Abstract:
A unique backup ring against ends of a sealing element features axial slots extending part way along a cylindrical segment of the backup ring. The slots end in rounded openings to relieve stress and a part of the cylindrical shape of the backup ring is solid. The slotted end of the cylindrical portion is tapered in section toward the end overlapping the sealing element. The face of the backup ring away from the sealing element is tapered and rides on an adjacent tapered surface away from the mandrel during the setting. The tapered seal end of the backup ring bends to reach the surrounding tubular before the balance of the cylindrical portion reaches the surrounding tubular. Extrusion along the mandrel is stopped by a mandrel seal on an adjacent wedge ring. The mandrel end of the backup ring has a peripheral stiffener to lend rigidity.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a Continuation-in-Part and claims priority to U.S. application Ser. No. 14/989,199 filed on Jan. 6, 2016. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The field of the invention is sealing systems for subterranean tools against tubular or open hole or cased hole and more particularly backup rings that are disposed at opposed ends of a sealing element assembly to contain the sealing element against axial extrusion. 
       BACKGROUND OF THE INVENTION 
       [0003]    In the unconventional drilling and completion industry, oil and gas deposits are often produced from tight reservoir formations through the use of fracturing and frack packing methods. To frack a well involves the high pressure and high velocity introduction of water and particulate media, typically a sand or proppant, into the near wellbore to create flow paths or conduits for the trapped deposits to flow to surface, the sand or proppant holding the earthen conduits open. Often, wells have multiples of these production zones. Within each production zone it is often desirable to have multiple frack zones. For these operations, it is necessary to provide a seal known as a frack packer, between the outer surface of a tubular string and the surrounding casing or borehole wall, below the zone being fractured, to prevent the pumped fluid and proppant from travelling further down the borehole into other production zones. Therefore, there is a need for multiple packers to provide isolation both above and below the multiple frack zones. 
         [0004]    A packer typically consists of a cylindrical elastomeric element that is compressed axially, or set, from one end or both by gages within a backup system that cause the elastomer to expand radially and form a seal in the annular space. Gages are compressed axially with various setting mechanisms, including mechanical tools from surface, hydraulic pistons, atmospheric chambers, etc. Setting typically requires a fixed end for the gages to push against. These fixed ends are often permanent features of a mandrel but can include a dynamic backup system. When compressed, the elastomeric seal has a tendency to extrude past the gages. Therefore, anti-extrusion backups have become common in the art. However, typical elastomeric seals maintain the tendency to extrude through even the smallest gaps in an anti-extrusion backup system. 
         [0005]    In cased-hole applications, anchoring of compression set packers is a common feature in the completion architecture. Anchoring is provided by wedge-shaped slips with teeth that ride up ramps or cones and bite into the casing before a packer is set. These systems are not part of the backup system nor are they designed to provide anti-extrusion. Often they are used in the setting of the packer to center the assembly which lowers the amount of axial force needed to fully set the elastomer seal. Once set, anchoring systems are also useful for the life of the packer to provide a uniform extrusion gap, maintain location and help support the weight of a bottom-hole assembly in the case of coiled tubing frack jobs. Anchors also prevent tube movement in jointed strings resulting from the cooling of the string by the frack fluid. Movement of the packers can cause them to leak and lose seal. 
         [0006]    In open-hole frack pack applications it is rarer for the packer to have anchoring mechanisms, as the anchor teeth create point load locations that can overstress the formation, causing localized flow paths around the packer through the near well-bore. However, without anchors, movement from the base pipe tubing can further energize the elastomeric seal. Energizing the seal from tube movement tends to overstress the near wellbore as well, leading to additional overstressing of the wellbore, allowing communication around the packer, loss of production, and potential loss of well control to surface. However, the art of anchoring has been reintroduced in new reservoirs in deep-water open-hole fracking operations. The current state of the art in open-hole frack pack operations requires a choice between losing sealing due to anchor contact induced fractures, packer movement, or over-energizing of the elastomeric element. 
         [0007]    Extrusion barriers involving tapers to urge their movement to block an extrusion path for a sealing element have been in use for a long time as evidenced by U.S. Pat. No. 4,204,690. Some designs have employed tapered surfaces to urge the anti-extrusion ring into position by wedging them outwardly as in U.S. Pat. No. 6,598,672 or in some cases inwardly as in U.S. Pat. No. 8,701,787. Other designs simply wrap thin metal rings at the extremities of the sealing element that are designed to contact the surrounding tubular to create the anti-extrusion barrier. Some examples of these designs are U.S. Pat. No. 8,479,809; U.S. Pat. No. 7,708,080; US 2012/0018143 and US 2013/0147120. Of more general interest in the area of extrusion barriers are U.S. Pat. No. 9,140,094 and WO 2013/128222. 
         [0008]    These solid rings used in the past against the ends of the sealing element assembly still had issues with preventing axial extrusion and provided a great deal of resistance in the setting process. Accordingly, a backup ring with axial slots having rounded ends was developed where the slots go part way down the cylindrical portion of the backup ring assembly and the cross-sectional shape of the cylindrical portion is tapered down in a direction toward the free end of the cylindrical portion. The face opposite the contact face with the sealing element is abutted to a sloping surface to allow the backup ring to ride up radially away from the mandrel during the setting. The tapered segment flexes toward the surrounding tubular during setting movement and the remainder of the cylindrical portion then arrives to contact the surrounding tubular. The non-slotted portion of the cylindrical shape acts as a barrier against the surrounding tubular. A seal on an adjacent wedge ring that is against the mandrel ultimately stops axial extrusion along the mandrel. 
         [0009]    In some applications the gap across which the seal is expected to function is quite large placing such applications beyond the limits of the design in U.S. Pat. No. 6,598,672. There is a need for an extended reach design that can withstand the pressure differentials. This need is addressed with a wedge shaped extrusion ring assembly that, depending on the gap to be spanned is pushed on opposing ramps along a pedestal ring for extended reach when contacted by an outer support ring. To fixate the extrusion ring in the extended position an outer support ring also moves into contact with the extrusion ring in its extended position on the pedestal ring. In the extended reach configuration of the extrusion ring, the backup ring moves part way toward the surrounding tubular or borehole. In shorter reach applications the extrusion ring can move out to the surrounding tubular or borehole wall on one side of the pedestal ring and the outer support ring is eliminated. The backup ring is wedged against the surrounding borehole wall to allow it to act as an anchor for the plug that has the sealing system. In the extended reach configuration the reaction forces from the extrusion ring are directed into the abutting backup ring and into the setting system so that the backup ring is prevented from being squeezed out of its wedged position against the pedestal ring. The present invention is focused on the extrusion ring abutting the ends of the sealing element and the various features and movement of that ring to provide reliable barrier against extrusion along the borehole wall. 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 the associated drawings while understanding that the hall scope of the invention is to be found in the appended claims. 
       SUMMARY OF THE INVENTION 
       [0010]    A sealing element is flanked by wedge-shaped extrusion ring assemblies. The extrusion rings are continuous for 360 degrees and are slotted from the outside dimension and alternatively from the inside dimension to allow the diameter to increase to the surround tubular or open hole. The extrusion rings climb a ramp on an adjacent pedestal ring on the way out to the borehole wall. Depending on the dimension of the gap to be spanned the extrusion ring slides a variable distance up the pedestal ring ramp. An optional anchor ring is initially forced up an opposite ramp of the pedestal ring. If the sealing gap is short the anchor ring can be eliminated. For larger gaps the anchor ring moves out far enough toward the borehole wall to contact the extrusion ring located on an opposing ramp of the pedestal ring so that reaction forces are directed to keep the anchor ring wedged in position for support of the extrusion ring assembly. 
         [0011]    A unique backup ring against ends of a sealing element features axial slots extending part way along a cylindrical segment of the backup ring. The slots end in rounded openings to relieve stress and a part of the cylindrical shape of the backup ring is solid. The slotted end of the cylindrical portion is tapered in section toward the end overlapping the sealing element. The face of the backup ring away from the sealing element is tapered and rides on an adjacent tapered surface away from the mandrel during the setting. The tapered seal end of the backup ring bends to reach the surrounding tubular before the balance of the cylindrical portion reaches the surrounding tubular. Extrusion along the mandrel is stopped by a mandrel seal on an adjacent wedge ring. The mandrel end of the backup ring has a peripheral stiffener to lend rigidity. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1 a    is a prior art perspective view of split extrusion rings keyed together with splits opposed at 180 degrees shown in the run in condition; 
           [0013]      FIG. 1 b    is the view of  FIG. 1 a    in the expanded condition showing the size increase for the split in the adjacent rings; 
           [0014]      FIG. 2  is a section view in the run in position for a long reach embodiment; 
           [0015]      FIG. 3  is the view of  FIG. 2  in the set position; 
           [0016]      FIG. 4 a    is a perspective view of the extrusion ring in the run in position; 
           [0017]      FIG. 4 b    is the view of  FIG. 4 a    in the set position; 
           [0018]      FIG. 5  is a side view of a backup ring that is located next to a sealing element; 
           [0019]      FIG. 6  is a perspective view of an optional anchoring ring shown in the run in condition; 
           [0020]      FIG. 7  is a section view of a short reach embodiment in the run in position; 
           [0021]      FIG. 8  is the view of  FIG. 7  in the set position; 
           [0022]      FIG. 9  is a perspective view of  FIG. 3 ; 
           [0023]      FIG. 10  is a section view of the backup showing its axial slots; 
           [0024]      FIG. 11  is a perspective view of the ring of  FIG. 10 ; 
           [0025]      FIG. 12  is a section view of a sealing assembly with the backup ring of  FIG. 10  in the run in position; 
           [0026]      FIG. 13  is the view of  FIG. 12  during the setting; 
           [0027]      FIG. 14  is the view of  FIG. 13  after the setting is complete; 
           [0028]      FIG. 15  is a detailed view of circle D in  FIG. 14 ; 
           [0029]      FIG. 16  is an outside view of the assembly shown in  FIG. 12 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0030]    To appreciate the benefits of the present invention it is necessary to review the state of the art in compression set element extrusion barriers. The sealing element design is typically one or more rubber sleeves that are axially compressed against a surrounding tubular. Extrusion barriers can be one or more layers of flexible thin sheet located at an end of a sealing assembly. As the sealing element deforms due to axial compression the extrusion barrier rings such as item 64 in U.S. Pat. No. 5,311,938 bends with the end of sealing element and makes contact with the opposing wall to bridge the sealing gap with the idea that the rubber is prevented from extruding axially. While serviceable this design has issues in releasing which sometimes led to the packer getting stuck even when the sealing element extended and relaxed but the extrusion ring did not relax. 
         [0031]      FIG. 1 a    shows another extrusion barrier ring assembly using a pair of split rings  10  and  12  that have splits  14  and  16  respectively. The rings  10  and  12  are keyed to prevent relative rotation to keep the splits  14  and  16  spaced 180 degrees apart. When the sealing element is axially compressed these rings are moved out radially on a ring with a taper to contact the surrounding tubular as the gaps  14  and  16  get substantially larger. The enlarged gaps still created issues for rubber extrusion for the sealing element particularly in high pressure high temperature applications. With pressure differentials of over 10,000 PSI extrusion past assemblies shown in  FIGS. 1 a  and 1 b    was still a significant concern. 
         [0032]    The present invention addresses this concern in high temperature and high pressure applications by the creation and application of a 360 expandable ring design featuring alternating inner and outer radially oriented slits. For low and medium reach the expandable ring rides up a wedge ring until the surrounding tubular or the open hole borehole is contacted. In high reach application an outer expandable ring of a similar design rides on an opposite side of a wedge ring until forced into supporting contact of the principal expandable ring pushing the principal expandable ring against the surrounding borehole or tubular. The expandable rings can be made of Teflon or another flexible material that is sufficiently resilient while resistant to high temperatures and well fluids. 
         [0033]      FIG. 2  shows the basic layout for a long reach application. Sealing element  20  can optionally have a filler ring  22  in the center. The assemblies on opposed ends of the element  20  are preferably mirror image and so they will be described only for one side with the understanding that the opposed side is an identical mirror image. An extrusion barrier in the form of an expanding ring  24  is attached to the element  20  and is sufficiently flexible to move with it.  FIG. 5  shows a section view of the bonded expanding ring  24 . Ring  24  prevents the sealing element from escaping the cut slots of ring  34  and better conformability to the casing inside diameter or the borehole wall  54 . It could be made of non-metallic material or very ductile metallic material. 
         [0034]    It has sides  26 ,  28  and  30  against seal  20  and a ramp surface  32 . Inner expandable ring  34  rides on ramp  32  on one side and ramp  36  of ramp ring  38 . Ring  38  has another ramp  40  opposite ramp  36  on which rides outer expandable ring  42 . Ramp  44  on outer expandable ring  42  rides on ramp  40  of ring  38 . On the other side ramp  46  rides on ramp  48  of setting ring  50 . The setting sequence results from relative movement between rings  50  and  52 . Usually one is moving while the other is stationary.  FIG. 3  shows the result of the relative movement. The element  20  is up against the borehole wall or surrounding tubular  54  as is the adjacent ring  24 . Ring  38  has shifted toward element  20  by going under ring  24  that is continuously supported for 360 degrees by expandable ring  34 . Inner expandable ring  34  has moved against the borehole wall or tubular  54  by sliding along opposed ramp surfaces  32  and  36 . The outer expandable ring  42  has moved out on ramps  40  and  48  until its surface  56  engages surface  58  of inner expandable ring  34  to wedge it against the borehole wall or tubular  54 . The new relative position of rings  50  and  52  can be releasably locked to hold the  FIG. 3  set position until it is time to retrieve the packer. The abutting of rings  42  and  34  allows ring  34  to travel further out radially than in the  FIG. 8  embodiment which is otherwise the same except outer expandable ring  42  is not shown because the required radial movement in  FIG. 8  is much less than in  FIG. 3 . As a result in  FIG. 8  the inner expandable ring  34  simply rides out on ramps  36  and  32  until contact is made with the borehole wall or tubular  54 . Ring  38  abuts ring  50  and does not go under ring  24  as in  FIG. 3 . The reach in  FIG. 8  is much shorter than in  FIG. 3 . 
         [0035]      FIGS. 4 a  and 4 b    show ring  34  in the run in and the set positions respectively. An outer face  60  continues along a tapered surface  62  to internal surface  64  seen as the inner parallel surface of a trapezoidal section in  FIG. 3  and a continuous line in perspective in the views of  FIG. 4 . Slots  66  circumferentially alternate with slots  68  and are radially oriented to preferably align with the center of ring  34 . Slots  66  start at the outer face  60  and slots  68  start at the surface  64 . Slots  68  end in a transverse segment  70  and slots  66  end in a transverse segment  72 . The transverse segments are there to limit stress as the slots  66  and  68  open up as the sealing element  20  is set against the borehole wall or tubular  54 . Outer expandable ring  42  is shown in perspective in  FIG. 6  and essentially has a similar slot configuration as described in  FIGS. 4 a  and 4 b    with the section profile being different as shown in  FIGS. 2 and 3 . However it is the same continuous 360 degree design for the ring  42  as the ring  34  with alternating slots with transverse end portions that start from opposing ends of the ring structure. Specifically, slots  80  and  82  start respectively at outer face  84  and inner dimension  86  seen as a ring in  FIG. 6  and as a flat in section in  FIG. 2 . The slots extend radially and preferably in alignment with the center of ring  42 . Alternatively the slots can extend axially but radially is preferred. At the respective ends of slots  80  and  82  are transverse ends  88  and  90 . As ring  42  expands from the  FIG. 2  to the  FIG. 3  position, the slots  80  and  82  open up to allow the diameter to increase until surface  56  hits surface  58  of inner expandable ring  34  as shown in  FIG. 3 . 
         [0036]    Rings  34  and  40  can be Teflon, metallic, composite to name a few examples. The shape can be created with lasers or wire EDM fabrication methods. Although in  FIGS. 2 and 3  a single inner ring  34  and outer ring  40  are illustrated multiple pairs of such rings that function in the same way can be used. In the case of  FIGS. 7 and 8  multiple pairs of expandable ring  36  and ramp ring  38  can be used and they can operate in the same manner as illustrated for a single such pair of rings as shown in  FIGS. 7 and 8 . The 360 degree design for rings  34  and  42  combined with solid expandable ring  24 , which prevents the rubber element  20  from escaping through cut slots in ring  34  and improves conformance to tubular or borehole inside diameter dramatically reduces extrusion of seal  20  even though the slots expand for the larger set position. The 360 degree feature of the rings  34 ,  42  and  24 , if used, limit the extrusion gaps and allow a given sealing system  20  to be serviceable in higher pressure differential applications without extrusion risk. The design is modular so that it is simple to switch between the  FIG. 2  and  FIG. 7  configurations for different applications. The ring  42  backing up the ring  34  wedges ring  34  in the  FIG. 3  set position wedges in ring  34  to hold it in position against high differential pressures that can exceed 10,000 PSI. The slot ends can be a transverse slot or an enlarged rounded end or other shape that limit stress concentration at the ends of the radial slots. 
         [0037]    A preferred design for backup ring  24 ′ is shown in  FIGS. 10 and 11 . It features a cylindrically shaped component  100  that transitions to a tapered segment  102  that ends at an enlarged end  104  that turns inwardly toward mandrel  105  shown in  FIG. 8 . The cylindrically shaped component is tapered to its minimum thickness at end  106 . An array of slots  108  start at end  106  and extend generally axially to rounded ends  110  that are there to reduce stress concentration at the ends of slots  108 . The slots  108  are preferably equally spaced and of uniform width and length. The preferred length is less than half of the axial length of the cylindrically shaped component  100 . The tapered section allows greater flexibility near end  106  during the setting as shown in  FIG. 13  such that end  106  and some of the adjacent cylindrically shaped segment  100  that has slots  108  makes initial contact with the surrounding borehole wall  112 . As the setting movement continues the cylindrically shaped component  100  continues to make contact with the borehole wall  112  past the rounded ends  110  of slots  108  so that a slot free segment of the cylindrically shaped component then makes contact with the borehole wall  112 . The slots  108  make the end  106  more flexible to allow early initial movement toward the borehole wall  112  with reduced radial pushing force so that the end  106  is preferably already in contact with the borehole wall  112  before the internal pressure of the sealing assembly  20  get very high as it is axially compressed to be radially extended against the surrounding borehole wall  112 . On further axial compression of the sealing assembly  20  the non-slotted portion of the cylindrically shaped segment  100  makes contact with borehole wall  112  to close off axial slots  108  as potential extrusion paths. As that happens the tapered segment  102  is backed up by ring  34  that has a tapered surface  62  that conforms to the angle of the tapered segment  102 . Enlarged end  104  serves as a stiffening rib near the mandrel  105  but is driven away from mandrel  105  in the set position of  FIGS. 14 and 15 . There is a path for the material of seal assembly  20  to pass under wedge ring  38  until that path is closed with a seal  114  against mandrel  105  in groove  116 . During the setting the enlarged end  104  contacts wedge ring  38  and rides up inclined surface  36  of wedge ring  38 . 
         [0038]    Backup ring  24 ′ performs markedly better than backup ring  24  in high pressure and high temperature applications. One of the reasons is that there are slots  108  and a tapered section near end  106 . This allows early movement of end  106  against the borehole wall  112  with the onset of application of the compressive setting force. The slotted portion of the cylindrically shaped segment  100  can establish itself against the borehole wall  112  before the internal pressure on the sealing element assembly  20  increases significantly so that extrusion into the slots  108  can start. While the seal material fills the slots  108  those slots get closed off quickly before the internal pressure in the seal material  20  increases appreciably as the set position is achieved. The contact of the non-slotted portion of the cylindrically shaped component  100  with the borehole wall provided strength due to absence of slots  108  and closure at the rounded slot ends  110  against axial extrusion along the borehole wall  105 . At the same time the seal  114  in groove  116  in wedge ring  38  prevents extrusion along mandrel  105  even though some small part of the seal assembly  20  does move axially under the wedge ring  38  as shown in  FIGS. 14 and 15 .  FIG. 16  shows the arrangement can be symmetrical about opposed ends of the sealing element assembly  20 . 
         [0039]    The teachings of the present disclosure may be used in a variety of well operations. These operations may involve using one or more treatment agents to treat a formation, the fluids resident in a formation, a wellbore, and/or equipment in the wellbore, such as production tubing. The treatment agents may be in the form of liquids, gases, solids, semi-solids, and mixtures thereof. Illustrative treatment agents include, but are not limited to, fracturing fluids, acids, steam, water, brine, anti-corrosion agents, cement, permeability modifiers, drilling muds, emulsifiers, demulsifiers, tracers, flow improvers etc. Illustrative well operations include, but are not limited to, hydraulic fracturing, stimulation, tracer injection, cleaning, acidizing, steam injection, water flooding, cementing, etc. 
         [0040]    The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below: