Patent Publication Number: US-7896090-B2

Title: Stroking tool using at least one packer cup

Description:
FIELD OF THE INVENTION 
     The field of this invention is downhole tools of the type that extend a piston in response to pressurizing an annular space and more particularly where the space is sealed with a packer cup. 
     BACKGROUND OF THE INVENTION 
     In a subterranean environment the expansion of tubulars frequently requires force applied to a swage that cannot be delivered through the surface equipment. To accomplish such expansions an assembly of tools has been used that has a swage at the lower end and a resettable anchor at the upper end. In between is a stroking tool. Applying pressure in a string that supports this assembly first sets the anchor and then pressurizes an annular chamber between a housing and a piston that is inside it. The annular space is sealed with end seals between the relatively movable components. The swage is secured to the movable piston. Extension of the piston drives the swage through the tubular. If the expansion is top down, at the end of the piston stroke the applied pressure in the running string is removed and weight is set down. Removal of the internal pressure in the running string allows the anchor to collapse so that the set down weight acts to bring the housing back over the extended piston. This re-cocks the piston for a repeat of the previous cycle until the swage is driven as far through the tubular as the application requires. 
     Such stroking tools as used by Baker Oil Tools for its LinEXX Hydraulic Expansion System have used stacks of chevron seals to seal the variable volume annular space that drives the piston. The problem with sealing with the chevron seal stacks is the expensive surface preparation of the moving surface that goes past the seals. In some versions the contact surface was chrome plated after an expensive surface cleaning operation to remove burrs and other surface irregularities. In some instances the piston was a machined part adding to the product cost. 
     Other stroking tools such as the Hydraulic Setting Tool for Top Set Packers sold by Baker Oil Tools under Product Family H26534 used an annular variable volume cavity whose ends were sealed with o-ring seals. Depending on the cleanliness of the pressurizing fluid, the service life of the o-ring seals could be significantly reduced. 
     U.S. Pat. No. 6,189,621 illustrates the use a downhole shuttle device with a peripheral seal and an onboard pump so that operation of the pump pulls suction ahead of the seal on the shuttle and the pump discharge goes uphole of the barrier seal so as to propel the shuttle in the downhole direction. 
     In a new design with an objective of reducing constructed cost while maintaining or enhancing service life, the preferred embodiment of the present invention seeks to create a variable volume space with lower cost components some of which are readily commercially available. At least one packer cup is deployed to seal the variable volume space during piston extension. Preferably, the opposed ends of the variable volume space are sealed with packer cups whose orientation puts the broad surface area of the cup against the surface where relative movement occurs. In alternative embodiments the packer cup can be used to drive a string in the wellbore. Alternate applications are envisioned beyond stroking a swage to expand a tubular. 
     SUMMARY OF THE INVENTION 
     A tool for subterranean use envisions relative movement between a housing and a piston by pressurizing and removing pressure in a variable volume defined between them. The variable volume is sealed with packer cups preferably with one supported from the piston and the other off the housing and in opposed orientations so that the broad surface area on each packer cup abuts the surface where relative movement takes place. The downhole tasks accomplished with the relative movement can be varied and include tubular expansion, setting packers or shifting sleeves, for example. Alternative embodiments envision use of a single or multiple packer cups tied to a structure that needs to be driven and building pressure behind a packer cup or reducing pressure ahead of it to advance it. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a section view of a stroker using two packer cups; and 
         FIG. 2  is a system where a packer cup can be used to drive a tubular string into a wellbore. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  illustrates how the relative movement is generated with applied pressure to ports  10  leading to a variable volume cavity  12 . A tubular string  14  has an anchor schematically illustrated by arrow  16  for selective grip on an existing tubular string  18  shown discontinuously at opposed ends of  FIG. 1 . String  18  has a taper  20  leading to a smaller diameter section  22  to be expanded. Arrows  24  represent a swage secured to a lower end of a piston assembly  26 . The piston assembly  26  is movable with respect to string  14  which acts as a stationary mandrel when anchored to the tubular string  18  at anchor  16 . In the view of  FIG. 1  the assembly  26  has been propelled downhole to the fullest extent with respect to the mandrel  14  that is needed to define the variable volume cavity  12 . A travel stop (not shown) can be used to limit the movement of the assembly  26  in the direction of arrow  28  with respect to mandrel  14 . After the position of  FIG. 1  is reached, the pressure in the mandrel  14  is removed to release the anchor  16  and weight is set down from the surface. Assembly  26  stays put as the mandrel  14  with the packer cup  30  move in tandem toward the now stationary assembly  26  and packer cup  32  that is attached to it. This happens because the weight of assembly  26  is resting on progressively moving taper  20  whose location changes with each stroke of assembly  26 . 
     Looking specifically at the orientation of packer cups  30  and  32  it can be seen that the packer cup  30  has a neck  34  that includes a bore  36  that abuts the mandrel outside diameter  38 . As used herein, the terms “packer cup” or “cup” or “cup seal” or “exterior opening skirt type cup” are intended to encompass a variety of shapes that include an opening and experience an enhancement of seal contact force when pressure is applied in the opening. Thus the illustrated “L” shapes are envisioned as well as other shapes such as, for example, “U” or “V” shapes. There can be an o-ring in bore  36  to seal against surface  38 . There is no relative movement between the packer cup  30  and the surface  38  so an o-ring seal is satisfactory in that location. The packer cup  30  further has a downhole oriented skirt  40  having a lower end opening  42  looking in the downhole direction of arrow  28 . The large outer surface  44  of the skirt  40  is in contact with the moving inside surface  46  of the assembly  26 . 
     Those skilled in the art comparing packer cups  30  and  32  will notice that cup  32 is oriented as a mirror image of cup  30  and is further turned inside out in comparison to cup  30 . Neck  48  has an outer sealing surface  50  that abuts inside surface  52  of bottom sub  54  of assembly  26 . An o-ring seal (not shown) can span surfaces  50  and  52  and is preferably put into a groove (not shown) in surface  50 . The skirt  56  has an open end  58  oriented uphole in the opposite direction from arrow  28 . The skirt  56  has an inner surface  60  that contacts the outer surface  62  of the mandrel  14 . 
     Those skilled in the art will appreciate that pressure applied through ports  10  to variable volume cavity  12  will go into the open areas defined by ends  42  and  58  so as to push the skirt  40  and its outer surface  44  against surface  46  of the assembly  26  as the assembly  26  moves relatively as the volume of chamber  12  increases. Similarly, pressure into opening  58  pushes surface  60  of skirt  56  into the outside surface of  62  of assembly  26 . By putting the largest surface area of a given skirt against a relatively moving surface the sealing quality is greatly improved without expensive surface preparation. Surfaces  46  and  62  can have a cursory pass to blast grit and the skirts in the configurations illustrated should provide reliable sealing for a reasonable service life without issues of leakage. 
     While the design in  FIG. 1  is the preferred embodiment, other variations are contemplated. The cup seal can be used at on only one end. Multiple seals  30  or  32  with the same orientation on a given end, such as  30 A, can be used to back each other up so that if one is damaged an adjacent one can take its place so that the seal is not lost. The size of the skirts on either of the seals can be larger than the diameter of surface  46  as in the case of seal  30  or smaller than the outside diameter  62  in the case of seal  32  so that in either or both cases there is an interference fit on assembly. The material choice for the seals  30  and  32  has to be compatible with the well conditions and the expected number of cycles during a reasonable service life. The seals have to withstand the delivered pressure differentials and can have inserts in the skirts to provide an assist to sealing beyond the initial interference fit referred to above. The inserts can be in the form of metallic or composite bands or by using blends of different materials such as rubber of different grades to resist hoop stresses from differential pressure loading. The inserts can be axially oriented or in the form of rings  64  and  66  (shown in  FIG. 2 ) among other possible shapes. 
     Referring to  FIG. 2 , a tubular string  68  is delivered on a string  70  with a cup seal  72  closing off the lower end of annular space  74 . Openings  76  allow access to pressurize space  74  from within the string  70 . String  70  can support string  68  for delivery to a specific location. If the outer string  68  gets difficult to advance in tandem with string  70  the two strings can be decoupled to allow relative movement between them and pressure applied to string  70  can advance string  68  relative to it within predetermined travel limits. Through a series of pressuring cycles followed by removal of pressure and setting down weight on string  70 , string  70  can continue to be a guide to string  68 . Clearly the two strings would be still secured to each other within limits of relative movement so that they would not fully detach when string  68  is powered by pressure delivered at ports  76 . This is but an example of how a single packer cup or a plurality of packer cups oriented the same way can be used to create relative motion of downhole components to accomplish a given task. The string  68  once properly placed and supported can be released from the run in string  70  for removal of string  70  with cup seal or seals  72 . 
     It should be noted that the relationship between what has been described as the stationary member and the moved member can be reversed. In the  FIG. 1  embodiment, for example, the assembly  26  can be selectively anchored and the mandrel  14  can be secured to a swage such as  24 . The packer cups  30  and  32  will be oriented differently so that their respective skirts  40  and  56  are up against a surface where relative movement occurs. 
     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.