Abstract:
A energy transfer device ( 10 ) is provided that is capable of transferring the energy output from one pyrotechnic device ( 52 ) to another device ( 78 ) for initiating firing thereof. Device ( 10 ) comprises a device housing ( 12 ) in which a deformable device insert ( 14 ) is received. Device insert ( 14 ) comprises a central passageway ( 34 ) for transmitting the output from a pyrotechnic device ( 52 ), including energy, gasses, and/or solids, to another pyrotechnic device ( 78 ). The passageway ( 34 ) conducts the pyrotechnic device output to a precise location on the second pyrotechnic device ( 78 ) where firing is most effectively initiated. The energy transfer device ( 10 ) may be employed as a part of a tool ( 44 ) used in well completion operations.

Description:
RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Patent Application No. 61/637,541, filed Apr. 24, 2012, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed toward an energy transfer device that is configured to transmit energy released from the output of a first pyrotechnic device to a second pyrotechnic device in order to initiate firing of the second pyrotechnic device. The energy transfer device absorbs energy released by the output charge of the first pyrotechnic device, such as a time delay fuse, and directs at least a portion of the energy toward the second pyrotechnic device in a controlled manner so as to efficiently and reliably facilitate firing of the second pyrotechnic device. 
     2. Description of the Prior Art 
     Pyrotechnic devices are commonly employed to ignite or detonate explosive charges in a variety of industrial applications such as oil well completion operations. Time delay fuses are exemplary pyrotechnic devices that can be used to initiate detonation of the explosive material used in the blasting operation. Time delay fuses are generally available in predetermined delay time increments. However, in certain applications, longer time delays are desired beyond what a single time delay fuse is configured to supply. In such instances, blasting operators may stack a plurality of fuses in series with the expectation that the output charge from one fuse will ignite the primer or ignition charge of the next fuse. 
     Time delay fuses generally are not designed or configured for use in this manner. Thus, in certain circumstances, the output charge from the time delay fuse can fail to ignite the adjacent fuse, thereby resulting in failure to detonate the primary explosive used in the blasting operation. In the context of downhole operations, failure to detonate the primary explosive may require that the tool including the primary explosive be run back up the hole and a new string of time delay fuses be installed. Pulling pipe string is an expensive and time-consuming operation. The presence of explosive devices further complicates this operation due to their inherently dangerous nature. 
     Therefore, there exists a need in the art for reliably effecting transfer of the output energy from one time delay fuse to another ensuring that the subsequent fuse in the chain ignites. 
     SUMMARY OF THE INVENTION 
     The present invention provides a solution to this problem by providing an energy transfer device configured to transfer the energy output from a first pyrotechnic device to a second pyrotechnic device for initiating firing of the second pyrotechnic device. In one embodiment, the energy transfer device comprises a metallic body having a forward section configured to be placed adjacent the first pyrotechnic device and an aft section configured to be placed adjacent the second pyrotechnic device. The metallic body further includes an axial passageway extending therethrough. The passageway includes a first segment extending through the body forward section and a second segment extending through the body aft section. The body forward section is deformable by the energy output from the first pyrotechnic device such that the diameter of the passageway first segment is narrowed thereby forming a constriction in the passageway. 
     According to another embodiment of the present invention, there is provided an energy transfer device configured to transfer the energy output from a first pyrotechnic device to a second pyrotechnic device for initiating firing of the second pyrotechnic device. The energy transfer device comprises a device housing including a central bore extending therethrough, and a device insert carried by the housing within the bore. The housing includes a housing forward section and a housing aft section. The insert comprises an insert forward section and an insert aft section and an axial passageway extending therethrough. The housing forward section and the insert forward section are configured for placement adjacent the first pyrotechnic device, and the housing aft section and the insert aft section are configured for placement adjacent the second pyrotechnic device. The insert forward section is deformable by the energy output from the first pyrotechnic device such that a constriction is formed in the passageway. 
     According to yet another embodiment of the present invention, there is provided a tool for delivering a pyrotechnic charge downhole in a well. The tool comprises a time delay fuse and an energy transfer device. The energy transfer device comprises a device housing including a central bore extending therethrough, and a device insert including an axial passageway extending therethrough. The device housing includes a housing forward section and a housing aft section. Likewise, the device insert also includes an insert forward section and an insert aft section. The device insert is configured to be positioned within the housing bore. The insert forward section is deformable by the energy output from a first pyrotechnic device such that a constriction is formed in the passageway. 
     In still another embodiment according to the present invention, there is provided a method of igniting a pyrotechnic charge downhole in a well. A first pyrotechnic device, an energy transfer device, and a second pyrotechnic device are provided. The energy transfer device comprises a metallic body having a forward section, an aft section, and an axial passageway extending therethrough. The first pyrotechnic device is ignited to detonate an output charge. At least a portion of the energy from the output charge is directed through the axial passageway toward the second pyrotechnic device thereby igniting the second pyrotechnic device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an energy transfer device according to one embodiment of the present invention; 
         FIG. 2  is an exploded, perspective view of the energy transfer device of  FIG. 1  illustrating the two-part construction thereof; 
         FIG. 3  is a schematic view of the energy transfer device utilized in a downhole tool in conjunction with time delay fuses; 
         FIG. 4  is a cross-sectional view of the energy transfer device insert in its pre-firing configuration; and 
         FIG. 5  is a cross-sectional view of the energy transfer device insert post-firing showing deformation of the insert and the formation of a passageway constriction. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the Figures, and in particular  FIGS. 1 and 2 , an energy transfer device  10  according to one embodiment of the present invention is shown. Device  10  is a dynamic device that is configured to limit and convert a detonating output of a time delay fuse or similar device so that the output is suitable to ignite another time delay fuse or similar device without damaging the input and resulting in a failure to ignite. Device  10  is of two-piece construction comprising a device housing  12  and a device insert  14 . Housing  12  comprises a metallic body  13  that includes a generally cylindrical forward section  16  configured to be placed adjacent to and facing the pyrotechnic device that is supplying the energy to be transferred to another pyrotechnic device and a generally cylindrical aft section  18  configured to be placed adjacent to and facing the pyrotechnic device receiving the transferred energy. In certain embodiments, forward section  16  may have a larger outer diameter than aft section  18 . The outer surface of forward section  16  comprises threads  20  that permit housing  12  to be secured within a tool, such as might be used in downhole blasting operations. Body  13  comprises an axial bore  22  extending therethrough that is sized to receive device insert  14 . Bore  22  includes a forward segment  24  and an aft segment  26 , with said forward segment  24  generally having a greater diameter than aft segment  26 , although this need not always be the case. 
     Device insert  14  comprises a metallic member  28  including a forward section  30  and an aft section  32 . Forward section  30  is configured to be received within forward segment  24  of bore  22 , and aft section  32  is configured to be received within aft segment  24  of bore  22 . As best shown in  FIG. 4 , insert  14  further comprises a central, axial passageway  34  extending therethrough comprising respective forward and aft segments  35 ,  37 . In certain embodiments, forward segment  35  may present a length that is less than the length of segment  37 . Moreover, the diameter of segment  35  is less than the diameter of segment  37 . 
     As discussed in greater detail below, passageway  34  operates as a conduit directing the output energy from one pyrotechnic device located adjacent forward sections  16  and  30  toward the second pyrotechnic device located adjacent aft sections  18  and  32 . The forward section  30  of device insert  14  comprises a circumscribing channel  36  that is configured to receive an O-ring  38 . O-ring  38  provides a seal between insert  14  and housing  12 , and also assists in maintaining insert  14  within bore  22  upon assembly of device  10 . 
     Forward section  30  of insert  14  generally is of greater diameter than aft section  32 , thus corresponding with the general configuration of bore  22 . The junction between forward section  30  and aft section  32  comprises a shoulder  40  that abuts a similarly configured shoulder  42  defining the junction between forward section  16  and aft section  18  of housing  12 . The contacting engagement of both shoulders  40 ,  42  ensures proper mating of insert  14  and housing  12 . 
     In certain embodiments, housing  12  and insert  14  can be manufactured from a variety of metals, including stainless steel, although different stainless steel alloys may be selected individually for each piece. In one particular embodiment, housing  12  may comprise 17-4 (AMS 5643) stainless steel, whereas insert  14  may comprise 304 or 304L stainless steel. In preferred embodiments, insert  14  comprises a metal having hardness and tensile strength values lower than the metal from which housing  12  is formed. As explained in greater detail below, manufacturing housing  12  and insert  14  from different materials permits insert  14  to undergo deformation upon firing of the first pyrotechnic device, while housing  12  resists deformation thereby permitting its reuse. It is notable, too, that device  10  does not itself comprise any pyrotechnic material. 
     While the embodiments of device  10  illustrated and described herein are of two-piece construction, it is within the scope of the present invention for device  10  to be of single-piece construction comprising a unitary body and a central, axial passageway. Such a single-piece device would retain the external configuration of housing  12  and the internal configuration of insert  14 , namely passageway  34 , described above. 
     As shown in  FIG. 3 , energy transfer device  10  can be installed within a tool  44 , such as a firing head, for use in downhole blasting operations. Accordingly, tool  44  may be configured for attachment to a downhole pipe string or other downhole tool. Tool  44  generally comprises a firing section  46  that includes a firing head  48  equipped with a firing pin  50 . Firing section  46  further comprises a first time delay fuse  52  disposed within a bore  54  formed in the firing section. Fuse  52  generally comprises a primer  56 , one or more time delays  58 , and an output charge  60 . In certain embodiments, output charge  60  may comprise 2,2′,4,4′,6,6′-hexanitrostilbene (HNS-II). Other components that may be present within fuse  52  include one or more sections of ignition composition  62 , an ignition charge  64 , and a transfer charge  66 . Firing section  46  also includes an internally threaded end region  68  configured for attachment to an externally threaded region  70  of a tool transfer section  72 . 
     Energy transfer device  10  is received in region  70 . Threads  20  of device  10  are configured to mate with corresponding threads  74  of region  70  to secure device  10  therein. Device housing  12  may further include a pair of slots  76  formed in the face of forward section  16  that are configured to receive a tool used in the installation of device  10  within section  70 . A second time delay fuse  78  is received within a bore  80  formed in transfer section  72  and positioned adjacent the aft section  18  of device housing  12 . Fuse  78  may be constructed identically to fuse  52 , or it may be configured differently, such as possessing greater or fewer time delays  58 . At the end opposite from energy transfer device  10 , transfer section  72  comprises an internally threaded end region  82  that is similar in configuration to end region  68 . End region  82  is configured for attachment to an additional transfer section  72  if further overall time delay is required. Alternatively, another type of pyrotechnic charge may be coupled with end region  82 , such as the working explosive for the blasting operation. 
     During operation of tool  44 , firing head  48  is actuated according to any means known to those of skill in the art and results in driving firing pin  50  toward time delay fuse  52  Firing pin  50  strikes primer  56  thereby igniting fuse  52 . Combustion of the pyrotechnic material of which fuse  52  is comprised continues through output charge  60 . The detonation of output charge  60  releases heat, gas, and/or solid particulates that are directed toward the energy transfer device, and specifically the respective faces of forward sections  16  and  30 . The hot gasses generated by output charge  60  are directed through passageway forward segment  35  and exit device  10  via passageway aft segment  37 . As noted above, device insert  14  may be constructed from material that is subject to deformation by the heat and gasses released by output charge  60 , whereas housing  12  may be constructed from a material that is more resistant to being deformed by the output of fuse  52 . Accordingly, upon detonation of output charge  60  the energy, hot gas and/or solids directed toward insert  14  cause the insert forward section  30  to deform. This deformation is shown in  FIG. 5 . 
     Particularly, the face  84  of forward section  30 , which is initially planar, deforms thereby narrowing the diameter of passageway forward segment  35  and creating a constriction  86  therein. In one exemplary embodiment, passageway forward segment  35  has an initial diameter of 0.094 inch. A typical ambient temperature time delay fuse detonating output deforms the insert material to decrease the passageway forward segment diameter to between about 0.040-0.050 inch. The output of a time delay fuse at elevated temperature produces a 25% deeper dent in a steel test dent block and also decreases the insert port diameter to 0.030-0.039 inch. The decrease in passageway open area with a time delay fuse output is between 3.5 to 9.8 times depending on the strength of the detonation. When in use and acted on by the donor detonating device (e.g., fuse  52 ), deformation/denting of insert  14  absorbs a portion of the detonation energy. The geometry and material characteristics of insert  14  cause partial closing of the passageway forward segment  35  when used in close proximity to a detonating output that is capable of denting steel. It has been discovered that strong detonations cause more deformation thereby closing the passageway forward segment  35  to a smaller diameter and further limiting the detonation impact while still allowing sufficient ignition gasses and particles to pass through. Hence this action is self-regulating pending the power output level of the donor detonating device. 
     The constriction  86  in passageway forward segment  35  allows pressure from output charge  60  (e.g., a combination of the detonation pressure and heat from the HNS-II, the azide output energy and the output initiator energy, hot metal fragments, molten metal and slag) to be released over a longer time. Deformation from the HNS-II creates a conical impression, which is often covered with a slag after the deformation of face  84 . Detonation of HNS-II usually only leaves black soot, thus, in certain embodiments, the observed slag on and in insert  14  indicates a flow of gasses and solids though the passageway  34  after the initial impact from detonation. 
     The two-part construction of device  10  permits housing  12  to be reused by simply replacing insert  14 . Passageway aft segment  37  can have a larger initial diameter than passageway forward segment  35 . The larger-diameter segment  37  functions as a renewable passage to ensure tool wear does not affect performance and to ensure the diameter and concentricity are controlled. It is noted that the area nearest to the input of the next delay usually expands also and would be a wear point if it were part of the re-useable tooling. 
     The energy, gas and/or solid products generated by combustion of output charge  60  are then carried through passageway  34  toward fuse  78 . Upon reacting aft face  88  of insert  14 , the hot gas and/or solids are focused directly on the primer  56  of fuse  78  and ensure ignition thereof. Thus, device  10  effectively and reliably transfers the output of fuse  52  to fuse  78  and ensures that the firing sequence, which began with firing head  48 , continues. The output charge  60  of fuse  78  may then be transferred to another fuse through attachment of another transfer section  72  to end region  82 , or to another type of pyrotechnic device such as another firing head or an explosive charge that might be used in the blasting operation.