Abstract:
Internal and external metal-to-metal radially interfering seals are provided for an annular chamber. Typically, an annular chamber is used in tubular goods to be part of the hydraulic control circuitry, such as for operating subsurface equipment such as a subsurface safety valve. Resilient seals are eliminated and sealing reliability is enhanced by a design which features metal-to-metal seals internally and externally, preferably assembled by an external two-step thread. The radial interference seal, which is internally disposed, is constructed so as to be incapable of experiencing tensile loads. This reinforces joint integrity by minimizing stresses on thin components.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of application Ser. No. 08/787,781, filed on Jan. 23, 1997, which was a file wrapper continuation of application Ser. No. 08/555,597, filed on Nov. 9, 1995, now abandoned, which was a continuation of application Ser. No. 08/036,345, filed on Mar. 24, 1993, now issued as U.S. Pat. No. 5,496,044. This application is also a continuation of application Ser. No. 08/594,503, filed on Jan. 31, 1996, now abandoned, which was a continuation of application Ser. No. 08/341,433, filed on Nov. 17, 1994, now abandoned, which was a divisional of application Ser. No. 08/036,345, filed on Mar. 24, 1993, now issued as U.S. Pat. No. 5,496,044. 
    
    
     FIELD OF THE INVENTION 
     The field of this invention relates to sealing technology, particularly those seals used in downhole tools for sealing annular chambers. 
     BACKGROUND OF THE INVENTION 
     In the past, tubing strings have employed various devices which have needed pressure chambers for actuation of various components. In some of these layouts, a separate connection outside the tubing string is provided for hydraulic control pressure. This pressure is used to selectively actuate a subsurface safety valve, depending on the configuration. Occasionally, the control components in the hydraulic circuit, for actuation of such downhole components as a subsurface safety valve, fail. For example, the hydraulic piston that is actuated by the control circuit, which is in fluid communication with an annular chamber, occasionally sticks or experiences seal failure.. When this occurs, it is not possible to use the hydraulic forces in the control circuit to actuate the subsurface safety valve, or some other downhole component as required. When these circumstances occur, it is desirable to lower a substituted component through the tubing and position it appropriately to accomplish the task of the part rendered inoperative due to control circuit failure. At the same time, it is desirable to use the hydraulic control pressure to actuate this newly inserted component in the tubing or wellbore. 
     When these situations occur, it has become desirable to lower a penetrating tool to the desired depth and bore laterally into the hydraulic control circuit chamber. In order to facilitate the fluid communication into the control circuit, an annular chamber is provided so that upon reaching the proper depth, radial puncture in any direction will assure fluid communication into the annular chamber. Stated differently, if the control circuit flowpath extending adjacent the tubular were strictly longitudinal, the puncture device would have to be properly oriented so that when it was actuated to perform a radial puncture, it would be in alignment with the longitudinal flowpath of the control circuit. 
     In the past, sealing annular control circuit chambers has been and continues to be of concern. 
     Accordingly, one of the objects of the present invention is to provide an annular chamber, such as those used in control circuits where the annular chamber extends in the tubular goods and is sealed internally and externally by metal-to-metal seals. It is a further object of this invention to eliminate resilient seals for sealing annular chambers used in control circuits or other application in tubular goods for downhole use. 
     SUMMARY OF THE INVENTION 
     Internal and external metal-to-metal radially interfering seals are provided for an annular chamber. Typically, an annular chamber is used in tubular goods to be part of the hydraulic control circuitry, such as for operating subsurface equipment such as a subsurface safety valve. Resilient seals are eliminated and sealing reliability is enhanced by a design which features metal-to-metal seals internally and externally, preferably assembled by an external two-step thread. The radial interference seal, which is internally disposed, is constructed so as to be incapable of experiencing tensile loads. This reinforces joint integrity by minimizing stresses on thin components. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional elevational view showing the annular chamber with a sealing assembly using resilient seals. 
     FIG. 2 is a sectional elevational view of the apparatus of the present invention showing the annular pressurized chamber with internal and external metal seals. 
     FIG. 3 shows the operation with an insert valve installed after penetration into the chamber. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates the annular chamber with a sealing assembly. There, an annular chamber  10  is internally sealed by resilient seals  12  and  14 . A connection  16  is provided to allow introduction of control hydraulic pressure. The hydraulic pressure enters chamber  10  and flows through passage  18  until it reaches piston  20 . The movement of piston  20  can be used to actuate a downhole component, such as a subsurface safety valve. Threads  22  and  24  in conjunction with sealing surfaces  28  and  30  have been used for external seals for chamber  10 . This two-step thread employed a torque shoulder  26  and opposed sealing surfaces  28  and  30 . 
     The apparatus of the present invention, as shown in FIG. 2, still has the connection  16  leading into the chamber  10 . Chamber  10  is in flow communication with passage  18  for actuation of subsurface component, such as a subsurface safety valve, by pressure applied to connection  16 . The internal seals for chamber  10  comprise opposed surfaces  32  and  34 . In a preferred embodiment, there is radial interference between the pin  36  and the box  38 . The upper end  40  of pin  36 , due to the absence of threads, is incapable of being subjected to tensile loads. This is significant because upper end  40  is a thin-walled component of pin  36  and could be subject to fracture under tensile loads following radial puncture. In order to provide the interference force that keeps mating surfaces  32  and  34  together, a two-step thread  42  and  44  is employed. The two-step thread  42  and  44  has a form known to those skilled in the art and further comprises a pair of sealing surfaces  46  and  48 . A torque shoulder  50  assists in the makeup of the two-step thread  42  and  44 . The thread form of threads  42  and  44  can be overhung so that, in conjunction with the torque shoulder  50 , the sealing surfaces  46  and  48  are drawn to their opposed surface. There is a preferably slight interference fit radially for the paired surfaces  46  and  48 . In the preferred embodiment, the sealing surfaces  32 ,  34 ,  46 , and  48  are slightly tapered in the range of 0-20° from the longitudinal axis of the pin  36  and box  38 . 
     Another feature of the apparatus of the present invention is the configuration of chamber  10 . Chamber  10  has a thin-walled section  52 . This facilitates the radial puncture procedure by providing a thin wall  52  for the puncture apparatus. As a result, the puncture procedure can be concluded more quickly since there is less metal to penetrate. At the same time, the inner wall of the pin  36  has sufficient structural rigidity to withstand the desired interference fit radially at mating surfaces  32  and  34 , as well as the expected internal pressures in chamber  10 . 
     Referring now to FIG. 3, an insert valve  60  is lowered into bore  54 . Valve  60  latches on to bore  54  in the customary manner such as using locking collets in a manner well-known in the art. With chamber  10  punctured to create port  56 , the insert valve  60  may be operated by applying pressure at inlet  16 , which flows through a channel  62  to a piston  64 . Seals  66  seal off the lower end of passage  62 . Additionally, seals  68  seal off passage  62  at the upper end. Accordingly, pressure applied to inlet  16  is communicated against piston  64  to actuate its movements so that the valve  60  can continue to operate using the control circuit pressure communicated through chamber  10 . The insert valve  60  takes the place of subsurface safety valve  70 , which is pushed out of the way upon insertion of the insert valve  60 . 
     Normally, the subsurface components are actuated by a control circuit pressure applied at connection  16 . Typically, the applied pressure at port  16  actuates a piston which in turn ties into the final controlled component (not shown). However, if for any reason, the piston (such as  20  shown in FIG. 1) fails to operate and another replacement component is inserted through the bore  54 , it is desirable to redirect the pressure in the control circuit from chamber  10  directly into the newly installed component. Those skilled in the art will appreciate that the replacement component inserted through the bore  54  has its own actuating mechanisms responsive to hydraulic pressure. At that point in time with thin wall  52  having been penetrated by a penetrating tool, the control circuit pressure in chamber  10  is redirected into the replacement component. The replacement component (not shown) straddles the opening  56  which is placed there as a result of the operation of the penetrating tool. Thereafter, the replacement downhole component can be actuated using pressure applied at port  16 . Now, instead of directing the pressure downwardly through passage  18 , the pressure is redirected through opening  56  into the replacement subsurface component so that it can be actuated and operations resumed. 
     It can be seen that internal pressure applied in bore  54  also urges the sealing surfaces  32  and  34  into greater contact, thus promoting the internal seal of chamber  10 . 
     The elimination of the flexible seals, is a significant improvement in reliability of these critical joints that are part of the hydraulic circuit for key downhole components. Unreliability in the sealing of the joints in the control circuit, such as at chamber  10 , can adversely effect the longevity of the control system. By virtue of the addition of the internal and external metal seals, reliability has been approved. Assembly has also been facilitated since in the past the resilient seals, such as cup-shaped seals, were extremely difficult to install without doing damage to the seals during assembly. With the metal-to-metal seals internally and externally, assembly has been greatly facilitated as it is now guided by the two-step thread  42  and  44 . 
     In another feature of the present invention, a method has been developed to create a pin  36  and box  38  arrangement so that an annular cavity is created, with the annular space sealed internally and externally with metal-to-metal seals. The method of the present invention overcomes the prior problem in attempting to build such an apparatus because there previously did not exist the means of economically controlling the needed metal-to-metal interferences so that the seals could be reliably created internally and externally to the annular chamber. The proper amount of interference is important to ensure sealing integrity. However, too much interference can tend to create galling and prevent the easy assembly of the joint. Due to the close manufacturing tolerances required, construction of annular chambers with metal-to-metal internal and external seals have not been commercially available in the past. The threaded connection  42  and  44  has a center locating shoulder  50  which carries the torque of the made-up connection. The shoulder  50  also positions the contacting surface  32  and  34  on the pin nose  40  and the mating opposed surfaces in the box, as well as on the other end involving the contacting surfaces  46  and  48  on the box nose and its mating surface on the pin. In the preferred embodiment, the pin and box are made so as to have radial interference of about 0.0025 inch per inch of diameter. It has generally been found that lesser degrees of interference do not provide for an adequate seal, while substantially greater interference presents a hazard of galling. The pin  36  and box  38  are designed such that the pin nose is thin-walled but abuts the relatively thick main section of the box  38 . Therefore, internal pressures in bore  54  actually promote internal sealing, while the substantial thickness of box  38  adjacent pin nose  40  provides the structural rigidity for the internal sealing. The same concept applies on the external joint at sealing surfaces  46  and  48 . While the box nose is relatively a thin-walled member, it is mounted opposite the thick-walled portion of the pin. Accordingly, external pressures in the annulus applied to the pin  36  and box  38  promote sealing externally at sealing surfaces  46  and  48 . 
     The method of the present invention applies a technique wherein the pin and box are manufactured using the same baseline dimensions. The manufacturing baseline dimension is taken from the torque shoulder  50  on both the pin and box. Based on this starting dimension, the extension portion is developed which includes sealing surfaces  32  and  34 . Since the base dimension is taken from shoulder  50 , the exact location of mating surfaces  32  and  34  can be positioned with the desired amount of interference in a manufacturing process that allows for specific control of the tolerances. This ensures that the proper amount of the desired radial interference is built into the pin  36  and the box  38  such that when they are put together, there will be sufficient force to ensure the seal yet an interference amount short of a situation where galling can occur. The pin nose  40  is not manufactured with a torque shoulder due to the difficulty in manufacturing tolerances of having two torque shoulders seat simultaneously. The torque shoulder  50 , along with precise control of the dimensions of the pin nose  40  and the mating portions of box  38 , removes the need for an internal torque shoulder or threads. However, the base reference technique using torque shoulder  50  or another starting reference point can be employed to optionally produce a pin/box joint involving an annular space in between, with an internal as well as external torque shoulder. Through the use of a common reference point, the particular interference range at the pin nose is accomplished by dimensional control of the surfaces adjacent the pin nose. Since a common reference point is used for the mating surfaces adjacent the pin nose, the tolerance spread of mating surfaces  32  and  34  can be controlled to within the same tolerance as the mating surfaces  46  and  48 . 
     The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made without departing from the spirit of the invention.