Abstract:
Methods and apparatus for rotating a stripper assembly in use with a rotating drilling head. A drive system is disposed external to the rotating drilling head and generates rotational motion to match the rotation of a drillstring running through the rotating drilling head. A connection transfers rotational motion from the drive system to the stripper assembly. In one embodiment, the drive system comprises a housing disposed about the drillstring and a one or more contact members connected to said housing and operable to contact the drillstring. One or more biasing members urge the contact members into contact with the drillstring so as to transfer rotational motion from the drillstring to the housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The present application claims the benefit of 35 U.S.C. 111(b) provisional application Ser. No. 60/530,314 filed Dec. 17, 2003, and entitled Rotating Drilling Head Drive. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   Not Applicable. 
   FIELD OF THE INVENTION 
   The present invention relates generally to methods and apparatus for driving the rotating components of a rotating drilling head. More specifically the present invention relates to methods and apparatus for rotating the sealing element of a rotating drilling head in coordination with a rotating drilling string passing through the sealing element. 
   BACKGROUND 
   Rotating drilling heads employ elastomeric sealing elements to effectuate a seal between a rotating drillstring and the stationary head. The elastomeric sealing element is mounted on bearings that allow the sealing element to rotate with the drillstring. In most conventional drilling operations, the drilling head is positioned below the drill floor and above the blowout preventer. The drilling head operates to divert pressurized drilling fluids, and other materials flowing up through the wellbore, away from the drill floor. 
   In rotary drilling operations, the drillstring is rotated by a kelly drive or a top drive. A kelly drive engages a faceted member of the drill string, or kelly, that is connected to the drillstring. The kelly drive is often powered by a rotary table on the drill floor. Many rotating drilling heads are configured to be rotated by interfacing with the kelly either directly, or through a mechanical interface. 
   Top drive drilling systems rotate the drillstring using an electric or hydraulic motor mounted directly to the top of the drillstring. In top drive drilling systems no kelly is used and the rotating drilling head has to rely on the friction contact between the sealing element and the drillstring to rotate the sealing element. This friction contact is often insufficient to cause sufficient rotation of the sealing element, resulting in relative rotary motion between the drill pipe and the sealing element. A relative rotary motion between the sealing element and the drill pipe can lead to excessive wear in the sealing element, thus reducing the effective life of the seal. 
   Accordingly, there remains a need to develop methods and apparatus for rotating the sealing element of a rotating drilling head that overcome certain of the foregoing difficulties while providing more advantageous overall results. 
   SUMMARY OF THE PREFERRED EMBODIMENTS 
   The embodiments of the present invention are directed to methods and apparatus for rotating a stripper assembly in use with a rotating drilling head. The preferred drive systems seek to synchronize the rotation of the rotating head sealing element with the rotation of the drillstring passing through the sealing element in order to reduce wear on the sealing element. A drive system is disposed external to the rotating drilling head and generates rotational motion to match the rotation of a drillstring running through the rotating drilling head. A connection transfers rotational motion from the drive system to the stripper assembly. In one embodiment, the drive system comprises a housing disposed about the drillstring and a one or more contact members connected to said housing and operable to contact the drillstring. One or more biasing members urge the contact members into contact with the drillstring so as to transfer rotational motion from the drillstring to the housing. 
   In one embodiment, a drive system comprises a housing containing roller assemblies that contact the drillstring. The housing is coupled to the sealing element of a rotating drilling head such that the sealing element rotates with the housing. The roller assemblies are urged into contact with the drillstring by a biasing member that maintains a contact force on the drillstring but allows tool joints and other increased diameter objects to pass through the roller assemblies. The contact force on the drillstring creates a friction force that causes the roller assemblies and housing to rotate with the drillstring, thus driving the sealing element of the drilling head. 
   In another embodiment, a drive system comprises a casing surrounding the drillstring and linking the sealing element of a rotating drilling head to the rotary table on the drill floor. The rotary table is rotated in unison with the drillstring such that the casing rotates the sealing element in unison with the drillstring. In certain embodiments, the casing has an upper and lower section that are rotationally coupled but are allowed to translate axially relative to each other, thus allowing for variation in the distance between the rotary table and the drilling head. 
   In another embodiment, a drive system comprises a rotating motor adapted to directly rotate the sealing element of a rotating drilling head. In one embodiment, a gear is coupled to the sealing element and engaged with a pinion powered by a hydraulic or electric motor. A control system operates the motor so as to rotate the sealing element in unison with the drillstring. 
   Thus, the present invention comprises a combination of features and advantages that enable it to overcome various shortcomings of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more detailed description of the preferred embodiment of the present invention, reference will now be made to the accompanying drawings, wherein: 
       FIG. 1  illustrates an exemplary drilling rig arrangement; 
       FIG. 2  illustrates an exemplary rotating drilling head; 
       FIG. 3  illustrates a partial sectional elevation view of one embodiment of a rotating drilling head drive system; 
       FIG. 4  illustrates a partial sectional plan view of the drive system of  FIG. 3 ; 
       FIG. 5  illustrates a partial sectional elevation view of an alternate embodiment of a rotating drilling head drive system; 
       FIG. 6  illustrates a partial schematic view of an alternate embodiment of a rotating drilling head drive system; 
       FIG. 7  illustrates a partial sectional elevation view of one embodiment of a rotating drilling head drive system; 
       FIG. 8  illustrates a partial sectional plan view of the system of  FIG. 7 ; and 
       FIG. 9  illustrates a partial sectional elevation view of the drive system of  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness. The present invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results. 
   In particular, various embodiments described herein thus comprise a combination of features and advantages that overcome some of the deficiencies or shortcomings of prior art rotating drilling head systems. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art upon reading the following detailed description of preferred embodiments, and by referring to the accompanying drawings. 
   Referring now to  FIG. 1 , there is shown a conventional rig  10  for rotating a drill bit  12  on the end of a drillstring  14  for drilling a well bore  16 . The drillstring  14  extends through a blowout preventer (“BOP”) stack  18  located beneath the rig floor  20  and includes a plurality of drill pipes  14  extending to the drill bit  12 . The drillstring  14  transmits rotational and axial movements to the drill bit  12  for drilling the well bore  16 . The drilling rig  10  includes a rotary table  22  connected to the floor  20  of rig  10 . Torque is transmitted to drillstring  14  by rotary table  22  or a top drive system suspended in the rig  10 . 
   Drilling fluids, often referred to as drilling mud, are pumped downward through drillstring  14  under high pressure, through drill bit  12  and then return upwardly via the annulus  44  formed between well bore  16  and drillstring  14 . The returning drilling fluid is diverted beneath the rig floor  20  to a mud reservoir  24  by means of a device commonly referred to in the industry as a rotating drilling head assembly  26 . Pump  28  draws drilling fluid from reservoir  24  and pumps it back into drillstring  14 . 
   A rotating drilling head assembly  26  is typically mounted below the floor  20  of the drilling rig  10  on the top of the BOP stack  18  to redirect the drilling fluid returning from the well bore  16  and to allow rotation and deployment of the drillstring  14  through the rotary table  22 . Rotating drilling head  26  includes a sealing element  30  that seals the annulus between drillstring  14  and the drilling head. Thus, drilling fluid is forced out through outlet  32  into reservoir  24 . During normal drilling operations, the blowout preventers are maintained in the “open” position, leaving only rotating drilling head  26  to contain any pressure within wellbore  16  and divert the returning pressurized drilling fluids away from the rig  10 . 
     FIG. 2  illustrates a typical prior art rotating drilling head assembly  26  having an outer stationary housing or bowl  48  and an inner drive ring  50  with a bearing assembly  52  disposed in between allowing drive ring  50  to rotate within bowl  48 . Outer bowl  48  includes a flange  54  for mounting the assembly  26  to the BOP stack and a flow diverter port or outlet  32  having a flange  58  for the attachment of a pipe extending to the mud reservoir. Assembly  26  further includes stripper assembly  60 , which is slidably received within drive ring  50  and connected to the upper end of drive ring  50  by a retaining clamp  62  allowing stripper assembly  60  to rotate with inner drive ring  50 . 
   Stripper assembly  60  includes sealing element, or stripper rubber,  30  bonded to inner drive bushing  34 . Inner drive bushing  34  has a faceted profile  44  that can be engaged to impart torque onto stripper assembly  60 . Non-rotary seals  70  and  72 , respectively, serve to isolate bearing assembly  52  from drilling fluids and to keep lubricating fluid from escaping the bearing assembly. Sealing engagement between sealing element  30  and drillstring  14  is effectuated by the sealing element being stretched to fit around the drillstring. 
   Referring now to  FIGS. 3 and 4  a rotating drilling head drive system  100  is shown engaged with drillstring  14  and rotating drilling head assembly  26 . Drive system  100  comprises housing  110  and roller assemblies  120 . Housing  110  includes an upper portion  112  containing roller assemblies  120  and a lower portion  114  having a faceted outer surface adapted to engage faceted surface  44  of stripper assembly  60 . Each roller assembly  120  includes roller  122 , shaft  124 , biasing members  126 , and base  128 . 
   Roller  122  engages drillstring  14  and is rotatably mounted to shaft  124 . Shaft  124  is supported by biasing members  126 , which push roller  122  against drillstring  14 . Biasing members  126  are affixed to housing  110  by base  128 . Rollers  122  are preferably constructed from a material having a surface that will provide sufficient contact with drillstring  14  without damaging the drillstring. For example, roller  122  may be constructed from a steel core covered with a resilient coating. 
   Rollers  122  are urged against drillstring  14  by biasing members  126 . Biasing members  126  act to apply sufficient force to maintain the contact of rollers  122  on drillstring  14  but also allow increased diameter portions of the drillstring, such as tool joint  50 , to pass through the rollers. Biasing members  126  are supported by base  128 , which is attached to housing  110 . Biasing members  126  may be coil springs, leaf springs, hydraulic springs, or any other type of biasing system that support rollers  122 . 
   Drillstring  14  is moved axially while being rotated about its longitudinal axis. Rollers  122  allow for axial translation of drillstring  14 . Rollers  122  grip drillstring  14  so that the rotation of the drillstring imparts a torque on housing  110  that is transferred through faceted members  114  and  44  into stripper assembly  60 . Thus, stripper assembly  60  will rotate with substantially the same rate of rotation as drillstring  14 , reducing wear on the stripper assembly. 
   Drive system  100  is shown having three rollers  122  but any number of rollers may be used to achieve sufficient transfer of torque to the drive system from drillstring  14 . In the preferred embodiments, the surface area of the engagement between drive system  100  and drillstring  14  is maximized in order to minimize the contact stress, or pressure, on the drillstring. Non-rolling contact members could also be used as an alternative to rollers  122 , as long as wear to drillstring  14  is minimized. 
   Drive system  100  is shown as an additional component that interfaces with stripper assembly  26  but it could also be integrated into the stripper assembly. In certain embodiments, drive system  100  may be locked, or otherwise releasably latched, to stripper assembly  26  to maintain the position of the drive system during back-reaming or to provide positive engagement during installation and removal of the drive system. As an alternative to engaging stripper assembly  26 , drive system  100  may also be constructed to directly engage the rotating section of bearing assembly  52 . 
   Referring now to  FIG. 5 , an alternative drive system  130  is shown connecting drilling head  26  to rotary table  22 . Drive system  130  includes an upper casing  132  and a lower casing  134  joined at connection  140 . Upper casing  132  has upper end  138  coupled to rotary table  22  so that the rotary table can be used to rotate the upper casing. Connection  140  transfers torque from upper casing  132  to lower casing  134 . Connection  140  preferably allows axial translation between casings  132  and  134  so as to allow for height variations between drill floor  20  and drilling head  26 . Lower casing  134  has a faceted lower end  136  adapted to interface with faceted profile  44  of stripper assembly  60 . 
   Therefore, the rotation generated by rotary table  22  is transferred through upper casing  132  and lower casing  134  into stripper assembly  60 . Because the relative rotary slippage between stripper assembly  60  and drillstring  14  is reduced, the service life of the stripper assembly is increased. In the preferred embodiments, rotary table  22  is synchronized with the rotation of drillstring  14  so as to closely match the rotation of the drillstring and stripper assembly  60 . In top drive drilling systems, this synchronization is likely carried out by a control system regulating the rotational speed of the top drive and the rotary table. 
   Referring now to  FIG. 6  a second alternative drive system  150  is shown. Drive system  150  includes a drive pinion  152  that engages corresponding gear  63  attached to flange  62 . Flange  62  is connected to the rotating portion of head  26  such that stripper assembly  60  rotates with the flange. Drive pinion  152  is rotated by hydraulic motor  154 , which is powered by pump  156  and controlled by controller  158 . In alternate embodiments, an electric, pneumatic, or other motor may replace hydraulic motor  154 . 
   The speed of motor  154  is controlled so as to rotate stripper assembly  60  at the same rotational speed of a drillstring passing through the stripper assembly, which reduces wear on the stripper assembly. Thus, in the preferred embodiments controller  158  is linked to the drilling control system so as to match the rotational speed of stripper assembly  60  to the rotational speed of a top drive or kelly drive. 
   Referring now to  FIGS. 7-9 , a rotating drilling head drive system  200  is shown engaged with drillstring  14  and rotating drilling head assembly  26 . Drive system  200  comprises housing  210 , roller assemblies  220 , and adapter plate  230 . Housing  210  comprises an upper portion  212  containing roller assemblies  220  and drive lugs  215  that connect housing  210  to adapter plate  230 . Adapter plate  230  is connected to stripper assembly  60  via bolts  232  or some other rigid connection. Roller assemblies  220  engage drillstring  14  and transfer torque from the drillstring through adapter plate  230  to stripper assembly  60 . 
   As can be seen in  FIG. 9 , each roller assembly  220  includes roller  221 , upper link  222 , and lower link  223 . Lower links  223  are pivotally connected to housing base plate  214  by individual lower anchor blocks  224 . Upper links  222  are pivotally connected to follower plate  216  by individual upper anchor blocks  225 . Biasing member  218  is disposed between follower plate  216  and housing base plate  214  so as to urge the follower plate upward. Biasing member  218  may be one or more coil springs, a hydraulic spring system, or any other system for urging follower plate  216  upward. 
   The upward movement of follower plate  216  and upper anchor blocks  225  moves rollers  221  inward toward the center of housing  210  and drillstring  14 . Rollers  221  allow drillstring  14  to move axially while being rotated about its longitudinal axis. Biasing member  218  applies sufficient force to maintain the contact of rollers  221  on drillstring  14  but also allow increased diameter portions of the drillstring, such as tool joint  50 , to pass through the rollers. 
   Rollers  221  are preferably constructed from a material having a surface that will provide sufficient contact with drillstring  14  without damaging the drillstring. For example, rollers  221  may be constructed from steel cores having a concave outer surface covered with a resilient coating. Drive system  200  is shown having three rollers  221  but any number of rollers may be used to achieve sufficient transfer of torque to the drive system from drillstring  14 . In the preferred embodiments, the surface area of the engagement between drive system  200  and drillstring  14  is maximized in order to minimize the contact stress, or pressure, on the drillstring. 
   To install drive system  200 , follower plate  216  is pushed downward, compressing biasing member  218  and moving rollers  221  outward. Follower plate  216  may be maintained in the lowered position by a retainer pin (not shown) or other member that fixes the position of the follower plate relative to housing  210 . Once drillstring  14  is disposed within drive system  200 , the retainer pin is released and biasing member  218  urges follower plate  216  upward, moving rollers  221  inward until they contact the drillstring. 
   Drive lugs  215  are L-shaped members that engage slots  234  on adapter plate  230 . As housing  210  is rotated clockwise by the rotation of drillstring  14 , the horizontal portion of drive lugs  215  prevent vertical disengagement of the lugs and adapter plate  230 . Therefore, system  200  will rotate stripper assembly  60  whether drillstring  14  is being moved downward, such as in normal drilling, or upward, such as during backreaming. Lugs  215  can be disengaged from slots  234  by rotating drillstring  14 , and therefore housing  210 , counterclockwise and upward. 
   While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.