Patent Publication Number: US-2020300042-A1

Title: Self-aligning bearing assembly for downhole motors

Description:
BACKGROUND OF THE DISCLOSURE 
     1. Field of the Disclosure 
     This disclosure relates generally to oilfield downhole tools and more particularly to bearing assemblies utilized for drilling wellbores. 
     2. Background of the Art 
     To obtain hydrocarbons such as oil and gas, boreholes or wellbores are drilled by rotating a drill bit attached to the bottom of a drilling assembly (also referred to herein as a “Bottom Hole Assembly” or (“BHA”). The drilling assembly is attached to the bottom of a tubing, which is usually either a jointed rigid pipe or a relatively flexible spoolable tubing commonly referred to in the art as “coiled tubing”. The string comprising the pipe or the tubing and the drilling assembly is usually referred to as the “drill string”. When jointed pipe is utilized as the tubing, the drill bit is rotated by rotating the jointed pipe from the earth&#39;s surface and/or by a drilling motor such as a mud motor contained in the drilling assembly. In the case of a coiled tubing, the drill bit is rotated by the drilling motor. During drilling, a drilling fluid (also referred to as the “mud”) is supplied under pressure into the tubing. The drilling fluid passes through the drilling assembly and then discharges at the drill bit bottom. The drilling fluid provides lubrication to the drill bit and carries to the earth&#39;s surface rock pieces disintegrated by the drill bit in drilling the wellbore. The drilling motor is rotated by the drilling fluid passing through the drilling assembly. A drive shaft connected to the motor and the drill bit rotates the drill bit. 
     A substantial amount of current drilling activity involves drilling deviated and horizontal wellbores to more fully exploit hydrocarbon reservoirs. Often referred to as directional drilling, this drilling technique can provide boreholes that have relatively complex well profiles. One known deflection tool for directional drilling has a housing with an inner surface and an outer surface, the inner surface having an inner surface longitudinal axis and the outer surface having an outer surface longitudinal axis that is offset and/or at an angle from the inner surface longitudinal axis. As a result, the outer diameter of the tilted drive sub is remaining straight with comparison to the mud motor&#39;s outer diameter while the internal bearing components are radially offset and/or offset at some predetermined angle. This concept allows to bring the position of the tilt relatively close to the drill bit. The effective bit to bend distance, known as one of the parameters for the design of a directional drilling motor, can be minimized using this approach. The bit to bend distance is defined by the distance from the inclined bearing axis intersection point with the longitudinal tool axis to the bit face for this concept. One drawback of the prior art tilted drive sub design is the inability to change the offset angle without parts exchange and also complete disassembly / assembly of the bearing unit. Other known tools for directional drilling are bent subs or adjustable kickoff (AKO) tools. These tools utilize a deflection device that creates a tilt in the outer housing of a BHA. The tilt angle of the AKO can be adjusted on a rig floor. 
     Because adjustable kickoff tools are positioned uphole of a bearing section, these assemblies are known to exert high side loads and bending moments at the drill bit, the stabilizer, and the bend, caused by the large bit to bend distance, thus creating high bit offset. This is especially the case when they are used for drilling a straight section of the wellbore. In such instances, the housing, which includes the bend, is rotated. High side load in combination with misalignment of the bearing / drive shaft axes and the housing axis contributes to wear and damage of the radial and/or axial bearing. Bearing wear is known to be one major contributor to service limitation and repair costs. 
     Another known tool for directional drilling is a rotary steering system configured for directional drilling with continuous rotation from the earth&#39;s surface. Rotary steering systems may utilize a so-called non-rotating sleeve that is rotatably disposed around the drill string by means of a bearing system. Actuator elements are used to push the non-rotating sleeve outwards to create a deflection on the drill string. The deflections on the drill string create high side loads and bending moments on the drill string and/or the non-rotating sleeve which may create a higher probability for damage or wear in the bearing system supporting the non-rotating sleeve. A similar embodiment comprises a non-rotating stabilizer that is rotatably disposed around the drill string utilizing a bearing system. 
     The present disclosure addresses these and other drawbacks of the prior art directional drilling tools and generally addresses the need for more robust and durable devices for drilling wellbores. 
     SUMMARY OF THE DISCLOSURE 
     In aspects, the present disclosure provides an apparatus for use in a wellbore in a subterranean formation. The apparatus may include a drill string section; a drive shaft disposed in the drill string section, a bearing assembly connected to the drive shaft, the bearing assembly including at least one axial bearing and at least one radial bearing; and an alignment assembly connecting the bearing assembly to the drill string section. The bearing assembly may include at least one axial bearing and at least one radial bearing. The alignment assembly may have a first alignment member and a second alignment member slidingly engaging one another to allow at least a portion of the drive shaft to tilt relative to the drill string section. 
     In aspects, the present disclosure provides a method for performing an operation in a wellbore in a subterranean formation. The method includes the steps of positioning a drive shaft in a drill string section; connecting a bearing assembly to the drive shaft using an alignment assembly, the bearing assembly including at least one axial bearing and at least one radial bearing, the alignment assembly having a first alignment member and a second alignment member; and allowing at least a portion of the drive shaft to tilt relative to the drill string section using the alignment assembly by having the first alignment member and the second alignment member slidingly engage one another. 
     Examples of certain features of the disclosure have been summarized rather broadly in order that the detailed description thereof that follows may be better understood and in order that the contributions they represent to the art may be appreciated. There are, of course, additional features of the disclosure that will be described hereinafter and which will form the subject of the claims appended hereto. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed understanding of the present disclosure, reference should be made to the following detailed description of the embodiments, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals, wherein: 
         FIG. 1  illustrates a drilling system made in accordance with one embodiment of the present disclosure; 
         FIG. 2A  schematically illustrates a drill string section with a self-aligning bearing assembly made in accordance with one embodiment of the present disclosure; 
         FIG. 2B  schematically illustrates the contours of the sliding surfaces used in the  FIG. 2A  embodiment; 
         FIGS. 3A-B  illustrate polycrystalline diamond compact (PDC)inserts that may be used with a self-aligning bearing assembly made in accordance with one embodiment of the present disclosure; 
         FIG. 4  illustrates anti-rotation elements in accordance with one embodiment of the present disclosure for locking portions of the self-aligning bearing assembly; 
         FIG. 5  illustrates protection members made in accordance with one embodiment of the present disclosure; 
         FIGS. 6A-B  illustrate bearing assembly behavior for conventional bearing arrangements and bearing arrangements according to the present disclosure, respectively; 
         FIGS. 7 and 8  illustrate a fixed eccentricity member for providing a predetermined tilt for a drive shaft in accordance with one embodiment of the present disclosure; 
         FIGS. 9A-D  illustrate an adjustable eccentricity member for providing an adjustable amount of tilt for a drive shaft in accordance with one embodiment of the present disclosure; 
         FIG. 10A  illustrates geometric properties in accordance with one embodiment of the present disclosure; 
         FIG. 10B  illustrates geometric properties of a prior art system; 
         FIG. 10C  illustrates drilling properties in accordance with one embodiment of the present disclosure; 
         FIG. 10D  illustrates drilling properties of a prior art system 
         FIG. 11  illustrates another embodiment of a self-aligning bearing in accordance with the present disclosure; and 
         FIG. 12  illustrates a downhole steerable drilling assembly that may use the teachings of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     As will be appreciated from the discussion below, aspects of the present disclosure provide a steerable system for drilling wellbores. In general, the described steering methodology involves deflecting the angle of the drill bit axis relative to the longitudinal tool axis. 
     Referring now to  FIG. 1 , there is shown one illustrative embodiment of a drilling system  10  utilizing a steerable drilling assembly or bottomhole assembly (BHA)  12  for directionally drilling a wellbore  14 . While a land-based rig is shown, these concepts and the methods are equally applicable to offshore drilling systems. The system  10  may include a drill string  16  suspended from a rig  20 . The drill string  16 , which may be jointed tubulars or coiled tubing (not shown), may include power and/or data conductors (not shown) such as wires for providing bidirectional communication and power transmission. In one configuration, the BHA  12  includes a drill bit  30 , a sensor sub  32 , a communication and/or power module  34 , a formation evaluation sub  36 , and one or more rotary power devices  38  such as drilling motors (e.g. electrical motors or mud motors). The sensor sub  32  may include sensors and tools for measuring a direction of at least a part of the drill string  16  and/or BHA (e.g., BHA azimuth, inclination, toolface, and/or BHA coordinates, etc.). The sensors and tools may be positioned relatively close to the drill bit  30  for measuring near-bit direction or near-bit position. The sensors and tools may be configure for making measurements while the drill string  16  is rotationally stationary or while the drill string  16  is rotating to generate stationary or rotary directional surveys, respectively. The sensor sub  32  may include two (2) or three (3) axis accelerometers, magnetometers, gyroscopic devices and signal processing circuitry. The system may also include information processing devices such as a surface controller  50  and/or one or more downhole controller  42 . The drill bit  30  may be rotated by rotating the drill string  16  and/or by using a drilling motor, or other suitable rotary power device  38 . By drilling motor, it is meant mud motors, turbines, electrically powered motors, etc. Communication between the surface controller  50  and the BHA  12  may use uplinks and/or downlinks generated by a mud-driven alternator, a mud pulser, a mud siren, or a mud valve as known in the art, and/or may be conveyed using the drilling fluid column. Alternatively or in addition, uplinks and/or downlinks may be conveyed using acoustic conductors, electric conductors (e.g., hard wires), and/or optical conductors (e.g., optical fibers). The signals used for communication may be drilling fluid pressure variations, acoustic signals, electric / electromagnetic signals including radio-frequency signals, and/or optical signals. The BHA  12  may also include a steering system configured to adjust or control a direction of at least a part of the BHA  12  to drill wellbore  14  into a desired direction. Examples of steering assemblies are tilted motors, kickoff motors, adjustable kickoff motors, tilted drive shafts (also known as tilted drive subs), or rotary steerable systems. As will be discussed in greater detail below, the BHA  12  may include a self-aligning bearing assembly that reduces wear of bearings during directional drilling and other situations. 
     Referring to  FIG. 2A , there is sectionally illustrated a self-aligning bearing assembly  100  for directionally drilling a borehole in a subterranean formation. The term “self-aligning” in this context means that the bearing assembly is configured to adjust its direction in response to forces applied to the bearing assembly. Examples of bearing assembly  100  include a friction bearing, such as a plain bearing, jewel bearing, journal bearing, plate bearing, Michell bearing, and a rolling-element bearing such as a ball bearing or a roller bearing. In general, those skilled in the art will appreciate that in cases sliding surfaces as presented below may be replaced by ball bearings or roller bearings. While this disclosure generally refers to sliding surfaces, it is therefore clear for those skilled in the art that sliding surfaced in this context may include ball bearings or roller bearings. Alternatively or in addition, embodiments of the bearing assembly  100  may include tapered and/or spherical bearings. The bearing assembly  100  is positioned on a drive shaft  110  connecting a drill bit  30  ( FIG. 1 ) to a rotary power device  38  ( FIG. 1 ) to convey torque created by the rotary power device  38  to the drill bit  30  to rotate the drill bit  30  ( FIG. 1 ) by the rotary power device  38  ( FIG. 1 ). The bearing assembly  100  includes an upper dynamic thrust bearing  102 , a lower dynamic thrust bearing  104 , and a dynamic radial bearing  106 . The bearing assembly  100  is connected to a shaft (not shown), such as a flexible shaft, an articulated shaft, and a Cardan shaft, via bonnet  108 . Bonnet  108  may include means to divert a flow of drilling fluid from an inner bore of bonnet  108  to the annulus between bonnet  108  and tool housing  101 . The upper dynamic thrust bearing  102 , the lower dynamic thrust bearing  104 , and the dynamic radial bearing  106  are rotationally fixed to drive shaft  110 , so that the upper dynamic thrust bearing  102 , the lower dynamic thrust bearing  104 , and the dynamic radial bearing  106  rotate with the same rotational velocity as the drive shaft  110  about the length axis of the drive shaft  110 . In the embodiments of this disclosure, axial bearing and thrust bearing have the same broad meaning. Axial or thrust bearings prevent movement along a rotation axis while at the same time allow rotation about that rotation axis. Similarly, in the embodiments of this disclosure, the terms radial bearing and journal bearing have the same broad meaning. Radial or journal bearings prevent movement perpendicular to an rotation axis while at the same time allow rotation about the rotation axis. Consequently, the terms “axial” bearing and “thrust” bearing will be used interchangeably in that broad meaning and the terms “radial” and “journal” bearings will be used interchangeably in that broad meaning. For example, the terms “axial” or “thrust” bearings as used herein may comprise bearings with sliding surfaces that are not perpendicular to the rotation axis but may be tapered or tilted with respect to the rotation axis and may comprise sliding surfaces that are plane or curved such as spherical or elliptical surfaces. Further, the terms “radial” or “journal” bearings as used herein may comprise bearings with sliding surfaces that are not cylindrical with respect to the rotation axis and may comprise sliding surfaces that are tapered, tilted, or curved with respect to the rotation axis. Moreover, the terms “axial”, “thrust”, “radial”, or “journal” bearings may also be understood to comprise more than one bearing or more than one pair of sliding surfaces. The terms “lower”, “downward”, “downhole”, etc. and “upper”, “upward”, “uphole”, etc. respectively describe axial directions along the wellbore  14  ( FIG. 1 ) towards or away from drill bit  30  ( FIG. 1 ). 
     The bearing assembly  100  includes a self-alignment assembly  120  that reduces the detrimental effects on the bearings  102 ,  104 ,  106  from deflection of a drive shaft  110  relative to a tool housing  101 . In one non-limiting embodiment, the self-alignment assembly  120  includes a plurality of interconnected members that allow an amount of articulation; i.e., ability to pivot or tilt relative to one another. This articulation allows the self-alignment assembly  120  to passively accommodate the forces of the drilling process. The members can include an upper static thrust bearing  122 , a carrier ring  124 , and a lower static thrust bearing  126 . Upper dynamic thrust bearing  102  and upper static thrust bearing  122  as well as lower dynamic thrust bearing  104  and lower static thrust bearing  126  comprise opposing sliding surfaces at least portions of which are plane and perpendicular to the longitudinal axis of the drive shaft  110 . In the embodiments of this disclosure, “perpendicular” has a broad meaning. A surface is perpendicular to an axis when the angle between axis and surface is between 45° and 135°. For example, a surface is perpendicular to an axis when the angle between axis and surface is between 75° and 105°. Similarly, radial bearing  106  and lower static thrust bearing  126  have opposing sliding surfaces at least portions of which are cylindrical about the longitudinal axis of the drive shaft  110  and, thus, in at least one cross section perpendicular to the longitudinal axis of the drive shaft  110  and comprising the radial bearing  106 , perpendicular to a line that is perpendicular to the longitudinal axis of the drive shaft  110 . This arrangement of plane and cylindrical sliding surfaces ensures that, for the relatively fast rotation, the sliding surfaces are plane at least in a direction perpendicular to the sliding movement. Sliding surfaces that are plane at least in a direction perpendicular to the sliding movement are beneficial as they are generally less prone to wear. The upper static thrust bearing  122 , the lower static thrust bearing  126 , and the carrier ring  124  are rotationally fixed to tool housing  101  as described in more detail below, so that the upper static thrust bearing  122 , the lower static thrust bearing  126 , and the carrier ring  124  rotate with the same rotational velocity as the tool housing  101  about the length axis of the housing  101 . The carrier ring  124  includes an inner contoured surface  130  that contacts an outer contoured surface  132  of the lower static thrust bearing  126 . Likewise, the upper static thrust bearing  122  may have an inner contoured surface  160  that contacts an outer contoured surface  162  of the carrier ring  124 . Upper static thrust bearing  122  and lower static thrust bearing  126 . may be fixedly connected at one or more connections  89 , e.g. by threads, welds, adhesive attachments, anti-rotation elements, or similar. Likewise, tool housing  101  and carrier ring  124  may be fixedly connected at one or more connections  89 , e.g. by threads, welds, adhesive attachments, anti-rotation elements, or similar. Alternatively, upper static thrust bearing  122  and lower static thrust bearing  126  may be one integral part, and/or tool housing  101  and carrier ring  124  may be one integral part. Further, at least one of upper static thrust bearing  122 , lower static thrust bearing  126 , and carrier ring  124  may comprise two or more parts (not shown) that are connected, e.g. connected by threads, welds, adhesive attachments, anti-rotation elements, or similar, in a way that prevents relative rotation and/or linear movement of the two or more parts. A bearing assembly  100  with one integral part comprising upper static thrust bearing  122  and lower static thrust bearing  126  and/or tool housing  101  and carrier ring  124  may be made, e.g. by additive manufacturing such as but not limited to  3 D printing. Alternatively or in addition, bearing assembly  100  may comprise integral half shells (not shown) comprising two or more of the parts shown in  FIG. 2A  and suited to assemble at least parts of bearing assembly  100 . 
     Referring to  FIG. 2B , there are shown the contoured surfaces  130 ,  132 ,  160 , and  162 . In one arrangement, the contoured surfaces  130 ,  132  are aligned with a surface defined by a sphere  164  around a center point  168  and the contoured surfaces  160 ,  162  are aligned with a surface defined by a sphere  166  with the same center point  168 . The spheres  164  and  166  have different diameters but share the common center point  168 . The common center point  168  is located on the axis of drive shaft  110 . While, in general, a center point of a sphere is mathematically infinitely small, the common center point  168  is not so limited. That is, the common center point  168  may actually comprise a region within which the center points of the spheres  164  and  166  are located and which is small enough to avoid damages to the alignment assembly  120  when upper static thrust bearing  122 , carrier ring  124 , and lower static thrust bearing  126  are moving with respect to each other. For example, the common center point  168  may comprise a region with an extension that is smaller than 30% of the radii of spheres  164  and  166 . For example, the common center point  168  may comprise a region with an extension that is smaller than 10% of the radii of spheres  164  and  166 . For example, the common center point  168  may comprise a region with an extension that is smaller than 3% of the radii of spheres  164  and  166 . The surfaces  130 ,  132  and  160 ,  162  are arranged and positioned to allow the lower static thrust bearing  126  and the upper static thrust bearing  122  to rotate or pivot in a ball joint fashion about an axis perpendicular to the length axis of drive shaft  110  ( FIG. 2 ). During this motion, there is relative sliding motion between the surfaces  130  and  132  and surfaces  160  and  162 . Surfaces  160  and  162  account for axial and radial bearing loads directed opposite to those directed into surfaces  130 ,  132 . Since spherical surface  130 ,  132  and  160 ,  162  share a common center point  168 , a point of bearing tilt is defined at the common center point  168 . 
     There are three areas through which torque is frictionally transferred from the drive shaft  110  into the bearing assembly  100 . These include an upper thrust area  134  between the upper dynamic thrust bearing  102  and the upper static thrust bearing  122 , an inner bearing area  136  between the radial bearing  106  and the lower static thrust bearing  126 , and a lower thrust area  138  between lower dynamic thrust bearing  104  and the lower static thrust bearing  126 . In the displayed assembly, the upper thrust area  134  transfers torque from the drive shaft  110  into the bearing assembly  120  by friction that is created of downward directed loads  170 , caused by operations such as back-reaming, pulling or hydraulic thrust caused by the rotary power device  38  ( FIG. 1 ). The lower thrust area  138  transfers torque from the drive shaft  110  into the bearing assembly  120  by friction that is created of upward directed loads  172  mainly caused by the drilling weight, sometimes also referred to as weight on bit (WOB). 
     To enhance performance and service life, bearing surfaces, such as opposing surfaces of upper dynamic thrust bearing  102 , upper static thrust bearing  122 , radial bearing  106 , lower static thrust bearing  126 , and lower dynamic thrust bearing  104  may include surface treatments and features, including but not limited to flame spray coatings, high velocity oxygen fuel (HVOF) spray coatings, laser weld coatings, ceramic inserts, tungsten carbide inserts (T 2 A), and diamond bearing elements to reduce abrasive wear.  FIGS. 3A-B  illustrate diamond bearing elements  149 , such as polycrystalline diamond compact (PDC) bearing elements that may also be distributed on the bearing surfaces described above and other surfaces to provide greater resistance to wear. As shown, the elements  149  may be disposed on an end face  151  as shown in  FIG. 3A  (e.g., an end face of upper dynamic thrust bearing  102  or radial bearing  106  in  FIG. 2 ) and/or on an inner circumferential surface and/or outer circumferential surface  153  as shown in  FIG. 3B  (e.g. outer circumferential surface of radial bearing  106  or inner circumferential surface of lower static thrust bearing  126 ). 
     Referring to  FIG. 4 , in one arrangement, anti-rotation elements  140  are positioned between the carrier ring  124  and the lower static thrust bearing  126  to prevent relative rotational movement about the longitudinal drive shaft axis between lower static thrust bearing  126  and carrier ring  124  and ultimately between upper static thrust bearing  122 , lower static thrust bearing  126 , carrier ring  124 , and tool housing  101  . Anti-rotation elements  140  may prevent relative rotation about a first axis but may allow relative rotation about a second axis. For example, anti-rotation elements  140  may prevent relative rotation about the longitudinal drive shaft axis while allowing relative rotation about an axis that is perpendicular to the longitudinal drive shaft axis. For instance, the anti-rotation elements  140  may be disposed in elongated slots  142  formed in either or both of the inner and outer contoured surfaces  130 ,  132  ( FIG. 2 ) and can be positioned at the surface of sphere  164  that is associated with outer contoured surface  132  and in a plane perpendicular to the longitudinal drive shaft axis that includes the common center point  168 . The slots  142  are elongated parallel with the longitudinal axis of the drive shaft. The anti-rotation elements  140  have the freedom to move along the elongated slots  142 , which allows the upper static thrust bearing  122  and the lower static thrust bearing  126  to incline or tilt with respect to carrier ring  124  about an axis that is perpendicular to the longitudinal drive shaft axis in a desired direction. This arrangement locks the three translational degrees of freedom and the rolling degree of freedom (about the longitudinal tool axis) of the bearing assembly  100 , while keeping the pitching and yawing degree of the drive shaft  110  free in any direction about an axis that is perpendicular to the longitudinal drive shaft axis (omni-directional tilt) and the rotating degree of the drive shaft  110  about the longitudinal drive shaft axis free. Respectively opposing sliding surfaces of upper dynamic thrust bearing  102  and upper static thrust bearing  122 , radial bearing  106  and lower static thrust bearing  126 , as well as lower static thrust bearing  126  and lower dynamic thrust bearing  104  allow for the rotation about the longitudinal axis of the drive shaft while limiting the axial and lateral movement of the drive shaft  110 . At the same time, opposing inner contoured surface  160  and outer contoured surface  162 , as well as inner contoured surface  130  and outer contoured surface  132  allow for the omni-directional tilt of the drive shaft  110 , the upper dynamic thrust bearing  102 , the radial bearing  106 , the lower dynamic thrust bearing  104  and their opposing sliding surfaces in upper static thrust bearing  122  and lower static thrust bearing  126  while limiting the axial and lateral movement of the drive shaft  110 , the upper dynamic thrust bearing  102 , the radial bearing  106 , the lower dynamic thrust bearing  104  as well as the rotation of tool housing  101 , carrier ring  124 , upper static thrust bearing  122 , and lower static thrust bearing  126  with respect to each other. Hence, this arrangement ensures that, for the relatively fast rotation about the longitudinal drive shaft axis, the sliding surfaces are plane at least in a direction of the sliding movement (plane or cylindrical surfaces) while for the relative slow pitching and yawing movement, opposing sliding surfaces are at least partially of spherical shape to ensure the omni-directional tilt. The arrangement also ensures that in the self-aligning bearing assembly  100 , the opposing sliding surfaces supporting the rotational movement about the longitudinal axis of the drive shaft  110  tilt about an axis perpendicular to the longitudinal drive shaft axis with substantially the same angle. For example, in the arrangement as shown in  FIGS. 2, 2A, 4, and 5 , when the drive shaft  110  tilts with an angle a about an axis perpendicular to the longitudinal axis of the drive shaft  110 , the self-aligning bearing assembly  100  ensures that the respectively opposing sliding surfaces of upper dynamic thrust bearing  102  and upper static thrust bearing  122 , radial bearing  106  and lower static thrust bearing  126 , as well as lower static thrust bearing  126  and lower dynamic thrust bearing  104  tilt with substantially the same angle a. Notably, the self-aligning bearing assembly is a passive element that does not receive external power and/or communication to provide this function. In one non-limiting embodiment, the anti-rotation element  140  may be rigid bodies, such as pins, keys, balls, or cylinders, such as metal pins, keys, balls or cylinders that physically contact the carrier ring  124  and the lower static thrust bearing  126 . In another non-limiting embodiment anti-rotation elements  140  can alternatively be flexible members that have flexibility to deform along the elongated slots  142 , hence allowing the upper static thrust bearing  122  and the carrier ring  124  to incline or tilt even without sliding movement of the whole anti-rotation elements  240  with respect to the upper static thrust bearing  122  and the carrier ring  124 . That is, only a portion of anti-rotation element  240  slide along the elongated slots  142  to allow the upper static thrust bearing  122  and the carrier ring  124  to incline or tilt. Flexible anti-rotation elements  140  could be spring elements (e.g. helical springs, leaf springs) or other connecting elements that offer sufficient flexibility to account for the relatively small movement along the elongated slots  142  with deformation of the anti-rotation elements  140  (connecting elements), even when the anti-rotation elements  140  are rigidly coupled to one or both of the upper static thrust bearing  122  and the carrier ring  124 . 
     Referring to  FIG. 5 , there are illustrated protection features  150  that may be used to prevent particles in a fluid surrounding the tool housing  101  from entering and damaging the internal components of the bearing assembly  100 . The protection features  150  may be a protective covering, such as a sleeve or bellows that seal the gaps  144  between the components of the bearing assembly  100 . The protection features  150  prevent fluids with entrained abrasive material from entering into the gaps  144 . As opposed to sleeves or bellows as illustrated in  FIG. 5 , the protection features  150  might also be of other types such as, but not limited to O-Ring seals, hydraulic seals, metal bellows, barrier fluids, labyrinth seals between upper static thrust bearing  122  ( FIG. 2 ) and carrier ring  124  ( FIG. 2 ), as well as between carrier ring  124  ( FIG. 2 ) and lower static thrust bearing  126  ( FIG. 2 ), respectively. As would be apparent to those skilled in the art, protection features  150  may be omitted in favor of erosion/abrasion wear resistant materials or coatings at the sliding surfaces for upper static thrust bearing  122 , carrier ring  124  and lower static thrust bearing  126  or any other part of bearing assembly  100  as displayed in  FIG. 2 . protection features  150  may not prevent fluid from flowing between sliding surfaces, such as sliding surfaces of thrust bearing  102 , upper static thrust bearing  122 , radial bearing  106 , lower static thrust bearing  126 , and lower dynamic thrust bearing  104  for lubrication and cooling purposes. Additionally, a mechanical protection feature  152  such as a sleeve may be used to cover and mechanically protect the entire bearing assembly  100  from damaging contact with external features such as borehole wall or cuttings (not shown). The mechanical protection feature  152  may be formed of rubber, plastic, a metal, or any other suitable material. The protective cover may also carry a stabilizer centralizing the assembly inside the borehole wall. In such cases, the centralizing element additionally carries a protective layer made of a suitable wear resistant material, such as but not limited to tungsten carbide. 
       FIGS. 6A  and B schematically illustrative the behavior of a conventional bearing assembly and a bearing assembly according to the present teachings, respectively. The bearings illustrated therein have been simplified for clarity.  FIG. 6A  illustrates thrust bearings  400 ,  401  that are rigidly coupled to a drive shaft  110  and a radial bearing  402  that is rigidly coupled to a housing  411 when encountering a drive shaft deflection  404  with respect to the housing. As can be seen, the shaft deflection  404  causes non-parallel contact between the sliding surfaces  406 ,  408  and  407 ,  409  of the thrust bearings  400 ,  401 , respectively, as well as between sliding surfaces  410 ,  412  of the radial bearing  402  and the drive shaft  110 . This non-parallel contact could lead to line contact; i.e., a load on a relatively small area as opposed to a distributed load. Line contacts can cause extreme contact pressures in the drilling application, ultimately leading to premature defects or failure. 
       FIG. 6B  schematically illustrates how thrust bearings  420 ,  421  and a radial bearing  422  provided with alignment features according to the present teachings follow the deflection  424  of a drive shaft  110  without creating any non-parallel contact of sliding surfaces, line contacts or significant righting moment. As can be seen, the shaft deflection  424  does not cause uneven contact between the sliding surfaces  426 ,  428  and  427 ,  429  of the thrust bearings  420 ,  421  or between the sliding surfaces  430 ,  432  of the radial bearing  422  and the drive shaft  110 . Rather, the sliding surfaces  426 ,  428 ,  427 ,  429 ,  430 ,  432  remain generally parallel and are not subjected to line contact. Thus, bearing assemblies according to the present disclosure significantly reduce bearing damages in applications for directional drilling involving a directional drilling motor, e.g. a directional drilling motor that is equipped with a fixed or adjustable bend housing uphole of the bearing section. 
     Thus, it should be appreciated that the teachings of the present application can protect radial and axial (journal) bearings from damage due to intentional and unintentional misalignment of bearings in response to misalignment of a drive shaft. Shaft deflection, typically caused by side loads as described above, can affect the surfaces of a thrust bearing in a similar fashion as the surfaces of radial bearing. Thus, embodiments of the present disclosure comprise the combination of the radial and thrust or axial bearing into one assembly that is protected by a common self-alignment bearing assembly  100 . Combining the radial and thrust bearings into one assembly beneficially allows the pitching and yawing degree of freedom (omni-directional tilt) of the non-rotating bearing elements, aligning with the rotating bearing in the event of drive shaft deflection in a relatively short assembly. 
     The above-described embodiments of the self-alignment bearing assembly  100  is only one non-limiting arrangement of the present disclosure. For instance, the  FIG. 2A  embodiment positions the alignment features, e.g., the outer and inner contoured surfaces  130 ,  132  and  160 ,  162 , on the housing, which is at a different rotational velocity or stationary relative to the drive shaft  110 . In other embodiments, these features may be on the drive shaft  110  and thereby rotate with the drive shaft  110  about the longitudinal axis of the drive shaft  110 . It should be noted that since the deflection is primarily aligned with the housing and in direction of the housing bend, the use of the self-alignment features at the housing would be relatively stationary. If the alignment features are connected to the drive shaft  110 , then the deflection changes every shaft revolution. 
     Bearing assemblies according to the present disclosure may be used in a variety of configurations for downhole tools. One non-limiting configuration involves a downhole tool for directional drilling. In particular, the disclosed bearing assemblies may be used with steerable drilling systems that utilize a tilted drive shaft (also known as tilted drive sub,  FIGS. 7-9D ). In  FIG. 7 , there is shown a section of a bottomhole assembly  12  that includes the drill bit  30 , a drive shaft  110 , and the bearing assembly  100 . Tilting the drive shaft effects a change in drilling direction by influencing the way the drill bit  30  and bottom hole assembly  12  lays in the previously drilled hole so as to influence the tilt  216  of the drill bit  30 . The end effect is that the drill bit face points or tilts in a selected orientation for the selected new direction of the hole. 
     Referring to  FIGS. 7, 8, and 9A , in embodiments, one or more components of the bearing assembly  100  may include one or more eccentricity members having an eccentricity and/or a geometry that is tilted or asymmetric with respect to the longitudinal tool axis and that causes a deflection of the drive shaft  110  and the drill bit  30  with respect to a longitudinal tool axis  218  of the drill string section  219 . The deflection may cause a tilt that is relatively fixed, e.g. a tilt that cannot be adjusted. Referring to  FIGS. 7 and 8 , for instance, the upper bearing  210  may be an eccentricity member constructed to have a wall thickness asymmetric with respect to a longitudinal tool axis  218  that results in one portion  212  of the wall being thicker than another portion  214  of the wall. The variation in thickness causes the drive shaft to have a tilt  216  relative to the longitudinal tool axis  218 . In order to adjust the tilt to a different angle, the assembly as displayed in  FIG. 7  needs to be disassembled to exchange the upper bearing component  210  with one that has a different eccentricity and thus causes a different tilt. A higher tilt would be beneficial to drill narrower curvatures, while a smaller tilt would be beneficial to drill straighter sections and do corrections only. Advantageously, the self-aligning bearing assembly  100  ( FIG. 2 ) orients the thrust and radial bearings described previously. Also, identical components can be used for bearing assembly  100  regardless of eccentricity of upper bearing  210  to reduce potential damage to bearing surfaces from misalignment. 
     In embodiments, the upper bearing  210  may be configured to have an adjustable tilt; e.g., a tilt axis adjustable between no tilt and a tilt of about 1°, or a higher value such as 5°.  FIGS. 9A-D  illustrate an upper bearing  210  that uses two or more eccentricity members to vary the tilt angle. The two components may move relative to one another such that the eccentricities either offset one another to minimize a tilt angle or complement one another to maximize tilt angle. Of course, the eccentricities may also be set to provide an intermediate tilt angle value. 
     Referring to  FIGS. 9A-B , in one non-limiting embodiment, a first eccentricity member, also known as upper bearing  210  generates a first eccentricity using a bearing housing  310  having an eccentric inner surface, creating the first eccentricity member. The bearing housing  310  includes an inner contour  320  that is eccentric and/or at an angle with respect to the longitudinal tool axis  342 . For example, as shown in  FIG. 9A  the bearing housing  310  includes an inner contour  320  that is eccentric and/or at an angle with respect to an outer contour  322  of the housing wall such that a first enlarged portion  323  is formed, hence bearing housing  310  has one side with an enlarged wall thickness and one opposite side with a narrower wall thickness. The eccentric and/or asymmetric inner contour  320  of bearing housing  310  is complementary to a second eccentricity member, such as female radial bearing  324 . Referring to  FIGS. 9A  and C, another eccentric and/or asymmetric eccentricity member is formed using a female radial bearing  324  with an outer contour  316  that is eccentric to the inner radial bearing surface  318 . Thus, the female radial bearing  324  has a first side with an enlarged wall portion  325  and an opposing side with a narrower wall thickness. The female radial bearing  324  can be rotated inside the contour  320  of bearing housing  310  about its center line  340  by means of a keyed connection  331  between an upper housing  103  and the female radial bearing  324 . 
     In one non-limiting configuration, the upper housing  103  and the female bearing housing  310  are connected through a threaded portion  105 . To adjust the tilt, the upper housing  103  is rotated about its center line  342  with respect to the bearing housing  310 . Differences in thicknesses of the bearing housing  310  and the female radial bearing  324  adjusts the relative rotary angle between the upper housing  103  and the bearing housing  310 . This is also reflected by the tilt between the center line  340  of the bearing (also known as bearing axis) and the center line  342  of the upper housing  103  (also known as longitudinal tool axis  218  ( FIG. 7 ) of the drill string section  219  ( FIG. 7 )). Referring to  FIG. 9B , in one embodiment, the maximum tilt created by aligning both enlarged portions  323 ,  325  towards the same side is 1° and the thread pitch of threaded portion  105  is  4  mm per revolution. Referring to  FIG. 9D , a half shell ring  330  may be installed between upper housing  103  and female bearing housing  310 . Use of half-shell rings  330  with various widths may result in various distances between upper housing  103  and bearing housing  310  when screwed together. It is apparent, that with the pitch of the thread, the various distances between upper housing  103  and bearing housing  310 , upper housing  103  and bearing housing  310  will have various azimuthal offsets with respect to each other when screwed together. For example, with a width of half-shell ring  330  that is reduced by  1  mm, upper housing  103  and bearing housing  310  are rotated about 90° with respect to each other, thus reducing the tilt to about 0.5°. A respective rotation of 180°, achieved by a reduction in thicknesses of the shell rings of 2 mm, would yield to a 0° tilt (straight assembly) as shown in  FIG. 9C .  FIG. 9A  also shows the distance “bit to bend” from the point of intersection  347 , where the two center lines  340  and  342  intersect, at common center point  168  defined by the spherical surface of the self-alignment bearing assembly  100  to the bit face  31  of the drill bit  30   
     Thus, it should be appreciated that manipulation of the angle and/or the thickness of the half shell rings  330  and thus of the tilt angle can create and/or define a tilt in the bearing assembly  100 . The spherical surfaces  160 , 162  and  130 ,  132  allow for such adjustment without creating line contact in the actual sliding surfaces of upper dynamic thrust bearing  102 , upper static thrust bearing  122 , radial bearing  106 , lower static thrust bearing  126 , and lower dynamic thrust bearing  104  as explained earlier. 
       FIG. 10A and 10C  illustrate the advantages of one non-limiting embodiment of a drilling system  10  according to the present disclosure over a prior art system, such as an AKO, as depicted in  FIG. 10B and 10D .  FIG. 10A  illustrates a drilling assembly  500  having a drill bit  504 , a self-aligning bearing assembly  100 , one or more stabilizers 506 ,  510 , and a drilling motor  508 . This self-aligning bearing assembly  100  in accordance with the embodiment discussed above allows the position of the tilt to be brought very close to the drill bit. The same amount of tilt would lead to extremely high forces in the bearings when used without the self-assigning bearing assembly  100  to create the same bit to bend distance, which ultimately would lead to high wear in the bearings. The effective bit to bend distance  502 , known as one of the critical parameters for the design of a directional drilling motor can therefore be minimized using this approach. The bit to bend distance  502  is defined by the distance from the inclined bearing axis intersection point with the longitudinal tool axis to the bit face. Referring now to  FIG. 10B  it can be seen that in prior art systems without a self-aligning bearing assembly as described above, the bend above a bearing assembly always creates a larger bit to bend distance to keep the wear in the bearings within an acceptable range than an assembly according to the present disclosure which allows the bend to be positioned at the position of the lower bearing. 
       FIG. 10A  shows a drilling assembly  500  according to the present disclosure that includes a self-aligning bearing assembly  100  as discussed previously disposed in a BHA  502  having a drill bit  504 . The BHA  502  may further include a upper stabilizer  506 , a drilling motor  508 , and a lower stabilizer  510 . The drilling assembly  500  has a bit to bend distance  512  as measured from the bend point  514 , which may be the center point  168  inside the bearing assembly  100  as discussed with respect to  FIG. 2B , to the drill bit  504 .  FIG. 10B  illustrates a conventional system that has an upper stabilizer  602 , a drilling motor  604 , an AKO sub  606 , a lower stabilizer  608 , and a drill bit  610 . The drilling assembly  600  has a bit to bend distance  612  as measured from the bend point  614  at the AKO sub  606  to the drill bit  610 . As is apparent, the  FIG. 10A  drilling assembly  500  beneficially has a bit to bend distance  512  shorter than that of the conventional system  600  as displayed in  FIG. 10B . 
       FIG. 10C  and  FIG. 10D  illustrate the potential difference resulting from small versus larger bit to bend distance. During rotary drilling, the entire drill string rotates. Thus, the bit to bend distance can influence the degree to which an over gauge hole will be formed. Due to the relatively small bit to bend distance, the  FIG. 10A  drilling assembly  500  would create a relatively small over gauge hole as shown in  FIG. 10C . In  FIG. 10C , the drill bit  504  is circumscribed by a circle  520 , which depicts the over gauge hole caused by the bit offset  524  at the drill bit  504 . The  FIG. 10B  conventional drilling assembly  600 , which has a larger bit to bend distance  612 , would create a much larger bit offset  624  as shown in  FIG. 10D . In  FIG. 10D , the drill bit  610  is circumscribed by a circle  620 , which depicts the over gauge hole caused by the bit offset  624  at the drill bit  610 . This relatively large bit offset  624  causes a larger over gauge hole size during rotary drilling and also create higher side loads, affecting bearing and stabilizer wear and durability. Additional negative effects are well known to those skilled in the art and include borehole quality issues, lower ROP caused by the higher volume of rock being cut, issues in cuttings transport, issues in completions while setting casing and cementing, and others. 
     Referring to  FIG. 11 , there is illustrated an alternate embodiment of a self-aligning bearing assembly  200  for directionally drilling a borehole in a subterranean formation. The bearing assembly  200  includes an upper dynamic thrust bearing  102 , a lower dynamic thrust bearing  104 , and a dynamic radial bearing  106 . The bearing assembly  200  is connected to a drive shaft  110 . The upper dynamic thrust bearing  102 , the lower dynamic thrust bearing  104 , and the dynamic radial bearing  106  are rotationally fixed to drive shaft  110 , so that the upper dynamic thrust bearing  102 , the lower dynamic thrust bearing  104 , and the dynamic radial bearing  106  rotate with the same rotational velocity as the drive shaft  110  about the length axis of the drive shaft  110 . The bearing assembly  200  includes a self-alignment assembly that reduces the detrimental effects on the bearings  102 ,  104 ,  106  from deflection of a drive shaft  110  relative to a tool housing  101 . In one non-limiting embodiment, the self-alignment assembly includes a plurality of interconnected members that allow an amount of articulation; i.e., ability to pivot or tilt relative to one another. This articulation allows the self-alignment assembly to passively accommodate the forces of the drilling process. The members can include an upper static thrust bearing  122 , a carrier ring  224 , and a lower static thrust bearing  126 . Upper dynamic thrust bearing  102  and upper static thrust bearing  122  as well as lower dynamic thrust bearing  104  and lower static thrust bearing  126  comprise opposing sliding surfaces at least portions of which are plane and perpendicular to the longitudinal axis of the drive shaft  110 . Similarly, radial bearing  106  and bearing carrier  280  have opposing sliding surfaces at least portions of which are cylindrical about the longitudinal axis of the drive shaft  110  and, thus, in at least one cross section perpendicular to the longitudinal axis of the drive shaft  110  and comprising the radial bearing  106 , perpendicular to a line that is perpendicular to the longitudinal axis of the drive shaft  110 . The upper static thrust bearing  122 , the lower static thrust bearing  126 , and the bearing carrier  280  are rotationally fixed to tool housing  101  as described in more detail below, so that the upper static thrust bearing  122 , the lower static thrust bearing  126 , and the bearing carrier  280  rotate with the same rotational velocity as the tool housing  101  about the length axis of the housing  101 . The bearing carrier  280  includes an inner contoured surface  260  that contacts an outer contoured surface  262  of the lower static thrust bearing  126 . Likewise, the upper static thrust bearing  122  may have an inner contoured surface  230  that contacts an outer contoured surface  232  of the bearing carrier  280 . Upper static thrust bearing  122  and lower static thrust bearing  126  may be fixedly connected, e.g. by threads, welds, adhesive attachments, anti-rotation elements, or similar. Likewise, tool housing  101  and bearing carrier  280  may be fixedly connected, e.g. by threads, welds, adhesive attachments, anti-rotation elements, or similar. Alternatively, upper static thrust bearing  122  and lower static thrust bearing  126  may be one integral part, and/or tool housing  101  and bearing carrier  280  may be one integral part. Further, at least one of upper static thrust bearing  122 , lower static thrust bearing  126 , and bearing carrier  280  may comprise two or more parts (not shown) that are connected, e.g. connected by threads, welds, adhesive attachments, anti-rotation elements, or similar, in a way that prevents relative rotation and/or linear movement of the two or more parts. A bearing assembly  100  with one integral part comprising upper static thrust bearing  122  and lower static thrust bearing  126  and/or tool housing  101  and bearing carrier  280  may be made, e.g. by additive manufacturing such as but not limited to 3D printing. Alternatively or in addition, bearing assembly  200  may comprise integral half shells (not shown) comprising two or more of the parts shown in  FIG. 11  and suited to assemble at least parts of bearing assembly  200 . 
     Still referring to  FIG. 11 , there is shown contoured surfaces  230 ,  232 ,  260 , and  262 . In aspects, the arrangement shown in  FIG. 11  is similar to the arrangement shown in  FIG. 2A  and  FIG. 2B . The combined axial and radial bearing assembly displayed in  FIG. 11  uses contoured surfaces  230 ,  232 ,  260 ,  262  at least partially contoured along spheres  264  and  266  having radii R 1  and R 2  that are equal or similar in dimension. For example, in one arrangement, the contoured surfaces  230 ,  232  are aligned with a surface defined by sphere  264  around a center point  268  and the contoured surfaces  260 ,  262  are aligned with a surface defined by sphere  266  with the same center point  268 . The spheres  264  and  266  have equal or at least similar diameters and share the common center point  268 . Comparably, in  FIGS. 2A and 2B , the carrier ring  124  is carrying both contoured surfaces  132  and  160  at the uphole side of the center  168 . In this arrangement, spheres  164  and  166  define the width of carrier ring  124 , which is also defined by a minimum width as a function of the load carrying capacity, therefore defining a minimum difference between sphere sizes  164  and  166 . Alternatively for the arrangement shown in  FIG. 11 , the spheres  264  and  266  can be of same or similar size when the corresponding surfaces  230 / 232  and  260 / 262  are located on either side of the center point  268 . For example, surfaces  230 / 232  corresponding to sphere  264  are located uphole of the center point  268  while surfaces  260 / 262  corresponding to sphere  266  are located downhole the center point  268 . The surfaces  230 ,  232  and  260 ,  262  are arranged and positioned to allow the lower static thrust bearing  126  and the upper static thrust bearing  122  to rotate or pivot in a ball joint fashion about an axis perpendicular to the length axis of drive shaft  110  . During this motion, there is relative sliding motion between the surfaces  230  and  232  as well as between surfaces  260  and  262 . Surfaces  260  and  262  account for axial and radial bearing loads directed at least partially opposite to those directed into surfaces  230 ,  232 . Since spherical surface  230 ,  232  and  260 ,  262  share a common center point  268 , a point of bearing tilt is defined at the common center point  268 . 
     In the arrangement of  FIG. 11 , there are a plurality of areas through which torque is frictionally transferred from the drive shaft  110  into the bearing assembly  200 . The plurality of areas through which toque is frictionally transferred include an upper thrust area  134  between the upper dynamic thrust bearing  102  and the upper static thrust bearing  122 , an inner bearing area  136  between the radial bearing  106  and the static bearing carrier  280 , and a lower thrust area  138  between lower dynamic thrust bearing  104  and the lower static thrust bearing  126 . In the displayed assembly, the upper thrust area  134  transfers torque from the drive shaft  110  into the bearing assembly  120  by friction that is created of downward directed loads  170  ( FIG. 2A ), caused by operations such as back-reaming, pulling or hydraulic thrust caused by the rotary power device  38  ( FIG. 1 ). The lower thrust area  138  transfers torque from the drive shaft  110  into the bearing assembly  120  by friction that is created of upward directed loads  172  ( FIG. 2A ) mainly caused by the drilling weight, sometimes also referred to as weight on bit (WOB). 
     Still referring to  FIG. 11 , anti-rotation elements  240  are positioned between the carrier ring  224  and the static bearing carrier  280  to prevent relative rotational movement about the longitudinal drive shaft axis between static bearing carrier  280  and carrier ring  224  and ultimately between upper static thrust bearing  122 , static bearing carrier  280 , carrier ring  224 , and tool housing  101 . Anti-rotation elements  240  may prevent relative rotation (e.g. relative rotation induced by torque that is frictionally transferred) about a first axis but may allow relative rotation about a second axis. For example, anti-rotation elements  240  may prevent relative rotation about the longitudinal drive shaft axis while allowing relative rotation about an axis that is perpendicular to the longitudinal drive shaft axis. For instance, the anti-rotation elements  240  may be disposed in elongated slots  242  formed in either or both of the inner and outer contoured surfaces of static bearing carrier  280  and carrier ring  224  and can be positioned at the surfaces of spheres  264 ,  266  and in a plane perpendicular to the longitudinal drive shaft axis that includes the common center point  268 . The slots  242  are elongated parallel with the longitudinal axis of the drive shaft. The anti-rotation elements  240  have the freedom to move along the elongated slots  242 , which allows the upper static thrust bearing  122  and the static bearing carrier  280  to incline or tilt with respect to carrier ring  224  about an axis that is perpendicular to the longitudinal drive shaft axis in a desired direction. This arrangement locks the three translational degrees of freedom and the rolling degree of freedom (about the longitudinal tool axis) of the bearing assembly  200 , while keeping the pitching and yawing degree of the drive shaft  110  free in any direction about an axis that is perpendicular to the longitudinal drive shaft axis (omni-directional tilt) and the rotating degree of the drive shaft  110  about the longitudinal drive shaft axis free. In one non-limiting embodiment, the anti-rotation element  240  may be rigid bodies, such as pins, keys, balls, or cylinders, such as metal pins, keys, balls or cylinders that physically contact the carrier ring  124  and the static bearing carrier  280 . In another non-limiting embodiment anti-rotation elements  240  can alternatively be flexible members that have flexibility to deform along the elongated slots  242 , hence allowing the upper static thrust bearing  122  and the static bearing carrier  280  to incline or tilt even without sliding movement of the anti-rotation elements  240  with respect to the upper static thrust bearing  122  and the static bearing carrier  280 . Referring to  FIG. 12 , there is shown another bottomhole assembly  800  that uses a sleeve  822  that rotates at a speed that is different to the rotational speed of the drive shaft  110  that drives the drill bit  30 . For example, sleeve  822  may rotate significantly slower than the inner drive shaft  110  and the drill bit  30  or may rotate not at all. E.g. for a rotary steerable system, the upper bearing may be a self-aligning combined axial/radial bearing  120  as described previously while the lower bearing  810  is a non self-aligning radial bearing. A deflection of the sleeve  822  with respect to the inner shaft is created by pads  820  on the sleeve  822  that may be actuated and pressed against the borehole wall to steer the BHA  800 . One or more stabilizers (not shown) uphole of the combine axial/radial bearing  120  may support the creation of the deflection. 
     While the foregoing disclosure is directed to the one mode embodiments of the disclosure, various modifications will be apparent to those skilled in the art. For example, while most of the embodiments are illustrated with respect to a motor or a tilted drive shaft, it is obvious that in other embodiments, the invention can advantageously be used with respect to the bearings of a rotary steerable system. It is intended that all variations within the scope of the appended claims be embraced by the foregoing disclosure.