Abstract:
Apparatus and method are provided for select-firing of perorating guns or activating other equipment in a well, such as a bridge plug. Double-pole double-throw electronic relays, used along with diodes that block voltage below a selected level, are used to control access of positive or negative voltages to blasting caps. Firing of a blasting cap causes an open circuit across the blasting cap and shifting of a relay. Alternate application of negative and positive voltages allows activation of multiple devices in a well.

Description:
BACKGROUND OF INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to perforating well casing. More particularly, apparatus and method are provided for selective firing of multiple guns with a relay switch. 
         [0003]    2. Description of Related Art 
         [0004]    Casings in wells for producing or injecting fluids are cemented in a wellbore and holes are formed in the casing at selected locations opposite certain subterranean formations by a device called a “perforating gun.” The gun usually is made up of shaped charges that are detonated by a blasting cap. The cap is activated by an electrical current. In many wells it is desirable to perforate casing over larger distances in the wellbore than can be accommodated by one perforating gun. To avoid running perforating guns hi the wellbore and withdrawing the spent charges repeatedly, it is advantageous to place a plurality of perforating charges or groups of charges in the well simultaneously and to shoot the charges selectively when placed opposite the selected subterranean formation. This capability is called “select-fire,” and it is old in the art. 
         [0005]    Examples of apparatus for selectively firing perforating charges are disclosed in U.S. Pat. Nos. 5,531,164; 5,700,969; and 7,387,162. The electrical circuits in the devices are designed such that charges are fired sequentially by alternately applying a negative and a positive electrical voltage to the device. The circuits also include a mechanical device, referred to as a “dart.” The dart is disposed between chambers of a perforating charge or multiple charges that are to be fired selectively. The function of the dart is to electrically ground a blasting cap in the adjacent second chamber when the charges are fired in a first chamber. The electrical circuits are such that the perforating charges cannot be fired until the blasting cap for those charges is grounded. The dart moves in response to the shockwave pressure in the first chamber to place electrical conductors in contact, thus grounding the blasting cap. 
         [0006]    One problem with darts is that about 1 in 120 devices now in use in industry fail and cause a misfire (lack of firing) of subsequent charges in a sequence of select-fire charges. This failure requires that the perforating apparatus be withdrawn from a well and another apparatus run into the well. This can be a very costly failure, particularly in deep wells, offshore wells and other wells in high-cost operating areas. 
         [0007]    What is needed is a device and an electrical circuit to replace the mechanical darts such that select-firing can be achieved by alternating the electrical voltage applied to the device between positive and negative and switching to sequentially activate blasting caps, which may be used to fire perforating charges or perform other downhole operations. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    A select-fire device is provided employing an electronic relay circuit. 
         [0009]    A test device is provided that may be used to reset the respective switch relays for reuse (of the device) or to verify that the circuit is operable before deploying the select-fire device in a well. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
         [0010]    The numerals identify the same part in each drawing. 
           [0011]      FIG. 1  is an electrical schematic of one embodiment of the electronic switch disclosed herein. 
           [0012]      FIGS. 2(   a ),  2 ( b ) and  2 ( c ) illustrate one embodiment of the mechanical arrangement of a perforating tool with the switches disclosed herein. 
           [0013]      FIG. 3  is an electrical schematic of a test and resetting circuit device showing the resetting of a negative switch. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referring to  FIG. 1 , one embodiment of an electrical circuit for use with blasting caps to provide an electronic switch is shown. Variable voltage power supply and polarity switch  100 , preferably capable of supplying positive or negative voltage from 0 to about 100 VDC, is used to send voltage to supply voltage wire  50 , which has internal resistance  101  (about 100 ohms). With the relays as shown in  FIG. 1 , a negative voltage is applied first. With positive switch relay  41  positioned as shown, the negative voltage passes through negative switch relay  31  and bottom switch relay  21  to Zener diode  22 , which blocks voltages below 10 V. Zener diode  22  serves a safety function, not allowing lower stray voltages to pass. Negative voltage is increased to overcome the Zener voltage of Zener diode  22 , pass through diode  25   a,  fuse  24 , and activate blasting cap  10 , which may have a resistance of 51 ohms. Blasting cap  10  is normally used to activate a bridge plug (not shown), which is activated to form a plug in a casing below perforations. Bottom switch  20  and blasting caps  10  and  11  may not be present if no other device is to be activated in the casing before perforating. 
         [0015]    When blasting cap  10  is activated by negative voltage, it becomes an open circuit. The negative voltage then passes through diode  25   b  and overcome the Zener voltage of Zener diode  26 , which may be a 75 V diode. Negative voltage then passes through relay coil  27  (2000 ohm) and resistor  28  (1000 ohm) to ground, switching relay  21 . To activate blasting cap  11  for firing the first perforation charge or charges, a positive voltage is applied to line  50 , which will then overcome the Zener voltage of Zener diode  29 , pass through diode  25   c,  fuse  24   b  and blasting cap wire  51  to cap  11 . When cap  11  becomes an open circuit, the positive voltage will be applied to coil  37  of relay  31 , switching this relay of negative switch  30 . The positive voltage is blocked by diode  35   a,  which blocks voltages below 400 V. Blasting cap  12  may then the activated by applying a negative voltage at power supply and polarity switch  100 . When blasting cap  12  becomes an open circuit, the negative voltage passes diode  45   b,  Zener diode  46  and switches relay  41  of positive switch  40 . Subsequently, application of positive voltage may be applied to blasting cap wire  51  and used to activate blasting cap  13 . Additional switches may be added, each switch alternating as positive and negative switch, and operating as described for switches  30  and  40 . 
         [0016]    The components of the circuit illustrated in  FIG. 1  may have the following values and identifications:
   Blasting caps  10 ,  11 ,  12  and  13 —51 ohms   Relays  21 ,  31  and  41 —DPDT latching relays, such as Teledyne 422-H-26     22 ,  29 ,  39 ,  49 —10 V Zener diode     24   a,    24   b,    34 ,  44 —1.25 amp fuses     25   a,    25   b,    25   c,    35   a,    35   b,    45   a,    45   b —blocking diodes (400 V)     26 ,  36 ,  46 —75 V Zener diodes     27 ,  37 ,  47 —2000 ohm relay coils     28 ,  38 ,  48 —1000 ohm resistors   
 
         [0025]    Referring to  FIGS. 2(   a ),  2 ( b ) and  2 ( c ), three sections of select fire perforating device  200  are shown. Positive switch  40  is shown in  FIG. 2(   a ), negative switch  30  in  FIG. 2(   b ) and bottom switch  20  in  FIG. 2(   c ). Supply voltage wire  50  enters the top of device  200  in  FIG. 2(   a ). A selected number of switches such as the positive switch  40  and negative switch  30  may be combined in device  200 . Bottom switch  20  may be designed to operate two blasting caps, one of which is electrically connected to wire  50  exiting the bottom of device  200 , as shown in  FIG. 2(   c ), and the other is cap  11 . Blasting cap  11  is connected to primacord  11 A, which causes firing of perforating charge  11 B. Charge  11 B may be a selected number of charges fired at the same time. Similarly, negative switch  30  is electrically connected to blasting cap  12 , which operates as described above on  12 A and  12 B. Positive switch  40  is electrically connected to blasting cap  13 , which operates as described above on  13 A and  13 B. Seals  202 ,  204 ,  206 ,  208 ,  210  and  212  prevent well fluids from contacting electronic boards  40 A,  30 A and  20 A. 
         [0026]    Dual switch latching relays  21 ,  31  and  41  ( FIG. 1 ) have two distinct sides, switching and resetting. Relay switching coils  27 ,  37  and  47  are used to change the state of the switch and allow direct contact between supply voltage line  50  and the next blast cap wire  51 . Coils  27 A,  37 A and  47 A are used to verify the state of the latch and reset the switch. Both relay switching wiper connections  27 ,  37  and  47  and relay resetting wiper connections  27 A,  37 A and  47 A are directly connected internally through a switching and resetting wiper link  32 , as shown in the figures. One side of dual switch latching relays cannot be activated without activating the other side. 
         [0027]    Referring to  FIG. 3 , an electrical schematic of test and resetting circuit device  54  is shown during the process of resetting negative switch  30  from the “fired” to the “armed” state. The left hand side of  FIG. 3  shows dual switch latching relay  31  of negative switch  30  in the “fired” state. After use in the perforating gun assembly  200 , negative switch  30  can be reset and reused. Test and resetting circuit device  54  can be connected through test circuit connector  61  to switch test connector  62  mounted on printed circuit board  60  within the negative switch  30 , for example. The same applies for positive switch  40 . Once test and resetting circuit device  54  is connected to a “fired” negative switch  30 , red “fired” light emitting diode (LED)  47  is illuminated by current passing through a circuit made through DC power supply  53 , test circuit connector  61 , switch test connector  62  and relay resetting wiper connection  33   a  on the dual switch latching relay  31 , out to normally-open resetting wiper connection  33   b,  back to switch test connector  62 , test circuit connector  61 , through LED  47 , and 2 k ohm resistor  51 . Resetting of the negative switch  30  dual switch latching relay  31  is accomplished by depressing the normally-open push button switch  52 . When push button switch  52  is depressed, it completes two circuits. The first circuit allows current to flow through push button switch  52 , the green “reset” light emitting diode (LED), test circuit connector  61  switch test connector  62 , relay positive resetting coil connection of relay coil  37 A on the dual switch latching relay  31  of negative switch  30 , through the relay negative coil connection, back to the switch test connector  2 , into the test circuit connector  61  and into the negative side of the 16-24 VDC power supply  53 . This circuit allows relay resetting coil  37 A to switch the relay switching wiper connection  32  and relay resetting wiper connection  33   a  connected through the switching and resetting wiper link  32 , from the “fired” state to the “armed” state. Once relay resetting coil  37 A is energized, the “armed” circuit is completed. The “armed” circuit is made when LED  48  is illuminated by current passing through a circuit made through DC power supply  53 , test circuit connector  61 , switch test connector  62 , relay resetting wiper connection  33   a  on the dual switch latching relay  31 , out to the normally-closed resetting wiper connection  33   c,  back to switch test connector  62 , test circuit connector  61 , through LED  48 , and 2 k ohm. resistor  55 . Once dual switch latching relay  31  is in this final state, illustrated on the right-hand side of  FIG. 3 , negative switch  30  is ready for removal of the test and resetting circuit device  54  and loading within the perforating gun assembly  200 . 
         [0028]    A suitable relay for the disclosed apparatus is model 422H or 422KH dual switch latching relay available from Teledyne, Inc. A suitable Zener diode is 1N5347, 10V Zener Voltage, available from ON Semiconductor. or 1N5374 75 Zener Voltage, available from ON Semiconductor. The range depends on the shooting voltage of the perforating assembly. 
         [0029]    Although the present invention has been described with respect to specific details, it is not intended that such details should be regarded as limitations on the scope of the invention, except to the extent that they are included in the accompanying claims.