Abstract:
A retaining device for a threaded connection that is expanded holds the connection together to prevent leakage. In a two step thread the retention device is located between the steps and comprises a nose in a groove that holds aligned surfaces together for a metal to metal connection and allows for relative axial movement at the same time.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/266,839 filed Dec. 4, 2009. 
     
    
     FIELD OF THE INVENTION  
       [0002]    The field of the invention is threaded connections and more particularly connections for subterranean use and most particularly connections that are expanded as part of a tubular string that extends to a subterranean location. 
       BACKGROUND OF THE INVENTION  
       [0003]    Tubular strings are formed with threaded connections made up at the surface with tongs and then run in downhole to a desired location. More recently the assembled tubular string is expanded after it is properly positioned downhole. The string can be expanded into another preexisting string already in the wellbore that can have a bell at the lower end so that after expansion both connected strings have a common inside diameter. Other configurations can occur that call for expansion of all or part of a tubular string where the length of the expansion includes the threaded joints that connect the tubulars that make up the string. 
         [0004]    The problem that occurs when a threaded connection is expanded and some separation occurs in the thread to make it no longer gas tight. One reason for this is the tendency of the box and pin ends to curl as a reaction to the expansion force at the noses of the pin and the box. Solutions to address this problem have been proposed particularly at the pin end that focused on pre-stressing the pin end by bending it on makeup from the longitudinal axis with a groove formed at the base of the box. The box end was cantilevered on a fulcrum with the idea that expansion would make the box nose curl in against the pin while the retention of the pin nose by a groove in the box base would prevent curling in of the pin nose. These approaches to sealing the ends of a thread both against pressure within the tubular and pressure on the outside facing the annular space in a wellbore are illustrated in U.S. Pat. No. 7,585,002. The retention device for the pin end that was located on the box was a reverse shoulder  26 . Its purpose was to plastically deform the pin end so that at a location away from the pin end a part of the pin wall could contact the box wall for sealing. 
         [0005]    Another approach in the context of a two step thread was to put resilient seals between the steps and to further provide in association with the seals between the steps mating wicker surfaces with the idea that the expansion would squeeze the resilient seal and the wicker surfaces would hold together better than smooth overlapping surfaces that got pushed together as a swage was advanced through the threaded connection. Variations on this approach are illustrated in U.S. Pat. No. 6,792,665. One of the issues with resilient seals is temperature service limit. In deeper wells the operating temperatures can exceed 150° C. which approached or exceeded the service limit of most seal materials such as elastomers. The other issue was a lack of residual contact pressure in the area between the thread steps after expansion that limited the effectiveness of a metal to metal seal in that area. The radial expansion resulted in wall thinning to conserve volume and as result the force holding the mating metal surfaces between thread steps was reduced. A more effective way to hold the thread together during and after expansion was needed that would take into account the axial dimension changes that resulted from radial expansion as well as changes in wall dimensions. In the past, leakage has resulted from expansion of threaded connections because of the resulting pin and box separation along the thread as a result of the expansion process. 
         [0006]    Still other designs relating to expanding threaded connections are illustrated in: U.S. Pat. No. 5,462,315; US 2007/0035131A1; U.S. Pat. No. 6,554,287B1; US 2003/0067166A1; US 2005/0236834A1; 
         [0007]    U.S. Pat. Nos. 5,415,442 and 6,322,110. At least some of these references show the opposed projections on the pin and the box that overlap each other and contact upon makeup or on expansion. The present invention addresses this need by providing a mechanism to retain the connection together despite expansion where, in one embodiment, the threaded connection is retained together between steps while the retention device allows for relative axial movement between the pin and the box. 
         [0008]    The present invention is for a connection that does not necessarily have to be expanded. The features of the invention can be employed to enhance sealing in a threaded connection even for connections that are simply threaded together with tongs and run into a subterranean location. These and other features of the present invention will become more apparent to those skilled in the art by a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims. 
         [0009]    The following US Patents and Applications illustrate known thread forms that can be used in conjunction with the present invention: 2008/0277933; U.S. Pat. Nos. 7,588,269 and 6,254,146. 
       SUMMARY OF THE INVENTION  
       [0010]    A retaining device for a threaded connection that optionally can be expanded holds the connection together to prevent leakage. In a two step thread the retention device is located between the steps and comprises a nose in a groove that holds aligned surfaces together for a metal to metal connection and allows for relative axial movement at the same time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]      FIG. 1  is a section view of the connection made up and before expansion showing the retention between the steps in a two step thread; 
           [0012]      FIG. 2  is a close up of  FIG. 1  showing the result of expansion with at least one end free to move; 
           [0013]      FIG. 3  is a close up view of  FIG. 1  showing the results of expansion with both ends of the connection restrained from moving. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]      FIG. 1  shows a box  10  connected to a pin  12 . They are preferably connected by a two step thread  14  and  16 . The box end  18  is preferably cantilevered about a fulcrum  20  with the intent that the end  18  will curl toward the pin  12  due to expansion and seal the gap  22  to the surrounding annular space  24 . The pin end  26  is cantilevered about a fulcrum  28 . While employing the invention in a two step thread is preferred the specific design of the thread form and the way the ends  18  and  26  are treated is not the focus of the invention. Rather in a two stage thread application, which is the preferred embodiment, the invention focuses on features of the pin  12  and the box  10  that are disposed between the thread steps  14  and  16 . Broadly stated there are interlocking shapes between the pin  12  and the box  10  that tolerate relative axial movement and hold the pin  12  to the box  10  in zone  30 . The interlocking shapes in one form can be fingers  32  and  34  mounted respectively on the box  10  and the pin  12 . The fingers  32  and  34  point in opposed directions so that when the pin  12  is made up to the box  10  finger  32  defines an annular groove  36  into which finger  34  enters. In the preferred embodiment on makeup and without expansion there is contact of surface  38  of finger  32  with surface  40  of the pin  10  on one side and contact with surface  42  of finger  32  with surface  44  of finger  34 . This is more clearly seen in the close up views of  FIG. 2  although that FIG. shows the expanded condition. Alternatively and within the scope of the invention, the fingers  32  and  34  can come into sealing contact initially after expansion is completed or during the expansion itself while maintaining sealing contact thereafter to the conclusion of the expansion. Similarly the finger  34  on the pin  12  also has a side surface  46  to contact surface  48  on the box  10 . It is preferred that the initial fit of finger  34  in groove  36  and the fit of finger  32  in groove  50  is at least a clearance fit although an interference fit is preferred to maintain sufficient contact pressure for an effective gas tight metal to metal seal on makeup even without any expansion. 
         [0015]    The side surfaces  44  and  46  could be parallel to each other or taper toward each other in a direction toward the end of finger  34  in groove  36 . The same is the case for the corresponding finger  32 . The rounded ends of fingers  32  and  34  facilitate the manufacturing process. It is intended that at makeup and after expansion the metal to metal seal is in the contact location for the fingers  32  and  34  along their sidewalls as they retain the expanded thread together whether it is a single step thread or a multiple step thread. The presence of the restraint that provided a metal to metal seal and allows for relative axial movement is applicable both at an end or both ends of a thread form as it is between steps of a multi-step thread form. 
         [0016]    Referring back to  FIG. 1  the box  10  has a taper  52  on its exterior located just below the lower end of thread  14 . Pin  12  has a taper  54  about even with its finger  34 . Those skilled in the art will appreciate that these tapers increase the wall thickness and are placed there to control stress concentration and to influence the fingers  32  and  34  to flex during expansion so that their respective longitudinal axes while remaining aligned with respect to each other are both skewed with respect to the longitudinal axis  56  of the connection. This skew angle of preferably under 15 degrees adds a component of force normal to the longitudinal axis of the fingers  32  and  34  to push them together and enhance the metal to metal seal that is between them. The skew helps to maintain seal contact during or after expansion or increase break out torque during or after expansion. 
         [0017]    Those skilled in the art will also notice by comparing  FIG. 1  to  FIG. 2  or  3  that the finger tips as a result of expansion and relative axial movement induced by radial expansion have pulled away from the opposing bottoms of grooves  36  and  50  while holding some finger overlap to help maintain the metal to metal seal as between the fingers  32  and  34  contacting each other while holding together the thread forms  14  and  16  at the same time. 
         [0018]    While overlapping fingers  32  and  34  are illustrated as the preferred technique of retaining a pin to a box between stepped threads other equivalent structures that accomplish this purpose are also contemplated. While the fingers can contact each other with metal to metal contact it is also possible to optionally add a groove to one or both fingers and still use a resilient seal or seals in conjunction with metal to metal contact between the fingers. While a two step thread is preferred the invention is applicable to more complex threads with more than two steps and even a single step thread with the fingers or other equivalent devices disposed at one or opposed ends of a single stage thread. 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: