Abstract:
An initiator for initiating detonation in a detonation cord of a perforating system, where the initiator comprises a modular electronic igniter that quick connects into a portion of high explosive. The high explosive is disposed in a housing having an end of detonation cord crimped therein. The electronic igniter may be shipped to the field and/or stored separate from the high explosive then the two may be assembled just prior to deploying the perforating gun assembly in a wellbore. Various methods of quick connecting the electronic igniter to the high explosive may be used.

Description:
BACKGROUND 
     1. Field of Invention 
     The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a perforating system. Yet more specifically, the present invention relates to a modular initiator for use in a perforating gun system. 
     2. Description of Prior Art 
     Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically completed by coaxially inserting a pipe or casing into the wellbore. The casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore. 
     Perforating systems typically comprise one or more perforating guns strung together, these strings of guns can sometimes surpass a thousand feet of perforating length. In  FIG. 1  an example of a perforating system  4  is shown. For the sake of clarity, the system  4  depicted comprises a single perforating gun  6  instead of a multitude of guns. The gun  6  is shown disposed within a wellbore  1  on a wireline  5 . The perforating system  4  as shown also includes a service truck  7  on the surface  9 , where in addition to providing a raising and lowering means, the wireline  5  also provides communication and control connectivity between the truck  7  and the perforating gun  6 . The wireline  5  is threaded through pulleys  3  supported above the wellbore  1 . As is known, derricks, slips and other similar systems may be used in lieu of a surface truck for inserting and retrieving the perforating system into and from a wellbore. Moreover, perforating systems may also be disposed into a wellbore via tubing, drill pipe, slick line, coiled tubing, to mention a few. 
     Included with the perforating gun  6  are shaped charges  8  that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the shaped charge high explosive is detonated, the force of the detonation collapses the liner and ejects it from one end of the charge  8  at very high velocity in a pattern called a “jet”  12 . The jet  12  perforates the casing and the cement and creates a perforation  10  that extends into the surrounding formation  2 . 
     The shaped charges  8  are typically connected to a detonating cord, which when detonated creates a compressive pressure wave along its length that initiates shaped charge detonation. An initiator  14  is typically used to set off detonation within the detonation cord.  FIG. 2  provides a side cross sectional view of a typical initiator  14  having leads ( 16 ,  17 ) secured in an end cap  20  of the initiator  14  and connected on their lower terminal ends via a frangible bridge  18 . The initiator  14  is typically controlled at surface where an electrical signal is sent via the wireline  5  to one of the leads ( 16 ,  17 ). In the example of  FIG. 2  current from the electrical signal flows from lead  17  to lead  16  through the frangible bridge  18 . The bridge  18  is made from a conductive material and includes generally a narrowed portion that heats and disintegrates under the applied current load. An amount of high explosive  22  is disposed in a housing  24  adjacent the frangible bridge  18  which is ignitable in response to the energy dissipated during the frangible bridge  18  disintegration. An end of a detonation cord  26  is positioned adjacent the lower end of the high explosive  22  and may be crimped  28  into place. Combustion of the high explosive  22  is readily transferred to the adjacent detonation cord  26  which detonates the cord  26  that in turn detonates the shaped charges  8 . 
     Generally the initiators are connected to the perforating cords in the field just prior to use. Thus they are shipped to the field with the electrical portions and high explosive coupled together in a single unit. Because of the risks posed by the high explosives and the threat of a transient electrical signal, shipment and storage of the initiators is highly regulated, this is especially so when being shipped to foreign locations. Additional problems may be encountered in the field when connecting initiators to the detonation cord. Perforating guns when delivered to the field generally have the shaped charges and detonation cord installed; to facilitate initiator connection some extra length of detonation cord is provided within the gun. Connecting the initiator to the detonation cord involves retrieving the free end of the detonation and cutting it to a desired length then connecting, usually by crimping, the initiator to the detonation cord. These final steps can be problematic during inclement weather. Additionally, these final steps fully load a perforating gun and thus pose a threat to personnel in the vicinity. Accordingly benefits may be realized by reducing shipping and storage concerns, increasing technician safety, and minimizing the time required to finalize gun assembly in the field. 
     SUMMARY OF INVENTION 
     Disclosed herein is a perforating gun initiator comprising, a first housing, a high explosive within the first housing, a detonation cord disposed proximate the high explosive, and an electronic igniter in a second housing selectively quick coupled with the high explosive. The electronic igniter comprises an explosion initiating bridge element. An electrical signal source may be included in communication with the bridge element for providing a signal for initiating detonation of the high explosive. In one embodiment, the electronic igniter comprises an end cap, electrical contact leads axially extending through the end cap, a bridge element connected between the contact leads; and an annular insert extending from the end cap. A bore may be provided in the high explosive for receiving the annular insert therein. A quick connect assembly may optionally be employed for providing quick coupling engagement between the electronic igniter and the high explosive. An embodiment of the quick connect assembly comprises an upper portion and a lower portion, each of which affixable to one of the electronic igniter or high explosive, snap members extending from the upper portion, and receptacles formed in the lower portion formed to receive the snap members. The quick connect assembly may also optionally comprise an overshot skirt extending from the outer radius of the electronic igniter formed to quick connect with a collar on the high explosive. The perforating quick connect assembly may also optionally comprise a series of hooks and loops. In another embodiment, the quick connect assembly comprises a corresponding lip and groove on one of the annular insert outer surface and bore inner surface. 
     Also disclosed herein is an initiator for use in igniting a detonation cord of a perforating system, the initiator comprising, high explosive in a housing, detonating cord in explosive communication with the high explosive; an explosion initiating frangible bridge member coupled to the high explosive; wherein the bridge member is in electronic communication with a detonation signal; and a quick connect assembly affixed between the bridge member and the high explosive. 
     The present disclosure also includes method of forming a perforating system comprising, connecting a detonation cord to a shaped charge disposed in a perforating gun, positioning a high explosive into detonating proximity with the detonation cord, quick connecting an electronic igniter to the high explosive, where the electronic igniter comprises a frangible bridge member, and connecting the frangible bridge member to a detonating signal source. The electronic igniter of this method may comprise electrical leads in electrical communication via the frangible bridge member, and end cap having passages therethrough in which the leads are positioned. The further optionally comprises disposing the perforating gun within a wellbore, lowering the perforating gun proximate to a location to be perforated, supplying an electrical detonation signal to the bridge member thereby disintegrating the bridge member to create a source of ignition of the high explosive. Alternatively included with the present method is a step of assembling the perforating system at an assembly site and separately shipping to the assembly site the high explosive and electronic igniter. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is partial cutaway side view of a prior art perforating system in a wellbore. 
         FIG. 2  illustrates a cutaway side view of a prior art perforating gun initiator. 
         FIG. 3  is a side cutaway view of an embodiment of an initiator. 
         FIG. 4  is a side perspective view of an embodiment of a portion of the initiator of  FIG. 3 . 
         FIGS. 5   a - 5   d  are side cutaway views of embodiments of initiators and coupling devices. 
     
    
    
     While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF INVENTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
     It is to be understood that the invention is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the invention is therefore to be limited only by the scope of the appended claims. 
     The disclosure herein is directed to an initiator for use in initiating the detonation of a detonation cord used in a perforating gun system. The initiator described herein comprises an electronic portion and a high explosive portion. The electronic and high explosive portions are both modular elements that are distinct and separate from one another, but can be quickly connected during assembly or makeup of a perforating gun system. The separate and modular characteristic of these elements allows these portions of the initiator to be shipped and stored separate from one another. Separate shipping and storage significantly reduces the issues encountered due to domestic and foreign regulations regarding high explosives. Also enhanced is the safety of assembling a perforating gun system using the initiator as described herein. 
       FIG. 3  represents a side cross sectional view of an embodiment of an initiator assembly  30  having the novel features as described herein. The initiator assembly  30  comprises an electronic igniter  32  shown connected to a portion of high explosive  42 , where the high explosive  42  is formed within a housing  44 . The electronic igniter  32  comprises an end cap  34  having a generally cylindrical configuration with its lower planar surface generally aligned with the upper planar surface of the high explosive  42 . A bore  45  extends from the high explosive  42  upper planar surface and runs generally coaxial with the axis A x  of the initiator assembly  30 . The bore  45  is formed to receive an annual insert  40  which extends from the end cap  32  lower planer surface. 
     A frangible bridge element  38  (or bridge member) is shown disposed proximate to the lower terminal end of the insert  40 , the bridge element  38  is disposed generally perpendicular to the axis A x  of the initiator assembly  30 . Electrical leads ( 35 ,  36 ) are electrically connected to the bridge element  38  and respectively on distal ends of the bridge element  38  proximate to the inner wall of the insert  40 . The leads ( 35 ,  36 ) extend upward and perpendicular from the bridge element  38  and through the end cap  34  via passages ( 37 ,  39 ) formed to receive the leads ( 35 ,  36 ) therethrough. The upper ends of the leads ( 35 ,  36 ) are in electrical communication with a signal source (not shown) for delivering an explosive signal through the leads to the bridge element  38 . 
     The modular aspect of the electronic igniter  32  and the configuration of the explosive  42  within its housing  44  allow these two members to be quickly connected together in a quick connect operation, just prior to fully assembling a perforating system for deployment into a well bore and used in initiating detonation of an associated detonation cord  46  for perforating a well bore. 
       FIG. 4  provides a perspective view of one embodiment of the electronic igniter  32 . In this view, the insert  40  shown as a generally annular member having a bridge element  38  extending along the opening at the terminal end of the insert  40 . The end cap  34  receives the upper end of the insert where the insert is affixed therein. Although the bridge element  38  is shown as an elongated member with a substantially consistent cross sectional area, it can tale on many different forms. The bridge element  38  however should be formed from an electrically conducting material disintegratable with an appropriate amount of electrical current flowing therethrough. Moreover, the disintegrative effect of the bridge element  38  should be sufficient to initiate high explosive  42  detonation. It is believed that it is well within the capabilities of those skilled in the art to form an appropriately dimensioned bridge element and apply a proper amount of electrical current there-through to produce an explosion initiating bridge element for initiating high explosive detonation. 
     Schematically provided in  FIG. 3  is an optional communication module  49  for controlling electrical power from upper lead  74  to the electronic initiator  32  and to an upper lead  73  from the electronic initiator  32 . In one example, the communication module  49  forms an open circuit between the upper lead  74  and an intermediate lead  75  thus preventing power from reaching the electronic initiator  32 . The communication module  49  is configured to respond to receiving a pre-designated signal or sequence of signals via the upper lead  74  by closing an internal circuit thereby providing electrical communication between the upper lead  74  and the intermediate lead  75 . The pre-designated signal may be sent from a controller or operator at the surface, and include an identifier or address recognizable by the communications module  49 . The communications module  49  may also be configured to acknowledge the pre-designated signal and respond with a signal indicating the acknowledgement. The acknowledgement reflects receipt of the pre-designated signal and may note the communications module  49  has switched into a closed circuit thereby allowing electrical power to be transmitted to the electrical initiator  32 . Electrical power for activating the initiator assembly  30  may be provided with or subsequent to the pre-designated signal (also referred to as an arming signal) or may be sent after the acknowledgement signal has been received. 
     Proper disintegration of the bridge element  38  typically requires a threshold voltage which often exceeds the voltage provided via the lead  35  or the associated wireline. Thus a step up module  47  may optionally be provided for attaining the threshold voltage. Thus in one mode of operation of the initiator assembly  30  of  FIG. 3 , the step up module  47  increases the voltage the electrical power it receives from the communications module  49  via the intermediate lead  75  to at least the threshold voltage. Optionally, as shown in  FIG. 3 , space may exist between the bridge element  38  and explosive  42 . 
     Various embodiments of quick connection assemblies are provided in  FIGS. 5   a  through  5   d . However, any manner of coupling the modular electronic igniter to a high explosive for use in forming a perforating system detonation initiator can be employed with the present device. For the purposes of discussion herein a quick connection or quick connection assembly, means forming a connection between two members by urging the two members together with an opposing force. Optionally, quick connection can also mean bringing any two elements together with opposing force and rotating one or both of the members, the rotation preferably is less than 360°. 
     In the quick connect embodiment shown in  FIG. 5   a , a coupling  48  affixes the electronic igniter  34   a  to an amount of explosive  42   a . The coupling  48  comprises an upper portion  50  disposed within an annular groove  51  where the groove  51  is formed on the lower outer periphery of the end cap  34   a . The upper portion  50  includes a downwardly extending snap member  52  whose cross sectional area varies along its length. In the embodiment shown the snap member  52  is a generally spherical member connected to the upper portion  50  via a base portion  53 . The coupling  48  further comprises an annular lower portion  54  affixed on the upper planar surface of the high explosive  42   a , wherein the lower portion  54  circumscribes a portion of the insert  40  that extends into the bore  45  of the explosive  42   a . Receptacles  56  are shown provided within the lower portion  54  configured to receive the snap members  52  therein. Preferably, the corresponding diameters of the snap members  52  and receptacles  56  are substantially the same such that an urging force is required to insert the snap members  52  within their receptacles  56 . This results in a press fit allowing for a quick connect between the electronic igniter  34   a  and the explosive  42   a . The press fit can not only be quick connected, but also retains the modular units together into a single cohesive initiator suitable for use in initiating detonation of an associated detonation cord  46 . 
     An optional embodiment of a coupling  48   a  is provided in side cross sectional view in  FIG. 5   b . In this embodiment the coupling  48   a  comprises an annular overshot skirt  58  which extends from the outer periphery of the end cap  34   b  downward. A groove  62  is formed on the outer surface of the upper end of the high explosive  42 , a ring like collar  60  resides on the outer circumference of the groove  62 . The collar  60  is generally coaxial with the overshot skirt  58  and has an outer diameter substantially the same as the inner diameter of the overshot skirt  58 . Accordingly, downward sliding of the overshot skirt  58  over the collar  60  can quickly connect the electronic initiator  34   b  to the high explosive  42   b . Optionally small ball bearings  66  may be included in receptacle wells  64  formed in the collar  60 . Corresponding indentations  68  may be formed on the inner surface of the overshot skirt  58  and formed for mating cooperation with the ball bearing  66 . 
     As shown in side cross sectional view in  FIG. 5   c  a quick connection assembly for coupling an electronic initiator  34   c  to a high explosive  42   c  may comprise a series of opposingly formed hooks and loops  70  wherein a series of hooks may be glued or otherwise secured to the bottom planar surface of the electronic igniter  34   c  and corresponding loops glued or otherwise secured to the upper most surface of the high explosive  42   c . In partial cross sectional view,  FIG. 5   d  illustrates a lip and groove arrangement for quick connecting an electronic initiator  34   d  to high explosive  42   d . Here a lip  41  is formed on the outer surface of the insert  40   b  extending downward from the end cap  43   d . A corresponding groove  43  is formed within the bore  45   a  and configured to provide a press fit and quick connection coupling between the electronic igniter and the high explosive  42   d.    
     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.