Patent Publication Number: US-11047200-B2

Title: Stripper element for wells and reinforcing insert therefor

Description:
FIELD OF THE INVENTION 
     The present invention relates to sealing elements, commonly referred to as stripper rubbers, which are used in wells to seal around drill pipes and other tubulars and to strip away mud, debris, and fluid as the drill pipe or other tubular is pulled out of the well. The present invention also relates to reinforcing inserts for these sealing elements and to methods of forming the reinforcing inserts and sealing elements. 
     BACKGROUND OF THE INVENTION 
     For drilling and other operations in oil and/or gas wells, water wells, and other types of wells, one or more sealing elements, commonly referred to as stripper rubbers, are typically installed at the wellhead to seal around drill pipes, kellies, bottom hole assemblies and/or other tubulars and to strip away mud, debris and fluid from the exterior of the tubular as it is pulled out of the well. 
     By way of example, but not by way of limitation, stripper rubbers are often configured to include: a generally cylindrical upper section; a reinforcing metal insert which is molded into at least the upper section; a frusto-conical lower section which converges inwardly as it extends downwardly from the upper section; and a passageway which extends longitudinally through the stripper rubber element for receiving the drill pipe or other tubular. 
     Except for the reinforcing insert, the upper and lower sections of the stripper rubber are typically formed of natural or synthetic rubber material, a urethane material, or other stretchy elastic material which is sufficiently durable and wear resistant for use in such applications. As used herein and in the claims, unless otherwise expressly limited, the term “stripper rubber” refers to and includes stripper elements formed of any such materials. 
     The inside diameter of the longitudinal passageway of the stripper rubber will typically be less than the outside diameter of the drill pipe or other tubular so that the stretchy material of the stripper rubber conforms to and provides a tight seal around the exterior of the tubular as the tubular moves longitudinally through and/or rotates within the stripper rubber. In addition, the pressure in the well also acts against the tapered exterior of the lower frusto-conical section of the stripper rubber to push the stripper radially inward and thereby further tighten the seal around the tubular. 
     The reinforcing metal insert used in the upper section of the stripper rubber provides a supporting structure for bolts, or other attachments, used for installing the stripper rubber and also reinforces the stripper rubber against deformation. One well known type of reinforcing metal insert comprises a longitudinally extending, generally cylindrical body portion having a bolting flange formed on the upper longitudinal end thereof. 
     When forming the stripper rubber, the reinforcing metal insert is placed in the stripper mold so that the rubber, urethane or other stretchy material used for forming the stripper rubber encases all, or at least a portion, of the metal insert. 
     Due to their size, bulkiness, materials of construction, and manufacturing costs, the metal inserts used in stripper rubbers are too expensive to simply be disposed of after use and must be recovered, refurbished, and reused. Unfortunately, however, the recovery and refurbishing process for the metal inserts is also very costly, labor intensive, and time consuming. When a spent stripper rubber is removed from a well after use, the user must pay to have the spent element shipped back to the manufacturer. The manufacturer must then remove the rubber, urethane or other molded material which encases and is bonded to the metal insert. Next, the surface of the metal insert must be grit blasted in accordance with NACE SSPC SP 10 requirements to a near white metal finish. The surface of the metal insert must then also be primed prior to being placed in a stripper element mold to be re-encased in, and bonded with, the new rubber or urethane material. Finally, the refurbished and restored element must be shipped back to the user. 
     Consequently, for the reasons stated above, there has been a long-felt and unsatisfied need in the industry for an improved reinforcing insert for stripper rubber elements which (a) is much less costly to produce, (b) can be economically disposed of after use rather than having to be recovered, refurbished and reused, (c) is compatible and readily bonds with the urethane or other stretchy material used for encasing the insert and forming the stripper rubber, and (d) is substantially equivalent or superior to the prior metal inserts in terms of the reinforcing strength and resistance to deformation which it provides. 
     SUMMARY OF THE INVENTION 
     The present invention satisfies the needs and alleviates the problems discussed above. The present invention provides a molded reinforcing insert for stripper rubbers which (a) costs much less to produce than the prior metal inserts and (b) is substantially equivalent or superior to the prior metal inserts in terms of performance, strength, and resistance to deformation. Moreover, the stripper rubber produced using the inventive, low cost molded insert can be economically disposed of after use and simply replaced. 
     In one aspect, there is provided a reinforcing insert for reinforcing a stripper rubber for a drill pipe or other well tubular. The reinforcing insert preferably comprises: (i) a longitudinal axis which extends through the insert; (ii) a metal ring, or a circular arrangement of individual threaded inserts, which surrounds the longitudinal axis; (iii) a molded insert material in which the metal ring or the circular arrangement of individual threaded inserts is encased, the molded insert material having a Shore D hardness value of at least 55; and (iv) a plurality of bolting holes which extend through the metal ring, or through the individual threaded inserts, and through the molded insert material in which the metal ring or the circular arrangement of individual threaded inserts is encased. 
     In another aspect, there is provided a reinforcing insert, for reinforcing a stripper rubber, which preferably comprises: (i) a longitudinal axis which extends through the reinforcing insert; (ii) a longitudinally extending body portion of the reinforcing insert which is formed of a molded insert material having a Shore D hardness value of at least 55; (iii) a plurality of voids which extend radially through the longitudinally extending body portion of the reinforcing insert for filling the voids with a stripper material when installing the reinforcing insert in the stripper rubber; and (iv) a radially extending attachment ring portion of the reinforcing insert which surrounds the longitudinal axis and extends radially outward from an upper end of the longitudinally extending body portion. The radially extending attachment ring portion of the reinforcing insert comprises a metal ring, or a circular arrangement of individual threaded inserts, encased in the molded insert material 
     In another aspect, there is provided a stripper rubber for a drill pipe or other well tubular. The stripper rubber preferably comprises: (i) a longitudinal axis which extends through the stripper rubber and (ii) a passageway which extends longitudinally through the stripper rubber for receiving the drill pipe or other well tubular. The stripper rubber is preferably formed of a molded stripper material having a Shore A hardness value of not more than 85. The stripper rubber preferably further comprises a reinforcing insert which is at least partially encased in the molded stripper material of the stripper rubber and which surrounds the longitudinal axis. The reinforcing insert preferably comprises: (a) a metal ring or a circular arrangement of individual threaded inserts and (b) a molded insert material, different from the molded stripper material, in which the metal ring or the circular arrangement of individual threaded inserts is encased. The molded insert material preferably has a Shore D hardness value of at least 55. 
     In another aspect, there is provided a method for forming a stripper rubber for a drill pipe or other well tubular. The method preferably comprises the step of (a) positioning a circular metal ring in an insert mold for forming a molded reinforcing insert, the metal ring comprising (i) an inner edge, (ii) an outer edge, (iii) a radial width which extends from the inner edge to the outer edge, (iv) an upper radial surface, (v) a lower radial surface. (vi) a longitudinal thickness which extends from the upper radial surface to the lower radial surface, and (vii) a plurality of bonding voids which extend longitudinally through the metal ring from the upper radial surface to the lower radial surface. 
     Next, the inventive method preferably comprises the steps of: (b) filling the insert mold and the bonding voids of the metal ring with an insert molding material having a Shore D hardness value of at least 55; (c) curing the insert molding material to form the molded reinforcing insert, the molded reinforcing insert comprising the metal ring encased in the insert molding material and a plurality of bolting holes which extend through the metal ring and through the insert molding material in which the metal ring is encased; (d) removing the molded reinforcing insert from the insert mold; (e) placing the molded reinforcing insert in a stripper mold for forming the stripper rubber; (f) filling the stripper mold with a stripper molding material, different from the insert molding material, having a Shore A hardness value of not more than 85; and (g) curing the stripper molding material to form the stripper rubber. At least a portion of the molded reinforcing insert is encased in the stripper molding material of the stripper rubber. In addition, the stripper rubber comprises a passageway which extends longitudinally through the stripper rubber for receiving the drill pipe or other well tubular. 
     Further aspects, features, and advantages of the present invention will be apparent to those in the art upon examining the accompanying drawings and upon reading the following Detailed Description of the Preferred Embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top perspective view of an embodiment 2 of the molded reinforcing insert provided by the present invention. 
         FIG. 2  is a perspective view of a metal bolting ring  12  used in the inventive reinforcing insert  2 . 
         FIG. 3  is a plan view of the metal bolting ring  12 . 
         FIG. 4  is an elevational side view of the metal bolting ring  12   
         FIG. 5  is a cutaway view of the inventive molded reinforcing insert  2 . 
         FIG. 6  is a cutaway elevational view of an embodiment  20  of the stripper rubber provided by the present invention. 
         FIG. 7  is a top view of the inventive stripper rubber  20 . 
         FIG. 8  is a circular arrangement  68  of individual threaded inserts  60  which replace the metal ring  12  in an alternative embodiment of the inventive reinforcing insert. 
         FIG. 9  is a perspective view of an alternative embodiment  70  of the molded reinforcing insert provided by the present invention. 
         FIG. 10  is an elevational side view of the inventive molded reinforcing insert  70 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment 2 of the molded reinforcing insert provided by the present invention is illustrated in  FIGS. 1-5 . The molded insert  2  is molded as a single piece which preferably comprises: a longitudinal axis  4  which extends through the molded insert  2 ; a longitudinally extending body portion  6  of the molded insert  2  which preferably entirely surrounds or substantially surrounds the longitudinal axis  4 ; and a radially extending attachment ring portion  8  of the molded insert  2  which surrounds the longitudinal axis  4  and extends radially outward from an upper end  10  of the longitudinally extending body portion  6 . The molded insert  2  further comprises a continuous metal ring  12  which is encased in the molded material of the radially extending attachment ring portion  8  of the insert  2  and which also surrounds the longitudinal axis  4 . 
     The insert molding material used in forming the longitudinally extending body portion  6  and the radially extending attachment ring portion  8  of the molded insert  2 , and which encases the metal ring  12 , is preferably an elastomer or other polymer material having a high Shore D hardness value of at least 55, or at least 60, or in the range of from 60 to 90, or at least 65, or in the range of from 65 to 85. 
     Examples of elastomers and other polymer materials which can be formulated to provide high Shore D hardness values suitable for use in forming the molded insert  2  include, but are not limited to, polyurethanes (e.g., polyether polyurethanes, polyester polyurethanes, and polycarbonate-based polyurethanes), epoxies, polyolefins, and cross-linked polymers. The insert molding material used for forming the molded insert  2  and encapsulating the metal ring  12  is most preferably a polyurethane. Examples of commercially-available prepolymers preferred for use in forming the molded insert  2  include: (a) Adiprene® LF 750D, a TD-terminated polyether prepolymer available from Chemtura Corporation, which is preferably cured using 4,4′-Methylenebis(2-chloroaniline) or Dimethylthiotoluenediamine to a Shore D hardness of 73-75 or (b) PROXIMA® HPR 2100, a thermoset resin available from Materia, Inc. which provides a Shore D hardness of 82. 
     The elastomer or other polymer material used for forming the molded insert  2  can also include one or more fillers or other additives for increasing the hardness or density of the insert molding material, or for improving other properties. Examples of possible additives include but are not limited to ceramic fiber, fiberglass, carbon fiber. Kevlar® and similar materials. 
     The integrally molded combination of the longitudinal body portion  6  and the radial attachment ring portion  8  of the reinforcing insert  2  give the surrounding wall of the insert  2  an inverted L cross-sectional shape. The longitudinal length  14  of the longitudinally extending body portion  6  of the molded insert  2  is preferably in the range of from about 0.75 to about 5 times (more preferably from about 1 to about 3 times) the radial width  16  of the radially extending attachment ring portion  8 . The longitudinally extending body portion  6  is preferably a generally cylindrical structure having a plurality, preferably a series, of substantially right angle, triangular strengthening brace structures  22  which are integrally formed during the molding process between the outer side wall  24  of the longitudinally extending body portion  6  and the lower surface  26  of the radially extending attachment ring portion  8  of the molded insert  2 . 
     As will be discussed more fully below, a plurality of circular holes, apertures of other shapes, or other voids  18  (preferably a series of voids  18  located between the substantially triangular strengthening brace structures  22 ) are preferably formed radially through the longitudinally extending body portion  6  of the molded insert  2  for assisting in bonding the inventive molded insert  2  in the inventive stripper rubber  20 . 
     The metal ring  12  which is encased in the molded insert material of the radially extending attachment ring portion  8  of the insert  2  is preferably a flat, circular metal ring which comprises: an inner circular edge  28  which surrounds the longitudinal axis  4 ; an outer circular edge  30  which surrounds the longitudinal axis  4 ; a radial width  32  which extends from the inner edge  28  to the outer edge  30 ; an upper radial surface  34  which extends from the inner edge  28  to the outer edge  30 ; a lower radial surface  36  which extends from the inner edge  28  to the outer edge  30 ; and a longitudinal thickness  38  which extends from the upper radial surface  34  to the lower radial surface  36 . 
     The metal ring  12  also preferably comprises a plurality (preferably a series) of circular holes, apertures of other shapes, or other bonding voids  40  which extend longitudinally through the metal ring  12  from the upper radial surface  34  to the lower radial surface  36  and which are filled, during the process of molding the inventive reinforcing insert  2 , with the high hardness insert molding material. 
     The longitudinal thickness  38  of the metal ring  12  is preferably in the range of from about ⅛ inch to 7/16 inch or from ⅛ inch to ⅜ inch. The thickness  38  of the metal ring  12  is more preferably in the range of from 3/16 inch to 516 inch and is most preferably about % inch. Examples of metals suitable for use in forming the metal ring  12  include, but are not limited to, mild steel and stainless steel. 
     The metal ring  12  is preferably a bolting ring which also comprises a plurality of bolting holes  42  which extend longitudinally through the metal ring  12 . More preferably, the metal ring  12  has a series of the bolting holes  42  formed therethrough such that the bonding voids  40  of the metal ring  12  are located between the bolting holes  42 . For each of the bolting holes  42 , the metal ring  12  also preferably comprises at least one of (a) a nut or other internally threaded element  44  which is welded to the upper radial surface  34  of the metal ring  12  in alignment with the bolting hole  42  and/or (b) a nut or other internally threaded element  46  which is welded to the lower radial surface  36  of the metal ring  12  in alignment with the bolting hole  42 . Each of the internally threaded elements  44  and  46  is preferably a serrated flange locknut which is welded to the metal ring  12 . 
     During the molding process for forming the inventive molded insert  2 , the high hardness insert molding material is prevented from blocking the bolting holes  42  of the metal ring  12  so that the bolting holes  42  also extend through the insert molding material which encases the metal ring  12  (i.e., through the upper surface  25  and the lower surface  26  of the radially extending attachment ring portion  8  of the molded insert  2 ). 
     Although the metal ring  12  and the radially extending attachment ring portion  8  of the molded insert  2  have been describe as having bolting holes  42  provided therethrough which will be used for bolting the inventive stripper rubber  20  in place in a drilling head system or elsewhere at the wellhead, it will be understood that cam pins or other attachment structures or elements can alternatively project from or be provided by the metal ring  12 , and/or by the radially extending attachment ring portion  8  of the molded insert  2 , for installing the stripper rubber  20  for service at the wellhead. 
     In a first stage of the method of the present invention, the inventive reinforcing insert  2  is preferably formed by: (a) grit blasting the surfaces of the metal ring  12  and applying a primer thereto; (b) positioning the treated metal ring  12  in a mold for forming the molded reinforcing insert  2 ; (c) filling the insert mold, and the bonding voids  40  of the metal ring  12 , with the high hardness elastomer material or other high hardness polymer material (i.e., the insert molding material); (d) curing the insert molding material so that the inventive reinforcing insert  2  is formed as one continuous piece which includes the radially extending attachment ring portion  8  of the insert  2 , with the metal ring  12  encased therein, and preferably also includes the longitudinally extending body portion  6 ; and (d) removing the molded reinforcing insert  2  from the insert mold. 
     In an alternative embodiment, the metal ring  12  of the inventive reinforcing insert  2  can be replaced with a plurality of individual threaded inserts  60 . Each of the individual threaded inserts  60  preferably comprises: a metal plate (e.g., a wide metal washer)  62  having a bolting hole  64  formed therethrough; a nut or other internally threaded element  66  which is welded to the upper surface of the plate  62  in alignment with the bolting hole  64 ; and/or a nut or other internally threaded element  66  which is welded to the lower surface of the metal plate  62  in alignment with the bolting hole  64 . The internally threaded elements  66  used in forming the individual inserts  60  are preferably locknuts having serrated flanges. In forming the alternative embodiment of the inventive reinforcing insert, the individual threaded inserts  60  are preferably held on pins in the mold for the reinforcing insert in a circular bolting arrangement  68  as illustrated in  FIG. 8 . 
     In yet another alternative embodiment, the individual threaded inserts can be T-nuts. 
     After the inventive reinforcing insert  2  is formed, the reinforcing insert  2  is used in accordance with a second stage of the method of the present invention to produce the inventive stripper rubber  20  by: (a) grit blasting the surfaces of the reinforcing insert  2  and applying a primer thereto; (b) placing the reinforcing insert  2  in a stripper mold for forming the stripper rubber  20 ; (c) filling the stripper mold, and the voids  18  of the longitudinally extending body ring portion  6  of the molded insert  2 , if present, with a stretchy, elastic, stripper molding material; (d) curing the stripper molding material; and (e) removing the inventive stripper rubber  20  from the stripper mold. 
     The inventive stripper rubber  20  formed by the inventive two stage process preferably comprises: (a) an upper longitudinal segment or portion  48  of the stripper rubber  20  in which the inventive reinforcing insert  2  in its entirety, or at least the longitudinally extending body portion  6  thereof if present, is encased; (b) a lower segment  50  of the stripper rubber  20  which preferably tapers inwardly (in a straight, curved or other manner) as it extends downwardly from the upper segment  48 ; and (c) a generally cylindrical or other passageway  52  which extends longitudinally through the upper and lower segments  48  and  50  of the stripper rubber  20  for receiving a drill pipe or other well tubular. The upper and lower longitudinal segments  48  and  50  surround the common longitudinal axis  4  of the stripper rubber  20  and the reinforcing insert  2 . The upper longitudinal segment  48  of the inventive stripper rubber  20  will preferably be generally cylindrical in shape or will preferably taper slightly inward (in a straight, curved or other manner) as it extends downwardly to the lower segment  50 . The lower segment  50  will preferably be generally frusto-conical in shape. 
     When the inventive reinforcing insert  2  is fully encased in the upper segment  48  of the inventive stripper rubber  20 , the stretchy, elastic, stripper molding material used for molding the stripper rubber  20  will preferably be prevented during the molding process from blocking at least the upper ends  54  of the bolting holes  42  of the reinforcing insert  2  so that the bolting holes  42  also extend upwardly through the upper end  55  of the upper segment  48  of the inventive stripper rubber  20 . The series of bolting holes  42  preferably encircles the upper longitudinal end of the central, longitudinal passageway  52  of the stripper rubber  20 . 
     The selection of the particular stretchy, elastic material used for molding the inventive stripper rubber  20  can vary depending upon such factors as the drilling medium involved and the dynamic pressures found in the drilling location, as well as the temperature of the drilling mud. The stretchy, elastic, stripper material used for molding the inventive stripper rubber  20  will preferably be an elastomer or other material having a Shore A hardness value of not more than 90, or not more than 85, or not more than 80, or not more than 75. Examples of elastomer materials suitable for forming the inventive stripper rubber  20  include, but are not limited to, polyurethane, natural rubber, butyl rubber, and nitrile rubber. 
     Although the molded reinforcing insert  2  has been described as having both (a) a radial ring portion  8  comprising the metal ring structure  12  encased in the insert molding material and (b) an integrally molded body portion  6  which extends longitudinally from the ring portion  8 , the inventive reinforcing insert  2  can alternatively be formed without the longitudinally extending body portion  6 . This is illustrated by the alternative embodiment  70  of the inventive reinforcing insert shown in  FIGS. 9 and 10 . The inventive reinforcing insert  70  is a molded flat ring structure wherein a metal bolting ring structure  12  as described above, or a circular arrangement of threaded inserts  60 , is encased in any of the same insert molding materials as previously discussed for forming the reinforcing insert  2 . The molded reinforcing insert  70  preferably comprises: an upper radial surface  72 ; a lower radial surface  74 ; a plurality of bolting holes  76  which extend longitudinally through the reinforcing insert  70  from the upper surface  72  to the lower surface  74 , and which also extend through the bolting ring structure  12  or threaded inserts  60  encased within the insert  70 ; and a plurality of holes, apertures or other bonding voids  78  which extend through the insert  70  from the upper surface  72  to the lower surface  74 . The boding voids  78 , which will be filed with the stripper molding material during the stripper rubber molding process, are preferably positioned between the bolting holes  76 . 
     Thus, the present invention is well adapted to carry out the objectives 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, the invention is not limited in its application to the details of the preferred embodiments. Numerous changes and modifications will be apparent to those in the art. Such changes and modifications are encompassed within this invention as defined by the claims. In addition, unless expressly stated, the phraseology and terminology employed herein are for purposes of description and not limitation.