Abstract:
The present invention provides a sealing assembly for protecting a downhole connection. The sealing assembly comprises independently energized metal-metal seals and a housing that prevents the energization of individual seals from affecting other seals.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This is a divisional of U.S. Ser. No. 10/024,410, filed Dec. 18, 2001. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    The subject matter of the present invention relates to providing redundant metal-metal seals to protect downhole communication lines from the surrounding environment.  
           [0003]    Communication lines are used in a wide range of applications in the oilfield industry. The communication lines transmit monitored data regarding downhole conditions such as temperature and pressure to surface instrumentation. The communication lines can also be used to send information down the well from the surface. Additionally, communication lines may also be used to electrically power downhole equipment. Communication lines may include electrical conduits, optical fibers, hydraulic lines and other methods for data or power transmission.  
           [0004]    In environments such as those encountered in downhole wells, the communication lines are exposed to hostile conditions such as elevated temperatures and pressures. To protect the fragile communication lines from the hostile conditions, the communication lines are generally carried within protective tubing that provides an environmental seal. Problems arise when the seal must be broken during assembly, installation and/or repair of the communication line. For example, in downhole applications, in order for the communication line to be fed through production equipment such as packers, the line must be cut and then spliced with the downstream line. Thus, after splicing, the communication line must once again be sealed from the harsh environment.  
           [0005]    There exists, therefore, a need for an apparatus and method of sealing communication lines from the surrounding environment. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0006]    [0006]FIG. 1 provides a sketch of a downhole electric splice assembly that incorporates the redundant metal-metal seal assembly.  
         [0007]    [0007]FIG. 2 provides an illustration of the configuration of the seal assembly  1  used to pressure test the primary seal. 
     
    
     DETAILED DESCRIPTION  
       [0008]    In the following detailed description of the subject matter of the present invention, the apparatus and method of providing redundant metal-metal seals for communication lines is principally described with reference to downhole well applications. Such description is intended for illustration purposes only and is not intended to limit the scope of the present invention. In addition to downhole well applications, the present invention can be used with any number of applications such as pipeline monitoring, subsea well monitoring, and data transmission, for example. Furthermore, the communication lines may comprise electrical wiring, fiber optic wiring, hydraulic lines, or any other type of line which may facilitate transfer of information, power, or both. All such types of communication lines are intended to fall within the purview of the present invention. However, for purposes of illustration, the present invention will be principally described as being used in downhole well applications.  
         [0009]    [0009]FIG. 1 provides a sketch of a downhole electric splice assembly that incorporates the redundant metal-metal seal assembly, indicated generally as numeral  1 , of the present invention. In FIG. 1, the cables  5  are spliced together within a housing  10 . Each of the cables  5  are carrying two communication lines  22 ,  23  from which spliced connections  20   a ,  20   b  are formed. The spliced connections  20   a ,  20   b  are located within an internal cavity  15  within the housing  10  and are each housed within protective casings  25   a ,  25   b.    
         [0010]    It should be noted that the spliced connections  25   a ,  25   b  shown in FIG. 1 are intended to illustrate one possible application of the present invention, and are not intended to limit the inventions scope. The present invention can be used with all types of communication line connections and is not limited to spliced connections.  
         [0011]    The primary metal-metal seal is formed by a pair of ferrules  30 ,  32 . The primary seal is energized and held in place by action of the primary retainer  35 . In the embodiment shown, the primary retainer  35  comprises securing dogs  36  and a threaded outer diameter  37 . The securing dogs  36  correspond to mating dogs on an installation tool (not shown). In one embodiment, the installation tool has a circumferential gap that enables it to be installed and removed over the cable  5 . The installation tool is used to apply torque to the primary retainer  35 , which in turn imparts a swaging load on the ferrules  30 ,  32  and imparts contact stress between the ferrules  30 ,  32  and the cable  5  and between the ferrules  30 ,  32  and the housing  10 . As such, a seal is formed by the ferrules  30 ,  32  between the housing  10  and the cable  5 . The swaging load and contact stress, and thus the seal, is maintained by the threaded outer diameter  37  of the primary retainer  35 .  
         [0012]    It should be noted that the above description of the primary retainer  35  is exemplary of one particular embodiment of the retainer  35 , and is not intended to limit the scope of the invention. There are any number of embodiments of the primary retainer  35  that can be used to advantage in the sealing assembly  1 . The primary retainer  35  is any means capable of energizing the ferrules  30 ,  32  and maintaining the primary seal.  
         [0013]    In some instances, to ensure a proper seal, it may be necessary to coat the ferrules  30 ,  32  with a soft metal such as gold. Typical cable  5  are characterized by non-circularity or non-uniformity of surface. Although the process of swaging the ferrules  30 ,  32  on the cable  5  deforms the surface considerably, often it is not enough to provide sufficient local contact stresses between the ferrules  30 ,  32  and the troughs existing in the surface of the cable  5 . Thus, the metal-metal seal cannot withstand a substantial pressure differential for a long duration of time. Coating the ferrules  30 ,  32  with a soft metal causes the troughs to be filled with the soft metal, substantially increasing the local contact stresses.  
         [0014]    The secondary metal-metal seal is formed by a seal element  40  having a conical section  41  that corresponds with a mating section  14  of the housing  10 . The secondary metal-metal seal provides redundancy to prevent leakage between the housing  10  and the seal assembly  1 . The conical section  41  is forced into sealing contact with the mating section  14  by action of a secondary retainer  45 . Similar to the primary retainer  35 , the secondary retainer  45  comprises securing dogs  46  and a threaded outer diameter  47 . As with the primary retainer  35 , an installation tool (not shown) is used to apply torque to the secondary retainer  45 , which in turn imparts contact stress between the conical section  41  and the mating section  14  to form a seal therebetween. The contact stress of the shouldered contact is maintained by the threaded outer diameter  47  of the secondary retainer  45 . It should be noted that the primary gap  85  that exists between the primary retainer  35  and the seal element  40  ensures that the process of energizing the secondary metal-metal seal does not affect the contact stresses on the primary seal between the housing  10  and the cable  5 . It should further be noted that in one embodiment, the seal element  40  comprises one or more ferrules forced into sealing contact with the mating section  14  of the housing  10 .  
         [0015]    As discussed above with reference to the primary retainer  35 , it should be noted that the description of the secondary retainer  45  is exemplary of one particular embodiment of the retainer  45 , and is not intended to limit the scope of the invention. There are any number of embodiments of the secondary retainer  45  that can be used to advantage in the sealing assembly  1 . The secondary retainer  45  is any means capable of energizing and maintaining the secondary seal.  
         [0016]    The tertiary metal-metal seal is formed by a pair of ferrules  50 ,  52  that engage the end  42  of the seal element  40 . The tertiary metal-metal seal, energized by the end plug  55 , provides redundancy to prevent leakage between the cable  5  and the seal assembly  1 . As with the ferrules  30 ,  32  of the primary seal, in certain instances, the ferrules  50 ,  52  of the secondary seal are coated with a soft metal to increase the local contact stresses with the cable  5 . A secondary gap  90  exists between the secondary retainer  45  and the end plug  55  that prevents the energizing load from affecting the mating components on the secondary seal. Load transmitted to the end of the secondary retainer  45  is dissipated through the end plug  55  to the housing  10 . The end plug  55  further comprises a pressure port  62  and one or more elastomeric seals  60   a ,  60   b  that enable pressure testing (as will be discussed below) of the seal assembly  1 .  
         [0017]    To isolate all the seals from axial loading, vibration and shock conveyed from the cables  5   a ,  5   b , an anchor  65  is energized against the cable  5  by action of the end nut  70 . In one embodiment, the anchor  65  is a collet style anchor.  
         [0018]    [0018]FIG. 2 provides an illustration of the configuration of the seal assembly  1  used to pressure test the primary seal. Testing of the primary seal requires insertion of spacers  75 ,  80  to prevent accidentally engaging the secondary and tertiary seals. In one embodiment, the spacers  75 ,  80  are constructed with a circumferential gap to enable installation and removal from the seal assembly  1 . The first spacer  75  prevents the conical section  41  of the seal element  40  from contacting the mating section  14  of the housing  10  to form the secondary metal-metal seal. Likewise, the second spacer  80  prevents the ferrules  50 ,  52  from engaging the end  42  of the seal element  40  to form a seal. To test, fluid is pumped through the pressure port  62 . The fluid is prevented from escaping the housing  10  opposite the primary seal by the one or more elastomeric seals  60   a ,  60   b . After testing, the spacers  75 ,  80  are removed and the seal cavity is cleared of the test fluid. Subsequently, the secondary and tertiary seals are energized as described above, and the anchor  65  is installed and energized.  
         [0019]    In one embodiment, pressure testing of the secondary and tertiary seals is done by pumping a fluid that cures into a gel under downhole conditions through the pressure port  62 . After testing, the pressure port  62  is plugged to maintain the gel within the seal assembly  1 . The gel protects the secondary and tertiary seals from corrosion due to exposure to completion or produced fluids. Further, the gel acts to protect the seals from the effects of shock and vibration.  
         [0020]    Referring back to FIG. 1, one method of verifying successful secondary and tertiary sealing is achieved by use of a chemical that produces an exothermic reaction when exposed to the test fluid. In this method, the chemical is deposited via porous bags into the interior of the housing  10 . Failure of either seal causes the test fluid to invade the interior of the housing  10  and the resultant differential temperature increase can be read by thermal strips (not shown) placed on the outer diameter of the housing  10 .  
         [0021]    Another method of verifying successful secondary and tertiary sealing is to load the interior of the housing  10  with a porous bag containing small hollow beads made of a material that emits noise upon failure. The increase of pressure in the interior of the housing  10  due to a failed seal causes the hollow beads to fail, emitting a sound that can be picked up by a sonic sensor.  
         [0022]    Yet another method of verifying successful secondary and tertiary sealing include using an ultrasonic sensor to detect the presence of test fluid in the interior of the housing  10 . Similarly, a sonic sensor can be used to detect the change in acoustic response due to test fluid in the interior of the housing  10 . A portable x-ray machine can also be used to detect the presence of test fluid in the interior of the housing  10 .  
         [0023]    The invention being thus described, it will be obvious that the same may be varied in many ways. For example, it is not necessary that one or both gaps  85 ,  90  exist within the seal assembly  1 . The gaps  85 ,  90  are useful to allow independent loading, prevent undue loading and to enable various pressure testing methods, but are not necessary for the function of the seal assembly  1 . Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such are intended to be included within the scope of the following non-limiting claims: