each other while bearing high axial loads. Friction between contact areas of the thrust bearings during rotation can generate high levels of heat. Much of the heat is dissipated by drilling fluid within the turbodrill itself. However, high temperatures may still be experienced at the contact areas. These high temperatures can damage the super hard materials of the thrust bearings, thereby reducing the life of the thrust bearings.

[0007] In some turbodrills, only a small portion of the total amount of drilling fluid may pass through the thrust bearings, while most of the drilling fluid simply flows by. To avoid problems with overheating, the bearing pads are spaced apart to allow drilling fluid to pass between the bearing pads. However, this configuration may still dissipate heat insufficiently. Additionally, larger gaps between the bearing pads means there is less contact area in each thrust bearing, thereby requiring more thrust bearings in the turbodrill for a given axial load. To increase the flow of drilling fluid through the thrust bearings, flow restrictions may be introduced to reduce the amount of drilling fluid that completely bypasses the thrust bearings. Alternatively, the drilling fluid may be routed through the thrust bearings by cutting off alternative flow paths with seals. US Patent No. 7,255,480, incorporated by reference herein, discloses fluid flows through bearings to aid in cooling. The outer housings surrounding and supporting the bearings may be used to force fluid through the bearings. However, both the flow restrictions and forced routing result in greater pressure drops through the turbodrill. Because there may typically be on the order of

14 to 18 thrust bearings within a single turbodrill, the overall energy losses can be significant.

[0008] Accordingly, a thrust bearing with improved bearing heat dissipation and reduced energy losses maybe beneficial.

SUMMARY OF THE DISCLOSURE

[0009] In one aspect, embodiments of the present disclosure relate to a thrust bearing for a turbodrill, the thrust bearing including a first ring attached to a rotatable shaft of the turbodrill, a first plurality of bearing pads disposed on the first ring, a second ring attached to a housing of the turbodrill, and a second plurality of bearing pads disposed on the second ring and opposing the first plurality of bearing pads on the first ring. Further, the first plurality of bearing pads are in load-bearing engagement with the second plurality of bearing pads, and an orientation of the first plurality of bearing pads diverts fluid radially through the thrust bearing.

[0010] In another aspect, embodiments of the present disclosure relate to a turbodrill including a housing configured to connect to a drill string at an upper end, a rotatable shaft configured to connect to a drill bit at a lower end, and a thrust bearing including a first ring attached to the shaft of the turbodrill, a first plurality of bearing pads disposed on the first ring, a second ring attached to the housing of the turbodrill, and a second plurality of bearing pads disposed on the second ring and opposing the first ring. Further, the first plurality of bearing pads are in a load-bearing engagement with the second plurality of bearing pads, and an orientation of the first and second plurality of bearing pads diverts fluid radially through the thrust bearing.

[0011] Other aspects and advantages of the disclosure will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS [0012] FIG. 1 shows a prior art turbodrill.

[0013] FIGS . 2A and 2B show a prior art thrust bearing.

[0014] FIGS. 3 A through 3 E show thrust bearings in accordance with embodiments of the present disclosure.

[0015] FIG. 4A shows a bearing pad for a thrust bearing in accordance with embodiments of the present disclosure.

[0016] FIG. 4B shows a layout view for manufacturing the bearing pads of FIG. 4A in accordance with embodiments of the present disclosure.

[0017] FIG. 4C shows thrust bearings including the bearing pads of FIG. 4A in accordance with embodiments of the present disclosure.

[0018] FIGS. 4D and 4E show bearing pads of a thrust bearing in accordance with embodiments of the present disclosure.

[0019] FIG. 5A shows a bearing pad for a thrust bearing in accordance with embodiments of the present disclosure.

[0020] FIG. 5B shows a layout view for manufacturing the bearing pads of FIG. 5 A in accordance with embodiments of the present disclosure.

[0021] Fig. 5C shows a thrust bearing including the bearing pads of FIG. 5A in accordance with embodiments of the present disclosure.

[0022] FIG. 6 shows a thrust bearing ring without bearing pads in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

[0023] The present disclosure relates generally to methods for cooling thrust bearings for a turbodrill, and, more particularly, to thrust bearings having bearing pads arranged to divert drilling fluid through the thrust bearings using the rotation of the rotor/shaft relative to the housing. The end faces of the bearing pads comprise a super-hard material from a group including polycrystalline diamond, cubic boron nitride ("CBN"), and silicon carbide-diamond composite.

[0024] Embodiments of the present disclosure may be configured to induce fluid flow radially through the thrust bearings by shaping and arranging the bearing pads to divert the fluid. The bearing pads include surfaces which are generally angled with respect to the direction of rotational movement. Rotation of the thrust bearing, and the orientation of the bearings pads on the thrust bearing, will cause the angled surfaces to "cut" into the fluid stream and divert the drilling fluid in a radial direction

between the bearing pads. In this manner, a portion of the drilling fluid may be induced to flow radially between the load-bearing bearing pads of the thrust bearings, thereby improving cooling of the bearing pads through convection. The rotation of a rotor relative to a stator provides the mechanical energy for the thrust bearing to divert the drilling fluid between the bearing pads.

[0025] FIGS. 3A through 3D show embodiments of thrust bearings including bearing pads oriented to divert drilling fluid to cool the bearing. Referring to FIG. 3A, a simplified drawing of a partial cross-section of a turbodrill is shown. It is understood that a turbodrill may contain a plurality of thrust bearings, for example, in some embodiments, 12 to 18 thrust bearings may be included. The quantity generally depends on the size of the turbodrill and the application for which the turbodrill is intended. The thrust bearing includes a ring 130 attached to a shaft 140, and a ring 150 attached to a turbodrill housing 160. Methods for attaching the ring 130 to the shaft 140 are known to those skilled in the art, and as such, are not shown in detail herein. Because the ring 130 is attached to the shaft 140, it rotates with the same speed as that of the shaft 140.

[0026] Multiple thrust bearing stages may be arranged in series in the turbodrill.

Typically, a majority of the thrust bearing stages are configured to withstand a downward thrust from the fluid as it travels down through the turbodrill. In this context, a "downward" thrust means that the thrust is towards the general direction of the bit, even though the turbodrill may be pointed horizontally, for example, as opposed to vertically. A generally lesser number of the bottom most thrust bearings in the stack are configured to withstand an upward thrust from force applied to the drill bit. One of ordinary skill in the art will understand that there may be an appropriate number of thrust bearings to withstand the different loads.

[0027] As such, the thrust bearings configured to withstand the downward thrust may be arranged as shown in FIG. 3A, in which fluid flows radially inward through the bearing pads. Arrows "A" show the normal path of drilling fluid flow, while arrows "B" show the path of drilling fluid that is actively diverted by the bearing pads 110 of the thrust bearings. As shown, fluid is diverted radially inward through the thrust bearings. The direction of shaft rotation "C" of shaft 140 is also shown. In contrast, the thrust bearings configured to withstand the upward thrust may be installed in a manner opposite, and are shown in FIG. 3B. Arrows "A" show the normal path of

drilling fluid flow, while arrows "B" show the path of drilling fluid diverted by the bearing pads 110 of the thrust bearings. As shown, fluid is diverted radially outward through the thrust bearings.

[0028] The bearing pads 110 are disposed in a radial pattern upon ring 130, and as shown in FIG. 3C, may include semicircular bearing pads 170. For simplicity, in FIG. 3 C, only one ring 130 of the thrust bearing is shown. The mating ring 150 (of FIG. 3A) is attached to the housing 160.

[0029] FIG. 3D illustrates a front view of the ring 130 of FIG. 3C. The semicircular bearing pads 170 may include a substantially planar leading face 171 and a cylindrical trailing face 172. In certain embodiments, the leading face 171 may be non-planar as an alternative, for example, radiused, irregular, or other non-planar profiles. As attached to ring 130, a semicircular bearing pad 170 is disposed such that the leading face 171 is oriented at an angle θ with respect to a radial plane 173 extending from an axis 174 of the ring 130. The angle θ is positive whether the leading face 171 is slanted clockwise or counter-clockwise with respect to the radial plane 173 extending from the axis 174 of the thrust bearing. Each of the semicircular bearing pads 170 may be oriented at substantially the same angle θ and spaced azimuthally around the ring 130. When rotating, the leading faces 171 actively divert drilling fluid radially between the semicircular bearing pads 170 to provide cooling. The mating ring 150 (of FIG. 3A) may have a similar arrangement of bearing pads, such that when facing the ring 130 on the shaft, the bearing pads are oriented in opposite directions (i.e. one clockwise, the other counter-clockwise).

[0030] The semicircular bearing pads 170 of FIG. 3D may be cut from a cylindrical

PDC cutter insert normally used for drill bits by making a cut across the center of the cylindrical PDC cutter. In this manner, two semicircular bearing pads 170 may be manufactured from one cylindrical PDC cutter insert with a single cut, which may be done using wire electrical discharge machining (wire EDM). Alternatively, the semicircular bearing pad 170 may be initially pressed into the semicircular shape. The semicircular bearing pads 170 may be rounded or chamfered at the edges of the leading face 171 to prevent chipping during use and to introduce fluid flow between the semicircular bearing pads 170. The semicircular bearing pads 170 may be attached to the ring 130 by brazing or other methods of high-strength attachment.

[0031] As compared to conventional cylindrical bearing pads, the semicircular shape of the semicircular bearing pads 170 may provide an advantage in that the semicircular shape provides a leading face 171 that can be oriented at an angle θ to act as a fluid diverter. The semicircular shape allows for a range of angles θ, from about 5 degrees to about 45 degrees. In one embodiment, angle θ may be between about 10 and about 30 degrees. In another embodiment, angle θ may be about 15 degrees. Alternatively, one of ordinary skill in the art will understand that the bearing pads may be rotated to an angle greater than 45 degrees by changing the number of bearing pads.

[0032] Referring to FIG. 3E, the bearing pads may be formed as a "truncated" cylinder bearing pad 180. As opposed to the semicircular bearing pads 170 shown in Figure 3C, the truncated bearing pads 180 may have less than a half of their original circumference removed, leaving a substantially planar leading face surface 181. Given the same distance between bearing pads as the design of FIG. 3D, the design of FIG. 3 E offers greater bearing surface area. However, only one truncated cylinder bearing pad 180 may be cut from one cylindrical PDC insert. As in the embodiment of 3D, leading face 181 is oriented at an angle θ with respect to a radial plane 183 extending from an axis 184 of the ring 130, causing fluid to be diverted radially when the ring 130 is rotated. In this embodiment, angle θ may range from about 5 degrees to about 35 degrees.

[0033] Turning to FIG. 4A, an embodiment is shown in which a bearing pad 110 (of

FIG. 3A) is formed as a block bearing pad 410. A block bearing pad 410, as shown in the embodiment of FIG. 4A, includes four primary faces, which may have rounded edges therebetween. The leading face 411 may include a beveled edge 416 to reduce the risk of chipping. The other three primary faces are the back face 412, the outer face 413, and the inner face 414. The back face 412 is planar, while the outer face 413 and inner face 414 may be planar, as shown, or may be formed on radii that approximately match the radii of the outer and inner diameters, respectively, of the ring upon which block bearing pads 410 are disposed.

[0034] A pair of block bearing pads 410 may be formed from a single large cylindrical PDC insert 420, as shown in FIG. 4B. In such an embodiment, the block

bearing pad 410 may include a radiused face 415 having a radius approximating the radius of the cylindrical PDC insert, which is represented by circle 420.

[0035] Referring to FIG. 4C, planar leading face 411 of block bearing pad 410 may be oriented at an angle θ when disposed on ring 430. As with the previous embodiments, the angled leading faces 411 may divert fluid into gap 431 between adjacent block bearing pads 410 when the ring is rotated, thereby cooling the bearing. The radiused face 415 may facilitate the entrance of fluid into the gap 431 between adjacent bearing pads 410. The block bearing pad is designed such that when assembled into ring 430, the gap 431, between adjacent bearing pads 410, is substantially constant. In other words, when assembled onto ring 430, the leading face 411 of one bearing pad 410 will be substantially parallel to the back face 412 of an adjacent bearing pad 410. As defined herein, "substantially parallel" means that the leading face 411 of bearing pad 410 and the back face 412 of adjacent bearing pad 410 may have an angle between them of zero to 10 degrees without departing from the scope of the present disclosure. By maintaining a substantially constant gap 431, the amount of bearing surface area may be maximized. Thus, ring 430 including block bearing pads 410 offers greater bearing surface area than the rings of FIGS. 3 C and 3D, and thereby may provide increased load bearing capacity. The angle θ of the leading face 411 with respect to the plane extending from the axis of the thrust bearing ring may be between 4 degrees and 91 degrees. In the embodiment shown in FIG 4C, the angle θ is approximately 20 degrees.

[0036] FIG. 4D shows an embodiment of a bearing ring 430 including block bearing pads 410 in which angle θ of the leading face 411 is approximately 90 degrees. In this embodiment, the leading face 411 and inner face 414 may be collinear, as shown. The extent to which fluid may be diverted is primarily a function of the value of angle θ. An angle θ of about 5 degrees may be considered the minimum value below which the fluid diversion of the bearing is negligible, while an angle θ of about 90 degrees, as defined herein, may be a practical limit as dictated by the geometry of the bearing pads 410. For ease of manufacture from a single PDC insert, it may be practical to limit angle θ to 45 degrees or less. On the other hand, increasing angle θ above 45 degrees increases the efficiency of the fluid diversion action, but may require a larger bearing pad, which may be difficult to manufacture with existing PDC press technology. Alternatively, FIG. 4E shows a similar bearing pad shape manufactured

from multiple components. In the exemplary embodiment of FIG 4E, the three components 417, 418, and 419 are considered to make up a whole bearing pad 410. However, the gaps 432 between individual components within an bearing pad must be small as compared to the gaps 431 between adjacent bearing pads, or the efficiency of the fluid diversion will be reduced. Optimally the width of gaps 432 should be as close to zero as possible to prevent fluid from escaping or dispersing through the gaps.

[0037] Turning to FIGS. 5A through 5C, an embodiment is shown in which a bearing pad 110 (of FIG. 3A) is formed as a shaped bearing pad 510 which, similarly to the block bearing pads 410 of FIG. 4B, allows for further improved utilization of the cylindrical PDC inserts from which the shaped bearing pads 510 may be manufactured. A shaped bearing pad 510 may include edge geometry defined by various combinations of radii, straight lines, mathematical formulae, or free-form shapes. As shown in FIG. 5B, two shaped bearing pads 510 may be formed from a single PDC insert 520. The back face 512 of shaped bearing pad 510 may approximately match the radius of cylindrical PDC insert 520 as shown. The radius of leading face 511 of shaped bearing pad 510 may be equal to or slightly larger than the radius of the back face 512, such that a substantially uniform gap 531 exists between adjacent shaped bearing pads 510 when assembled into a ring 530, as shown in FIG. 5C. Outer face 513 may optimally be formed on a radius slightly less than that of the outer diameter 533 of ring 530, and inner face 514 may optimally be formed on a radius slightly greater than that of the inner diameter 534 of ring 530.

[0038] As with other embodiments, shaped bearing pads 510 may be cut from a PDC insert using wire EDM, and brazed onto a ring 530. As assembled into the ring 530, the leading face 511 has an average angle θ which forces fluid between the shaped bearing pads 510 when the bearing is rotated, thereby cooling the bearing. For the purposes of describing this embodiment, the terms "average angle θ" and "angle θ" shall be used interchangeably. The angle θ of the leading face 51 1 with respect to a plane 573 extending from an axis 574 of the thrust bearing ring 530 may be between about 4 degrees and about 91 degrees, hi some embodiments, the efficient use of as- manufactured PDC bearing pads will result in an angle θ of between about 20 degrees and about 45 degrees. However, shaped bearing pads may be manufactured from more than one component, similarly to the block bearing pads 410 of FIG. 4E, in

order to provide a practical way to increase angle θ to as much as 90 degrees, thereby increasing the efficiency of fluid diversion.

[0039] For simplicity, the bearing pads in the above embodiments are described as being made of PDC bearing material. However, material selection of the bearing pads is not limited to polycrystalline diamond, and as such, may include other super-hard materials, for example CBN or silicon carbide-diamond composite. For these purposes, a super-hard material may be defined as any material having a hardness in excess of 2000 Vickers. Either polycrystalline diamond or CBN may be bonded to a tungsten carbine substrate, which in turn may be brazed onto a flat end surface of the ring. Ring materials may include steel and tungsten carbide. Alternatively, pockets may be formed in the ring to accommodate the shape of each bearing pad. Pockets may keep the bearing pads in place better than brazing alone. However, fully formed pockets may substantially increase machining costs for each thrust bearing.

[0040] FIG. 6 shows a ring 630 for a thrust bearing in accordance with embodiments of the present disclosure. The ring 630 is configured to accommodate the block bearing pad 410 shown in FIGS. 4A and 4B. Instead of fully formed pockets, the ring 630 includes radial ribs 631, which are angled to match the back face of a specific bearing pad. Referring back to FIG. 4A, the back face 412 of block bearing pad 410 matches with side 632 of radial rib 631. Leading face 411 of the block bearing pad 410 matches with side 633 of the radial rib 631. After placement between the radial ribs 631, the bearing pads 410 may be brazed into place. The radial ribs 631 provide mechanical support in addition to the brazing, while being less expensive to machine than fully formed pockets. The radial ribs 631 may also help position the bearing pads during the brazing operation. While FIG. 6 illustrates straight ribs, as might be used with the block bearing pads of FIG. 4A, it is understood that ribs may also be formed on a ring to conform to other bearing pad geometries.

[0041] The above-described embodiments provide bearing pads for thrust bearings that are shaped and/or oriented to actively divert drilling fluid while rotating. The various shaped bearing pads described above may be azimuthally distributed to provide more bearing area than the typical cylindrical bearing pads known in the art. The improved flow characteristics may also provide greater cooling of the thrust bearing, even with closer azimuthal spacing between the bearing pads. Improved

cooling can increase the lifetime of the thrust bearing by decreasing the temperature of the bearing pads.

[0042] An advantageous aspect to the above-described embodiments is that the increased flow across the thrust bearing can be accomplished without introducing further flow restrictions in the mud motor to force drilling fluid through the thrust bearing. The above-described embodiments instead convert a small amount of mechanical energy from the rotor to induce radial flow through the thrust bearing, thereby cooling the bearing using less energy than would result from further restricting flow through the mud motor.

[0043] While various embodiments of the disclosure have been shown and described, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised that do not depart from the spirit and teachings of the disclosure. The embodiments herein are exemplary only, and are not limiting. Many variations and modifications of the methods and apparatus disclosed herein are possible and within the scope of the disclosure. Accordingly, the scope of protection is not limited by the description set out above, but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims.