Abstract:
A convertible rotary seal has a housing for receiving a polish rod. A mandrel is rotatably mounted in the seal housing and surrounds the polish rod. A wear sleeve surrounding the mandrel engages a primary seal. A secondary seal engages the mandrel and polish rod and rotates therewith but may be converted for use as a static seal if necessary. A locking mechanism selectively secures the mandrel in a stationary orientation with respect to the seal housing. Fluid that leaks past the primary seal will be detectible through an external orifice. If a leak in the primary seal is detected via the external port, then the mandrel may be secured in a stationary orientation with respect to the housing and the secondary seal may be reconfigured to operate as a stationary seal until such time as the rotary sealing unit can be overhauled.

Description:
FIELD OF THE INVENTION  
       [0001]     This invention relates generally to a wellhead stuffing box for sealing engagement with a polish rod. More particularly, the invention relates to a stuffing box having a primary and a secondary seal for use with a rotating polish rod.  
       BACKGROUND OF THE INVENTION  
       [0002]     In a standard wellhead, a stuffing box is used to provide a rotary seal around the polish rod of a rod string, which is used to drive a downhole pump. A typical stuffing box is constructed of a generally tubular housing that is threaded onto an upwardly projecting portion of a wellhead. The polish rod extends through the wellhead and through the stuffing box housing. An annular space is formed between stuffing box housing and the polish rod. Typically, a stack of compressible packing rings are positioned in the annular space to form a seal around the polish rod. An internal radial shoulder in the stuffing box housing supports the packing rings at a bottom end of the stack. An annular packing gland is typically positioned at the top of the stack of packing rings. An internally threaded compression nut is threaded onto an externally threaded upper end of the stuffing box housing to force the packing gland downwardly to compress the packing rings against the radial shoulder of the stuffing box housing. When the packing rings are compressed, the packing rings experience radial expansion, so that the rings seal against the polish rod and also against the inside surface of the stuffing box housing.  
         [0003]     Problems associated with typical stuffing boxes include leakage and packing wear. A problem with progressive cavity pumps in particular is that the rod string is oftentimes not perfectly straight. Additionally, the rod string tends to oscillate during rotation, which can exacerbate packing wear and may result in the escape of pressurized well fluid.  
         [0004]     Therefore, it is desirable to provide a stuffing box having a primary and a secondary seal to increase reliability of the stuffing box. It is further desirable to be able to detect when the primary seal has developed a leak so that repairs can be made before well fluid can escape. Once primary seal leakage is discovered, it is desirable for the stuffing box to have features that enable the stuffing box to be adapted for continued use with the secondary seal until such time as repairs can be made in a convenient and cost effective manner. Additionally, it is desirable to provide a sleeve for shielding the polished rod from sealing elements during operation to avoid polish rod wear.  
       SUMMARY OF THE INVENTION  
       [0005]     The rotary seal unit (“RSU”) of the invention is characterized by seal elements, such as lip seals, that run on a rotating mandrel. By utilizing a rotating mandrel the polish rod is isolated from running elements, which eliminates wear of the polish rod. A top part of the mandrel has a chamber containing a poly seal that seals and grips the polish rod. The polish rod drives the mandrel, which is sealed by multiple lip seals. The space between the multiple lip seals communicates through various machined holes and cavities with an exterior port. An operator may open the exterior port to check for fluid. A fluid presence proximate the exterior port indicates a failure of one or more of the lower lip seals. Thus, the failure of the RSU may be detected before well fluid leakage occurs.  
         [0006]     Replacement of a drivehead rotary seal requires removal of the drivehead, which can be a time consuming and perhaps untimely procedure. The RSU of the invention allows for the drivehead to be shut down and for the mandrel to be locked to the body of the RSU. The top seal, e.g., a poly seal, may then be replaced by a stationary seal such as Teflon and graphite packing. Once the packing is installed, the top seal becomes static. In this way the RSU of the invention may be operated as a conventional stuffing box until replacement of the RSU is convenient to field operations.  
         [0007]     Advantages of the RSU of the invention include utilizing multiple lip seals as a primary seal and utilizing a secondary static seal that includes conventional poly-style packing. The system of the invention provides an early warning in advance of a primary seal failure. In the event of a primary seal failure, the secondary seal can be converted to avoid an unscheduled shutdown of the pumping system. The secondary sealing system operates as a conventional stuffing box using Teflon and graphite packing that can continue to be utilized until a maintenance event can be scheduled, thus avoiding a costly addition shut-down.  
         [0008]     An added benefit of the RSU of the invention is reduced polished rod wear. The primary seals are designed so that while in operation the wear to the polished rod is reduced or eliminated.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is a perspective view of the convertible rotary seal of the invention.  
         [0010]      FIG. 2  is a cross sectional view of the convertible rotary seal of  FIG. 1 .  
         [0011]      FIG. 3  is an enlarged view of lower seal assembly of the cross sectional view of the convertible rotary seal shown in  FIG. 2 .  
         [0012]      FIG. 4  is a cross-sectional view taken along line  4 - 4  of  FIG. 2 .  
         [0013]      FIG. 5  is a cross-sectional view taken along line  5 - 5  of  FIG. 2 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]     Referring now to  FIGS. 1-5 , rotary seal  10  for a progressive cavity pump drivehead is shown. Rotary seal  10  includes a housing  12 . Housing  12  is preferably made up of a bearing housing  14  ( FIGS. 1 and 2 ) and a seal housing  40 . Bearing housing  14  defines an inside surface  16  having an interior ring  18  ( FIG. 2 ). Interior ring  18  defines an upper shoulder  20  and a lower shoulder  22 . Bearing housing  14  defines an upper diameter  24  and a lower flange  26 . Bearing housing  14  additionally defines an orifice  28  that receives an upper breather petcock  30  ( FIGS. 1 and 2 ). Bearing housing  14  further defines a plurality of bolt receiving holes  32  and an upper surface of the bearing housing  14 .  
         [0015]     As can best be seen in  FIG. 3 , housing  12  additionally is made up of seal housing  40  ( FIGS. 1-5 ). Seal housing  40  defines an interior cavity  42  ( FIGS. 2 and 3 ) having a first or mating section  44  of a first diameter, a second or seal section  46  having a lower diameter  48  and a larger upper diameter  50 . Interior cavity  42  of seal housing  40  additionally includes a third or sleeve section  52  having a diameter and a fourth or lower section  54  having a diameter. Seal housing  40  further defines a booth flange or upper flange  56  and a lower flange  58 . Seal housing  40  defines an orifice  60  for receiving a lower breather or leak detection petcock  62  ( FIGS. 2-5 ) at second or seal section  52 . Orifice  60  communicates interior cavity  42  of seal housing  40  with an exterior of seal housing  40 . Seal housing  40  further defines at least one roll pin orifice  64  in the lower surface thereof. Cap screws  66  pass through lower flange  26  of bearing housing  14  and upper flange  56  of seal housing  40  for securing bearing housing  14  to seal housing  40 .  
         [0016]     Still referring primarily to  FIG. 3 , a stationary cartridge  70  ( FIGS. 2-5 ) is located in the second or seal section  46  of seal housing  40 . Stationary cartridge  70  has an outside surface that has a first outside diameter  72  in mating contact with the lower diameter  48  of second or seal section  46  of seal housing  40 . Stationary cartridge  70  additionally has a second larger outside diameter  74  that communicates with the larger upper diameter  50  of the second section  46  of seal housing  40 . The outside surface of stationary cartridge  70  and the inside surface of interior cavity  42  of seal housing  40  define annular space  76  ( FIGS. 3-5 ) therebetween. Annular space  76  is in communication with orifice  60  of seal housing  40 .  
         [0017]     Still referring to  FIG. 3 , stationary cartridge  70  has an inside surface that defines an upper inside diameter  78  and a lower inside diameter  80  wherein lower inside diameter  80  defines an annular plane  82  and a lower lip seal receiving area. Stationary cartridge  70  defines an interior annular groove  86  on upper inside diameter  78 . Stationary cartridge  70  further defines an orifice  88  in communication with interior annular groove  86  on upper inside diameter  78  of stationary cartridge  70  for communicating with annular space  76 . Stationary cartridge  70  defines a plurality of bolt receiving orifices  90  on an upper surface thereof. Stationary cartridge  70  further defines at least one roll pin orifice  92  on a lower surface thereof.  
         [0018]     Roll pin  100  is preferably located in roll pin orifice  64  of seal housing  40  is preferably partially inserted within roll pin orifice  92  of stationary cartridge  70  for preventing rotation of stationary cartridge  70  with respect to seal housing  40 . A first O-ring is located between the second or seal mating section  46  of seal housing  40  and the upper inside diameter  78  of stationary cartridge  70 . A second O-ring is also located between the second or seal section  46  of seal housing  40  and the lower inside diameter  80  of stationary cartridge  70 .  
         [0019]     A lower lip seal spacer  110  is received within the upper inside diameter  78  of stationary cartridge  70 . An O-ring seal is preferably provided between stationary cartridge  70  and lower lip seal spacer  110  for forming a seal therebetween. Lower lip seal spacer  110  communicates with annular plane  82  of stationary cartridge  70 . Lower lip seal spacer  110  defines a tapered inside surface defining a middle lip seal receiving area.  
         [0020]     Upper lip seal spacer  120  is received within upper inside diameter  78  of stationary cartridge  70 . Upper lip seal spacer  120  communicates with an upper surface of lower lip seal surface  110 . Upper lip seal spacer  120  defines a tapered inside surface defining an upper lip seal receiving area. Upper lip seal spacer  120  additionally defines a spacer orifice  124  that is in communication with interior annular groove  86  of stationary cartridge  70 .  
         [0021]     Upper lip seal  126  is located adjacent to the upper lip seal receiving area of upper lip spacer  120 . Middle lip seal  128  is located adjacent the middle lip seal receiving area of lower lip seal spacer  110 . Additionally, lower lip seal  130  is located adjacent the lower lip seal receiving area of stationary cartridge  70 . An O-ring is provided between the inside surface of stationary cartridge  70  and outside surface of upper lip seal spacer  120  for forming a seal therebetween. The O-ring is located above spacer orifice  124  of upper lip seal spacer  120  and also above interior annular groove  86  and orifice  88  of stationary cartridge  70 .  
         [0022]     Cartridge lid  140  is located within second section  46  of seal housing  40 . Cartridge lid  140  communicates with an upper surface of stationary cartridge  70 . Cartridge lid  140  defines a plurality of bolt receiving orifices  142 . A plurality of bolts  144  are received in bolt receiving orifices  142  of cartridge lid  140  and in bolt receiving orifices  90  of stationary cartridge  70  for securing cartridge lid  140  to stationary cartridge  70 .  
         [0023]     For purposes of this application, in the exemplary embodiment, stationary cartridge  70 , upper lip seal spacer  120 , lower lip seal spacer  110 , upper lip seal  126 , middle lip seal  128 , and lower lip seal  130  shall be collectively referred to herein as lower seal assembly  150  ( FIGS. 2 and 3 ).  
         [0024]     Snap ring  152  is received within a groove formed on an inside surface of second section  46  of seal housing  40 . Snap ring  152  is provided for securing lower seal assembly  150  within seal housing  40 .  
         [0025]     Wear sleeve  160  ( FIGS. 2-5 ) is located inside of lower seal assembly  150 . Wear sleeve  160  has an outside surface in sealing communication with an inside surface of upper lip seal  126 , middle lip seal  128 , and lower lip seal  130 . Wear sleeve  160  additionally defines a drive screw orifice  162  ( FIG. 3 ).  
         [0026]     Referring now primarily to  FIG. 2 , a rotary mandrel  170  has an outer surface that defines cap screw threads  172  on an upper end thereof. Outer surface of rotary mandrel  170  additionally defines a first diameter  174  and minor flange  176  that defines a shoulder, a second diameter  178  that defines threads  180  ( FIGS. 2 and 3 ) on a lower portion thereof, and a third diameter  182  ( FIG. 3 ) for mating against an inside surface of wear sleeve  160 . Rotary mandrel  170  additionally defines radial drive screw orifice  184  ( FIG. 3 ) and a lower end of rotary mandrel  170  at third diameter  182 . Rotary mandrel  170  has an interior surface defining a tapered upper chamber  186  and a longitudinal interior space  188 . O-rings are located between the inside surface of wear sleeve  160  and an outer surface of rotary mandrel  170  at third diameter  182 .  
         [0027]     As shown is  FIG. 3 , lock nut  200  is threadably connected to rotary mandrel  170  via threads  180 . Lock washer  202  is in communication with an upper surface of lock nut  200 .  
         [0028]     Referring back to  FIG. 2 , lower tapered roller bearing  210  is located between an inside surface of bearing housing  14  and outer surface of rotary mandrel  170  at second diameter  178  of rotary mandrel  170 . Lower tapered roller bearing  210  communicates with lock nut  200  and lower shoulder  22  on inside surface  16  of bearing housing  14 .  
         [0029]     Upper tapered roller bearing  220  is located between the inside surface of bearing housing  14  and outer surface or rotary mandrel  170  at second diameter  178  of rotary mandrel  170 . Upper tapered roller bearing  220  communicates with upper shoulder  20  on inside surface  16  of bearing housing  14 . Grease seal  222  is located between upper diameter  24  of bearing housing  14  and minor flange  176  of rotary mandrel  170 .  
         [0030]     Lock out plate  230  has an inside diameter that surrounds first diameter  174  of rotary mandrel  170 . Lock out plate  230  preferably defines a plurality of bolt receiving holes  232  therein. A plurality of cap screws  234  are received within bolt receiving holes  232  of lock out plate  230  and within bolt receiving holes  32  of bearing housing  14 . Cap screws  234  are provided for securing lock out plate  230  to bearing housing  14 .  
         [0031]     A seal, such as polypak seal  240 , is received within tapered upper chamber  186  of rotary mandrel  170 . Polypak seal  240  has an inside diameter and an outside diameter. Polypak seal washer  242  is in communication with an upper surface of polypak seal  240  with an upper tapered chamber  186  of rotary mandrel  170 . For purposes of this application, polypak seal  240  and polypak seal washer  242  shall be referred to as upper seal assembly  250 .  
         [0032]     Mandrel drive cap  260  has an inside surface defining threads that are threadably received on cap screw threads  172  on the upper portion of rotary mandrel  170 . The inside surface of mandrel drive cap  260  additionally defines an inwardly protruding ring  262  and an upper inside surface  264 . Inwardly protruding ring  262  communicates with an upper surface of rotary mandrel  170 .  
         [0033]     Mandrel compression drive  270  has an upper section in communication with upper inside surface  264  of mandrel drive cap  260 . Mandrel compression drive  270  further defines a tapered lower section for communicating with tapered upper chamber  186  of rotary mandrel  170 . A transition between an upper section of mandrel compression drive and the tapered lower section of the mandrel compression defines a lip  272  that communicates with inwardly protruding ring  262  of mandrel drive cap  260 . Lock ring  274  is received within an annular groove defined by upper inside surface  264  of mandrel drive cap  260  for securing mandrel compression drive  270  partially within mandrel drive cap  260 .  
         [0034]     Polished rod  280  is received within rotary mandrel  170 . Polished rod  280  communicates with mandrel compression drive  270  and the upper seal assembly  250 . Polished rod  280  additionally passes through the longitudinal interior space  188  of rotary mandrel  170 .  
         [0035]     As shown in  FIG. 3 , drive screw  290  is received within drive screw orifice  162  of wear sleeve  160  and within drive screw orifice  184  of rotary mandrel  170  for selective engagement with polished rod  280 .  
         [0036]     In practice, rotary seal unit  10  of the invention utilizes rotating mandrel  170  to isolate polish rod  280  from running elements, such as upper lip seal  126 , middle lip seal  128 , and lower lip seal  130 . By isolating polish rod  280  from lip seals  126 ,  128  and  130 , wear of polish rod  280  is eliminated. Tapered upper chamber  186  of mandrel  170  contains upper seal assembly  250  that seals and grips polish rod  280  so that polish rod  280  drives mandrel  170 . Multiple lip seals  126 ,  128 , and  130  form a seal therebetween. Space between multiple lip seals  126 ,  128  and  130  communicates with exterior orifice  60  through orifice  88  in stationary cartridge  70  and spacer orifice  124  in upper lip seal spacer  120 . An operator may open lower breather petcock  62  in orifice  60  to check for the presence of fluid. Fluid proximate exterior orifice  60  indicates a failure of one or more of lip seals  128  and  130 . Thus, sealing failure of RSU  10  may be detected prior to external leakage of well fluid.  
         [0037]     Replacement of a rotary seal unit  10  requires removal of the drivehead, which is a time consuming procedure. Further, an unexpected failure of a rotary seal unit  10  may necessitate untimely and costly downtime for the well. RSU  10  of the invention allows for the drivehead to be shut down and for mandrel  280  to be locked to the body or housing  12  of RSU  10 . Once the drivehead is shut down, the upper seal assembly  250 , e.g., the poly seal may be replaced by packing such as a Teflon and graphite packing. Once the packing is installed, the upper seal assembly  250  becomes static and seals against the rotating polish rod  280 . Once the packing is installed in the upper seal assembly  250 , RSU  10  may be operated as a conventional stuffing box until replacement of the RSU is convenient to field operations.  
         [0038]     Advantages of the RSU of the invention include utilizing a primary seal and a secondary static seal for increased reliability. An accessible external port provides an early warning in advance of a primary seal failure. In the event of a primary seal failure, a secondary seal can be converted to avoid an unscheduled shutdown of the pumping system. The secondary sealing system operates as a conventional stuffing box using Teflon and graphite packing that can continue to be utilized until a maintenance event can be scheduled, thus avoiding a costly addition shut-down.  
         [0039]     An added benefit of the RSU of the invention is reduced polished rod wear. The primary seals are designed so that while in operation the wear to the polished rod is reduced or eliminated.  
         [0040]     Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned above as well as those inherent therein. While presently preferred embodiments have been described for purposes of this disclosure, numerous changes and modifications will be apparent to those skilled in the art. Such changes and modifications are encompassed within the spirit of this invention as defined by the appended claims.