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BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This technology relates to oil and gas wells, and in particular to a well component having a sealing profile that includes engaging protrusions with collapsible tubes therebetween. 
     2. Brief Description of Related Art 
     Typical oil and gas wells include multiple components, such as, for example, wellheads, annular seals, and tubing hangers. During some phases of operation, it is desirable to seal the interfaces between the well components to prevent fluids from passing between the well components. To increase the ability of components to seal together, some well components are equipped with protrusions, sometimes referred to as wickers, on at least one of adjacent components. These protrusions serve to engage with the surface of an adjacent well member to increase sealing between the well components. 
     One problem with the use of such protrusions to enhance sealing is hydraulic lock. Hydraulic lock occurs when well fluid fills the valleys between the protrusions and becomes trapped when the protrusions engage an adjacent well component surface. Because most well fluid is not compressible, the fluid filled valleys prevent or restrict movement of the protrusions toward an opposing surface. To eliminate this problem, different technologies have been used. 
     One such technology includes the use of collapsible foam, which fills the valleys, displacing the well fluid therefrom. The foam typically consists of a large quantity of small hollow balls, or glass beads, which are collapsible when compressed. As the protrusions engage an opposing surface, the foam is crushed by the opposing surface. The use of collapsible foam, however, can be problematic. For example, the small glass beads are difficult to embed on the valleys between protrusions, requiring a special coating process during the manufacturing of the well components. Furthermore, as the beads are crushed, the crushed pieces of the beads accumulate in the bottom of the valleys, ultimately filling the valleys enough that the “bite” between the protrusions and an opposing surface is impeded. 
     SUMMARY OF THE INVENTION 
     Disclosed herein is an assembly for overcoming hydraulic pressure between components in a well. The assembly has a housing with an inner surface, and a tubular member inserted in the housing and having an outer surface. A plurality of protrusions, separated by gaps or valleys, extends from the inner and/or outer surfaces, and engage an opposing surface upon energization of the tubular member. A metal to metal seal is pressed against and deformed by the intrusions. A plurality of hollow tubes is positioned in the gaps or valleys between the protrusions, and are designed to collapse as the protrusions engage the metal to metal seal. 
     Also disclosed herein is a method of forming a wellhead assembly having an outer wellhead member and an inner wellhead member, and a curved surface with protrusions that extend from surfaces of either the outer or inner wellhead member toward the other of the outer or inner wellhead member. The method includes retaining compressible fluid in gaps between the protrusions, and sealing an annulus adjacent the curved surface by urging a seal against the protrusions that compresses the compressible fluid. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a side cross-sectional view of example well components, including sealing protrusions; 
         FIG. 2  is an enlarged side cross-sectional view of the protrusions of  FIG. 1 , and further illustrated are tubes according to an embodiment of the present technology; 
         FIG. 3  is an enlarged side cross-sectional view of the protrusions and tubes of  FIG. 2  in a collapsed configuration; 
         FIG. 4  is an enlarged side cross-sectional view of example well components according to another embodiment of the present technology; and 
         FIG. 5  is an alternate enlarged side cross-sectional view of the example well components of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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. 
       FIG. 1  is a side cross-sectional view of a seal assembly  10  according to an embodiment of the present technology. The seal assembly  10  is shown in a wellhead  12  having an inner surface  14  which defines a bore  16 . In the embodiment shown, a tubing hanger  18  is positioned in the bore  16  of the wellhead  12 . A sealing mechanism  20  is positioned between the wellhead  12  and the tubing hanger  18 , and seals the space therebetween to prevent fluid from passing between the wellhead  12  and the tubing hanger  18 . 
     In the embodiment of  FIG. 1 , the sealing mechanism has a first leg  22  and a second leg  24 , which are separated by a sealing mechanism gap  26 . The first leg  22  and second leg  24  are joined at bottom ends thereof at an intersection  28 . The first and second legs  22 ,  24  have a thickness that is small enough to allow deflection of the first and second legs  22 ,  24  toward or away from the tubing hanger  18  and the wellhead  12 , respectively. 
     To seal the gap between the wellhead  12  and the tubing hanger  18 , the sealing mechanism  20  is placed in the bore  16  between the wellhead  12  and the tubing hanger  18  so that an inner surface  30  of the inner leg  22  is adjacent the outer surface  32  of the tubing hunger  18 , and an outer surface  34  of the outer leg  24  is adjacent the inner surface  14  of the wellhead  12 . An energizing element  36  is then inserted into the sealing mechanism gap  26  between the first and second legs  22 ,  24 . The thickness T 1  of the energizing element  36  is slightly larger than the width T 2  of the sealing element gap  26 . As a result, when the energizing element  36  is forced into the sealing element gap  26 , it pushes the first and second legs  22 ,  24  radially apart into respective sealed engagement with the inner surface  14  of the wellhead  12  and the outer surface  32  of the tubing hanger  18  respectively. 
     In order to enhance the ability of the first and second legs  22 ,  24  to seal against the wellhead  12  and the tubing hanger  18 , the sealing mechanism  20  in the embodiment of  FIG. 1  includes protrusions  38  that extend from the tubing hanger  18  or the wellhead  12  toward the sealing mechanism legs  22 ,  24 . In an example, the protrusions  38  circumscribe the respective inner and outer surfaces  14 ,  32  of the wellhead  12  and tubing hanger  18 . Optionally, the protrusions  38  have a chisel-like cross section with upper and lower radial sides that extend obliquely away from surfaces  14 ,  32  and intersect to form a point distal from the surfaces  14 ,  32 . As the legs  22 ,  24  are energized and pushed toward the tubing hanger  18  and wellhead  12  the protrusions  38  engage the legs  22 ,  24 , thereby improving the seal between the sealing mechanism  20 , and the tubing hanger  18  and wellhead  12 . Although the protrusions  38  are shown to be extending from the tubing hanger  18  and wellhead  12  toward the sealing mechanism  20 , they could also extend in the opposite direction, from the sealing mechanism  20  toward the tubing hanger  18  or wellhead member  20 . In addition, although the protrusions  38  are shown contacting both the first and second legs  22 ,  24  of the sealing mechanism  20 , the protrusions  38  could be provided on only one side of the sealing mechanism  20 . 
     One problem that can occur when using protrusions  38  in conjunction with a sealing mechanism  20  is the problem of hydraulic lock. For example, in a configuration such as that of  FIG. 1 , where the protrusions  38  extend from the tubing hanger  18  and wellhead  12  toward the sealing mechanism  20 , the protrusions  38  typically remain disengaged from the surfaces of the sealing mechanism  20  when the sealing mechanism  20  is not energized. In such a configuration, well fluid fills the space between the sealing mechanism  20  and the tubing hanger  18  and wellhead  12 . In particular, well fluid surrounds the protrusions  38  and fills valleys  40  or gaps between the protrusions  38 . Upon energization, as the first and second legs  22 ,  24  of the sealing mechanism  20  approach the tubing hanger  18  and wellhead  12 , the inner surface  30  of the first leg  22  contacts the protrusions  38  on the outer surface  32  of the tubing hanger  18 , and the outer surface  34  of the second leg  24  contacts the protrusions  38  on the inner surface  14  of the wellhead  12 . This contact isolates the valleys  40  between the protrusions  38 , which are filled with well fluid. The fluid trapped in the valleys  40  is not compressible, and causes the valleys  40  to become multiple pressurized chambers that push back against the legs  22 ,  24  of the sealing mechanism  20 . This “push back” is known as hydraulic lock, which is an undesirable hydraulic force acting opposite the radial force of the legs  22 ,  24  when they are energized. In situations where hydraulic lock occurs, energizing the legs  22 ,  24  requires enough force be applied to overcome the hydraulic lock and sealingly engage with the protrusions  38 . Reducing hydraulic look reduces the forces necessary to achieve sealed engagement between the legs  22 ,  24  and the protrusions  38 . 
     Referring to  FIG. 2 , there is shown an embodiment of the technology designed to eliminate the problem of hydraulic lock by displacing well fluids in the valleys  40  with collapsible tubes  42 . In  FIG. 2 , wellhead  12  is shown positioned adjacent the second leg  24  of the sealing mechanism  20 . Protrusions  38  extend from the surface of wellhead  12  toward the sealing mechanism  20 . Also shown in  FIG. 2  are tubes  42 , positioned in valleys  40  between the protrusions  38 . One purpose of the tubes  42  is to displace well fluid in the valleys  40  by occupying the space in the valleys  40  between the protrusions  38 . The tubes  42  are filled with air, or other compressible fluid, and are designed to collapse as the outside surface  34  of the second leg  24  of the sealing mechanism  20  engages the protrusions  38 , as shown in  FIG. 3 . The collapse of the tubes  42  opens a void  44  in the collapsed portion of the tube  42 . The void  44  accepts well fluid that previously filled interstitial spaces  46  (shown in  FIG. 2 ) between the second leg  24  of the sealing mechanism  20  and the protrusions  38 . Movement of the well fluid from the interstitial spaces  46  into the voids  44 , allows further penetration of the protrusions  38  into the outer surface  34  of the second leg  24  without hydraulic lock. 
     As shown in  FIGS. 2 and 3 , in some embodiments the profiles of the valleys  40  between the protrusions  38  may be contoured to accept the tubes  42 . For example, where the tubes  42  have circular cross-sections, the bottom of each valley  40  may have a radius  48  that corresponds to, and is in close contact with, the outer surface  50  of the tubes  42 , so that there is minimal or no space between the bottom portion of the valleys  40  and the tubes  42 . In this configuration, the amount of space in the valleys  40  that is occupied by the tubes  42  can be maximized. Furthermore, the radius  48  may extend more than 180 degrees around the bottom of each valley  40  so that a portion of the protrusions  38  juts axially into the valley  40  proximate its peak, thereby creating indented ridges  52  that allow the tubes  42  to be snapped into place in the valleys  40 . In an example, the ridges  52  retain the tubes  42  within the valleys  40 . 
     Although the tubes  42  of  FIGS. 2 and 3  are shown to have circular cross sections, it is to be understood that the tubes  42  can have any shape capable of collapsing upon engagement of the protrusions  38  with a well member. In addition, the tubes  42  can be made of any appropriate material, such as, for example, titanium, aluminum, or steel. Optionally, the tubes  42  may be made from a material that is elastic. The stiffness of the material from which the tubes  42  are made can be less than that of the surrounding well components, thereby ensuring the tubes  42  collapse before adjoining components begin to deform. Furthermore, the tubes  42  can have a uniform wall thickness, as shown, or variable wall thickness. Such variable wall thickness can be designed to cause the tubes  42  to collapse in a predetermined way, or at predetermined pressures depending on the individual circumstances of the well in which the tubes  42  are used. In some embodiments, the tubes  42  may have a wall thickness capable of withstanding up to about 15 kips per square inch before collapsing. 
     In an example of practice, the tubes  42  of the present technology are inserted into the valleys  40  between the protrusions  38  before the system is assembled. After insertion of the tubes  42 , the system is assembled so that a first well component, which may be, for example, a wellhead, surrounds a second well component, such as, for example, an annular seal. In alternate embodiments, the first and second well components could be other well components, such as, for example, an annular seal and a tubing hanger. In addition, the protrusions  38  could be located on any surface of either the first or second well components. When the tubes  42  are inserted between the protrusions  38  they substantially fill the valleys  40  between the protrusions  38 . Thereafter, one of the wellhead members, such as, for example, the annular seal, can be energized, which cases the protrusions to engage an opposing surface. As the protrusions  38  engage the opposing surface, the opposing surface contacts the tubes  42  and ultimately causes them to collapse. Alter the tubes collapse, the opposing surface can continue to move toward and engage the protrusions  38  without experiencing hydraulic lock. 
     In another example embodiment, shown in  FIGS. 4 and 5 , a tube  42  can be used to reduce hydraulic lock between a casing hanger  54  and a stab seal  56 . In such an embodiment, the stab seal  56  is introduced into the casing hanger  54  and is designed to seal against an inner surface  58  of the casing hanger  54  in upper  60  and lower  62  locations (shown in  FIG. 5 ). As the stab seal  56  is lowered into the casing hanger  54 , well fluid can become trapped in a pocket  64  between the stab seal  56  and casing hanger  54 , and between the upper and lower sealing locations  60 ,  62 . By positioning a collapsible tube  42  in this pocket  64 , hydraulic lock can be reduced or eliminated in the same way as described above with regard to the embodiments of  FIGS. 1-3 . 
     For example, as shown in  FIG. 4 , the tube  42  has an outer surface  50 , and the inner surface of the easing hanger  54  can be machined to have a recess  66  that corresponds to the outer surface  50  of the tube  42 . In addition, the tube  42  may have a diameter large enough to extend inwardly from the inner surface  58  of the casing hanger  54  into the path of the stab seal  56 . As the stab seal  56  is lowered into the casing hanger  54 , as shown in  FIG. 5 , the outer surface  68  of the stab seal  56  contacts and collapses the tube  42 , and contacts and seals against the inner surface  58  of the casing hanger  54  at the lower location  62 . Thereafter, the stab seal  56  continues to move downward until its outer surface  68  contacts and seals against the inner surface  58  of the easing hanger  54  at the upper location  60 . The area occupied by the tube  42 , which, as described above, is filled with a compressible fluid, displaces well fluid in the pocket  64  as the outer surface  68  of the stab seal  56  contacts and seals against the inner surface  58  of the casing hanger  54 , thereby preventing hydraulic lock. 
     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:
An well assembly having a housing with an inner surface, the assembly including a tubular member inserted in the housing and having an outer surface. The assembly further includes a plurality of protrusions extending from one of the inner or outer surfaces, the protrusions separated by gaps defined between adjacent protrusions. In addition, the well assembly includes a metal to metal seal pressed against and deformed by the protrusions. A plurality of hollow tubes are provided for insertion in the gaps between the protrusions, the tubes being collapsible upon engagement with the metal to metal seal.