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This application claims the benefit under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser. No. 60/825,179, entitled, “SPECIAL ENERGIZED METAL-TO-METAL SEAL FOR DOWN HOLE STATIC SEAL APPLICATION,” which was filed on Sep. 11, 2006, and is hereby incorporated by reference in its entirety. 

   BACKGROUND 
   The invention generally relates to forming a metal-to-metal seal in a well. 
   Polymer seals, which include rubber and plastic seals, are commonly used in downhole tools. Polymer seals are often used due to their flexibility, resilience and their ability to seal uneven or irregular surfaces. However, for some downhole environments, such as environments that present extremely high or low temperatures or corrosive fluids (as examples), conventional polymer materials may not be suitable. Furthermore, even in applications in which polymer seals may be used, material degradation, failure and property variations due to environmental changes may make the use of polymer seals challenging. A backup system typically is used with a polymer seal due to the seal&#39;s poor anti-extrusion resistance. 
   A metal seal may be used in a downhole application in place of a polymer seal. Metal seals generally exhibit superior stable mechanical and physical properties, as compared to polymer seals. However, seal design typically is more challenging for metal seals because the sealing mechanism is different from that of polymer seals. For example, a metal seal typically requires significantly more surface finishing and significantly more contact stress on the sealing surface. 
   SUMMARY 
   In an embodiment of the invention, a seal assembly that is usable with a well includes a metal body that is adapted to expand radially inwardly and radially outwardly in response to the body being longitudinally compressed between compressing surfaces. The metal body includes first and second surfaces that do not conform to the compressing surfaces before longitudinal compression of the body and are adapted to contact the compressing surfaces. 
   Advantages and other features of the invention will become apparent from the following drawing, description and claims. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a schematic diagram illustrating a cylindrical-type metal seal assembly before a metal seal ring of the assembly is set according to an embodiment of the invention. 
       FIG. 1A  is an enlarged view of the seal ring of  FIG. 1  according to an embodiment of the invention. 
       FIG. 2  is a schematic diagram of the metal seal assembly of  FIG. 1  after the metal seal ring is set according to an embodiment of the invention. 
       FIGS. 3 ,  5 ,  7  and  9  are schematic diagrams depicting metal seal assemblies that include metal seal rings before the seal rings are set according to embodiments of the invention. 
       FIGS. 4 ,  6 ,  8  and  10  are schematic diagrams depicting the seal assemblies of  FIGS. 3 ,  5 ,  7  and  9 , respectively, after the metal seal rings of the assemblies are set according to embodiments of the invention. 
       FIGS. 11 and 12  are cross-sectional diagrams of seal rings according to embodiments of the invention. 
       FIGS. 13 ,  14  and  15  are cross-sectional diagrams of energizing rings according to embodiments of the invention. 
       FIG. 16  depicts a cross-sectional view of a seal element made from two different metals according to an embodiment of the invention. 
       FIG. 17  depicts a seal assembly having a seal element formed from two different metals according to an embodiment of the invention before the seal element is set. 
       FIG. 18  depicts the seal assembly of  FIG. 17  after the assembly is set according to an embodiment of the invention. 
       FIGS. 19 ,  21 ,  23 ,  25  and  27  depict different seal assemblies before seal rings of the assemblies are set according to embodiments of the invention. 
       FIGS. 20 ,  22 ,  24 ,  26  and  29  depict the seal assemblies of  FIGS. 19 ,  21 ,  23 ,  25  and  27 , respectively, after the seal rings of the seal assemblies are set according to embodiments of the invention. 
       FIG. 28  depicts an intermediate state of the seal assembly of  FIGS. 27 and 29  during the setting of the seal assembly according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a metal seal assembly  10  in accordance with embodiments of the invention may be used to form a seal between an inner tubular member  30  and an outer tubular member  20  in a well. As an example, the outer tubular member  20  may be a casing string, and the inner tubular member  30  may be a work or production string, although the tubular members  20  and  30  may be different components in other embodiments of the invention. 
   Both tubular members  20  and  30  are generally concentric with and generally extend along a longitudinal axis  12  of the well. In general, the metal seal assembly  10  includes a cylindrical and metallic seal ring  40 , which has a thickness profile and other geometrical features that cause the ring  40  to expand both radially inwardly and radially outwardly when longitudinally compressed to form the seal between the tubular members  20  and  30 . 
   As depicted in  FIG. 1 , the longitudinal compression of the seal ring  40  may be achieved using upper  14  and lower  16  thimbles, or gauges, in accordance with some embodiments of the invention. In general, the gauges  14  and  16  may have relatively flat annular surfaces  18  and  21 , respectively, for purposes of engaging upper  42  and lower  44  surfaces, respectively, of the seal ring  40 . Unlike the flat surfaces  18  and  21 , the surfaces  42  and  44  of the seal ring  40  are inclined, another feature of the seal ring  40 , which causes the seal ring  40  to buckle when longitudinally compressed. 
   Referring to  FIG. 1A , in accordance with some embodiments of the invention, the radial thickness of the seal ring  40  varies from its ends where the ring  40  is the thickest to the midsection  48  wherein the ring  40  is the thinnest. Other thickness variations for the seal ring  40  (a uniform thickness for the seal ring, for example) are contemplated and are within the scope of the appended claims. 
   To achieve thickness variations, the inner surface of the seal ring may be sloped with respect to a reference horizontal line at an angle α. The upper  42  and lower  44  surfaces of the seal ring  40  may each be sloped with respect to the reference horizontal line by a smaller angle β. 
   Referring to  FIG. 2 , when the seal ring  40  is longitudinally compressed, inner rounded surfaces  51  and  53  of the seal ring  40  contact and generally form seals with the outer surface of the inner tubular member  30 . Additionally, the outer surface of the seal ring  40  near the midsection of the ring  40  forms a corresponding sealing contact  55  between the seal ring  40  and the inner surface of the outer tubular member  20 . As also depicted in  FIG. 2 , when the seal ring  40  is longitudinally compressed, the upper  42  and lower  44  surfaces of the ring  40  generally conform to the corresponding gauge surfaces  18  and  21 , respectively. 
   In accordance with some embodiments of the invention, the seal ring  40  may be primarily formed from annealed copper material and may have a longitudinal dimension of approximately seven inches. The extrusion gap may be approximately 0.178 inches diametrically. The seal ring  40  may be made from other material and may have different dimensions, in accordance with other embodiments of the invention. For example, instead of copper, other materials for the seal ring  40  may be selected for any number of reasons, such as corrosive effects, strength, cost, etc. As a more specific example, a seal element that is made from nickel or a nickel alloy may have increased suitability for corrosive environments. As further described above, the seal element may be formed from different metals, which are selected for performing different functions. 
   The seal ring  40  may have a variety of different inner diameters, outer diameters, lengths, outer side angles and inner side angles, depending on the particular embodiment of the invention. The particular ring size may be determined by the inner diameter of the outer tubular member  20 , the gauge  16 ,  18  outer diameter and a mandrel outer diameter, or different combinations of the above. The α angle (see  FIG. 1A ) at which the thickness of the seal ring  40  changes as well as the β incline angle of the surface  42 ,  44  may vary between ten and seventy degrees (as examples), depending on the particular embodiment of the invention. The outer side angle may be the same or different from the inner side angle, depending on the particular embodiment of the invention. These angles impart thickness variations to aid in achieving the desirable seal deformation. Thus, many variations are contemplated and are within the scope of the appended claims. 
     FIG. 3  depicts a metal seal assembly  59 , which may be used in place of the metal seal assembly  10  in accordance with some embodiments of the invention. Referring to  FIG. 3 , the seal assembly  59  includes upper  60  and lower  70  metal seal rings, each of which has a curved radial cross-section. The upper seal ring  60  is concave toward an energizing ring  75  (of the seal assembly  59 ) that is disposed between the rings  60  and  70 ; and the lower seal ring  70  is located below the energizing ring  75  and is also concave with respect to the ring  70 . As depicted in  FIG. 3 , the energizing ring  75  generally has a V-shaped radial cross section. In general, the vertex of the cross-section of the energizing ring  75  is located near the outer surface of the inner tubular member  30  in accordance with some embodiments of the invention. It is noted that the cross-sectional shape of the seal ring  60 ,  70  is depicted as an example, as the seal ring may be elliptical, V-shaped hemi-circular or other shapes, depending on the particular embodiment of the invention. Regardless of the particular profile, the seal ring  60 ,  70  opens up in both radially inward and radially outward directions. Therefore, longitudinal pressure may be applied by the gauges  14  and  16  to deform the seal elements  60 ,  70  to achieve relatively high contact stress and better sealing performance. 
   Although the energizing ring  75  is depicted in  FIG. 3  as being V-shaped, it is noted that the energizing ring  75  may have other cross-sectional profiles, depending on the particular embodiment of the invention. For example, depending on the particular embodiment of the invention, the energizing ring  75  may have a rectangular, trapezoidal or other radial cross-sectional shape. The combination of the seal ring(s) and the energizing ring(s) allows the seal ring to deform and seal on both the inner and outer surfaces of the tubular members  20  and  30 , respectively.  FIG. 4  depicts the seal assembly  59  of  FIG. 3  when the seal rings  60  and  70  are longitudinally compressed to form sealing contacts  62  and  64  with the inner surface of the outer tubular member  20  and the outer surface of the tubular member  30 , respectively. 
     FIG. 5  depicts a metal seal assembly  89 , which may be used in accordance with other embodiments of the invention. As compared to the seal assembly  59  of  FIGS. 3  and  4 , the seal assembly  89  includes a single curved seal ring  60 , which has the same orientation as the seal ring  60  of the assembly  59 . The seal assembly  89  includes an energizing ring  90 , which is located below the seal ring  60  and has a trapezoidal radial cross-section so that the seal ring  60  is compressed between the relatively flat surface  18  of the upper gauge  14  and a relatively inclined surface  91  of the energizing ring  90 . The seal ring  60  deforms as depicted in  FIG. 6  when set to form an outer sealing contact  93  and an inner sealing contact  95 . 
   Referring to  FIG. 7 , in accordance with other embodiments of the invention, the upper  60  and lower seal rings  70  may be used in another metal seal assembly  99 , which has a design similar to the metal seal assembly  59  of  FIG. 3 . However, in the seal assembly  99 , the energizing ring  75  is replaced with an energizing ring  100 , which has a square radial cross section. The seal rings  60  and  70  deform as depicted in  FIG. 8  to form inner  101  and outer  106  sealing contacts. 
   Referring to  FIG. 9 , in yet another variation, a metal seal assembly  109  includes a curved seal ring  110  that is longitudinally compressed between the upper gauge  14  and a curved, or ramped, surface  120  of the inner tubular member  30 . Alternatively, the surface  120  may be part of a lower gauge separate from the inner tubular member  30 , in accordance with embodiments of the invention. Movement of the upper gauge  14  with respect to the surface  120  compresses the curved seal ring  110 , as shown in  FIG. 10  to produce inner  113  and outer  115  sealing contacts. 
   As examples of other potential seal element designs,  FIGS. 11 and 12  depict a circularly curved ring  150  and a V-shaped seal ring  160 , respectively, in accordance with other embodiments of the invention. The seal ring  150  has a circular radius such that the ring  150  is concave with respect to the energizing element (not shown). The seal ring  160  of  FIG. 12  has its vertex contacting the energizing element (not shown in  FIG. 12 ) or upper gauge before deformation of the element  160 . 
   As examples of other possible energizing ring designs in accordance with embodiments of the invention,  FIG. 13  depicts an energizing ring  170 , which includes an upper V-shaped surface and a lower V-shaped surface  174 .  FIG. 14  depicts an energizing ring  180 , of a different radial trapezoidal cross-section having upper  182  and lower  184  inclined surfaces.  FIG. 15  depicts an energizing ring  190 , which includes a curved upper surface  190  and a curved lower surface  194 . As can be seen, many variations are contemplated, and all of which are within the scope of the appended claims. 
   The seal ring may be formed of soft metals, like copper, nickel or any other material with low yield stress. A benefit of using soft metal is that the seal deforms relatively easily with low setting forces. Another benefit in using soft metal is that the seal conforms to a rough sealing surface. In other embodiments of the invention, the seal element may be formed from high yield metals. In these embodiments of the invention, the seal deformation may be reversible if the element is deformed in its elastic region. 
   The energizing ring may also be formed from a high yield and high strength metal because it is used to energize the seal element and support after seal deformation. Shaped memory alloys may also be used with and without energizing rings. The additional advantage of using shaped memory alloys is the alloys may be allowed to change shapes depending on the external stimuli, such as temperature, electromagnetic field, etc. 
   Referring to  FIG. 16 , in accordance with some embodiments of the invention, a seal ring  200  may be formed from both soft and high yield metals. In this regard, one part  201  of the seal element  200  may be formed from a high yield metal, which is elastic and includes rounded portions  210  and  208  to form sealing contacts. The seal element  200  also includes a soft metal to form a soft metal contact  220 , which is embedded in the part  201  to form a sealing contact on the inner surface of the outer tubular member  20 . 
   As another example,  FIG. 17  depicts a seal assembly  228 , which has top  230 , middle  232  and bottom  234  seal rings, which may be formed from different metals to serve different functions. For example, one or more of the rings  230 ,  232  and  234  may be formed from a metal that is suitable for anchoring the seal assembly  228  (for packer and bridge plug applications); and/or one of more of the rings  230 ,  232  and  234  may be formed from a metal that is suitable for forming a seal between the inner  30  and outer  20  tubular members when the seal assembly  228  is compressed ( FIG. 18 ). Thus, in accordance with some embodiments of the invention, one or more of the rings  230 ,  232  and  234  may anchor a particular downhole component to a wellbore wall or well casing, depending on whether the well is cased. As depicted in  FIG. 17 , all three rings  230 ,  232  and  234  may have V-shaped cross-sections, with the top  230  and bottom  234  rings opening toward the outer tubular member  20  and the middle ring  232  opening toward the inner tubular member  30  (as a non-limiting example). 
   The seal assembly  228  may contain different metals for redundancy purposes. Because the seal assembly  228  may function as an anchoring device for packer and bridge plug applications, conventional slips may be eliminated. The seal element may be welded onto the seal surfaces due to high contact stress. 
   In accordance with some embodiments of the invention, part of the seal assembly may have an array of annular grooves to enhance the interaction between the seal and contact surface and to improve the anchoring effect as well. Other advantages such as low setting force and good swab-off resistance may also be achieved using these metal seals. 
   Holes may be drilled through on one side of seal, for purposes of not interfering with the sealing function. The drilled holes may help bleed off trapped pressure inside cavity between seal and inner tubular sealing surfaces. The holes may also help pressure energize the seal under differential pressure holds. Likewise, having one side of the seal open ended will accomplish the same result, allowing well bore pressure, and/or applied differential pressure to further enhance sealing capabilities. This would be similar in application to that of a packer cup. 
   The seal designs that are set forth herein may also be used with polymer material, e.g., part of metal seal element can be coated with rubber or plastic material. The advantage of this type of seal will be high contact stress that cannot be achieved with polymer seals only. In this application, seal is activated by applying axial compressive load or other methods, such as heat for seals made of shape memory alloys. 
   For some seal applications involving tool or small seal movement, a special device with spring type mechanism may be incorporated since metal-to-metal seals may have reduced flexibility for the movement. 
   Other variations are contemplated and are within the scope of the appended claims. For example,  FIG. 19  depicts a metal seal assembly  300  in which a seal ring  330  is compressed between two gauges  314  and  320 . The upper end of the seal ring  330  is received in a shoulder  331  that is formed in the lower end of the gauge  314  to cause the seal ring  330  to deform when compressed, as depicted in  FIG. 20 . The seal ring  330  may be attached or unattached to the gauge  314 , depending on the particular embodiment of the invention. As shown in  FIG. 20 , when compressed, a middle point  323  of the compressed seal ring  330  forms a seal with the inner surface of the outer tubular member  20 ; and an end  324  of the seal ring  330  forms a seal point with the outer surface of the inner tubular member  30 . 
   Referring to  FIG. 21 , as an example of another variation, a seal ring  340  of a seal assembly  339  may be longitudinally compressed between gauges  341  and  343 . The seal ring  340  is bent, or curved at its ends  342  and  344 , which form corresponding seal contacts  352  and  354 , respectively, as depicted in  FIG. 22 , when the seal element  340  is longitudinally compressed. Additionally, a midpoint of the seal ring  340  forms a seal contact  350  (see  FIG. 22 ) with the inner surface of the outer tubular member  20  when the ring  340  is compressed. 
   Referring to  FIG. 23 , in accordance with other embodiments of the invention, a seal ring  360  of a metal seal assembly  359  may be generally radially bowed outwardly so that a center, or midsection  361 , of the seal ring  360  has the maximum radius. Referring also to  FIG. 24 , when longitudinally compressed, seal contacts  362  and  364  are formed at ends  367  and  369  of the seal ring  360 , with the midpoint  361  of the seal ring  360  forming a seal contact  370  with the inner surface of the outer tubular member  20 . 
   Referring to  FIG. 25  in yet another variation, a seal ring  380  of a metal seal assembly  379  may be an annularly disposed tubular ring, in accordance with some embodiments of the invention. In this regard, the seal ring  380  may be heated and radially compressed until an oval cross-section is achieved; and then, the seal ring  380  may be annealed in order to obtain the required hardness. When the seal ring  380  is compressed, as depicted in  FIG. 26 , the setting force returns the ring  380  back to its circular cross-section (or at least a slight oval cross-section) to form sealing contact  392  and  394  with the outer  20  and inner  30  tubular members, respectively. 
   As an example of another variation,  FIG. 27  depicts a metal seal assembly  400  in accordance with other embodiments of the invention. The seal assembly  400  includes a V-shaped radial cross-section metal seal ring  410  that includes a V-shaped opening  414  to receive a outer cone  404 . The outer cone  404  is attached to an inner cone  402  by a shear screw  408 . 
   Referring to  FIG. 28  (which depicts an intermediate state during the setting of the seal assembly  400 ), when the seal element  410  is initially compressed, the outer cone  404  contacts the seal element  410  first, forcing the element  410  to contact the inner surface of the outer tubular member  20 . Referring to  FIG. 29 , when the setting force exceeds the shear value of the screw  408 , the inner cone  402  is rammed into the seal element  410 , thereby forming sealing contacts  412  and  411  with the outer  20  and inner  30  tubular members, respectively. 
   Another approach involves a two set step that would independently drive the element  410  to the outer tubular member  20  in one step, and drive the element  410  into the inner tubular member  30  in the another step (the order is not important). This could lead to a solution that would decrease the setting force by eliminating the combined drag force of current ring designs, by eliminating the simultaneous drag of the ring on both tubular member  20  and  30  during the setting process. 
   The metal seal assemblies, which are disclosed herein may be used for numerous applications in the downhole environment, such as bridge plugs, straddles, retrofit locks, sliding sleeves, communications orifice &amp; sleeves, liner hangers, permanent &amp; retrievable packers, spool tree plugs, polished bore receptacle (PBR), seal assemblies, lateral windows &amp; junctions, surface pressure control equipment, wireline stuffing boxes &amp; grease injection heads, sub-sea riser, as just a few examples. 
   While the present invention has been described with respect to a limited number of embodiments, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.

Summary:
A seal assembly that is usable with a well includes a metal body that is adapted to expand radially inwardly and radially outwardly in response to the body being longitudinally compressed between compressing surfaces. The metal body includes first and second surfaces that do not conform to the compressing surfaces before longitudinal compression of the body and are adapted to contact the compressing surfaces.