Abstract:
A housing, mandrel and bearing assembly positionable in a wellbore includes a torque transmission member adapted to connect to a source of rotational torque (e.g. a downhole motor power output) and a tubular mandrel adapted to connect to a drill bit. A lower tubular housing is adapted to contain a lower bearing and catch sleeve assembly. The catch assembly is adapted to retain the mandrel in the lower housing if the mandrel breaks. An upper tubular housing contains an upper bearing and is adapted to connect to a housing of the downhole motor. A method of assembling the downhole housing, mandrel and bearing assembly is disclosed.

Description:
CLAIM OF PRIORITY 
       [0001]    This application is a continuation of and claims the benefit of priority to U.S. application Ser. No. 13/166,080, filed Jun. 22, 2011, incorporated herein by reference 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates generally to improvements in downhole drilling equipment and more particularly pertains to a new improved housing, mandrel and bearing assembly for transmitting power from a downhole drilling motor output to a drill bit. 
       BACKGROUND 
       [0003]    Downhole drilling motors have been used for many years in the drilling of oil and gas wells and other wells. In the usual mode of operation, the rotational power output shaft of the motor and the drill bit will rotate with respect to the housing of the motor. The housing, in turn, is connected to a conventional drill string composed of drill collars and sections of drill pipe. This drill string extends to the surface. Drilling fluid is pumped down through the drill string to the bottom of the hole and back up the annulus between the drill string and the wall of the bore hole. The drilling fluid cools the drill bit and removes the cuttings resulting from the drilling operation. In the instances where the downhole drilling motor is a hydraulic powered type, such as a positive displacement type motor, the drilling fluid also supplies the hydraulic power to operate the motor. See  FIG. 1 . 
         [0004]    Virtually all downhole drilling motors have three basic components: 
         [0005]    1. Motor section 
         [0006]    2. Vertical thrust bearings 
         [0007]    3. Radial bearings 
         [0008]    The bearings can be placed in a separate package or unit at the motor section and thus can be used on any type of motor (i.e., turbodrills, positive displacement motors, etc.). 
         [0009]    There are two basic types of downhole drilling motors: 
         [0010]    1. Turbodrills 
         [0011]    2. Positive displacement motors. 
         [0012]    Turbodrills utilize the momentum change of drilling fluid (i.e., mud) passing through curved turbine blades to provide power to turn the bit. Turbodrills turn at speeds of 600 to 3,000 rpm. Positive displacement motors have fixed volumetric displacement and their speed is directly proportional to the flow rate of the hydraulic power fluid. 
         [0013]    There are two basic types of positive displacement motors in use: 
         [0014]    1. Moineau motors have a helical rotor within the cavity of a stator which is connected to the housing of the motor. As the drilling fluid is pumped down through the motor, the fluid rotates the rotor. 
         [0015]    2. Vane motors have large volumetric displacement and therefore deliver higher torques at lower speeds. 
         [0016]    Thrust bearing failure in downhole motors is a problem because of high dynamic loads produced by the action of the bits and by drill string vibrations. One major oil company placed a recorder at the hole bottom and found that dynamic loads were often 50% higher than the applied bit weight. It was found on occasion that the bit bounced off the bottom and produced loads in excess of 120,000 pounds when drilling at an applied bit weight of 40,000 pounds. See discussion in U.S. Pat. No. 4,246,976, incorporated by reference. These high loads can cause rapid failure of the thrust bearings and bearing mandrels; consequently, these bearings must be greatly over-designed to operate in the hostile downhole environment. 
         [0017]    At least three types of thrust bearings have been used in downhole drilling motors: 
         [0018]    1. Rubber friction bearings 
         [0019]    2. Ball or roller bearings 
         [0020]    3. PDC Diamond Bearings. 
         [0021]    Radial bearings are required between the bearing housing and the rotating mandrel transmitting power from the motor power output to the bit. Radial bearings are usually subjected to lower loads than the thrust bearings and therefore have much longer life. The basic types of radial bearings used in downhole motors are: 
         [0022]    1. Marine bearings 
         [0023]    2. Roller or ball bearings 
         [0024]    3. Metal to metal carbide bearings. 
         [0025]    Most motors contain metal to metal radial bearings. These bearings are frequently lubricated by circulating mud through them. However, some bearing systems are sealed and are lubricated using lubricant (grease/oil) injected into the bearing by a hydraulic piston assembly. 
         [0026]    For a further discussion of downhole drilling motors and their operations, see U.S. Pat. Nos. 3,840,080; 4,246,976; 4,492,276; 5,495,900; 5,090,497; 6,183,226; 6,905,319 and Canadian Patent No. 2,058,080, incorporated by reference. 
       SUMMARY 
       [0027]    The present disclosure pertains to a new improved housing, mandrel and bearing assembly for transmitting power from a source of rotational torque (e.g. a downhole drilling motor output) to the drill bit. Rotational power=torque×RPM/5250. The invention provides a reduced length housing, bearing and mandrel assembly used in downhole drilling operations. 
         [0028]    Reduced length provides the following advantages: Ability to more effectively navigate around deviated sections of the wellbore by reducing friction caused as a section of the bottom hole assembly goes in and out of these deviated sections, which ultimately causes premature wear on internal components. Secondly, a reduced bit to bend allows the drill motor to build greater angle with less of an incorporated fix bend to get to desired lateral. This reduced degree bent housing ultimately reduces wear and tear on internal components. 
         [0029]    As used in this document, “tubular” refers to a generally cylindrical member with a longitudinal passage therethrough. The longitudinal passage may be formed therein or bored therethrough. 
         [0030]    A housing, mandrel and bearing assembly postionable in a wellbore is disclosed herein. In some implementations the assembly includes a torque transmission member (e.g. a flex shaft) having an upper end adapted to receive rotational torque power (e.g. from a downhole motor power output), a lower portion with a longitudinal cavity with an open lower end, at least a portion of said cavity having an internal connector, and a lower end having an external connector. The assembly further includes a tubular mandrel adapted at a lower end to connect to a drill bit, said tubular mandrel having an upper portion of the tubular mandrel with an external surface including a connector adapted to connect to the internal connector in the longitudinal cavity of the torque transmission member, a longitudinal passage through the mandrel from an upper end to the lower end, a shoulder disposed on a portion of the external surface of the tubular mandrel between the upper portion of the tubular mandrel and a lower portion of the tubular mandrel, said upper portion having a first outside diameter d1 and said lower portion having a second outside diameter d2, wherein the second outside diameter d2 is greater than the first outside diameter d1. The assembly further includes a lower tubular housing having a longitudinal passage from an upper end of the lower tubular housing to a lower end of the lower tubular housing, an upper portion having a connector, a shoulder disposed between the upper portion of the lower tubular housing and a lower portion of the lower tubular housing, said upper portion having a first inside diameter d3 and said lower portion having a second inside diameter d4, wherein the second inside diameter d4 is greater than the first inside diameter d3. The assembly further includes an upper tubular housing having a longitudinal passage from an upper end of the upper tubular housing to a lower end of the upper tubular housing, said longitudinal passage having a lower portion with an internal diameter adapted to receive an upper bearing, said lower portion of the longitudinal passage adapted to connect to the connector on the upper portion of the lower tubular housing. An upper bearing disposed in the longitudinal passage of the upper tubular housing contacting the lower end of the torque transmission member and a lower bearing disposed in the longitudinal passage of the lower tubular housing contacting the shoulder of the lower tubular housing. It will be understood by those skilled in the art that various types of thrust bearings and radial bearings, as known in the art, may be used in the practice of this invention. 
         [0031]    In some implementations the lower tubular housing has a longitudinal passage from an upper end of the lower tubular housing to a lower end of the lower tubular housing and an upper portion having a connector. The assembly further includes an upper tubular housing having a longitudinal passage from an upper end of the upper tubular housing to a lower end of the upper tubular housing, said longitudinal passage having a lower portion with an internal diameter adapted to receive an upper bearing, said lower portion of the longitudinal passage adapted to connect to the connector on the upper portion of the lower tubular housing. An upper bearing disposed in the longitudinal passage of the upper tubular housing contacting the lower end of the torque transmission member and a lower bearing disposed on the tubular mandrel and contacting the lower tubular housing. It will be understood by those skilled in the art that various types of thrust bearings and radial bearings, as known in the art, may be used in the practice of this invention 
         [0032]    In some implementations the assembly may further include an upper preload spring(s) adapted to keep the upper bearing in compression and a lower preload spring(s) adapted to keep the lower bearing in compression. 
         [0033]    In some implementations, the assembly may include a tubular catch sleeve disposed on a lower portion of the tubular mandrel. The tubular catch sleeve having an internal passageway adapted to contact the shoulder of the tubular mandrel and an exterior surface adapted to be received in the longitudinal passage of the lower housing. The tubular catch sleeve further includes an upper end having a connector adapted to connect to the lower bearing and a portion of the internal passageway in the tubular catch sleeve having a connector adapted to connect to a connector on a portion of the tubular mandrel. The connector in the internal passageway of the tubular catch sleeve is selected from the group consisting of hex, threaded, spline or pin connectors. 
         [0034]    In some implementations the downhole housing, mandrel and bearing assembly may further include at least one radial receptacle disposed in the lower portion of the tubular mandrel for receiving a locking pin to secure the tubular catch sleeve to the tubular mandrel. 
         [0035]    The assembly may further include a radial sleeve (e.g. radial bearing) disposed in the lower end of the lower housing around the tubular mandrel and a retaining member that retains the radial sleeve in the lower tubular housing, wherein an upper end of said radial sleeve is adapted to abut a lower end of the tubular catch sleeve when during drilling operations in a wellbore the tubular mandrel shears into an upper and lower portion, and the lower portion of the tubular mandrel is removed with the lower housing from the wellbore. 
         [0036]    As noted above, various types of radial and thrust bearings known in the art may be used in the practice of this invention. In some implementations the upper bearing comprises at least an upper race member, a lower race member, and a plurality of thrust balls disposed there between, wherein the upper race member has an upper end adapted to contact the torque transmission member (e.g. flex shaft) thereby securing the upper race to the torque transmission member such that the upper race member rotates with the torque transmission member when the torque transmission member and the tubular mandrel are rotated during drilling operations. The lower race member has a lower end adapted to contact an upper end of the lower tubular housing thereby securing the lower race to the lower tubular housing when the torque transmission member and the tubular mandrel are rotated during drilling operations. 
         [0037]    As noted above, various types of radial and thrust bearings known in the art may be used in the practice of this invention. In some implementations, the lower bearing comprises at least an upper race member, a lower race member, and a plurality of thrust balls disposed there between, wherein the lower race member of the lower bearing has a lower end that is adapted to contact the upper end of the catch assembly, thereby securing the lower race member to the tubular catch sleeve as the torque transmission member and the tubular mandrel are rotated during drilling operations. The upper race member of the lower bearing is adapted to contact the shoulder in the lower housing thereby securing the upper race member to the lower housing as the torque transmission member and the tubular mandrel are rotated during drilling operations. 
         [0038]    A method of assembling the downhole drilling assembly is disclosed. The method may include providing a tubular mandrel having a bit box at a lower end adapted to connect to a drill bit, said tubular mandrel having an upper portion of the tubular mandrel having a connector adapted to connect a rotatable torque transmission member to a source of rotational torque, a shoulder is disposed on a portion of the tubular mandrel between the upper portion of the tubular mandrel and a lower portion of the tubular mandrel. A radial sleeve is provided and slid over the tubular mandrel from the top and down over the mandrel until the radial sleeve is proximal to the upper end of the bit box. A tubular catch sleeve is then slid over the top of the tubular mandrel and down over the mandrel until a lower connector disposed in an internal passageway through the tubular catch sleeve and is positioned in contact with a connector of the mandrel, such that the tubular catch sleeve abuts the shoulder of the tubular mandrel and the tubular catch sleeve is secured to the tubular mandrel. A lower bearing is then slide over the tubular mandrel and positioned on a top of the tubular catch sleeve. 
         [0039]    A lower tubular housing is slid over the tubular mandrel and positioned such that a shoulder of the lower tubular housing contacts the upper end of the lower bearing. An upper bearing is then slid over the mandrel and positioned in contact with the lower tubular housing. A longitudinal cavity in a lower portion of a torque transmission member is positioned over the upper end of the tubular mandrel and connects the torque transmission member to the upper end of the tubular mandrel. An upper tubular housing is positioned over the torque transmission member and the upper tubular housing is connected to the lower tubular housing. 
         [0040]    In some implementations, before sliding the radial sleeve over the tubular mandrel, a retaining member is slid downwardly from the upper end of the tubular mandrel until it is proximal to an outer radius of the bit box at the lower end of the mandrel. Then the radial sleeve is slid over the tubular mandrel from the top until it is proximal to the retaining member and the retaining member is inserted into the lower end of the lower housing after sliding the lower tubular housing over the tubular mandrel. The retaining member is adapted to prevent the radial sleeve from sliding out the lower end of the lower tubular housing. Alternatively, after sliding the lower tubular housing over the tubular mandrel the retaining member (e.g. a split retaining ring) is inserted in a lower end of the lower tubular housing. 
         [0041]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0042]      FIG. 1  is a schematic illustrating a typical drilling system using a downhole drilling motor assembly. 
           [0043]      FIG. 2  is a cross-section of a prior art bearing and bearing mandrel assembly of a prior art downhole motor. 
           [0044]      FIG. 2A  is a cross-section of the bearing mandrel of the prior art assembly of  FIG. 2 . 
           [0045]      FIG. 3  is a cross-section of a housing, mandrel and bearing assembly of the present disclosure. 
           [0046]      FIG. 4  is an enlarged cross-section of an upper portion of the assembly of  FIG. 3 . 
           [0047]      FIG. 4A  is a cross-section illustrating a portion of a flex shaft of the assembly of  FIG. 4 . 
           [0048]      FIG. 4B  is a lateral cross-section of the flex shaft of  FIG. 4A  taken at section AA. 
           [0049]      FIG. 4C  is a cross-section of a bearing assembly member of  FIG. 4 . 
           [0050]      FIG. 4D  is a lateral cross-section of an upper end of the bearing assembly member of  FIG. 4  taken at Section AA. 
           [0051]      FIG. 4E  is a cross-section of the upper end of the lower housing of  FIG. 4 . 
           [0052]      FIG. 4F  is a lateral cross-section of the upper end of the lower housing of  FIG. 4  taken at section BB. 
           [0053]      FIG. 5  is a cross-section of a lower portion of the assembly of  FIG. 3 . 
           [0054]      FIG. 5A  is a cross-section illustrating a portion of a tubular mandrel and a catch assembly of  FIG. 5 . 
           [0055]      FIG. 5B  is a lateral cross-section of the tubular mandrel and the catch assembly of  FIG. 5A  taken at section CC of  FIG. 5 . 
           [0056]      FIG. 5C  is a cross-section of a lower bearing assembly of  FIG. 5 . 
           [0057]      FIG. 5D  is a lateral cross-section of the lower bearing assembly of  FIG. 5  taken at section DD. 
           [0058]      FIG. 6  is a cross-section illustrating the flow of drilling fluid down the drill string, through a downhole drilling motor, through the assembly of  FIG. 3 , out a bit and up the annulus of the wellbore. 
           [0059]      FIGS. 7A and 7B  are a cross-section illustrating the transfer of downward force and upward force from a drill string through the assembly of  FIG. 3  to a drill bit. 
           [0060]      FIGS. 8A to 8K  are partial cross-sections illustrating the sequential steps of assembling the housing, mandrel and bearing assembly of  FIG. 3 . 
           [0061]      FIGS. 9A and 9B  are a cross-section illustrating the assembly of  FIG. 3  before failure of the mandrel and after failure of the mandrel, wherein the catch sleeve and radial sleeve maintain the broken mandrel in the assembly. 
           [0062]      FIG. 10  is a cross-section of a prior art bearing used in a downhole motor. 
           [0063]      FIG. 11  is a cross-section of the upper housing and the upper and the lower bearing assemblies of the assembly of  FIG. 3 . 
       
    
    
       [0064]    Like reference symbols in the various drawings indicate like elements. 
       DETAILED DESCRIPTION 
       [0065]      FIG. 1  illustrates a simplified schematic of a drilling operation. A drill string  310  extends to the surface  348  where it is connected to a kelly  320 , mounted in a rotary table  330  of a drilling rig  340  to provide rotation to the drill string  310  when a downhole motor is not used to provide rotation to the bit. Alternatively, top drive systems are suspended in a rig derrick  342  and provide rotation directly to the drill string  310 . Drilling fluid  350  is pumped down through the drill string  310  to the bottom of the bore hole  360  and back up the annulus  362  between the drill string  310  and the wall of the bore hole  360 . The drilling fluid cools the drill bit  370  and removes the cuttings resulting from the drilling operation. 
         [0066]    In certain drilling situations, including but not limited to directional drilling, it is useful to use a downhole drilling motor assembly  301  to provide rotation to the bit. In such situations the downhole motor assembly  301  is inserted into the drill string  310  above the drill bit  370 . In the instances where the downhole drilling motor is a hydraulic type, such as a progressive cavity type motor, the drilling fluid  350  also supplies the hydraulic power to operate the motor. 
         [0067]    Various types of downhole drilling motors may be employed for the purpose of the invention such as electrical motors and hydraulic motors. Suitable hydraulic motors are turbines, vane motors and Moineau motors. See discussion in background section of this document about various types of drilling motors. 
         [0068]    A Moineau motor is very useful for application in the present invention since this type of motor is provided with a flexible connection between the rotor and power output shaft to compensate the eccentric movement of the rotor in the housing during operation of the motor. The invention is not restricted to the use of a Moineau motor. Any type of downhole motor known in the art may be used with the bearing mandrel and bearing assembly of the present invention. 
         [0069]      FIG. 2  illustrates a partial cross-section of a prior art downhole motor bearing assembly and bearing mandrel assembly. A downhole drilling motor (not shown) transmits power from the motor power output  491  to a bearing mandrel  490  that contacts radial bearings  493  and thrust bearings  492  housed in a bearing housing  494 . The mandrel&#39;s distal (lower) end  497  includes a bit box  498  connection for connection to a drill bit. The box connection results in assembly configurations that does not allow the mandrel to be assembled by insertion of the mandrel through the proximal (upper end)  499  of the bearing housing  494 . These prior art configurations have mandrels with stepped down profiles  496  on which a bearing spacer  495  makes contact.  FIG. 2A  illustrates one embodiment of a cross-section of the prior art bearing mandrel  490 . 
         [0070]    As weight is applied on the bit, a downward force DF will move down the drill string through the motor and to the mandrel  490 . As the mandrel  490  moves downward, bearing spacer  491  will push thrust bearings  492  down. Bearing spacer  495  will contact mandrel  490  at the step down  496 . When it does, it will provide weight to the bit to start drilling. An equal and opposite upward force UF will be exerted by the bottom of the bore hole below the bit. 
         [0071]      FIG. 3  illustrates a partial cross-section of a downhole motor assembly  301  that includes a tubular housing  302  that is preferably formed of steel. Disposed within the tubular housing  302  is a power unit having a stator  306  and a rotor  308  connected to a power output assembly  309 . The power output assembly  309  may be attached directly to the housing, mandrel and bearing assembly  100  according to one embodiment of the present invention or may include intermediate assemblies that ultimately connect to the housing, mandrel and bearing assembly  100  of the present invention. 
         [0072]    Referring to both  FIGS. 1 and 6 , in operation, drilling fluid  350  (also known in the art as drilling mud) is pumped down the interior of a drill string attached to the downhole drilling motor  301 . Drilling fluid  350  enters the drilling motor  301  having a pressure that is a combination of pressure imposed on the drilling fluid by pumps at the surface and the hydrostatic pressure of the above column of drilling fluid  350 . The pressurized fluid entering a cavity in the motor, in cooperation with the lobes of the stator  306  and the geometry of the stator  306  and rotor  308  causes the lobes of the stator to deform and the rotor to turn to allow the drilling fluid  350  to pass through the motor  301 . Drilling fluid  350  subsequently exits through ports (referred to in the art as jets) in drill bit  370  and travels up the annulus  362  between the bit  370 , the assembly  100  of the present invention and the downhole motor assembly  301  and drill string  310 , and is received at the surface  348  where it is captured and pumped down the drill string  310  again. 
         [0073]    Referring to  FIGS. 3 through 5D , therein is illustrated one embodiment of a downhole housing, mandrel and bearing assembly  100  of the present invention. The assembly has a torque transmission member (e.g. flex shaft  20 ) with an upper end  21  adapted to connect to a downhole motor power output  309 . The flex shaft has a lower portion  27  with a longitudinal cavity  23 , at least a portion of said cavity having female threads  24  and a lower end  25  having a male hex connector  26 . It will be understood that other forms of connectors such as spline connectors, pins and threaded connectors may be used. 
         [0074]    The assembly further includes a tubular mandrel  30  adapted at a lower end  31  to connect to a drill bit. The outer surface of the mandrel is generally cylindrical (except as noted herein) with an outer diameter that is smaller than the inner diameter of an upper housing  70  and a lower housing  60 , allowing the mandrel to rotate in the housings. The mandrel has an upper portion  33  with an outer surface containing male threads  34  adapted to connect to the female threads  24  of the lower portion  27  of the flex shaft  20 . The mandrel includes a longitudinal passage  32  through the mandrel from an upper end  35  to the lower end  31 . A shoulder  37  is disposed between the upper portion  33  having a first outside diameter d1 and a lower portion  36  having a second outside diameter d2, wherein the second outside diameter d2 is greater than the first outside diameter d1. A series of flats (see  FIGS. 5 and 5B ) are disposed on the outer surface in the lower portion  36  of the mandrel  30  to form a male hex connector  38  upon which a catch assembly  110  is positioned. It will be understood that the series of flats may be six as in a hex connector or may be 2 or more flats that are sized and configured to mate with an interior surface of the catch assembly  110  and connect the mandrel to the catch assembly such that the catch assembly rotates with the mandrel during drilling operations, and does not rotate about the mandrel. It will be understood that other forms of connectors such as spline connectors, pins and threaded connectors may be used. 
         [0075]    The assembly further includes a lower tubular housing  60  having a longitudinal passage  66  from an upper end  61  of the housing to a lower end  63  of the housing. The lower tubular housing includes an upper portion  65  having male threads  68  disposed on at least a portion of an external surface. A shoulder  67  is disposed between the upper portion  65  having a first inside diameter d3 and a lower portion  69  having a second inside diameter d4 wherein the second outside diameter d4 is greater than the first outside diameter d3. The upper end  61  further includes a male hex connector  62 . It will be understood that the male connector may include a series of 6 flats as in a hex connection or may include two or more flats wherein the flats are configured to mate with a female connector of a bearing race member  87  to be joined to the male connector  62 . It will be understood that other forms of connectors such as spline connectors, pins, and threaded connectors may be used. 
         [0076]    The assembly further includes an upper tubular housing  70  having a longitudinal passage  76  from an upper end  71  of the housing to a lower end  73  of the housing. The passage has a lower portion  74  with an internal diameter adapted to receive an upper bearing assembly  80 . The lower portion  74  of the internal passage  76  has female threads  75  disposed on at least a portion of an internal surface of the internal passageway, said threads adapted to connect to the male threads  68  of the upper portion of the lower tubular housing  60 . The upper housing further includes an upper portion  77  adapted to connect to a stator  302  of a downhole drilling motor  301 . 
         [0077]    The assembly  100  further includes an upper bearing assembly  80  (see  FIGS. 4 and 5 ) disposed in the internal passageway  76  of the upper housing  70 , wherein the upper bearing assembly has at least three bearing race members each having a generally cylindrical body. An upper end race member  82  has an upper end having an upper female hex box connector  83  (see  FIGS. 4C and 4D ) adapted to receive the male hex connector  26  of the flex shaft  20  (see  FIGS. 4A and 4B ). The hex connector secures the upper race  82  to the flex shaft such that the upper race rotates with the flex shaft and with the mandrel  30  as the flex shaft and mandrel are rotated in drilling operations. It will be understood that other forms of connectors such as spline connectors, pins and threaded connectors may be used. A middle race member  86  is disposed below the upper race member  82  and separated by a plurality of thrust balls  85 . The middle race section  86  is free to rotate with and about the mandrel during drilling operations. A lower end race member  87  is disposed below the middle race member  86 . The lower race member has a lower end that includes a lower female hex box connector  89  that secures the lower race member to the male hex connector  62  at the upper end  61  of the lower tubular housing  60  (see  FIGS. 4E and 4F ). It will be understood that other forms of connectors such as spline connectors, pins and threaded connectors may be used. Therefore, the lower end race member  87  is fixed to the lower housing  60  and does not rotate with the mandrel  30 . A plurality of thrust balls  85  are disposed between the middle race member  86  and the lower race member  87 . 
         [0078]    The assembly further includes a lower bearing assembly  90  disposed in the internal passageway  66  of the lower housing  60 , wherein the bearing assembly has an upper race member  92  that is adapted to be received in the shoulder  67  of lower housing  60 . Upper race member  92  may rotate about the mandrel during rotation of the mandrel during drilling operations. A middle race member  96  is disposed below the upper end race member  92  and separated by a plurality of thrust balls  95  (see  FIGS. 5D and 5C ). The middle race section  96  is free to rotate with and about the mandrel during drilling operations. A lower end race member  93  is disposed below the middle race member  96 . The lower race member has a lower end that includes a lower female hex box connector  94  that secures the lower race member to a male hex connector  116  at the upper end of a catch assembly  110  (see  FIGS. 5A and 5B ). It will be understood that other forms of connectors such as spline connectors, pins and threaded connectors may be used. Therefore, the lower race member  93  is fixed to the catch assembly  110  and rotates with the mandrel  30 . The catch assembly  110  is secured to the mandrel as described later herein. Therefore, the race member  93  rotates with the mandrel. A plurality of thrust balls  85  are disposed between the middle race member  96  and the lower race member  93  (see  FIGS. 5C and 5D ). 
         [0079]    The assembly further includes an upper preload spring assembly  130  disposed in an exterior circumferential recess  29  in the lower portion  27  of the flex shaft  20 . The spring assembly has a first resilient member  131  with a first end contacting a ledge  28  in recess  29  and a second end contacting a first end of a spacer member  132 ; and a second resilient member  133  with a first end contacting a second end of spacer member  132  and a second end contacting the upper end of the upper bearing assembly member  82 . 
         [0080]    The assembly further includes a lower preload spring assembly  140  disposed in an exterior circumferential recess  119  in catch sleeve  110 . The spring assembly has a first resilient member  141  with a first end contacting a ledge  113  in recess  119  and a second end contacting a first end of a spacer member  142 ; and a second resilient member  143  with a first end contacting a second end of spacer member  142  and a second end contacting the lower end  97  of the lower bearing assembly  90 . 
         [0081]    The assembly further includes a radial sleeve  120  disposed in the lower end  63  of the lower housing  60 . The radial sleeve  120  is locked within the lower housing by vertical dowel pin  124  that maintains the radial sleeve rotating with the lower housing around the mandrel during motor operation. The radial sleeve is held within the housing  60  with the retaining ring  122 . This retaining ring  122  serves to hold the radial sleeve within housing  60  and extract the lower mandrel  30  and catch sleeve  110  in the event of a fracture within the upper section of the mandrel (see  FIGS. 9A and 9B ). 
         [0082]    The assembly further includes a catch sleeve  110  having an internal passageway  112  adapted to contact the shoulder  37  of the tubular mandrel. The catch sleeve further includes an exterior surface adapted to be received in longitudinal passageway  66  of lower housing  60 , and an upper end  115  having an upper male hex connector  116  adapted to receive the female hex connector  94  of the bearing  90 . As illustrated in  FIGS. 5 ,  5 A and  5 B, the tubular mandrel  30  has a portion of the exterior surface wherein the outer perimeter is configured as a hexagon in the portion of the mandrel on which the catch sleeve  110  is disposed. The catch sleeve passageway has an internal surface wherein the perimeter is configured as a hexagon adapted to mate with the outer surface of the tubular mandrel. It will be understood that other forms of connectors such as spline connectors, pins and threaded connectors may be used. When the catch sleeve  110  is in position the catch sleeve will move with the rotating mandrel during drilling operations, not about the mandrel. The assembly  100  further includes at least two radial receptacles  39  disposed in the lower portion  36  of the tubular mandrel, each of said receptacles is adapted to receive a locking pin  41 . The pins secure the catch assembly to the mandrel. 
         [0083]    The unique design of the assembly  100  provides many advantages over the prior art designs. For example, if the mandrel  30  were to break above the catch sleeve the mandrel can be removed from the wellbore  360  together with the upper  70  and lower  60  housings using the drill string  310 . This configuration is desirable as it prevents the undesirable situation of leaving a portion of broken mandrel  30  and drill bit  370  in the wellbore, which must be retrieved in a difficult operation often referred to in the art as “fishing.” Due to the unique configuration of the assembly of the present invention the broken mandrel  30  and drill bit  370  would be pulled from the wellbore using the drill string. Because of the configuration of the catch sleeve  110 , the mandrel  30  and lower housing  60 , the mandrel will not fall out of the lower housing  60  and be left in the wellbore  360 . 
         [0084]    Referring now to  FIG. 7A , wherein the transfer of downward force DF through the assembly  100  to the bit  370  during drilling operations is illustrated. Downward force DF is transmitted through the upper housing  70  and lower housing  60  through the lower bearing  90  and catch sleeve  110  to the shoulder  37  of the mandrel  30  and through the mandrel to the bit  370 . When pulling the drill string  310  from the hole, removal force RF is transferred through the upper bearing  80  to the flex shaft  20  which is connected to the mandrel  30 , and through the mandrel  30  to the bit  370  (see  FIG. 7B ). 
         [0085]      FIGS. 8A to 8K  are partial cross-sections illustrating the sequential steps of assembling the housing, mandrel and bearing assembly of  FIG. 3 . In step  1 , the mandrel  30 , as illustrated in  FIGS. 3 ,  4  and  5 , and described above, is provided. A retaining ring  122  is slid downward from the top of the mandrel  30  until it rests on an outer radius of the bit box (See  FIG. 8A ). 
         [0086]    In step  2 , a radial sleeve  120  is slid over the mandrel from the top until it rests on the retaining ring (see  FIG. 8A ). 
         [0087]    In step  3  (see  FIG. 8B ), a catch sleeve  110  is slid over the top of the mandrel until the lower female hex connector is positioned over the male hex connector of the mandrel and the catch sleeve abuts the shoulder  37  of the mandrel. 
         [0088]    In step  4  (see  FIG. 8B ), locking pins  41  are inserted into receptacles  39  in mandrel  30  to secure the catch sleeve to the mandrel. 
         [0089]    In step  5  (see  FIG. 8C ), one or more lower preload spring assemblies  140  are inserted onto the catch sleeve and positioned in recess  119  of the catch assembly  110 . 
         [0090]    In step  6  (see  FIG. 8D ), lower bearing assembly  90  is slid over the mandrel and positioned on the top of catch sleeve  110 . 
         [0091]    In step  7  (see  FIG. 8E ), lower housing  60  is slid over the mandrel and positioned such that a ledge contacts the upper end of the lower bearing assembly. Retaining ring  122  is inserted into the lower end of the lower housing. The retaining ring  122  keeps the radial sleeve  120  from falling out the lower end of the housing  60 . 
         [0092]    In step  8  (see  FIG. 8F ), upper bearing assembly  80  is slid over the mandrel and positioned with the lower female hex connector of the bearing assembly onto the upper male hex connector of the lower housing. 
         [0093]    In step  9  (see  FIG. 8G ), preload spring assembly  130  is slid over the mandrel and positioned adjacent the bearing assembly  80  to bias the bearing assembly members together and in contact with the housing  60 . 
         [0094]    In step  10  (see  FIG. 8G ), flex shaft  20  is positioned over the upper end of the mandrel and threadedly connected to the upper end of the mandrel. 
         [0095]    In step  11  (see  FIG. 8H ), upper housing  70  is positioned over the flex shaft  20  and threadedly connected to lower housing  60 . 
         [0096]    In step  12  (see  FIG. 8I ), the power output  309  and rotor  308  of downhole motor  301  is connected to the flex shaft  20 . 
         [0097]    In step  13  (see  FIG. 8J ), the stator  306  and motor housing  302  is positioned over the rotor and upper end of the flex shaft. 
         [0098]    In step  14  (see  FIG. 8K ), the upper end of motor housing  302  is connected to a cross-over sub that is connected to drill string  310 . 
         [0099]    Referring to  FIG. 10 , wherein a cross-section of a prior art bearing system  580  inside housing  560  is illustrated. The bearing races are formed from an inside member  582  and an outside member  584 . This assembly requires more machining and assembly time than the bearing assemblies  80  and  90  of the present invention (see  FIG. 11 ). Bearing assemblies  80  and  90  are separated by housing  60 . 
         [0100]    Bearing races  82 ,  86 ,  87 ,  92 ,  96 , and  93  are a single construction saving time and money in manufacturing an assembly when compared to prior art assembly  560 . 
         [0101]    It will be understood that threaded and hex connectors have been disclosed and described in the drawings and specifications; the present invention may use various types of connectors. 
         [0102]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention.