Abstract:
An annular seal is made of a collapsible bellows. The bellows can function as an anchor or a seal and is easily set into position using relative component movement. The bellows folds can be slanted and their outer sealing edges can have different profiles to meet expected conditions. The bellows is expanded for insertion to reduce its outer dimension and sets by compaction as a result of relative movement. The bellows can be straight or tapered and is settable with a minimal axial force.

Description:
This invention was made with support from the United States Government under contract DE-AC04-94AL85000 awarded by the U.S. Department of Energy. The Government has certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The field of this invention relates to sealing or anchoring devices, particularly those useful for downhole service as packers or anchors. 
     BACKGROUND OF THE INVENTION 
     Many types of devices for sealing or anchoring in a passage which is meant to include open or cased holes are known in the art. Some types involve mechanical squeezing of sealing elements by longitudinal relative movement which results in radial expansion of the sealing elements to close off a wellbore. One example of such a packer is a retrievable design shown in U.S. Pat. No. 5,273,109. Other designs are known as inflatables and can be advanced thru-tubing. Typical of such designs is U.S. Pat. No. 4,979,570. These designs incorporate an inflatable element generally covered by overlapping slats with one or more sleeves to act as sealing elements covering a portion of the overlapping slats. 
     The packers that compress annular seals longitudinally to squeeze them in the radial direction can require radial expansions as much as 10%, which necessitates considerable longitudinal or axial force. Some seals have been made hollow or porous to reduce the force required to set them. However, hollow or porous seals are subject to decrease in size or collapse as the pressure increases and, thus, are unsuitable for high ambient pressures. 
     One of the objects of the present invention is to overcome the high setting forces required for prior designs so that a packer or plug can be provided which requires only minimal force to engage and disengage or change the size of the seal. Another objective of the present invention is to provide a seal whose performance is unaffected by ambient pressure. 
     Bellows of one type or another have been used for expansion joints to compensate for thermally induced forces. U.S. Pat. No. 4,332,401 illustrates an expansion joint for casing used in injecting steam into wells. U.S. Pat. No. 5,421,241 illustrates the use of a bellows in a gas lift valve construction. U.S. Pat. No. 5,143,158 illustrates the use of bellows in a subsea wellhead apparatus. U.S. Pat. No. 5,119,861 illustrates the use of compressible elastomers to create a pipe plug. Also of interest in the general area of sealing devices are U.S. Pat. Nos. 5,348,087; 2,157,449 (Canadian); U.S. Pat. Nos. 5,303,518; 5,185,806; 5,119,861; as well as a multi-component compressible sealing member sold under the trademark HEXPAK® by Petroleum Engineering Services Inc. of Houston, Tex. This packer employs a sealing element system made of an outer elastomer membrane that is wrapped around a metal sleeve seal mandrel. An inner elastomer provides rubber pressure during pack-off to expand the seal mandrel and ensure solid pack-off state is achieved and molding to the inner casing contour is perfected. 
     The prior designs for seals leave unanswered the need for a sealing device which sets with low forces yet reliably seals against differential pressures, such as in downhole applications. The apparatus of the present invention employs an annular bellows as the seal element which requires minimal force to engage and disengage or change in size. One of the objects of the present invention is to allow a bellows to significantly change its diameter as compared to prior designs involving compression of elements with an axial force. Another objective of the invention is to provide a bellows that can be made from solid materials so that its performance is not affected by ambient pressures. Bellows elements can be readily stacked to achieve multiple independent sealing surfaces without additional design complexity or required increases in engagement force. Accordingly, using the bellows of the present invention, if only one of the multiple ribs which contact the outer pipe are in a pit or crack-free location, the seal becomes effective. Another object of the invention is to provide a greater seal the higher the differential pressure applied. Another objective is to minimize extrusion potential and damage by virtue of the configuration of the design, which facilitates the sealing process, even if there is misalignment of the components supporting the bellows or variability in pipe diameter. Another objective is to be able to make the bellows seal from a wide variety of materials, all of which can functionally operate due to the low engagement force required. These and other objectives will become more apparent to those of skill in the art from a review of the preferred embodiments described below. 
     SUMMARY OF THE INVENTION 
     An annular seal is disclosed made of a collapsible bellows. The bellows can function as an anchor or a seal and is easily set into position using relative component movement. The bellows folds can be slanted and their outer sealing edges can have different profiles to meet expected conditions. The bellows is expanded for insertion to reduce its outer dimension and sets by compaction as a result of relative movement. The bellows can be straight or tapered and is settable with a minimal axial force. 
    
    
     DETAIL DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the bellows in an expanded position within casing. 
     FIG. 2 is the view of FIG. 1, showing the bellows compacted. 
     FIG. 3 is a detailed view of the compacted bellows, showing rounded edges for sealing. 
     FIG. 4 is an alternative of FIG. 3, showing flat edges on the bellows for sealing. 
     FIG. 5 is an alternative embodiment to FIG. 1, showing a slidable collar employing a drag device to allow the bellows to expand during insertion. 
     FIG. 6 is an alternative to FIG. 5 where a slidable collar directly drags on the wellbore during insertion to expand the bellows. 
     FIG. 7 is a view of a tapered bellows in the expanded position for run-in. 
     FIG. 8 is the view of FIG. 7 with the bellows in a compressed position for sealing in the casing. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 represent a schematic view of the preferred embodiment of the present invention. As shown in FIG. 1, the wellbore, which includes uncased as well as casing  10 , is to be sealed off in a typical wellbore. Although the invention is well suited for wellbore applications, use as an anchor or a plug in any passage is contemplated. “Passage” as used herein includes wellbores. There are two components that move relatively to accomplish this objective. An inner tube or mandrel  12  includes a collar  14  which supports end  16  of bellows  18 . In the embodiment of FIG. 1, the bellows  18  is straight cut, illustrating a zigzag pattern. However, other types of collapsible bellows are also within the scope of the invention. The bellows  18  can be made of any material resilient enough to be formed into a bellows and which can fold and extend without damage and is compatible with well fluids and temperatures. Some examples are rubber and PTFE. The opposite end  20  of the bellows  18  is retained to a retaining ring  22  which is optionally mounted to a latch collar  24 . In this option the collar  24  has a ball  26  which is biased by spring  28 , which is in turn held in position by a plug  30 . These components can be more clearly seen in FIG.  3 . Ball  26  initially sits in groove  32  during run-in, thus helping to hold the bellows  18  in the expanded position where it has a smaller diameter to facilitate running in. When fully compressed as shown in FIGS. 3 or  4 , the bellows increases in outer diameter by over 10% from its expanded position to its compressed position and the ball  26  lands in groove  34 , shown in FIG. 1 to assist in holding the bellows  18  in the compressed position such as shown in FIGS. 3 and 4. The latch collar  24  is held in position a sufficient distance from collar  14  to allow expansion of the bellows  18  to reduce its outside diameter for run-in. Since FIG. 1 is a schematic drawing, those skilled in the art will appreciate that known techniques involving relative movement for setting packer elements of the elastomeric type can be employed in actuation of the bellows  18  from the position shown in FIG. 1 to the position shown in FIG.  2 . Thus, for example, any type of running tool that can either hold the mandrel  12  stationary while advancing the latch collar  24  or vice versa (which is preferred) i.e., holding the latch collar  24  stationary while picking up the mandrel  12  will result in compaction or folding of the bellows  18  from the position shown in FIG. 1 to the position shown in FIG.  2 . The preferred technique, showing the uphole advancement of the collar  14 , is illustrated in FIG.  2 . Various releasable locks can optionally hold the set position of FIG.  2  and can be overcome with a force to break a pin that holds a lock ring to allow reextension after compaction. The bellows  18  can also be expanded by fluid pressure which drives a movable piston, holding one end of the bellows  18  away from an opposing fixed end. Setting can be accomplished by relative movement which can displace fluid from under the bellows  18  or a piston connected to it. Alternatively, the piston can be held by fluid pressure in the bellows expanded position and returned to a bellows compacted position by a return spring or applied fluid force. Other known variations to accomplish relative movement in a packer to set its sealing element can be employed without departing from the spirit of the invention. 
     FIG. 2 also illustrates the use of beveled washers known as Belville washers  19  as a backup for the bellows  18 . Washer or washers  19  can fold toward a flat position to reduce the size of the extrusion gap for the bellows  18 . The washer  19  can also be incorporated into the bellows  18  or otherwise positioned between the collar  24  and the bellows  18  as shown in FIG.  1 . The washer  19  reduces the gap to less than 0.01 inch which is comparable to a narrow range of gaps where O-rings are used. 
     The folds  36  of the bellows  18  can have a slope as indicated by arrow  38  with respect to the longitudinal axis  40 . The sloping feature gives the folds  36  a chevron-like appearance when collapsed and further assists in resisting differential pressures which are higher in the downhole region  42  than in the uphole region  44 . The slope angle if used can be as high as about 60°, or as shown in FIG. 8, it can be eliminated completely. Variations of the folds  36  are shown in FIGS. 3 and 4. A similar angle is indicated for the disposition of the folds  36  in FIGS. 3 and 4, as shown in FIG.  2 . In FIG. 3, the edges  46  are rounded, while in FIG. 4, the edges  48  are squared off or flat. 
     Referring now to FIG. 7, an alternative design for the bellows  18  is illustrated in that there is a decreasing taper toward the downhole region  42 . The end  16  is attached directly to the mandrel  12 , while the opposite end  20  is secured to a ring  50 . Ring  50  can drag on the casing  10  to expand the taper bellows during run-in. When the assembly A has reached the desired depth in the casing  10 , an upward pull is applied to the mandrel  12  to set the tapered bellows as shown in FIG. 8. A slant feature to the folds  36 , as shown in FIGS. 3 and 4, can also be incorporated in the design of FIGS. 7 and 8. The ring  50  provides sufficient resistance to allow the folds  36  to compress, as shown in FIG. 8, when an upward pull is applied to the mandrel  12 . Ring  50  is connected to a sleeve  52  which may be engaged by setting tools of known designs for the creation of relative movement between sleeve  52  and mandrel  12  to allow re-extension of the bellows  18  for removal from the wellbore. Sleeve  52  may also be hydraulically actuated. In an alternative embodiment, ring  50  can be integrated with bellows  18  as a thick end section so that it fits loosely over mandrel  12 . In this embodiment, sleeve  52  would not be used for setting bellows  18 . Ring  50  can be the same material as bellows  18  or another material compatible with wellbore conditions. Bellows  18  can be made with an internal threaded nipple at end  16  and the mandrel  12  can be simply screwed into the nipple for rapid assembly. When ring  50  drags on casing  10  during run-in, the bellows  18  is extended. When the proper depth is reached, the mandrel  12  is picked up and with ring  50  against the casing  10 , the bellows  18  is compressed. One form of release is to fail the connection at end  16  by an upward pull on the mandrel  12  so as to literally pull the mandrel  12  out through ring  50 . The ring  50  is later fished and when pulled uphole extends the bellows  18  for retrieval. 
     The various designs including that shown in FIG. 7 can also be actuated with a misalignment between mandrel  12  and casing  10 . Some misalignment between mandrel  12  and ring  20  can also be tolerated so long as it doesn&#39;t prevent relative movement of mandrel  12  with ring  50  engaged to the casing  10 . Misalignment in the order of about 30° can be tolerated. 
     Yet another alternative to the preferred embodiment of the present invention is illustrated in FIGS. 5 and 6. In FIG. 5, the bellows  18  is retained on end  16  to the mandrel  12 . The opposite end  20  is retained to a sliding collar  54 , which has a drag device such as a spring-like extension member  56  extending therefrom. Collar  54  can alternatively have teeth to bite into casing to allow compression and subsequent reextension of the bellows  18 . The drag device  56  can ride on the casing  10  to urge the bellows  18  into an expanded position for run-in. Upon reaching the desired depth, the mandrel  12  is picked up and the drag device  56  engages the casing  10  to allow compression of the bellows  18 . A retrieval tool of a known design, shown schematically as  58 , retains the slide collar  54  as the mandrel  12  is pushed downwardly to again extend the bellows  18  so that it can be retracted from the wellbore. The design in FIG. 6 is similar to that in FIG. 5 except that the sliding collar  54  can drag directly on the casing  10  so as to provide sufficient resistance to expand the bellows  18  for run-in and to provide sufficient initial grip to allow folding of the bellows  18  into a sealing engagement with the casing  10 . Retrieval of the seal of FIG. 6 again involves the use of a known retrieving tool to grab the sliding collar  54  and hold it in position as the mandrel  12  is pushed downhole to again re-expand the bellows  18  to reduce its outside diameter so that it can be pulled out of the hole. 
     It should be noted that the slope built into the latch collar  24 , or other back-up device for the bellows  18 , enhances the performance of the bellows  18  because it facilitates the folding of the folds  36  during relative movement between the mandrel  12  and the latch collar  24 . Ideally, the inside diameter of the bellows  18  should be such that when it is in a relaxed state, that is neither compressed nor extended, the bellows  18  slides without binding over the mandrel  12 . Normally, the outside diameter of the bellows  18  should be such that when in a relaxed state, the bellows  18  touches the inside diameter of the casing  10 . As shown in FIGS. 5 and 6, the bellows  18  is normally inserted in an orientation where the slide collar  54  is on the low-pressure side of the seal. The other end  16  of the bellows  18  is firmly attached to the mandrel  12 . A sloping back-up member such as latch collar  24  or even slide collar  54 , as shown in FIGS. 5 or  6 , acts to eliminate gaps and any potential to extrude the bellows material. As shown in FIGS. 3 and 4, the outer edge of the bellows is shaped to modify the footprint of the bellows  18 . FIG. 4 illustrates a flat outer shape so that the bellows can more fully fill any void spaces in the inside wall of the casing  10 . 
     To facilitate the collapse of the folds  36 , the bellows profile, i.e., size, shape, physical properties, material choice, and taper angle preferably up to about 15°, can be changed such that the folds successfully start folding at the fold  36  closest to the latch collar  24 , which is held fixed as the bellows  18  is collapsed. Pitch is the peak-to-peak distance such as between adjacent peaks  21  and  23 . Taper is the angle formed by a line connecting peaks  21  and  23  and central axis  25  in the relaxed state for bellows  18 . Reverse slope is the angle formed by the folds of bellows  18  shown in FIG.  2  and axis  40 . The bellows  18  can have one or more openings  59  so that the fluids or gases, which are contained within the bellows in area  60 , can be displaced through such openings  59  to allow the bellows  18  to collapse fully. Other liquid or gas-venting techniques from underneath the bellows in area  60 , such as a check valve or a low-pressure reservoir, can be employed without departing from the spirit of the invention. 
     It should also be noted that the outside diameter of the bellows  18  can be larger than the inside diameter of the casing. However, during run-in when the bellows  18  is in the stretched position, its outside diameter is smaller than the inside diameter of the casing to allow insertion. Upon the completion of relative movement as previously described, using a bellows  18  with its largest fold  36  bigger than the inside diameter of the casing ensures that the fold or folds  36  properly engage the inside surface of the casing  10  and further that such engagement occurs at an angle as represented by arrow  38  of FIG.  2 . 
     Those skilled in the art will appreciate that a variety of known packer designs can be adapted to the bellows seal  18  illustrated in the figures. The bellows  18  can be used in conjunction with slips to further secure its position against differentials from uphole or downhole. The actuation which causes relative movement can be done mechanically or hydraulically, and the movement can be locked in by lock rings of a known design which, for the purposes of removal, can be sheared out through the use of known retrieving tools which provide the necessary forces to cause the appropriate relative motion to release slips and at the same time, stretch or expand the bellows  18 . However, since the apparatus of the present invention focuses on the nature of the seal or anchoring device being used and is employable in packers or bridge plugs or anchors of known construction, only the bellows  18  and its mounting details have been shown in detail, while the remaining components of the packer, plug or anchor have either been represented schematically or omitted as details that are well-known to those of ordinary skill in this art. 
     The design shown in the figures can function as an anchoring mechanism as well as or in lieu of being a seal. If the bellows  18  is metallic, its longitudinal collapse and radial growth against the inside surface of the tubular such as a casing  10  will provide anchoring. The bellows  18  can be a composite which is partly metal and partly an elastomer. In that respect it can function both as an anchor as well a seal. Apart from elastomers such as rubber or soft metals, other materials can be used for the bellows  18 . A distinctive feature of the bellows  18  is that minimal force is required for large changes in diameter. This feature makes it possible to use materials that may not be compressible enough to be used in traditional packer designs. For example, PTFE, common sold under the trademark TEFLON®, can be used for the bellows  18 . The design of the bellows  18  makes it possible to choose seal materials based on their chemical and temperature resistance, even though they are not compressible enough for traditional packer designs. Another alternative for the bellows design  18  is to provide an overlay of a softer material which is flexible over a harder metallic composite or other nonmetallic bellows so that the softer material engages the inside surface of the casing or tubular  10 . This type of construction is also usable in open-hole where there is no casing. In open-hole, there is a need to seal against a potentially irregular outer surface. Accordingly, the advantage of having a continuous surface of soft deformable material for contact with the wellbore wall is desirable. 
     The taper feature as illustrated in FIG. 7 shows a decreasing taper from top to bottom of the bellows  18 . This configuration allows extra drag near the ring  50  to assist in stretching the bellows  18  while it is run into the hole and at the same time minimizing wear at the narrow portion of the bellows  18  from contact with the inside surface of the casing  10 . A taper design such as shown in FIG. 7 allows the bellows to work in a wider range of outer tubular diameters while still having some portion of the bellows providing the optimum diameter. 
     In the preferred embodiment, a latch collar or backing plate  24 , whose outer diameter is just under the minimum diameter of the hole, is preferably used adjacent end  20  of the bellows  18 . The latch collar  24  protects the bellows seal  18  from abrading against the inside walls of the casing  10  during run-in into the wellbore. It also supplies a back-up to the bellows  18  when it is compressed, as shown in FIG.  2 . 
     Instead of the zigzag design shown in FIG. 1, the folds  36  can be more of a reversing U-bend shape without departing from the spirit of the invention. Instead of the constant pitch shown in FIG. 1, the configuration of the individual folds  36  can vary along the length of the bellows  18 . Larger and smaller folds can alternate to create a sawtooth pattern. In one embodiment, alternative folds  36  can be in contact with the inside surface of the casing  10 , depending on the initial configuration of the bellows  18 . The sliding collar  54 , as shown in FIGS. 5 and 6, can also be rotationally released or shearably released to facilitate reexpansion of the bellows  18  for release of the assembly A. One way to facilitate insertion and removal of the assembly A is to temporarily secure the position of the slide collar  54  to the mandrel  12  with the bellows  18  in an expanded position during run-in. Any connection between the mandrel  12  and the sliding collar  54  can be disengaged with a twist force applied to the mandrel  12 , using a drag or fixation device such as  56  or direct contact between the sliding collar  54  and the casing  10  as the mechanism for allowing relative rotation. The relative rotation frees the sliding collar  54  from its connection with the mandrel  12  such that upward movement of the mandrel  12  folds the folds  36  of the bellows  18 . In order to release, a downward force is placed on the mandrel  12  and a twist in the reverse direction reengages the sliding collar  54  to the mandrel  12  to hold the bellows  18  in the expanded position for removal. 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.