Abstract:
A mandrel is formed with a projection, depression or a surface irregularity to retain the seal material sealing a passage in the mandrel or an annular space around it against differential pressure. The material can be a shape memory or swelling material.

Description:
FIELD OF THE INVENTION 
       [0001]    The field of this invention is subterranean plugs or annular seals that experience pressure differential and more particularly mandrel adaptations designed to retain a material such as a shape memory or swelling material in position against such pressure differentials through mechanical retention. 
       BACKGROUND OF THE INVENTION 
       [0002]    Swelling members have been secured to mandrels in a variety of way. One way is to mount the swelling member on a longitudinally split base and secure the base to the mandrel by closing the split base around the mandrel and inserting a long tapered pin. The swelling material itself is secured to the base with adhesives or other chemical bonding techniques. Illustrative of this design is U.S. Pat. No. 7,730,940. 
         [0003]    Another technique is to use rigid rings secured to the mandrel on either end of the sealing element to hold it in position as shown in US Publications 2010/0116496 and 2009/0229816. Yet another way is to shrink fit or create tension in the element adjacent the mandrel in an effort to hold it in position and prevent leak paths along the mandrel and element interface. These concepts are illustrated in U.S. Pat. Nos. 7,441,596 and 7,681,653. 
         [0004]    Other designs couple end retention with booster devices to enhance the radial seal force applied beyond the swelling such as by sliding a wedge under the swelling element from at least one end. An example of this design is U.S. Pat. No. 7,552,768. Flexible stacks of notched rings have been disposed at opposed ends of a swelling element with a through bolt extending through the element to pull the end ring stacks toward each other. This is shown in US Publication 2010/0038074. Sometimes the swelling material is located in an inflatable to assist the inflatable in holding a seal as shown in U.S. Pat. No. 7,597,152. Other multi-layered designs of swelling sealing systems are shown in U.S. Pat. No. 7,422,071 and US Publication 2009/0178800. 
         [0005]    This design uses a single or series of undercut profiles, slots or retentive groove in the mandrel ID or OD depending on where the material is to be retained. The undercut profile allows for greater mechanical retention of the plug material resisting displacement while experiencing a pressure differential. 
         [0006]    The present invention addresses the issue of annular seal or tubular plug retention against pressure differentials in a simplified manner using features of the mandrel or the surrounding tubular and positioning the material adjacent to the mandrel surface formation which can be in the form of a projection or depression or a combination so that the material is better retained against pressure differentials when sealing at a subterranean location. The materials can be shape memory materials or swelling materials. These and other aspects of the present invention will be more readily understood by those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while understanding that the full scope of the invention is to be found in the appended claims. 
       SUMMARY OF THE INVENTION 
       [0007]    A mandrel is formed with a projection, depression or a surface irregularity to retain the seal material sealing a passage in the mandrel or an annular space around it against differential pressure. The material can be a shape memory or swelling material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a section view of a plug located opposite an internal projection on the mandrel for fixation against pressure differential in opposed directions; and 
           [0009]      FIG. 2  shows an annularly shaped sealing element to seal an annular space where the mandrel has a depression to assist in fixation against pressure differential. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0010]      FIG. 1  shows a tubular  10  having an inside diameter  12  in which there is an internal projection  14  that is straddled by a plug  16 . The projection  14  has sloping surfaces  18  and  20  that come to a point  22 . The plug  16  has an upper end  24  and a lower end  26  that straddle the surfaces  18  and  20  and the point  22  where they meet. The surface  18  helps resist net forces in the direction of arrow  28  and the surface  20  resists forces in the direction of arrow  30 . 
         [0011]    The plug  16  can be a shape memory polymer that tends to get softer when swelling to a larger dimension and needs fixation assistance that the projection  14  can provide. Other materials that swell can also be used. Other alternatives are swelling rubber or foams or retained mineral clays such as bentonite. While two surfaces  18  and  20  that intersect have been illustrated, either surface can be omitted so that fixation boost occurs in a single preferred direction rather than opposed directions. While surfaces  18  and  20  are shown flat they can be rounded or irregular and can also feature a surface roughness to aid retention of the plug  16 . 
         [0012]    Instead of the projection  14  the inside wall  12  can be surface roughened to enhance the grip of the plug  16  on the inside diameter or wall  12 . Alternatively, the projection  14  can be flipped so it is a recess while still being subject to the alternatives described above when it is in the form of a recess. Depending on the length of the plug  16  and the surfaces  18  and  20  more than one protrusion  14  or its described variations can underlie a single plug. Alternatively, the single plug  16  that is illustrated can be a stack of plugs to seal the interior of the tubular  10 . 
         [0013]      FIG. 2  illustrates an annular seal  32  on a mandrel  34  and inside of a tubular or casing  36 . The mandrel  34  has a recess  38  that is triangularly shaped with flat side  40  toward the lower end. In this configuration the seal  32  can withstand differentials in the direction of arrows  42  or  44  but preferentially in the direction of arrow  42  because of the location of flat side  40 . While a triangularly shaped recess  38  is shown, those skilled in the art will appreciate that recesses of other shapes can be used. Alternatively or additionally the outer surface  46  can be roughened to strengthen the grip on seal  32  against differential pressure. A projection such as described in  FIG. 1  can be used in the  FIG. 2  design instead or in addition to the recess  38 . The single recess  38  can be multiple recesses arranged in mirror image triangles so that their flat sides are opposed to better resist differentials in directions  42  and  44 . Additionally, a series of similarly oriented recesses can be placed in succession under the seal  32 . 
         [0014]    All variants discuss for  FIG. 1  are intended to be applicable to the  FIG. 2  design and vice versa. Apart from the illustrated triangular recess other more complicated shapes such as a T-shaped recess are contemplated. 
         [0015]    Those skilled in the art will appreciate that the various embodiments are simple voids or projections or surface textures designed to enhance grip against pressure differential in an environment where a tubular is plugged or an annular space around a tubular is to be sealed. Different shape configurations are employed with an eye toward enhancing the security of the grip against a differential pressure. While the surfaces can be optionally adhesive coated or the plug itself can be placed in position with an exterior adhesive coat, the use of adhesives is totally optional. Mechanical fasteners are not required. The shape can be machined or otherwise formed to the inside or outside of the mandrel, depending on the configuration used. 
         [0016]    In another alternative the seal  32  can be used as shown in  FIG. 1  as well as a plug  16  shown in  FIG. 1 . The plug  16  can be installed in position before the tubular  10  is run into the well or it can be inserted later with the tubular  10  already located at the subterranean location. 
         [0017]    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.