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[0001]    This invention relates to equipment used on a drillstring to reduce the rotational friction between the rotating drillstring and the borehole wall. The said equipment is particularly useful in the oil, gas and mining industries especially, but not exclusively, for drilling of high angle, horizontal and extended reach wells.  
         BACKGROUND OF THE INVENTION  
         [0002]    In order to drill a well, a drillstring is assembled above a drill bit. The drillstring is used to transfer the rotary motion from the surface equipment to the drill bit, thereby causing the drill bit to rotate and penetrate the sub surface formation. However, the torque required at surface to rotate the drill bit is substantially increased due to the friction caused by contact between the drillstring and the wall of the borehole. Furthermore, the rotational contact between the drillstring and the borehole wall causes wear on drillstring as well as causing damage and wear to the steel cased section of the borehole wall. Conventionally, the drilling process also involves pumping of drilling fluid down the bore through the inside diameter of the drillstring to improve the drilling performance of the bit, to assist with cooling and lubrication of the bit as well as providing the means to transfer the drill cuttings to surface. Conveyance of the drill cuttings is a function of well depth, well profile, shape and size of drill cuttings, mechanical properties of the drilling fluid and the capacity of surface mud pumps.  
           [0003]    Conventional friction reducing drill pipe components are shown, for example, in UK Patent nos. 2299598 and 2304763.  
         SUMMARY OF THE INVENTION  
         [0004]    As those skilled in the art will appreciate, an accumulation of drill cuttings in the well bore is a major obstacle in any drilling operation as it can increase downhole friction, thus increasing the amount of torque required, and in some instances can lead to the drillstring getting stuck in hole. For these reasons, efficient drilling fluid circulation is essential.  
           [0005]    According to the present invention, there is provided a component for forming part of a drill string, the component comprising a mandrel having couplings for connection with the drill string, a bearing member mounted on the mandrel and a sleeve member mounted on the bearing member.  
           [0006]    Preferably, the bearing member is an inner bearing member, and the sleeve member is an outer sleeve member.  
           [0007]    Preferably, the component further comprises first and second retaining members for retaining the inner bearing member, and the outer sleeve member on the mandrel. Typically, the retaining members also prevent longitudinal movement of the inner bearing member, and the outer sleeve member, on the mandrel. Typically, at least one of the first and second retaining members is removable or retractable from the mandrel, and more preferably, is removable or retractable from the mandrel to permit the inner bearing member, and the outer sleeve member, to be removed from the mandrel. Most preferably, one of the first and second retaining members is removable from the mandrel by removing one or more fixture devices, and typically, the other of the first and second retaining members is integral with the mandrel.  
           [0008]    Preferably, the inner bearing member is provided in at least two portions, the portions preferably when brought together forming a substantially tubular member. More preferably, there are two portions, each portion comprising a half cylindrical member. Preferably, the at least two portions are mounted in a recess of the mandrel, the recess comprising a reduced diameter portion with reference to the diameter of the drill string, and particularly to the diameter of the joints of the drill string. Typically, the outer sleeve member is arranged coaxially with the inner bearing member in use of the component, and preferably, a selective locking mechanism is provided to prevent relative rotational movement between the inner bearing member and the outer sleeve member in use of the component. The selective locking mechanism may comprise a first locking device provided on the inner bearing member and a second locking device provided on the outer sleeve member. Preferably, the first locking device is provided on the outer surface of the inner bearing member and the second locking device is provided on the inner surface of the outer sleeve member. More preferably, the first and second locking devices interact with one another to provide the locking action. Typically, the first and second locking devices are formations provided on the respective surfaces of the inner bearing member and outer sleeve member, and more preferably, the formations are arranged longitudinally at least partly along the length of the respective inner bearing member and outer sleeve member. Optionally, a third locking device, which may be in the form of a key, may be provided to interact with the first and second locking devices to provide the locking action.  
           [0009]    Preferably, the component further comprises a second inner bearing member which is typically provided in at least two portions, the portions preferably when brought together forming a substantially tubular member. More preferably, there are two portions, each portion comprising a half cylindrical member. Preferably, the at least two portions are mounted in the same recess of the mandrel that the two portions of the first inner bearing member are mounted. Preferably, the first and second bearing members each comprise a device which separates the outer sleeve member from the mandrel. Typically the separating device is a flange.  
           [0010]    Preferably, the first inner bearing member is capable of rotation with respect to the second inner bearing member.  
           [0011]    Preferably, a selective locking mechanism is provided to prevent relative rotational movement between the second inner bearing member and one of the first and second retaining members in use of the component. The selective locking mechanism may comprise a first locking device provided on the second inner bearing member and a second locking device provided on the said one of the retaining members. Preferably, the first locking device is provided on the outer surface of the second inner bearing member and the second locking device is provided on the inner surface of the said one of the retaining members. More preferably, the first and second locking devices interact with one another to provide the locking action, Typically, the first and second locking devices are formations provided on the respective surfaces of the second inner bearing member and said one of the retaining members, and more preferably, the formations are arranged longitudinally at least partly along the length of the respective second inner bearing member and said one of the retaining members. Optionally, a third locking device, which may be in the form of a key, is provided to interact with the first and second locking devices to provide the locking action.  
           [0012]    Preferably, the outer sleeve member is a one-piece outer sleeve member. Preferably, the mandrel is a one-piece or unitary mandrel body.  
           [0013]    The component may be dismantled by removing one of the retaining devices and removing, if present, the second inner bearing member, and then removing the outer sleeve member over one end of the mandrel, and then removing the first inner bearing member. A section of the mandrel directly above and/or below the first and/or second retaining member may be spirally milled and fluted to provide integral spiral blades.  
           [0014]    Preferably, the mandrel, stops, outer sleeve member, inner bearing member(s) and the retaining devices are made of steel, but the inner bearing member(s) and/or outer sleeve member may also be made from high temperature/high impact/wear resistant ceramics, such as alumina ceramic, polymers or metals other than steel. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:  
         [0016]    [0016]FIG. 1 shows a cross sectional view of a mandrel body forming part of a first embodiment of the present invention;  
         [0017]    [0017]FIG. 2 shows a side view of the mandrel body of FIG. 1 provided with an outer sleeve member and a pair of inner bearing members together forming the first embodiment of the present invention;  
         [0018]    [0018]FIG. 3 shows a cross-sectional plan view through section  3 - 3  of the mandrel body, outer sleeve member and inner bearing member of FIG. 2;  
         [0019]    [0019]FIG. 4 shows a cross-sectional plan view through section  4 - 4  of the mandrel body, and second retaining member of FIG. 2;  
         [0020]    [0020]FIG. 5 shows a cross sectional view of a mandrel body forming part of a second embodiment of the present invention;  
         [0021]    [0021]FIG. 6 shows a side view of the mandrel body of FIG. 5;  
         [0022]    [0022]FIG. 7 shows a plan view through section C-C of the mandrel body of FIG. 6;  
         [0023]    [0023]FIG. 8 is a cross sectional view of one of a pair of first inner bearing members for mounting on the mandrel body of FIG. 5;  
         [0024]    [0024]FIG. 9 is a side view of the one first inner bearing member of FIG. 8;  
         [0025]    [0025]FIG. 10 is a first end view of the one first inner bearing member of FIG. 8;  
         [0026]    [0026]FIG. 11 is a second end view of the one first inner bearing member of FIG. 8;  
         [0027]    [0027]FIG. 12 is a side view of one of a pair of second inner bearing members for mounting on the mandrel body of FIG. 5;  
         [0028]    [0028]FIG. 13 is a cross sectional view of the one second inner bearing member of FIG. 12;  
         [0029]    [0029]FIG. 14 is a first end view of the one second inner bearing member of FIG. 12;  
         [0030]    [0030]FIG. 15 is a second end view of the one second inner bearing member of FIG. 12;  
         [0031]    [0031]FIG. 16 is a side view of a locking ring for mounting on the mandrel body of FIG. 5;  
         [0032]    [0032]FIG. 17 is a first end view of the locking ring of FIG. 16;  
         [0033]    [0033]FIG. 18 is a second end view of the locking ring of FIG. 16;  
         [0034]    [0034]FIG. 19 is a side view of an outer sleeve for mounting on the mandrel body of FIG. 5;  
         [0035]    [0035]FIG. 20 is a side view of a cross section through the outer sleeve of FIG. 19;  
         [0036]    [0036]FIG. 21 is a first end view of the outer sleeve of FIG. 19;  
         [0037]    [0037]FIG. 22 is a side view of a rectangular longitudinal groove formed on the inner bore of the outer sleeve of FIG. 19;  
         [0038]    [0038]FIG. 23 is a plan view of a cross section through the outer sleeve of FIG. 19; and  
         [0039]    [0039]FIG. 24 shows a side view of a cross section through the mandrel body of FIG. 5 provided with an outer sleeve member and a pair of first inner bearing members and a pair of second inner bearing members together forming the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0040]    A mandrel body  5  forming part of a first embodiment of a friction reducing drill string component  1  in accordance with the present invention is shown in FIG. 1. The mandrel body  5  comprises a male pin end  10  and female box end  11 , both of which  10 ,  11  are provided with standard API screw threads to permit the mandrel body  5  to be included in a drill string (not shown). The mandrel body  5  further comprises a mandrel bore  12 , mandrel body upper neck  13   a,  mandrel body lower neck  13   b  and a mandrel body recess  13   c,  a threaded bore  14  and an integral first stop  15  Accordingly, the mandrel body  5  is a one-piece component. It should be noted that the first stop  15  may be lengthened, and also that the first stop may be spirally milled on it&#39;s outer surface to form integral blades proposed for hydra-mechanical and hydra-dynamic drill cuttings bed removal.  
         [0041]    [0041]FIG. 2 illustrates the assembly arrangement of an outer sleeve  21 , inner bearing members  20  and retaining systems  15 ,  16  in place on the mandrel body  5  to form the friction reducing drill string component  1  in accordance with the present invention. Also shown in FIG. 2 are a removable second stop  16  having circular access ports  17 , a one piece outer sleeve  18  which is preferably provided with straight or spiral blades  21 , a two-piece inner sleeve  20  flanged at it&#39;s lower end, longitudinal dove-tailed grooves  22   a  formed on the inner surface of the outer sleeve  18 , and longitudinal dove-tailed integral splines  22   b  formed on the outer surface of the inner bearing members  20 . The second stop  16  is in the form of an annular ring  16 . It should be noted that the dove-tailed splines  22   b  and grooves  22   a  preferably do not extend the entire length of the sleeves.  
         [0042]    As shown in FIGS. 2 and 3, the inner bearing members  20  are formed from two half-cylinder shaped inner bearings  20   a  and  20   b.    
         [0043]    In order to assemble the friction reducing drill string component  1 , the inner bearing members  20   a ,  20   b  and are positioned around the mandrel body  5  within the mandrel body recess  13   c,  such that the flange is arranged at the lower in use end of the component  1 .  
         [0044]    Thereafter, the one piece outer sleeve  18  is slid over the mandrel body upper neck  13   a.  After lining up the dove-tailed grooves  22   a  with the dove-tailed splines  22   b,  outer sleeve  18  will slide over the inner bearing members  20  in a downward sliding manner until the lower end of the outer sleeve is rests directly on top of the flanged end of the inner bearing members  20  The second stop  16  is then slid over the mandrel body upper neck  13   a  and is lowered downwardly toward the outer sleeve  18  until each access port  17  lines up with it&#39;s corresponding threaded bore  14 . The second stop  16  is then secured on mandrel body upper neck  13   a  as illustrated in FIG. 4.  
         [0045]    As shown in FIG. 3, the dove-tailed fitting arrangement of the outer sleeve  18  over the inner bearing members  20  prevents relative circumferential movement between the inner bearing members  20  and the outer sleeve  18 .  
         [0046]    As shown in FIG. 4, the second stop  16  is secured to the mandrel body upper neck  13   a  by means of a number of threaded retaining bolts  24  protruding through the respective circular access port  17 , fitted and screwed into each corresponding threaded bore  14  and tightened to a specified torque A locking clip  26  is then fitted into a locking clip recess  25  on each circular access port  17 , this being a secondary safety measure to prevent the threaded locking bolt  24  from accidental unwinding and dislodgement.  
         [0047]    When the outer sleeve  18  and inner bearing members  20   a,    20   b  are mounted on the mandrel body  5 , and secured in position by the retaining devices  16 ,  15 , the outside diameter of the outer sleeve  18  is sufficiently greater than the outside diameter of the drill pipe tool joints (not shown) which form the rest of the drill string. In this manner, when the friction reducing drill string component  1  is installed in the drill string, only the outer surface of the outer sleeve  18  will contact the wellbore wall and the drill pipe tool joint is not in contact with the wellbore wall. During the rotary drilling operation, the outer sleeve  18  is in contact with the bore wall and does not rotate whilst the mandrel body  5  rotates with the drillstring. Therefore there will be no rotational contact between the drillstring and the wellbore wall, and this ensures the protection of drillstring as well as the steel cased section of the well against damage and wear. On the other hand, the outside diameter of the mandrel body recess  13   c  here referred to as ‘d’ is smaller than the outside diameter of drill pipe tool joint here referred to as ‘D’. Hence, in rotary drilling mode the rotary surface contact circumference of the drillstring is effectively reduced by π×(D−d). In other words, the torque or friction created is reduced In addition, the first embodiment of the component  1  has the advantage that the pair of inner bearing members  20  can be formed from a different, and preferably less expensive material, than the outer sleeve  18  and in this manner, the inner bearing members  20  can be designed to be sacrificed and replaced when required.  
         [0048]    Referring now to FIGS.  5  to  24 , a mandrel body  105  forming part of a second embodiment of a friction reducing drill string component  100  in accordance with the present invention is shown in FIG. 5. The mandrel body  105  again comprises a male pin end  110  and female box end  111  in a similar fashion as the mandrel  5 . The mandrel body  105  also comprises a mandrel bore  112 , mandrel body upper neck  113   a,  mandrel body lower neck  113   b  and a mandrel body recess  113   c,  a number of threaded bores  114  and an integral first stop  115 . It will be noted that the integral first stop  115  formed in the mandrel body  105  is above the mandrel body recess  113   c,  whereas the integral first stop  15  formed in the mandrel body  5  of the first embodiment is below the mandrel body recess  113   c.  Accordingly, the mandrel body  105  is again a one-piece component. The first stop  115  is spirally milled on its outer surface to form integral blades  150  for hydra-mechanical and hydra-dynamic drill cuttings bed removal.  
         [0049]    [0049]FIG. 24 illustrates the assembly arrangement of an outer sleeve  121 , a pair of first inner bearing members  120  flanged at their upper ends, a pair of second inner bearing members  155  flanged at their upper ends and retaining systems  115 ,  116  in place on the mandrel body  105  to form the friction reducing drill string component  100  in accordance with the second aspect of the present invention. Also shown in FIG. 24 is a removable second stop  116  having circular access ports  117  (shown in FIGS.  16  to  18 ), a one piece outer sleeve  118  which is provided with spiral, blades  121 , longitudinal rectangular shaped grooves  122   a  formed on the inner surface of the outer sleeve  118 , and longitudinal rectangular grooves  122   b  formed on the outer surface of the first pair of inner bearing members  120 , and longitudinal rectangular grooves  122   c  formed on the outer surface of the second pair of inner bearing members  155 . The second stop  116  is in the form of an annular ring  116 , and is provided with longitudinal rectangular grooves  122   d  formed on its outer surface. It should also be noted that the rectangular grooves  122   a,    122   b,    122   c  and  122   d  preferably do not extend the entire length of the respective outer sleeve  118 , first pair of inner bearing members  120 , second pair of inner bearing members  155  and second stop  116 .  
         [0050]    As shown in FIGS.  8  to  11 , the first pair of inner bearing members  120  are formed from two half-cylinder shaped inner bearings  120 , and as shown in FIGS.  12  to  15 , the second pair of inner bearing members  155  are formed from two half-cylinder shaped inner bearings  155 .  
         [0051]    In order to assemble the friction reducing drill string component  100 , the first pair of inner bearing members  120  are positioned around the mandrel body  105  within the mandrel body recess  113   c,  such that the flange is arranged at the upper in use end of the component  100 . A rectangular longitudinal key (not shown) is then placed into each groove  122   b  of the first pair of inner bearing members  120 .  
         [0052]    Thereafter, the one piece outer sleeve  118  is slid over the mandrel body lower neck  113   b.  After lining up the rectangular grooves  122   a  with the rectangular longitudinal keys, the outer sleeve  118  is slid over the inner bearing members  120  in an upward sliding manner until the upper end of the outer sleeve  118  rests directly against the underside of the flanged end of the first pair of inner bearing members  120 .  
         [0053]    The second pair of inner bearing members  155  are then positioned around the mandrel body  105  within what is left open of the mandrel body recess  113   c , such that the flange of the second pair of inner bearing members  155  is arranged at the lower end of the outer sleeve  118  and the first pair of inner bearing members  120 .  
         [0054]    A rectangular longitudinal key (not shown) is then placed into each groove  122   c  of the second pair of inner bearing members  155 .  
         [0055]    The second stop  116  is then slid over the mandrel body lower neck  113   b  and, after lining up the rectangular grooves  122   d  with the rectangular longitudinal keys, the second stop  116  is slid over the second pair of inner bearing members  155  in an upward sliding manner toward the flange of the second pair of inner bearing members  155  until each access port  117  lines up with it&#39;s corresponding threaded bore  114 . The second stop  116  is then secured on mandrel body lower neck  113   b  with suitable threaded retaining bolts (not shown) and associated locking clips (not shown).  
         [0056]    As shown in FIG. 5, the mandrel body  115  is provided with a further circumferential groove or recess  113   d,  around which a metal circlip (not shown) may be fitted. This further metal circlip and recess  113   d  provides a tertiary safety mechanism to prevent the dislodgement of the second retaining system (in the form of the second stop  116 ) if the primary safety mechanism (in the form of the bolts) and secondary safety mechanism (in the form of the associated locking clips) were to fail.  
         [0057]    The rectangular fitting arrangement between the grooves  122   a  of the outer sleeve  118 , the rectangular keys and the grooves  122   b  of the first pair of inner bearing members  120  prevents relative circumferential movement between the first pair of inner bearing members  120  and the outer sleeve  118 . Also, the rectangular fitting arrangement between the grooves  122   d  of the second stop  116 , the rectangular keys and the grooves  122   c  of the second pair of inner bearing members  155  prevents relative circumferential movement between the second pair of inner bearing members  155  and the second stop  116 .  
         [0058]    Accordingly, the second embodiment of the component  100  has the advantage that the first  120  and second  155  pairs of inner bearing members can be formed from a different, and preferably less expensive material, than the outer sleeve  118  and in this manner, the first  120  and second  155  pairs of inner bearing members can be designed to be sacrificed and replaced when required. In addition, when the outer sleeve  121  contacts the wellbore wall, no portion of the mandrel  115  is in direct contact with the outer sleeve  118 , and since the outer sleeve  118  is preferably formed from a relatively hard wearing material, the lifespan of the mandrel body  115  is increased. In addition, it is only the first  120  and second  155  pairs of inner bearing members that provide the bearing surfaces with the mandrel  115 , and so the material from which they are formed can be chosen to be less likely to damage the mandrel body  115 . In other words, it is only the first  120  and second  155  pairs of inner bearing members that are in direct contact with the mandrel body  115  and the outer sleeve  121  is not in direct contact with the mandrel body  115 .  
         [0059]    Thus, the embodiments of the present invention provide a robust, fail safe mechanical, non-rotating stand-off on the drillstring so as to remove the rotational contact between the drillstring and the bore wall and therefore prevent damage or wear of drillstring and the cased section of the bore. The embodiments described herein also provide a means to reduce the rotational friction surface area of the drillstring, and therefore reduce the torque required to rotate the drill string at the surface. Furthermore, the embodiments described herein also provide a combined hydra-mechanical and hydra-dynamic means of agitating the cuttings bed in order to improve the drilling fluid circulation.  
         [0060]    Furthermore, the embodiments of the present invention provide the advantage that they allow for removal of the outer sleeve  18 ;  118  without dismantling of the mandrel body  5 ;  115  or outer sleeve  18 ;  118  or heat expansion of the outer sleeve  18 ;  118  and yet allow the effective inside diameter of the rotatable part of the component  1 ;  100  that is the combination of the inner bearing member  20 ;  120  and the outer sleeve  18 ;  118  to be smaller than the outside diameter of the upper and lower ends of the mandrel body  5 ;  115 , hence providing a smaller bearing surface area between the inner bearing member  20 ;  120  and the mandrel body  5 ;  115  which results in lowered friction and torque. These features make the embodiments of the present invention a fail safe, easy to disassemble and re-assemble drillstring component  1 ;  100  which reduces drilling torque due to the reduced friction surface area between the rotatable part of the component  1 ;  100  (the combination of the inner bearing member  20 ;  120  and the outer sleeve  18 ;  118 ) and the mandrel body  5 ;  115 .  
         [0061]    Modifications and improvements may be made to the embodiments hereinbefore described without departing from the scope of the invention. For instance, the mandrel body  5 ;  115  may take the form of a full length (range  1  being 20 foot in length, range  2  being 31 foot in length or range  3  being 40 foot in length) drillpipe (not shown), or may take the form of drillpipe pup joints (not shown) of any length.

Summary:
A friction and/or torque reducing drillstring component has a one-piece mandrel body  5  with a mandrel body recess  13   c  considerably smaller than mandrel upper neck  13   a  and mandrel body lower neck  13   b,  dressed with an outer sleeve  18  which is interlocked with a two-piece inner bearing  20  through several integral dove-tailed splines  22   b  and grooves  22   a.  The combination of the outer sleeve  18  and inner bearing  20  is restricted in vertical movement over the said mandrel body  5  by an integral, optionally spirally, bladed first stop  15  and a removable second stop  16.  The removable second stop  16  is locked onto the mandrel body upper neck  13   a  by means of threaded retaining bolts  24.  Once the second stop  16  is removed, the one-piece outer sleeve  18  is retractable over the mandrel body upper neck  13   a  to allow the removal of the two-piece inner bearing  20.  A second inner bearing  155  may also be provided.