Multi-component Anti-extrusion Barrier for a Compression Set Subterranean Barrier

Abstract

A backup ring assembly is disposed between opposed cones. The assembly rides up a wedge ring to contact a surrounding tubular when the opposed cones are pressed axially together to also compress the sealing element. The backup ring assembly has nested split rings that are slant cut for the split. The split for the nested rings can be circumferentially aligned or offset. Another ring is stacked axially adjacent the nested rings and has a slant cut for a split that is preferably rotated from the slant cuts of the nested rings. The interface of the nested rings can be along a line that is parallel to the mandrel axis or askew to the mandrel axis. The preferred material is a non-metallic composite material.

Description

FIELD OF THE INVENTION

The field of the invention is backup ring assemblies that address element extrusion issues and more particularly designs involving non-metallic components for future milling out configured to radially extend without damage and without leaving extrusion openings.

BACKGROUND OF THE INVENTION

Packers and bridge plugs have sealing elements that are axially compressed to radially expand and seal off one part of a wellbore from another. The act of axial compression of the sealing element and the differential pressure when the set packer or bridge plug is in service tends to force the sealing element to extrude axially. Barriers of different styles have been used in the past in various locations to counteract this tendency to extrude. US Publication 2004/0036225 shows a pair of axially stacked rings 270,280 that have a triangular cross-section and are pushed out radially together to control extrusion. US Application 2009/0255690 shows a combination of axially stacked slotted rings 72 working in conjunction with an adjacent 1-shaped backup ring that is attached to an end of a sealing element. The slots are offset in each row of the stack to prevent a barrier from opening up. U.S. Pat. No. 8,016,295 shows a helical backup ring that grows in radial dimension when axially compressed. It features tapered ends so that the ends can sit flush to the adjacent structure. In US Publication 2011/0036561 the extrusion barrier is a series of arcuate ring segments that overlap at their ends so that as a slip ring made of wedge segments grows in diameter the extrusion segments separate but continue to overlap to close off any extrusion paths. US Publication 2010/0276137 illustrates a vertically stacked end ring design with slots where the assembly is pushed out against the borehole wall by axial compression of the sealing element 14. The rings are taught to be made of a variety of non-metallic materials including composites. In other designs the sealing element itself has a fibrous layer internally next to a cable layer to prevent seal element extrusion as described in U.S. Pat. No. 7,510,015.

Some packers or bridge plugs are designed to be milled out at a later time after they are set. To facilitate the milling out some of the parts are made of a soft material such as composite materials such as the mandrel and the cones that compress the sealing element. In most instances the backup rings have been made of metallic materials out of a need to give them the strength required to resist element extrusion. However, the use of metals for the backup rings also has an undesirable effect of increasing the time to accomplish the milling out. On the other hand, use of non-metallic backup rings brings up service issues that have in the past kept such systems from being deployed. The non-metallic materials have more limited flexibility and can be subject to snapping if they are flexed too much in any direction.

The present invention provides an assembly that serves as a backup ring that is made from a non-metallic material preferably composites and uses a radial nesting of rings to minimize flexing of each ring as their diameter is increased when riding up a ramped ring adjacent the sealing element. An adjacent ring axially abuts the radially nested rings with an offset cut so as to avoid opening extrusion barriers on radial growth. The nested rings are also slant cut to prolong the overlap as their diameter grows. These and other features of the present invention will be more readily apparent from a review of the details of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.

SUMMARY OF THE INVENTION

A backup ring assembly is disposed between opposed cones. The assembly rides up a wedge ring to contact a surrounding tubular when the opposed cones are pressed axially together to also compress the sealing element. The backup ring assembly has nested split rings that are slant cut for the split. The split for the nested rings can be circumferentially aligned or offset. Another ring is stacked axially adjacent the nested rings and has a slant cut for a split that is preferably rotated from the slant cuts of the nested rings. The interface of the nested rings can be along a line that is parallel to the mandrel axis or askew to the mandrel axis. The preferred material is a non-metallic composite material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a run in view of the backup ring assembly;

FIG. 2 is the view of FIG. 1 in the set position for the backup ring assembly;

FIG. 3 is an end view of one of the split rings showing the scarf cut;

FIG. 4 is the view along lines 4-4 of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 a packer P has a mandrel 10 with a center line 12 that is inserted into a borehole 14 can be open or cased hole. A sealing element 16 is flanked on opposed sides with wedge rings 18 and 20 that are tapered to present opposed ramps 22 and 24 that are disposed in planes that intersect the centerline 12. Cones 26 and 28 are brought together axially along the mandrel 10 in a manner known in the art to set the sealing element to the sealed position of FIG. 2. Such relative movement of the cones 26 and 28 also brings the wedge rings 18 and 20 closer together as they translate without rotation along the mandrel 10 as can be seen by comparing FIGS. 1 and 2. The backup ring assemblies 30 and 32 are disposed in mirror image orientation on the ramps 22 and 24 respectively.

Each of the assemblies 30 and 32 comprise at least three rings 34, 36 and 38. Rings 34 and 36 are nested and are preferably concentrically disposed about the mandrel 10. Surfaces 39 and 40 respectively on rings 34 and 36 are flush against an adjacent cone such as 26 or 28. Ring 38 is preferably trapezoidal in section and has a side 42 that sits up against surfaces 44 and 46 of adjacent rings 34 and 36. Rings 34 and 38 have sloping sides 48 and 50 that ride on surfaces 22 or 24 of the wedge rings 18 or 20. Rings 36 can also have an undercut 52 or 54 that raises off the mandrel 10 in the run in condition or those surfaces can be flush with the mandrel 10 for run in as another option.

In section, ring 34 is preferably a rectangle but can be a square or a trapezoid, for example. Ring 36 in section can be a quadrilateral but can have other shapes. These two shapes preferably have a side in common such as surfaces 56 and 58 and in section the line that represents their contact can be oriented parallel to axis 12 as shown or at a skew to that axis. Preferably rings 34 and 38 have contact surfaces 60 and 62 that that are oriented flush to the borehole 14 and generally parallel to the axis 12.

FIG. 3 shows the cut that is preferably in each of the rings 34, 36 and 38 but is illustratively shown for ring 34. The split 64 is a scarf cut along a plane that intersects the axis 12 so that sliding ends 66 and 68 can move relative to each other while remaining in contact and without opening up a gap. The cut 64 in rings 34 and 36 that are radially one outside the other can be circumferentially aligned or offset. From the perspective of the sealing element 16 putting the cut 64 of the ring 38 at a circumferentially offset location from the split 64 in the ring pair 34 and 36 prevents an extrusion gap from opening. The stacking radially of the rings 34 and 36 reduces the amount of radial deflection that each has to have to reach the borehole wall 14. The location of the nested rings 34 and 36 between a cone such as 26 and ring 38 as they ride together along sloping ramp 22 until surfaces 60 and 62 contact the borehole 14 provide structural support to the nested rings 34 and 36 to keep them from twisting or separating at the cut 64. Surfaces 60 and 62 do not need to engage the borehole 14 at the same time but that is one possibility. If surface 60 engages first the presence of the ramp 22 or 24 will aid the adjacent surface 62 to continue outward movement until contact is made with the borehole 14. Similarly engagement of assembly 30 to the borehole 14 can occur before assembly 32 makes contact but as long as setting pressure continues to be applied the assembly on the other side of seal 16 will make contact with the borehole 14.

As shown in FIG. 4 the rings 34, 36 and 38 have a height h that extends in a radial direction from mandrel 10 to an end 74 and between adjacent straight sides 70 and 72 that are preferably in parallel planes but can be converging or diverging as alternative designs. In essence the rings are discs with an open interior to fit either around the mandrel 10 as in the case of rings 36 and 38 or against another ring such as ring 34 having an opening that rests on ring 36.

Preferably the assemblies 30 and 32 should be made from a drillable soft material such as the preferred material which is a composite.

Those skilled in the art will appreciate that a non-metallic backup ring assembly is provided that is less stressed due to the reduced radial growth brought about by nesting two or more rings in one row that is abutted by another ring in an adjacent row to provide lateral stability in the set position. The rings are slant cut with the abutting ring to the nested rings having a circumferentially offset slant cut from either of the nested rings whose slant cuts can be aligned or offset. While a single row of nested rings that are preferably coaxial is described additional rows of nested rings can be used if there is space depending on the size of the packer. Another option is to sandwich a row of nested rings between single rings on opposed sides with at least some of the rings having a split cut at a slant. The cut angle can vary with respect to the axis 12 in a range of 25-75 degrees. The material for all the rings can be identical or alternatively the materials can be different while all preferably are non-metallics.

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:

Claims

1. An extrusion barrier assembly for a compression set sealing element that selectively isolates one subterranean location from another, comprising:

a sealing element mounted on a mandrel;

an axially movable compressing assembly for said sealing element mounted on said mandrel;

said extrusion barrier comprising at least one row of radially nested rings mounted over said mandrel, said rings extending in a radial direction from said mandrel to an end between straight sides and at least a portion of said rings are driven away from said mandrel by said compressing assembly.

2. The assembly of claim 1, wherein:

said rings are split to define adjacent ends.

3. The assembly of claim 1, wherein:

said split is in a plane that is skewed to an axis of said mandrel.

4. The assembly of claim 2, wherein:

said splits are circumferentially aligned.

5. The assembly of claim 2, wherein:

said splits are circumferentially offset.

6. The assembly of claim 2, wherein:

said ends overlap each other after said compressing assembly drives said nested rings.

7. The assembly of claim 1, wherein:

said rings are made of a non-metallic material.

8. The assembly of claim 7, wherein:

said rings are made of a composite material.

9. The assembly of claim 2, further comprising:

an additional row with at least one additional ring adjacent said nested rings.

10. The assembly of claim 9, wherein:

said additional ring is split to define adjacent ends.

11. The assembly of claim 10, wherein:

said split in said additional ring is circumferentially offset from said split in said nested rings.

12. The assembly of claim 11, wherein:

said ends of said additional ring overlap each other after said compressing assembly drives said nested rings.

13. The assembly of claim 12, wherein:

said additional ring is made of a non-metallic material.

14. The assembly of claim 13, wherein:

said additional ring is made of a composite material.

15. The assembly of claim 2, further comprising:

at least one wedge ring between said sealing element and said extrusion barrier that presents a ramp for said extrusion barrier as said extrusion barrier is moved away from said mandrel by said compressing assembly.

16. The assembly of claim 15, wherein:

said split is in a plane that is skewed to an axis of said mandrel.

17. The assembly of claim 16, wherein:

said ends overlap each other after said compressing assembly drives said nested rings.

18. The assembly of claim 17, wherein:

said rings are made of a non-metallic material.

19. The assembly of claim 18, further comprising:

an additional row with at least one additional ring adjacent said nested rings. said additional ring is split to define adjacent ends;

said ends of said additional ring overlap each other after said compressing assembly drives said nested rings.

20. The assembly of claim 19, wherein:

said split in said additional ring is circumferentially offset from said split in said nested rings.

said additional ring is made of a non-metallic material.