Abstract:
Backup rings are disposed on opposed sides of a sealing element. The backup rings are initially bow shaped in the run in position. Opposed ends of the bow shape are brought together to extend the extrusion barriers and compress the sealing element. The relative axial movement that brings the opposed ends of the bow shape together results in radially extending the bow shape. The bow shape is reformed into a teardrop shape that extends radially beyond a pinch location created by relative axial movement of adjacent support members coming closer together. A sealing element extends radially during the deployment of the extrusion barriers and is contained between them. The extension of the extrusion barriers allows conformance to surface irregularities in the surrounding tubular or wellbore wall.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of the invention is seal backup systems for subterranean packers and more particularly conforming backup members that adapt to any out of roundness or irregularity of the surrounding tubular or wellbore wall. 
       BACKGROUND OF THE INVENTION 
       [0002]    When packers are set to isolate zones in a subterranean location the differential pressure across the sealing element can force that element to extrude axially in the direction of the pressure differential. Backup ring structures have been used to address the tendency to extrude under differential pressure loading. A collection of segments that overlap and can be forced out by relative axial component movement have been tried such as in US Publication 2011/0036561 and US Publication 2010/0071908. Despite the use of many segments to make an annular backup assembly the nature of the way the parts fit together and move radially does not always allow the components to adequately conform to out of roundness or surface irregularities of the surrounding tubular or the wellbore wall. 
         [0003]    Some designs provided cup shaped backup ring stacks that has staggered slots as between layers as an extrusion barrier in expansion ranges up to 25%. U.S. Pat. No. 6,827,150 is an illustration of one such design. Others are U.S. Pat. No. 7,128,145; US Publication 2004/0149429 and 2005/0115720. Other high expansion packer designs are US Re 32,831; U.S. Pat. Nos. 6,311,778; 6,318,461 and 6,164,375. 
         [0004]    Despite the variation of designs for backup rings as extrusion barriers the issue of gaps around the periphery remained and is addressed by the present invention. 
         [0005]    In the field of metal to metal seals a design has been developed that features a bow shaped sealing element that is axially compressed at opposed base locations and then pinched between two relatively movable members as the element extends to make metal to metal contact with the opposing tubular as illustrated in US Publication 2009/0071641. In one embodiment soft metals or elastomers can be added at the opposing wall contact location to address the wall imperfections of the surrounding tubular to enhance the performance of the seal. A variation of this design for seals uses a flimsy metal annular shape filled with rubber and compressed on opposed ends so that the metal outer shape obtains structure from the interior fill material to seal against the surrounding tubular. This design is shown in U.S. Pat. No. 5,775,429 with many variations including an application as an extrusion barrier in  FIGS. 8 and 9 . 
         [0006]    The present invention focuses on improving performance of backup rings where conformance to irregular surfaces is a feature. Axial relative movement results in collapsing a bow shaped backup ring on either side of a sealing element when the backup rings are converted to a teardrop shape by pinching along a length of the radially extending shape with relative axial movement between compressing members that support the ends of the bow shape. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and associated drawings while recognizing that the full scope of the invention is to be found in the appended claims. 
       SUMMARY OF THE INVENTION 
       [0007]    Backup rings are disposed on opposed sides of a sealing element. The backup rings are initially bow shaped in the run in position. Opposed ends of the bow shape are brought together to extend the extrusion barriers and compress the sealing element. The relative axial movement that brings the opposed ends of the bow shape together results in radially extending the bow shape. The bow shape is reformed into a teardrop shape that extends radially beyond a pinch location created by relative axial movement of adjacent support members coming closer together. A sealing element extends radially during the deployment of the extrusion barriers and is contained between them. The extension of the extrusion barriers allows conformance to surface irregularities in the surrounding tubular or wellbore wall. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic view of one embodiment of a backup ring disclosed herein in a run in condition; 
           [0009]      FIG. 2  is a schematic view of the embodiment of  FIG. 1  illustrated in a set position; 
           [0010]      FIGS. 3A-3F  represent sequential views of the seal of  FIG. 1  withdrawing from the set position during retrieval; 
           [0011]      FIG. 4  is a schematic view of an alternate embodiment in a run in condition; and 
           [0012]      FIG. 5  is the embodiment of  FIG. 4  in a set position; 
           [0013]      FIG. 6  is a section view of a packer using the extrusion barriers and shown in the run in position; and 
           [0014]      FIG. 7  is the view of  FIG. 1  in the set position. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0015]    Initially it is to be understood that the backup ring created as disclosed herein performs better in one respect due to its teardrop cross sectional shape. The shape itself helps to absorb backlash in the setting force and therefore renders the backup ring more reliable. This is described in more detail in connection with one embodiment of a backup ring that forms the stated shape. It is also to be understood that although the drawings hereof illustrate a backup ring that bows radially outwardly, the components can easily be reversed such that the backup ring will bow radially inwardly such that the backup ring will be formed against a tubular radially inwardly disposed of the backup ring device rather than radially outwardly of the backup ring device as specifically illustrated. 
         [0016]    Referring to  FIG. 1 , an embodiment of a backup ring  10  in accordance with this disclosure is illustrated. The backup ring  10  comprises a backup ring body  12  having a first end ring  14  and a second end ring  16 . Backup ring body  12  comprises a backup ring bridge  18  and first and second backup ring legs  20  and  22 . The legs terminate at roots  36  and  38 . Backup ring  10  further includes configurations capable of causing the backup ring body to collapse axially into a set position such as, for example, two gauge rings  24  and  26 , each disposed in operable communication with one end of the backup ring body  12 . While gauge rings are specifically disclosed, the terms as used herein are intended to convey any configuration capable of loading the backup ring body  12  to set the backup ring  10  and to be instrumental in retrieving the backup ring  10 . This “operable communication” as noted is, in one embodiment, a fixed connection to each end ring  14  and  16 , respectively, while in other embodiments it can float. The fixed connection as illustrated is adjacent roots  36  and  38 . The gauge rings  24  and  26  are also in supportive communication with the legs  20  and  22 , respectively. As can be readily seen in  FIG. 1 , each gauge ring includes an angled surface identified by the numerals  28  and  30 , respectively. The surfaces  28  and  30  are roughly parallel to the legs  20  and  22  although not in contact therewith prior to the setting sequence for the backup ring  10 . These surfaces  28  and  30  come in contact with the legs  20  and  22  during the setting sequence to support the same as will be better appreciated after exposure to the operation section of this document. 
         [0017]    Also visible in  FIG. 1  are two radiuses  32  and  34  provided one on each of gauge rings  24  and  26 , respectively. The radiuses, in one embodiment, are in a range of about 0.13 to about 0.16 inch. While a wider range is also operable, it has been found that the range of about 0.13 to about 0.16 is effective in minimizing stress in the backup ring body  12  during setting. This is also the purpose for which the angled surfaces  28  and  30  are provided. The angle of the surfaces  28  and  30  is selected to coincide with the angle of legs  20  and  22  as noted above in order to support these structures thereby preventing significant bending thereof during setting of the backup ring  10 . Angles for surfaces  28  and  30  range in particular embodiments from about 45 degrees to about 90 degrees. As illustrated, the angles are both about 60 degrees. The range indicated has been found to work well though it is to be appreciated that angles outside the exemplary range are also contemplated but may not reduce stress in legs  20  and  22  to the extent of the reduction found in the identified range. 
         [0018]    The prevention of bending reduces work hardening effects that would otherwise be experienced in these locations. Such reduction in work hardening effectively equates to more residual elasticity in the material of the seal in locations of the seal (legs and roots) that will be subject to bending stresses upon retrieval of the seal. During setting of the seal the bending stress is localized in the bridge  18  and in retrieval, bending stress is localized in the legs and roots. Generally, materials that are somewhat ductile can be bent at least once without breaking, work hardening, of course, building within the material during this and any subsequent bending stress. Since in the disclosed backup ring, the configuration ensures that bending is experienced substantially only once in each localized area of the backup ring body  12 , the likelihood of each localized area enduring sufficient stress to rupture is dramatically reduced. The protective action of the surfaces  28  and  30  extends to both the legs  20  and  22  and leg roots  36  and  38 , respectively. By avoiding stress in these structures during setting of the backup ring  10 , the ability to retrieve the backup ring  10 , without suffering a rupture of the backup ring, is facilitated. It is further noted that in the backup ring  10 , nowhere is there a sharp bend of the material of the backup ring body  12 . Rather, all bends are gradual thereby spreading the stress over a broader area of the backup ring material. This avoids point stresses that generally create weaknesses in the backup ring both while being initially deformed and certainly while being retrieved. As such, embodiments of the invention alleviate the problem found in the prior art as noted above. 
         [0019]    One last point that should be made prior to a discussion of actuation of an exemplary backup ring  10  is that backup ring body  12  is a machined part in one embodiment such that there are no, or extremely little, residual stresses in the body  12  in the position shown in  FIG. 1 . Little residual stress in the backup ring body  12  prior to deformation in use is a benefit as this helps to minimize the magnitude of stresses experienced by the body  12  during setting. As the purpose of this configuration is the reduction in initial stress of the body  12 , it is noted that an alternate arrangement is that body  12  could be a preformed and stress relieved component for some applications or even a molded component for some applications. Again, the important thing is that the position illustrated at the roots  36  and  38  is a position of the backup ring body  12  that should exist prior to setting of the backup ring, with very little residual stress. Further, stress is not introduced into roots  36  and  38  during the setting of the backup ring  10  due to the configuration of the gauge rings thereby retaining elasticity of the material of the body  12  in the legs and the roots. This is to the operator&#39;s advantage during retrieval of the backup ring  10 , as noted above. 
         [0020]    Referring now to  FIGS. 1 and 2  simultaneously, setting of backup ring  10  is illustrated. Backup ring  10  is set through the application of an axial load resulting in the space between the gauge rings diminishing. This can be effected in a number of ways including: 1) by causing at least one of the gauge rings to move toward the other of the gauge rings while the “other” gauge ring is stationary; 2) to cause one ring to move toward the “other” ring while the other ring moves away from the one ring more slowly than the one ring is moving toward the other ring; or 3) to cause one ring to move toward the other ring while the other ring is moving towards the one ring. For illustrative purposes, the drawings and description herein are directed to an embodiment where gauge ring  24  is moved while gauge ring  26  remains stationary through, for example, operable contact with an anchoring mechanism (not shown). 
         [0021]    Due to the shape of body  12 , one will appreciate that axial shortening thereof will necessarily cause the body  12  to bulge outwardly. What may not be immediately appreciated from the drawings, however, is the action of gauge rings  24  and  26  on the process. As gauge rings  24  and  26  are moved so that they are closer to one another, surfaces  28  and  30  come into contact with legs  20  and  22 , respectively. As contact is made in this location, the legs  20  and  22  are substantially supported such that they and the roots  36  and  38  from which the legs extend experience very little bending stress while the backup ring  10  is being set. Since the distance between gauge rings  24  and  26  is still being reduced, however, the backup ring body  12  must necessarily still react. Due to the supported condition of legs  20  and  22 , a great majority of the bending stress in the body  12  is concentrated in the bridge  18 . The stress in bridge  18  causes it to bow outwardly until it makes contact with an inside surface  40  of a tubular in which the backup ring  10  is being set. Once contact is made at surface  40 , a load useful for creating the desired backup ring begins to build. As gauge rings  24  and  26  continue to be urged into closer proximity with one another it will become apparent that radiuses  32  and  34  are also important to reducing stress in the backup ring body  12 . In the position of  FIG. 2 , it will be easily appreciated that were the radiuses to be significantly sharper, much higher stress would be experienced by the backup ring body  12  at the contact point with such radiuses. It has been determined by the inventors hereof that a radius range of from about 0.13 inches to about 0.16 inches produces a desirably low stress in the backup ring body  12 . 
         [0022]    It is to be appreciated from  FIG. 2  that the bridge  18  is deformed such that over an axial length thereof, more than 180 degrees of repositioning is represented. In other words, the bridge  18  is deformed from relatively flat to beyond U-shaped. In the illustrated embodiment of  FIG. 2 , it will be appreciated that the bridge is nearly a closed teardrop shape  44 . In the condition illustrated in  FIG. 2  substantial sealing force is applied to surface  40  such the pressure may be held in either direction relative to backup ring  10 . Important to notice as well is that because of the teardrop shape of bridge  18 , backlash in the setting system is better absorbed than in prior art backup ring systems. This is because with a reduction in the sealing force at gauge rings  24  and  26  move slightly away from each other. When this occurs, elastic resilience in the bridge  18  will tend to straighten the two sides  46  and  48  of the teardrop shape  44 . This will tend to increase loading at interface  50  with surface  40  rather than to reduce loading at interface  50  which would have been common in the prior art. 
         [0023]    Referring now to  FIGS. 3   a  through  3   f  retrieval of backup ring  10  is illustrated in sequence. It is important to note in this sequence of drawings the relative positions of the legs  20  and  22  versus the teardrop shape  44  as they are illustrated in  FIGS. 3   b  and  3   c . Upon review of these figures it will become apparent to one of ordinary skill in the art that the teardrop shape  44  is maintained substantially intact while the legs  20  and  22  and the roots  36  and  38  are subjected to tensile bending stress and experienced a greater degree of movement. This is beneficial since as noted above the legs and roots are protected from bending stress during initial setting of this backup ring. Therefore they have significantly greater elasticity than the bridge  18 , which has been work hardened, at this stage in use of the backup ring  10 . With reference to  FIG. 3   d , it can be ascertained that the bridge  18  has begun to reopen but it is also important to note that the interface  50  has come out of contact with surface  40  by a significant margin at this point in the retrieval process. While more bending stress is being added to bridge  18  at this point in the process a rupture is less likely to create a problem. Moving on to  FIGS. 3   e  and  3   f  the backup ring has already been substantially withdrawn and again rupture at this point is less damaging. It will also be appreciated by the reader at legs  20  and  22  and roots  36  and  38  are now significantly deformed but because this deformation is the first bending stress experienced by those components, they are highly likely to survive that stress. 
         [0024]    The foregoing description might be reasonably understood to relate to only a symmetrically positioned backup ring. It is to be appreciated however that depending upon the type of movement utilized during the setting process it is sometimes advantageous to prepare the backup ring  10  as a non-symmetrical device. More specifically, and utilizing one-gauge-ring movement as an example, if gauge ring  24  is moved toward gauge ring  26  while gauge ring  26  is held in a stationary position it is reasonably likely that the teardrop shape  44  will contact the inside surface  40  (at interface  50 ) before the backup ring  10  is fully set. While it is subtle in the drawings utilized to exemplify the invention, careful consideration of the illustrated position of interface  50  relative to a centerline of the backup ring  10  will show that it is offset in the direction of gauge ring  24 . This is because of the contact with surface  40  prior to fully setting of the backup ring  10 . Once contact is made at interface  50 , the positioning of side  48  is relatively fixed and the positioning of side  46  will continue to change. Side  46  will deflect under the impetus of gauge ring  24  to have a greater curvature than that of side  48 . Because it is desirable to promote symmetry as much as practicable in teardrop  44  it may be desirable in certain applications to vary a thickness of the backup ring body  12  over its length. More specifically is possible to utilize thickness of backup ring body  12  to encourage early deformation in some portions of the backup ring body  12  and delayed deformation in other portions of the backup ring body  12 . Generally speaking in order to enhance symmetry in the teardrop  44  a lesser thickness at the more relatively fixed end of backup ring body  12  will allow side  48  to more readily deform into a desirable position. Likewise, while the angles of the angled surfaces  28  and  30  and the radiuses  32  and  34  need not be symmetrical and in some applications may be better operable by being disparate. It is further to be understood that although the disclosure hereinabove describes an embodiment where each component is mirrored on both axial ends of the backup ring  10 , albeit not necessarily with the identical dimensions or shapes, the teardrop shape can still be created with asset of the identified components on but one axial side of the backup ring  10  with the other side being simply attached to a carrier component. 
         [0025]    Referring now to  FIGS. 4 and 5 , an alternate embodiment is illustrated having a separate material  52  to enhance sealing properties of the bridge  18  at a seal interface thereof and against the inside surface  40 . Although the material  52  is illustrated as a separate piece from the material of the bridge, it is also contemplated that the material  52  could be a coating on the bridge or the bridge could be that material. Whether configured as a separate piece or as a coating, the material  52  is a relatively soft material such as soft metal like copper, gold, silver, palladium, platinum, tin, lead, bismuth, etc, or alloys of these metals that can be applied to the bridge by such methods as plating, brazing, thermal spray, sputtering, etc. or elastomers, or plastic materials such as Teflon, Polyetheretherketones (PEEK), etc. that can be applied and/or bonded by various industry recognized processes, which enhances the sealing operation by deforming easily to imperfections in the inside surface  40  as well as geometric variations in the backup ring due to the eccentric bending that occurs therein. In all other respects, the configuration is the same as that of the foregoing disclosure. 
         [0026]    Referring now to  FIGS. 6 and 7  the run in and set positions of the backup rings  70  and  80  described in detail above are shown with the sealing element  90  in between and all parts supported on the mandrel  100 . Shoulder  110  is stationary and sleeve  120  is pushed toward shoulder  110  to obtain the set position of  FIG. 7 . Alternatively shoulder  110  can be a part of a movable sleeve that is not shown so that opposed relative movement squeezes the backup rings  70  and  80  to extend to the surrounding tubular or wellbore wall  130  preferably before the sealing element  90  is radially extended to engage the wall  130 . When the backup rings  70  and  80  in position against tubular or wall  130  the changing shape of the sealing element  90  can occur in a contained space as illustrated in  FIG. 7  where the element  90  is schematically illustrated as substantially filling the space between the end rings  70  and  80 . The teardrop shape  140  generally conforms to the surface or wall  130  and preferably seals against it although perfect sealing is not critical in a backup ring application as it would be in a sealing application as discussed in US Publication 2009/0071641. 
         [0027]    Although shown in pairs in  FIGS. 6 and 7  if the pressure differential is only expected in a single direction then one of the backup members illustrated can be used instead of an opposed pair. Even when a pair is used as illustrated their configurations need not be identical and dimensional variations can be used to compensate for expected wall irregularities or variations in differential extrusion forces after the set position is achieved. Although the seal  90  is shown as a single sleeve, that illustration is schematic and the seal assembly can be a collection of sleeves and spacers that are made of the same or differing materials. Alternatively, two or more backup rings such as  70  or  80  can be placed on either side or both sides of the sealing element  90 . The actuation system that extends the backup rings  70  or  80  can be mechanical or pressure set or simply with use of string weight to set down weight to extend the rings. 
         [0028]    The sealing element  90  can be bonded to the backup rings  70  and  80  so that retraction of sleeve  120  will first extend ring  70  and then relax the sealing element  90  followed by a retraction of element  80  so that the assembly can be retracted from the subterranean location or relocated and redeployed. 
         [0029]    It should be noted that although the foregoing discussion has focused upon the creation of a backup ring, further contemplated is the addition of a roughened surface at the interface of the bridge and a separate structure to act as an anchoring device. The anchoring function can range from a partial anchor and a backup ring to an anchor alone depending upon the desired purpose of the device. 
         [0030]    While preferred embodiments have been shown and described, modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation.