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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND 
     1. Field of Invention 
     The invention is directed to bearing assemblies and, in particular, to longitudinally compressible bearing assemblies for conventional motors used in downhole tools for compensating longitudinal movement of a portion of the downhole tool during operation in an oil, gas, and/or water well. 
     2. Description of Art 
     Rotatable drill strings having a drill bit at a lowermost end are known in the art. Bearing assemblies for such drill strings are also known in the art. In general, a motor is included in the drill string in close proximity to the drill bit. Rotation of the drill bit by the motor can cause the drill bit to cut or abrade the formation to form the wellbore. The bearing assembly permits rotation of the drill bit by the motor, yet allows the remainder of the drill string to remain stationary, i.e., not rotated. 
     SUMMARY OF INVENTION 
     Broadly, bearing assemblies for inclusion in tubular strings disposed in a wellbore comprise a compensator member operatively associated with a bearing member. A rotatable tubular is operatively associated with the bearing assembly so that rotation of the entire tubular string having the bearing assembly is not required when the tubular is rotated. The compensator member includes an expanded position and a plurality of compressed positions. In each of the compressed positions, the compensator member is biased toward the expanded position. 
     The compensator member can comprise a chamber which is operatively associated with a slidable member. The chamber permits the slidable member to slide longitudinally relative to the bearing member so that a rotatable downhole tool, such as a drill bit, can absorb forces acting upward on the drill bit. In doing so, the chamber becomes energized which facilitates returning the compensator member to the expanded position after the upward force dissipates. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a partial cross-sectional view of a specific embodiment of a downhole tool having a bearing assembly disclosed herein shown in an expanded position. 
         FIG. 2  is a partial cross-sectional view of the bearing assembly of  FIG. 1  shown in a compressed position. 
     
    
    
     While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF INVENTION 
     As discussed above, broadly, the bearing assemblies comprise a slidable member and a compensator member. Referring to the particular embodiment of  FIGS. 1-2 , bearing assembly  20  comprises a slidable member operatively associated with a compensator member. Slidable member comprises mandrel  21  having outer wall surface  22 , inner wall surface  23  defining mandrel bore  24 , and longitudinal axis  27 . Outer wall surface  22  includes shoulder  25 . Mandrel  21  is operatively associated with a rotating downhole tool such as drill bit  80  which is operatively associated with rotating tubular  78  through any known fastener device known in the art, including but not limited to, threads (not shown). An upper end of rotatable tubular  78  is operatively associated with a motor (not shown). Activation of the motor causes rotatable tubular  78  to rotate which, in turn, causes drill bit  80  to rotate so that an object such as the formation of a wellbore can be drilled or abraded away. 
     Secured to outer wall surface  22  of mandrel  21  is shroud  30 . Shroud  30  includes upper end  31 , lower end  32 , outer wall surface  33 , and inner wall surface  34  defining shroud bore  35 . Upper end  31  includes opening  36  in fluid communication with shroud bore  35 . Opening  36  defines shroud shoulder  38 . Lower end  32  of shroud  30  is secured to outer wall surface  22  of mandrel  21  by any device or method known in the art, including but not limited to threads (not shown). As shown in  FIG. 1 , a portion of outer wall surface  22  of mandrel  21 , shoulder  25 , and inner wall surface  34  of shroud  30  partially define chamber  39 . Seal  26  is disposed between outer wall surface  22  of mandrel  21  and inner wall surface  34  of shroud  30  to prevent leakage from chamber  39 . 
     An actuator shown as piston  40  is partially disposed within chamber  39 . In the embodiment of  FIGS. 1-2 , piston  40  comprises a sleeve member having lower end  41 , upper end  42 , outer wall surface  43  and inner wall surface  44 . Outer wall surface  43  is in sliding engagement with inner wall surface  34  of shroud  30  and inner wall surface  44  is in sliding engagement with outer wall surface  22  of mandrel  21 . Seals  48 ,  49  ( FIG. 2 ) reduce the likelihood of fluid leakage between the engagement of outer wall surface  43  with inner wall surface  34  and between the engagement of inner wall surface  44  with outer wall surface  22 . 
     Upper end  42  of piston  40  is secured to bearing assembly  60  through any device known in the art, including but not limited to threads (not shown). Bearing assembly  60  includes upper end  61 , lower end  62 , upper portion  63 , and lower portion  64 . Lower portion  64  is secured to upper end  42  of piston  40  and, in the embodiment of  FIGS. 1-2 , is secured to inner wall surface  82  of housing  85 , discussed in greater detail below. Suitable devices and methods for securing lower portion  64  to outer wall surface  22  include welding or threads (not shown). Upper portion  63  is in friction fit between inner wall surface  82  of housing  85  and outer wall surface  79  of rotating tubular  78 . Thus, upper portion  63  is not prohibited from rotating. Upper portion  63  and lower portion  64  are operatively associated with bearing  70  shown in  FIGS. 1-2  as ball bearings. 
     A lower portion of piston  40  is disposed within chamber  39 , a portion of upper end  42  of piston  40  is disposed outside of chamber  39  so as to facilitate connection to lower portion  64 , and a middle portion of piston  40  is disposed within opening  36  of upper end  31  of shroud  30 . Thus, chamber  39  is closed off by a portion of piston  40  being disposed within opening  36 . 
     In addition, because piston  40  is in sliding engagement with inner wall surface  34  of shroud  30  and outer wall surface  22  of mandrel  21 , chamber  39  is divided by piston  40  into two portions: upper portion  51  (shown in  FIG. 2 ) and lower portion  52 . Lower portion  52  can be at atmospheric pressure, can include a hydraulic fluid, a compressible gas or other fluid, or a compressible device, e.g., an elastomeric sleeve or spring, that is biased toward upper end  31  of shroud  30 , i.e., the arrangement shown in  FIG. 1  which is referred to as an expanded position because in this position, gap  95  is present between upper end  31  of shroud  30  and lower end  62  of bearing assembly  60 . 
     Gap  95  can have any dimensions desired or necessary to facilitate longitudinal or vertical movement of shroud  30  and, thus, mandrel  21  and drill bit  80 . As will be understood by persons skilled in the art, the size of gap  95  can be modified to allow greater, or lesser, vertical movement of shroud  30 . Vertical movement of shroud  30  and, thus, mandrel  21  and drill bit  80 , allows drill bit  80  to absorb shocks or other forces or stimuli that could otherwise cause drill bit  80  to bounce off of the object being drilled or cause the drill string to buckle or otherwise be damaged. Accordingly, vertical movement of shroud  30  and, thus, mandrel  21  and drill bit  80  facilitate maintaining engagement of drill bit  80  with the object being drilled, instead of bouncing off of the object, so that interruptions of drilling operations are minimized. 
     Bearing housing  85  is disposed over shroud  30  and includes outer wall surface  81  and inner wall surface  82  defining bore  83 . In the embodiment of  FIGS. 1-2 , upper portion  63  is in a friction fit relationship with inner wall surface  82  of bearing housing  85  and lower portion  64  is secured to inner wall surface  82  of bearing housing  85 . Lower portion  64  can be secured to inner wall surface  82  through any device or method in the art such as welding or threads. As piston  40  is secured to lower portion  64  and lower portion  64  is secured to inner wall surface  82  of housing  85  in the embodiment of  FIGS. 1-2 , piston  40  is not rotatable. Outer wall surface  33  of shroud  30 , however, is in sliding and rotatable engagement with inner wall surface  82  of bearing housing  85 . Further, as neither of shroud  30  nor mandrel  21  are fixed to piston  40  or housing  85 , shroud  30  and mandrel  21  are not prohibited from rotating. As a result, any residual rotation force imparted to shroud  30  or mandrel  21  by rotating tubular  78  can cause shroud  30  and mandrel  21  to rotate. 
     In one operation of a specific embodiment of the bearing assemblies as disclosed herein, the bearing assembly is disposed in a bearing housing and operatively associated with a rotatable tubular which is connected to a drill bit. The rotatable tubular is operatively associated with a motor that rotates the tubular. The mandrel and motor are included in work or tool string, also referred to as a drill string, and disposed within a wellbore so that an object within the wellbore can be drilled, milled, etc. 
     Upon reaching the desired location within the well, the motor is activated and the tubular rotated. As a result, the drill bit rotates and drills, mills, abrades, etc. an object within the wellbore. In certain embodiments, the object being drilled is the formation itself. In other embodiments, the object is a packer, cement, bridge plug, stuck tool, or other device or component disposed within the wellbore. 
     During drilling operations, a force can be encountered that tries to move the drill bit. The force can be initiated any source, including but not limited to, by the contour of the object being drilled or by a change in the density of the object being drilled. The bearing assembly includes a compensator member that can compensate or counteract an upward force acting on the drill bit and, thus, the tubular. In the embodiment of  FIGS. 1-2 , the compensator member comprises chamber  39 . As illustrated in  FIGS. 1-2 , when an upward force acts on drill bit  80 , drill bit  80  forces mandrel  21  and, thus, shroud  30  move upward. In so doing, mandrel  21  and shroud  30  slide along piston  40  and the compensator member, i.e., chamber  39 , moves from its expanded position ( FIG. 1 ) toward one of its plurality of compressed positions (one of which is shown in  FIG. 2 ). As a result, chamber  39  becomes energized, e.g., the fluid or gas, spring, elastomeric sleeve, and the like, disposed within lower portion  52  of chamber  39  is compressed, and the bearing assembly absorbs at least some of the upward force acting on the drill bit. 
     After the upward force acting on drill bit  80  dissipates, the energized compensator member moves from a compressed position toward the expanded position. Due to the absorption of the upward force, the amount of time, if any, that the drill bit is disengaged from the object being drilled is minimized. 
     In embodiments in which one or more of an elastomeric material, spring, or other biased member or device is disposed within chamber  39 , these biased member(s) or device(s) facilitate returning the compensator member toward the expanded position. 
     It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. For example, lower portion  64  can be in rotatable engagement with outer wall surface  82  of housing  85 . Moreover, gap  95  can be extended longitudinal to permit additional longitudinal movement of shroud  30  and, thus, mandrel  21 . In addition, piston  40  is not required to be piston or a sleeve piston as shown in  FIGS. 1-2 . Further, the bias provided by lower portion  52  of chamber  39  is not required to be provided by a fluid or elastomer, but can include any other biased member such as a coiled spring or Belleville washers and the like. Additionally, it is to be understood that the bearing assemblies disclosed and taught herein can be used in connection with any downhole tool in which one component is rotated and another remains stationary, including mills or abrading downhole tools used in cased wellbores. Moreover, it is to be understood that the term “wellbore” as used herein includes open-hole, cased, or any other type of wellbores. In addition, the use of the term “well” is to be understood to have the same meaning as “wellbore.” Moreover, in all of the embodiments discussed herein, upward, toward the surface of the well (not shown), is toward the top of Figures, and downward or downhole (the direction going away from the surface of the well) is toward the bottom of the Figures. However, it is to be understood that the tools may have their positions rotated in either direction any number of degrees. Accordingly, the tools can be used in any number of orientations easily determinable and adaptable to persons of ordinary skill in the art. Moreover, the mandrel and the shroud can be formed from a single unitary tubular member. Accordingly, the invention is therefore to be limited only by the scope of the appended claims.

Summary:
Bearing assemblies for downhole tools include a compensator member operatively associated with a slidable member and a bearing member. The slidable member is movable longitudinally relative to the bearing member. Such movement of slidable member occurs when a force acts upwardly on the downhole tool. Thus, the slidable member facilitates absorption of the upward force acting on the downhole tool. During movement of the slidable member, the compensator member is moved from its expanded position to one of its plurality of compressed positions. As a result, the compensator member becomes biased or further biased toward the expanded position. After the upward force dissipates, the compensator member releases some of its stored energy to move from a compressed position toward the expanded position. Longitudinal movement of the slidable member facilitates maintaining engagement of the downhole tool in its working position so that interruptions of operations are minimized.