Patent Publication Number: US-11391126-B2

Title: Modular gun system

Description:
RELATED APPLICATIONS 
     This application is a bypass continuation application of PCT/US21/39278, filed Jun. 26, 2021, which claims priority to U.S. Provisional Application No. 63/044,886, filed Jun. 26, 2020. 
    
    
     BACKGROUND OF THE INVENTION 
     Generally, when completing a subterranean well for the production of fluids, minerals, or gases from underground reservoirs, several types of tubulars are placed downhole as part of the drilling, exploration, and completions process. These tubulars can include casing, tubing, pipes, liners, and devices conveyed downhole by tubulars of various types. Each well is unique, so combinations of different tubulars may be lowered into a well for a multitude of purposes. 
     A subsurface or subterranean well transits one or more formations. The formation is a body of rock or strata that contains one or more compositions. The formation is treated as a continuous body. Within the formation hydrocarbon deposits may exist. Typically a wellbore will be drilled from a surface location, placing a hole into a formation of interest. Completion equipment will be put into place, including casing, tubing, and other downhole equipment as needed. Perforating the casing and the formation with a perforating gun is a well-known method in the art for accessing hydrocarbon deposits within a formation from a wellbore. 
     Explosively perforating the formation using a shaped charge is a widely known method for completing an oil well. A shaped charge is a term of art for a device that when detonated generates a focused output, high energy output, and/or high velocity jet. This is achieved in part by the geometry of the explosive in conjunction with an adjacent liner. Generally, a shaped charge includes a metal case that contains an explosive material with a concave shape, which has a thin metal liner on the inner surface. Many materials are used for the liner; some of the more common metals include brass, copper, tungsten, and lead. When the explosive detonates, the liner metal is compressed into a super-heated, super pressurized jet that can penetrate metal, concrete, and rock. Perforating charges are typically used in groups. These groups of perforating charges are typically held together in an assembly called a perforating gun. Perforating guns come in many styles, such as strip guns, capsule guns, port plug guns, and expendable hollow carrier guns. 
     Perforating charges are typically detonated by detonating cord in proximity to a priming hole at the apex of each charge case. Typically, the detonating cord terminates proximate to the ends of the perforating gun. In this arrangement, an initiator at one end of the perforating gun can detonate all of the perforating charges in the gun and continue a ballistic transfer to the opposite end of the gun. In this fashion, numerous perforating guns can be connected end to end with a single initiator detonating all of them. 
     The detonating cord is typically detonated by an initiator triggered by a firing head. The firing head can be actuated in many ways, including but not limited to electronically, hydraulically, and mechanically. 
     Expendable hollow carrier perforating guns are typically manufactured from standard sizes of steel pipe with a box end having internal/female threads at each end. Pin ended adapters, or subs, having male/external threads are threaded one or both ends of the gun. These subs can connect perforating guns together, connect perforating guns to other tools such as setting tools and collar locators, and connect firing heads to perforating guns. Subs often house electronic, mechanical, or ballistic components used to activate or otherwise control perforating guns and other components. 
     Perforating guns typically have a cylindrical gun body and a charge tube, or loading tube that holds the perforating charges. The gun body typically is composed of metal and is cylindrical in shape. Charge tubes can be formed as tubes, strips, or chains. The charge tubes will contain cutouts called charge holes to house the shaped charges. 
     It is generally preferable to reduce the total length of any tools to be introduced into a wellbore. Among other potential benefits, reduced tool length reduces the length of the lubricator necessary to introduce the tools into a wellbore under pressure. Additionally, reduced tool length is also desirable to accommodate turns in a highly deviated or horizontal well. It is also generally preferable to reduce the tool assembly that must be performed at the well site because the well site is often a harsh environment with numerous distractions and demands on the workers on site. 
     Electric initiators are commonly used in the oil and gas industry for initiating different energetic devices down hole. Most commonly, 50-ohm resistor initiators are used. Other initiators and electronic switch configurations are common. 
     Modular or “plug and play” perforating gun systems have become increasingly popular in recent years due to the ease of assembly, efficiencies gained, and reduced human error. Most of the existing plug and play systems either (1) utilize a wired in switch and/or detonator, or (2) require an initiating “cartridge” that houses the detonator, switch, electrical contacts and possibly a pressure bulkhead. The wired in switch/detonator option is less desirable, because the gun assembler must make wire connections which is prone to human error. The initiating cartridge option is less desirable because the cartridge can be a large explosive device—in comparison to a standard detonator—thus takes up additional magazine space at the user facility. There is a need for a modular perforating system in which no wire connections are required by the user AND the switch and pressure bulkhead are in pre-assembled in the gun assembly rather than in the initiating cartridge. The detonator for the proposed system has no wires and allows for simple arming by the user in the field. 
     SUMMARY OF EXAMPLE EMBODIMENTS 
     An example embodiment may include a perforating gun system comprising a cylindrical housing with a bottom end and a top end, a prewired loading tube assembly disposed within the cylindrical housing and having a corresponding bottom end and top end, an upper end fitting having a door for receiving a detonator and securing it into a recess coupled to the top end of the prewired loading tube and the top end of the cylindrical housing, a lower end fitting coupled to the bottom end of the prewired loading tube and the bottom end of the cylindrical housing, an upper electrical connections coupled to the upper end fitting, a lower electrical connections coupled to the bottom end fitting, a selective switch coupled to a detonator connector receptacle disposed within the upper end fitting, and a detonator electrically coupled to the selective switch and further disposed within the door of the upped end fitting. 
     An alternative embodiment may include having the upper end fitting disposed within the pre-wired loading tube houses a selective switch in which the end fitting contains a portion to receive an auto-shunting modular detonator by electrically connecting it to a mating receptacle of a selective switch and affixing the auto-shunting modular detonator proximate to a detonating cord. It may include a means for auto-shunting the detonator. It may include coupling a baffle to the bottom end of the cylindrical housing. The prewired loading tube may further include an insulated wire which is terminated at the selective switch in the upper end and a pressure bulkhead coupled to the lower end. The selective switch may be grounded to the loading tube. The loading tube may be electrically connected to the baffle. It may include having shaped charges installed into the loading tube, in which the shaped charges are held in place by a locking means fixed to the shaped charge. It may include having a detonating cord coupled to the back of the shaped charges with a detonating cord locking means. The detonating cord may be terminated into a detonating cord orifice integral with the end fitting. The detonator may be located adjacent to the detonating cord in an end-to-end configuration. The detonator may have an auto-shunting feature that does not unshunt until a mating receptacle is inserted. The selective switch may have a ribbon pigtail with the un-shunting receptacle attached. The receptacle connected to the switch may be attached to the end of the detonator, disengaging the shunt of the detonator. 
     An example embodiment may include a pre-wired shaped charge loading tube assembly comprising a cylindrical housing with a bottom end and a top end, an upper end fitting having a door for electrically receiving a detonator and securing it into a recess coupled to the top end of the prewired loading tube and the top end of the cylindrical housing, a lower end fitting coupled to the bottom end of the prewired loading tube and the bottom end of the cylindrical housing, an upper electrical connections coupled to the upper end fitting, lower electrical connections coupled to the bottom end fitting, a selective switch coupled to a detonator connector receptacle disposed within the upper end fitting, and a detonator electrically coupled to the selective switch and further disposed within the door closed into the recess of the upper end fitting. 
     An example embodiment may include a method of perforating a wellbore comprising coupling a pre-wired first end fitting with a first end of a shaped charge loading tube, coupling a pressure bulkhead at the first end fitting and the first end of the shaped charge loading tube, coupling a pre-wired second end fitting with a second end of a shaped charge loading tube, wherein the second end fitting centers and orients the loading tube and embodies a selective switch, feed through contact and orifices to insert a wireless detonator from the outer end and detonating cord into the inner end, inserting a detonator into a door incorporated into end fitting and closing the door into a recess of the end fitting such that the explosive end of the detonator is adjacent to the detonating cord in an side-by-side configuration, and pre-wiring the loading tube with insulated wire, wherein the wire is terminates at the selective switch in the second end fitting and the pressure bulkhead at the first end fitting. 
     An alternative embodiment may include centering the loading tube using the first end fitting within a perforating gun body. It may include electrically contacting the pre-installed insulated wire disposed within the loading tube to the pressure bulkhead contact adjacent. It may include pre-installing the baffle in the pin end of the gun carrier. It may include grounding the selective switch to the shaped charge loading tube. It may include inserting the shaped charges into the shaped charge loading tube. It may include locking the shaped charges into place within the shaped charge loading tube. It may include inserting detonating cord into the back of each shaped charge disposed within the shaped charge loading tube via locking features fixed to the shaped charge. It may include inserting the termination of a detonating cord into the end fitting. It may include inserting a wireless detonator into the end fitting from outside of the perforating gun assembly such that the explosive load end of the detonator is adjacent to the detonating cord in an end to end position. The wireless detonator may have an auto-shunting feature that does not un-shunt until a mating receptacle is inserted. The selective switch may have a ribbon pigtail with the un-shunting receptacle attached. It may include inserting the wireless detonator wherein the connector receptacle connected to the switch is attached to the end of the detonator, disengaging the shunt of the detonator. It may include screwing together the loaded perforating modular gun assemblies wherein the top contact makes electrical contact to the bottom contact of the adjacent gun assembly. It may include swaging and threading the outer diameter of a pin end of the perforating gun. It may include installing a pin by pin tandem sub into a box end of perforating gun assembly having a box by box gun body. It may include selectively initiating the detonator of the perforating gun. It may include pre-assembling spring-loaded top contact wires coupled to the selective switch. It may include connecting the through wire of the selective switch to the insulated wire of the loading tube. The output wires of the selective switch may be insulated ribbon or wires which has the detonator connector receptacle affixed to its end. It may include inserting the detonating cord through the inner end of the end fitting and a detonator from the outer end such that the detonator is adjacent to the detonating cord on the horizontal axis of the gun body. It may include overlapping the detonating cord and the detonator to form a side by side explosive coupling. It may include installing the pressure bulkhead into the baffle of the pin end of the gun carrier. It may include coupling the pressure bulkhead into a pin-by-pin tandem sub, wherein the tandem sub is inserted into the first end of the gun carrier. It may include coupling the pressure bulkhead into the second end of the gun carrier. It may include arming the perforating gun by inserting a wireless electric detonator, connector end facing up, into the end fitting detonator orifice. It may include attaching the selective switch to the pre-wired loading tube and wiring the detonator connector receptacle pass through to the upper end fitting. It may include connecting the insulated wire to the switch within the lower end fitting, in which the detonator connector receptacle wire runs the length of the loading tube and the receptacle end passes through the upper end fitting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a thorough understanding of the present invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings in which reference numbers designate like or similar elements throughout the several figures of the drawing. Briefly: 
         FIG. 1  shows an example embodiment of a modular gun system cross section. 
         FIG. 2  shows a close up of an example embodiment of the end of a modular gun system cross section. 
         FIG. 3  shows an example embodiment of an end of a modular gun system cross section. 
         FIG. 4  shows an example embodiment of two modular perforating guns coupled together. 
         FIG. 5  shows an example embodiment of perforating gun assembly. 
         FIG. 6  shows an example embodiment of an end fitting with a door to receive an initiator. 
         FIG. 7  shows a side cross section view of an example embodiment of an end fitting with a door to receive an initiator. 
         FIG. 8A  shows an example embodiment of an end fitting with a door to receive an initiator. 
         FIG. 8B  shows an example embodiment of an end fitting with a door to receive an initiator. 
         FIG. 9A  shows an example embodiment of an end fitting with a door to receive an initiator. 
         FIG. 9B  shows an example embodiment of an end fitting with a door to receive an initiator. 
         FIG. 9C  shows an example embodiment of an end fitting with a door to receive an initiator. 
         FIG. 10  shows an example embodiment of an end fitting in a perforating gun assembly. 
         FIG. 11A  shows an example embodiment of an end fitting with a door to receive an initiator. 
         FIG. 11B  shows an example embodiment of an end fitting with a door to receive an initiator. 
         FIG. 12A  shows a modular connector assembly. 
         FIG. 12B  shows a modular connector assembly. 
         FIG. 12C  shows a cross section of a modular connector assembly. 
         FIG. 13A  shows a side cross section of a modular connector assembly. 
         FIG. 13B  shows a top cross section of a modular connector assembly. 
         FIG. 13C  shows a side cross section of a modular connector assembly. 
         FIG. 13D  shows a top cross section of a modular connector assembly. 
         FIG. 13E  shows a side cross section of a modular connector assembly. 
         FIG. 13F  shows a top cross section of a modular connector assembly. 
         FIG. 14A  shows a connector for a modular connector assembly. 
         FIG. 14B  shows a connector for a modular connector assembly. 
         FIG. 15A  shows a receptacle for a modular connector assembly. 
         FIG. 15B  shows a receptacle for a modular connector assembly. 
         FIG. 16A  shows a side cross section of a modular connector assembly. 
         FIG. 16B  shows a top cross section of a modular connector assembly. 
         FIG. 16C  shows a side cross section of a modular connector assembly. 
         FIG. 16D  shows a top cross section of a modular connector assembly. 
         FIG. 16E  shows a side cross section of a modular connector assembly. 
         FIG. 16F  shows a top cross section of a modular connector assembly. 
         FIG. 17A  shows a cross section of a partially inserted shunt and initiator connection. 
         FIG. 17B  shows a cross section of a fully inserted shunt and initiator connection. 
         FIG. 18  shows a cross section view of a self-shunting coaxial male and female connector. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION 
     In the following description, certain terms have been used for brevity, clarity, and examples. No unnecessary limitations are to be implied therefrom and such terms are used for descriptive purposes only and are intended to be broadly construed. The different apparatus, systems and method steps described herein may be used alone or in combination with other apparatus, systems and method steps. It is to be expected that various equivalents, alternatives, and modifications are possible within the scope of the appended claims. 
     Terms such as booster may include a small metal tube containing secondary high explosives that are crimped onto the end of detonating cord. The explosive component is designed to provide reliable detonation transfer between perforating guns or other explosive devices, and often serves as an auxiliary explosive charge to ensure detonation. 
     Detonating cord is a cord containing high-explosive material sheathed in a flexible outer case, which is used to connect the detonator to the main high explosive, such as a shaped charge. This provides an extremely rapid initiation sequence that can be used to fire several shaped charges simultaneously. 
     A detonator or initiation device may include a device containing primary high-explosive material that is used to initiate an explosive sequence, including one or more shaped charges. Two common types may include electrical detonators and percussion detonators. Detonators may be referred to as initiators. Electrical detonators have a fuse material that burns when high voltage is applied to initiate the primary high explosive. Percussion detonators contain abrasive grit and primary high explosive in a sealed container that is activated by a firing pin. The impact of the firing pin is sufficient to initiate the ballistic sequence that is then transmitted to the detonating cord. 
     An example embodiment may comprise a modular perforating gun system in which the selective switch is embodied in the end fitting of the loading tube assembly of the perforating gun. The top or bottom end fitting is designed to hold a selective switch, a feed through contact and orifices to insert the detonator from one end and the detonating cord from the other. The opposite end fitting is designed to connect to a pressure bulkhead containing the feed through contact. Ground is made through charge tube to the end fitting to bulkhead to baffle to gun body. The loading tube is prewired and terminated to the pressure bulkhead feed through contact at one end and the selective switch at the other end. The gun carrier is box by pin with bottom of gun carrier having a swaged and threaded end. Alternatively, may have a thin shoulder pin-pin tandem sub. 
     An example embodiment is shown in  FIGS. 1-3 . The example embodiment includes a perforating gun assembly  10  having a cylindrical body housing  11 , in the charge tube  14 , with a lower end  32  and an upper end  33 . A baffle  12  with a pressure bulkhead bottom contact  17  disposed therein is further coupled to the lower end  32  of the cylindrical body housing  11 . 
     A charge tube  14  is loaded with shaped charges  18  and disposed within, and coupled to, the cylindrical body housing  11 . In this example embodiment, the charge tube  14  may be pre-wired. The baffle  12  is adjacent to the lower end fitting  13  which is coupled to the lower end  34  of the charge tube  14 . A charge tube is also known as a loading tube. The charge tube  14  has loading tube cutouts  29  located proximate to the lower end  34  and loading tube cutouts  28  located proximate to the upper end  35 . The charge tube  14  has a lower end fitting  13  located proximate to the lower end  34  and a upper end fitting  50  located proximate to the upper end  35 . A locking means for shaped charges  18  may include the tabs  30  located on shaped charges  18 . A detonator cord locking means may include the retainer fitting  31  located on the end of the shaped charges  18 . The selective switch  20  is grounded to the cylindrical body via ground wire  61  coupled to grounding screw  62 . Signal wire  60  is used to send signals through perforating gun  10  and is pre-wired into the charge tube  14 . Signal wire  60  is insulated from the cylindrical body  11 , which is conductive and acts as a ground. A detonating cord  40  is coupled to each of the shaped charges  18 . A ground wire  61  from the selective switch  20  is coupled to the charge tube  14  via fastener  62 . The upper end fitting  50  includes a door  80  that is adapted to receive the detonator  21 . Door  80  is hinged, it opens outward, and it snaps into a closed position in a recess, aligning the detonator in a side-by-side configuration with the end of the detonating cord, in the end fitting  50 . The signal is conducted through the upper end fitting  50  via feed thru spring  82  and the ground is conducted through the upper end fitting  50  via ground spring  81 . 
     The upper end fitting  50  includes a selective switch  20 , a wireless detonator  21 , a detonating cord orifice  19 , and a top contact  16  in  FIG. 2 . A closer view of upper end fitting  50  is shown in  FIG. 2 . The ground lug  62  and ground wire  61  allows the selective switch  20  to be grounded to the charge tube  14 . The selective switch  20  is connected to the wireless detonator  21  via the modular connector assembly  85 . The modular connector assembly  85  has an auto-shunting feature whereby the wireless detonator  21  is shunted until the correct connector is inserted. A detonating cord  40  wraps around the outside of the charge tube  14 , connecting to each of the shaped charges  18  via connectors  31 , and terminates within the charge tube  14 , through the loading tube cutout  28 , and into the detonating cord orifice  19 , which is located proximate to the wireless detonator  21 . The detonating cord  40  may be located in an end-to-end or side-by-side configuration with the wireless detonator  21 . The modular connector assembly  85  may include the example embodiments in  FIGS. 12A-18 , as disclosed herein. 
     The lower end  34  of the perforating gun assembly  10  is shown in  FIG. 3  including a baffle  12  coupled to the lower end  34  and located proximate to the lower end fitting  13 . The pressure bulkhead bottom contact  17  is coupled to an insulated wire  27 . The loading tube  14  includes shaped charges  18  having locking tabs  30  for locking into the loading tube  14 . The shaped charges  18  have detonating cord locking clips  31  that couple to a detonating cord  40  wrapped along the outside of the loading tube  14 . Ground contact with the charge tube  14  is maintained by spring connection  76  coupled to the lower end fitting  13  via fastener  75 . 
     Two perforating guns, a lower gun  100  and an upper gun  200  are shown in  FIG. 4  depicting a close up of the gun-to-gun connection. The two perforating guns  100  and  200  are configured similarly and this example embodiment shows how the guns are coupled together. The perforating gun  100  has a charge tube  114  located within a cylindrical body  111 . The charge tube  114  contains shaped charges  118  coupled to detonating cord  140  and an upper end fitting  150 . Upper end fitting  150  contains a selective switch  120  coupled to a wireless detonator  121 , which is further located adjacent to a detonating cord end  119 . Detonating cord end  119  may include a booster. Pressure Bulkhead bottom contact  217  is disposed within and coupled to bottom end fitting  212 . Perforating gun  200  also contains a charge tube  214  located within a cylindrical body  211  and containing perforating charges  250  coupled to detonating cord  240 . Perforating gun  200  also has an upper fitting  250  that contains a selective switch  220  coupled to a wireless detonator  221  via modular connector assembly  285 , which is further located adjacent to a detonating cord end  219 . Detonating cord end  219  may have a booster. Signal wire  160  is used to send signals through perforating gun  100  and is pre-wired into charge tube. Signal wire  160  is insulated from the cylindrical body  111 , which is conductive and acts as a ground. The selective switch  120  is grounded to the cylindrical body via ground wire  161  coupled to grounding screw  162 . Signal wire  260  is used to send signals through perforating gun  200  and is pre-wired into charge tube. Signal wire  260  is insulated from the cylindrical body  211 , which is conductive and acts as a ground. The selective switch  220  is grounded to the cylindrical body via ground wire  261  coupled to grounding screw  262 . Bulkhead contact  117  provides the signal continuity to signal wire  160 . Ground spring strap  176  coupled to the end fitting via fastener  175  grounds the charge tube  114 . Upper end fitting  150  contains an outward opening door  180  that is coupled via modular connector assembly  185  to detonator  121 . Door  180  is hinged, it opens outward, and it snaps into a closed position in a recess, aligning the detonator in a side-by-side configuration with the end of the detonating cord, in the end fitting  150 . Feed thru spring  182  provides signal continuity through the upper end fitting  150 . Ground spring  181  provides ground continuity between the upper end fitting  150  and the bottom end fitting  212 . Ground spring strap  276  coupled to the end fitting  213  via fastener  275  further grounds the charge tube  214 . Charge tube  214  contains shaped charges  218 . The modular connector assembly  185  and  285  may include the example embodiments in  FIGS. 12A-18 , as disclosed herein. 
     An example embodiment is disclosed in  FIG. 5  of a perforating gun assembly  310 . It includes a gun body  314  containing a charge tube  311 . The first end of the charge tube  311  is coupled to the first end of the gun body  314  via lower end fitting. The second end of the charge tube  311  is coupled to the second end of the gun body  314  via upper end fitting  350 . Upper end fitting  350  includes an integrated switch and contains a detonator underneath detonator door  380 . Door  380  is hinged, it opens outward, and it snaps into a closed position in a recess, aligning the detonator in a side-by-side configuration with the end of the detonating cord, in the end fitting  350 . The charge tube includes cutouts  329  for the shaped charges  318 . A signal wire  360  carries an electrical signal to the switch located in the upper end fitting  350 . The shaped charges  318  are contained in the charge tube  311 . The shaped charges  318  are coupled to the detonating cord  340 . Electrical wire  360  transmits signals to the integrated switch located into the upper end fitting  350 . 
     An example embodiment is disclosed in  FIG. 6  of the upper end fitting  350 . Upper end fitting  350  includes an integrate switch  320  and a detonator  321  contained underneath detonator door  380 . It also includes a ground spring  381  for maintaining a ground connection through the upper end fitting  350 . It also includes a feed thru spring  382  for conveying electrical signals through the upper end fitting  350 . Ground spring  381  conveys the ground through the upper end fitting. 
     An example embodiment is disclosed in  FIG. 7  of the upper end fitting  350  installed within a perforating gun assembly  310 . Housing  311  contains an upper end fitting  350  includes an integrated switch  320  and a detonator  321  contained underneath detonator door  380 . It also includes a ground spring  381  for maintaining a ground connection through the upper end fitting  350 . It also includes a feed thru spring  382  for conveying electrical signals between the electrical pin  383 , the integrated switch  320 , and the signal wire  360 . Sub  384  contains electrical pin  383  that contacts with feed thru spring  382 . Detonating cord  340  is coupled to the shaped charges  318  located in the charge tube  314 . 
     An example embodiment is disclosed in  FIGS. 8A and 8B  of the upper end fitting  350  partially outside of the gun body  314 . Upper end fitting  350  includes an integrated switch  320  and a detonator  321  contained underneath detonator door  380 . It also includes a ground spring  381  for maintaining a ground connection through the upper end fitting  350 . It also includes a feed thru spring  382  for conveying electrical signals through the upper end fitting  350 . Detonating cord  340  is detonated by the detonator  321  located in detonator door  380 . Signal wire  360  sends the initiation signal to the initiator  321 . The detonator  321  is received by modular connector assembly  385  which may include an auto-shunting feature. The modular connector assembly  385  may include the example embodiments in  FIGS. 12A-18 , as disclosed herein. 
     An example embodiment is disclosed in  FIGS. 9A, 9B, and 9C  of the upper end fitting  350 . Upper end fitting  350  includes an integrated switch  320  and a detonator  321  contained underneath detonator door  380 . It also includes a ground spring  381  for maintaining a ground connection through the upper end fitting  350 . It also includes a feed thru spring  382  for conveying electrical signals through the upper end fitting  350 . The detonator install tool  386  is shown having a handle  391 , a head  390 , with an extension  389  having a radial opening  392  for holding a detonator  321 . The pins  393  and tap  387  help hold the detonator  321  in place when installing or removing. Tap  387  engages tab  388  to positively engage with the detonator  321 . The detonator  321  is plugged into connector  381 . 
     An example embodiment is disclosed in  FIG. 10  of the upper end fitting  350 . Upper end fitting  350  includes an integrated switch  320  and a detonator  321  contained underneath detonator door  380 . It also includes a ground spring  381  for maintaining a ground connection through the upper end fitting  350 . It also includes a feed thru spring  382  for conveying electrical signals through the upper end fitting  350 . In this view the shaped charges  318  are secured by locking tabs into the charge tube  311 . Charge tube  311  containing shaped charges  318  is slideably engaged with the gun housing  314 . Signal wire  360  and detonating cord  340  are wrapped around the charge tube  311 . The gun housing  314  has internal threads having a thread cutout  395  for allowing the nut  394  on the upper end fitting  350  to slide past the threads. 
     An example embodiment is disclosed in  FIGS. 11A and 11B  of the upper end fitting  350 . Upper end fitting  350  includes an integrated switch  320  and a detonator  321  contained underneath detonator door  380  that closes into recess  398 . It also includes a ground spring  381  for maintaining a ground connection through the upper end fitting  350 . It also includes a feed thru spring  382  for conveying electrical signals through the upper end fitting  350 . The detonator  321  is plugged into connection  381  having a header connector  396  and a receptacle connector  397 . 
     A modular initiator is depicted in  FIG. 12A  and  FIG. 12B . The modular initiator serves the purpose of providing a high energy output to initiate a second explosive device such as a detonating cord, a booster, a power charge, or propellant. The modular initiator requires electrical input to transfer electrical energy into a high energy output. The modular initiator contains a rigid connector for the purpose of assembling the initiator to a receiving circuit or installing in a contact block such that it may function as a standalone unit. The modular initiator may be used in a variety of explosive systems requiring electrical initiation. 
     A contact block provides electrical feed through to allow the modular initiator to function without the need for additional electrical connections. The electrical circuit may be a printed circuit board, flexible circuit board, or other commonly used electrical boards or combinations. There may be many features included in the circuitry including switches, safety features, RF isolation, two-way communication with the surface, temperature measurement circuitry, pressure measurement circuitry, and other features not directly required for initiating the modular initiator. Electrical energy will pass through the electrical circuit to initiate the modular initiator through a rigid connector. 
     Referring to  FIGS. 12A, 12B, and 12C , a modular connector assembly  410  has a receptacle  412  having a latch  416  and contacts  420  are coupled to the connector  413 . Connector  413  includes contact blades  419  that engage with the contacts  420 . The contact blades  419  are further coupled to the resistors  417   a  and  417   b  via resister leads  418 . Resister leads  418 , which may be continuous portions of contact blades  419 , are coupled to corresponding resistors  417 . A shell  411  is crimped onto the connector  413 . Wire  414  and  415  are coupled to the receptacle  412 . The design is such that each wire  414  or  415  has a corresponding contact  20 , a corresponding contact blade  419 , a corresponding resistor lead  418 , and a corresponding resistor  417   a  or  417   b . Latch  416  locks the receptacle  412  into the connector  413 . 
     Referring to  FIGS. 13A, 13B, 13C, 13D, 13E, and 13F , a side cross section and corresponding side cross section of the modular connector assembly  410  are shown in different stages of engagement. Stage 1 is depicted by  FIGS. 13A and 13B . In stage 1 the receptacle  412  is partially inserted into the connector  413 , approximately one-third or less of the way inserted, there is no electrical connection between the receptacle  412  and connector  413  and the shunt, represented by shunt contacts  422   a  and  422   b , are in the shunted position. In this configuration the modular connector assembly  410  is self-protected from radio frequency signals and stray voltages. As can be seen in  FIG. 13B , the shunt contacts  422   a  and  422   b  are electrically in contact with each other, forming an electrical shunt between contact blades  419   a  and  419   b . The latch  416  is not engaged. The signal contacts  420   a  and  420   b  are not engaged with the corresponding blades  419   a  and  419   b . The separator  421 , a non-conductive wedge shaped part of the receptacle  412 , is not engaged with the shunt contacts  422   a  and  22   b . Contact blades  419   a  and  419   b  have corresponding resistor contacts  418   a  and  418   b . The wires  414  and  415  can be arranged side by side, or opposite of each other, depending on the application. 
     Stage 2 is depicted in  FIGS. 13C and 13D  when the receptacle  412  is approximately between one third and two thirds of the way inserted into the connector  413 . Here electrical connections have been established between the receptacle  412  and the connector  413  while the shunt remains in place due to shunt contacts  422   a  and  422   b  still being in contact. In this state the modular connector assembly  410  is electrically protected by the initiator shunt and the circuit connected to the receptacle and is in a transition state. As can be seen in  FIG. 13D , the shunt contacts  422   a  and  422   b  are electrically in contact with each other, forming an electrical shunt between contact blades  419   a  and  419   b . The latch  416  is deflected, but not engaged. The signal contacts  420   a  and  420   b  are engaged with the corresponding blades  419   a  and  419   b . The separator  421 , is beginning to make contact with the shunt contacts  422   a  and  422   b , but it has not yet separated them. 
     Stage 3 is depicted in  FIGS. 13E and 13F  when the receptacle  412  is more than two thirds of the way inserted into connector  413 . The receptacle  412  is in electrical communication with the connector  413  and is no longer shunted. As can be seen in  FIG. 13F , the shunt contacts  422   a  and  422   b  are not electrically in contact with each other due to separator  421  wedging them apart, therefore contact blades  419   a  and  419   b  are unshunted. The latch  416  is engaged into the connector  413 . The signal contacts  420   a  and  420   b  are engaged with the corresponding blades  419   a  and  419   b.    
       FIGS. 14A and 14B  show additional detail of the connector  413 . The contact blades  419   a  and  419   b  and their corresponding shunt contacts  422   a  and  422   b  are shown. Furthermore, contact blades  149   a  and  419   b  have corresponding resistor contacts  418   a  and  418   b.    
       FIGS. 15A and 15B  show additional detail of the receptacle  412 . The latch  416  is integrally formed to the receptacle. The wires  414  and  415  can be arranged side by side, or opposite of each other, depending on the application. In  FIG. 15A  one wire is strain-relieved while the other is not. In  FIG. 15B  both wires are strain relieved. 
     Referring to  FIGS. 16A, 16B, 16C, 16D, 16E, and 16F  a side cross section and corresponding side cross section of the modular connector assembly  500  are shown in different stages of engagement. A modular connector assembly  500  has a receptacle  512  having contacts  520  are coupled to the connector  513 . Connector  513  includes contact blades  519  that engage with the contacts  520 . The contact blades  519  are further coupled to the resistors  517   a  and  517   b  via resister leads  518 . Stage 1 is depicted by  FIGS. 16A and 16B . In stage 1 the receptacle  512  is partially inserted into the connector  513 , approximately one-third or less of the way inserted, there is no electrical connection between the receptacle  512  and connector  513  and the shunt, represented by shunt contacts  522   a  and  522   b , are in the shunted position. In this configuration the modular connector assembly  500  is self-protected from radio frequency signals and stray voltages. As can be seen in  FIG. 16B , the shunt contacts  522   a  and  522   b  are electrically in contact with each other, forming an electrical shunt between contact blades  519   a  and  519   b . A latch may be used in this configuration to ensure a positive and locking engagement, but it is not shown. The signal contacts  520   a  and  520   b  are not engaged with the corresponding blades  519   a  and  519   b . Therefore, the wires  514  and  515  are not connected. The separator  521 , a non-conductive part of the receptacle  512 , is not engaged with the shunt contacts  522   a  and  522   b . Housing  531  is coupled to connector  513 . 
     Stage 2 is depicted in  FIGS. 16C and 16D  when the receptacle  512  is approximately between one third and two thirds of the way inserted into the connector  513 . Here electrical connections have been established between the receptacle  512  and the connector  513  while the shunt remains in place due to shunt contacts  522   a  and  522   b  still being in contact. In this state the modular connector assembly  500  is electrically protected by the initiator shunt and the circuit connected to the receptacle and is in a transition state. As can be seen in  FIG. 16D , the shunt contacts  522   a  and  522   b  are electrically in contact with each other, forming an electrical shunt between contact blades  519   a  and  519   b . The signal contacts  520   a  and  520   b  are engaged with the corresponding blades  519   a  and  519   b , however, because of the shunting, the signal contacts  520   a  and  520   b , and their corresponding wires  514  and  515 , are connected. The separator  521 , is beginning to make contact with the shunt contacts  522   a  and  522   b , but it has not yet separated them. 
     Stage 3 is depicted in  FIGS. 16E and 16F  when the receptacle  512  is more than two thirds of the way inserted into connector  513 . The receptacle  512  is in electrical communication with the connector  513  and is no longer shunted. As can be seen in  FIG. 16F , the shunt contacts  522   a  and  522   b  are not electrically in contact with each other due to separator  521  wedging them apart, therefore contact blades  519   a  and  519   b  are unshunted, and thus wires  514  and  515  are no longer in contact with each other. The signal contacts  520   a  and  520   b  are engaged with the corresponding blades  519   a  and  519   b.    
     An example embodiment of a shunting initiator connection may include modular connector assembly  700  with contact circuit is shown in  FIGS. 17A and 17B . It has a detonator shell  701 , a short/shunt tab  702 , a shunt lift mechanism  703 , an electrical contact pin  704 , a connector housing  705 , and an electrical contact circuit  706 . There may be a plurality of pins  704  that are shunted by a single short/shunt tab  702 .  FIG. 17A  shows an example where the modular connector assembly  700  is partially inserted and  FIG. 17B  shows an example where the modular connector assembly  700  is fully inserted. 
     An example embodiment of a self-shunting coaxial connector is shown in  FIG. 18 . A coaxial male connector  800  has an electrically conductive line  803 , it may be coupled to a positive wire, and an outer electrically conductive spring contact  802 , that may be coupled to a negative wire. The spring contact  802  is by default in contact with line  803  due to a springing action, which provides a self-shunting feature for the male connector  800 . The female connector  801  has an outer electrically conductive radial portion  804 , a radial insulator  806 , and an inner receptacle  805  that is electrically conductive. Inner receptacle  805  is coupled to a line  807 . When the male connector  800  is initially inserted into the female connector  800 , the spring contact  802  makes electrical contact with the radial portion  804  and the line  803  makes electrical contact with the receptacle  805 . The curvature  808  of the spring contact  902  interfacing with the curvature  809  of the female connector forces the spring contact  802  away from the line  803  as the male connector  800  is fully inserted into the female connector  801 , thus removing the shunt after first establishing electrical contact. 
     Wireless detonator, as used in this specification, is defined as a detonator that is pre-wired prior to installation and does not require any wiring in the field to function. This wireless capability allows the detonator to become effectively a plug-and-play device that establishes the necessary electrical connections for its function by plugging it into the perforating gun. 
     The example embodiments disclose a modular gun system that is a box by pin design consisting of a steel loading tube with an end fitting pre-installed at each end. One end fitting centers and orients the loading tube and embodies a selective switch, feed through contact and orifices to insert a wireless detonator from the outer end and detonating cord into the inner end. 
     The loading tube is pre-wired with insulated wire which is terminated at the selective switch in one end fitting and the pressure bulkhead at the opposite end. The opposite end fitting centers the loading tube and provides electrical contact from the pre-installed insulated wire on the loading tube to the pressure bulkhead contact adjacent to the end fitting. The pressure bulkhead is pre-installed into a baffle in the pin end of the gun carrier. The selective switch is grounded to the loading tube which is electrically connected to the baffle which is threaded into the gun carrier. 
     Charges are inserted into the loading tube and held in place by locking features fixed to the shaped charge. Detonating cord is inserted into the back of each charge via locking features fixed to the shaped charge. The detonating cord terminates into the detonating cord orifice in the end fitting. A wireless detonator is inserted into the end fitting from outside of the gun assembly such that the explosive load end of the detonator is adjacent to the detonating cord in an end to end position. The wireless detonator has an auto-shunting feature that does not un-shunt until a mating receptacle is inserted. 
     The selective switch has a ribbon pigtail with the un-shunting receptacle attached. After inserting the wireless detonator, the connector receptacle connected to the switch is attached to the end of the detonator, disengaging the shunt of the detonator. The loaded and armed modular gun assemblies are screwed together such that the top contact makes electrical contact to the bottom contact of the adjacent gun assembly. The box by pin gun configuration is accomplished by swaging and threading the outer diameter of one end of the gun. Alternatively, the pin end is accomplished by installing a pin by pin tandem sub into one box end of a box by box gun body. 
     The end fitting is purposefully designed via a mold or machining method to house a selective switch designed to selectively initiate the detonator of a perforating gun. The end fitting is pre-assembled with a spring-loaded top contact wired to the input of the selective switch. The end fitting is pre-assembled such that the through wire of the selective switch is connected to the insulated wire pre-installed onto the loading tube. The end fitting is pre-assembled such that the output wires of the selective switch are insulated ribbon or wires which has the detonator connector receptacle affixed to its end. The end fitting is purposefully designed via a mold or machining method to insert detonating cord through the inner end and a detonator from the outer end such that the detonator is adjacent to the detonating cord on the horizontal axis of the gun body. Alternatively, the end fitting is designed such that the detonating cord and detonator overlap each other such that the end of the detonating cord and detonator are side by side. 
     The pressure bulkhead is pre-installed into the baffle of the pin end of the gun carrier. Alternatively, the pressure bulkhead is pre-installed into the pin by pin tandem sub which is inserted into one end of the gun carrier. Alternatively, the pressure bulkhead is pre-installed to the end of the charge tube end fitting. The gun assembly is armed by inserting a wireless electric detonator, connector end facing up, into the end fitting detonator orifice, followed by attaching the connector receptacle attached to the end fitting into the outer end of the detonator. 
     The selective switch is attached to, or contained within, the pre-wired loading tube and the wires with the detonator connector receptacle pass through the upper end fitting. The selective switch is contained within the lower end fitting, wherein the insulated wire is connected to the switch within the same lower end fitting and the detonator connector receptacle wire runs the length of the loading tube and the receptacle end passes through the upper end fitting. 
     The application for the example embodiments may be used with different types of initiators including resistor based bridgewire initiators, exploding bridge wire initiators, exploding foil initiators, and any other style of electric or electronic initiator. The modular initiator in the example embodiment is a packaged unit, which may include resistors, capacitors, or other electrical components. It may include a circuit board or other electronic circuitry. The modular initiator may be assembled or incorporated into an electrical circuit as a new assembly. The modular initiator may function as a standalone unit. A contact assembly without electronic circuitry may be employed which would receive the initiator and pass through electrical signals to the initiator. 
     The modular initiator includes a shell containing a high explosive such as lead azide, RDX, HMX, HNS, a bridge element or foil initiator, and electrical components such as resistors, capacitors, spark gaps, electronic circuits, etc. The modular initiator may contain a rigid connector. The rigid connector may be incorporated in many configurations. The rigid connector may be a male pin-style or female style socket. The connector may incorporate a shunting mechanism. The purpose of the shunting mechanism is to act as a protective barrier against radio frequency (RF) energy and stray electrical energy by electrically shorting the contacts. The short length and removal of leg wires also creates RF resistance. The modular initiator must be protected from RF when transported off-site on public roads. The modular initiator could be installed to an electronic circuit with its own RF protection during the installation process. For situations where the shunt must be removed, a safety housing can be employed to protect personnel if the modular initiator were to initiate during installation. Robotics installation methods could also be used when shunting is not available. 
     Auto-Shunting Electrical Connection or Auto-Shorting Electrical Connection (ASEC)—An ASEC is an electrical connection comprising at least one connector with a self-contained feature which electrically shorts two or more electrical contact paths of the connector when the connector is disconnected from, in the process of being disconnected from, or is being connected to a mating connector which includes at least one design feature which disengages the shorting feature of the first connector after electrical contact is established or allows the shorting feature of the first connector to reengage before electrical contact is broken. 
     Auto-Shunting Electric Initiator or Auto-Shorting Electric Detonator (ASED)—An ASED is an electric or electronic initiator of any variety in which electrical energy is converted to an high energy output wherein the electric or electronic initiator includes the attached connector of an ASEC with the self-contained feature to electrically short two or more electrical contact paths and the electrical contact paths of the ASEC connector include the electrical contact paths of the electric or electronic initiator and at least part of the path through which electrical energy is converted to a high energy output. 
     Initiators may be used to initiate a perforating gun, a cutter, a setting tool, or other downhole energetic device. For example, a cutter is used to cut tubulars with focused energy. A setting tool uses a pyrotechnic to develop gases to perform work in downhole tools. Any downhole device that uses an initiator may be adapted to use the modular connector assembly disclosed herein. 
     Although the invention has been described in terms of embodiments which are set forth in detail, it should be understood that this is by illustration only and that the invention is not necessarily limited thereto. For example, terms such as upper and lower or top and bottom can be substituted with uphole and downhole, respectfully. Top and bottom could be left and right, respectively. Uphole and downhole could be shown in figures as left and right, respectively, or top and bottom, respectively. Generally downhole tools initially enter the borehole in a vertical orientation, but since some boreholes end up horizontal, the orientation of the tool may change. In that case downhole, lower, or bottom is generally a component in the tool string that enters the borehole before a component referred to as uphole, upper, or top, relatively speaking. The first housing and second housing may be top housing and bottom housing, respectfully. In a gun string such as described herein, the first gun may be the uphole gun or the downhole gun, same for the second gun, and the uphole or downhole references can be swapped as they are merely used to describe the location relationship of the various components. Terms like wellbore, borehole, well, bore, oil well, and other alternatives may be used synonymously. Terms like tool string, tool, perforating gun string, gun string, or downhole tools, and other alternatives may be used synonymously. The alternative embodiments and operating techniques will become apparent to those of ordinary skill in the art in view of the present disclosure. Accordingly, modifications of the invention are contemplated which may be made without departing from the spirit of the claimed invention.