Abstract:
A casing hanger seal assembly utilizes a deformable metal body and elastomeric seal rings which are O-rings. The seal rings are located in grooves in unbonded condition in the metal body. The inner wall of the metal body is tapered, matching the taper on the exterior of the casing hanger. The inner wall is sized so that it will be deformed outward as the body of the seal assembly is moved further downward. This causes the seal rings on the outer diameter of the body to engage the wellhead housing inner cylindrical wall. In a second version, the seal ring on the outer wall of the body is initially fully recessed. A deformable rib is located inward from the base of the groove. The rib presses the base of the groove outward.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to seals for wellhead equipment, and in particular to a seal that has a metal carrier that carries elastomers for sealing between a casing hanger and a wellhead housing and which expands radially. 
     2. Description of the Prior Art 
     A common well completion system employs a casing hanger which lands in a wellhead housing. The casing hanger has an exterior wall spaced inward from a cylindrical wall of the wellhead housing. The casing hanger is located at the upper end of the string of casing. After the casing has been cemented, a casing hanger seal locates in the annulus between the casing hanger and the wellhead housing. 
     There are many varieties of casing hanger seals. Some employ elastomeric seals. Others employ metal-to-metal seals. Others utilize a combination of both. While many of these seals are workable, a need exists for a low cost seal that requires a relatively low amount of torque to energize. 
     SUMMARY OF THE INVENTION 
     The casing hanger employed with this invention has a tapered wall tapered at an angle of about four degrees. The seal that locates between the tapered wall and the cylindrical wall of the wellhead housing has a metal body. The inner wall of the metal body is tapered at the same angle as the tapered wall of the casing hanger. The outer wall is cylindrical. 
     At least one groove is located on the inner wall of the body and at least one groove is located on the outer wall of the body. Inner and outer O-rings locate in these grooves, each positioned in unbonded condition to the metal body. 
     The inner diameter of the metal body is dimensioned so that it will preferably contact the tapered wall before the outer wall of the metal body touches the wellhead housing. Continued downward force causes the metal body to radially expand, permanently deforming the metal body. This expansion causes the other O-ring to be pressed against the cylindrical wall of the wellhead housing. 
     In one embodiment, the inner and outer O-rings protrude slightly from their respective grooves initially. In another embodiment, the outer O-ring is initially fully recessed within its groove. A protuberance or rib is located on the inner wall, radially inward from the outer groove. The protuberance has a smaller inner diameter than any other portion of the inner wall of the metal body. The protuberance contacts the tapered wall initially prior to any contact by any other portions of the body. Continued downward force causes the rib to move the base of the outer groove radially outward. This pushes the O-ring from its fully recessed position to a protruding position for sealing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a quarter sectional view illustrating a casing hanger seal shown installed between a casing hanger and a wellhead housing, the casing hanger seal being constructed in accordance with this invention. 
     FIG. 2 is a sectional view of an alternate embodiment of a casing hanger seal, shown prior to being set. 
     FIG. 3 is a sectional view of the seal of FIG. 2, shown installed between a casing hanger and a wellhead housing. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, wellhead housing 11 is conventional. Wellhead housing 11 has an axial bore with an inner cylindrical wall 13. An annular recess 15 is formed in cylindrical wall 13. 
     A casing hanger 17 is shown landed in wellhead housing 11. Casing hanger 17 will be secured to the upper end of a string of casing (not shown). Casing hanger 17 has an axial bore 19 that is coaxial with the bore of wellhead housing 11. Casing hanger 17 has an exterior tapered wall 21 that is spaced radially inward from cylindrical wall 13. Tapered wall 21 is tapered at an angle of about four degrees relative to the axis of bore 19. 
     Tapered wall 21 has a lower end that terminates at an upward facing shoulder 23. The outer diameter of tapered wall 21 at shoulder 23 is larger than the outer diameter of the upper end of tapered wall 21. Casing hanger 17 carries a split retaining ring 25. Retaining ring 25 will move from a retracted position to an expanded position shown. In the expanded position, retaining ring 25 engages recess 15. Casing hanger 17 has conventional flowby slots 27 to allow cement flow returns. Casing hanger 17 has exterior threads 29 located above tapered wall 21. 
     A seal assembly 31 seals to tapered wall 21 and cylindrical wall 13. Seal assembly 31 has a metal body 33, which is preferably of steel. Body 33 has an inner wall 35 that is tapered at the same angle of taper as tapered wall 21. Inner wall 35 thus has a larger inner diameter at its lower end than at its upper end. The inner diameter at the lower end of inner wall 35 initially in an undeformed state, is not as large as the outer diameter of tapered wall 21 at shoulder 23. Consequently, when body 33 is lowered over lower casing hanger 17, the inner wall 35 will contact tapered wall 21 and stop further downward movement while the lower end of body 33 is still spaced a half inch or so above shoulder 23. Continued downward force will push body 33 to the position in which its lower end is close to or contacting shoulder 23, however body 33 has to permanently deform and radially expand in order to do so. 
     Body 33 has an outer wall 37 that is cylindrical. Outer wall 37 has an outer diameter that is initially slightly less than the inner diameter of cylindrical wall 13. Consequently, when body 33 reaches the initial contact position with tapered wall 21 during installation, outer wall 37 will be spaced inward slightly from cylindrical wall 13. Continued downward force will permanently deform the entire metal body 33, expanding outer wall 37 so that normally it will contact cylindrical wall 13 prior to the lower end of body 33 touching shoulder 23. Preferably the amount of expansion is about 0.015 inch radially. Or, if considered as diameter, the outer diameter of outer wall 37 will expand about 0.030 inch. The expansion of outer wall 37 is uniform from the upper end to the lower end of body 33. The tolerance is selected so that preferably the outer wall 37 has reached its full expansion and is touching cylindrical wall 13 before the lower end of body 33 contacts shoulder 23. 
     In the embodiment of FIG. 1, inner wall 35 has three inner grooves 39, each axially spaced apart from the other. Each inner groove 39 extends circumferentially around inner wall 13. Also, preferably there are three outer grooves 41, each axially spaced apart from the other and extending circumferentially around outer wall 37. Each inner groove 39 is spaced radially inward from one of the outer grooves 41. Each of the inner and outer grooves 39, 41 has a base that is concave and arcuate when viewed in transverse cross-section. 
     An inner O-ring 43 locates within each inner groove 39. Inner O-ring 43 is an elastomer, initially circular in transverse cross-section in a plane that is parallel to the axis of body 33. Each inner O-ring 43 is conventional, and protrudes slightly from its groove 39 prior to reaching the sealing position shown in FIG. 1. Similarly, each outer groove 41 contains an outer O-ring 45. Each outer O-ring 45 has the same cross-sectional diameter in transverse cross-section. Preferably the radial depths of each inner groove 39 and each outer groove 41 are selected so that approximately ten percent of each inner O-ring 43 and outer O-ring 45 will protrude beyond its respective groove prior to setting. That is, in the undeformed condition, the transverse cross-sectional diameter of each O-ring 43, 45 is ten percent greater than the radial depth of each groove 39, 41. 
     In the embodiment of FIG. 1, an inner test port groove 47 locates between the lower inner O-rings 43. Similarly, an outer test port groove 49 locates between the lower two outer O-rings 45. Each test port groove 47, 49 extends circumferentially around the metal body 33. At least one test port passage 51 extends radially between inner and outer test port grooves 47, 49. A test port 53 extends radially through the sidewall of wellhead housing 11. A check valve 55 locates in test port 53. This allows hydraulic test pressure to be applied between two of the outer O-rings 45 and two of the inner O-rings 43 for test purposes. The lowest O-ring 39, 41 serves to isolate the application of test pressure so as to allow test pressure to be applied to the lower side of the intermediate O-rings 39, 41. The upper two O-rings 39, 41 serve as primary seals. Test pressure can also be applied to the upper O-rings 39, 41 from above by applying hydraulic pressure to the wellhead housing bore 13. 
     The means for moving seal assembly 31 downward includes a drive nut 57. Drive nut 57 is a solid metal ring that has inner threads that secure to the external threads 29. Drive nut 57 has lugs 59 on its upper end for engagement by a running tool. Drive nut 57 is rotatable relative to seal assembly 31. A split ring 61 maintains engagement of drive nut 57 with body 33. Split ring 61 locates in mating recesses formed in body 33 and in drive nut 57. 
     In the operation of the embodiment of FIG. 1, after casing hanger 17 has been installed, and cementing completed, the operator will place seal assembly 31 in the space between the casing hanger 17 and wellhead housing 11. The operator rotates drive nut 57. The first contact that will occur will be the contact of tapered inner wall 35 with tapered wall 21 of casing hanger 17. Because the undeformed inner diameter at the lower end of inner wall 35 is less than the outer diameter of tapered wall 21 at its lower end, this contact will occur when body 33 is a half inch or so above shoulder 23. At the initial point of contact, prior to any deformation of body 33, the outer wall 37 of body 33 will be spaced inward from wellhead housing 11. The outer O-rings 45 may also be spaced inward, or due to tolerances, they may slightly touch at this point. Outer O-rings 45 will not be in sealing engagement, however, at this point. 
     Continued rotation of drive nut 57 forces body 33 further downward. As body 33 moves further downward, the tapered wall 21 begins expanding body 33. Body 33 undergoes permanent deformation, and will expand in its inner and outer diameters until outer O-rings 45 are in sealing engagement with cylindrical will 13. Sealing engagement of outer O-rings 45 occurs before body 33 touches shoulder 23. Preferably outer wall 37 contacts wellhead housing cylindrical wall 13 before the lower end of body 33 contacts shoulder 23. Shoulder 23 avoids overtorque by limiting the downward travel of body 33. Due to tolerances, body 33 may contact shoulder 23 after O-rings 45 seal but before outer a 37 contacts cylindrical wall 13, and in this instance outer wall 37 will remain spaced slightly from cylindrical wall 13. Once the proper travel has been reached, outer O-rings 45 will be in sealing engagement with inner cylindrical wall 13, being squeezed in the amount of about ten percent. Body 33 will contact and move retaining ring 25 outward into engagement with recess 15 during this downward movement. 
     If testing is desired, the operator will apply hydraulic fluid pressure through valve 55. The liquid will flow through test port 53 and through test passage 51. The liquid flows around test grooves 47 and 49. The pressure is applied between the lowermost O-rings 43, 45, and the intermediate O-rings 43, 45. The pressure is monitored to determine if any leakage exists. 
     FIGS. 2 and 3 illustrate an alternate embodiment. In this embodiment, seal assembly 63 also has a metal deformable body 65. Body 65 has an inner wall 67 that is tapered at the same angle of taper as tapered wall 21&#39;. Body 65 has an outer wall 69 that is cylindrical. In its undeformed condition, outer wall 69 is slightly less in outer diameter than the inner diameter of inner cylindrical wall 13&#39; of wellhead housing 11&#39;. 
     An outer groove 71 is formed in outer wall 69. Outer groove 71 has a base 71a that is concave and generally V-shaped in transverse cross-section in an undeformed condition. An outer seal ring 73 locates in outer groove 71. Outer seal ring 73 is preferably an O-ring, circular in transverse cross-section. In the initial undeformed state prior to installation, seal ring 73 will be fully recessed within outer groove 71. No portion of seal ring 73 will protrude from outer groove 71. The depth of outer groove 71 from base 71a to outer wall 69 is slightly greater than the transverse cross-sectional diameter of seal ring 73. 
     A protuberance or rib 75 locates on inner wall 67. Rib 75 is formed radially inward from base 71a. Rib 75 is also generally V-shaped in transverse cross-section prior to deformation. Rib 75 protruded radially inward past inner wall 67 a distance equal to deflection distance 77. Deflection distance 77 is an amount that rib 75 will deform when seal assembly 63 is set. Base 71a and rib 75 thus combine to provide a web with a general V configuration and thinner in cross-section than any other portion of body 65. Test passage grooves 78 are located above and below rib 75 at the point where rib 75 joins inner wall 67. A radial passage 80 extends through body 65 for communicating test pressure through a check valve (not shown). 
     A pair of inner seal rings 79 locate above and below rib 75. Inner seal rings 79 are located in grooves and are preferably O-rings, circular in transverse cross-section. Rib 75 has an undeformed inner diameter that is less than an inner diameter of the inner O-rings 79. 
     An isolation or lower outer seal ring 81 locates below outer seal ring 73. Seal ring 81 is also preferably an O-ring. The transverse cross-sectional diameter of outer seal ring 73 is larger than the cross-sectional diameters of seal rings 79 and 81. Seal rings 73, 79, 81 are unbonded within their respective grooves. 
     In the operation of the embodiment of FIGS. 2 and 3, when seal assembly 63 is lowered into the space between casing hanger 17&#39; and wellhead housing 11&#39;, rib 75 contacts tapered wall 21&#39; prior to any other contact of inner wall 67 with tapered wall 21&#39;. Seal ring 73 up until that point would be completely recessed within groove 71 so as to avoid any damage due to contacting any structure in the well as the seal assembly 63 is lowered. Continued rotation of drive nut 57&#39; causes the body 65 to move further downward. Tapered wall 21&#39; deforms rib 75 radially outward. As rib 75 moves radially outward, it pushes base 71a further outward, causing seal 73 to protrude from its groove 71. Rib 75 will move outward a distance equal to deflection distance 77. At the same time, tapered wall 21&#39; also moves body 65 radially outward, so that outer wall 69 will preferably touch housing cylindrical wall 13&#39; both above seal 73 and below seal 73. The outer diameter of outer wall 69 thus increases uniformly during this deformation. When the seal ring assembly 63 is fully set, the lower end of seal assembly 63 is preferably slightly above or just barely touching shoulder 23&#39;. 
     The invention has significant advantages. By using O-rings in unbonded conditions, the expense is lower than bonded specially shaped seals. The unbonded O-rings allow significant deformation of the metal body. The seal thus is of a low cost. Because the deformation occurs on a taper, and is radially outward, the amount of torque required is fairly low. This allows the use of a drive nut, rather than requiring a hydraulic actuator. In the alternate embodiment, the recessed seal ring is protected from damage while being lowered into the well. 
     While the invention has been shown in only two 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.