Patent Publication Number: US-2005133229-A1

Title: Universal pressure protector for a polish rod

Description:
FIELD OF THE INVENTION  
      The present invention relates to improvements to sealing a polish rod for a well. More particularly, apparatus is provided including a polish rod seal or is provided in addition to an existing stuffing box for better sealing the polish rod or for resisting high pressures such as those applied in flushing operations.  
     BACKGROUND OF THE INVENTION  
      As the oilfield industry develops into the future, a major concern is safeguarding the environment. Oil companies are recognizing that improvements must be made in the process of extracting oil. This extraction must be completed with as little harm to the surrounding environment as possible.  
      As is well known to those in the in the industry, a pump stator, such as the stator of a progressive cavity pump, is located downhole at the end of production tubing. A pump rotor engages the stator and is suspended from at a distal end of a rod string. The rod string is driven from surface through a polish rod connected to a wellhead drive assembly for lifting well fluid to surface. The polish rod is connected to the rod string extending downhole through a bottom-tapered rod coupler. The polish rod extends through a stuffing box to seal the rotating polish rod and well from the environment at surface. Typically very little pressure is applied to the stuffing box. A progressive cavity pump is subject to plugging at or adjacent the stator and rotor. Fluids are sometime pumped downhole to flush debris from the pump.  
      One major concern is well fluid leaking onto the ground from premature stuffing box failure; due to the high pressure being exerted on it while the well is being flushed. This flushing operation is done by pulling the rotor out of the stator by lifting the polish rod to the top of its bottom-tapered rod coupler. This allows the flush-by operation to then back-flush the production tubing to remove sandy oil that is blocking the free flow of oil. The pressure exerted onto the tubing is the same pressure exerted onto the stuffing box, which can reach levels of 2500 psig.  
      In Canadian patents #2353277, #2027373, and #2171495 it clearly shows that the main disadvantage in stuffing boxes is that they only seal around the polish rod extending therethrough. During flushing operations, greater force is exerted directly into the seal elements, which in turn causes the premature failure of the stuffing box.  
      What is needed is a device which aids in the longevity of existing stuffing boxes and greatly reduces the occurrence of well fluid leaking to atmosphere.  
     SUMMARY OF THE INVENTION  
      In one preferred embodiment, damage due to pressure exerted during flushing is avoided and wellhead drive assembly seals protected through a housing positioned between the wellhead drive assembly and the well. The housing is universal in that it is independent of the type of wellhead drive assembly or stuffing box; the housing need only be adapted to the polish rod. The housing introduces a sealing ring that seals around a tapered rod coupler of the polish rod for preventing high pressure from being exerted directly onto seal elements thereabove including whether the seal element are part of the housing or part of the wellhead drive assembly. Further, the housing spaces the wellhead drive assembly from the well as needed. Advantageously, a flange-to-flange end design of the housing allows installation of this device between any well flow tee of the well and the wellhead drive assembly.  
      In a broad aspect, apparatus is provided for sealing a polish rod below a wellhead drive assembly connected to a well, the polish rod having a tapered rod coupler at a bottom end, the apparatus comprising: a housing having a top end adapted for connection to the wellhead drive assembly and a bottom end adapted for connection to the well, the housing having a bore for passing the polish rod therethrough; and a sealing ring positioned in the bore adjacent the bottom end, wherein when the polish rod is lifted to contact the tapered rod coupler with the sealing ring the well is isolated from the top end of the housing.  
      The apparatus enables exercise of a method for sealing a polish rod below a wellhead drive assembly connected to a well while flushing the well under pressure, the polish rod having a tapered rod coupler at a bottom end, the method comprising: providing a housing between the wellhead drive assembly and the well the housing, the polish rod passing therethrough and having a reduced diameter section of the bore adjacent the housing&#39;s bottom end and sealing ring therebelow; lifting the polish rod to rest against the reduced diameter section and seal against the sealing ring; and applying pressure to the well for flushing the well wherein the sealing ring protects the wellhead drive assembly from the pressure in the well.  
      In another aspect of the invention, a system is provided for sealing a polish rod in a well comprising: a wellhead drive assembly having a polish rod sealing stuffing box adapted for connection to the well and the polish rod extending therethrough; a protector housing having a top end adapted for connection to the stuffing box and a bottom end adapted for connection to the well, the housing having a bore for passing the polish rod therethrough; and a polish rod seal in the bore of the housing, wherein the protector housing seals the polish rod before the polish rod extends through the stuffing box.  
      In another aspect, the life of the stuffing box of any wellhead drive assembly can extended through the installation of a polish rod seal of an embodiment of the invention. Where a wellhead drive assembly has a stuffing box connected to a well and the stuffing box and well having a standard flange connection therebetween then apparatus can be employed comprising: a housing having a bore for passing the polish rod therethrough; a standard flange at a top end of the housing for connection to the stuffing box of the wellhead drive assembly; a standard flange at a bottom end of the housing for connection to the well; and a polish rod seal in the bore of the housing, wherein the polish rod seal extends the longevity of the stuffing box. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional view of one embodiment of the housing for a cylindrical through-bore stuffing box unit with universal flanged connections; and  
       FIG. 2  illustrates greater detail of the internal components of the bore of the housing according to  FIG. 1 .  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Having reference to  FIG. 1 , one embodiment of the universal pressure protector  100  is shown comprising a housing  101  having a barrel  2 , a top flange  1  and a bottom flange  3 . The housing  101  is typically a one-piece cylindrical through-bore steel unit with universal flanged designed ends resembling a dumbbell shape. A polish rod can extend through the housing  101 .  
      The universal pressure protector  100  is for use with an oil well that has a rotary pump in which a polish rod is used to rotate the rotor of a down-hole pump on either a straight or slanted well. The housing  101  is typically mounted at surface between the top of a flow tee and the bottom end of a wellhead drive unit assembly. The wellhead drive unit assembly typically comprises an upper an existing stuffing box which restrains oil fluid leakage from the flow tee.  
      In one embodiment, the universal pressure protector  100  is an extender on oil wells when more distance is needed between the flow tee and wellhead drive unit assembly.  
      The top flange  1 , such as an industry standard RTJ R31 flanged end (ASME B16.5 Class 300-8-bolt flange for nominal 3″ pipe), is bolted to the bottom of a stuffing box of an oil well drive unit (not shown). The flange-to-flange design of a R31 type flange is capable of bolting under any current brand or type of wellhead drive unit assembly and flow tee or well that is used on a rotary drive oil well which is known to applicant.  
      The barrel  2  has an outer thick wall of the through-bore barrel that houses the inner parts of the universal pressure protector  100 . The bottom flange  3 , a R31 flange designed end, is bolted to the top of an oil well flow tee (not shown). High-pressure grease nipple entries allowing lubrication of tapered brass bushings, packing, and cavity. Through-bore grease nipples  4 , 5  grease the packing, brass mandrel and bottom-tapered bushing (See  FIG. 2 ). A through-bore grease nipple  6  greases the top-tapered brass bushing and fills the top sealed cavity located between the top of the housing  101  and the bottom flange of a stuffing box.  
      The top and bottom flanges  1 , 3  are fit with inside threads  7 , 8  respectively which allow lock-down rings  21 , 13  to be screwed therein. The flanges  1 , 3  are fit with eight bolt holes  9  which enable bolting of the device  100  to either the flow tee with the bottom flanged designed end  3 , and the upper stuffing box with the top flanged designed end  1 .  
      In more detail, with reference to  FIG. 2 , the inner part of the through-bore barrel  2  has a bore  23  where the polish rod slides through. The bore houses the sealing components of this embodiment comprising: a sealing ring  11 , a bottom threaded lock-down ring  12  and setscrew  13 , a bottom bushing  14  with wiper rings  15 , grease mandrel  16 , a first plurality of packing rings  17 , spring  18 , a second plurality of packing rings  19 , a top bushing  20 , a top threaded lock-down ring  21  and setscrew  22 .  
      The bottom-tapered brass bushing  14  helps to centralize and stabilize the polish rod. The top-tapered brass bushing  20  also helps to centralize and stabilize the polish rod.  
      Teflon™ (trademark of Dupont) wiper rings  15  are recessed into the bottom-tapered brass bushing  14  which cleans off oil and sand from the polish rod as it is being lifted through the through-bore barrel  2 . The brass grease mandrel  16  allows grease to pass through and lubricate between the polish rod and bushings  20 , 14 .  
      A first plurality of packing rings  17  and a second plurality of packing rings  19  seal around the polish rod. The first and second plurality of packing rings  17 , 19  are sandwiched between the top and bottom bushings  20 , 14 . A spring  18 , when compressed, hold tension on these packing rings  17 ,  19 . The spring  18  can be positioned between the first and second plurality of packing rings  17 , 19 . The spring  18  is compressed when the threaded lock-down ring  21  is threaded into the housing  101  and locked with setscrew  22  at the top of cylindrical through-bore barrel  2 .  
      The threaded lock-down ring  21  is locked in with the setscrew  22 . Further the top-tapered brass bushing  20  is also pushed down by the top through-bore threaded lock-down ring  21 , compressing the spring  18  and packing rings  17 , 19  that seal around the polish rod.  
      The bore  23  forms a relatively reduced diameter section  10  of the through-bore barrel  2 . The bottom-reduced diameter section  10  of through-bore  23  secures the bottom-tapered bushing  12  in said through-bore  23 .  
      This reduced diameter section  10  is the point where the bottom-tapered rod coupler of a polish rod comes to rest when lifted out of the oil well production tubing in preparation for a flushing operation. This reduced diameter section  10  positions and stabilizes the bottom-tapered rod coupler of a polish rod during flushing operations and also keeps the bottom-tapered rod coupler from coming in contact with the bottom-tapered brass bushing  14 .  
      The sealing or rubber ring  11  seals around the top of the bottom-tapered rod coupler of the polish rod for sealing off oil fluid from entering the sealing elements thereabove during flushing operations. This rubber ring  11  is held in place by the bottom threaded lock-down ring  12  which has a through-bore center and is locked with a setscrew  13 .  
      Accordingly, in use, in preparation for a flushing operation, the polish rod is lifted to seal against the tapered rod coupler of the polish rod, thereby sealing the well from the wellhead drive assembly. When pressure resulting from the flush by operation is exerted on the well, any seals above the sealing ring, including the polish rod seals  19 , 17  and the existing stuffing box of the wellhead drive assembly are protected. The tapered rod coupler can rest against the reduced diameter section with the tapered rod coupler sealing against the sealing ring.  
      When the housing is bolted to the upper stuffing box of a wellhead drive unit assembly a sealed cavity is formed. The cavity can be filled with grease through the top grease nipple  6 .  
      Within the oilfield industry is found many different types of corrosive materials that will determine which types of materials are used to build a universal pressure protector  100 . This enables the adaptation for use under many unique conditions found throughout the oil fields. The outer shell, or flanges  1 , 3  and barrel  2 , can be made from many different types and grades of steel. The tapered brass bushings  20 , 14 , brass mandrel  16 , grease nipples  4 , 5 , 6 , inner spring  18 , packing rings  17 , 19 , Teflon™ rings  15 , rubber ring  11 , and lock-down rings  21 , 12  can all be made from many different types of material. Further, the Teflon™ rings, rubber ring, tapered brass bushings, brass mandrel, and packing rings can all be sized to fit any polish rod size.  
      The intended use of a Universal Pressure Protector is to protect well equipment above the flow tee on an oil well, by absorbing the brunt of the tubing pressure that is exerted from the well pump. This Universal Pressure Protector can also be used as an extender on oil wells when more distance is needed between the flow tee and the wellhead drive unit.