A perforating gun having a plurality of charges

Abstract: A perforating apparatus adapted to be disposed in a wellbore includes a plurality of shaped charges, an electrical current carrying conductor, and a plurality of exploding foil or exploding bridgewire initiators disposed, respectively, between the the plurality of charges and the current carrying conductor for simultaneously detonating thereby simultaneously detonating all of the plurality of shaped charges of the perforating apparatus in response to a current flowing in the conductor. Each of the shaped charges include a new secondary explosive primer disposed in the apex of the charge for detonating in response to a detonation of the exploding foil or exploding bridgewire initiator. The electrical conductor may include a flat cable having a plurality of such initiators spaced apart at predetermined intervals along the cable and adapted to wrap helically around the perforating apparatus until each of the initiators abut against a shaped charge of the plurality of charges in the perforating apparatus. In an alternate embodiment, the electrical current carrying conductor may include a flat sheet having a specific length and width and including a plurality of such initiators. The flat sheet is adapted to wrap around the entire circumference of the perforating apparatus until each of the initiators in the sheet abut against a shaped charge of the plurality of charges in the perforating apparatus. The current in the conductor may originate from a compressed magnetic flux (CMF) current pulse generator or from a charging capacitor of a conventional system including one or more charging capacitors and associated discharge switches. When the perforating apparatus includes a first and second perforator separated by an adaptor, the adaptor includes a pressure bulkhead adapted to seal the first perforator from the second perforator, an explosive disposed in contact against one side of the bulkhead and a piezoelectric ceramic disposed in contact against the other side of the bulkhead.

Description: This invention relates to a method and apparatus for initiating the detonation of a plurality of shaped charges in a perforating gun adapted to be disposed in a wellbore. Exploding bridge wire initiators and exploding foil initiators are known in the art. For example, U.S. Patent 3,181,463 to Morgan et al discloses an exploding bridge wire detonator. In addition, exploding foil "flying plate" initiators are known in the art: for example, U.S. Patent 4,788,913 to Stroud et al. entitled "Flying Plate Detonator using a High Density High Explosive" discloses an exploding foil flying plate initiator. U.S. Patent 5,088,413 to Huber et al, assigned to the same assignee as that of the present invention, entitled "Method and Apparatus for Safe Transport Handling Arming and Firing of Perforating Guns using a Bubble Activated Detonator" discloses an exploding foil "bubble activated" initiator, which utilizes a bubble instead of a flying plate to detonate an explosive charge. In addition, U.S. Patent 5,347,929 entitled "Firing System for a Perforating Gun including an Exploding Foil Initiator and an Outer Housing for conducting Wireline current and EFI current", assigned to the same assignee as that of the present invention, discloses a finng head, utilizing an exploding foil flying plate or the bubble activated initiator of the Huber et al patent, for use in a perforating gun. It is known in prior art perforating guns to use a detonating cord to initiate the detonation of a plurality of shaped charges. US patent 5 094 167 discloses a detonating device for simultaneously detonating a plurality of shaped perforating charges having an apex, using semiconductor bridge initiators located on the shaped charges. The initiator has input and output conductor lines, a switch and a semiconductor bridge. The semiconductor bridge includes two metal layers that are formed on a semiconductor substrate and connected to the input and output conductor lines. The two metal conductive layers are bridged by a pyrotechnic material that is configured to ignite when a pulse of current is transmitted through the conductor lines. The present invention seeks to provide a convenient and advantageous alternative to this prior art arrangement. In one aspect, the invention provides an apparatus for detonating a plurality of shaped perforating charges as set forth in claim 1. In another aspect, the invention provides an apparatus for detonating a plurality of shaped perforating charges as set forth in claim 2. In a further aspect, the invention provides a method of detonating a perforating gun as set forth in claim 5. Further scope of applicability of the present invention will become apparent from the detailed description presented hereinafter. It should be understood, however, that the detailed description and the specific examples, while representing a preferred embodiment of the present invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become obvious to one skilled in the art from a reading of the following detailed description. A full understanding of the present invention will be obtained from the detailed description of the preferred embodiment presented hereinbelow, and the accompanying drawings, which are given by way of illustration only and are not intended to be limitative of the present invention, and wherein: Figure 1 illustrates a perforating gun disposed in a wellbore including a plurality of shaped charges connected to either a detonating cord or an electrical conductor; Figures 2-3 illustrate the plurality of shaped charges of figure 1 connected to an electrical current carrying conductor, each shaped charge including an initiator, such as an exploding foil flying plate initiator, or an exploding foil bubble activated initiator, or an exploding bridgewire initiator; Figure 4 illustrates a cross section of the electrical current carrying conductor of figure 3; Figure 5 illustrates a section of figure 4 taken along section lines 5-5 of figure 4; Figure 6 illustrates an expanded view of one of the shaped charges of figures 2 or 3 including the current carrying conductor and an associated exploding foil "flying plate" initiator; Figure 7 illustrates a section of the current carrying conductor of figure 6 taken along section lines 7-7 of figure 6; Figure 8 illustrates an expanded view of one of the shaped charges of figures 2 or 3 including the current carrying conductor and an associated exploding foil "bubble activated" initiator; Figure 9 illustrates a section of the current carrying conductor of figure 8 taken along section lines 9-9 of figure 8; Figure 10 illustrates a conventional perforating gun having shaped charges which are connected to a conventional detonating cord; Figure 11 illustrates a perforating gun having shaped charges which are connected to an electrical conductor in the form of a foil strip which is longitudinally disposed within the perforating gun connected to each shaped charge and energized by a current pulse from, for example, a compressed magnetic flux (CMF) current pulse generator; Figure 12 illustrates a perforating gun having a first plurality of shaped charges which are connected to a first electrical conductor in the form of a foil strip which is helically wrapped around the perforating gun in a manner which allows the plurality of initiators of the foil strip to abut against their respective plurality of shaped charges, the first electrical conductor being energized by a current pulse from a first compressed magnetic flux (CMF) generator, and a second electrical conductor also in the form of a foil strip helically wrapped around the gun and energized by a second CMF generator; Figure 13 illustrates an external view of the foil strip of figure 12. Figure 14 illustrates an internal view of only one initiator of the plurality of parallel connected initiators which are disposed on the inside portion of the foil strip of figure 12; Figure 15 illustrates the electrical current path which traverses all of the parallel connected initiators disposed on the interior or inside portion of the entire foil strip of figure 12; Figure 16 illustrates a cross sectional view showing all of the individual layers which comprise the foil strip of figures 12-15; Figure 17 illustrates a shaped charge which is used in connection with an exploding foil (flying plate or bubble activated) initiator or an exploding bridgewire initiator of the perforating guns of figures 11, 12, and 26 where the shaped charge includes a pellet of secondary explosive which is responsive to a detonation of it's respective initiator for detonating the primary explosive in the shaped charge; Figure 18 illustrates a first embodiment of a prior art current pulse generator for generating a current pulse, where the current pulse energizes the flat cable conductor of figures 12, 13, and 15 or the sheet of initiators of figure 27 and detonates the initiators; Figure 19 illustrates a typical current pulse generated by the current pulse generator of figure 18; Figure 20 illustrates a second embodiment of a current pulse generator; Figure 21 illustrates a third embodiment of a prior art current pulse generator including a CMF current pulse generator having a capacitor discharge input; Figure 22 illustrates a fourth embodiment of a prior art current pulse generator including a CMF generator having a piezoelectric ceramic input; Figure 23 illustrates the fourth embodiment of the current pulse generator of figure 22 which is connected to a plurality of parallel connected initiators, such as the exploding foil flying plate or bubble activated initiators or the exploding bridgwire initiators, on the perforating gun of figures 11 and 12; Figures 24-27 illustrate another embodiment of the present invention including a sheet of initiators which has a width, where, instead of using the flat cable conductor of figures 12, 13, and 15, the sheet of initiators is wrapped around the entire circumference of the perforating gun of figure 12 until the width of the sheet is approximately equal to the circumference of the perforating gun; Figure 28 illustrates a section of figure 27 taken along section lines 21-21 of figure 27; Figure 29 illustrates a perforating apparatus including a first perforating gun, a second perforating gun, and a detonation transfer unit in accordance with another aspect of the present invention disposed between the first perforating gun and the second perforating gun for transferring a detonation wave from a first detonating cord of the first perforating gun to a second detonating cord of the second perforating gun of the perforating apparatus; and Figure 30 illustrates a more detailed construction of the detonation transfer unit of figure 29. Referring to figure 1, a perforating gun 10 is shown disposed in a wellbore 12. The perforating gun 10 includes a perforating gun carrier 14 in which a loading tube 16 is disposed. The loading tube 16 includes a plurality of phased mating holes, and a plurality of shaped charges 18 corresponding, respectively, with the plurality of phased mating holes. A conducting medium 20 is connected to the plurality of shaped charges 18, the conducting medium 20 conducting an energy package to each shaped charge for detonating the plurality of shaped charges 18. The conducting medium 20 may be an electrical current carrying conductor adapted for conducting an electrical current pulse, or it may be a detonating cord adapted for conducting a detonation wave. Normally, the conducting medium 20 is a detonating cord and the energy package is a detonation wave, the detonating cord conducting the detonation wave to each shaped charge and the shaped charges detonating in response to the detonation wave. When the shaped charges detonate, a jet is produced from each charge. Since the conducting medium 20 in this case is a detonating cord, each shaped charge 18 must include a special initiator consisting of an explosive which responds to the detonation wave by producing the jet from each shaped charge 18. However, it would be desirable to use a new conducting medium 20 for conducting a new energy package to the plurality of shaped charges 18. In that case, since the new energy package is conducting in the conducting medium 20, a new initiator must be used with each of the plurality of shaped charges. The new initiator responds to the new energy package conducting in the conducting medium by producing the jet from the shaped charges 18. The new conducting medium, the new energy package conducting in the new conducting medium 20, and the new initiator disposed within each shaped charge 18 is discussed below with reference to figures 2-31 of the drawings. Referring to figures 2-9, an electrical current carrying conductor 20-1 is shown connected to the plurality of shaped charges 18 of a perforating apparatus 10. A plurality of exploding foil flying plate or bubble activated initiators (EFI initiators) 20a are mounted on the current carrying conductor 20-1. Exploding bridgewire initiators could also be used. The plurality of EFI initiators 20a are disposed in physical contact with an apex of the respective plurality of shaped charges 18 in accordance with the present invention. In figure 2, the perforating gun 10 of figure 1 is again shown including the plurality of shaped charges 18 connected to the conducting medium 20 which, in this case, comprises an ordinary electrical current carrying conducting wire 20-1. The current conducting wire 20-1 of figure 2 is physically attached to the inside of the perforating gun carrier 14, and each of the plurality of shaped charges 18 is electrically connected to the current conducting wire 20-1. As will be shown in detail in figures 3-9, a plurality of exploding foil or exploding bridgewire initiators 20a are mounted on the conducting wire 20-1 and are disposed in contact with an apex of their respective plurality of shaped charges 18. The electrical initiators 20a are responsive to an ordinary electrical current conducting within the conducting wire 20-1 for producing a jet from each of the shaped charges 18. The electrical initiators 20a of figure 2 are known as an exploding foil initiators (EFI initiators) 20a. There are three types of exploding foil initiators: an exploding foil 'flying plate' initiator, an exploding foil 'bubble activated' initiator, and an exploding bridge wire initiator. As shown in figures 3-9, an exploding foil flying plate initiator 20a, or an exploding foil bubble activated initiator 20a, or an exploding bridgewire initiator is disposed between each shaped charge of the perforating apparatus and the current carrying conductor 20-1. In figure 3, the conducting medium 20 of figure 1 comprises an electrical current carrying conductor wire 20-1 for carrying an electrical current. A plurality of barrels 19 are disposed, respectively, between the plurality of shaped charges 18 and the current carrying conductor 20-1. As shown in the following figures of drawing, the current carrying conductor wire 20-1 includes a first copper foil having a plurality of EFI initiators 20a, a second copper foil connected to ground potential, and a plurality of polyimide insulating layers. In figure 4, the current carrying conductor wire 20-1 includes a first copper foil 20-1(a), having a plurality of EFI initiators 20a disposed thereon, located between a first polyimide layer 20b and a second polyimide layer 20c. A second copper foil 20d is disposed between the second polyimide layer 20c and a third polyimide layer 20e. The polyimide layers 20b, 20c, and 20e are approximately 0.025 inches in thickness. One type of polyimide material, which may be used as the polyimide layers 20b, 20c, and 20e, is known as "Kapton" (TM) . The Kapton polyimide material is manufactured by E.I. Dupont De Nemours, Incorporated (Dupont). The first copper foil 20-1(a) functions as a current carrying conductor for carrying electrical current to each of the plurality of EFI initiators 20a and ultimately to each of the plurality of charges 18. The second copper foil 20d functioning as a return path for the current to ground potential. In figure 5, a section of the current carrying conductor 20-1 of figure 4, taken along section lines 5-5 of figure 4, is illustrated. In figure 5, the first copper foil 20-1(a) is shown disposed over the second polyimide layer 20c. The first copper foil 20-1(a) includes a plurality of EFI initiators 20a spaced apart along the surface of the first copper foil, and each EFI initiator 20a on the first copper foil 20-1(a) includes a first part 20a2, a bridge 20a1, and a second part 20a3. If the width of the copper foil 20a is "W", each bridge 20a1 has a width "w", where the width "w" is much less than the width "W". As a result, in response to a current "I" of sufficient magnitude and duration flowing through the bridges 20a1, the bridges 20a1 will vaporize, creating an open circuit and producing a plasma gas directly above each bridge. The second copper foil 20d does not include any such bridges 20a1, the width of the second copper foil 20d being of constant width "W". Referring to figures 6 and 7, a 'flying plate' type of exploding foil initiator 20a is used with each of the shaped charges 18 of the perforating gun of figure 2. In figure 6, one of the barrels 19 is shown disposed between one of the shaped charges 18 and the current carrying conductor 20-1 (which embodies the flying plate initiator 20a) of the perforating gun of figure 2. In figures 6 and 7, a flying plate 20b1 in figure 6 is shown "flying" within a hole 19a in the barrel 19. The hole 19a of barrel 19 is disposed directly above the bridge 20a1 of figure 7 of the first copper foil 20-1(a). The flying plate 20b1 is actually a part of the first polyimide layer 20b, the flying plate 20b1 being a disc which was sheared off from the first polyimide layer 20b when a current "I" of sufficient magnitude flowed through the EFI initiator 20a of the first copper foil 20-1(a) of figure 7 and vaporized the bridge 20a1 of the EFI initiator 20a of the first copper foil 20a producing the plasma gas. A flying plate detonator is shown and discussed in U.S. Patent 4,788,913 to Stroud et al, entitled "Flying Plate Detonator using a High Density High Explosive", the disclosure of which is incorporated by reference into this specification. A functional description of the operation of a shaped charge 18 of the perforating gun of figure 2 including an exploding foil flying plate initiator for use in connection with the shaped charge 18 of the perforating gun is set forth in the following pargraphs with reference to figures 6 and 7 of the drawings. In figure 6, assume a current "I" is flowing in the first copper foil 20-1(a). The current "I" is not a transient current, but is a direct current of sufficient time duration and magnitude to vaporize, approximately simultaneously, all of the bridges 20a1 of the EFI initiator 20a of the first copper foil 20-1(a) of figure 5. When the plurality of bridges 20a1 associated with each of the plurality of EFI initiators 20a vaporize, a corresponding plurality of high pressure plasma gas is produced. This plurality of high pressure gas associated with the plurality of bridges 20a1 produces a corresponding plurality of turbulence areas, and the plurality of turbulence areas are disposed directly under a plurality of portions of the first polyimide layer 20b. The plurality of portions of the first polyimide layer 20b are, in turn, disposed directly under the plurality of holes 19a associated with a respective plurality of barrels 19. As a result of these turbulence areas, a plurality of discs (the flying plate 20b1) are sheared off from the first polyimide layer 20b, the discs being forced to fly within the holes 19a of barrels 19. Therefore, in figure 6, the "flying plate" 20b1 is shown flying within hole 19a of barrel 19. The shaped charges 18 each include a secondary explosive pellet 18a, the pellet 18a being an HE pellet. Eventually, the flying plate 20b1 will impact the secondary explosive (HE pellet) portion 18a of the shaped charge 18. When this occurs, the secondary explosive pellet 18a detonates thereby detonating the shaped charge 18 and forming a jet which projects from the shaped charge and perforates a formation traversed by the wellbore, as shown in figure 1. As shown in figure 7, when the bridge 20a1 of the EFI initiator 20a of the first copper foil 20-1(a) vaporizes, an open circuit condition occurs. As a result, a first part of first copper foil 20a2 is physically and electrically disconnected from a second part of the first copper foil 20a3. Referring to figures 8 and 9, a 'bubble activated' type of exploding foil initiator is used with each of the shaped charges 18 of the perforating gun of figure 2. In figure 8, one of the barrels 19 is disposed between one of the shaped charges 18 and the current carrying conductor 20-1 (which embodies the exploding foil 'bubble activated' initiator 20a) of the perforating gun of figure 2. In figure 8, a bubble 20b2 is shown expanding within a hole 19a in the barrel 19. The hole 19a of barrel 19 is disposed directly above the bridge 20a1 of the first copper foil 20-1(a). The bubble 20b2 is actually a part of the first polyimide layer 20b, the bubble 20b2 forming from the first polyimide layer 20b when a current "I" of sufficient magnitude flows through the EFI initiator 20a of the first copper foil 20-1(a) and vaporizes the bridge 20a1 of the EFI initiator 20a of the first copper foil 20-1(a). The bubble activated initiator is discussed in detail in U.S. Patent 5,088,413 to Huber et al, entitled "Method and Apparatus for Safe Transport Handling Arming and Firing of Perforating Guns using a Bubble Activiated Detonator", the disclosure of which is incorporated by reference into this specification. A functional description of the operation of the shaped charge 18 of the perforating gun of figure 2 including an exploding foil bubble activated initiator for use in connection with the shaped charge 18 of the perforating gun is set forth in the following pargraphs with reference to figures 8 and 9 of the drawings. In figures 8 and 9, assume a current "I" is flowing in the first copper foil 20-1(a). The current "I" is not a transient current, but is a direct current of sufficient time duration and magnitude to vaporize, approximately simultaneously, all of the bridges 20a1 of the EFI initiators 20a on the first copper foil 20-1(a) of figure 5. When one of the bridges 20a1 vaporize, a plasma gas is produced, the plasma gas producing a turbulence directly under that portion of the first polyimide layer 20b which is disposed directly under the hole 19a of the barrel 19. As a result of this turbulence, a bubble 20b2 is formed from the first polyimide layer 20b, the shape and size of the bubble 20b2 being controlled by the shape and size of the hole 19a of barrel 19. Therefore, in figure 8, the bubble 20b2 is shown expanding within hole 19a of barrel 19. The shaped charges 18 each include a secondary explosive (HE pellet) portion 18a. Eventually, the bubble 20b2 will impact the secondary explosive pellet 18a of the shaped charge 18. When this occurs, the secondary explosive pellet 18a detonates thereby detonating the shaped charge 18 and forming a jet which projects from the shaped charge and perforates a formation traversed by the wellbore, as shown in figure 1. As shown in figure 9, when the bridges 20a1 of the EFI initiators 20a of the first copper foil 20-1(a) vaporize, an open circuit condition occurs with each bridge 20a1. As a result, as shown in figure 9, since each of the bridges 20a1 of the EFI initiators 20a are now open circuited, a first part 20a2 of the EFI initiators 20a of the first copper foil is physically and electrically disconnected from a second part 20a3 of the EFI initiator 20a of the first copper foil. As a result, when the conducting medium 20 of figure 1 is an electrical current carrying conductor, such as the current carrying conductor wire 20-1 of figure 4, and when an exploding foil flying plate or bubble activated initiator of the type described above with reference to figures 3-9 is used to detonate the shaped charges 18, and when a current of sufficient magnitude and time duration flows in the first copper foil 20-1(a) of conductor 20-1, the exploding foil flying plate or bubble activated initiators 20a will simultaneously detonate, and the simultaneous detonation of the EFI initiators 20a will, in turn, simultaneously detonate all of the shaped charges 18 of the perforating gun 10 of figures 1 and 2. Referring to figure 10, a conventional perforating gun is illustrated. The conventional perforating gun includes a plurality of shaped charges 30 connected to a detonating cord 32. A detonator 34 initiates the propagation of a detonation wave in the detonating cord 32 in response to a current propagating in the electrical conductor 36. The detonation wave detonates the shaped charges thereby producing a jet 38 from each of the shaped charges 30. Referring to figure 11, a new perforating gun in accordance with the present invention, similar to the new perforating gun of figure 2, is illustrated. The new perforating gun of figure 11 includes a plurality of shaped charges 40 connected to an electrical current carrying conductor 42. As will be discussed later in this specification, the conductor 42 includes a plurality of initiators 20a, such as an exploding foil flying plate initiator 20a of figures 6-7 or an exploding foil bubble activated initiator 20a of figures 8-9 or an exploding bridge wire initiator. The plurality of initiators 20a on the conductor 42 are disposed, respectively, adjacent to the plurality of shaped charges 40 for simultaneously detonating all of the charges in response to a simultaneous detonation of the plurality of initiators 20a. The conductor 42 is electrically connected to a current pulse generator 44. As will be noted later in this specification, the current pulse generator 44 can be either a charging capacitor circuit, or a parallel-connected charging capacitor circuit, or a compressed magnetic flux (CMF) current pulse generator. Referring to figure 12, a preferred embodiment of the new perforating gun of figure 11 in accordance with the present invention is illustrated. In figure 12, a first plurality of phased shaped charges 40a are disposed on one side of the new perforating gun. A first electrical current carrying flat cable conductor 42a (hereinafter, the "flat cable conductor 42a") is helically wrapped around the plurality of shaped charges 40a. The flat cable conductor 42a is shown to be wrapped around the plurality of shaped charges 40a within the interior of the loading tube 45 of the new perforating gun of figure 12, although the flat cable conductor 42a could just as easily be wrapped around the plurality of shaped charges 40a and around the exterior of the loading tube 45 of the new perforating gun of figure 12. The flat cable conductor 42a contacts the apex of each of the first plurality of shaped charges 40a. The flat cable conductor 42a is approximately 1.25 inches in width. The flat cable conductor 42a is a flat electrical current carrying conductor and it includes a plurality of initiators 20a spaced apart at periodic intervals along the length of the flat cable conductor 42a. When the flat cable conductor 42a is wrapped around the plurality of shaped charges 40a, the plurality of initiators 20a on the flat cable conductor 42a abut, respectively, against the apex of the first plurality of shaped charges 40a. The flat cable conductor 42a is electrically connected to a first current pulse generator 44a for generating a pulse of current which approximately simultaneously detonates the plurality of initiators 20a on the flat cable conductor 42a. The first current pulse generator 44a is actually a compressed magnetic flux (CMF) current pulse generator 44a (hereinafter called the "first CMF current pulse generator 44a"). The first CMF current pulse generator 44a receives a detonation wave from a detonator 48 and generates a current pulse in response to the detonation wave. The detonator 48 can be any typical detonator, such as a percussion detonator, an electric detonator, or an exploding foil initiator detonator, or an exploding bridge wire initiator detonator. However, in addition, a second plurality of phased shaped charges 40b are disposed on the other side of the new perforating gun of figure 12. A second electrical current carrying flat cable conductor 42b (hereinafter, the flat cable conductor 42b) is helically wrapped around the plurality of charges 40b and within the interior of the loading tube 45 on the other side of the new perforating gun of figure 12, although the flat cable conductor 42b could just as easily be wrapped around the plurality of charges 40b and around the exterior of the loading tube 45. The flat cable conductor 42b contacts the apex of each of the second plurality of shaped charges 40b. The flat cable conductor 42b is a flat electrical current carrying conductor. As a result, the flat cable conductor 42b also includes a plurality of initiators 20a spaced at periodic intervals along the length of the flat cable conductor 42b. The initiators 20a can be the flying plate initiator, the bubble activated initiator, or the exploding bridgewire initiator. When the flat cable conductor 42b is wrapped around the plurality of shaped charges 40b, the plurality of initiators 20a on the flat cable conductor 42b abut, respectively, against the apex of the second plurality of shaped charges 40b. The flat cable conductor 42b is electrically connected to a second current pulse generator 44b which is actually a second compressed magnetic flux (CMF) current pulse generator 44b. The first and second CMF current pulse generator 44a and 44b are each described in an article entitled "Small Helical Flux Compression Amplifiers", by J.E. Gover, O.M. Stuetzer, and J.L. Johnson, of Sandia Laboratories, Albuquerque, New Mexico, printed in Megagauss Physics and Technology, 1979, the disclosure of which is incorporated by reference into this specification. An intermediate adaptor 46 separates the one side of the new perforating gun from the other side and functions to convert an electrical current pulse in the end of the first cable 42a into a detonation wave which initiates the generation of a current pulse from the second CMF current pulse generator 44b. The intermediate adaptor 46 includes an EFI firing head 46c connected to the end of the first flat cable conductor 42a. The EFI firing head 46c is identical to the EFI firing head 124 which is discussed below with reference to figure 23 of the drawings. The EFI firing head 46c functions to receive the current pulse propagating in the end of the first flat cable conductor 42a and to detonate an explosive pellet disposed within the firing head 46c. The intermediate adaptor 46 further includes a first detonating cord 46a connected to the EFI firing head 46c and responsive to the detonation of the explosive pellet in the EFI firing head 46c for initiating the propagation of a detonation wave in the first detonating cord, and a second detonating cord 46b disposed in side-by-side abutment with the first detonating cord 46a. In operation, when the current pulse propagating in the end of the first flat cable conductor 42a energizies the EFI firing head 46c, an explosive pellet in the firing head 46c detonates, which, in turn, initiates the propagation of a detonation wave in the first detonating cord 46a. Since the second detonating cord 46b is disposed in side-by-side abutment with the first detonating cord 46a, the detonation wave in the first detonating cord 46a transfers to the second detonating cord 46b. Therefore, a detonation wave now propagates in the second detonating cord 46b, and this detonation wave energizes the second CMF generator 44b. As a result, the second CMF generator 44b generates a second current pulse in response thereto. A functional description of the operation of the new perforating gun of figure 12 will be set forth in the following paragraph with reference to figure 12 of the drawings. The first CMF current pulse generator 44a receives a detonation wave from the detonator 48 and generates a current pulse in response therto. The current pulse propagates through the flat cable conductor 42a thereby detonating, approximately simultaneously, all of the initiators 20a disposed on the flat cable conductor 42a. Since the initiators 20a on the flat cable 42a abut, respectively, against the first plurality of shaped charges 40a, when the initiators on the flat cable conductor 42a simultaneously detonate, the first plurality of shaped charges 40a also detonate approximately simultaneously. The intermediate adaptor 46 converts the current pulse in the flat cable conducotr 42a into a second detonation wave. As a result, in response to the second detonation wave, the second CMF current pulse generator 44b generates a second current pulse. The second current pulse propagates through the flat cable conductor 42b thereby detonating, approximately simultaneously, all of the initiators disposed on the flat cable conductor 42b. Since the initiators on the flat cable conductor 42b abut, respectively, against the apex of the second plurality of shaped charges 40b, when the initiators on the flat cable conductor 42b detonate simultaneously, the second plurality of shaped charges 40b also detonate approximately simultaneously. Referring to figures 13-16, a detailed construction of the first electrical current carrying flat cable conductor 42a and the second electrical current carrying flat cable conductor 42b of figure 12 is illustrated. Since the first and second flat cable conductors 42a and 42b are flat, ribbon like cables, they each have two sides, an external side which does not abut the apex of a shaped charge and an internal side which does abut the apex of the shaped charge. In accordance with a preferred embodiment of the present invention, a plurality of exploding foil (flying plate, or bubble activated, or exploding bridgewire) initiators 20a, similar to the EFI initiators 20a on the first copper foil 20-1(a) shown in figures 4 and 5, are disposed on the internal side of the flat cables 42a and 42b, and they are spaced apart at periodic intervals along the internal side of the cable 42a and 42b. The external side of the flat cables 42a and 42b is shown in figure 13 and the internal side of the flat cables 42a and 42b is shown in figure 14. In figure 13, a view of a portion of the external side of the first and second flat cable conductors 42a and 42b of figure 12 is illustrated. Since the external side of the flat cables face externally, the external side does not abut against the apex of any shaped charge 40 of figure 12. In figure 13, the external side of the flat cable conductors 42a and 42b includes a plurality of external initiator terminals 42a1. Since, in the preferred embodiment, an exploding foil (flying plate or bubble activated or exploding bridgewire) initiator (EFI) is the preferred type of initiator, hereinafter, each of the plurality of initiator terminals 42a1 will be referred to as "external EFI terminals 42a1". Each external EFI terminal 42a1 includes a pair of EFI attach holes 42a1(a), an EFI alignment hole 42a1(b), a charge jacket attachment hole 42a1(c), a ground relief 42a1(d), and a high voltage relief 42a1(e). In order to fully understand the construction of the "external" EFI terminal 42a1, it is necessary to understand the construction of the "internal" side of the flat cable conductors 42a and 42b of figure 12. Accordingly, refer to the figure 14 description below. Referring to figure 14, a view of a portion of the internal side of the first and second flat cable conductors 42a and 42b of figure 12 is illustrated. Since the flat cable conductors 42a and 42b of figure 12 each include a plurality of exploding foil initiators 20a, in figure 14, the construction of a single exploding foil initiator (EFI initiator) 20a (similar to the EFI initiator 20a of figure 5 which includes the the first part 20a2, the bridge 20a1, and the second part 20a3) is illustrated. Figure 14 actually illustrates a view of the external EFI terminal 42a1 of figure 13 from the "internal" side of the first and second flat cable conductors 42a and 42b. Recall from the above description in connection with figures 6 and 7 that a flying plate 20b1 is sheared out from a first polyimide layer 20b when a bridge 20a1 of the EFI initiator 20a on a first copper foil 20-1(a) vaporizes in response to a current flowing from the first part 20a2 of the first copper foil 20-1(a), through the narrow bridge 20a1 of width "w", to the second part 20a3 of the first copper foil. In figure 14, each of the exploding foil initiators 20a, disposed on the "internal" side of the first and second flat electrical current carrying cable conductors 42a and 42b of figure 12, includes a first part 20a2 (see figure 7) which is connected to one of the EFI attach holes 42a1(a) of figure 13 and a second part 20a3 which is connected to the other of the EFI attach holes 42a1(a) of figure 13. A bridge 20a1 (similar to bridge 20a1 of figure 7) is the narrow portion of the EFI initiator 20a which is electrically connected between the first part 20a2 of the EFI initiator 20a and the second part 20a3 of the EFI initiator 20a. Referring to figure 15, a view of the internal side of the first and second flat conductor cables 42a and 42b of figure 12 is illustrated. Figure 15 actually represents a view of the entire electrical current path which is disposed on the internal side of the first and second flat conductor cables 42a and 42b of figure 12 and which includes all of the parallel connected exploding foil (flying plate or bubble activated or exploding bridgewire) initiators. Recall from the above description in connection with figures 6-9 that an EFI initiator 20a is comprised of at least two layers: a first copper foil 20-1(a) for conducting a current, and a second copper foil 20d which functions to provide a return path for the current to ground potential. The first copper foil 20-1(a) of figure 6 conducts a current pulse through the bridge 20a1 of the EFI initiator 20a on the first copper foil 20-1(a), the bridge 20a1 separating the first part 20a2 of the first copper foil 20-1(a) 20a2 from the second part 20a3 of the first copper foil. Recall also that the second copper foil 20d functions as a ground potential providing a return path for the current flowing in the first copper foil 20-1(a). In figure 15, an electrical current path associated with a plurality of parallel connected EFI initiators 20a disposed on the internal side of the flat cable conductors 42a and 42b is denoted by the element numeral 54. An electrical current path associated with the return path to ground potential is denoted by the element numeral 56. The electrical current path 54, including a plurality of parallel connected EFI initiators 20a, is connected to a voltage supply 50 via a spark gap switch 52. Note that the electrical current path 54 includes a first plurality of parallel connected exploding foil initiators 20a4 which receive a current from the voltage supply 50, a second plurality of parallel connected exploding foil initiators 20a5, a third plurality of parallel connected exploding foil initiators 20a6, and a fourth plurality of parallel connected exploding foil initiators 20a7. The first, second, third, and fourth plurality of exploding foil initiators 20a4-20a7 in figure 15 are each identical to the exploding foil initiator 20a shown in figure 14 of the drawings. As noted by the direction of the arrows in figure 15, the current from the voltage supply 50 flows through the electrical current path 54 as follows: in a first direction through the first plurality of initiators 20a4, then in a second direction opposite to the first direction through the second plurality of initiators 20a5, then in a third direction opposite to the second direction in the third plurality of initiators 20a6, and then in a fourth direction opposite to the third direction in the fourth plurality of initiators 20a7. The current from the fourth plurality of iniitators 20a7 flows back to the voltage supply 50 via the return electrical current path 56 in figure 15. As a result, the first, second, third, and fourth plurality of exploding foil initiators 20a4, 20a5, 20a6, and 20a7 in figure 15 all detonate substantially simultaneously in response to the current pulse originating from the voltage supply 50 and flowing through all of the initiators. Referring to figure 16, a cross sectional view of the flat cable conductors 42a and 42b, including all of the individual layers of the first and second flat cables 42a and 42b of figure 12, is illustrated. In figure 16, the flat cable conductors 42a and 42b of figures 12, 13 and 15 each include: a two (2) Mil Kapton layer 42a2; an adhesive layer 42a3; a two (2) ounce copper layer 42a4 which conducts a current to the first copper foil 20-1(a) of figures 6-9; a two (2) mil Kapton layer 42a5 which includes the second polyimide layer 20c of figures 6-9; a two (2) ounce copper layer 42a6 which includes the second copper foil 20d return current path of figures 6 and 8; an adhesive layer 42a7; a two (2) mil Kapton layer 42a8 which includes the third polyimide layer 20e of figures 6 and 8; and a one (1) mil copper "EFI layer" 20a, disposed on top of the two mil Kapton layer 42a2, which is the EFI layer shown in figure 14 of the drawings and which includes the first part 20a2, the bridge 20a1, and the second part 20a3 of the first copper foil 20-1(a) shown in figures 7 and 9 of the drawings. As shown in figure 6, a plate 20b1 is sheared off from the first polyimide layer 20b in response to the current (I) flowing in the bridge 20a1 of the EFI layer 20a and the plate 20b1 flies through the hole 19a in the barrel 19 eventually impacting a secondary explosive pellet 40a1 of the shaped charges 40a/40b shown in figure 17 of the drawings. Referring to figure 17, a cross sectional view of the shaped charges 40a and 40b shown in figure 12 is illustrated. The shaped charges 40a and 40b each include a metal liner 40a3, a metal case 40a4, a main body of high explosive 40a2 disposed between the metal liner 40a3 and the metal case 40a4, and a secondary explosive pellet 40a1 disposed in the apex of each shaped charge. The apex of each shaped charge is adapted to abut against the hole 19a of the barrel 19 of an EFI initiator 20a, as shown in figure 16, in a manner which guarantees that the hole 19a of the barrel 19 is disposed directly above and in direct alignment with the secondary explosive pellet 40a1 of the shaped charge 40a or 40b. In accordance with another aspect of the present invention, the secondary explosive pellet 40a1 of the shaped charge 40a and 40b of figure 17 must be comprised of a special explosive composition which will detonate when the flying plate 20b1 of figure 6 impacts the pellet 40a1, or when the expanding bubble 20b2 of figure 8 impacts the pellet 40a1, or when a detonation wave in a detonating cord impacts the pellet 40a1. After extensive experimentation, it has been discovered that the special explosive composition of the secondary explosive pellet 40a1 must be selected from a group consisting of: HNS-IV, NONA, HMX, RDX, PETN, TATB, ABH, BTX, DPO, DODECA, Tripicryl-trinitrobenzene, barium styphnate, and metallic picrate salts. At low temperatures, for best performance, the secondary explosive pellet 40a1 should be selected from the following group: PETN, RDX, and HMX; however, at high temperatures, for best performance, the secondary explosive pellet 40a1 should be selected from the following group: ABH, BTX, DPO, NONA, DODECA, Tripicryl-trinitrobenzene, barium styphnate, and metallic picrate salts. However, the main body of explosive 40a2 can be selected from the following group: RDX, HMX, or HNS. One of the special explosive compositions disclosed in the above group will work in connection with some type of exploding foil initiator, or in connection with a semiconductor bridge initiator (of the type disclosed in U.S. Patent 5,094,167 to Hendley Jr.), or in connection with some type of an exploding bridgewire initiator. In the normal construction of a shaped charge, all explosives are pressed under a common load so that initiation sensitivity is not controlled independently from charge performance (higher pressing forces tend to desensitize the charge and cause misfires). In accordance with still another aspect of the present invention, during manufacture of the shaped charge 40a and 40b of figure 17, the main body of explosive 40a2 is pressed independently of the pressing of the secondary explosive pellet 40a1. The main body of explosive 40a2 is pressed to a separate "high" density, but the secondary explosive pellet 40a1 is pressed to a separate "low" density. The "high" density of the main body of explosive 40a2 may be defined as that density which is above ninety percent (90%) of the theoretical maximum crystal density. The optimal "low" density of the "HNS IV" secondary explosive pellet 40a1, for example, would be 1.57 grams/cc. Recall that initiation of the pellet 40a1 must occur in response to detonation of either an EFI initiator 20a or a detonating cord. Pressing the pellet 40a1 to a separate low density relative to that of the main body of explosive 40a2 optimizes the initiation sensitivity of the secondary explosive pellet 40a1. The aforementioned optimized initiation sensitivity of the pellet 40a1 is required since the pellet must be initiated by detonation of either the EFI initiator 20a (which includes the Exploding Bridge Wire) or the detonating cord. Referring to figures 18-23, various embodiments of the current pulse generator 44 of figure 11 are illustrated. In figures 18 and 19, a first embodiment of the current pulse generator 44 of figure 11 is illustrated. The current pulse generator 44 can comprise a conventional charging capacitor and discharge swith arrangement. For example in figure 18, a high voltage source 60 is connected to a charging capacitor 62 via a charging resistor 64. The charging capacitor 62 is connected to a discharge switch 66. The voltage source 60 charges the capacitor 62. When the capacitor 62 is completely charged, the discharge switch 66 changes from a open circuit to a short circuit condition allowing a discharge current pulse stored in the form of a charge in the capacitor 62 to discharge through the short circuited discharge switch 66. The discharge current pulse (also known as an injection current) energizes the flat cable conductor 42 in figure 11 and flat cable 42a in figure 12. Figure 19 illustrates the exact nature of this discharge current pulse from the capacitor 62. In figure 20, a second embodiment of the current pulse generator 44 of figure 11 is illustrated. In figure 20, the current pulse generator 44 could comprise a high voltage source 70 connected to a first charging resistor 72, a second charging resistor 74, a third charging resistor 76 and a fourth charging resistor 78. The first charging resistor 72 is connected to a first charging capacitor 80, and the first charging capacitor 80 is connected to a charge bank (1) 84 via a discharge switch 82. The charge bank (1) 84 comprises a first plurality of the shaped charges 40 of figure 11 of the perforating apparatus. The second charging resistor 74 is connected to a second charging capacitor 86, and the second charging capacitor 86 is connected to a charge bank (2) 88 via an explosive ionization gap 90. The charge bank (2) 88 comprises a second plurality of the shaped charges 40 of the perforating apparatus of figure 11. The third charging resistor 76 is connected to a third charging capacitor 92, and the third charging capacitor 92 is connected to a charge bank (3) 94 via an explosive ionization gap 96. The charge bank (3) 94 comprises a third plurality of the shaped charges 40 of the perforating apparatus of figure 11. The fourth charging resistor 78 is connected to a fourth charging capacitor 98, and the fourth charging capacitor 98 is connected to a charge bank (4) 100 via an explosive ionization gap 102. The charge bank (4) 100 comprises a fourth plurality of the shaped charges 40 of the perforating apparatus of figure 11. The charging capacitors are sized for about 0.3 uf times the number of charges it will fire. These capacitors are charged to a voltage of about 2 to 5 kV depending upon the length of the line and whether it will fire an EFI or an EBW initiator. In operation, the voltage source 70 charges the first charging capacitor 80. When the discharge switch closes it's circuit in response to the charge on the capacitor 80, a first discharge current flows from capacitor 80 to the charge bank (1) 84 thereby simultaneously detonating the first plurality of shaped charges. In the meantime, the voltage source 70 has already fully charged the other remaining charging capacitors, that is, the second, third, and fourth charging capacitors 86, 92, and 98. When the last charge of said first plurality of shaped charges of charge bank (1) 84 has detonated, the explosive ionization gap 90 allows a second discharge current to flow from the second charging capacitor 86 to the charge bank (2) 88 thereby simultaneously detonating the second plurality of shaped charges. When the last charge of said second plurality of shaped charges of charge bank (2) 88 has detonated, the explosive ionization gap 96 allows a third discharge current to flow from the third charging capacitor 92 to the charge bank (3) 94 thereby simultaneously detonating the third plurality of shaped charges. When the last charge of said third plurality of shaped charges of charge bank (3) 94 has detonated, the explosive ionization gap 102 allows a fourth discharge current to flow from the fourth charging capacitor 98 to the charge bank (4) 100 thereby simultaneously detonating the fourth plurality of shaped charges. In figure 21, a third embodiment of the current pulse generator 44 of figure 11 is illustrated. In figure 21, the current pulse generator 44 could comprise a compressed magnetic flux (CMF) current pulse generator. The CMF generator is described in an article entitled "Small Helical Flux Compression Amplifiers" by J.E. Gover, O.M. Stuetzer, and J.L. Johnson, Sandia Laboratories, Albuquerque, New Mexico, printed in "Megagauss Physics and Technology", 1979, the disclosure of which is incorporated by reference into this specification. The CMF generator is also described in an article entitled "The Central Power Supply", Showcase for Technology, conference and exposition, 1981, the disclosure of which is incorporated by reference into this specification. The CMF current pulse generator of figure 21 includes a source of injection or seed current 110, such as a capacitor discharge system which dumps energy from a capacitor into the inductance coil 114. The injection current source 110 is connected to a crow bar switch 112. The crow bar switch 112 is further connected to an inductance coil 114. An armature 116 os disposed within the center of the inductance coil 114. The armature 116 includes an explosive 116a which is detonated in response to a detonation wave from a detonating cord or a detonator. The last turn of the inductance coil 114 is connected to a load 118, such as the flat cable conductor 42a or the flat cable conductor 42b in figure 12 of the drawings. Recalling that the flat cable conductors 42a and 42b of figure 12 each include a plurality of the exploding foil (flying plate or bubble activated) initiators 20a shown in figure 14 of the drawings, the load 118 of figure 21 comprises a plurality of the exploding foil initiators 20a shown in figure 14. In operation, a current from the injection current source 110 is injected into the inductance coil 114. When the current in the coil 114 is near maximum, the explosive filled armature 116 is detonated from one end (e.g., from a detonating cord). The armature 116 begins to expand from one end (the left hand end in figure 21). As the armature 116 expands, the crow bar switch 112 is shorted out, and the coils of the inductance coil 114 are shorted out in sequence. Recall that, when the individual coils of the inductance coil 114 short out, since the magnetic field generated by the inductance coil 114 must remain constant, the current in the remaining coils of the inductance coil 114, which are not shorted out, must increase in amplitude thereby producing a pulse of current having an increasingly greater amplitude. Therefore, the current in the remaining coils of the inductance coil 114 increases in amplitude until it reaches a maximum in the last remaining coil of the inductance coil 114 which has not yet been shorted out by the expanding armature 116. The current in the last remaining coil of inductance coil 114 is typically 50 to 100 times the injection current from the injection current source 110. Thus, by selecting the correct number of turns of the inductance coil 114 and the injection current from injection current source 110, a sufficient output current can be obtained from the CMF current pulse generator 44 of figure 21 to fire several hundred initiators (EFI or EBW initiators) associated with several hundred shaped charges 40a or 40b of the perforating gun of figure 12. In figure 22, a fourth embodiment of the current pulse generator 44 of figure 11 is illustrated. Figure 22 illustrates another embodiment of the compressed magnetic flux (CMF) current pulse generator shown in figure 21. However, in figure 22, instead of using the separate source of injection or seed current 110 shown in figure 21, a piezoelectric ceramic 120, configured for a high output current and voltage, stores energy and therefore can be used as the source of injection current. The piezoelectric ceramic 120 encloses an armature 116 containing an explosive 116a, where the explosive 116a can be detonated by another exploding foil initiator, an exploding bridewire, or a standard electric detonator. In addition, a percussion detonator or a trigger charge booster activated by one of many available firing heads will detonate the explosive 116a in the armature 116. A crow bar switch 112 is connected to an inductance coil 114, the inductance coil 114 enclosing the armature. The last turn of the inductance coil 114 is connected to a load 118, which can be one of the plurality of exploding foil initiators 20a of figure 14 arranged on a flat conductor cable similar to flat cable 42a and 42b in figure 12. A certain spacing is chosen between the piezoelectric ceramic 120 and the inductance coil 114. This certain spacing must be used to allow the field in the coil 114 to build to near maximum before sequential shorting of the coil 114 commences. The certain spacing distance corresponds to the detonation velocity of the armature multiplied by the time required to charge the coil 114. The certain spacing distance is approximately 100 mm for a typical system but would vary depending upon the coil 114 size, inductance of the coil 114, and explosive type of the explosive 116a. In operation, the explosive 116a in the armature 116 is detonated by the detonator 48 of figure 12. Detonation of the explosive 116a produces an explosive shock in the armature 116. The explosive shock from the armature 116 releases the energy stored in the piezoelectric ceramic 120 and pumps the energy into the inductance coil 114. In response to the release of the energy from the piezoelectric ceramic 120, a current begins to flow from the ceramic 120 to the inductance coil 114. However, the armature explosive 116a has been detonated. As a result, the armature 116 expands in it's radial dimension, the expansion propagating from the left hand side of the armature 116 in figure 22 to the right hand side in figure 22. This propagating expansion of the armature 116 shorts out the crow bar switch 112, and then begins to short out each of the individual turns of the inductance coil 114, starting with the first turn of the coil 114 on the left hand side of the figure 22 and ending with the last turn on the right hand side of figure 22. Since the magnetic field produced by the coil 114 must remain constant, since the number of turns of the coil 114 which are not short circuited by the expanding armature is decreasing, the current in the remaining coil turns must increase to a maximum. When all turns of coil 114 are short circuited except for the last turn, the current in the last turn 114a has reached it's maximum value. This current in the last turn 114a is used to energize the load 118. As a result, all of the bridges 20a1 of all of the exploding foil initiators 20a or exploding bridgewire initiators on the flat cable 42a and 42b of figure 12 are substantially simultaneously vaporized. Referring to figure 23, the CMF generator 44 of figure 22 is again shown in figure 23. The output of the CMF generator 44 is shown connected to a plurality of the exploding foil initiators 20a of figure 14, where a first plurality of exploding foil initiators 20a is connected in parallel to a second plurality of such initiators 20a, the second plurality being connected in parallel to a third plurality of such initiators 20a, and the third plurality being connected in parallel to a fourth plurality of such initiators 20a. The explosive 116a in the armature 116 is detonated by a detonation wave propagating in a detonating cord 122. The detonating cord 122 has a booster 122a which is detonated by a firing head 124. The firing head 124 is discussed in U.S. Patent 5,347,929, entitled "Firing System for a Perforating gun Including an Exploding Foil Initiator and an Outer Housing for Conducting Wireline Current and EFI Current", the disclosure of which has already been incorporated by reference into this specification. The functional operation of the CMF generator in figure 23 is the same as that which is described above with reference to figure 22. However, the last turn 114a of the coil 114, which is not short circuited by the expanding armature 116, has a maximum pulse of current 114a1 flowing therein. This maximum pulse of current 114a1 substantially simultaneously detonates each of the exploding foil initiators 20a disposed on the surface of the flat cable conductor 42a and 42b of figure 12. Referring to figures 24-28, another embodiment of the present invention is illustrated. In this embodiment, instead of using a flat conductor cable 42a and 42b having a plurality of initiators disposed thereon, as shown in figures 12-16, to detonate the plurality of shaped charges in a perforating gun as shown in figure 12, a sheet containing a plurality of initiators, adapted to wrap around the entire circumference of the perforating gun of figure 12, is utilized. When the sheet containing the plurality of initiators is wrapped around the entire circumference of the perforating gun of figure 12, each of the initiators on the sheet will abut against the apex of it's corresponding shaped charge for detonating the charge. The initiators on the sheet may each include an exploding foil (flying plate or bubble activated) initiator or an exploding bridgewire initiator. In figure 24, a perforating gun 130 includes a shaped charge 132. In the actual embodiment, the perforating gun 130 includes a plurality of shaped charges 132. The perforating gun 130 is the same perforating gun as that which is shown in figure 12, except that the flat cable conductors 42a and 42b of figure 12 are each replaced by a sheet 134 containing a plurality of EFI initiators 20a as shown in figures 24-28 (hereinafter called "the sheet of initiators"). In figure 24, the sheet of initiators 134 is shown laying flat before the sheet has been wrapped around the circumference of the perforating gun 130. The sheet 134 has an external side 134a and an internal side 134b, and, in figure 24, the sheet 134 includes an initiator 136. In the actual embodiment, the sheet 134 includes a plurality of initiators 134 corresponding, respectively, to the plurality of shaped charges 132 of the perforating gun 130. In the preferred embodiment, the initiator 136 is an exploding foil initiator 20a identical to the exploding foil initiator 20a shown in figure 14 of the drawings. The charge 132 includes an apex 132a. In figure 25, the sheet 134 has been wrapped around the entire circumference of the perforating gun 130 until the initiator 136 abuts against the apex 132a of the shaped charge 132. In figure 26, a three dimensional view of the perforating gun 130 of figures 24-25 is illustrated. Since the width "W" of the sheet 134 (see figure 27) is approximately equal to the circumference of the perforating gun 130, the sheet of initiators 134 is physically wrapped around the entire circumference of the perforating gun 130 until the width "W" of the sheet 134 equals the circumference of the gun 130. The wrapping of the sheet 134 around the circumference of the gun 130 takes place in a manner which allows each of the plurality of EFI initiators 136 on the sheet to abut against the apex 132a of their respective shaped charges 132. As a result, when the initiator 136 detonates, the shaped charge 132 will detonate. The initiator 136 includes external initiator terminals 136a disposed on the external side surface of the sheet 134, similar to the external initiator terminals 42a1 shown in figure 13. In figure 27, the external side 134a of the sheet of initiators 134 of figure 26 is shown laying flat on a surface and illustrating a plurality of the external initiator terminals 136a. In the preferred embodiment, the initiator 136 is an exploding foil initiator 20a, similar to the exploding foil initiator shown in figure 14 of the drawings. Therefore, the external initiator terminals 136a in figure 27 are terminals, disposed on the external side 134a of the sheet of initiators 134, associated with an exploding foil initiator 20a. Each of the external initiator terminals 136a include an EFI alignment hole 136a1, a charge jacket attachment hole 136a2, and a pair of EFI attach holes 136a3, similar to the alignment hole 42a1(b), attachment hole 42a1(c), and EFI attach holes 42a1(a) shown in figure 13 in connection with the flat cables 42a and 42b. The EFI attach holes 136a3 are first and second terminals, the first terminal of the EFI attach hole 136a3 being electrically connected to the first part 20a2 of the exploding foil initiator 20a of figure 14, the second terminal of the EFI attach hole 136a3 being electrically connected to the second part 20a3 of the exploding foil initiator 20a of figure 14. Figure 28 illustrates a partial cross-section of one of the exploding foil initiators 20a of figure 27 taken along section lines 28-28 of figure 27. In figure 28, the sheet of initiators 134, in cross section, has the same layers as that which is discussed above with reference to figure 16 of the drawings. However, for purposes of simplicity, in figure 28, only three layers of the sheet of initiators 134 is illustrated: a first two (2) ounce copper layer 42a4 wnich conducts a current to each of the plurality of exploding foil initiators 20a; a second two (2) mil Kapton layer 42a5 which represents the second polyimide layer 20c of figures 6-9; and a third two (2) ounce copper layer 42a6 which represents the second copper foil 20d functioning as a return current path to ground potential in figures 6 and 8. The exploding foil initiators 20a, being electrically connected to the first copper layer 42a4, is energized by a current conducting along the first copper layer 42a4 from the current pulse generator (CPG) 44 of figure 11, and it is also electrically connected to ground potential via the third copper layer 42a6. When the bridge 20a1 of the exploding foil initiator 20a vaporizes in response to the current from first copper layer 42a4, a flyer or bubble is formed from the first polyimide layer 20b, the flyer/bubble propagating through the hole 19a in barrel 19 thereby impacting the secondary explosive pellet 40a1 in shaped charge 40a. As noted above in the discussion with reference to figure 17, since the pellet 40a1 is comprised of the aforementioned special explosive composition, the pellet 40a1 detonates the shaped charge 40a. Referring to figure 29, a perforating apparatus is illustrated. This perforating apparatus includes a first perforating gun 137, a second perforating gun 141, and a detonation transfer unit 140 disposed between the first perforating gun 137 and the second perforating gun 141. A first detonating cord 138 is connected to and is associated with the first perforating gun 137. A second detonating cord 142 is connected to and is associated with the second perforating gun 141. A detonator 158 is connected to the second detonating cord 142. The detonator 158 may be an exploding foil initiator detonator, or an exploding bridgewire initiator detonator, or an electric detonator. The detonation transfer unit 140, which separates the first perforating gun 137 from the second perforating gun 141, is interconnected between the first detonating cord 138 and the detonator 158. A detailed construction of the detonation transfer unit 140 of figure 29 is discussed below with reference to figure 30 of the drawings. Referring to figure 30, a more detailed construction of the detonation transfer unit 140 of figure 29 is illustrated. In figure 30, the detonation transfer unit 140 includes a pressure bulkhead 152 which is adapted to isolate and insulate the pressure which exists within the interior of the first perforating gun 137 from the pressure which exists within the interior of the second perforating gun 141. An end of the first detonating cord 138 of the first perforating gun 137 of figure 29 is disposed in abutment against one side of an explosive plane wave generator 138A, with is, in turn, disposed in abutment against one side of the pressure bulkhead 152. A piezoelectric ceramic disc 156 is disposed in abutment against the other side of the pressure bulkhead 152. The piezoelectric ceramic 156 stores energy and is connected to the detonator 158 of figure 29 associated with the second detonating cord 142 of the second perforating gun 141 in figure 29. When a first detonation wave from the first detonating cord 138 hits the explosive plane wave generator 138A, the resultant explosive plane wave is transferred through the bulkhead 152 to the piezoelectric ceramic 156 disposed on the other side of the bulkhead 152 thereby causing the energy stored in the piezoelectric ceramic 156 to dump into the detonator 158. As a result, a second detonation wave propagates from the detonator 158 into the second detonating cord 142 of the second perforating gun 141 of figure 29. A functional description of the operation of the present invention is set forth in the following paragraphs with reference to figure 3 through figure 31 of the drawings. This functional description will involve the perforating apparatus of figure 12, having the flat cable conductors 42a and 42b which helically wrap around the perforating apparatus in a manner which abuts against the apex of each shaped charge, and the perforating apparatus of figure 26, having the sheet of initiators 134 which wraps around the entire circumference of the perforating apparatus 130. In figure 11, the current pulse generator 44 must generate a current pulse, similar to the current pulse shown in figure 19, in order to substantially simultaneously detonate the plurality of shaped charges 40 of the perforating apparatus in figures 11 and 12. In the preferred embodiment, the current pulse generator 44 is the compressed magnetic flux (CMF) current pulse generator 44 shown in figure 23 of the drawings. Recall that the CMF generator 44 is described in a first article entitled "Small Helical Flux Compression Amplifiers" by J.E. Gover, O.M. Stuetzer, and J.L. Johnson, Sandia Laboratories, Albuquerque, New Mexico, printed in "Megagauss Physics and Technology", 1979, and in a second article entitled "The Central Power Supply", Showcase for Technology, conference and exposition, 1981, the first and second articles being incorporated by reference into this specification. In figure 23, the exploding foil initiator (EFI) firing head 124 detonates the booster 112a of the detonating cord 122. Recall that the firing head 124 is described in U.S. Patent 5,347,929, entitled "Firing System for a Perforating gun Including an Exploding Foil Initiator and an Outer Housing for Conducting Wireline Current and EFI Current", the disclosure of which has been incorporated by reference into this specification. The detonating cord 122, in turn, detonates the explosive 116a of armature 116. The explosive detonation of the explosive 116a causes the piezoelectric ceramic 120 to release it's stored energy. As a result, a current begins to flow in the inductance coil 114. Detonation of the explosive 116a in the armature 116 causes the armature 116 to expand in it's diameter dimension, the expanded diameter propagating from left to right in figure 23. The expanded diameter of the armature 116 begins to short circuit the turns of the inductance coil 114, beginning with the left-most turn of the coil 114. The short circuit of coils 114 propagates from the left side of coil 114 to the right side in figure 23 until only one turn 114a of the coil 114 remains which is not short circuited. The magnetic field produced by the coil 114 must remain constant. Therefore, since the number of turns of the coil 114 is decreasing, the current in the remaining coils which are not short circuited must increase. As a result, a maximum pulse of current 114a1 flows in the one last remaining turn 114a of the inductance coil 114. This maximum pulse of current 114a1, shown in figure 23, flows into the plurality of initiators 20a in figure 23. In figure 12, the maximum pulse of current flows from the CMF generator 44a into the flat cable conductor 42a. In figure 15, when the spark gap switch 52 begins to conduct (changes from an open circuit to a closed short circuit condition), this maximum pulse of current, from the last turn 114a of coil 114 of figure 23, flows on the internal side (the internal side being shown in figure 14) of the flat cable conductor 42a as follows: into the electrical current path 54 of figure 15, and begins to flow into the first plurality of parallel connected exploding foil initiators 20a4, then into the second plurality of parallel connected exploding foil initiators 20a5, then into the third plurality of parallel connected exploding foil initiators 20a6, then into the fourth plurality of parallel connected exploding foil initiators 20a7, and then into the return electrical current path 56 to ground potential. When this maximum pulse of current flows into the first plurality of parallel connected EFI initiators 20a4, it flows into first, second, third and fourth EFI initiators 20a. In figures 5 and 14, when the maximum pulse of current flows into an EFI initiator 20a, it first flows into the first part 20a2 of the EFI initiator 20a, then into the bridge 20a1, and then into the second part 20a3 of the EFI initiator 20a. When the maximum pulse of current flows through the bridge 20a1, the bridge 20a1 vaporizes producing a plasma gas which creates a turbulence in the region immediately above the bridge 20a1. In figures 6 and 8, in response to the turbulence produced in the region immediately above the bridge 20a1, in figure 6, a disc 20b1 is sheared out from the first polyimide layer 20b, the disc 20b1 flying through a hole 19a in the barrel 19 and impacting the secondary explosive pellet 18a in figure 6 (40a1 in figures 16 and 17). When the disc impacts the pellet 18a, the shaped charge 18 in figure 6 (40a in figure 17) detonates. However, in figure 8, in response to the turbulence, a bubble 20b2 is formed from the first polyimide layer 20b, the bubble 20b2 impacting the secondary explosive pellet 18a (40a1 in figures 16 and 17) thereby detonating the shaped charge 18 in figure 8 and 40a in figure 17. When the last shaped charge 40a of the first perforating gun of the perforating apparatus of figure 12 detonates, the pulse of current conducting in the end of the first flat cable conductor 42a energizes the firing head 46c of the intermediate adaptor 46 of figure 12. In figure 12, when the EFI firing head 46c receives the pulse of current conducting in the flat cable conductor 42a, a pellet in the firing head 46c detonates. Detonation of the pellet in the firing head 46c initiates the propagation of a first detonation wave in the first detonating cord 46a of the intermediate adaptor 46. Since the second detonating cord 46b of intermediate adaptor 46 is disposed in side-by-side abutment with the first detonating cord 46a, the first detonation wave in the first detonating cord 46a transfers to the second detonating cord 46b. Therefore, a second detonation wave now propagates in the second detonating cord 46b, and this detonation wave energizes the second CMF generator 44b. As a result, the second CMF generator 44b produces another maximum pulse of current, and that pulse of current propagates through the second flat conductor cable 42b in figure 12, detonating the plurality of shaped charges 40b of the second flat cable conductor 42b in the same manner as described above in connection with the first flat conductor cable 42a in figure 12. Assume that the perforating gun in figure 12 does not use a flat conductor cable. Assume, instead, that a sheet of initiators, such as the sheet of initiators 134 shown in figure 26 of the drawings, is wrapped completely around the entire circumference of the perforating gun of figure 12. Based on that assumption, a functional description is set forth below with reference to figures 23-28 of the drawings. In figure 26, perforating gun 130 (the same gun as shown in figure 12 except the flat cable conductors 42a and 42b are not used) has a sheet of initiators 134 wrapped completely around the circumference of the perforating gun 130. In figure 23, the CMF generator 44 produces the pulse of current 114a1 in the same manner described above in connection with the perforating gun of figure 12. In figure 26, the pulse of current 114a1 flows into the sheet of initiators 134. In figure 28, when the pulse of current 114a1 has flowed into the sheet of initiators 134, the current pulse 114a1 flows into the first two (2) ounce copper layer 42a4, into the EFI attach hole 136a3, and into the EFI initiator 20a. Recalling that the EFI initiator 20a includes the first part 20a2, the bridge 20a1, and the second part 20a3 (see figure 14), the pulse of current 114a1 flows through the first part 20a2, the bridge 20a1, the second part 20a3, into the EFI attach hole 136a3, and into the third two (2) ounce copper layer 42a6 to ground potential. The bridge 20a1 vaporizes producing a turbulence directly above the bridge 20a1 of the EFI initiator 20a. As noted in the above description, this turbulence either shears out a disc from the first polyimide layer 20b, the disc flying through the hole 19a in barrel (figure 6), or a bubble 20b2 is formed in the first polyimide layer 20b (figure 8), the bubble 20b2 impacting the secondary explosive pellet 18a/40a1 and detonating the shaped charge 18/40a. As a result, when the pulse of current 114a1 enters the flat cable conductor 42a/42b of figure 12, or enters the sheet of initiators 134 of figures 26 and 27, all of the initiators (whether they are EFI flying plate or bubble activated initiators 20a or exploding bridgewire initiators) on the flat cable 42a/42b or on the sheet of initiators 134 will detonate substantially simultaneously. In addition, since an electrical current carrying conductor is used to substantially simultaneously detonate a plurality of shaped charges in a perforating gun, detonating cords are no longer needed. The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims: An apparatus for detonating a plurality of shaped perforating charges (40a), each of said charges having an apex, comprising: current pulse generating means (44) responsive to a stimulus for generating a pulse of current; flat cable conductor means (42a) electrically connected to said current pulse generating means, helically wrapped around and in contact with said plurality of charges (40a), and responsive to said pulse of current for conducting said pulse of current; and a plurality of exploding foil initiator means (20a) electrically connected to said conductor means, connected, respectively, to the apex of said plurality of charges, and responsive to said pulse of current conducting in said conductor means for substantially simultaneously detonating in response to said current, each of said plurality of exploding foil initiator means including, a first conductor means (20a2) for receiving said pulse of current and conducting said current, electrically conductive bridge means (20a1) electrically connected to said first conductor means and connected to the apex of one of said charges for conducting said current and vaporizing when said current exceeds a predetermined level, and second conductor means (20a3) electrically connected to said bridge means for receiving said said pulse of current from said bridge means and conducting said current, said bridge means of said plurality of exploding foil initiator means substantially simultaneously vaporizing and changing from a short circuit to an open circuit condition in response to said current when said current exceeds said predetermined level, said plurality of shaped charges substantially simultaneously detonating when said bridge means of said plurality of initiator means substantially simultaneously change to said open circuit condition. An apparatus for detonating a plurality of shaped perforating charges (132), each of said charges having an apex, comprising: current pulse generating means (44) responsive to a stimulus for generating a pulse of current; flat sheet conductor means (134) having a length and width, electrically connected to said current pulse generating means, wrapped completely around a circumference of said plurality of shaped charges until said width of said sheet conductor means is approximately equal to said circumference, disposed in contact with said plurality of charges, and responsive to said pulse of current from said current pulse generating means for conducting said pulse of current; and a plurality of exploding foil initiator means (20a) electrically connected to said flat sheet conductor means, connected, respectively, to the apex of said plurality of charges, and responsive to said pulse of current conducting in said conductor means for substantially simultaneously detonating in response to said pulse of current, each of said plurality of exploding foil initiator means including, a first conductor means (20a2) for receiving said pulse of current and conducting said current, electrically conductive bridge means (20a1) electrically connected to said first conductor means and connected to the apex of one of said charges for conducting said current and vaporizing when said current exceeds a predetermined level, and second conductor means (20a3) electrically connected to said bridge means for receiving said said pulse of current from said bridge means and conducting said current, said bridge means of said plurality of exploding foil initiator means substantially simultaneously vaporizing and changing from a short circuit to an open circuit condition in response to said current when said current exceeds said predetermined level, said plurality of shaped charges substantially simultaneously detonating when said bridge means of said plurality of exploding foil initiator means substantially simultaneously change to said open circuit condition. A perforating apparatus adapted to detonate, comprising: a plurality of shaped perforating charges adapted to detonate, each of said charges having an apex; and a detonating apparatus according to claim 1; said perforating apparatus detonating when said charges simultaneously detonate. Adapted to detonate, comprising: a perforating apparatus of claim 3, adapted to detonate, comprising: wherein said perforating apparatus has a circumference, and wherein said electrical current carrying conductor means comprises: a plurality of shaped perforating charges adapted to detonate, each of said charges having an apex; and a detonating apparatus according to claim 2; said perforating apparatus detonating when said charges simultaneously detonate. A method of detonating a perforating gun, said gun including a plurality of shaped charges (40a) having an apex comprising the steps of: (a) conducting a current pulse in an electrical current carrying conductor (42a), said conductor including a plurality of exploding foil initiators (20a) each said exploding foil initiator including a first part (20a2) electrically connected to said conductor, an electrically conductive bridge (20a1) electrically connected to said first part and disposed adjacent to an apex of a respective shaped charge, and a second part (20a3) electrically connected to said bridge and to said conductor; said conductor comprising a flat conductor cable adapted to be helically wrapped around said plurality of shaped charges; (b) receiving said current pulse from said conductor into said first part of said exploding foil initiator; (c) receiving said current pulse from said first part into said bridge; (d) receiving said current pulse from said bridge into said second part; (e) vaporizing said bridge and creating a turbulence in response to said current pulse; and (f) detonating said charge in response to said turbulence, said perforating gun detonating when said charge detonates. The method of claim 5, wherein the conducting step (a) comprises the step of: (g) transmitting said current pulse from a current pulse generator (44); and (h) receiving said current pulse from said current pulse generator into said electrical current carrying conductor, said current pulse conducting in said conductor when said current pulse is received therein. The method of claim 6, wherein the transmitting step (g) comprises the step of: detonating an explosive in an armature; conducting a current in an inductive coil (114), said coil having turns; and sequentially shorting out the turns of said coil in response to the detonating step, said current pulse transmitted from said current pulse generator being the current in a last one of the turns (114a) of said coil which is not shorted out.

Inventors: ASELTINE CLIFFORD L, BROOKS JAMES E, LERCHE NOLAN C, PARROT ROBERT A, ROZEK KENNETH E, ASELTINE, CLIFFORD L., BROOKS, JAMES E., LERCHE, NOLAN C., PARROT, ROBERT A., ROZEK, KENNETH E.
Applicants: SCHLUMBERGER HOLDINGS, SCHLUMBERGER SERVICES PETROL, SCHLUMBERGER TECHNOLOGY BV, SCHLUMBERGER HOLDINGS LIMITED, SCHLUMBERGER TECHNOLOGY B.V., SERVICES PETROLIERS SCHLUMBERGER
Application year: 1995
Main classification: E21B43
IPC codes: E21B43, F42D1