Wellbore packer back-up ring assembly, packer and method

A back-up ring assembly for a wellbore packer that acts as an extrusion limiter for a packing element and engages the wellbore bore, also operating as a slip to anchor the packer in place. A wellbore packer includes a back-up ring that includes a gripping structure on its outer wall-contacting surface that acts both to back up the extrusion of the packing element and to engage the wellbore wall.

FIELD OF THE INVENTION

A wellbore tool is disclosed. In particular, the invention relates to a wellbore packer and back-up ring assembly.

BACKGROUND

Wellbore packers are known that are used to create a seal in a wellbore. The term “wellbore packer” may be used to also encompass a bridge plug, a straddle tool, etc., all of which are employed in wellbore operations to control fluid flow. A wellbore packer is deployed in a well to be expanded between a mandrel and a constraining wall, such as an open wellbore wall, a lined wellbore wall or another liner. The mandrel may have an open bore or may be sealed against fluid flow. The mandrel is often part of a larger structure, such as a wellbore string.

Sometimes, a wellbore tool is needed that operates both to create a seal about, and anchor, the mandrel in a wellbore. Such a tool has a requirement for both a sealing mechanism and an anchoring mechanism. As such, some packers have both a sealing element and mechanism for expanding that sealing element and a separate anchoring slip system and a mechanism for driving the slips against the constraining wall in which the tool is positioned.

The packing element is often formed of deformable materials such as rubber or other elastomers and is squeezed with compression, either mechanically applied or hydraulically applied. When the packing element is squeezed out, it expands radially outwardly and is driven into contact against the constraining wall in which the tool is positioned. At the same time, the backside of the packing element is sealed up against the mandrel and a seal is achieved. The best seal is achieved when the packing element is kept from axially extruding, as such extrusion may lead to seal damage and failure.

The anchoring slip system, for example, may include a cone system including an inclined frustoconical wedge that forces the slip against the constraining wall in which the tool is positioned. It may also contain a ratcheting device called a mandrel lock that locks the slip in the anchored position.

The anchoring slip system is offset axially along the mandrel from the packing element.

SUMMARY

In accordance with a broad aspect of the invention, there is provided a wellbore packer back-up ring assembly for limiting the extrusion of a packing element comprising: a first back-up ring adapted to be positioned about a mandrel at a first end of the packing element; and a second back-up ring adapted to be positioned about the mandrel spaced from the first back-up ring and at a second end of the packing element; wherein the first back-up ring and the second back-up ring each include an inner facing annular surface and an outer facing annular surface defining an outer diameter across the back-up ring and including a gripping structure capable of biting into a constraining surface in a well and each being expandable to increase the outer diameter to expand radially outwardly.

In accordance with another broad aspect of the invention, there is provided a wellbore packer comprising: a mandrel, a deformable packing element surrounding the mandrel and adapted to be radially expanded out from the mandrel, the deformable packing element including an end; a back-up ring surrounding the mandrel and positioned adjacent the end of the deformable packing element, the back-up ring having an inner facing annular surface and an outer facing annular surface defining an outer diameter across the back-up ring, the back-up ring being expandable to increase the outer diameter to expand out from the mandrel alongside the deformable packing element and the outer facing annular surface including a gripping structure capable of biting into a constraining surface in a well.

In accordance with another broad aspect, there is provided a method for sealing an annular area in a wellbore, comprising: positioning a wellbore packer in a wellbore adjacent a constraining wall, the wellbore packer including a mandrel, a deformable packing element surrounding the mandrel and adapted to be radially expanded out from the mandrel, the deformable packing element including an end; a back-up ring surrounding the mandrel and positioned adjacent the end of the deformable packing element, the back-up ring having an inner facing annular surface and an outer facing annular surface defining an outer diameter across the back-up ring, the back-up ring being expandable to increase the outer diameter to expand out from the mandrel alongside the deformable packing element and the outer facing annular surface including a gripping structure; driving the back-up ring to expand radially outwardly to increase the outer diameter and to drive the gripping structure into engagement with the constraining wall; and applying a force on the deformable packing element to expand it radially outwardly such that it fills a gap between the back-up ring, the mandrel and the constraining wall.

DESCRIPTION OF VARIOUS EMBODIMENTS

The description that follows, and the embodiments described therein, is provided by way of illustration of an example, or examples, of particular embodiments of the principles of various aspects of the present invention. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the invention in its various aspects. In the description, similar parts are marked throughout the specification and the drawings with the same respective reference numerals. The drawings are not necessarily to scale and in some instances proportions may have been exaggerated in order more clearly to depict certain features.

A packing element back-up system has been invented that acts to limit packing element extrusion and also serves to anchor a packer in a wellbore. A packer has been invented including a packing element back-up system that also serves as an anchoring slip system. A method for sealing a wellbore has also been invented.

Back-up rings act as extrusion limiters and supports for the packing element. For example, a back-up ring may surround the packer mandrel on one or both ends of the packer element. The back-up ring can expand radially out to increase its outer diameter, and sometimes its radial thickness, when a driving force such as compression is applied thereto. The back-up ring can expand out to close any gap through which the packing element might otherwise extrude axially. As such, the packer element may be supported and backed up by the back-up ring to prevent axial extrusion and breakdown of the packer element.

The back-up ring is an annular structure capable of radial expansion in response to a driving force. In one embodiment, the back-up ring is a solid ring formed of a material, such as polytetrafluoroethylene (PTFE, Teflon™) or titanium, which is capable of radial expansion. In another embodiment, the back-up ring may include an annular member with a spiral cut extending along at least some portion of the ring's circumference which may radially expand by slipping along the spiral cut. In such a ring, a complete annular wall structure is maintained even though the ring expands because the sides along the spiral cut maintain an overlapping arrangement when the ring expands. In another embodiment, the back-up ring includes a slit cut through its thickness to allow radial expansion of the ring. However in such a ring, generally there will be a plurality of rings that overlap axially such that the slit of the ring, when expanded and therefore pulled open, does not form an opening through which the packing element can extrude. At least one ring of the plurality of rings is therefore capable of radial expansion, as by including a slit, being formed in the shape of a C or a helical member.

With reference toFIGS. 1 and 2, for example, a portion of a wellbore packer10is shown. Packer10includes a mandrel12, a deformable packing element14surrounding the mandrel and adapted to be radially expanded out from the mandrel; and a back-up ring16surrounding mandrel12and positioned adjacent an end of the deformable packing element such that the packing element is able to contact it when radially expanded. While some packers may include only one back-up ring, the present packer includes a second back-up ring18positioned adjacent the opposite end of the packing element. In this embodiment, the two back-up rings are substantially similar in form and operation and, therefore, the description of one applies to the other. To facilitate understanding, therefore, the following description will focus on back-up ring16.

Back-up ring16has an inner facing annular surface16aand an outer facing annular surface16band side walls16cextending therebetween. The outer facing annular surface defines an outer radius R for the back-up ring, as installed, measured from the packer center axis x. Back-up ring16is radially expandable, arrows B, to increase the outer radius and when expanded (FIG. 2) ring16extends out a distance from the mandrel alongside the deformable packing element14than the distance it extended before expansion.

Outer facing annular surface16bincludes one or more gripping structures22thereon capable of biting into a constraining wall24in a well in which the packer is positioned. As such, outer facing annular surface16bof the back-up ring acts like a slip to anchor the packer when expanded out into engagement with the constraining surface.

In use, packer10may be employed to create a seal in an annular area in a wellbore. To do so, packer10is positioned in a wellbore adjacent constraining wall24with an annular area26between them (FIG. 1). The back-up ring and the deformable packing element are then driven to expand. This expansion may be simultaneous or one at a time. However, in the end as shown inFIG. 2, back-up ring16expands radially outwardly to increase the outer radius R and to drive the gripping structure22into engagement with the constraining wall and deformable packing element14is expanded radially outwardly such that it substantially fills a gap between side wall16cof the back-up ring, mandrel12and constraining wall24.

Mandrel12acts as a support for the other packer elements. In this embodiment, mandrel12is a robust tubular member having a generally cylindrical outer surface. The mandrel may have a center bore12a, as shown, or have a solid body, depending on the nature of the seal that is desired to be installed. Mandrel12may be a portion of a wellbore string or a tool body.

Packing element14is often formed of deformable materials such as rubber or other elastomers and upon application of compressive forces, arrows C, thereto is squeezed radially out, arrows E. When the packing element is squeezed out,FIG. 2, its outer facing surface14bis driven into contact with constraining wall24and at the same time, the backside14aof packing element14becomes pressed against the mandrel. As such, element14forms a seal in the annular area between the mandrel and the constraining wall such that fluids are prevented from passing through the annular area.

In the illustrated embodiment, deformable packing element14includes a plurality of components including a main, annular sealing element14c, and deformable guide rings14d,14e. The guide rings are positioned at the edges of the main sealing element and, while deformable, are generally more durable than the main element. Thus, they transition the forces through the packing element and prevent edge damage. Rings14d,14emay be formed of various materials that are deformable, likely have a hardness greater than the main element14cand have a hardness less than back-up rings16,18. For example, rings14d,14emay be formed of a harder durometer rubber than element14c, a filled-rubber (for example rubber reinforced with metal, for example steel, fibers), a deformable metal (for example, brass or some steels), or a plastic. In the illustrated embodiment, for example, element14cis formed of rubber, ring14dis formed of PTFE, ring14eis formed of a deformable metal softer than brass and rings16,18are formed of brass.

Back-up rings16,18act as supports for packing element14and limit its axial extrusion, relative to the mandrel long axis x. Back-up ring16, for example, surrounds mandrel12alongside element14and can be expanded radially out to increase its outer radius R and when a driving force such as compression, arrows C, is applied thereto. The back-up ring can expand out to close any gap through which the packing element might otherwise extrude axially. As such, back-up rings16,18support and back-up packing element14to guide it into engagement with the constraining wall over a controlled axial length such that the sealing force is concentrated in this area and to prevent axial extrusion and breakdown of the packing element.

Back-up rings16,18are annular structures capable of radial expansion in response to a driving force. In this illustrated embodiment, back-up rings16,18each include a pair of sub rings. In a multipart back-up ring, at least one of the sub rings can expand. In this embodiment, each sub ring16′,16″ has a cut (cannot be seen) extending through the thickness thereof such that each ring can expand by pulling apart at the cut. As a result of the cut, the sub rings16′,16″ each have a C-shaped form. In the non-expanded position, the cut is generally closed tight, substantially without any open gap between the cut ends. When an expansive force is applied, each sub ring pulls apart at its cut and expands to increase its diameter. While the cuts allow for sub ring expansion, they are kept to a minimum to limit openings for element extrusion. For example, generally each sub ring16′,16″ has at most one cut such that it can expand, but presents only one possible opening through which extrusion can occur and it remains as one piece even when expanded. The cut can be made along a plane parallel with the center axis x. However, such a cut does create an opening extending fully through the ring or sub ring along axis x, which presents a direct path for extrusion. As such a cut that extends along a plane parallel with the center axis x should be limited and for example, limited to use in a ring where there is structure, such as a sub ring or guide ring, to block any extrusion fully through the back-up ring, as described herein below. Where there is no structure in a blocking position relative to the cut, to further limit extrusion through the cut, it can be made along a plane out of parallel with the axis x such that there is no direct axial path through the back up ring.

Rings16′,16″ are positioned in side-by-side relation and arranged that the axis of one sub ring16′ is substantially coaxial with the axis of the other sub ring16″. Also, the inner diameter of one sub ring16′ no greater than the outer diameter of the other sub ring16″ such the sub rings overlap along the long axis of mandrel. Sub rings16′,16″ are connected but rotationally moveable each to the other about their center axes. In the illustrated embodiment, for example, sub rings16′,16″ are connected through interfacing sides having connecting male and female parts. For example, sub ring16′ has an annular protrusion32extending about its interfacing side and sub ring16″ has an annular groove34extending about its interfacing side. Protrusion32and groove34are selected to have similar curvature and sufficient tolerances such that the sub rings can slip rotationally relative to each other, for example, when they are expanding, but hold together and substantially act as a unitary member in the radial direction.

In use, sub ring16′ is rotated relative to sub ring16″ such that the cut in one does not line up with the cut in the other. As such, the cut of sub ring16′, when expanded and therefore pulled open does not form an opening fully through the back-up ring through which the packing element could extrude. Instead, any extrusion through the one sub ring at the opening at the cut is stopped by a solid wall of the other sub ring.

One or, as shown, both sub rings16′,16″ of back-up ring16include gripping structures22on their outer facing surface. Gripping structures22may include teeth (wickers) (as shown), grit, surface roughening formed on the material of the ring or through material inserts (such as buttons, sand, diamonds, etc). As such, when the sub ring16is expanded out, gripping structures22anchor into constraining wall24. Gripping structures22may be selected to dig into a casing surface by 0.010 to 0.030 inch and therefore need only be 0.050 to 0.060 inches high.

The gripping structures are formed to resist axial movement of the packer along wall24. In some embodiments, gripping structures22can be formed to be directional, to resist axial movement of the packer in a certain direction (up or down). For example, gripping structures22can be angled to resist axial movement in one direction while allowing it in another direction. With reference to ring18, angled gripping structures include a slipping side22a, which defines an obtuse angle relative to the direction of movement, and a gripping side22b, which has an orthogonal or acutely angled side relative to the direction of movement. The illustrated gripping structures22are each angled to resist axial movement in one direction, with those on sub rings16′,18′ resisting movement towards the left (towards surface) and those on sub rings16″,18″ resisting movement towards the right (further downhole). However, since structures22on sub rings16′,18′ are oppositely angled to the structures on sub ring16″,18″ each ring16,18resists movement in both the axially upward and the axially downward directions.

The expansion of rings16,18may be driven in a number of ways. In the illustrated embodiment, expansion force is driven by frustoconical guide surfaces36,36acarried on the mandrel in cooperation with a compressive force exerted by actuating member38. In this embodiment, the compressive force is applied to rings16,18and element14by actuating member which includes a single drive ring that drives the components against a fixed shoulder at surface36a. Since shoulder36acannot move, any force applied by member38results in a compressive force along the entire arrangement of components14,16and18. However, it is to be understood that drivers could be positioned at both ends, if desired.

Back-up ring16, for example, surrounds mandrel12and is positioned adjacent surfaces36,36ain a position to be lifted by it, when surface36is urged beneath the ring. For example, when a compressive force is exerted by member38, guide surface36passes beneath ring16and acts to move ring16radially outwardly into contact with constraining wall24. As will be appreciated, the outer diameter of the mandrel at surfaces36,36aand the thickness of rings16,18must be selected with consideration as to the distance across annular space24.

To more efficiently and stably translate compressive axial motion into radially directed force to drive ring16radially outwardly, inner facing annular surface16amay be shaped frustoconically to have an angled face substantially similar to that of frustoconical guide surface36.

The compressive force, arrows C, is also applied to packing element14to expand the element radially into contact with constraining wall24. Ring16, being radially expanded against wall24, supports the respective ends of element14during deformation.FIG. 2shows packing element14following deformation and expansion into contact with constraining wall24. During application of compressive force, the packing element is urged radially outwardly and rings16,18travel along the frustoconical guide surfaces36,36aand are thus pushed radially outwardly. This positions the rings to support the axial ends of the packing element14, thereby preventing extrusion of the packing element axially along the annular space26and thus holds element14in a shape which provides a good sealing abutment with wall24.

In the illustrated embodiment, ring16is also frustoconically formed on its inner facing annular surface16aadjacent element14. In particular, the inner facing annular surface16aof sub ring16′ is formed to taper inwardly and the adjacent edge of element14, in this embodiment, ring14e, is frustoconically formed to protrude beneath ring16. As compressive forces urge the parts to axially compress, ring16tends to move radially outwardly ahead of element14to reach its abutting position against wall24ahead of the full expansion of the packing element, such that advantageously element14tends not to become pinched between ring16and wall24and therefore cannot block the gripping engagement of structures22with wall24.

Member38, or member36, may include a lock structure38ato lock the compressive force into the packer. For example, member38may include a body lock ring structure such as a ratchet. The lock structure may be releasable if it is desirable to have an option to unset the packer.

The foregoing packer allows the elimination of a separate anchoring system. The combined functions of, extrusion limiting and anchoring, back-up ring16may allow a reduction in the total length and complexity of a packer, but without losing functionality. Also, only one lock structure need be employed, further reducing the overall packer length.

Another packer with back-up rings116,118is shown inFIG. 3. Back-up rings116,118are also multipart rings having a pair of sub rings116′,116″ positioned in side-by-side relation. However, in this embodiment, only one sub ring116″ of the two sub rings expands outwardly and only that sub ring has gripping structures122on its outer facing annular surface116b″.

Ring116′ is a base, sliding sub ring and sub ring116″ is capable of radial expansion. Sub rings116′,116″ are positioned in side-by-side relation such that they overlap along the long axis of mandrel even when sub ring116″ is fully expanded. Sub rings116′,116″ are connected but rotationally moveable each to the other about a center axis. In the illustrated embodiment, for example, sub rings116′,116″ are connected through interfacing sides having connecting male and female parts. For example, sub ring116′ has an annular protrusion132extending about its interfacing side and sub ring116″ has an annular groove134extending about its interfacing side. Protrusion132and groove134are selected to have similar curvature and sufficient tolerances such that the sub rings can slip rotationally relative to each other. For example, when sub ring116″ expands, it can radially expand relative to sub ring116′, but the interaction of the protrusion and the groove prevent the sub rings from falling apart in use.

Ring116″ is cut through its thickness at one point along its circumference such that it can expand. Since sub ring116″ expands out away from sub ring116′, the opening that forms at the cut when the sub ring is expanded is not blocked by any other member. Thus, the cut extends slightly helically and is not directly along a path parallel to the axis, as this deters extrusion through the opening that forms at the cut.

Unlike the back-up ring ofFIG. 1, ring116expands upon itself because sub rings116′,116″ have reverse frustoconical forms on their interfacing sides. In particular, base sub ring116′ has a protruding frustoconical surface (an obtusely angled face) on its interfacing side against which an undercut frustoconical surface (acutely angled face) of the expandable sub ring116″ is set. The frustoconical curvatures along the interfacing sides are substantially mirror images of each other. Axial compression, arrows C1, against the sides of the ring, therefore, is reacted to force expandable sub ring116″ to expand radially outwardly. In particular, compression causes sub ring116″ to ride up along the frustoconically formed face of sub ring116′. As force is applied, arrow C1, the inclined faces cause the parts to shift on each other, such that: sub ring116″ moves up, arrow B1, in particular, radially outwardly relative to the other sub ring116′, which is restrained from behind by mandrel112, such that it substantially can't move.

In this embodiment, rings116,118each have gripping structures122to engage the constraining well against which they are expanded. In this embodiment, rings116,118are formed of a durable metal such as brass, but which is softer than steel, the material from which the constraining wall may be formed. As such, gripping structures122are formed on inserts123, for example buttons, diamond, sand, that are installed in the outer surfaces of the expandable rings. Inserts123may include or be formed of materials harder than steel such as carbide, diamond, sand, etc.

Gripping structures122, in this embodiment, are in the form of angled teeth to permit sliding movement inwardly along the direction compressing element114but to resist any axial movement in the reverse direction. As such, rings116,118tend not to resist any compressive movement after biting into the constraining wall and allow continued compression if necessary to completely expand element114.

Rings116,118, therefore, expand in diameter when compressed and act as a back-up, to guide the expansion of the packing element. The packing element114comes into contact with the ring but cannot extrude past it. The back-up rings are directly adjacent the packing element act at each end thereof and act to constrain the packing element and to reduce the area where the rubber can try to extrude during pressuring and temperature operations. In addition, rings116,118act as slips to anchor the packer against axial sliding movement along the wellbore.

In another embodiment, as shown inFIG. 4, a back-up ring216may include an annular member with a spiral cut230extending along at least some portion of the ring's circumference. The ring may radially expand by slipping along the spiral cut. In such a ring, a complete annular wall structure is maintained even though the ring expands because the sides along spiral cut230maintain an overlapping arrangement when the ring expands. Outer facing annular surface216bincludes gripping structures222thereon such as teeth formed as elongate annular ridges. In this embodiment, gripping structures222are formed to allow rotational sliding of ring about its center axis x, to permit the ring to retain some ability to continue expansion even after contacting the constraining wall. However, structures222are formed to resist axial sliding of ring216, along axis x, in at least one direction after the ring has contacted a constraining wall.

In another embodiment, the back-up ring is a solid ring formed of a material, such as PTFE or titanium, which is capable of radial expansion and carries gripping structures on its outer facing annular surface. However, care may be taken to ensure that the material of the ring is sufficiently strong to effectively act as an anchor for the packer. Generally, therefore, a back-up ring according to this invention is formed of material including metal such as brass, steel, titanium or a polymer filled with metal and has an incomplete ring form, such as by inclusion of an axial or spiral cut.

In the present invention, instead of a separate anchoring mechanism and back-up rings, a combined function back-up ring is provided. The back-up rings instead of serving one purpose, both reduce the extrusion gap and also to anchor into the surrounding structure. As noted above, this allows a simpler and shorter packer to be constructed. Separate slips may not be necessary and in fact it is desired to provide a packer tool without a separate slip assembly.