Abstract:
A spring for use in downhole tools delivers a high force over a long deflection in a relatively uniform fashion. The spring is a tubular shape that is preferably metallic and is preferably plastically deformed into an undulating walled tube either before assembly into a downhole tool or downhole after assembly to the downhole tool. Alternatively the shape can be machined. Spacer rings are used inside and outside the tube as it is compressed to obtain the desired corrugated wall pattern and to prevent localized buckling that can cause wall failure. The spring can conduct pressurized fluids and be rotationally locked to transmit torque and to facilitate milling out. Some machining internally and/or externally can assist in forming the desired corrugated wall shape.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of this invention is springs and more particularly springs for downhole use where high force and a long deflection range is needed where the spring is a tubular structure created by compressive loading before or after assembly into a downhole tool. 
       BACKGROUND OF THE INVENTION 
       [0002]    Tubular shapes with wavy edges made from rubber or other plastics generally by molding the shape and compressing it when in service to serve as a spring are well known as shown in U.S. Pat. No. 5,141,697 (ribs control buckle locations); U.S. Pat. No. 4,235,427 (bellows wall on plastic tube); U.S. Pat. No. 5,326,083 (elastomer tubular shape for automotive use; U.S. Pat. No. 3,037,764 (elastomer tube with external scores used as a spring); U.S. Pat. No. 5,868,384 (steel tube surrounded by rubber cylinder with both compressed to make a spring with an internal stiffener); U.S. Pat. No. 3,409,284 (molded rubber cylindrical shape used a spring); U.S. Pat. No. 3,315,951 (bellows shaped rubber tube with ribs); U.S. Pat. No. 5,351,844 (elastomer cylindrical shape with metal end plates used as a spring and U.S. Pat. No. 6,250,617 (bellows shaped rubber tube with metal rings at the bellows peaks to hold an outside dimension in a surrounding tube). WO 8901577 shows what appears to be a fabricated metal bellows for a low force application with opposed or offset undulations used as a spring for sensitive instruments that require low hysteresis such as with measuring instruments. It does not appear that the unique shape is made by simple compression and the shape may be fabricated and rolled into a tube. The key seems to be the positioning of the bends with respect to the neutral axis. 
         [0003]    U.S. Pat. No. 6,896,049 illustrates a metal cylinder compressed to the point of collapse to use as a seal at the outward buckle locations. U.S. Pat. No. 6,182,755 assigned to Sandia and written by me years ago is for a pre-made metallic bellows that is run in under tension and is made to fold downhole under a compressive force until the folds engage a surrounding surface for sealing. 
         [0004]    Most of the references described above are compressed cylinders used as springs and made from resilient rubber structures that are molded to have an undulating wall or scored or ribbed to control where and the extent of buckling that occurs under compressive force as a way to control the force delivered by the spring. Clearly many of these are bulky structures not at all suitable for being a component of a downhole tool that needs significant spring force to create some motion in the operational sequence of a downhole tool. 
         [0005]    Some of these references use a fabricated bellows or a scored cylinder not for spring use but for sealing. 
         [0006]    The present invention has a variety of aspects. The structure in one embodiment can be created downhole when a cylinder assembled to a tool is compressed downhole. The present invention has a rotational locking feature in a spring. It allows taking flow through a spring as a pressure conductor. Compressing a cylinder between a mandrel on the inside and a cover tube on the outside is another feature of the invention. The use of a cylindrical spring in a metal to metal seal in a packer is an application of the present invention. 
         [0007]    Some packers used downhole employ metal to metal sealing technology against large differential pressures and in hostile temperature environments. In such applications a large spring force is required over a long displacement to retain the metal to metal seal and to compensate for anticipated temperature differentials that can also affect the set of the metal to metal seal. A large spring force may be also required to compensate for the axial backlash (slop) inherent in locking devices such as body lock rings or ratchets that occurs when removing the setting force. 
         [0008]    Accordingly, the present invention seeks to provide such a structure that will function in this service as well as other high demand spring applications in space limited environments such as those that the art described above are not designed to be used. Those skilled in the art will appreciate that tubular springs of the present invention can retain pressure differentials, transmit torque and can be fixedly retained at the ends to facilitate mill out of the tool in which they are mounted. Such tubular springs can be mounted to an assembled tool as cylinders and compressed into operating shape downhole or they can be deformed prior to assembly and compressed into position in a downhole tool assembly. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings, recognizing that the full scope of the invention is given by the claims. 
       SUMMARY OF THE INVENTION 
       [0009]    A spring for use in downhole tools delivers a high force over a long deflection in a relatively uniform fashion. The spring is a tubular shape that is preferably metallic and is preferably plastically deformed into an undulating walled tube either before assembly into a downhole tool or downhole after assembly to the downhole tool. Flexible rings, split rings, or “C” rings are used inside and outside the tube as it is compressed to obtain the desired corrugated wall pattern and to prevent localized buckling that can cause wall failure. The spring can conduct pressurized fluids and be rotationally locked to transmit torque and to facilitate milling out. Some machining internally and/or externally can assist in forming the desired corrugated wall shape. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a section view of a metal to metal sealing packer in the run in condition using the spring of the present invention; 
           [0011]      FIG. 2  is the view of  FIG. 1  in the set position; 
           [0012]      FIG. 3  is a view of one embodiment of the spring of the present invention using integral exterior ribs and shown in a pre-deformed state; 
           [0013]      FIG. 4  is a view of another embodiment of the spring of the present invention showing the use of internal and external removable rings for shape control before deformation; 
           [0014]      FIG. 5  is the view of  FIG. 4  showing how the rings control the bellows shape that results from longitudinal deformation; 
           [0015]      FIG. 6  is the view of  FIG. 3  shown after longitudinal deformation. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0016]      FIG. 1  illustrates an application of the present invention in a packer P. A mandrel  10  has attachment locations  12  and  14  for a setting tool that can shift sleeve  16  while retaining mandrel  10  to set the packer P. When the setting tool (not shown) is actuated the slips  18  are set first as shown in  FIG. 2  followed by the collapsing and outward movement of the seal  20  as can also be best seen when comparing  FIGS. 1 and 2 . The seal  20  has a small dimension to allow clearance for run in and is shaped and scored so that it collapses about its center  22  to form a rounded edge that is driven radially into the surrounding tubular  24 . While the structure of seal  20  is a known product now offered by Baker Hughes Incorporated, the device that retains the sealing force is now the tubular spring  26  of the present invention. As seen in these FIGS. it has a tubular shape with an undulating wall. In the preferred embodiment is it a metallic tube that is capable of delivering a force in excess of 80,000 pounds onto the set seal  22  over a deflection distance of about 0.16 inches depending on the diameter and wall thickness and the nature of the wall corrugations. 
         [0017]      FIG. 1  shows the spring  26  already having the undulating wall when assembled to the packer P for run in. Optionally, the initial shape can be generally cylindrical with possibly grooves machined internally and/or externally to predispose bending into a bellows shape. The setting tool (not shown) that is used to set the packer P can also be in the input force to transform the initial shape of the spring  26  from generally cylindrical to bellows shaped as shown in  FIG. 1 . In the course of reshaping the spring  26  downhole, the seal  20  and the slips  18  can be set. 
         [0018]      FIGS. 4 and 5  illustrate a way the spring  26  can be made at the surface or downhole. A body  28  has end connections  30  and  32 . In between is a generally cylindrical wall  34  that preferably has a series of machined recesses  36  on the outer surface and/or recesses  38  on an inside surface. These recesses thin the wall and thus encourage inward bending  40  and outward bending  42  about a neural axis  44  as shown in  FIG. 5 . Internal rings  46  and external rings  48  deployed before the onset of longitudinal deformation help create the resulting bellows shape shown in  FIG. 5 . These rings lend structural strength to the wall  34  as it collapses from longitudinal compression. The wall  34  preferably plastically deforms to the bellows shape from an initial generally cylindrical shape inside and out. However, after the plastic deformation the bellows or undulating shape retains flexibility to deliver the high forces needed to keep the seal  20  against the surrounding tubular  24  regardless of pressure or thermal gradients when the seal  20  is in the set position. It should be noted that the design just described with the rings  46  and  48  which are preferably split rings so that they can be simply installed can be used with a spring  26  assembled into the packer P before running downhole. In that instance, the setting tool (not shown) for the packer P will accomplish the deformation. The rings  46  and  48  will still be there downhole after deformation or can be removed before running downhole. While the spring  26  can still have some operability with the rings  46  and  48  remaining in position greater functionality can be obtained if the material for the rings is selected to dissolve or otherwise go away upon exposure to well fluids and temperatures. Additionally and optionally, the rings  46  and  48  can be shape memory alloys that go through the transition temperature at expected downhole conditions to push out in the case of rings  46  and to push in in the case of rings  48  to encourage the formation of the desired undulating wall shape for the spring  26 . 
         [0019]      FIGS. 3 and 6  show another design for the spring  26 . There are end connections  50  and  52  that are shown as flanges but can be other designs that permit one or both ends to be fixed against rotation in a tool such as packer P into which the spring is assembled. Rotationally locking any embodiment of the spring is helpful in a mill out situation to keep the spring  26  from spinning when the mill tries to drill it out. In between connections  50  and  52  there is a wall  54  that can have thin portions  56  from external machining. A series of radially extending ribs  58  extend preferably integrally from the wall  54  to periodically strengthen it so that wall deflection on longitudinal compression will occur in the thin wall portions  56 . Spacer rings  60  limit how close the rings  58  can get together on longitudinal deformation forces being applied to wall  54 . As shown in  FIG. 6 , the ribs  58  abut the rings  60  to create preferably equal undulations  62  to give shape to spring  26  in this embodiment. As before, the rings  60  are preferably split to make mounting over flanges  50  or  52  possible and to facilitate removal after longitudinal deformation. The rings  60  can be from a material that dissolves or otherwise goes away under normal well fluid conditions or temperatures in the event the shape of spring  26  is created by the setting tool that sets the tool in which the spring  26  is mounted, such as packer P. 
         [0020]    Although packers that seal metal to metal have been discussed as an application, those skilled in the art will appreciate that other downhole tools can benefit from the spring of the present invention and the manner in which it can be produced. Other examples of possible applications can be subsurface safety valves, disconnect couplings and adjustable swages to name a few applications. The materials for the spring  26  while being preferably metallic have to also be compatible with long term exposure to well conditions and the anticipated amount of cycling while in service as well as being able to provide the force needed in the tool in which the spring is deployed. The deformation of the original shape is preferably plastic which still allows flexure in the resulting shape to be able to deliver the required force over the needed deflection range. Alternatively, the desired shape can be obtained by machining a tubular shape with the desired wall characteristics. 
         [0021]    It should be noted that prior designs of metal to metal sealing packers tried coiled springs or a stack of Belleville washers. The stack of Belleville washers had significant dampening and friction effects from relative movement among the washers. This tubular spring  26  delivers more force over a comparable or longer deflection range than the previously used coiled springs while being smaller to fit into confined locations for downhole use. Another advantage is the ability of the spring  26  to conduct pressurized fluids for a variety of operational purposes in a downhole tool. By the same token, pressure differentials between the interior and exterior of the spring can be tolerated and the interior can also accommodate internal fluid dampening because of this structure. Alternatively the body of the spring can have openings provided for reasons such as drainage. Alternatively, wall openings can be provided and sized to provide a dampening action when the spring is run in fluid on one or both sides. 
         [0022]    The material for the spring can be uniform or dissimilar materials can be used to get desired properties for a given application. Tensile loads can also be applied to the spring  26  such as when applying a pulling force to release seal  20 . The spring can be heat treated after plastic deformation to relieve residual stresses. The number of peaks and valleys in the wall can be adjusted to the deflection required in the application for the desired applied operating force. 
         [0023]    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.