Abstract:
Casing segments and an expansion cone are positioned and cemented within a new section of a wellbore with a lower casing segment in an overlapping relationship with an upper casing segment. The lower casing segment is radially expanded such that an upper end of the lower casing segment comes into contact with the interior wall of the upper casing segment at the overlap region. The upper casing segment has an inward facing profile at the overlap region that includes a set of wickers that are driven into the lower casing exterior when it is expanded. This forms a metal-to-metal seal between the upper and lower casing segments at the overlap region.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to wellbore casing or liner and in particular to a high integrity hanger and seal used in casing while drilling operations. 
       BACKGROUND OF THE INVENTION 
       [0002]    In conventional well drilling, several casings  12 ,  14  are installed in the well borehole  10  to maintain the integrity of the borehole wall, as shown in  FIG. 1 . The installed casing  12 ,  14  further prevents undesired flow of drilling fluid into the formation or flow of fluid from the formation into the borehole  10 . An initial depth of the borehole  10  is drilled and a casing segment  12  is cemented in place. A subsequent casing  14 , which is to be installed in a lower segment of the borehole  10 , is lowered through the previously installed casing  12  of an upper borehole segment. 
         [0003]    The casing  14  to be installed in a lower segment may be hung at the wellhead  16  as shown in  FIG. 1 . The casing  14  of the lower segment is of smaller diameter than the casing  12  of the upper segment to allow passage of the subsequently installed casing  14  through the casing  12  of the upper segment. Thus, the casings  12 ,  14  are in a nested arrangement with casing diameters decreasing in downward direction Annuli are formed between the outer surfaces of the casings  12 ,  14  and the borehole wall to seal the casings  12 , 14  from the borehole wall. Cement is introduced into the annuli to cement the casings in place. Due to this nested casing arrangement, a relatively large borehole diameter is required at the upper part of the wellbore. A large borehole diameter typically involves increased costs due to heavy casing handling equipment, large drill bits and increased volumes of drilling fluid and drill cuttings. Drilling rig time is involved due to required cement pumping, cement hardening, equipment changes due to large variations in hole diameters to be drilled, and the large volume of cuttings drilled and removed. 
         [0004]    To try and remedy the issues with the nested casing arrangement, expandable tubulars have been employed for the sections of casing, or liner, below the upper section of casing. The subsequent expandable tubular is lowered into a portion of the well drilled out below the upper casing. Once in place, the tubular is expanded radially such that the bore diameter is approximately slightly less that of the upper casing. An overlap exists between the upper and lower casing segments that creates a seal between the segments when the tubular is expanded. However, due to well pressure and thermal growth, the seal may lose integrity. 
         [0005]    A need exists for a technique that addresses one or more of the limitations of the existing procedures for forming new sections of casing in a wellbore. The following technique may solve these problems. 
       SUMMARY OF THE INVENTION 
       [0006]    In an embodiment of the present technique, a casing may be comprised of a plurality of casing segments joined approximately end to end, with each casing segment comprising a wicker profile formed on the interior surface at one end of the casing segment. Once the casing segment is cemented in place within the well borehole, a subsequent casing segment having a smaller diameter than that of the cemented casing may be lowered on a drill string through the initial, cemented casing. The drill string may extend past the lower end of the subsequent, lower casing where a bottom hole assembly (“BHA”) is attached to the drill string. The BHA may comprise a drilling head and an underreamer. The drilling head and underreamer rotate during drilling operations to drill a desired length below the end of the initial casing segment. Once the drilling operation is complete, the BHA may be retrieved and the subsequent casing is cemented in place in a conventional manner such that a portion of the subsequent casing segment overlaps with the wicker profile of the initial, upper casing segment. 
         [0007]    In an illustrated embodiment, a pig or expandable cone may then be run into the bore of the lower, subsequent casing on a string to radially expand the lower casing along its length. As the lower casing segment is radially expanded by the pig, the portion of the lower casing segment that overlaps with the wicker profile of the upper casing is deformed onto the wicker profile to form a metal-to-metal seal. The wicker profile bites into the exterior surface of the subsequent casing segment In addition to forming a high integrity metal to metal seal, the wicker mechanism can function as a casing hanger while the cement cures. The procedure described above may be repeated until the desired length of casing is installed. 
         [0008]    The combination of the wicker profile, and the radial expansion of each subsequent casing segment to form a metal-to-metal seal against the wicker profile, improves sealing between casing segments while reducing the telescoping and borehole reduction effect. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a sectional view of a casing arrangement of the prior art. 
           [0010]      FIG. 2  is a sectional view of joined casing segments, in accordance with an embodiment of the invention. 
           [0011]      FIG. 3  is a sectional view of overlap or packoff region, in accordance with an embodiment of the invention. 
           [0012]      FIG. 4  is a sectional view of a casing while drilling operation, in accordance with an embodiment of the invention. 
           [0013]      FIG. 5  is a sectional view of a casing while drilling operation, in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to  FIG. 2 , an embodiment of the invention shows a portion of a casing  20  is within a well borehole  24 . Cement  22  is introduced into an annulus formed by the borehole  24  and the casing  20  to hold the casing  20  in place. In this embodiment, the casing  20  may be comprised of a plurality of segments, for example, an upper or initial casing or liner segment  28  is joined at one end with a lower or subsequent liner or casing segment  26 . The term “liner” refers to casing that has its upper end a short distance above a previously installed string. A casing string normally extends to a wellhead at the surface. The terms “liner” and “casing” are used interchangeably herein. 
         [0015]    An overlap region, tubular seal section, or packoff  32 , shown in more detail in  FIG. 3 , exists at approximately where the segments  28 ,  26  are joined to each other after the lower casing segment  26  has been radially expanded. The upper casing segment  28  has an exterior surface  34  that is in contact with the cement  20  and also has an inner bore  30 . Likewise, the lower casing segment  26  has an exterior surface  38  that is in contact with the cement  20  and has an inner bore  36 . The inner bore  36  of the lower casing segment  26  has a diameter that is slightly smaller than the diameter of the inner bore  30  of the upper casing segment  28 . 
         [0016]    Referring to  FIG. 3 , an embodiment of the invention shows an enlarged illustration of the overlap region  32  in a set position, with the lower casing segment  26  radially expanded. In the set position, the exterior surface  38  of the lower casing segment  26  is sealingly engaged with a wicker profile  40  formed onto an interior end of the upper casing segment  28 . Wickers  40  are not threads, but a series of small triangular-shaped, parallel grooves and ridges on the sealing surface. The wickers may have a depth ranging from 1/16″ to ⅛″. The wickers  40  are formed from metal and bite into the exterior surface  38  of the lower casing segment  26  to form a metal-to-metal seal to create a better seal than a smooth surface. Initially, the wicker profile  40  may also function as a hanger to support the weight of the lower casing  26  prior to the cement  20  curing around lower casing  26 . Further, the interior of the overlap region  32  may comprise a set of grooves  42  above and below the wicker profile  40 . The grooves  42  initially may allow a drill head to be located during casing while drilling operations. Once a drilling operation is completed, the grooves  42  may further function as pockets into which the lower casing segment  26  may extrude to thereby provide a secondary sealing function. Although a downward facing shoulder is shown, a shoulder is not necessary. 
         [0017]    During casing operations as shown in  FIGS. 4 and 5 , the upper casing segment  28  may be lowered into the well borehole  24  and cased with cement  22  that is pumped through the bore of the upper casing  28  and back up the annulus in a conventional manner as taught by US 2007/0175665, hereinafter referenced in its entirety. If the upper casing segment  28  is the first segment then it may be hung from a hanger at the wellhead (not shown). As described in  FIGS. 2 and 3 , the overlap or packoff region  32  is formed on the lower, interior end of the upper casing segment  28 . 
         [0018]    The wellbore will be drilled deeper, either with a drill pipe string or by liner drilling. Continuing to refer to  FIG. 4 , the lower or subsequent casing segment  26  may be lowered into the well borehole  14  through the interior of the upper casing  28 . In this embodiment, the lower casing segment  26  is suspended from a drill string  50  via a sub  52  attached to the drill string for liner drilling. That is, the well is being drilled while casing  26  is being run into the well. The sub  52  may be ported to allow for the flow of drilling mud and other fluid during drilling operations. The drill string  50  may extend through the sub  52  and past the lower end of the lower casing  26  where a bottom hole assembly (“BHA”)  60  is attached to the drill string  50 . The BHA may comprise a drilling head  62  and a collapsible underreamer  64  that may radially extend beyond the exterior surface  38  of the lower casing segment  26 . The drilling head  62  along with the underreamer  64  rotate during drilling operations to drill a desired length below the end of the upper casing segment  28 . Once the desired drilled length is achieved, the underreamer  64  is collapsed and the BHA  60  may be retrieved. 
         [0019]    As shown in  FIG. 5 , the lower casing segment  26  may be conventionally cemented, such as by reference to US 2007/0175665, and a pig or expandable cone  70  may then be run into the bore of the lower casing  26  on a string  72 . The outer diameter of the pig  70  is expandable to be slightly larger than the bore of the lower casing segment  26  to allow the pig  70  to exert a force Fo ( FIG. 3 ) to radially expand the lower segment  26  or at least an overlapping portion of lower segment  26 . Pig  70  is normally lowered into lower casing  26 , then radially expanded and pulled upward. Several techniques for expanding pig  70  are known in the art, such as in U.S. Pat. No. 7,195,061, for example. As the lower casing segment  26  is radially expanded by the pig  70 , a portion of the lower casing segment  26  that overlaps with the overlap region  32  of the upper casing  28  is deformed onto the wicker profile  40  ( FIG. 3 ) to form a metal-to-metal seal. The wicker profile  40  bites into the exterior surface  38  of the lower casing segment  26  that is within the overlap region  32  as previously shown in  FIG. 3 . The inner diameter of the overlapping portion of lower casing will be the same or approximately the same as the inner diameter of the non-overlapping portion of the upper casing  28 . Optionally, the entire length of lower casing  26  could be expanded, rather than just the one overlapping portion. If the entire length is expanded, the resultant inner diameter will equal or nearly equal the inner diameter of upper casing  28 . 
         [0020]    The exterior surface  38  of the lower casing may be formed of a softer metal than that of the wickers  40  or wickers  40  may contain an inlay of soft metal. Further, the wickers  40  may be formed from a different type of metal that is harder than that of the rest of the upper casing  28 , such as Inconel® 725. The yield strength of carbon steel casing is approximately 55 to 110 ksi, depending on the application. The wickers may have 120 ksi minimum yield strength and a hardness can vary between roughly less than 20 Rockwell C (“HRC”) to greater than roughly 37 HRC. The higher hardness of the wickers  40  ensures biting into the lower casing  28  overlap region. In addition, any portion of the lower casing segment  28  that remains above the overlap region  32  may be cut-off and removed, if desired. No additional sealing or pachoffs are required. The procedure described above may be repeated to install additional liner strings. Further, each metal-to-metal seal formed may be tested by pressurizing the interior of the casing and observing any drop in pressure. 
         [0021]    While the invention has been shown in only one of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.