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RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 61/439,217, filed Feb. 3, 2011, the full disclosure of which is hereby incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of Invention 
         [0003]    The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a modular apparatus for providing communication between members of a downhole string. Yet more specifically, the present invention relates to a cartridge inserted into an end of a perforating gun equipped with a receptacle or contact at both ends for connection to a signal line through a perforating gun string. 
         [0004]    2. Description of Prior Art 
         [0005]    Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore. The casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore. 
         [0006]    Perforating systems typically comprise one or more perforating guns strung together, these strings of guns can sometimes surpass a thousand feet of perforating length, but typically shorter in a wireline application. In  FIG. 1  an example of a prior art perforating system  10  is shown disposed in a wellbore  12  and made up of a string of perforating guns  14  connected in series. Typically, subs  15  may connect adjacent guns to one another. The perforating system  10  is deployed from a wireline  16  that spools from a service truck  18  shown on the surface  20 . Generally, the wireline  16  provides a raising and lowering means as well as communication and control connectivity between the truck  18  and the perforating system  10 . The wireline  16  is threaded through pulleys  22  supported above the wellbore  12 . In some instances, derricks, slips and other similar systems are used in lieu of a surface truck for inserting and retrieving the perforating system into and from a wellbore. Moreover, perforating systems may also be disposed into a wellbore via tubing, drill pipe, slick line, coiled tubing, to mention a few. 
         [0007]    Included with each perforating gun  14  are shaped charges  24  that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the high explosive in a shaped charge  24  is detonated, the force of the detonation collapses the liner and ejects it from one end of the shaped charge  24  at very high velocity in a pattern called a “jet”  26 . The jet  26  perforates casing  28  that lines the wellbore  12  and cement  30  and creates a perforation  32  that extends into the surrounding formation  34 . 
         [0008]    Shown in  FIG. 2  is a sectional view of the prior art perforating gun  14  of  FIG. 1 . As shown, the shaped charges  24  are typically connected to a detonating cord  36 , which when detonated creates a compressive pressure wave along its length that initiates detonation of the shaped charges  24 . A detonator  38  is typically used to set off detonation within the detonation cord  36 . In  FIG. 1 , the detonator  38  is shown in a firing head  40  provided in the string of perforating guns  14 . Initiating detonation of the detonation cord  36  generally takes place by first sending an electrical signal from surface  20  to the detonator  38  via the wireline  16 . Referring back to  FIG. 2 , an upper connection sub  42  contains a terminal  44  for receiving signals transmitted along the wireline  16 . A signal line  46  attaches to the terminal  44  and conveys signal(s) from the wireline  16  to the remaining portions of the perforating system  10 , including the detonator  38 . Multiple connectors  48  are used to make up the signal line  46  through the successive connecting subs  15  and perforating guns  14 . The signal through the signal line  46  initiates high explosive in the detonator  38  that transfers to the attached detonation cord  36 . Detonators  38  may sometimes be provided within connecting subs  15  for transferring the detonating charge along the entire string of perforating guns  14 . Without proper continuity between the wireline  16  and detonator(s)  38 , the shaped charges  24  cannot be detonated. However, failure points in the signal line  46  are introduced with each connector  48 . 
         [0009]    Generally the detonators are connected to the detonating cords in the field just prior to use. Thus they are shipped to the field with the electrical portions and high explosive coupled together in a single unit. Because of the risks posed by the high explosives and the threat of a transient electrical signal, shipment and storage of the detonators is highly regulated, this is especially so when being shipped to foreign locations. Additional problems may be encountered in the field when connecting detonators to the detonating cord. Perforating guns when delivered to the field generally have the shaped charges and detonating cord installed; to facilitate detonator connection some extra length of detonating cord is provided within the gun. Connecting the detonator to the detonating cord involves retrieving the free end of the detonating cord and cutting it to a desired length then connecting, usually by crimping, the detonator to the detonating cord. These final steps can be problematic during inclement weather. Additionally, these final steps fully load a perforating gun and thus pose a threat to personnel in the vicinity. Accordingly benefits may be realized by reducing shipping and storage concerns, increasing technician safety, and minimizing the time required to finalize gun assembly in the field. 
       SUMMARY OF INVENTION 
       [0010]    Disclosed herein is an example of a perforating string insertable into a wellbore. In this example the perforating string is made up of a perforating gun having an upstream end with a receptacle fitting, a signal line with an end electrically connected to the receptacle fitting. Included with the example perforating string is a cartridge sub having a connector inserted into electrical connection with the receptacle fitting, a detonator in the cartridge sub and having a detonating end adjacent to and directed towards the upstream end, and a lead line in the cartridge sub having an end in selective communication with an electrical source and another end in communication with an inlet to the detonator. Optionally, the connector is an annular member that circumscribes a downstream end of the cartridge sub, and wherein the connector coaxially inserts into the receptacle fitting. In an embodiment, the perforating string further includes a switch in the lead line for selectively regulating electricity to the detonator. In this example, a ground lead is optionally included that is connected between the detonator and the switch, wherein the switch selectively communicates the ground lead to ground. In one example, the switch, the lead line, and the detonator are provided within an elongated body that coaxially inserts within an annular housing to define the cartridge sub. In one optional embodiment, further included with the perforating string is a transfer lead line having an end in selective communication with the electrical source and another end in communication with the connector for selectively providing communication between the electrical source and the signal line. A downstream cartridge sub may also optionally be included that has an inlet line in electrical communication with the signal line, an outlet lead line in communication with a bridge plug assembly, so that when an electrical signal is applied to the signal line, the electrical signal is transferred through the downstream cartridge sub to the bridge plug assembly for deploying a bridge plug in the bridge plug assembly. 
         [0011]    Also provided herein is an example of a connector assembly for connecting an upstream perforating gun to a downstream perforating gun. In one example the connector assembly includes an annular housing, an elongated cartridge body inserted within the housing, an annular connector provided on a downstream end of the body and inserted into electrical contact with a receptacle in the downstream perforating gun, a detonator in the cartridge body for initiating a detonating cord in the perforating gun, and a lead line in the cartridge body having an end in selective communication with an electrical source and another end electrically connected to the connector. Optionally, a switch may be included in the body that is connected to the lead line and to an inlet line on the detonator. Also further Optionally included is an outline line that connects between the switch and the detonator, and a ground line that connects between the switch and ground, so that when a detonation signal and detonation current is sent to the switch, the inlet line, outlet line, and ground line form a circuit for flowing current through the detonator for initiating detonation of the detonator and the detonating cord. 
         [0012]    An example method of perforating is provided herein that in one example includes providing a perforating gun with shaped charges, a detonation cord, a receptacle connection, and a signal line in communication with the receptacle connection. A cartridge sub is also provided that has an upstream end, a downstream end, a connector in the downstream end, and a lead line electrically connected to the connector. In the example method, the connector is connected with the signal line by inserting the downstream end of the cartridge sub into the receptacle connection, the shaped charges are detonated by providing a detonation signal to the detonator. In one example, the step of providing a detonation signal to the detonator includes directing electricity from an electrical source to an inlet line connected to the detonator. Optionally in the method, a switch is provided in the cartridge sub for providing electrical communication between the electrical source and the detonator, and for providing electrical communication between an outlet line on the detonator and ground for completing an electrical circuit through the detonator. In one example of the method, the perforating gun is a downstream perforating gun. In this example, further includes is a step of diverting some of the electricity from the electrical source through the lead line, to the connector and the receptacle for initiating detonation of shaped charges in a perforating gun downstream of the downstream perforating gun. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]    Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
           [0014]      FIG. 1  is a partial sectional side view of a prior art perforating system in a wellbore. 
           [0015]      FIG. 2  is a side sectional view of a portion of a perforating string of  FIG. 1 . 
           [0016]      FIGS. 3 and 4  are side sectional views of a perforating system in accordance with the present disclosure. 
           [0017]      FIG. 5  is an example of a perforating string disposed in a wellbore in accordance with the present disclosure. 
       
    
    
       [0018]    While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
       DETAILED DESCRIPTION OF INVENTION 
       [0019]    The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
         [0020]    It is to he understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims. 
         [0021]    In  FIG. 3  an example embodiment of a perforating system  60  is shown in a side sectional view. In this example, the perforating system  60  includes perforating guns  62   1 ,  62   2  each having a series of shaped charges  64  disposed within. Each perforating gun  62   1 ,  62   2  further includes a detonating cord  66  disposed lengthwise therein so it is positioned proximate each of the shaped charges  64 ; thus when the detonating cord  66  is initiated, it may in turn initiate detonation of the shaped charges  64 . Initiating the detonation cords  66  forms a pressure wave that travels the length of the detonation cords  66 . In the example embodiment of  FIG. 3 , the pressure wave travels in the direction of arrows A, and as will be described in more detail below, an initiation signal reaches perforating gun  62   1  before reaching perforating gun  62   2 . Thus for the purposes of reference only, perforating gun  62   1  is referred to as an “upstream” gun whereas perforating gun  62   2  is referred to as a “downstream gun”. 
         [0022]    Coupled in series with the downstream perforating gun  62   2  is a cartridge sub  68  having a cartridge assembly  70  set within the housing of the cartridge sub  68 . In the embodiment of  FIG. 3 , the cartridge assembly  70  is shown made up of an elongated body  71 , and within the body  71  are a switch assembly  72  and an optional circuit board  74  for selectively performing switching operations within the switch assembly  72 . In one example of operation, the switch assembly  72  regulates transmission therethrough of electrical signals through the switch assembly  72  that are received by an inlet lead  76  in the cartridge sub  68  from the upstream perforating gun  62   1 . The switch assembly  72  also includes a ground lead  78  on the side with the inlet lead  76 ; the ground lead  78  is selectively in electrical communication with the switch assembly  72  such as by the switching action provided by the circuit board  74 . Exiting the switch assembly  72 , on a side opposite the inlet lead  76 , is a supply lead  80  that is in electrical communication with a communication line  82  shown extending within the downstream perforating gun  62   2 . In an example embodiment, inlet lead  76  selectively couples with an electrical source for receiving electricity. Also exiting the switch assembly  72  are a signal lead  84  and a ground lead  86 . In an example, the leads  84 ,  86  make up a detonator connection that provides selective electrical communication between the signal assembly  72  and a detonator  88  shown set in an end of the cartridge assembly  70  adjacent the downstream perforating gun  62   2 . As illustrated in  FIG. 3 , the modular cartridge assembly  70  can be inserted within the annular cartridge sub  68  for easy assembly and removed from within the cartridge sub  68  for replacement and/or repair. 
         [0023]    When an initiating signal is received by the switch assembly  72 , the circuit board  74  operates to provide an initiating current through the signal line  84  and further allow continuity between the ground lead  86  and ground lead  78 , thereby closing a circuit through the detonator  88  for initiating the detonator  88 . As shown, an end of the detonator  88  is directed towards the detonating cord  66  within the downstream perforating gun  62   2 , so that as the pressure wave of detonation passes along the length of the detonating cord  66 , the attached shaped charges  64  will in turn initiate to create perforations in an adjacent formation (not shown). Further illustrated in the embodiment of  FIG. 3 , a collar-like connector  90  is provided on the downstream end  91  of the cartridge sub  68 . In an example, the connector  90  is formed from a conductive material and is an annular member that circumscribes the downstream end  91 . Further in the example of  FIG. 3 , the diameter of the cartridge sub  68  reduces at the downstream end  91 . When the cartridge sub  68  is connected to the downstream perforating gun  62   2 , connector  90  coaxially inserts within an annular electrical receptacle  92  shown provided in the downstream perforating gun  62   2 . The electrical receptacle  92  is electrically conductive, so that the combination of the electrical receptacle  92  and connector  90  provides an electrical coupling between the exit lead  80  and communication line  82 . The coupling thus provides a means for transferring a signal or signals between the cartridge sub  68  and the downstream perforating gun  62   2 , and along the length of the perforating system  60 . It should be pointed out that the orientation of the cartridge sub  68  and perforating guns  62   1 ,  62   2  is reversible; so that when a string of multiple guns is formed, the signal that passes along the signal lines and through the switch assembly  72  may start at the lower end of a perforating gun string and travel upwards, or initiate at the upper end of the string and travel downwards within the wellbore. 
         [0024]      FIG. 4  illustrates an example embodiment of a lower end of the perforating system  60  and with an alternate embodiment of a cartridge sub  68 A. In this example, an inlet lead  76  and ground lead  78  extend through the cartridge assembly  70 A to a switch assembly  72 . However, the exit or downstream side of the switch assembly  72  includes a single continuous signal line  84 A that terminates at a connector  90 A. The example of the connector  90 A illustrated in  FIG. 4  is a hemispherical-shaped member with a collar-like base circumscribing a cylindrical tip of the cartridge assembly  70 A. Similar to the connector  90  of  FIG. 3 , connector  90 A of  FIG. 4  is formed from an electrically conducting material. Further, in the embodiment of  FIG. 4 , the perforating system  60  is set within a wellbore  93  lined with casing  94  that is cemented within the formation  96 . In this embodiment, a bridge plug  98  is shown set within a bridge plug sub  100  to form a bridge plug setting tool mounted on the end of the cartridge sub  68 A having the connector  90 A. Optionally, some other pressure actuated device may be provided on the end of the cartridge sub  68 A. In the example of  FIG. 4 , the connector  90 A contacts an igniter (not shown) in the bridge plug sub  100  thereby providing electrical continuity between the signal line  84 A and the igniter. Delivering an electrical signal or electricity can activate the igniter for setting the bridge plug  98 . Setting the bridge plug  98  can cause it to expand from within the bridge plug sub  100  and into contact with the inner circumference of the casing  94 , thereby pressure isolating that section of the wellbore from another. 
         [0025]    In one example embodiment, the connection between the cartridge sub  68  and upstream perforating gun may be a terminal assembly made up of a rod and pin connector, where the pin connector is mounted on a free end of the rod. In this example, a bushing circumscribes a mid-portion of the rod. The pin connector is in electrical communication with connector in the sub  68  by connections that extend through the end wall of the sub  68 . Circumscribing the portion of the terminal assembly adjacent the end wall is a spring connector that is in electrical communication with another connector in the sub  68  by connections extending through the end wall. Provided at a downstream end of the cartridge sub  68  opposite the terminal assembly is a downstream connector in which the exit lead  80  is connected at an end opposite its connection to the switch assembly  72 . Coaxially projecting from the end of the cartridge sub  68  and adjacent the detonator  88  is a spring connector; the spring connector communicates with the downstream connector by connection through the end wall at the downstream end of the sub  68 . 
         [0026]    The spring connectors can provide connectivity on the upstream and downstream sides of the cartridge sub  68 . More specifically when the cartridge sub  68  is inserted within an example embodiment of a perforating string  60 , a connector sub couples to the upstream end of the cartridge sub  68  and receives the terminal assembly, within an axial bore formed through the connector sub. A receptacle is formed within the connector sub at a location set back from the entrance to the bore. The receptacle provides terminals for communication between a signal wire within the connector sub and the pin connector. As such, a signal traveling through the signal wire is transmitted through the terminals to the pin connector for delivery to the switch assembly. Also the insertion of the downstream side of the cartridge sub  68  into an end of the downstream perforating gun  62   2 . A connection assembly may be set within a bore formed in the end of the downstream perforating gun  62   2 . The connection assembly can be made up of a disc-like flange member set into close contact with the spring connector. A cylindrically-shaped base may depend coaxially from a side of the flange opposite the spring connector and set within a reduced diameter portion of the bore. Setting the base and bore diameters at about the same value anchors the connector assembly within the perforating gun  62   2 . A communication line, similar to the line  82  of  FIG. 3 , may attach to the flange thereby providing communication from the exit lead  80 , through the assembly of connectors and spring connector, flange, and into and through the perforating gun  62   2 . 
         [0027]    One example of a substantially complete perforating system  60  in accordance with the present disclosure is shown in a partial sectional view in  FIG. 5 . In this example, a string  115  of perforating guns  62   1-n  is disposed within wellbore  93  for perforating through the casing  94  and into the surrounding formation  96 . Further in this example, the cartridge sub  68  and the string are oriented so that signals received in the switch assembly  72  are from a location farther downhole; thus signals traveling in the string in a direction towards the surface. Depending on the instructions programmed into the switch assemblies  72 , the direction of perforating may also travel upwards within the bore hole  92  rather than from the top to the bottom. 
         [0028]    In one example, the string  115  is assembled by providing cartridge subs  68  with a cartridge  70  within. Each of the cartridge subs  68  can then be coupled with a perforating gun  62  so connectors  90  in their respective downstream ends  91  mate into electrical receptacles  92  as illustrated in  FIG. 3 . Connector subs  116  may optionally be provided for coupling upstream ends of the cartridge subs  68  with an upstream perforating gun. As described above, engaging the cartridge sub  68  with the downstream perforating gun provides a generally seamless way of forming an electrical connection between adjacent bodies in a perforating string. Moreover, the electrical connection occurs substantially simultaneously with coupling of the cartridge sub  68  and perforating gun  62 , so that manually forming electrical connections is unnecessary. Thus by connecting a repeating series of perforating guns  62  and cartridge subs  68 , the string  115  can be formed so that electrical communication extends substantially the length of the string  115  via contact between successive connectors  90  and receptacles  92 . 
         [0029]    Further illustrated in the example embodiment of  FIG. 5  is a wire line  132  shown suspending the string of perforating guns  62  that is controlled from a surface truck  134 . An optional pulley system  136  aligns the wire line  132  above the wellbore  93 . An attachment sub  138  is provided on an upper end of the string for attachment and electrical connection between the perforating gun  62  and wire line  132 . A power source  140  and controller  142  are schematically depicted in communication with the surface truck  134 . The power source  140  and controller  142  also may selectively connect with the wireline  132 . While shown adjacent the surface truck  134 , the power source  140  and controller  142  may instead be housed in the surface truck  134 . In one optional embodiment, the controller  142  can generate and/or send control signals to the perforating gun string  115  via the wireline  132 . Thus examples exist wherein each cartridge sub  68  in the string  115 , and all components in each cartridge sub  68 , are in signal communication with the controller  142  by virtue of the connectivity between the connectors  90  and receptacles  92 . Similarly, electricity from the power source  140  can be delivered throughout the perforating string  115  and components therein for initiating detonation of the detonators  88  and bridge plug  98 . 
         [0030]    The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, the signals may include instructions for selective operation of the switch assemblies, may include electricity, or may be in the form of a pressure wave within a detonation cord. Optionally, instructions may be provided in the switch assemblies, either by storing the instructions in hardware, such as the circuit boards, or by signals traveling in the perforating string. Moreover, the connection embodiments described above may be used for connecting to any ballistic device in a downhole string. Examples include release tools, multiple backoff shots, firing heads, redundant firing heads, severing tools, setting tools, combinations thereof, and the like. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.

Summary:
A cartridge assembly for use with a perforating system having a contact terminal that connects to a perforating signal line when inserted into a receptacle end of a perforating gun. A detonator may be included in an end of the cartridge assembly for initiating a detonating cord in the perforating gun. The cartridge assembly is a modular unit that replaces the manual connections made when assembling a string of perforating guns. The cartridge assembly may optionally include a controller switch for controlling current flow through the cartridge assembly.