Abstract:
A stripper rubber comprising a resilient stripper rubber body, an insert support, and a plurality of stripper rubber inserts. The resilient stripper rubber body has a drillstring bore extending therethrough. The insert support is at least partially within the body. The insert support includes a central opening generally aligned with the drillstring bore thereby allowing a drillstring to pass jointly through the central opening and the drillstring bore. The plurality of stripper rubber inserts are each at least partially disposed within the body. The inserts are arranged in a side-by-side manner around the drillstring bore with a first end portion thereof pivotably engaged with the insert support. Each one of the inserts is offset from the drillstring bore for precluding the inserts from being exposed from within the body at the drillstring bore.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is a continuation of, and claims priority from, U.S. patent application Ser. No. 10/845,786, filed May 12, 2004, now U.S. Pat No. 7,240,727, by the present inventor, and entitled “Armored Stripper Rubber”. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a long-lasting, deformation-resistant, rubber or elastomer-based seal having a configuration for dynamically sealing against tubular members or drillstring components movable longitudinally through the seal. In particular, the invention relates to stripper rubbers, inserts, and insert assemblies, for stripper rubbers used with rotating control heads, rotating blowout preventers, diverter/preventers and the like, in oil, gas, coal-bed methane, water or geothermal wells. 
     BACKGROUND OF THE INVENTION 
     In the drilling industry, seals are used in various applications including rotating blowout preventers, swab cups, pipe and Kelly wipers, sucker rod guides, tubing protectors, stuffing box rubbers, stripper rubbers for coiled tubing applications, snubbing stripper rubbers, and stripper rubbers for rotating control heads or diverter/preventers. Stripper rubbers, for example, are utilized in rotating control heads to seal around the rough and irregular outside diameter of a drillstring of a drilling rig. 
     Stripper rubbers are currently made so that the inside diameter of the stripper rubber is considerably smaller (usually about one inch) than the smallest outside diameter of any component of a drillstring. As the components move longitudinally through the interior of the stripper rubber, a seal is continuously affected. 
     Stripper rubbers affect self-actuating fluid-tight seals in that, as pressure builds in the annulus of a well, and in the bowl of the rotating control head, the vector forces of that pressure bear against the outside surface or profile of the stripper rubber and compress the stripper rubber against the outside surface of the drillstring. The pressure forces complement the stretch-fit forces already present in the stripper rubber. The result is an active mechanical seal the increases the seal strength as the well bore pressure increases. 
     Well pressure forces often distort the elastic profile of a stripper rubber, deforming the shape from that of a cone to that of a donut. Lowering an oil tool through the stripper rubber often causes the deformed, rolled up, rubber to temporarily uncurl, but the rubber quickly returns to the deformed donut shape once it is re-pressurized. Wear and tear on the stripper rubber occurs, therefore, not only from frictional forces between the rubber and a longitudinally moving oil tool, but from the mechanical forces acting on the rubber as it rolls up and unrolls during drilling operations. 
     Stripper rubbers seal around rough and irregular surfaces of varying diameters such as those found around a drill pipe, tool joints, or a Kelly, and are operated under drilling conditions where strength and resistance to wear are prized attributes. When using a stripper rubber in a rotating control head, the longitudinal location of the rotating control head is fixed due to the mounting of a stripper rubber onto a bearing assembly. The bearing assembly allows the stripper rubber, or stripper rubbers, to rotate with the Kelly or drillstring, but restrains the stripper rubber from longitudinal, axial, movement. Wear of the interior surface of a stripper rubber is caused by relative longitudinal movement of the drillstring components, including the end to end coupling areas of larger diameter joints and the larger diameter of tools that bear against a stripper rubber. 
     Wear and tear upon a stripper rubber from frictional and mechanical forces will, over a period of time, cause a thinning or weakening of the elastic material to the point that the stripper rubber will fail. Such wear is exacerbated by the movement of multiple lengths of a drillstring through the stripper rubber, such as when a drillstring is “tripped” into or out of the well. Furthermore, the stretch-fit of the rubber rapidly becomes exhausted, and the rubber fails to seal the well. Rapid exhaustion of the rubber remains a persistent problem, and requires frequent, sometimes as often as weekly, replacement of the stripper rubber. 
     Metal structures, called “inserts,” embedded in the rubber portion of a stripper rubber are used to provide connectors and structural support to the rubber. For example, U.S. Pat. No. 5,647,444, issued to the present inventor, discloses a dual stripper rubber apparatus. Each stripper rubber provides a pair of circular spring inserts that circumnavigate the packer perpendicular to the drillstring bore. The springs provide structural support to the rubber, yet permit the rubber to dilate so that pipe joints or tools can pass through the drillstring bore of the stripper rubbers. 
     Wear is present in all drilling and production applications where a rubber seal or wiper is subjected to the relative movement of a component such as a drillstring tool. A long-felt need persists for a rubber seal or wiper that is resistant to wear, will withstand the great bore hole pressures of modern wells, and is capable of a longer service life than has been heretofore possible. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is further described in the detailed description that follows, by reference to the noted drawings by way of non-limiting examples of embodiments of the present invention, in which like reference numerals represent similar parts throughout several views of the drawings, and in which: 
         FIG. 1A  is an isometric-view schematic drawing of an insert assembly of one embodiment of the present invention in a contracted posture. 
         FIG. 1B  is an isometric-view schematic drawing of the insert assembly of  FIG. 1A  in a dilated posture. 
         FIG. 2A  is a side view of an insert assembly of  FIG. 1A . 
         FIG. 2B  is a side-view vertical cross-section of the insert assembly of  FIG. 2A  through line  1 - 1  . 
         FIG. 3  is an isometric-view schematic drawing of a support ring with a single unit of insert armor (finger) pendant therefrom. 
         FIG. 4  is a side-view schematic drawing of the support ring-finger assembly of  FIG. 3 . 
         FIG. 5  is an isometric-view schematic drawing of a support ring of one embodiment of the present invention. 
         FIG. 6  is an isometric-view schematic drawing of a finger insert of one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In view of the foregoing, the present invention, through one or more of its various aspects, embodiments and/or specific features or sub-components, is thus intended to bring out one or more of the advantages that will be evident from the description. The present invention is described with frequent reference to stripper rubber inserts. It is understood that a stripper rubber insert is merely an example of a specific embodiment of the present invention, which is directed generically to resilient substrate inserts within the scope of the invention. The terminology, therefore, is not intended to limit the scope of the invention. 
     Long lasting stripper rubbers have been a long felt need in the drilling industry. The advantage of a longer lasting stripper rubber is not only one of safety, but also one of expense since a longer lasting stripper rubber will reduce the number of occasions when the stripper rubber must be replaced, an expensive and time consuming undertaking. A further consideration is the tremendous borehole pressures encountered in modern drilling. Technology enables under balanced drilling. A challenge of modern drilling is to control the great and variable pressures of high-pressure reserves. 
     The present invention provides stripper rubbers, inserts, and stripper rubber-insert assemblies that substantially preserve the profile of the rubber under pressure. An advantage of preserving the rubber profile under pressure is that deformation of the rubber caused by the bore pressure of the well is significantly inhibited from blocking the passage of a tool or drillstring joint through the drillstring bore of the stripper rubber. 
     Another advantage of the present invention is that tools or drillstring joints are tripped up or down hole while the stripper rubber maintains a fluid-tight seal around the drillstring under the pressures of modern wells. The present invention permits the stripper rubber to dilate so that drillstring and tool joints can be tripped through the bore, and then contract around smaller diameter drilling tube with a fluid-tight seal. 
     Generally, stripper rubbers have a frusto-conical shape, being internally wider at the top than at the bottom. The interior shape facilitates passing a joint or tool downhole through the drillstring bore of the stripper rubber by providing a wide top opening to accommodate the tool joint, and tapering downward to a narrower interior opening at the bottom so that the rubber maintains a fluid-tight seal around the drillstring as the tool joint passes through. The resilient nature of the rubber permits the tapered portion of the stripper rubber to dilate so that the tool can pass through. 
     In the absence of external pressure, an annular void exists between the exterior surface of the drillstring and interior surface of the tapered rubber, approximately where the tapering begins at the top of the rubber and extending downward to where the rubber seals around the drillstring. The void exists because the exterior surface of the drillstring has a substantially uniform outer diameter whereas the interior surface of the stripper rubber tapers downward from wider to narrower. The tapered interior shape of the stripper rubber facilitates “stabbing” a tool joint through the drillstring bore of the stripper rubber, where the diameter of the tool joint is wider than the lower (narrow) portion of the interior of the stripper rubber drillstring bore. 
     In operation, upward and inward bore pressures from the well deform typical stripper rubbers and push rubber into the void, filling the void with pressurized rubber. It becomes difficult, therefore, to trip drillstring joints or tools through the stripper rubber. The advantages of the tapered shape of the stripper rubber are lost when the rubber is under pressure. 
     The present invention provides an armored stripper rubber with pivoting inserts that form a dynamic, dilatable and contractible external shell around the rubber. The shell is somewhat analogous to the shell of an armadillo or pill bug. The inserts act in concert to substantially maintain the profile of the rubber under pressure to significantly inhibit pressurized rubber from infiltrating into the void. An advantage of the present invention, therefore, is that tool or drillstring joints may pass through the stripper rubber without encountering a blockage of pressurized rubber filling the void. A further advantage of the present invention is that it increases the capability of the stripper rubber to provide an effective seal around the drillstring and drillstring components. That is, an effective seal is maintained at pressures that would cause prior art stripper rubbers to fail. 
     Referring to the drawings,  FIG. 1A  is an isometric-view schematic drawing of an insert assembly of one embodiment of the present invention in a contracted posture. Assembly  100  is depicted without the elastic sealing material, or other resilient substrate, in which the various inserts are at least partially embedded, in order to view the “cage” formed by the assembly of inserts provided by the present invention. 
     In broad strokes, assembly  100  includes support ring  500  and a plurality of insert “fingers”  600  pendant therefrom. Fingers  600  taper downward from support ring  500  and fit together to form a frusto-conical exterior shape. To provide dynamic resiliency, fingers  600  pivot from support ring  500  such that the narrow, bottom, portion of assembly  100  can dilate and contract, depending on the external diameter of the structure (not shown) disposed or passing through assembly  100 . 
     It is evident from the drawing that shell formed by the inserts in the contracted posture substantially prevents a stripper rubber from contracting to an internal bore diameter smaller than a pre-selected diameter, because the “plates” of the shell fit together and effectively stop further contraction, even under high pressure. Accordingly, the present invention effectively inhibits infiltration, such as puckering or inversion of the resilient substrate, into the drillstring bore of the stripper rubber, which typically occurs with prior art rubbers when they are exposed to downhole well pressures. 
       FIG. 1B  is an isometric-view schematic drawing of insert assembly  100  of  FIG. 1A  in a dilated posture. Insert fingers, or plates,  600  resiliently and elastically pivot radially inward and outward from support ring  500  to facilitate the passage of drillstring components through the drillstring bore of the stripper rubber while maintaining an effective fluid-tight seal around the drillstring. 
     Stripper rubbers having a connector insert that provides means for connecting the stripper rubber to an adapter, inner barrel, or other piece of drilling head equipment, are known in the art. To attach a stripper rubber of the present invention to an inner barrel or other piece of drilling head equipment, therefore, support ring  500  is connected to a connector insert (not shown). For example, support ring  500  may be spot welded, bolted, formed with, or otherwise adapted to a connector insert. 
     In alternative embodiments, however, support ring  500 , indeed, assembly  100 , is not attached directly to a connector insert, and relies, instead, on the mechanical bonding forces of the cured rubber (or other resilient substrate) of the stripper rubber to maintain an attachment to a connector insert. 
       FIG. 2A  is a side-view of an insert assembly of  FIG. 1A .  FIG. 2B  is a side view vertical cross-section of the insert assembly of  FIG. 2A  through line  1 - 1 . In the absence of well pressure, void  200  exists between exterior surface  210  of the drillstring, indicated by a vertical dashed line, and interior surface  220  of the stripper rubber. Annular seal point  230 , where tapered interior surface  220  of the stripper rubber contacts drillstring surface  210 , defines the lower perimeter of void  200 . 
     Although the rubber substrate of a stripper rubber is resilient or elastic to a certain extent, the substrate is, nevertheless, a cured polymer that generally requires substantial force to elastically deform. Under the well pressures of typical wells, and certainly under the high pressures of particular wells, the rubber substrate of a typical prior art stripper rubber would be forced upward, deforming the profile of the rubber such that the rubber at least partially fills void  200 . Catastrophic deformation is known to occur, where the stripper rubber deforms into void  200  to such an extreme, or with such force, as to “blowout” the rubber. “Blowout” is a misnomer, in that the rubber actually implodes inward, perforates, and pressurized fluids burst upward to blast out into the atmosphere. 
     The present invention, however, substantially overcomes the problem of blowouts. In the embodiment of  FIG. 2 , for example, finger inserts  600  provide structural support to the rubber substrate of the stripper rubber to substantially preserve its profile and inhibit the infiltration of void  200  by pressurized rubber. The insert cage around the exterior of the rubber and the drillstring through the stripper rubber drillstring bore, combine to confine the rubber such that, effectively, the rubber becomes less elastic. One advantage of the loss of elasticity is that the fluid-tight seal can be maintained at high pressures. Another advantage of the loss of elasticity is that blowouts are substantially reduced. 
     Exterior surface  610  of each finger  600  extends outward at least slightly beyond flush with exterior surface  240  of the rubber portion of the stripper rubber. When in a contracted posture, such as when pressurized, finger inserts  600  substantially encase the rubber substrate in a shell of rigid material, such as metal, which withstands the well pressure without substantial deformation. Accordingly, joints can be tripped through the stripper rubber without encountering a significant blockage of confined pressurized rubber. 
     Since fingers  600  are pivotally suspended from ring  500 , an additional benefit of the present invention is that the stripper rubber of the present invention is able to dilate, while maintaining a fluid-tight seal, to allow joints to trip through without compromising the seal, and then to contract around the drillingstring to preserve the fluid-tight seal after the joint has passed. Alternative embodiments further provide one or more circumferential spring inserts (not shown) axially positioned in the substrate to provide additional structural support or to reinforce the fluid-tight seal. 
     Support ring  500  is entirely embedded in the rubber substrate. The attachment of fingers  600  to support ring  500 , therefore, is reinforced by the rubber. 
       FIG. 3  is an isometric-view schematic drawing of support ring  500  with a single unit, or “finger,” of insert armor  600  pivotally pendant therefrom. Ring  500  defines drillstring bore  300 , through which lengths of drillstring, together with attendant joints or tools, are tripped up or down well. 
     Support ring groove  510  traverses the circumference of ring  500  perpendicular to drillstring bore  300 . Insert finger  600  is oriented such that surface  610  is an exterior surface and surface  620  is a side surface. The side opposite surface  610 , i.e., the interior surface of finger  600 , provides insert flange  630 , which extends inward toward bore  300 . Hinge portion  640  and groove  510  are cooperatively adapted to provide a pivoting attachment. Particular embodiments of the invention allow for insert finger  600  to “snap” on to support ring  500  at groove  510  to accomplish the pivoting attachment. Other embodiments (not shown) provide a pin and bore type hinge. 
       FIG. 4  is a side-view schematic drawing of the support ring-finger assembly of  FIG. 3 . Hinge portion  640  of insert  600  provides a convex extension, or lip,  650  (male) that mates with concave groove  510  (female) of support ring  500 . Alternative embodiments (not shown) of the invention provide an inverse relationship, wherein support ring  500  has a male, or convex, circumference  510 , and hinge portion  640  has a female, or concave portion  650 , that mate together to form a pivoting attachment. 
     Insert flange  630  is recommended to provide one or more flange bores  660 . Bores, or perforations,  660  become infiltrated with fluid rubber, or other suitable elastomeric material, during manufacture of the stripper rubber. Once the rubber is cured, bores  660  enhance the physical, mechanical, bond of insert  600  to the rubber substrate. 
       FIG. 5  is an isometric-view schematic drawing of support ring  500  of one embodiment of the present invention. The inner diameter of drillstring bore  300  should be sized to accommodate the largest joint or tool to be tripped through the stripper rubber. Accordingly, the present invention contemplates embodiments of varying diameters as defined by the diameter of bore  300 . 
     Support ring  500  is an insert that is entirely embedded in the rubber substrate of the stripper rubber. It is recommended that the exterior surface of ring  500  be as devoid as practicable of sharp edges or acute angles so as to minimize the ability of the ring to cut or shred the rubber as the result of shearing actions from elastic deformation. Chamfer  520 , for example, bevels an interior circumferential edge of ring  500  to reduce the sharpness of the edge. 
       FIG. 6  is an isometric-view schematic drawing of finger armor insert  600  of one embodiment of the present invention. The view features the interior side of insert  600 . Inserts are typically made of metal or metal alloys, but the present invention further contemplates that inserts may be synthetic, composite or any suitably durable material. Forming a strong bond between the insert and the rubber substrate is an engineering challenge recognized in the art. One strategy is to provide perforated inserts. 
     During production of the present invention, for example, fluid elastic material such as rubber, or any suitably resilient substrate, fills flange bores  660  so that, upon resilient hardening or curing of the substrate, finger  600  becomes mechanically embedded, except for exterior surface  610 , in the material and thus becomes an insert. In effect, flange  630  is gripped by the cured rubber through perforations  660  so that it is very difficult for insert  600  to slip out of the rubber. Beveled edges for perforations  660  reduce shear that would tend to cut the rubber. 
     While recommended, perforations  660  are not required. The particular number, shape, size, orientation, or other parameters of the perforations may be selected as desired or as recommended by experience. Alternative embodiments of the present invention, for example, provide perforations (not shown) through recesses  670  which extend out through exterior surface  610 . Particular embodiments of such perforations through recesses  670  provide a relatively small diameter bore proximate to recesses  670  opening to a relatively larger diameter bore proximate to surface  610 . Other means for enhancing the mechanical grip of the rubber on the insert include dimples (concave recesses), bumps (convex extensions), or any topological feature, or combinations thereof, that the rubber can grip. 
     To further enhance the strength of the insertion, one or more recesses  670  are filled with a bonding agent that provides, or improves, the chemical bond between the insert and the cured rubber. The combination of chemical bonding with mechanical gripping provides a highly reliable stripper rubber insert assembly. 
     Each finger insert  600  tapers downward at an angle compatible with the tapering of the stripper rubber. Side surface  620 , on each longitudinal side of insert  600 , is angled inward. When the insert “cage” of the depicted embodiment is assembled, with a plurality of finger inserts  600  pivotally suspended from a support ring, and the assembly is in a contracted posture, the inward angle of each side surface  620  is adapted so that fingers  600  substantially fit together to provide a shell of armor around the rubber substrate. See  FIG. 1 . In an embodiment having  12  finger inserts forming the cage, for example, each side surface  620  angles inward at 30°. The inward angle is adapted to provide a selected fit of the fingers, depending on the number of fingers provided in a selected embodiment of the invention. A significant feature of the cage of the present invention is that the cage stops further significant contraction of the stripper rubber once the plurality of fingers  600  are compressed together. 
     Operationally, a stripper rubber contracts under the pressure of a well. In fact, it is not uncommon for the rubber to invert or pucker under high pressure, thus compromising the seal and/or causing drillstring pipe to become stuck within the rubber. Inadequate structural support to stop the contraction and maintain the rubber profile is a prime contributing factor to such problems. 
     An advantage of the present invention is that, by virtue of fitting together to form a shell when the stripper rubber is exposed to operational well pressures, finger inserts  600  physically contact each other along sides  620  and stop the shell from contracting any smaller than a specific diameter. The shell substantially prevents inversion or puckering of the rubber and, thus, substantially reduces incidents of undesirable results from rubber deformation. 
     Particular embodiments of the present invention provide finger inserts  600  that extend substantially the entire longitudinal length of the stripper. Other embodiments provide inserts  600  that are some selected length shorter than the stripper rubber, so that a desired length of rubber extends beyond the bottom of the shell. A specific embodiment may be selected depending on the nature of the performance that is desired by the well operator. A longer insert provides greater structural support to reduce rubber deformation, whereas a shorter insert may provide a better fluid-tight seal. 
     The finger insert embodiment depicted in  FIG. 6  is formed to provide a finger shoulder  680  proximate to, and to either side of, hinge portion  640 . Alternative embodiments substantially eliminate finger shoulders  680 , so that hinge sides  690  are substantially contiguous with insert sides  620 . 
     Further advantages of the present invention include a stripper rubber that maintains its profile, that is, resists longitudinal elastic deformation from bore pressures acting on the resilient substrate. Another advantage of the present invention is a stripper rubber that withstands the high, sometimes explosive, bore hole pressures encountered in certain wells. By providing a stripper rubber that withstands high pressure, the present invention enables effective pressure control for high pressure wells. 
     Although the invention has been described with reference to several exemplary embodiments, it is understood that the words that have been used are words of description and illustration, rather than words of limitation. Changes may be made within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the invention in all its aspects. Although the invention has been described with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed; rather, the invention extends to all functionally equivalent technologies, structures, methods and uses, either now known or which become known, such as are within the scope of the appended claims.