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You are an expert at summarizing long articles. Proceed to summarize the following text: 
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This technology relates to oil and gas wells, and in particular to sealing mechanisms in packoff assemblies for use in oil and gas wells. 
         [0003]    2. Brief Description of Related Art 
         [0004]    Typical oil and gas wells have a wellhead. Strings of casing, each supported by a casing hanger, are lowered into the wellhead. Typically, the casing hanger is threaded, and is attached to a threaded upper end of the casing string. The casing hanger lands on a landing shoulder in the wellhead, or alternatively, may land on a previously installed casing hanger having a larger diameter. With the casing string in place, cement may be pumped down the casing until it comes back up the annulus around the casing. After the cement is pumped, a packoff assembly may be positioned between the wellhead and an upper portion of the casing hanger to seal the casing hanger annulus. 
         [0005]    Some older wellheads include packoff seals that are elastomeric, and that don&#39;t include any form of anti-extrusion device. Furthermore, many older oil wells are now being extended past the original design life of such packoff seals, and some are experiencing long term gas migration out to the larger diameter annuli, such as those where the packoff seals are located. In addition, this older equipment has often been in use for long periods of time, and drilling operation damage to surfaces of the wellhead and/or the casing hanger is possible. The packoff seals originally installed in the wells are often not suitable for overcoming these problems. For example, elastomeric seals are susceptible to degradation in their mechanical properties over time. Thus, as the life of the well becomes extended, the packoff seal may not be reliable. 
         [0006]    Attempts have been made to fix the problems associated with such older, inadequate packoff seals. In some instances, such seals have been replaced with newer flouroelastomer or elastomeric seal elements incorporating anti-extrusion devices. However, replacement and reinstallation of the packoff seals can be complicated, requiring the use of complex running tools and procedures. Furthermore, elastomeric seals are still subject to degradation when exposed to high pressure and temperature in the well. In addition, because surfaces of the well components may be damaged, achieving an adequate seal with a replacement packoff sealing assembly can be difficult. 
       SUMMARY OF THE INVENTION 
       [0007]    Disclosed herein is a packoff assembly for sealing the space between an inner well member and an outer well member when the packoff assembly is inserted therebetween. In some embodiments, the inner and outer well members may be a casing hanger and a wellhead, respectively. The packoff assembly includes a packoff body and a sealing mechanism. The sealing mechanism has an annular shape with a U-shaped cross-section that has a packoff body leg and a well component leg extending downward from a connecting section. 
         [0008]    The well component leg has a sealing surface that can seal against surfaces of the well members. In addition, the well component leg is elastically bendable so that it resists inward deflection toward the packoff body, and so that the sealing mechanism can be set without the use of an energizing ring. The packoff body leg may be configured for engagement with the packoff body. Alternatively, the packoff body leg may be integral to the packoff body. 
         [0009]    If the sealing mechanism is positioned on the inside of the packoff body, the sealing surface seals against the inner well member, which may be a casing hanger. Conversely, if the sealing mechanism is positioned outside the packoff body, the sealing surface seals against the outer well member, which may be a wellhead. In some embodiments, a sealing mechanism may be located on both the inside and the outside of the packoff body. The sealing mechanism may further include an inlay positioned on an outer surface of the well component leg, and configured to engage and seal against the well member when the sealing mechanism is positioned between the packoff body and the well member. One purpose of the inlay is to conform to imperfect or damaged surfaces of well components so that the sealing mechanism can form a tight seal with such surfaces. 
         [0010]    Also disclosed herein are additional features of the packoff assembly. For example, wiper rings may be attached to the packoff body below the sealing mechanisms to wipe the surfaces of the inner and outer well members as the packoff assembly is installed, thereby preparing the surfaces for sealing engagement with the sealing mechanisms. In addition, upper seals may be installed on the packoff body above the sealing mechanisms to shield the sealing mechanisms from pressures above the packoff assembly. Furthermore, a retainer plate may be connected to the bottom of the packoff body to retain the sealing mechanisms and wiper rings in place relative to the packoff body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The present technology will be better understood on reading the following detailed description of nonlimiting embodiments thereof, and on examining the accompanying drawings, in which: 
           [0012]      FIG. 1  is a perspective view of a sealing mechanism according to an embodiment of the present technology; 
           [0013]      FIG. 2  is an enlarged sectional view of a packoff assembly including the sealing mechanism shown in  FIG. 1 : 
           [0014]      FIG. 3  is a schematic cross-sectional view of a packoff assembly including the sealing mechanism of the present technology, with the packoff assembly inserted between a well head and a casing hanger; 
           [0015]      FIG. 3A  is an enlarged schematic cross-sectional view of the portion of the packoff assembly identified by area  3 A in  FIG. 3 ; 
           [0016]      FIG. 4  is a schematic sectional view of the sealing mechanism of the present technology and including an inlay; and 
           [0017]      FIG. 4A  is an enlarged cross-sectional view of the portion of the sealing mechanism identified by area  4 A in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    The foregoing aspects, features, and advantages of the present technology will be further appreciated when considered with reference to the following description of preferred embodiments and accompanying drawings, wherein like reference numerals represent like elements. In describing the preferred embodiments of the technology illustrated in the appended drawings, specific terminology will be used for the sake of clarity. However, the technology is not intended to be limited to the specific terms used, and it is to be understood that each specific term includes equivalents that operate in a similar manner to accomplish a similar purpose. 
         [0019]      FIG. 1  is a perspective view of a portion of a sealing mechanism  10 . The sealing mechanism  10  is an annularly shaped ring that has a U-shaped cross section  12 , including a packoff body leg  14  and a well component leg  16 . The legs  14 ,  16  are attached to, and extend downwardly from, a connecting section  17 . In certain embodiments, the sealing mechanism  10  is made of metal, and the packoff and well component legs  14 ,  16  are sufficiently stiff to resist inward deflection. The outer, lower surface of the well component leg  16  is a sealing surface  18 , configured to sealingly engage a surface of a well component, as described in detail below. In the embodiment shown, the sealing surface  18  extends radially outward beyond the upper portion of the well component leg  16 . The sealing mechanism may be made of metal. 
         [0020]    Referring now to  FIG. 2 , a packoff assembly  19  is shown, including a pair of sealing mechanisms  10 , which are shown installed on a packoff body  20  configured for insertion between well components, such as, for example, a casing hanger  22  and a wellhead  24  (shown in  FIG. 3 ). As shown, the sealing mechanisms  10  may be positioned so that the packoff body leg  14  is positioned toward the packoff body  20 . The packoff body leg  14  may be attached to the packoff body  20  by any appropriate means. The well component leg  16 , including the sealing surface  18 , is positioned away from the packoff body  20 . Alternatively, the sealing mechanism  10  may be integral to the packoff body  20 . In such an embodiment, the packoff body leg  14  may be omitted from the sealing mechanism  10 , and the connecting section  17  may connect the well component leg  16  directly to the packoff body  20 . 
         [0021]    In addition to the sealing mechanisms  10 , the packoff assembly  19  includes wiper rings  28 , upper and lower retainer spacers  30 ,  32 , upper packoff seals  34 , and a retainer plate  36 . The purpose of the wiper rings  28  is to wipe and clean the surfaces of the well components during installation of the packoff body  20 , as described in further detail below. The wiper rings  28  may be made of any suitable material. For example, in some embodiments, the wiper rings may be made of polytetraflouroethylene. The purpose of the upper and lower retainer spacers  30 ,  32  is to maintain the position of the sealing mechanisms  10  and the wiper rings  28  relative to the packoff body  20  and each other. The purpose of the upper packoff seals  34  is to provide an upstream seal between the packoff body  20  and adjacent well components above the sealing mechanisms  10 . Such an upstream seal may be beneficial, for example, to isolate the sealing mechanisms  10  from connection void test pressure or other upstream pressure. 
         [0022]    Retainer plate  36  may be positioned below the sealing mechanisms  10 , upper and lower retainer spacers  30 ,  32 , and wiper rings  28 , and maintains these elements in place relative to the packoff body  20 . To accomplish this, the retainer plate  36  protrudes radially beyond the lower end  38  of the packoff body  20  a distance sufficient to restrict downward movement of the sealing mechanisms  10 , upper and lower retainer spacers  30 ,  32 , and wiper rings  28  relative to the packoff body  20 . The retainer plate  36  may be releasably attached to the packoff body  20  by, for example, a fastener  40 . Fastener  40  may optionally be a bolt that threads into a corresponding recess  42  in the lower end  38  of the packoff body  20 . The ability to release the retainer plate  36  from the packoff body  20  is advantageous because it allows the removal and replacement of the sealing mechanisms  10 , upper and lower retainer spacers  30 ,  32 , and wiper rings  28 . 
         [0023]    The packoff assembly  19  shown in  FIG. 2  has the sealing mechanisms  10 , upper and lower retainer spacers  30 ,  32 , and wiper rings  28  installed on both inside and outside surfaces of the packoff body  20 . Such an embodiment is beneficial for forming a seal between the packoff body  20  and multiple well components (such as the casing hanger  22  and wellhead  24  shown in  FIG. 3 ). Alternatively, however, some embodiments may include only a single sealing mechanism  10 , upper and lower retainer spacer  30 ,  32 , and wiper spacer  28 . In such an embodiment, these components may be mounted either on the outside surface  44  or the inside surface  46  of the packoff body  20 . In any configuration, the packoff body leg  14  of the sealing mechanism  10  will be located adjacent to, and may engage, the packoff body  20 . In addition, the well component leg  16 , including the sealing surface  18 , will be located away from the packoff body  20 . 
         [0024]      FIG. 3  shows the packoff assembly  19  inserted between a casing hanger  22  and a wellhead  24  to seal the space between the casing hanger  22  and the wellhead  24 . A method of assembling and installing the packoff assembly  19  is described herein, and includes, prior to insertion, assembly of the packoff assembly  19 . In embodiments having an upper retainer spacer  30 , such as that shown in  FIG. 3 , the upper retainer spacer  30  is moved into place relative to the packoff body  20 . Thereafter, in embodiments where the sealing mechanism  10  is not integral to the packoff body  20 , the sealing mechanism  10  may be inserted onto the surface of the packoff body  20 . After the sealing mechanism  10  is installed on the packoff body  20 , the lower retainer spacer  32  and wiper ring  28  are moved into place relative to the packoff body  20 . Thereafter, the retainer plate  36  is attached to the lower end  38  of the packoff body  20 , thereby retaining the sealing mechanism  10 , upper and lower retainer spacers  30 ,  32 , and wiper ring  28  in place relative to the packoff body  20 . 
         [0025]    With the packoff assembly  19  thus assembled, it is ready for installation between well components, such as the casing hanger  22  and the wellhead  24 . To accomplish this, the packoff assembly  19  is run through a pressure management device (not shown), such as a blowout preventer, attached to the top of the well. From the pressure management device, the packoff assembly  19  is inserted into the space between the well components. During insertion, the wiper rings  28 , which are positioned below the sealing mechanisms  10 , wipe the surfaces of the well components, in order to remove debris and otherwise clean the surfaces. This is beneficial to provide better sealing between the surfaces of the well components and the sealing surfaces  18  of the sealing mechanisms  10  when the packoff assembly  19  is in place. 
         [0026]    In the embodiment shown, after insertion, the packoff assembly  19  is locked axially in place by a lock down screw  48 . The lock down screw  48  may pass through the wellhead  24  and engage a groove  50  in the packoff body  20 , thereby restricting axial movement of the packoff assembly  19  relative to the wellhead  24 . Alternate embodiments may provide different means of locking the packoff assembly  19  axially in place, and use of a lock down screw  48  is not required. For example, another embodiment might include an internal lock down ring (not shown) inserted above the packoff assembly  19  to prevent upward axial movement. 
         [0027]    As best shown in  FIG. 3A , upon insertion, the sealing surface  18  of the well component leg  16  contacts the surfaces of the well components, such as the casing hanger  22  or the wellhead  24 . The sealing surface  18  extends radially outward beyond the upper portion of the well component leg  16 , and, when the well component leg  16  is in an undeflected state, is arranged in a conical configuration around the sealing mechanism  10 . Upon further insertion and seating of the sealing mechanism  10 , however, the well component leg  16  is deflected toward the packoff body  20 . As the well component leg  16  is deflected toward the packoff body  20 , the sealing surface  18  shifts to a cylindrical configuration around the sealing mechanism  10 . The sealing mechanism  10  is preferably an elastic seal. Accordingly, although the well component leg  16  deflects upon insertion of the packoff assembly  19 , it regains its original undeflected configuration upon removal of the sealing mechanism  10  from between the well components. Furthermore, the elasticity of the sealing mechanism  10  allows for insertion and setting of the sealing mechanism  10  without an energizing ring. 
         [0028]    In one embodiment, the magnitude of the stiffness of the well component legs  16  allows deflection of the well component leg  16  and setting of the seal  10  with a relatively low set weight. For example, the set weight may be 25,000 pounds or less. Such a low set weight allows use of the seals in surface wellhead applications, and, in particular, large diameter casing annuli. In addition, because the sealing mechanism  10  is weight set, only a simple running tool is required for installation. 
         [0029]    Because the well component legs  16  are stiff, the inward deflection of the well component legs  16  is resisted by a resistive force F. The resistive force F is constantly maintained as long as the packoff assembly  20  is in place and the well component leg  16  of the sealing mechanism  10  is deflected inward toward the packoff body  20 . In addition, the resistive force F pushes the sealing surfaces  18  against the well components. Thus, a seal is formed between the sealing surfaces  18  and the well components. Because the sealing surfaces  18  of the sealing mechanism  10  are metal, and the surfaces of the well components are metal, the seal formed therebetween is a metal-to-metal seal. Thus, the seal is capable of withstanding higher pressures and temperatures than elastomeric or other types of seals. 
         [0030]    Referring to  FIGS. 4 and 4A , there is shown an embodiment of the present technology that includes an inlay  52 . The inlay  52  may be made of a metal that is softer than the metal of the well components. In one example embodiment, the inlay  52  is made of annealed silver. As shown in  FIGS. 4 and 4A , the inlay  52  may be attached to the well component leg  16  of the sealing mechanism  10 . In such an embodiment, the well component leg  16  of the sealing mechanism  10  has grooves  54 , which may be located on the sealing surface  18  of the well component leg  16 . Prior to insertion of the packoff assembly  19  into the space between the well components, the inlay  52  may be attached to the sealing surface  18  of the well component leg  16  by soldering, or other appropriate means. 
         [0031]    Thereafter, upon insertion of the packoff assembly  19  between the well components, as described above, the inlay  52  is compressed between the sealing surface  18  of the sealing mechanism  10  and the surface of a well component. Because the inlay  52  is made of a metal that is softer than the metal of the well component, the resistive force F (shown in  FIG. 3A ) that pushes the sealing surface  18  into the surface of the well component causes the inlay  52  to deform until it matches the contour of the surface of the well component. This feature is advantageous because it improves the seal between the sealing mechanism  10  and the well component, particularly where the surfaces of the well component are not smooth, have been damaged during operations, or otherwise have defects that would prevent an effective seal. Thus, the sealing mechanism  10  is suitable for use in retrofit applications, such as where a casing is leaking due to old or inadequate packoff sealing, and a more sure seal is needed. In addition to the seal created between the inlay  52  and the well component, the portion of the sealing surface  18  below the inlay  52  may also contact and seal against surfaces of the well component. 
         [0032]    While the technology has been shown or described in only some 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. Furthermore, it is to be understood that the above disclosed embodiments are merely illustrative of the principles and applications of the present invention. Accordingly, numerous modifications may be made to the illustrative embodiments and other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

Summary:
A packoff assembly for sealing a space between an inner well member and an outer well member. The packoff assembly has a packoff body, and a sealing mechanism with a U-shaped cross-section, including a packoff body leg and a well component leg extending substantially downward from a transverse connecting section. The well component leg is elastically bendable so that it resists inward deflection toward the packoff body and so that the sealing mechanism can be set without the use of an energizing ring. The packoff body leg is configured for engagement with the packoff body, and the well component leg has a sealing surface configured for sealing engagement with the inner or the outer well member.