Abstract:
A switch connectable to an upper explosive device and a lower explosive device in a perforation gun train is provided. The switch comprises a circuit, a portion of the circuit being openable upon detonation of the lower explosive device, and the switch being changeable from a first position to a second position upon the opening of the portion of the circuit. In the first position, current can flow to the lower explosive device but not to the upper explosive device. In the second position, opposing current can flow to the upper explosive device but not to the lower explosive device.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to the field of down-hole explosive perforation gun technology used in well operations. 
       BACKGROUND OF THE INVENTION 
       [0002]    A perforation gun train usually consists of several linear segments (sometimes also referred to as “gun segments”) which are each loaded with explosives and are separated by perforating gun switches. Existing technology for perforating gun switches typically uses mechanical contacts that close a circuit upon receiving the mechanical impulse from an explosive detonation. These switches are generally not reliable and depend on complicated systems of rigid mechanical tolerances, small parts, and stringent physical material properties to allow the switches to withstand the operating conditions and operate as intended. 
       SUMMARY OF THE INVENTION 
       [0003]    In accordance with a broad aspect of the present invention, there is provided a switch comprising a circuit, a portion of the circuit being openable upon a detonation and the switch being changeable from a first position to a second position upon the opening of the portion of the circuit. 
         [0004]    In accordance with another broad aspect of the present invention, there is provided a switch comprising an anti-fuse, the anti-fuse being breakable upon reacting to a detonation and the switch being changeable from a first position to a second position upon breakage of the anti-fuse. 
         [0005]    In accordance with another broad aspect of the present invention, there is provided a method of detonating a series of consecutive explosive devices comprising: providing a switch between a first explosive device and a second explosive device, the first and second explosive devices being a pair of adjacent explosive devices in the series, and the switch having a circuit for selectively communicating with either of the first and second explosive devices; sending current to the first explosive device and blocking current to the second explosive device; detonating the first explosive device, thereby providing a detonation force; and opening a part of the circuit using a portion of the detonation force, thereby blocking current to the first explosive device and sending an opposing current to the second explosive device. 
         [0006]    In accordance with another broad aspect of the present invention, there is provided a switch for use in an explosive firing system for a perforation gun train. The switch is used for detecting an explosion from a gun segment of the perforation gun train and for enabling a subsequent explosive gun segment within the train. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    Drawings are included for the purpose of illustrating certain aspects of the invention. Such drawings and the description thereof are intended to facilitate understanding and should not be considered limiting of the invention. Drawings are included, in which: 
           [0008]      FIG. 1   a  is a perspective view of one embodiment of a switch of the present invention; 
           [0009]      FIG. 1   b  is a cross-sectional view of the switch of  FIG. 1   a;    
           [0010]      FIG. 1   c  is a cross-sectional view of the switch of  FIG. 1   a , showing only selected components of the device; 
           [0011]      FIG. 2  is a schematic diagram of a negative switch fuse circuit for use in one embodiment of the switch; and 
           [0012]      FIG. 3  is a schematic diagram of a positive switch fuse circuit for use in another embodiment of the switch. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    The following detailed description of embodiments of the invention makes reference to the accompanying drawings in which like references indicate similar elements, showing by way of illustration specific embodiments of practicing the invention. Description of these embodiments is in sufficient detail to enable those skilled in the art to practice the invention. One skilled in the art understands that other embodiments may be utilized and that logical, mechanical, electrical, functional and other changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims. 
         [0014]    There is provided a switch for use in an explosive firing system for a perforation gun train. The switch is used for detecting an explosion from a gun segment of the perforation gun train and for enabling a subsequent explosive gun segment within the train. 
         [0015]    In one embodiment, each pair of consecutive gun segments in the gun train is separated by the switch. The switch provides activation control of an explosive device in each segment in a step sequence from the lowermost gun segment to the uppermost gun segment. Electrical circuitry in the switch activates and conducts current selectively in response to a detonation shock from an adjacent gun segment. One method of detecting the detonation of the adjacent gun segment is using the forces from the nearby explosion to break an electrical connection in the circuitry. The broken electrical connection causes the circuitry to conduct electricity in an alternative circuit path, which allows current to flow to a detonator of a subsequent gun segment. 
         [0016]    In a preferred embodiment, the explosive devices in the gun segments are shaped charges aimed toward the casing in a wellbore, such that most of the energy from the detonation of the explosives will be directed radially towards the inner surface of the wellbore. However, some energy from the detonation will be directed towards an adjacent gun segment and its associated explosive device, which preferably also comprises shaped charges. In response to this energy, the switch of the present invention reacts by arming the detonation or initiation component associated with and operative to detonate the explosive device in the adjacent gun segment. 
         [0017]    The switch is configured to not respond to forces that are incidental to the insertion and placement of the train of charges in the wellbore, or to handling forces during shipment or assembly. In this way, there will be no false positives or false negatives in the switch&#39;s status with respect to a detonation of a downward-adjacent charge. In a further embodiment, the switch operates to disable detonation of an upper explosive device after a detonation command has been sent to an adjacent lower explosive device but before the actual detonation of the lower device. The switch may serve as a safety device to help minimize the possibility of unexpected explosion during wellbore operations. 
         [0018]    Referring to  FIGS. 1   a ,  1   b , and  1   c , a switch  10  comprises a housing  12 , a piston  14 , and wires  15 ,  16  and  18 . Housing  12  has an inner surface defining an axially extending bore having an upper opening and a lower opening, at an upper end and a lower end of housing  12 , respectively. “Upper” and “up” as used herein denote a position that is closer to the well opening at the surface than “lower” and “below”. The bore includes an upper bore area  11   a  and a lower bore area  11   b . In one embodiment, housing  12  includes a shoulder  17  between upper bore area  11   a  and lower bore area  11   b  for preventing piston  14  from moving beyond a certain point up the bore towards the upper opening. In a further embodiment, shoulder  17  is formed by a radially inwardly extension on the inner surface of the bore. In yet a further embodiment, the outer surface of housing  12  includes grooves  20  for receiving seals  22 , such as for example o-ring seals. Housing  12  is made of durable materials that can withstand wellbore conditions, such as high pressures and high temperatures, and such materials include for example aluminum, steel, titanium, polymers, ceramics, etc. The materials may further include coatings, reinforcements, etc. 
         [0019]    Piston  14  includes a hole which extends therethrough between an upper piston face and a lower piston face. Piston  14  is disposed in lower bore area  11   b , at or near the lower opening, with the piston&#39;s upper piston face facing towards the upper opening of the bore. Piston  14  may substantially cover the lower opening of the bore. Piston  14  is preferably friction-fitted in lower bore area  11   b . Piston  14  may be made of various resilient materials capable of withstanding high temperatures, including for example polytetrafluoroethylene, polycarbonate, polyphenylene-sulfide, polyamide-imide, polyimide, semicrystalline thermoplastics, ceramics, etc. The upper piston face of piston  14  includes a protrusion  13  that extends axially upwardly away from the upper piston face towards upper bore area  11   a.    
         [0020]    A circuit board  24  is disposed in upper bore area  11   a , above piston  14 . Circuit board  24  includes an anti-fuse  25 . In one embodiment, anti-fuse  25  is positioned near protrusion  13  of piston  14 , while other components of circuit board  24  are positioned further away from protrusion  13 . In one embodiment, anti-fuse  25  comprises an electrical conduction pathway. The electrical conduction pathway may be a conductive wire or conductive circuit trace. Circuit board  24  is in communication with a lower wire  18 , which is connectable to a lower gun segment (not shown) in a gun train. In one embodiment, wire  18  extends from the bore through the hole in piston  14  to the outside of housing  12 . Circuit board  24  is also in communication with an upper wire  16 , which is connectable either to an upper gun segment (not shown) in the gun train or to a current supply above the switch. Circuit board  24  is further in communication with a detonator wire  15 , which is connectable to a detonator (not shown). The detonator, which may be an electrical fuse, may be associated with the explosive device in the upper gun segment. Both wires  15  and  16  may extend into the bore from the exterior of housing  12  through the upper opening. In one embodiment, the electronic components of circuit board  24  are solid-state electronics. 
         [0021]    Circuit board  24  may be partially or substantially shielded with a pressure barrier encapsulation material  26 , which includes for example foam, silicone, epoxy based potting materials. Material  26  helps protect circuit board  24  from any vibration and/or changes in pressure as a result of nearby explosions. Material  26  may also function to keep circuit board  24  in place within the bore. 
         [0022]    In operation, switch  10  has two positions: a fuse-intact position (as shown in  FIGS. 1   a ,  1   b , and  1   c ) and a fuse-broken position. In the fuse-intact position, wires  16  and  18  are in communication with the upper gun and lower gun segments, respectively, and wire  15  is in communication with the detonator of the upper gun segment. Also, the anti-fuse is not in contact with protrusion  13  when switch  10  is in the fuse-intact position. In the fuse-intact position, current is allowed to flow between wires  16  and  18  but no current flows through wire  15 . In the fuse-broken position, wire  16  is in communication with the upper gun segment and wires  15  and  16  are in communication with each other. Further, in the fuse-broken position, wire  18  is disconnected from circuit board  24  and the lower gun segment, and protrusion  13  is in contact with anti-fuse  25 , severing the electrical conduction pathway, thereby “breaking” anti-fuse  25 . Once anti-fuse  25  is broken, current can no longer flow between wires  16  and  18  but current is allowed to flow from wire  16  to wire  15  through the remaining intact portions of the circuit (“secondary circuit”). 
         [0023]    Switch  10  may operate in various ways and the following describes an example of how device  10  may operate. When the lower gun segment is undetonated, switch  10  is in the fuse-intact position. A current is supplied from wire  16  through circuit board  24  to wire  18 , providing a detonation charge to the lower gun segment via wire  18 . If the detonation charge is sufficient, the lower gun segment detonates and the detonation exerts an explosive force on to the lower end of housing  12  and the lower piston face of piston  14 . In one embodiment, the pressure exerted on the lower piston face from the detonation is approximately 30,000 psi. The explosive force pushes piston  14  upwards in housing  12  towards upper bore area  11   a , such that protrusion  13  impacts anti-fuse  25  and severs the electrical conduction pathway therein, thereby bringing switch  10  into the fuse-broken position. In one embodiment, the upward movement of piston  14  is restricted by shoulder  17 , such that piston  14  can move upwards until its upper piston face abuts against shoulder  17 . This restriction provided by shoulder  17  helps to ensure that the extent to which protrusion  13  can extend into upper bore area  11   a  is only sufficient to break anti-fuse  25 , but not sufficient to affect other parts of circuit board  24 . The upward movement of piston  14  may also disconnect wire  18  from circuit board  24 . Once anti-fuse  25  is broken, current is allowed to flow from wire  16  via the secondary circuit to wire  15 . In one embodiment, current is supplied through the secondary circuit to wire  15 , which is connected to a detonator of another gun segment, in order to detonate that gun segment in the gun train. In a further embodiment, switch  10  is placed in between each pair of consecutive gun segments in the gun train in order to detonate a series of segments in a particular order. 
         [0024]    The schematics in  FIGS. 2 and 3  each illustrate a sample circuit that may be used in circuit board  24  to detect the breakage of anti-fuse  25 .  FIG. 2  shows a negative switch fuse circuit  100  and  FIG. 3  shows a positive switch fuse circuit  200 .  FIGS. 2 and 3  each illustrate one sample configuration and a person skilled in the art will appreciate that other circuit configurations that operate substantially similarly may be used for the present invention. In a preferred embodiment, the electronic components in circuits  200  and  300  are solid-state electronics. 
         [0025]    Referring to  FIG. 2 , circuit  100  serves to switch a supply of current from one destination (e.g. the lower gun segment) to another destination (e.g. the secondary circuit) and the switch is generally initiated by an event (e.g. an explosion and/or detonation). In one embodiment, circuit  100  includes a silicon controlled rectifier (SCR)  102 , resistors  106  and  108 , and a diode  104 . Resistor  106  has a first terminal connected to the cathode of SCR  102 , and a second terminal connected to the gate of SCR  102 . The cathode of SCR  102  is also connected wires  16  and  18 . The first terminal of resistor  106  is also connected to upper wire  16 . Both terminals of resistor  106  are connected to lower wire  18 . Resistor  108  has a first terminal connected to the gate of SCR  102 , and a second terminal connected to the anode of SCR  102 . The first terminal of resistor  108  is also connected to lower wire  18 . The cathode of diode  104  is connected to the second terminal of resistor  108  and the anode of SCR  102 . The anode of diode  104  is connected to detonator wire  15 . In this circuit configuration, anti-fuse  25  is provided in an area of circuit  100  where resistors  106 ,  108  and the gate and cathode of SCR  102  connect to lower wire  18 . 
         [0026]    Various types of SCRs, diodes, and resistors may be used in circuit  100 . For example, in one embodiment, SCR  102  in circuit  100  is DR-DPAK-600V-IA5. In a further embodiment, the resistance of resistor  106  ranges between 142.5 K and 157.5 K, but is preferably 150 K. In a still further embodiment, the resistance of resistor  108  ranges between 307.8 K and 340.2 K, but is preferably 324 K. In another embodiment, diode  104  is DR-SOD123-1000-1A. 
         [0027]    In circuit  100 , the cathode and gate of SCR  102  are shorted together, which prevents SCR  102  from conducting current from its anode to its cathode and consequently prevents any current from flowing through the circuit to wire  15 . Current can, however, flow between upper wire  16  and lower wire  18 . 
         [0028]    Before an explosive charge is initiated in the lower gun segment, anti-fuse  25  of circuit  100  is intact such that lower wire  18  and resistors  106 ,  108  and SCR  102  are connected as described above. The explosive charge in the lower gun segment may be initiated by a supply of current from the upper gun segment, via upper wire  16 , to the lower gun segment, via lower wire  18 . The current required to initiate an explosive charge (the “firing threshold”) depends on the design of the detonator. In one embodiment, the firing threshold is greater than 0.2 amps. 
         [0029]    Once the explosive charge is initiated in the lower gun segment, the lower gun segment is detonated and the detonation breaks anti-fuse  25  as described above and disconnects wire  18 . After anti-fuse  25  breaks, the secondary circuit takes shape, wherein SCR  102  is allowed to conduct current. In the secondary circuit of circuit  100 , SCR  102  is on when a negative current threshold has been reached as determined by the ratio of resistor  108  to resistor  106 . When SCR  102  is on, current can flow through the secondary circuit to wire  15  to provide an energizing signal current to the detonator. The negative switch fuse circuit  100  is configured to only allow negative direct current (DC−) to flow from wire  16  to wire  15  in the secondary circuit. 
         [0030]    Referring to  FIG. 3 , circuit  200  serves to switch a supply of current from one destination (e.g. the lower gun segment) to another destination (e.g. the secondary) and the switch is generally initiated by an event (e.g. an explosion and/or detonation). In one embodiment, circuit  200  includes an SCR  202 , resistors  206  and  208 , and a diode  204 . Resistor  206  has a first terminal connected to the anode of SCR  202  and a second terminal connected to the gate of SCR  202  and a first terminal of resistor  208 . The anode of SCR  202  is also connected wires  16  and  18 . The first terminal of resistor  206  is also connected to wires  16  and  18 . Resistor  208  has a first terminal connected to the gate of SCR  202  and also the second terminal of resistor  206 . A second terminal of resistor  208  is connected to the cathode of SCR  202  and the anode of diode  204 . Both terminals of resistor  208  are connected by a wire. The cathode of diode  204  is connected to detonator wire  15 . The anode of diode  204  is connected to the cathode of SCR  202 . In circuit  200 , anti-fuse  25  is the wire connecting the terminals of resistor  208 . 
         [0031]    Various types of SCRs, diodes, and resistors may be used in circuit  200 . For example, in one embodiment, SCR  202  in circuit  100  is DR-DPAK-600V-IA5. In a further embodiment, the resistance of resistor  208  ranges between 142.5 K and 157.5 K, but is preferably 150 K. In a still further embodiment, the resistance of resistor  206  ranges between 307.8 K and 340.2 K, but is preferably 324 K. In another embodiment, diode  204  is DR-SOD123-1000-1A. 
         [0032]    In circuit  200 , the cathode and gate of SCR  202  are shorted together, which prevents SCR  202  from conducting current from its anode to its cathode and consequently prevents any current from flowing through the circuit to detonator wire  15 . Current can, however, flow between upper wire  16  and lower wire  18 . 
         [0033]    Before an explosive charge is initiated in the lower gun segment, anti-fuse  25  is intact such that the terminals of resistor  208  are connected by the wire, as described above. The explosive charge in the lower gun segment may be initiated by a supply of current from the upper gun segment, via upper wire  16 , to the lower gun segment, via lower wire  18 . 
         [0034]    Once the explosive charge is initiated in the lower gun segment, the lower gun segment is detonated and the detonation breaks anti-fuse  25  such that the wire connecting the terminals of resistor  208  is severed. The detonation also disconnects wire  18 . After anti-fuse  25  breaks, the secondary circuit takes shape, wherein SCR  202  is allowed to conduct current. In the secondary circuit of circuit  200 , SCR  202  is on when a positive current threshold has been reached as determined by the ratio of resistor  206  to resistor  208 . When SCR  202  is on, current can flow through the secondary circuit to wire  15  to provide an energizing signal current to the detonator. The positive switch fuse circuit  200  is configured to only allow positive direct current (DC+) to flow from wire  16  to wire  15  in the secondary circuit. 
         [0035]    The switch of the present invention uses solid-state electronics and a mechanically breakable “anti-fuse,” which aims to reduce the number of mechanical parts required, to reduce the complexity and tolerance requirements of the mechanical parts, and to allow the use of simpler manufacturing methods to automate production to help minimize the cost of manufacturing. 
         [0036]    In one embodiment, the circuit used in consecutive switches in the gun train alternates between a negative switch fuse circuit and a positive switch fuse circuit. In other words, if a first gun segment has a positive switch (i.e. a switch that has a positive switch fuse circuit) above it, a second gun segment immediately above the positive switch connected to the first gun segment will have a negative switch (i.e. a switch that has a negative switch fuse circuit) above it, and a third gun segment immediately above the negative switch connected to the second gun segment will have a positive switch above it, and so on. By alternating between negative switches and positive switches along the gun train, adjacent switches will have different circuits that allow current flow in opposite directions. This alternating switch configuration functions as a safety measure, which is to help prevent all the gun segments from detonating at the same time. 
         [0037]    For example, if a lowermost gun segment with a first detonator is connected to a positive switch above it, then only a negative current is allowed to flow through the switch to the first detonator. When the power to the first detonator reaches a predetermined threshold, the lowermost gun segment detonates, thereby breaking anti-fuse  25  of the positive switch above and enabling the secondary circuit to communicate with wire  15 . Wire  15  is in communication with a second detonator of a second lowermost gun segment, which is adjacent to the lowermost gun segment. Because of the configuration of the secondary circuit of the positive switch, negative current cannot flow through wire  15  to the second detonator, regardless of the magnitude of the current. The second lowermost gun segment has a negative switch above it. When the current supply is switched from negative to positive direct current, which may be done manually, then the secondary circuit of the positive switch will allow the positive current to flow through wire  15  to the second detonator to detonate the second lowermost gun segment, thereby breaking the anti-fuse of the negative switch above. The breaking of the anti-fuse of the negative switch enables the secondary circuit of the negative switch, which has a wire  15  in communication with a third detonator of a third lowermost gun segment above the second lowermost gun segment. However, the secondary circuit of the negative switch prevents positive direct current, regardless of its magnitude, from flowing through wire  15  to the third detonator. When the current is switched back to negative direct current, the secondary circuit of the negative switch allows the negative current to flow through wire  15  to the third detonator to detonate the third lowermost gun segment. The above-described alternating-switch configuration and detonation process may be carried out through the entire gun train. As such, alternating between positive and negative switches in a series of gun segments allows the sequential detonation of the gun segments in a controlled manner. 
         [0038]    In the foregoing specification, the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.