Patent Publication Number: US-2023142907-A1

Title: Frangible electrical contact for a perforating gun system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of U.S. provisional patent application Ser. No. 63/277,414 filed Nov. 9, 2021, and entitled “Frangible Electrical Contact for a Perforating Gun System,” which is hereby incorporated herein by reference in its entirety for all purposes. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     Hydrocarbons may be produced by drilling a wellbore into a subterranean earthen formation to provide fluid conductivity between the wellbore and a subterranean hydrocarbon bearing reservoir contained in the earthen formation. In some applications, the wellbore may be supported by a tubular casing string (also referred to simply as “casing”) which extends from the surface to a bottom or toe of the wellbore. Cement is typically pumped into the annular interface formed between a sidewall of the wellbore and an exterior of the casing string to secure and seal the casing string to the sidewall of the wellbore. In this arrangement, the casing string is then perforated at one or more desired locations within the wellbore. For example, the casing string may be perforated at a plurality of separate locations to provide fluid communication between the target hydrocarbon production zone and a central passage of the casing string. 
     Typically, the casing string is perforated by a perforating gun system including a tool string that is deployed along a wireline suspended from the surface. The tool string of the perforating gun system includes one or more perforating guns each including explosive charges but include other components such as to orient the explosive charges of the perforating guns and to control the detonation those charges. Often, one of the components for controlling the detonation is an electrical contact positioned at either end of the given perforating gun of the perforating gun system to make electrical contact with other components of the tool string. When the charges of the perforating gun are detonated, an intense pressure pulse and consequential violence and vibration is generated within each perforating gun which typically damages or destroys much of the internal components of the detonated perforating gun. Those damaged and destroyed components are further knocked around within the perforating gun by subsequent blasts of other perforating guns of the tool string. 
     In rare instances, the explosive forces generated by the detonation of the explosive charges of a perforating gun have dislodged an electrical connector of the perforating gun such that the connector projects partly into the annulus between the exterior of the perforating gun and the inside of the casing resulting in the tool string becoming jammed or caught within the casing string in which the tool string is positioned. It may be understood that having a tool string stuck in a wellbore is a potentially big, expensive, and embarrassing problem. Particularly, the maximum tension that the wireline may apply to the tool string to retract it from the wellbore is generally limited by the rated strength of the wireline cable. In such a scenario with a tool string stuck within a wellbore, the wireline operator has the means to release the wireline cable from the tool string when the tool string cannot be dislodged by recurring pushes and pulls by the cable along with intermittent applications of hydraulic pressure within the wellbore. Once the wireline operator has released from the tool string, a specialized rig is typically called to the wellsite to fish out the stuck tool string. These specialized fishing rigs are often expensive and the resulting downtime at the wellsite waiting for the wellbore to become accessible again can add significant expense to the plug-and-perf operation. 
     Increased reliability of tool strings and perforating guns and reduced risks for getting stuck in wellbores will always be valued in the industry. 
     SUMMARY 
     An embodiment of a perforating gun deployable in a wellbore as part of a tool string comprises an outer housing comprised of a generally tubular wall structure having a pair of opposed longitudinal ends and a central passage extending between the pair of longitudinal ends; a charge carrier assembly received in the central passage of the outer housing and comprising a tubular charge carrier having a pair of opposed longitudinal ends and at least one radially oriented receptacle configured to receive a combustive shaped charge; an initiator assembly, the initiator assembly including a detonator and an electrical switch configured to detonate the detonator in response to receiving a firing signal; and an electrical connector positioned in the central passage of the outer housing and electrically connected to the initiator assembly, the electrical connector comprising an electrical contact including a frangible conductor rod, the frangible conductor rod having a shear strength of 1,500 pound-force (lbf) or less. In some embodiments, the shear strength of the frangible conductor rod is 750 lbf or less. In some embodiments, the shear strength of the frangible conductor rod is 300 lbf or less. In certain embodiments, the electrical contact comprises an electrically insulating overmolded body surrounding the frangible conductor rod. In certain embodiments, the overmolded body has an axial length which is more than half of the axial length of the frangible conductor rod. In some embodiments, the electrical connector comprises a biasing member and the overmolded body comprises an enlarged diameter annular flange contacted by the biasing member to bias the electrical contact. In some embodiments, the electrical contact further comprises a protective boot positioned around one of the longitudinal ends of the frangible conductor rod. In certain embodiments, the charge carrier assembly comprises a pair of endplates each comprising a central passage and coupled to the longitudinal ends of the tubular charge carrier, wherein the electrical connector is received in the central passage of each of the endplates. In some embodiments, the frangible conductor rod comprises a pair of opposed longitudinal ends, a peripheral surface extending between the pair of longitudinal ends, and the one or more frangible features in the form of one or more frangible grooves formed in the outer surface, wherein at least one of the one or more frangible grooves defines a minimum cross-sectional area of the frangible conductor rod. In certain embodiments, the frangible conductor rod comprises a pair of opposed longitudinal ends, an outer surface extending between the pair of longitudinal ends, and the one or more frangible features in the form of one or more frangible grooves formed in the outer surface and spaced along a majority of the axial length of the frangible conductor rod. 
     An embodiment of a perforating gun deployable in a wellbore as part of a tool string comprises an outer housing comprised of a generally tubular wall structure having a pair of opposed longitudinal ends and a central passage extending between the pair of longitudinal ends; a charge carrier assembly received in the central passage of the outer housing and comprising a tubular charge carrier having a pair of opposed longitudinal ends and at least one radially oriented receptacle configured to receive a combustive shaped charge; an initiator assembly, the initiator assembly including a detonator and an electrical switch configured to detonate the detonator in response to receiving a firing signal; and an electrical connector receivable in the central passage of the outer housing and electrically connected to the initiator assembly, the electrical connector comprising a frangible conductor rod comprising an elongated body with a pair of opposed longitudinal ends, a peripheral surface extending between the pair of longitudinal ends, and one or more frangible grooves formed in the peripheral surface, wherein at least one of the one or more frangible grooves defines a minimum cross-sectional area of the frangible conductor rod and a combined axial length of the one or more frangible grooves is at least 2% of the axial length of the frangible conductor rod. In some embodiments, the frangible conductor rod comprises a plurality of frangible grooves. In some embodiments, wherein the frangible conductor rod has a shear strength of 1,500 pound-force (lbf) or less. In certain embodiments, the conductor rod extends from the pair of longitudinal ends to a center of the frangible conductor rod, and at least one of the one or more frangible grooves is located on a first side of the frangible conductor rod extending from a first of the pair of longitudinal ends to the center of the frangible conductor rod, and at least one of the one or more frangible grooves is located on a second side of the frangible conductor rod extending from a second of the pair of longitudinal ends to the center of the frangible conductor rod. In certain embodiments, the electrical contact comprises an electrically insulating overmolded body surrounding the frangible conductor rod. In some embodiments, the electrical connector comprises a biasing member and the overmolded body comprises an annular flange contacted by the biasing member to bias the electrical contact. In some embodiments, the electrical contact further comprises a protective boot positioned around one of the longitudinal ends of the frangible conductor rod. In some embodiments, the charge carrier assembly comprises a pair of endplates each comprising a central passage and coupled to the longitudinal ends of the tubular charge carrier, wherein the electrical connector is received in the central passage of one of the pair of endplates. 
     An embodiment of a perforating gun deployable in a wellbore as part of a tool string comprises an outer housing comprised of a generally tubular wall structure having a pair of opposed longitudinal ends and a central passage extending between the pair of longitudinal ends; a charge carrier assembly received in the central passage of the outer housing and comprising a tubular charge carrier having a pair of opposed longitudinal ends and at least one radially oriented receptacle configured to receive a combustive shaped charge; an, the initiator assembly including a detonator and an electrical switch configured to detonate the detonator in response to receiving a firing signal; and an electrical connector receivable in the central passage of the outer housing and electrically connected to the initiator assembly, the electrical connector comprising a frangible conductor rod comprising an elongate body, a pair of opposed longitudinal ends, a peripheral surface extending between the pair of longitudinal ends, and a plurality of frangible grooves formed in the peripheral surface and spaced along a majority of the axial length of the frangible conductor rod. In some embodiments, the conductor rod extends from the pair of longitudinal ends to a center of the frangible conductor rod, and at least one of the plurality of frangible grooves is located on a first side of the frangible conductor rod extending from a first of the pair of longitudinal ends to the center of the frangible conductor rod, and at least one of the plurality of frangible grooves is located on a second side of the frangible conductor rod extending from a second of the pair of longitudinal ends to the center of the frangible conductor rod. In some embodiments, the electrical contact comprises an electrically insulating overmolded body surrounding the frangible conductor rod. In certain embodiments, the electrical connector comprises a biasing member and the overmolded body comprises an annular flange contacted by the biasing member to bias the electrical contact. In certain embodiments, the electrical contact further comprises a protective boot positioned around one of the longitudinal ends of the frangible conductor rod. In some embodiments, the charge carrier assembly comprises a pair of endplates each comprising a central passage and coupled to the longitudinal ends of the tubular charge carrier, wherein the electrical connector is received in the central passage of one of the pair of endplates. 
     An embodiment of a method of providing a perforating gun deployable in a wellbore as part of a tool string comprises (a) forming an electrical connector of the perforating gun comprising an electrical contact including a frangible conductor rod whereby the frangible conductor rod is configured to yield in response to an application of a shear load to the electrical contact that is equal to or greater than a predefined shear load, (b) coupling the electrical connector with an initiator assembly of the perforating gun that comprises an electrical switch, (c) coupling the electrical connector with a charge carrier of the perforating gun having at least one radially oriented receptacle configured to receive an explosive charge detonatable by the initiator assembly when ballistically coupled to the initiator assembly, and (d) positioning the charge carrier in a central passage of an outer housing of the perforating gun. In some embodiments, (a) comprises forming one or more voids along an outer surface of a conductor rod of the electrical contact to reduce the shear strength of the electrical contact. In certain embodiments, the predefined shear load is less than a maximum shear load imposable by a surface wireline unit connected to the tool string. In certain embodiments, the method further comprises (e) deploying the perforating gun down into the wellbore with the tool string attached to the wireline unit. 
     Embodiments described herein comprise a combination of features and characteristics intended to address various shortcomings associated with certain prior devices, systems, and methods. The foregoing has outlined rather broadly the features and technical characteristics of the disclosed embodiments in order that the detailed description that follows may be better understood. The various characteristics and features described above, as well as others, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. It should be appreciated that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes as the disclosed embodiments. It should also be realized that such equivalent constructions do not depart from the spirit and scope of the principles disclosed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of exemplary embodiments of the disclosure, reference will now be made to the accompanying drawings in which: 
         FIG.  1    is a schematic, view of an embodiment of a system for completing a subterranean well; 
         FIG.  2    is a schematic side cross-sectional view of an embodiment of a perforating gun of the system of  FIG.  1   ; 
         FIG.  3    is an enlarged side view of an embodiment of a rod-shaped electrical contact of the perforating gun of  FIG.  2   ; and 
         FIG.  4    is an enlarged side cross-sectional view of the rod-shaped electrical contact of  FIG.  3   ; 
         FIG.  5    is a perspective view of an embodiment of a frangible conductor rod of the rod-shaped electrical contact of  FIG.  3   ; and 
         FIG.  6    is an additional enlarged side view comparable to  FIG.  2    showing the perforating gun and casing after the perforating gun has been fired. 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness. 
     In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. Any reference to up or down in the description and the claims is made for purposes of clarity, with “up”, “upper”, “upwardly”, “uphole”, or “upstream” meaning toward the surface of the borehole and with “down”, “lower”, “downwardly”, “downhole”, or “downstream” meaning toward the terminal end of the borehole, regardless of the borehole orientation. Further, the term “fluid,” as used herein, is intended to encompass both fluids and gasses. 
     As described above, in rare instances, a perforating gun of a tool string may become stuck downhole as a result of a rod-shaped electrical contact of a damaged perforating gun being partially or fully ejected from the damaged perforating gun. For example, the rod-shaped electrical contact may catch in an opening in the casing (e.g., a perf opening opened by the detonation of the perforating gun) or a joint or other irregularity along the inner surface of the casing string while also, at the same time, being caught somewhere along the tool string. As a result, the damaged perforating gun becomes stuck within the casing string, potentially requiring the wireline system from which the tool string is suspended to break off from the tool sting and gain removal of the tool string from the wellbore via expensive, specialized equipment delaying the completion of the wellbore and substantially increasing the cost for completing the wellbore. 
     Accordingly, embodiments of frangible electrical contacts for perforating guns are described herein which shear or otherwise yield in the event of the rod-shaped electrical contact jamming or snagging within a casing string. Particularly, the frangible electrical contact may be rod-shaped and may include one or more frangible features intended to reduce the bending strength and shear strength of the rod-shaped electrical contact. Having a reduced shear strength, the tension which may be applied to the wireline connected to the tool string by surface equipment of the wireline system may be sufficient to break apart the jammed rod-shaped electrical contact and thereby dislodge or free the tool string without having to release the wireline from the tool string. In this manner, the freed tool string may be retracted to the surface without the need for performing an expensive and time-consuming removal operation of the once stuck tool string. In some embodiments, the frangible features of the rod-shaped electrical contacts described herein take the form of frangible grooves formed in an outer surface of a frangible conductor rod of the rod-shaped electrical contact. The frangible grooves may define one or more minimum cross-sectional areas of the frangible conductor rod which deliberately weaken the conductor rod to bending and shear forces that may be applied thereto by a wireline system in the event of the frangible conductor rod becoming stuck in the wellbore. 
     Referring now to  FIG.  1   , a hydrocarbon production location or wellsite generally indicated by the arrow  10  is shown with wellbore  13  extending into a subterranean earthen formation  17  with a generally horizontal segment arranged in a target area of the earthen formation  17  that is anticipated to contain commercial quantities of hydrocarbons. Wellbore  13  is a cased wellbore including a casing string  12  secured and sealed to an inner surface or sidewall of the wellbore  13  using cement (not shown). The casing string  12  generally includes a plurality of tubular segments coupled together via a plurality of casing collars. 
     In this exemplary embodiment, located at the wellsite  10  is a surface assembly  11  positioned at the surface  5  with a tool string  20  deployed into a subterranean wellbore  13 . Surface assembly  11  may comprise any suitable surface equipment for drilling, completing, and/or operating well  20  and may include, in some embodiments, derricks, structures, pumps, wireline reel, wireline injector, electrical/mechanical well control components, etc. In this exemplary embodiment, among other equipment, surface assembly  11  includes a control system or firing panel  15  and a surface wireline unit or winch  16 , each shown schematically in  FIG.  1   . Tool string  20  is suspended within wellbore  13  from a flexible wireline  22  that extends from surface assembly  11  located at the surface  5 . Wireline  22  generally comprises an armored cable and includes at least one electrical conductor for transmitting power and electrical signals between tool string  20  and a control system or firing panel  15  of the surface assembly  11  located at the surface  5 . 
     Tool string  20  is generally configured to perforate the casing string  12  to provide for fluid communication between the earthen formation  17  and the wellbore  13  at one or more predetermined locations along the wellbore  13  and to thereby allow for the hydraulic fracturing of the formation  17  through the perforations formed in the casing string  12  and the subsequent production of hydrocarbons from the formation  17  into the wellbore  13  through the perforations. 
     In this exemplary embodiment, tool string  20  generally includes, among other components, a cable head  24  at an uphole end of the tool string  20 , a casing collar locator  26 , a direct connect sub  28 , a perforating tool or gun  100 , a setting tool initiator or firing head  40 , a setting tool  50 , and a downhole or frac plug  60  located at a downhole end of the tool string  20 . It may be understood that in other embodiments the configuration of tool string  20  may vary from that shown in  FIG.  1   . For example, in other embodiments, tool string  20  may include a plurality of the perforating guns  100 , one or more tandem subs connected between adjoining pairs of perforating guns  100 , and/or other equipment. The one or more tandem subs may provide a pressure barrier preventing a first detonated perforating gun from inadvertently destroying or detonating a second perforating gun of the tool string  20  that is located uphole from the first detonated perforating gun. It may also be understood that tool string  20  may include other additional components not shown in  FIG.  1   . 
     In this exemplary embodiment, cable head  24  is the uppermost component of tool string  20  and includes an electrical connector for providing electrical signal and power communication between the wireline  22  and the other components of tool string  20  downhole from the cable head  24  all the way to the downhole plug  60 . 
     Turning to  FIG.  2   , an exemplary perforating gun  100  is shown which includes one or more shaped charges  180  detonatable in response to the transmission of one or more electrical signals conveyed by the wireline  22  from the firing panel  15  at the surface  5 . Upon detonation, the one or more shaped charges  180  of perforating gun  100  produce one or more corresponding explosive jets (not shown in  FIG.  2   ) directed radially outwards and away from the perforating gun  100  and against casing string  12 . 
     Perforating gun  100  has a central or longitudinal axis  105  and includes an outer carrier or housing  102 , a charge carrier assembly  142  housed within the outer housing  102 , a plurality of explosive shaped charges  180 , and an initiator assembly  190  for selectably detonating the shaped charges  180 . Outer housing  102  is generally tubular in shape including a pair of longitudinally opposite ends  101 , a central bore or passage  103  defined by a generally cylindrical inner surface  104  extending between a pair of longitudinally opposite ends  101  of outer housing  102 , and a generally cylindrical outer surface  106  also extending between ends  101 . In this exemplary embodiment, a plurality of scallops or indentations  108  are formed in the outer surface  106  of outer housing  102 . Each scallop  108  defines a relatively thin-walled section of outer housing  102 . As will be described further herein, scallops  108  are intended to break-apart during detonation of the perforating gun  100  such that burrs are not formed along the periphery of the outer housing  102  which could catch against the casing string  12 . Additionally, the break-up of scallops  108  may permit the explosive jets generated by shaped charges  180  to more easily penetrate and punch through the outer housing  102 . In other embodiments, outer housing  102  may include a plurality of annular grooves or ring-like channels or indentations formed in outer surface  106  around the periphery of the housing  102  in lieu of scallops  108 . The annular grooves may forego the requirement of angularly aligning the shaped charges  180  of perforating gun  100  with scallops  108 . In still other embodiments, outer housing  102  may not include either scallops or annular grooves. Outer housing  102  may additionally include connectors (e.g., threaded connectors) at the ends  103  thereof for coupling with the direct connect sub  28  and firing head  40  (hidden from view in  FIG.  2   ), respectively, of tool string  20 . For example, outer housing  102  may include a pair of threaded connectors formed on the inner surface  104  thereof at ends  101 . Alternatively, outer housing  102  may include a pair of threaded connectors formed on the outer surface  106  thereof at one of or both ends  101 . 
     Charge carrier assembly  140  of perforating gun  100  is slidably received within the central passage  103  of outer housing  102 . In this exemplary embodiment, charge carrier assembly  140  generally includes a generally tubular charge carrier  142  and a pair of endplates  150 . Charge carrier  142  includes a pair of longitudinally opposed ends  143  and a central bore or passage  144  extending between the ends  143 . Charge carrier  142  may be cylindrical in shape but alternatively could comprise a variety of shapes and configurations including configurations that are not tubular and thus not including a central passage. In this exemplary embodiment, charge carrier  142  additionally includes a plurality of radial openings  146  which each receive a corresponding shaped charge  180 . Each shaped charge  180  includes a combustive or explosive material housed internally within a charge housing of the shaped charge  180 . While in this exemplary embodiment perforating gun  100  includes a plurality of openings  146  and shaped charges  180 , in other embodiments, perforating gun  100  may include only a single shaped charge  180  in a single corresponding radial opening  146  formed in the charge carrier  142 . 
     Endplates  150  of charge carrier assembly  140  are coupled to the ends  143  of charge carrier  142 . In this exemplary embodiment, each endplate  150  comprises a central passage  152  which houses a corresponding electrical connector  160 . Electrical connectors  160  electrically connect with corresponding electrical connectors of the direct connect  28  and firing head  40 , respectively, of tool string  20  to provide signal communication between charge carrier assembly  140  and the wireline  22 . In this exemplary embodiment, each electrical connector  160  generally includes a biasing member or element  162  and a rod-shaped electrical contact  200  biased by the biasing element  162 . The biasing element  162  of each electrical connector  160  is coupled to the rod-shaped electrical contact  200  and is configured to bias contact  200  outwardly from endplate  150  along the central axis  105  of perforating gun  100 . 
     In this exemplary embodiment, the rod-shaped electrical contacts  200  of the pair of electrical connectors  160  each project outwardly from their respective endplates  150 , thereby defining the maximum axial length of the charge carrier assembly  140 . In other embodiments, each electrical connector  160  may not include biasing element  162  and instead a counterpart contact may be biased back into contact with the rod-shaped electrical contact  200 . The rod-shaped electrical contacts  200  are typically received in concave (e.g., dish-shaped) receptacles of the corresponding electrical contact engaging in a male/female configuration with adjacent components of tool string  20  such as the direct connect  28  and firing head  40  to thereby form an electrical connection between perforating gun  100  and both the direct connect  28  and firing head  40 . Alternatively, electrical contacts  200  may engage planar surfaces of the corresponding electrical contacts rather than concave surfaces in an end-to-end arrangement. As will be described further herein, the rod-shaped electrical contact  200  of each electrical connector  160  has a predefined, intentionally frangible configuration configured to readily yield or break apart should the contact  200  become jammed or caught between the casing string  12  following the detonation of perforating gun  100 . 
     The initiator assembly  190  of perforating gun  100  controls the detonation of the shaped charges  180  of perforating gun  100  in response to receiving one or more electrical signals from the firing panel  15  of surface assembly  11 . While initiator assembly  190  is shown within outer housing  102 , in other embodiments, it may be located external housing  102  such as within an adjacently positioned tandem sub. Additionally, in this exemplary embodiment, initiator assembly  190  generally includes an electrical switch  192  and a detonator  194  electrically connected (e.g., wired, soldered, etc.) to the switch  192 . Switch  192  is connected to each of the electrical connectors  160  of charge carrier assembly  140  via a pair of electrical conduits or cables  196  which extend between switch  192  and electrical connectors  160 . 
     The electrical switch  192  of initiator assembly  190  is configured to selectably energize and thereby detonate the detonator  194  in response to receiving an appropriate firing signal from the firing panel  15 . In some embodiments, electrical switch  192  may comprise one or more diodes. In other embodiments, electrical switch  192  may comprise a digital switch including one or more processors and one or more memory devices coupled to the processor and which are configured to detonate the detonator  194  in response to receiving a firing signal from the firing panel  15  which is specifically addressed to the electrical switch  192 . For example, electrical switch  192  may detonate the detonator  194  in response to receiving a firing signal from the firing panel  15  at the surface  5  which includes an address which matches an associated address stored in the memory of electrical switch  192 . In this exemplary embodiment, detonator  194  is ballistically coupled to each shaped charge  180  by one or more detonator or “det” cords (not shown in  FIG.  2   ). However, in other embodiments, detonator  194  may alternatively be directly ballistically connected (without an intervening det cord) to one or more of the shaped charges  180 . 
     Referring now to  FIGS.  3 - 5   , an embodiment of a frangible, rod-shaped electrical contact  200  of perforating gun  100  is shown. In this exemplary embodiment, rod-shaped electrical contact generally indicated by the arrow  200  includes an inner, frangible metal conductor rod  230  and an outer insulating overmolded body  202  formed on the rod  230  along with an optional, protective boot  220  slipped over one end of the rod  230 . A principal design point for the electrical contact  200  is to be strong enough to serve as an electrical contact from manufacturing and assembly at the factory through the vibrations and other forces imposed while shipping the perforating gun  100  (including the electrical contact  200 ) to the wellsite  10 , running the assembly downhole into wellbore  13 , and during the detonation of the perforating gun  100 , but frangible enough to yield or break if dislodged into a bending or shear orientation or arrangement. As installed in the perforating gun  100 , a majority of the forces encountered by electrical contact  200  should be compressive with little or no bending force or shear force applied to the electrical contact  200 . And to the extent that any substantial bending or shear force were ever to be applied to the electrical contact  200 , the structure and physical integrity of the perforating gun  100  itself will likely have been compromised as well so the design of the electrical contact  200  is generally such that the contact  200  will yield and breakaway well within the forces that may be imposed on the tool string  20  while the wireline  22  is still attached. 
     Noting that the electrical contact  200  is comprised of two or three elements, depending on whether the boot  220  is included, the combined strength of these elements is generally what matters if the electrical connection ends up in an inconvenient place or orientation. Generally, most of the physical strength or robustness comes from the conductor rod  230 . As such, the frangible design of the electrical contact  200  is most revealed in the design of the conductor rod  230 . Frangible conductor rod  230  is shown as male contact in  FIGS.  3 - 5    although the configuration at a distal end  233  of the conductor rod  230  may alternatively have a cup shape to be deemed a female connection. The frangible nature of the design of conductor rod  230  is less about the maleness or femaleness of the actual connection other than the rod  200  being elongate and thus capable of catching in the wellbore and causing a stuck tool string within the wellbore. 
     Additionally, the wireline  22  has a predefined yield strength, and a working strength that may be approximately between 50% and 60% of the yield strength of the wireline  22  depending on the given application. A tension applied to the wireline  22  by the wireline winch  16  of surface assembly  11  that is equal to or less than the working strength (e.g., equal to or less than 50% of the yield strength of the physical cable comprising the wireline  22 ) will generally not damage or permanently deform the wireline  22 . In the event of the electrical contact  200  of perforating gun  100  becoming jammed or caught in casing string  12 , electrical contact  200  is configured to shear or otherwise yield to free the tool string  20  in response to applying a tension to the wireline  22  by wireline winch  16  that is equal to or less than the working strength of wireline  22 . It may be understood that typically the force applied to a jammed electrical contact  200  by the application of tension to wireline  22  will be a combination of bending and shear loads, and thus the shear strength of electrical contact  200  is less than the working strength of wireline  22  to ensure that the combined bending and shear loads applied to the jammed electrical contact  200  is sufficient to shear or otherwise yield the electrical contact  200  and thereby free the stuck tool string  20  such that the tool string  20  may be successfully retrieved to the surface  5  using the wireline  22 . It should be understood that a maximum shear load imposable by wireline winch  16  on electrical contact  200  is greater than the designed shear strength to which the electrical contact  200  is configured to yield such that an inadvertently displaced electrical contact  200  that has become wedged or otherwise stuck against the casing string  12  after the shaped charges  180  have been fired will not prevent recovery of the tool string  20 . In other words, the wireline operator will have the power required to shear through the stuck electrical contact  200  at one or more locations along the length of the electrical contact  200  and thereby continue with operations as normal rather than be forced to abandon the tool string  20  as stuck in the wellbore  13 . 
     As an example, the wireline  22  may have a yield strength of 11,000 pound-force (lbf) and a corresponding working strength of 5,500 lbf. In some embodiments, conductor rod  230  of electrical contact  200  has a shear strength of 1,500 lbf or less, substantially less than the 5,500 lbf working strength of wireline  22 . In other embodiments, conductor rod  230  has a shear strength of approximately between 1,000 lbf and 200 lbf such as, for example, 750 lbf, 500 lbf, 350 lbf, 300 lbf, and 250 lbf. It may be understood that the working and yield strengths of wireline  22  and the associated shear string of conductor rod  230  may vary substantially depending on the application. 
     In this exemplary embodiment, conductor rod  230  is generally long and relatively thin with a longitudinal first or inner end  231  (located at the left of  FIGS.  3 - 5   ) and a second or distal end  233  longitudinally opposed (located on the right in  FIGS.  3 - 5   ) to the inner end  231 . The conductor rod  230  further has a generally cylindrical body with an external, peripheral surface marked principally by segments  237  separated by necked down frangible grooves or voids  238  spaced along the length of conductor rod  230 . Distal end  233  of conductor rod  230  in this exemplary embodiment is arranged to be inserted into a complimentary socket  272  of electrical contact  270  to form an electrical connection therebetween. In other embodiments, instead of being received in a socket, distal end  233  of conductor rod  230  may contact a flat surface of electrical contact  270  in an end-to-end arrangement. In still other embodiments, distal end  233  of conductor rod  230  may comprise a female socket configured to receive a male end of the electrical contact  270 . Frangible conductor rod  230  comprises an electrically conductive material such as brass, aluminum, copper or other suitable electrically conductive materials. Additionally, while this exemplary embodiment shows frangible conductor rod  230  as being generally cylindrical, it should be understood that the shape and configuration of conductor rod  230  may vary in other embodiments without departing from the essential purpose and function. 
     Insulating body  202  of rod-shaped electrical contact  200  is arranged to cover a majority of the length of the conductor rod  230  with a plastic or other durable and electrically insulating material. In this exemplary embodiment, insulating body  202  may be overmolded onto the inner contact  210  and is formed from a polymer such as, for example, a synthetic polymer (e.g., Nylon) while many other options are readily available. However, it should be understood that while outer body  202  is sufficiently durable to withstand exposure to a wellbore environment, insulating body  202  is not configured to substantially enhance the bending or shear strength provided by the conductor rod  230  of the electrical contact  200 , although some marginal strengthening may be unavoidable. 
     Insulating body  202  generally extends along the conductor rod  230  exposing portions at each of the ends  231  and  233  thereof which externally project from the insulating body  202 . In this exemplary embodiment, insulating body  202  includes a first or inner end  203 , a second or outer end  205  longitudinally opposite inner end  203 , and a generally cylindrical outer surface  204  having a collar section  206  located generally in the longitudinal center of insulating body  202  and that has an enlarged diameter with respect to the rest of the insulating body  202 . The collar section  206  of outer surface  204  may be used in conjunction with a spring biasing system (not shown in  FIGS.  3 - 5   ) to better secure the physical and electrical connection of the conductor rod  230  to the female contact  270 . Additionally, insulating body  202  is formed as a tubular structure in this exemplary embodiment but it should be understood that the shape and configuration of insulating body  202  may take other forms. 
     The insulating body  202  of rod-shaped electrical contact  200  is generally configured to prevent or inhibit the conductor rod  230  from coming into direct electrical contact with another conductive member of perforating gun  100  such as charge carrier  142 . In other words, outer body  202  reduces the likelihood of rod-shaped electrical contact  200  shorting out while the tool string  20  is in any part of its operation. In some embodiments, a ratio of the axial length  207  (shown in  FIG.  3   ) of outer body  202  to the maximum axial length  235  (shown in  FIG.  4   ) of conductor rod  230  is approximately between 0.5:1 to 0.9:1; however, in other embodiments, the ratio of the axial lengths of outer body  202  and frangible conductor rod  230  may vary. 
     In this exemplary embodiment, protective boot  220  is provided near the distal end  233  of conductor rod  230  having generally tube shape to fit over the distal end  233 . As shown, the protective boot further  220  covers outer end  205  of the outer body  202  of rod-shaped electrical contact  200 . Protective boot  220  is formed from an electrically insulating material but potentially a relatively more pliable material to abut the counterpart connector  270  to shield the interface between distal end  233  of conductor rod  230  and a cup  272  of the counterpart connector  270  from having dust, shavings, contaminants or other debris from interfering with or compromising the electrical conductivity therebetween. For example, protective boot  220  may be formed from a polymer such as silicone other types of pliable electrically insulating materials. Protective boot  220  may be manually slid over the outer end  205  of outer body  202  until a terminal end of boot  220  abuts shoulder  208  of outer body  202  during the initial assembly of charge carrier assembly  140  or at a wellsite prior to the deployment of the tool string  20  into the wellbore  13 . 
     Referring still to  FIGS.  3 - 5   , in this exemplary embodiment, a retention groove  236  is formed in the outer surface  234  of frangible conductor rod  230  near the inner end  231  thereof and which is suited for connecting one of the electrical cables  196  of perforating gun  100 . Additionally, in this exemplary embodiment, the plurality of annular frangible grooves  238  of conductor rod  230  are formed or cut into the outer surface  234  of frangible conductor rod  230 . Although in this exemplary embodiment the frangible conductor rod  230  comprises frangible grooves  238 , in other suitable embodiments, the conductor rod  230  may have different features that are typically configured to yield to shear forces or bending forces. In some embodiments, the number and configuration of frangible grooves  238  is selected, or the conductor rod  230  is otherwise configured (e.g., without any grooves but including another feature affecting the shear strength of conductor rod  230 ), so as to provide the conductor rod  230  with a predefined and desired shear strength which is associated with the yield and working strengths of the wireline (e.g., wireline  22 ) from which the perforating gun  100  (comprising rod-shaped electrical contact  200 ) is to be deployed from. 
     In this exemplary embodiment, the frangible grooves  238  are spaced along the axial length of frangible conductor rod  230  between the inner end  231  and outer end  233  thereof such that any bending resistant segment between the grooves  238  that might hang up tool string  20  is relatively short (relative to the maximum length  235  of conductor rod  230 ) and will less likely prove to be a long enduring catch for the tool string  20 . In some embodiments, a ratio of a maximum length of a given segment  237  formed between a pair of adjacent grooves  238  to the maximum length  235  of conductor rod  230  is approximately 1:2 or less. In some embodiments, the ratio of the maximum length of a given segment  237  formed between a pair of adjacent grooves  238  to the maximum length  235  of conductor rod  230  is 1:4 or less. n certain embodiments, the ratio of the maximum length of a given segment  237  formed between a pair of adjacent grooves  238  to the maximum length  235  of conductor rod  230  is 1:6 or less. Additionally, the grooves  238  are spaced at intervals along a majority of the axial length of conductor rod  230  extending fully around the circumference of the conductor rod  230 . However, rather than circumferential grooves as with this exemplary embodiment, the grooves may alternatively take the form of notches or other voids formed in the periphery of conductor rod  230  that do not extend fully around the rod  230 , but still create designed yield points that can be positioned on opposing sides of conductor rod  230 . 
     Each frangible groove  238  reduces a cross-sectional area of the frangible conductor rod  230  along the axial length of the frangible groove  238 , thereby weakening the frangible conductor rod  230  in shear and in bending at the location of the frangible groove  238 . Particularly, in this exemplary embodiment, one or more of the frangible grooves  238  define a minimum cross-sectional area of the frangible conductor rod  230 . Given that frangible grooves  238  are spread out across the length of frangible conductor rod  230  a number of stress risers or locations of reduced shear strength are correspondingly spread at generally regular intervals on outer surface  234  along the length of frangible conductor rod  230 . In some embodiments, frangible grooves  238  may be cut into the outer surface  234  of frangible conductor rod  230  during the manufacturing of rod  230 . Alternatively, grooves  238  as well as conductor rod  230  itself may be formed through other processes such as through molding or additive manufacturing processes. 
     While in this exemplary embodiment a relatively large number of frangible grooves  238  (e.g., eleven frangible grooves  238 ) are formed in the outer surface  234  of frangible conductor rod  230 , in other embodiments, only a small number (e.g., two or three, etc.) or a single frangible groove  238  may be formed in outer surface  234 . In still other embodiments, conductor rod  230  may be of a single diameter that is small enough to shear or otherwise yield in response to the application of a tension force to the wireline  22  by wireline winch  16  that is less than a yield strength of the wireline  22 . However, generally the fewer frangible grooves  238  conductor rod  20  may have the greater the axial length of each frangible grooves  238  will be to ensure the conductor rod  230  is configured to yield at an equivalent shear or bending load. In each case, the combined axial length of the one or more frangible grooves  238  formed in outer surface  234  would comprise a significant share of the total axial length of frangible conductor rod  230 . For example, in some embodiments, a ratio of the combined or cumulative axial length of the one or more frangible grooves  238  to the maximum axial length  235  of conductor rod  230  ranges between 0.1:1 to 0.5:1; however, it may be understood that the ratio of the combined axial length of the one or more frangible grooves  238  and the axial length  235  of the frangible conductor rod  230  may vary in other embodiments. 
     As described above, the frangible grooves  238  of frangible conductor rod  230  weaken the frangible conductor rod  230  in shear and in bending. In other words, frangible grooves  238  are configured to reduce the amount of shear stress and bending force necessary to shear the rod-shaped electrical contact  200  into two separate pieces or bend the contact to allow the tool string to be withdrawn by the wireline  22 . For example, applying a sufficiently great shear stress to the rod-shaped electrical contact  200  will likely result in the rod-shaped electrical contact  200  breaking apart along one of the frangible grooves  238  of frangible conductor rod  230 . The presence of frangible grooves  238  therefore reduces the shear stress sufficient to result in such breaking apart of the rod-shaped electrical contact  200 , which may be useful in dislodging a perforating gun  100  which has become stuck downhole. Moreover, the degree of weakening may be predefined such that the electrical contact  200  itself is configured to yield in response to a predefined tension load being applied to the wireline  22  by wireline winch  16 . 
     As an example, and referring now to  FIG.  6   , this Figure illustrates an exemplary instance in which perforating gun  100  has been detonated to form perforations  18  in casing string  12  and in which, as a result of the detonation of perforating gun  100 , one of the rod-shaped electrical contacts  200  thereof has been partially ejected through an opening  109  (within one of the scallops  108 ) formed in the outer housing  102  of perforating gun  100  as a result of the detonation thereof. As shown in  FIG.  6   , a rod-shaped electrical contact without a frangible design like that of electrical contact  200  would result in the perforating gun  100  becoming undesirably locked to the casing string  12  due to the contact becoming wedged against and between the opening  109  and the slightly offset perforation  18  in the casing string  12 . 
     Conversely, with the frangible design of electrical contact  200  shown in  FIG.  6    (contact  200  is shown schematically in  FIG.  6   ), tension applied by wireline  22  from the surface assembly  11  is sufficient to cause the electrical contact  200  to yield by bending or potentially breaking in half, resulting in the perforating gun  100  being unstuck. The force applied by the wireline cable  22  produces a shear stress between the perforating gun  100  and the casing string  12 . Due to the reduced resistance to shear stress of the rod-shaped electrical contact  200  produced by frangible grooves  238 , the rod-shaped electrical contact  200  shears into multiple pieces (the shearing occurring across one of the frangible grooves  238  of contact  200 ) or simply bends the electrical contact in response to the application of the wireline force. Additionally, electrical contact  200  may be configured to yield (e.g., bend or shear apart) in response to the application of a predefined tension force applied by the wireline  22  to the stuck perforating gun  100 . The predefined tension force may be associated with a predefined shear or bending force applied by to the stuck electrical contact  200  that is sufficient to cause the electrical contact  200  to yield. For example, electrical contact  200  may be configured (through the configuration of conductor rod  230 ) to yield in response to a tension force applied to wireline  22  that is approximately equal to or greater than 200 lbf. 
     In certain embodiments, electrical contact  200  is configured to yield when only a portion of the reserve tension (e.g., less than 10% of the reserve tension, less than 25% of the reserve tension, less than 50% of the reserve tension, less than 75% of the reserve tension) imposable by wireline winch  16  is imposed on the wireline  22 . The “reserve tension” imposable by the wireline winch  16  is the tension in excess of the current tension imposed by the wireline winch  16 , where the current tension imposed by winch  16  may vary depending on the length of wireline  22  unspooled from the wireline winch  16  and extending from the wireline winch  16  to the tool string  20  positioned in wellbore  13 . As an example, in an embodiment in which wireline winch  16  has a reserve tension, in view of the configuration of the current configuration of the wireline system and position of tool string  20  in wellbore  13 , of 1,000 lbf, electrical contact  200  may be configured to yield at less than 200 lbf (20% of the reserve tension), less than 500 lbf (50% of the reserve tension), less than 750 lbf (75% of the reserve tension), etc. 
     Thus, as described above, by forming one or more frangible grooves  238  in the frangible conductor rod  230  of the rod-shaped electrical contact  200 , the shear strength and bend resistance of the rod-shaped electrical contact  200  may be reduced by a predefined, desired amount (e.g., to a desired or predefined shear strength) which the wireline  22  and surface assembly  11  are capable of applying to the rod-shaped electrical contact  200  in the event that the contact  200  should become ejected partially from perforating gun  100  and caught against the inner surface of casing string  12 . 
     The relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simplify subsequent reference to such steps.