Patent Publication Number: US-9896904-B2

Title: Rupture disc secondary seal assembly and related methods

Description:
The present application is a U.S. National Stage patent application of International Patent Application No. PCT/US2012/068215, filed on Dec. 6, 2012, the benefit of which is claimed and the disclosure of which is incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates generally to rupture discs and, more specifically, to a rupture disc secondary seal system that increases tool reliability. 
     BACKGROUND 
     Rupture discs have been utilized in downhole tools for some time. For example, a rupture disc may function as a safety valve when the annulus pressure reaches a predetermined value. At that pressure, the rupture disc will burst, thus causing the valve to isolate the workstring below the tool, establish communication between the annulus and the workstring above the tool, or some other desired function. 
     There are, however, disadvantages to conventional rupture disc designs. If the seal between the rupture disc and temporary air chamber coupled to the rupture disc is damaged, pressure may leak around the rupture disc and cause the tool to work improperly. Also, since conventional rupture discs are threaded into the tool housing using 1-1.5 threads, the rupture disc may loosen and back out of the housing before hydrostatic pressure is supplied. As a result, a gap is created between the bottom of the rupture disc and the tool housing which may also cause pressure leakage around the rupture disc. 
     In view of the foregoing, there is a need in the art for a rupture disc having a secondary sealing device, thus providing a more reliable rupture disc system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric illustration of a downhole tool comprising a rupture disc secondary seal assembly according to certain exemplary embodiments of the present invention; 
         FIGS. 2A, 2B and 2D  are cross-sectional views of a downhole tool comprising rupture disc secondary seal assembly according to certain alternate exemplary embodiments of the present invention; and 
         FIG. 2C  illustrates a sealing tape according to certain exemplary embodiments of the present invention. 
     
    
    
     DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     Illustrative embodiments and related methodologies of the present invention are described below as they might be employed in a rupture disc secondary seal assembly. In the interest of clarity, not all features of an actual implementation or methodology are described in this specification. Also, the “exemplary” embodiments described herein refer to examples of the present invention. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. Further aspects and advantages of the various embodiments and related methodologies of the invention will become apparent from consideration of the following description and drawings. 
       FIG. 1  illustrates an exemplary embodiment of a rupture disc secondary seal assembly  10  positioned along a downhole tool  5  according to certain exemplary embodiments of the present invention. Downhole tool  5  may be any variety of downhole hole tools, such as, for example, a Rupture Disc (“RD”) Safety Circulating Valve, RD Circulating Valve, Pump Through RD Safety Circulating Valve, Pump Through RD Safety Valve, ARMADA Sampler, Ful-Flo Sampler, ProPhase Electronic Tester/Circulating Valve, Below Packer Hydraulic Safety Joint, Multi-Purpose Tubing String Testing Valve, RD Tubing String Testing Valve, RD Pressure Test/Bypass Valve, Multi Service Valve, Surge Valve. As described herein, rupture disc secondary seal assembly  10  comprises a rupture disc having a primary and secondary seal. The secondary seal may take a variety of forms as described below including, for example, sealing tapes, liquid sealants, elastomeric seals and/or combinations of the same. Accordingly, a secondary seal is provided. 
       FIG. 2A  illustrates an exemplary embodiment of rupture disc secondary seal assembly  10  according to certain exemplary embodiments of the present invention. Here, rupture disc secondary seal assembly  10  includes a rupture disc housing  12  which has been coupled inside a bore  14  of downhole tool body  16 . As understood in the art, the surface  18  of downhole tool body  16  is a rounded flat surface utilized to pressure test rupture disc secondary seal assembly  10 . Also, as understood in the art, rupture disc secondary seal assembly  10  includes pin holes  13  which allow a tool (golf spike wrench, for example) to insert rupture disc housing  12  into bore  14 . A rupture disc  20  is positioned along the bore  22  of rupture disc secondary seal assembly  10 , which communicates with a temporary air chamber  24 . 
     As will be understood by those ordinarily skilled in the art having the benefit of this disclosure, temporary air chamber  24  is positioned between rupture disc secondary seal assembly  10  and a mandrel  26  which, in turn, allows movement of mandrel  26  once rupture disc secondary seal assembly  10  has been ruptured. A shear screw  28  is also shown coupled between mandrel  26  and downhole tool body  16  above rupture disc secondary seal assembly  10 . A seal  30  is positioned between downhole tool body  16  and mandrel  26  below temporary air chamber  24 . The exact design of downhole tool  5  is illustrated here for exemplary purposes only, as those ordinarily skilled in the art having the benefit of this disclosure realize that rupture disc secondary seal assembly  10  may be utilized in any variety of tools. 
     Still referring to  FIG. 2A , rupture disc housing  12  has been coupled to downhole tool  5  at coupling area  32 . In other words, coupling area  32  is an area along downhole tool  5  where rupture disc housing  12  and downhole tool body  16  join. In this exemplary embodiment, the outer diameter of rupture disc housing  12  includes threads which mate which threads along the inner diameter of downhole tool body  16 . However, those ordinarily skilled in the art having the benefit of this disclosure realize that other coupling methods may be utilized, such as, for example, the rupture disc may be held by a Smalley® snap ring/retainer ring in combination with a spring. At the lower end of coupling area  32  is a seal  34 , also known as the primary seal, positioned around the outer diameter of rupture disc housing  12 . As understood in the art, seal  34  protects against pressure leakage between rupture disc housing  12  and downhole tool body  16 . 
     In order to provide a secondary seal for rupture disc secondary seal assembly  10 , certain exemplary embodiments of the present invention utilize sealing tape  36  as a secondary seal positioned over coupling area  32 . Sealing tape  36  may be, for example, Teflon® tape or Nylon® reinforced tape, as will be understood by those ordinarily skilled in the art having the benefit of this disclosure. Nevertheless, sealing tape  36  is positioned over coupling area  32  such that its straddles the surface of downhole tool  5  on one end  38  and the surface of rupture disc housing  12  on the other end  40 . Sealing tape  36  comprises a suitable adhesive on its inner surface to ensure it adheres sufficiently. In this embodiment, sealing tape  36  is a washer-shaped piece of tape, having an opening  42  to expose bore  22  of rupture disc housing  12 , as shown in  FIG. 2C . As pressure is applied to rupture disc secondary seal assembly  10 , a portion of sealing tape  36  is forced down into coupling area  32 , thus providing a secondary seal. 
     In certain alternative exemplary embodiments, sealing tape  36  may also be a solid disc shaped piece of tape that extends over bore  22 . In another embodiment, sealing tape  36  may also be transparent so that the rupture rating of rupture disc  20  could be visible. In addition, in embodiments utilizing a solid disc shaped sealing tape  36 , the transparent tape would allow visual confirmation of whether rupture disc  20  has been ruptured. 
       FIG. 2B  illustrates yet another exemplary embodiment of the present invention. This embodiment is identical to that of  FIG. 2A , except that a seal  44  is positioned between sealing tape  36  and coupling area  32 . Seal  44  may be, for example, an elastomeric component or o-ring. Once sealing tape  36  is place atop seal  44 , it will hold it in place and protect it from the downhole environment. In an alternative embodiment, a suitable adhesive may be applied to the inner surface of seal  44  to adhere it to coupling area  32 . As hydrostatic pressure is applied to rupture disc secondary seal assembly  10 , seal  44  is forced down into coupling area  32 , thus effectively sealing coupling area  32 . Accordingly, a secondary seal is provided. 
     In yet another exemplary embodiment, rupture disc secondary seal assembly  10  comprises a liquid sealant applied on coupling area  32 . The liquid sealant may be, for example, a Teflon-based compound, as will be understood by those ordinarily skilled in the art having the benefit of this disclosure. For example, in the embodiment shown in  FIG. 2A , this exemplary embodiment would include applying a liquid sealant between sealing tape  36  and the top of coupling area  32 . In the embodiment of  FIG. 2B , for example, the liquid sealant may be applied between seal  44  and the top of coupling area  32 . Sealing tape  36  will protect liquid sealant from the downhole environment. In other embodiments, the liquid sealant may also be applied down along the threads of coupling area  32  in  FIG. 2A . In operation, as pressure is applied to rupture disc secondary seal assembly  10 , sealing tape  36  and liquid sealant is at least partially forced down into coupling area  32 , thus providing a second seal for rupture disc secondary seal assembly  10 . 
     In yet another exemplary embodiment, sealing tape  36  may be comprises of an elastomeric material with adhesive on one side. As would be understood by those ordinarily skilled in the art having the benefit of this disclosure, the adhesive used in this embodiment and others described herein, will be selected to withstand the downhole environment. In yet another exemplary embodiment, sealing tape  36  may also be made of a metallic foil material. Such metallic foil materials may include, for example, aluminum foil, copper foil, stainless steel foil or a corrosion-resistive such as, for example, Inconel. 
       FIG. 2D  illustrates yet another exemplary embodiment of the present invention. Here, rupture disc secondary seal assembly  10  is identical to the embodiment illustrated in  FIG. 2B , except that a metallic washer  46  is positioned between seal  44  and the surface above coupling area  32 . In some applications, seals  44  may extrude into the threaded connection along those coupling areas  32  which utilized threads. In this case, metallic washer  46  may be placed across coupling area  32 . In operations, once pressure is applied to rupture disc secondary seal assembly  10 , metallic washer  46  will partially mold down into coupling area  32  while seal  44  (elastomeric, for example) will seal around the outer edges of metallic washer  46 . Accordingly, a secondary seal is provided. 
     The exemplary secondary seals of the embodiments of rupture disc secondary seal assembly  10  may be applied to a downhole tool in a variety of ways. For example, sealing tape  36  may be placed on the handle portion of a golf spike wrench. The handle of the tool may then be placed over bore  22  of housing  12 . As a result, sealing tape  36  will be easily and properly aligned over coupling area  32 . In the alternative, however, the exemplary secondary seals described herein may be applied by hand. In addition, certain exemplary embodiments of the exemplary secondary seals described herein are rated to withstand pressures of 32,000 psi or higher. 
     Accordingly, exemplary embodiments of the present invention provide a number of advantages. For example, the present invention provide a secondary seal for the rupture disc and provides protection to the primary seal since the secondary seal keeps it isolated from external fluids. In addition, embodiments of the present invention utilizing a transparent sealing tape provide a tamper proof indication that the rupture disc is still tightly coupled to the body of the tool. In addition, by extruding into the coupling area, the present invention provides an indication that the primary seal has failed. Moreover, in embodiments utilizing metallic foil sealing tape and the elastomeric seal, the present invention will provide a secondary and tertiary seal for the rupture disc. Accordingly, through utilization of multiple seals along rupture disc secondary seal assembly, a highly reliable rupture disc is provided because, should one seal fail, there are one or more backup seals to ensure the disc will seal properly. 
     An exemplary embodiment of the present invention provides a rupture disc assembly utilized in a downhole tool, the rupture disc assembly comprising a rupture disc housing comprising a bore therethrough, the rupture disc housing being coupled along a body of the downhole tool at a coupling area, a rupture disc positioned along the bore of the rupture disc housing, and a secondary seal positioned over the coupling area between the rupture disc housing and the body of the downhole tool. In another embodiment, the coupling area is a threaded profile formed by mating threads on an outer diameter of the rupture disc housing and an inner diameter of the body of the downhole tool. In yet another, the secondary seal is sealing tape. In another, the secondary seal is a washer-shaped piece of sealing tape. In yet another, the secondary seal is transparent sealing tape. 
     Another exemplary embodiment of the present invention further comprises an elastomeric seal positioned between the sealing tape and the coupling area. Yet another further comprises a metallic washer positioned between the elastomeric seal and the coupling area. Another further comprises a liquid sealant applied between the sealing tape and the coupling area. In yet another, the secondary seal is elastomeric sealing tape or a sealing tape comprising metallic foil material. 
     An exemplary methodology of the present invention provides a method of utilizing a rupture disc assembly in a downhole environment, the method comprising coupling a rupture disc along a body of a downhole tool at a coupling area, the rupture disc comprising a housing comprising a bore therethrough and a rupture disc positioned along the bore of the housing. The method goes on to comprise applying a secondary seal over the coupling area between the housing and the body of the downhole tool. In another method, coupling the rupture disc along the body of the downhole tool further comprises providing the coupling area as a threaded profile formed by mating threads on an outer diameter of the housing and an inner diameter of the body of the downhole tool. In yet another, applying the secondary seal further comprises providing the secondary seal as sealing tape. In another, applying the secondary seal further comprises providing the secondary seal as a washer-shaped piece of sealing tape. 
     In another method, applying the secondary seal further comprises providing the secondary seal as transparent sealing tape. Yet another methodology comprises positioning an elastomeric seal between the sealing tape and the coupling area. Another further comprises positioning a metallic washer between the elastomeric seal and the coupling area. Yet another further comprises applying a liquid sealant between the elastomeric seal and the coupling area. In another, applying the secondary seal further comprises providing the secondary seal as an elastomeric sealing tape. In yet another, applying the secondary seal further comprises providing the secondary seal as a metallic foil sealing tape. 
     The foregoing disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the apparatus in use or operation in addition to the orientation depicted in the figures. For example, if the apparatus in the figures is turned over, elements described as being “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     Although various embodiments and methodologies have been shown and described, the invention is not limited to such embodiments and methodologies and will be understood to include all modifications and variations as would be apparent to one skilled in the art. Therefore, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.