Abstract:
A detonating cord interrupt device ( 140 ) is positionable between two segments of detonating cord ( 126, 134 ). The detonating cord interrupt device ( 140 ) includes a housing ( 130 ), a first booster ( 128 ) at least partially disposed within the housing ( 130 ) and a second booster ( 132 ) at least partially disposed within the housing ( 130 ) and having a spaced apart relationship with the first booster ( 128 ). A detonation transfer interrupt member ( 138 ) is removably positionable within the housing ( 130 ) in the space between the first and second boosters ( 128, 132 ) such that the transfer of a detonation from one of the first and the second boosters ( 128, 132 ) to the other of the first and the second boosters ( 128, 132 ) is prevented when the detonation transfer interrupt member ( 138 ) is positioned within the housing ( 130 ).

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    This invention relates, in general, to perforating a cased wellbore that traverses a subterranean hydrocarbon bearing formation and, in particular, to a detonating cord interrupt device for preventing the premature detonation of the shaped charges within a perforating gun assembly during transportation.  
         BACKGROUND OF THE INVENTION  
         [0002]    Without limiting the scope of the present invention, its background will be described with reference to perforating a subterranean formation with a perforating gun assembly, as an example.  
           [0003]    After drilling a section of a subterranean wellbore that traverses a formation, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within the wellbore. This casing string increases the integrity of the wellbore and provides a path for producing fluids from the producing intervals to the surface. Conventionally, the casing string is cemented within the wellbore. To produce fluids into the casing string, hydraulic openings or perforations must be made through the casing string, the cement and a short distance into the formation.  
           [0004]    Typically, these perforations are created by detonating a series of shaped charges that are disposed within the casing string and are positioned adjacent to the formation. Specifically, one or more charge carriers are loaded with shaped charges that are connected with a detonator via a detonating cord. The charge carriers are then connected within a tool string that is lowered into the cased wellbore at the end of a tubing string, wireline, slick line, coil tubing or other conveyance. Once the charge carriers are properly positioned in the wellbore such that the shaped charges are adjacent to the formation to be perforated, the shaped charges may be fired. If more than one downhole zone is to be perforated, a select fire perforating gun assembly may be used such that once the first zone is perforated, subsequent zones may be perforated by repositioning and firing the previously unfired shaped charges without tripping out of the well.  
           [0005]    The shaped charges used to perforate the casing include high explosives and must therefore be handled with extreme caution. For example, it is imperative that the high explosives are not prematurely initiated causing the shaped charge to detonate. Accordingly, in the interest of safety and due to governmental regulations relating to the transportation of explosive devices, perforating gun assemblies are typically not armed, i.e., the detonators are not installed, until the perforating gun assembly arrives at the rig site.  
           [0006]    It has been found, however, that installing detonators in the perforating gun assembly at the rig site has several drawbacks. For example, the person installing the detonators is commonly under a time constraint to complete to the installation as rig time is very expensive. In addition, the rig environment, such as weather conditions, work area, lighting and the like, may not be as conducive as the manufacturer&#39;s shop environment for the intricate assembly required during the installation of the detonators. Furthermore, the level of skill of the person installing the detonators at the rig site may not be as great as that of a technician in the manufacturer&#39;s shop. These inherent limitations of the rig environment have lead to mistakes being made in the installation of detonators into perforating gun assemblies resulting in the failure of certain perforating gun assemblies to fire.  
           [0007]    Therefore a need has arisen for an apparatus and method that provide for the safe transportation of an armed perforating gun assembly such that the intricate work of installing the detonators may be performed in the manufacturer&#39;s shop as opposed to the rig site. A need has also arisen for such an apparatus and method that prevent the premature detonation of the shaped charges in the armed perforating gun assembly. Further, a need has arisen for such an apparatus and method that minimize the required on site preparation of the armed perforating gun assembly.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention disclosed herein comprises a perforating gun assembly that provides for the safe transportation of an armed perforating gun assembly such that the intricate work of installing the detonators may be performed in the manufacturer&#39;s shop as opposed to the rig site. To achieve this result, the perforating gun assembly of the present invention uses a detonating cord interrupt device that prevents the premature detonation of the shaped charges in the armed perforating gun assembly. In addition, the detonating cord interrupt device requires minimal on site manipulation to allow a planned detonation of the shaped charges.  
           [0009]    The detonating cord interrupt device of the present invention comprises a housing, a first booster at least partially disposed within the housing, a second booster at least partially disposed within the housing and having a spaced apart relationship with the first booster and a detonation transfer interrupt member removably positionable within the housing in the space between the first and second boosters.  
           [0010]    In one embodiment, the detonation transfer interrupt member extends transversely through an opening in the housing. In this embodiment, the detonation transfer interrupt member may be a substantially cylindrical member that is inserted through a round opening in the housing. The detonation transfer interrupt member may be constructed from a variety of materials such as metals, polymers, elastomers and combination thereof.  
           [0011]    In operation, the detonating cord interrupt device prevents the transfer of a detonation from one of the boosters to the other booster when the detonation transfer interrupt member is positioned within the housing. Likewise, the detonating cord interrupt device allows the transfer of a detonation from one of the boosters to the other booster when the detonation transfer interrupt member is not positioned within the housing.  
           [0012]    The detonating cord interrupt device may be positioned within a detonating cord to prevent the premature propagation of a detonation wave through the detonating cord. For example, the detonating cord interrupt device may be positioned between a first and a second segment of a detonating cord. In this configuration, the first booster is operably associated with the first segment of detonating cord and the second booster operably associated with the second segment of detonating cord. More specifically, the first booster may be securably coupled to the first segment of detonating cord by crimping and the second booster may be securably coupled to the second segment of detonating cord by crimping. Likewise, the first and second boosters may be securably coupled to the housing by crimping.  
           [0013]    Such an arrangement, may be used within a perforating gun assembly such that the perforating gun assembly may be armed prior to transportation. The perforating gun assembly of the present invention comprises a plurality of shaped charges positioned within a charge carrier and a detonating cord having first and second segments. The second segment of the detonating cord is operably coupled to the shaped charges. A detonator is operably coupled to the first segment of the detonating cord and is operable to initiate a detonation within the first segment of the detonating cord. The detonating cord interrupt device is positioned between the first and second segments of the detonating cord to prevent a detonation of the shaped charges in the event of a premature initiation of the detonator.  
           [0014]    The charge carrier of the perforating gun assembly may be a ported carrier having ports substantially radially aligned with the shaped charges and a port axially aligned with the detonating cord interrupt device. Port plugs are secured within the ports to provide a fluid seal and prevent any fluids from entering the perforating gun assembly prior to firing.  
           [0015]    In another aspect, the present invention comprises a method for preventing the detonation of shaped charges in an armed perforating gun assembly. The method includes positioning a plurality of shaped charges within a charge carrier, operably coupling a detonating cord to the shaped charges, operably coupling a detonator to the detonating cord and positioning a detonating cord interrupt device within the detonating cord between the detonator and the shaped charges.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which:  
         [0017]    [0017]FIG. 1 is schematic illustration of an offshore oil and gas platform operating a perforating gun assembly of the present invention;  
         [0018]    [0018]FIG. 2 is a side view partially cut away of a perforating gun assembly of the present invention positioned within a wellbore;  
         [0019]    [0019]FIG. 3 is a side view of a detonator, two segments of detonating cord and a detonating cord interrupt device of the present invention;  
         [0020]    [0020]FIG. 4 is a cross sectional view of detonating cord interrupt device of the present invention positioned between two segments of detonating cord prior to a premature detonation;  
         [0021]    [0021]FIG. 5 is a cross sectional view of detonating cord interrupt device of the present invention positioned between two segments of detonating cord following a premature detonation;  
         [0022]    [0022]FIG. 6 is a cross sectional view of detonating cord interrupt device of the present invention positioned between two segments of detonating cord prior to a planned detonation;  
         [0023]    [0023]FIG. 7 is a cross sectional view of detonating cord interrupt device of the present invention positioned between two segments of detonating cord following a planned detonation; and  
         [0024]    [0024]FIG. 8 is a cross sectional view of an alternate embodiment of a detonating cord interrupt device of the present invention positioned between two segments of detonating cord.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts which can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention, and do not delimit the scope of the present invention.  
         [0026]    Referring initially to FIG. 1, a perforating gun assembly adapted for use in a wellbore operating from an offshore oil and gas platform is schematically illustrated and generally designated  10 . A semi-submersible platform  12  is centered over a submerged oil and gas formation  14  located below sea floor  16 . A subsea conduit  18  extends from deck  20  of platform  12  to wellhead installation  22  including blowout preventers  24 . Platform  12  has a hoisting apparatus  26  and a derrick  28  for raising and lowering pipe strings.  
         [0027]    A wellbore  36  extends through the various earth strata including formation  14 . Casing  38  is cemented within wellbore  36  by cement  40 . When it is desired to perforate casing  38  adjacent to formation  14 , a perforating gun assembly  42  is lowered into casing  38  via conveyance  44  such as a wireline, electric line or coiled tubing. Thereafter, an electric signal is sent to a detonator  46  which initiates the detonation of the shaped charges that are disposed within perforating gun assembly  42 . Upon detonation, perforations are created that extend outwardly through casing  38 , cement  40  and into formation  14 .  
         [0028]    Even though FIG. 1 depicts a vertical well, it should be noted by one skilled in the art that the perforating gun assembly of the present invention is equally well-suited for use in wells having other geometries such as deviated wells, inclined wells or horizontal wells. Also, even though FIG. 1 depicts an offshore operation, it should be noted by one skilled in the art that the perforating gun assembly of the present invention is equally well-suited for use in onshore operations.  
         [0029]    Referring now to FIG. 2, therein is depicted a perforating gun assembly  60  positioned in a wellbore  62  that penetrates formation  64 . A casing  66  lines wellbore  62  and is secured in position by cement  68 . A conveyance  70  is coupled to perforating gun assembly  60  at a cable head  72 . A collar locator  74  is positioned below cable head  72  to aid in the positioning of perforating gun assembly  60  in wellbore  62 .  
         [0030]    A fluid such as drilling fluid (not shown) fills the annular region between perforating gun assembly  60  and casing  66 . In the illustrated embodiment, perforating gun assembly  60  has a ported carrier  80  having port plugs  82  positioned therein that create a fluid seal and prevent any wellbore fluids from entering perforating gun assembly  60 . Radially aligned with port plugs  82  is a respective one of a plurality of shaped charges, such as shaped charge  86 . Each of the shaped charges includes an outer housing, such as housing  88  of shaped charge  86 , and a liner, such as liner  90  of shaped charge  86 . Disposed between each housing and liner is a quantity of high explosive.  
         [0031]    In the illustrated embodiment, the shaped charges are retained within carrier  80  by a support member  92  which includes an outer charge holder sleeve  94  and an inner charge holder sleeve  96 . In this configuration, outer charge holder sleeve  94  supports the discharge ends of the shaped charges, while inner charge holder sleeve  96  supports the initiation ends of the shaped charges. Disposed within inner tube  96  is a detonating cord  98 , such as a primacord, which is operable to detonate the shaped charges. In the illustrated embodiment, the initiation ends of the shaped charges extend across the cental longitudinal axis of perforating gun assembly  60  allowing detonating cord  98  to connect to the high explosive within the shaped charges through an aperture defined at the apex of the housings of the shaped charges.  
         [0032]    Each of the shaped charges is longitudinally and radially aligned with a port plug  82  in carrier  80  when perforating gun assembly  60  is fully assembled. In the illustrated embodiment, the shaped charges are arranged in a spiral pattern such that each shaped charge is disposed on its own level or height and is to be individually detonated so that only one shaped charge is fired at a time. It should be noted, however, by those skilled in the art that alternate arrangements of shaped charges may be used, including cluster type designs wherein more than one shaped charge is at the same level and is detonated at the same time, without departing from the principles of the present invention.  
         [0033]    Perforating gun assembly  60  also includes a detonator subassembly  100 . Detonator subassembly  100  has a ported housing  102  that receives a port plug  104 . Disposed within detonator subassembly  100  is a detonator  106  that is coupled to an electrical energy source via electrical wire  108 . Detonator  106  may be any type of detonator that is suitable for initiating a detonation in a detonating cord as the present invention is detonator independent, such detonators being of the type that are well known in the art or subsequently discovered. Detonator  106  is coupled to a segment of detonating cord  110 . Positioned between detonating cord  110  and detonating cord  98 , which extends into detonator subassembly  100  from carrier  80 , is a detonating cord interrupt device  112 .  
         [0034]    Detonating cord interrupt device  112  is used to selectively prevent and allow the propagation of a detonation from detonating cord  110  to detonating cord  98 . More specifically, when perforating gun assembly  60  is assembled in the shop, detonator  106  is installed within perforating gun assembly  60  along with the shaped charges. Importantly, for safety during transportation of the armed perforating gun assembly  60  from the shop to the rig site, detonating cord interrupt device  112  is positioned in its detonation interpret configuration within the explosive train between detonator  106  and the shaped charges. Accordingly, even if detonator  106  were to prematurely initiate a detonation, detonating cord interrupt device  112  would prevent the detonation wave from transferring from detonating cord  110  to detonating cord  98 .  
         [0035]    Once the armed perforating gun assembly  60  has been safely transported to the rig site, port plug  104  is removed such that a technician can reconfigure detonating cord interrupt device  112  from its detonation interpret configuration to its non detonation interrupt configuration. Thereafter, perforating gun assembly  60  may be attached to a conveyance and run downhole to the desired location. To detonate the shaped charges, an electrical signal is sent to detonator  106  via electrical wire  108  that initiates a detonation within detonating cord  110 . The detonation transfers from detonating cord  110  to detonating cord  98 , as explained in greater detail below, by passing through detonating cord interrupt device  112  in its non detonation interrupt configuration. The detonation wave then progresses through detonating cord  98  to initiate the detonation of the shaped charges, thereby perforating the well.  
         [0036]    Even though a single perforating gun assembly is depicted in FIG. 2, it should be appreciated by those skilled in the art that any number of perforating gun assemblies may be included in the tool string and are considered within the scope of the present invention as the number of perforating gun assemblies will be dependent upon the length of the interval or intervals being perforated as well as the number of intervals being perforated in a single trip using, for example, select fire perforating gun assemblies which will require multiple detonating cord interrupt devices. Also, even though perforating gun assembly  60  is depicted in a bottom up firing configuration, it should be understood by those skilled in the art that the present invention in equally well-suited for use in perforating gun assemblies having a top down firing configuration.  
         [0037]    Referring next to FIG. 3, therein is presented an enlarged view of a first portion of an explosive train according to the present invention that is generally designated  120 . Explosive train  120  includes detonator  122  that is coupled to an electrical input line  124  and to a segment of detonating cord  126 . On the opposite end of detonating cord  126  is a booster  128  that is securably coupled to detonating cord  126  by crimping. The opposite end of booster  128  (not visible in FIG. 3) extends into housing  130  and is secured therein by crimping housing  130 . Housing  130  may be constructed from a variety of materials including metals such as steels and aluminum, polymers or other suitably durable material. A booster  132  extends into the opposite end of housing  130  and is similarly secured therein by crimping housing  130 . Extending from the opposite end of booster  132  is a segment of detonating cord  134 . Housing  130  has an opening  136  through which a detonation transfer interrupt member  138  transversely extends. Detonation transfer interrupt member  138  may be constructed from any suitable material such as metals including steels, copper, aluminum and the like, polymers, elastomers or combination thereof and the like. Together, housing  130 , boosters  128 ,  132  and detonation transfer interrupt member  138  form detonating cord interrupt device  140 . Even though the coupling of the detonating cords to the boosters and the boosters to the housing has been depicted as crimping, it should be noted by those skilled in the art that other techniques could alternatively be used for such coupling, including, but not limited to, use of adhesives, a friction fit or combinations thereof and the like.  
         [0038]    As best seen in FIG. 4, detonating cord interrupt device  140  is in its detonation interrupt configuration prior to the detonation of either detonating cord  126  or detonating cord  134 . In the illustrated embodiment, detonating cord  126  includes explosive  142 , booster  128  includes explosive  144 , detonating cord  134  includes explosive  146  and booster  132  includes explosive  148 . As stated above, if one of the detonating cords were to be detonated when detonating cord interrupt device  140  is in its detonation interrupt configuration wherein detonation transfer interrupt member  138  is positioned with opening  136 , the detonation would not transfer to the opposing detonating cord.  
         [0039]    Specifically and as depicted in FIG. 5 in an idealized manner, following the detonation of detonating cord  126  and booster  128 , the detonation does not transfer to booster  132 , detonating cord  134  or any other explosive device in the downstream explosive train as detonation transfer interrupt member  138  is positioned within opening  136  of housing  130 . As such, detonating cord interrupt device  140  prevents the propagation of the detonation thereacross.  
         [0040]    Once the perforating gun assembly including detonating cord interrupt device  140  is ready to be fired, detonation transfer interrupt member  138  is removed from opening  136  in housing  130 , as best seen in FIG. 6. Thereafter and as depicted in FIG. 7 in an idealized manner, following the detonation of detonating cord  126  and booster  128 , the detonation transfers to the facing booster  132 , detonating cord  134  and any other explosive device in the downstream explosive train as detonation transfer interrupt member  138  is not positioned within opening  136  of housing  130 . As such, in this configuration, detonating cord interrupt device  140  allows the propagation of the detonation thereacross.  
         [0041]    Even though FIGS. 4-7 have depicted a gap between the ends of boosters  128 ,  132  and detonating cord interrupt device  140 , it should be understood by those skilled in the art that the optimal distance between the facing boosters will depend on a variety of factors such as the type of booster used, the diameter of housing  130  and the like. For example, it may be desirable in some cases to have the ends of the facing boosters contact the detonation transfer interrupt member when the detonation transfer interrupt member is positioned with the housing.  
         [0042]    Specifically, as depicted in FIG. 8, detonating cord interrupt device  240  includes a booster  228  that is connected to a segment of detonating cord  226 . Likewise, booster  232  is connected to a segment of detonating cord  234 . Boosters  228 ,  232  each extend into housing  230  such that their respective ends contact detonation transfer interrupt member  238  if detonation transfer interrupt member  238  is positioned with opening  236  of housing  230 . As illustrated, detonating cord  226  includes explosive  242 , booster  228  includes explosive  244 , detonating cord  234  includes explosive  246  and booster  232  includes explosive  248 . Detonating cord interrupt device  240  selectively prevents and allows the transfer of a detonation thereacross as described above with reference to detonating cord interrupt device  140 .  
         [0043]    Even though FIGS. 3-8 have depicted the detonation transfer interrupt member as being cylindrical and the opening in the housing of the detonating cord interrupt device as being round, it should be clearly understood by those skilled in the art that detonation transfer interrupt members having alternate shapes being positionable in correspondingly configured openings in the housing of the detonating cord interrupt devices is contemplated and considered within the scope of the present invention. Such other shapes including, but not limited to, detonation transfer interrupt members having square cross sections, rectangular cross sections, or other polygon shaped cross sections, oval cross sections or other symmetric or non symmetric cross sections.  
         [0044]    While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.