Abstract:
A packing element, which is a composite structure, is disclosed. Components contain the sealing portion to minimize extrusion. The element is retained in tension when running in to minimize damage. In the preferred embodiment, a collapsing sleeve transfers setting force applied at one end, to the opposite end to avoid the problem of bunching up the element adjacent to where it is being compressed which could, if not addressed, result in insufficiently low sealing contact pressure in regions remote from where the pushing force is applied.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 60/296,666, filed on Jun. 7, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The field of this invention is packers or plugs which undergo large expansions to set, such as through tubing, followed by setting in casing or open hole.  
         BACKGROUND OF THE INVENTION  
         [0003]    In through tubing and open hole applications, annular seals are required which have large radial expansion capabilities. For mechanically set elements, the larger the required radial expansion, the more serious the problem of element extrusion under high differential pressure loads. Extrusion would occur beyond the end rings placed there to control that condition. Various designs for backup rings have been tried with only limited success with the exception being where the extrusion gap around such rings is kept to a minimum. This situation usually involved a traditional casing packer application. Prior designs, in large expansion applications have allowed a gap to exist, which has been sufficiently large to allow extrusion to occur.  
           [0004]    Another problem plaguing prior designs of mechanically set packers has been the inability to get a proper set over the length of the element. This happened because element would be pushed from a first end and start to set from that end. If the end near where the setting force was being applied engaged the casing or the open hole, further pushing would not allow the balance of the element to be firmly pressed against the casing or borehole.  
           [0005]    The preferred embodiment of the present invention addresses these shortcomings of the past designs. It has a mechanism for setting from the end opposite of where the pushing force is being applied. Because of this, very long elements can be reliably mechanically set. The sealing element assembly includes a composite structure, which effectively closes the extrusion gap regardless of the large expansion. While the preferred embodiment accomplishes these objectives, the scope of the invention is far broader as will be explained in detail below and illustrated in the claims.  
           [0006]    Of interest with regard to prior designs are U.S. Pat. Nos. 2,132,723; 2.254,060; 2,660,247; 2,699214; 2,738,013; 2,738,014; 2,738,015; 3,392,785; 3,784,214; 4,258,926; 5,775,429; 5,904,354; and 5,941,313. Of more interest among this group of patents is U.S. Pat. No. 5,941,313. It discloses using deformable sheaths surrounding a material placed therein. This structure is taught for service as a main seal or a backup member to the seal but not both. The sheath is a thin walled tubular member formed from a metallic or other material having sufficient strength and elasticity to bend without fracturing. In some embodiments, a resilient material is overlaid on the sheath but no provisions are made to keep this layer from extruding upon set. In another embodiment, exterior deformation surfaces interact with the sheath to redirect its deformation. No explanation is offered as to how pushing on the sheath at a second end results in initial deformation of the sheath against the exterior deformation surface adjacent the first end.  
           [0007]    Testing by applicants has shown that one major concern with pressure set elements is that the element portions closer to where the element is being pushed expand first. This has the potential of weakening the grip of the remaining portions of the element. The present invention overcomes this problem by temporarily stiffening the end being pushed on to allow the remainder of the sealing element to contact the casing or the well bore. Thereafter, with the remote part of the element against a firm support, the proximate portion of the element is forced into sealing contact, overcoming the temporary stiffening. The invention encompasses a variety of ways to accomplish this objective and to prevent or minimize extrusion after the set.  
         SUMMARY OF THE INVENTION  
         [0008]    A packing element, which is a composite structure, is disclosed. Components contain the sealing portion to minimize extrusion. The element is retained in tension when running in to minimize damage. In the preferred embodiment, a collapsing sleeve transfers setting force applied at one end, to the opposite end to avoid the problem of bunching up the element adjacent to where it is being compressed which could, if not addressed, result in insufficiently low sealing contact pressure in regions remote from where the pushing force is applied. 
       
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is an outer view, partly in section, showing the innermost components adjacent to the mandrel;  
         [0010]    [0010]FIG. 2 is the view of FIG. 1 showing the internal sealing element:  
         [0011]    [0011]FIG. 3 is the view of FIG. 2 showing the layers above the internal sealing element:  
         [0012]    [0012]FIG. 4 is the view of FIG. 3 showing the outer sealing element that makes contact with the casing, tubular or borehole.  
         [0013]    [0013]FIG. 5 is a run in view of the assembly in part section;  
         [0014]    [0014]FIG. 6 is the view of FIG. 5 in the set position;  
         [0015]    [0015]FIG. 7 is a section view along lines  7 - 7  of FIG. 5;  
         [0016]    [0016]FIG. 8 is a section view along lines  8 - 8  of FIG. 5;  
         [0017]    [0017]FIG. 9 is a section view along lines  9 - 9  of FIG. 5.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    Referring to FIGS. 1 and 2 the mandrel  10  has a top thread  12  and a bottom thread  14  to allow running into a well. It further comprises a stationary sleeve  16  and a movable sleeve  18 . Sleeve  18  may be actuated in an up-hole direction by known techniques such as use of wellbore hydrostatic pressure against an atmospheric chamber or applied mechanical or hydraulic pressure or combinations of the above. On top of the mandrel  10  are a pair of collapsing sleeves  20  which preferably have openings  22  to selectively weaken them. In between the sleeves  20  is a spacer  24 , which preferably distributes what would be essentially a line contact between ends of sleeves  20  if they were stacked end to end. The spacer  24  can have opposing female receptacles to allow ends of adjacent sleeves  20  to be inserted so they can be guided and held in alignment as a force is applied to movable sleeve  18 . The reasons for using sleeves  20  can be better understood by examining FIGS. 1 and 2 together. As shown in FIG. 2, the internal sealing element  26  spans over sleeves  20  and spacer  24  as it extends between stationary sleeve  16  and movable sleeve  18 . It also covers a seal ring  28 , which has an internal o-ring  30  for the purpose of internal sealing along the mandrel  10 . The problem addressed by sleeves  20  is that when movable sleeve  18  is set in up-hole motion, the element  26 , in the absence of sleeves  20  will tend to bunch up and contact the casing or wellbore at end  32  rather than uniformly along its length or more preferably from the up-hole end  34 . Expansion initially at end  32  is not desirable because it can prevent sufficient contact pressure from reaching the up-hole end  34  for a proper seal.  
         [0019]    The present invention seeks to direct the pushing force from movable sleeve  18  through a mechanism other than the seal  26  for a predetermined portion of its length. Sleeves  20  have sufficient structural rigidity to redirect the pushing force from movable sleeve  18  to the up-hole segment  34  of the sealing element  26  such that the up-hole segment expands first into contact with the casing, tubular or wellbore. After sufficient contact pressure develops, further pushing by movable sleeve  18  collapses one or both sleeves  20  to allow the pushing force from movable sleeve  18  to go into the lower end  32  of the seal  26  and push it out into sealing contact in the manner just accomplished for up-hole segment  34 . The openings  22  are designed to allow sleeves  20  to buckle after up-hole segment  34  is in sealing contact, at which point, in the preferred embodiment they serve no further significant structural purpose. Sealing force on the lower segment  32  of the seal  26  is principally determined by the pushing force into the resilient lower segment  32  after the upper segment has set. Those skilled in the art can appreciate that one or more sleeves can be uses and that each sleeve can be in round or other cross-sectional shape. The column strength of multiple sleeves or even of a single sleeve  20  can vary along its length, by a variety of techniques. The opening, pattern, number, or size can be varied and/or the wall thickness can change along the length. Different materials can be used along the length. The objective of the various combinations described is to have sufficient aggregate column strength to transfer initial expansion by compression of seal  26  to its upper segment  34  first, through the sleeve or sleeves  20 . It is then preferred that after buckling. The sleeves  20  play a minimal part in the compression of the remainder of seal  26 , while recognizing that the mere presence of the collapsed sleeve  20  in the lower end  32  will, by its mere presence distribute some pushing force from movable sleeve  18  to lower end  32 . It should also be noted that sleeve or sleeves  20  could be complete cylinders, with or without a seam or sheet turned into a cylindrical shape or other shape by scrolling. Sleeves  20  can have longitudinal corrugations as another technique for adjusting their column strength. Instead of sleeves, other structures that have column strength to a point and then will buckle can be used to get the desired movement of seal  26  as described above. Some examples are stacked beveled washers, springs, rods and similar elongated structures that ultimately collapse, bend or deform under load. Also envisioned are materials whose properties can change in response to various fields or currents applied to them. Also envisioned is a variability on the hardness of seal  26  acting in conjunction with sleeves  20  to allow for segment  34  being less resistant to expansion so it will make sealing contact first and the balance getting progressively or suddenly stiffer or harder to promote the desired direction of expansion from up-hole segment  34  to downhole segment  32  of seal  26 .  
         [0020]    Apart from the problem of not getting enough contact pressure for a good seal, there is another potential problem that is addressed by the present invention. That problem is element extrusion through end gaps after setting. The solution of the preferred embodiment is shown in FIGS. 3 and 4. FIG. 3 illustrates the use of tubes  36  and  38 , which extend respectively from sleeves  16  and  18  and can be seen in the section view at the top of FIG. 3. Tubes  36  and  38  preferably do not cover the length of seal  26  leaving a gap  40  in between. The preferred material is a continuous-aramid, Kevlar or carbon fiber, tube that is mechanically secured at sleeves  16  and  18 . Tubes  36  and  38  are preferably constructed of braided fibers to facilitate radial expansion of not only seal  26  but also of outer seal  42  (FIG. 4), which is mounted in a recess  44  (FIG. 2) of seal  26 . In the preferred embodiment, the recess  44  is centrally mounted but offset locations can also be used. The recess  44  is optional but its use facilitates the resistance to extrusion after set, as will be explained below. The seal  26  can preferably be a solid rubber mass or segments or a particle material. A particle material offers an added advantage of being able to move freely during the setting operation and a greater ability to conform to irregularities in the shape of the wellbore. The use of tubes  36  and  38  further makes particle materials such as rubber useful because the rubber is elastic and can store energy, which is contained by tubes  36  and  38 . These strong tubes are a significant element in keeping the seal  26  from extruding past sleeves  16  or  18 . Tubes  36  and  38  can be used alone or can be reinforced with overlaying tube segments  37  (see FIG. 7), secured to sleeves  16  and  18 . Such reinforcing tubes can be of the same material or fiberglass matte or woven metal mesh. They would provide additional resistance to extrusion in an area where the mechanical stresses are the greatest.  
         [0021]    Another feature is the use of a tube  46 , which extends from sleeve  16  to sleeve  18  and is securely attached to both. It is preferably a reinforced steel mesh sleeve which provides support for the element  42  when set because it expands into contact with the casing, tubular or wellbore above and below element  42 , thus acting as an extrusion barrier for it. The actual main sealing occurs along the length of element  42  in contact with the wellbore, tubular, or casing. During run in, tube  46  keeps seal  26  in tension to reduce its profile and protects it from abrasion as it is run into the well. Additionally, as the depth increases the additional hydrostatic force applied to an unbalanced piston area in a hydrostatic setting mechanism, helps to keep the seal  26  taut. The use of a recess  44  to mount the seal  42  insures that portions of the tube  46  expand into contact with the wellbore, casing or tubular both above and below seal  42  and preferably in contact with it on both ends to prevent extrusion and, to a lesser extent, apply an additional sealing force.  
         [0022]    Optionally, a barrier material  48  having some lubricity can be applied over tube  46  but under seal  42 . The preferred material is PTFE and its presence keeps the seal  42  from bonding to seal  26  through tube  46 . Other materials such as a mold release can also be used. The objective is to keep adjacent seal components from bonding to each other. If the material further promotes sliding, due to its lubricating qualities, then its performance is even better. As previously stated, tubes  36  and  38  leave a gap  40  in between and the barrier material, preferably in the form of tape can span that gap  40 , thus keeping rubber from seal  42  from bonding to seal  26  at gap  40 . The presence of the barrier material  48  allows seal  46  to move into uniform contact with the surrounding environment without kinking or binding.  
         [0023]    Those skilled in the art will appreciate that the packing element described above insures proper expansion of the underlying or fill material of seal  26  beginning at the end furthest from where the expansion force is being applied. This is accomplished by channeling the applied force to the remote end by a force transfer mechanism such as sleeves  20 . The force transfer mechanism, by design, is overcome after the upper segment  34  is firmly against a surrounding surface to allow the balance of the seal  26  at its lower segment  32  to complete the expansion. While that is going on tubes  36  and  38  and any backup tubes guard against extrusion. The outer seal  42  can expand against the surrounding surface and be surrounded above and below by portions of the mesh tube  46 . For additional protection against extrusion, the ends of the sleeves  16  and  18  can have longitudinal splits giving the effect of long fingers. These fingers  50  are spread against the surrounding space to give an added extrusion barrier. They can be held together initially for run in so as to keep them out of the way. Additionally, tube  46  keeps the run in profile low as well as serving as an extrusion barrier to both seal  26  and outer seal  42 .  
         [0024]    The above description is representative of the preferred embodiment and the various modifications and alterations that can be made within the scope of the invention are clearly defined below in the appended claims: