Downhole firing tool

Abstract

The invention relates to downhole firing tools. In particular, a firing switch for a perforating gun with an EB switch port. The firing switch comprises a body portion configured to be located within the EB switch port, and an electronic addressable switch mechanically coupled to the body portion. The mechanical coupling of the body portion and electronic addressable switch may provide a substantially rigid firing switch.

Claims

1. A firing switch for a perforating gun with an EB switch port, the firing switch comprising: a body portion configured to be located within the EB switch port, and an electronic addressable switch mechanically coupled to the body portion.

2. The firing switch as claimed in claim 1, wherein the electronic addressable switch is mechanically coupled to the body portion by a removable mechanical coupling.

3. The firing switch as claimed in claim 1, wherein the electronic addressable switch is mechanically coupled to the body portion by a permanent mechanical coupling.

4. The firing switch as claimed in claim 1, wherein the mechanical coupling of the body portion and electronic addressable switch provides a substantially rigid firing switch.

5. The firing switch as claimed in claim 1, wherein the electronic addressable switch comprises a wiring interface.

6. The firing switch as claimed in claim 1, wherein the electronic addressable switch comprises a line in, a detonator firing line, and a detonator ground line.

7. The firing switch as claimed in claim 1, wherein the electronic addressable switch comprises a male protrusion, and the body portion of the firing switch comprises a female receiving portion, with the male protrusion of the electronic addressable switch being mechanically coupled to the female receiving portion of the body portion.

8. The firing switch as claimed in claim 7, wherein the mechanical coupling of the male protrusion and female receiving portion is by engagement of corresponding threaded sections.

9. The firing switch as claimed in claim 1, wherein a line in to the electronic addressable switch connects to a line out of the body portion via the mechanical connection between the electronic addressable switch and the body portion.

10. The firing switch as claimed in claim 1, wherein the electronic addressable switch comprises a microcontroller.

11. The firing switch as claimed in claim 1, wherein the electronic addressable switch comprises one or more electronically controlled short circuits.

12. The firing switch as claimed in claim 1, wherein the body portion includes a nut.

13. The firing switch as claimed in claim 1, wherein the body portion comprises one or more seals.

14. The firing switch as claimed in claim 1, wherein the firing switch is configured to be controlled by a surface panel.

15. An apparatus for firing a perforating gun string that includes at least a first gun, a second gun, and a gun sub that connects the first gun to the second gun, wherein the gun sub includes a port sized to fit a cylindrical switch that is 10 mm long and 19 mm in diameter, the apparatus comprising: a body portion having an outer cylindrical surface and a threaded portion, the body portion being configured to seat within the port of the gun sub; at least one sealing member configured to form a fluid seal between the outer cylindrical surface and an adjacent surface of the gun sub; an end pin extending from the body portion; and an electronic addressable switch mechanically coupled to the body portion and electrically connected to the end pin, the electronic addressable switch including a microcontroller configured to: (i) continually sample a line voltage applied to the electronic addressable switch to detect a communication signal, (ii) drive a circuit to provide a response to the communication signal, and (iii) force one or more sub-circuits within the electronic addressable switch to change an active state to that required by the communication signal.

16. The firing switch as claimed in claim 1, wherein the electronic addressable switch comprises a male protrusion, and the body portion of the firing switch comprises a female receiving portion, with the male protrusion of the electronic addressable switch being mechanically coupled to the female receiving portion of the body portion.

17. An apparatus for perforating a formation, comprising: a perforating gun string that includes at least a first gun and a second gun; a gun sub connecting the first gun to the second gun, wherein the gun sub includes a port sized to fit a cylindrical switch that is 50 mm (1.97 inches) long and 19 mm (0.75 inches) in diameter; a switch including: a body portion having an outer cylindrical surface and a threaded portion, the body portion being configured seat within the port of the gun sub and connect to the gun sub at the threaded portion; at least one sealing member configured to form a fluid seal between the outer cylindrical surface and an adjacent surface of the gun sub; an end pin extending through and from the body portion; and an electronic addressable switch mechanically coupled to the body portion and electrically connected to the end pin, the electronic addressable switch including a microcontroller configured to: (i) continually sample a line voltage applied to the electronic addressable switch to detect a communication signal, (ii) drive a circuit to provide a response to the communication signal, and (iii) force one or more sub-circuits within the electronic addressable switch to change an active state to that required by the communication signal.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

(2) FIGS. 1A, 1B, 2A, and 2B, show a schematic view of a firing switch according to the prior art;

(3) FIG. 3 shows a tool string according to the prior art;

(4) FIG. 4 shows an alternative tool string according to the prior art;

(5) FIG. 5 shows a cross sectional view of a firing switch according to a first embodiment of the invention; and

(6) FIG. 6 shows a perspective view of the firing switch according to the first embodiment of the invention;

(7) FIG. 7 shows perspective view of the firing switch prior to the mechanical coupling of the body portion and electronic addressable switch;

(8) FIG. 8 shows a schematic circuit diagram of the electronic addressable switch;

(9) FIG. 9 shows a schematic representation of a string of four perforating guns and a setting tool according to a second embodiment of the invention; and

(10) FIG. 10 shows the top three perforating guns of the string of perforating guns described with reference to FIG. 9.

DETAILED DESCRIPTION

(11) FIGS. 1 to 4 have been described above in the background to the invention.

(12) A Firing Switch

(13) FIG. 5 shows a firing switch 100 according to a first embodiment of the invention. The firing switch 100 comprises a body portion 102 mechanically and rigidly coupled to an electronic addressable switch 104. As can be seen, the body portion 102 and electronic addressable switch 104 form a single, substantially rigid, easily installed, part. The body portion 102 comprises an approximately cylindrical outer surface 106, including a threaded section 108. A nut 110 is located towards one end of the body portion 102, away from the end of the body portion 102 mechanically coupled to the electronic addressable switch 104. The nut 110 allows the easy installation of the body portion 102 inside an EB switch port of a gun sub or perforating gun, by engagement of the threaded portion 108 with a corresponding threaded portion of the EB switch port. An end pin 112 extends from the body portion 102, away from the electronic addressable switch 104, such that the distal end of the end pin 112 extends beyond the nut 110. The end pin 112 includes an O-ring seal 114, making the connection between the body portion 102 and the end pin 114 watertight. In an alternative arrangement, the seals may be replaced by moulded sections which make the connection between the body portion 102 and the end pin 114 watertight. The cylindrical outer surface 106 of the body portion includes two O-ring seals 116 to seal the connection between the body portion 102 and the EB switch port. The provision of the sealing arrangements allows a perforating gun in which the firing switch is installed to have bi-directional pressure isolation. This allows the gun sub or perforating gun in which the firing switch is installed to be inspected in the event of a misfire. The bi-directional pressure isolation protects the gun sub or perforating gun from well fluid entry from both above and below the gun sub or perforating gun. Therefore, if an adjacent perforating gun is fired, the interior of the present perforating gun remains un-flooded. So, for example, if the perforating gun misfires, it is possible to investigate the cause of the misfire when the perforating gun returns to the surface.

(14) The addressable electronic switch 104 comprises a printed circuit board 118 with a connection portion 120. The connection portion 120 comprises a threaded protrusion 122 which is configured to be located and engaged within a corresponding threaded receiving portion of the body portion 102. The connection portion 120 includes a line in to the electronic addressable switch 104. The end pin 112 provides a line out from the firing switch 100. The connection portion 120 therefore provides a simple and quick way of connecting the electronic addressable switch 104 and the body portion 102, both mechanically and electrically. The connection between the electronic addressable switch 104 and the body portion 102 also provides a ground for the electronic addressable switch.

(15) FIG. 6 shows a perspective view of the firing switch 100 where the body portion 102 and the electronic addressable switch 104 are mechanically coupled.

(16) FIG. 7 shows the electronic addressable switch 104 prior to being screwed into the body portion 102.

(17) FIG. 8 shows a schematic circuit diagram of the electronic addressable switch 104. The electronic addressable switch 104 comprises a printed circuit board with the layout as shown in FIG. 8. The electronic addressable switch 104 is controlled via serial communications from a surface panel through a single conductor wireline. When instructed by the surface panel, the electronic addressable switch will allow the operator to either communicate with the next switch in the string, or activate a detonator (or igniter). The electronic addressable switch 104 is connected to the wireline by a line in connection 802 and the armour of the wireline is used as a return connection. DC power and serial communications are sent via the wireline. Two outputs are provided, the line out 804 and the Det Out 806, both of which use the armour of the wireline as the return connection to the surface. The line out 804 is used to route the line in 802 to the next electronic addressable switch in the string. The Det Out 806 is controlled by the electronic addressable switch 104 to activate a detonator 808 connected between the Det Out 806 and the detonator ground connection.

(18) Various sub circuits are shown in FIG. 8. A PIC microcontroller 810 controls the operation of the addressable electronic switch 104. The microcontroller 810 continually samples the line voltage applied to the electronic addressable switch 104 to detect communications from the surface. On receipt of a valid communications packet from the surface, it drives the COMS TX circuit 812 to provide a response to the surface, and then sets its outputs to force the various switch sub-circuits within the electronic addressable switch to change their active state to that required by the surface command. A PSU 814 regulates the line voltage to provide a stable, low voltage to the control circuitry. The COMS TX 812 converts the low voltage output from the microcontroller 810 into current changes on the line in order to provide serial communications from the electronic addressable switch 104 to the surface equipment.

(19) A line out switch 816 comprises a normally open MOFSET switch, which is used to make or break the line passing through the module. The line out switch 816 is controlled by the microcontroller.

(20) A first arming switch ARM SW1 818 comprising a normally open MOSFET switch allows the line voltage to be applied to the detonator 808. To close the switch 818 the microcontroller 810 applies an AC logic signal. A second arming switch ARM SW2 820 comprises a normally closed MOSFET switch. The switch 820, when closed, short circuits the two detonator wires to prevent the detonator from firing due to a fault condition or from RF interference. The switch 820 has a very low impedance when in the closed position. When opened, the line voltage may be applied to the detonator 808. To open the switch 820 the microcontroller 810 applies an AC logic signal. A third arming switch ARM SW3 822 comprises a normally open MOFSET switch. Closing of this switch 822 allows the line voltage to be applied to the detonator 808. To close the switch 822 the microcontroller 810 applies a pulse width modulated logic signal to control the rate at which the switch 822 is closed.

(21) The electronic addressable switch 104 will power up with all sub-switches in their default state. If the electronic addressable switch 104 has previously been assigned an address it will respond and action commands to that address. If the electronic addressable switch 104 has not been allocated an address it will only respond to global (system) commands. Once the firing switch is powered up and configured the surface equipment will either be able to close the line out switch 816 or begin the detonator firing process. In order to fire a detonator the electronic addressable switch must have the line out switch 816 open and receive a series of three commands from the surface followed by an increase in line voltage, of greater than 10V, within a specified time after receipt of the first detonate command. If these criteria are not met the electronic addressable switch 104 will timeout and return to a safe state requiring the entire firing sequence to be repeated. If all of the firing criteria have been met the electronic addressable switch 104 will begin the firing process. The process will begin with the closing of the ARM SW1 switch 818, followed by the opening of the ARM SW2 switch 820. Once these two tasks have been completed the electronic addressable switch 104 will then gradually close the ARM SW3 switch to allow the voltage across the detonator 808 to rise at the pre-programmed ramp rate until it reaches the line voltage. Once line voltage has been achieved the ARM3 SW switch 822 will be fully closed allowing any changes of the line voltage to appear across the detonator 808. The electronic addressable switch 104 will remain in this state until it is powered down or the initiator is fired.

(22) A Tool String

(23) FIG. 9 is a schematic representation of a string of four perforating guns according to a second embodiment of the invention and a setting tool. The setting tool 900 comprises an igniter 904. The igniter 904 is connected to and controlled by an electronic addressable switch 909 of the adjacent perforating gun 906. The igniter 904 is also grounded on the body of the setting tool 900. The bottom perforating gun 900 is connected to the adjacent perforating gun 906. Each of the remaining perforating guns is identical in construction, and so the description of perforating gun 906 can be applied to each of the perforating guns 908, 910, and 912.

(24) The perforating gun 906 comprises an electronic addressable switch 909 mechanically and rigidly connected to a body portion 911. The electronic addressable switch 909 includes an interface with a line in 913, a detonator line out 914, and a detonator ground line 916. The detonator line out 914 runs to a detonator 918. The perforating gun 906 also comprises a line out 920 which extends from a pin protruding from the body portion 911. The electronic addressable switch 909 is configured to be protected by an addressable voltage switch 922 at the top of the gun string. The string of guns is arranged to be controlled by a surface panel 924. The basic function of the electronic addressable firing switch 909 is to either pass current coming into the switch via the line in 913 onto the adjacent, downhole, perforating gun 902, or to pass the current coming via the line in 913 to the detonator 918 via the detonator line 914.

(25) A Test and Configuration Method

(26) Before any of the firing switches can be addressed by any surface equipment equipped with a power supply of sufficient capacity to trigger a detonator or igniter, addresses must be programmed into each firing switch and in so doing, the correct wiring of each firing switch confirmed. Addresses are allocated using a surface test box, and only by using the surface test box. This is because if a gun is wired incorrectly, a surface panel could inadvertently trigger a detonator due to the wiring fault if said surface panel is able to output sufficient power to fire a detonator (typical minimum current required is 200 mA). The surface test box however, is designed with multiple separate current limiting circuits, each operating on a different principle. The absolute current which can be supplied by the surface test box is limited at half the minimum required to fire a detonator (i.e. 100 mA) but all through the testing stage of a string of firing switches according to the invention, the current is automatically limited to slightly (10 mA) more than the number of connected firing switches will require at any given time, thus the maximum current which could be applied to an incorrectly wired detonator is 10 mA.

(27) Ensuring that the first powered device connected to a ‘virgin’ gun string is one that not only performs a fully automated check of all the gun string wiring, but is also one that cannot fire a detonator, guarantees that once a panel with the power capability to fire a detonator is connected, all the wiring has been confirmed as being correct.

(28) The sequence to check, confirm, and configure a virgin gun string using a surface test box is:

(29) 1. Connect the surface test box to the topmost gun.

(30) 2. Switch on the surface test box which automatically performs a series of self-tests to confirm that all current limiting circuits are operating correctly.

(31) 3. Automatically set the surface test box current limit on all programmable current limit circuits to 1× addressable firing switch plus tolerance (Approximately 4 mA+10 mA).

(32) 4. Connect the surface test box output so powering up the first firing switch. (Note—all firing switch pass switches are set to OPEN by default so the lower pin of the first firing switch is, at this point, disconnected from the second device in the string).
5. Check that the current is as expected, displaying a warning to the operator if not.
6. Perform a communications check to the first firing switch.
7. Assign address 101 to the first firing switch.
8. Command firing switch with address 101 to perform a detonator test using its pulse width modulation circuitry.
9. Firing switch with address 101 sends back data indicating the state of its detonator output lines.
10. If firing switch with address 101 passes all tests, increase the programmable current limits by 1× firing switch.
11. Command firing switch with address 101 to close its pass switch.
12. Go to step 5 and repeat (assigning address 102, 103 etc.) until a firing switch indicates excess (4 ma<10 mA) current when its pass switch is closed (or until a fault condition is detected).
13. Assuming no fault condition is detected, on detecting increased current to the lower pin of a firing switch, command the firing switch to perform an igniter check using its pulse width modulation circuitry.
14. Firing switch 10[X] reports back the status of its igniter check. If the check passes then the firing switch is programmed as ‘Last Device, Igniter Attached’ and will subsequently close its pass switch only with a specific command from the surface panel.
15. Surface test unit is powered down and removed.

(33) Once each device is programmed, communication can be established with the string (once at a safe depth in the well) using a suitable surface panel.

(34) FIG. 10 shows the top three perforating guns of the string of perforating guns described with reference to FIG. 9, including an addressable voltage switch 922. An installation process and operation method is now described.

(35) The addressable voltage switch 922 is arranged to be compatible for deployment with various surface panel control units 924.

(36) The addressable voltage switch is used when the string of guns in placed downhole, in order to limit the power applied to the firing switches downhole. At times, up to 500V may be applied by the surface panel. Allowing for losses in the resistive downhole cable, the downhole voltage seen may be reduced to between 50V and 100V. Once the detonator has fired however, the load is removed and the downhole voltage can rise to a significant proportion of the applied surface voltage. The use of the addressable voltage switch almost instantaneously limits the voltage applied to the firing switches to a maximum of 100V, which allows the components making up the firing switches to be rated to a lower voltage than would otherwise be possible.

(37) A Firing Method

(38) In order to fire the string of perforating guns, a command is sent to the highest firing switch 912, instructing that firing switch to close its pass switch. This applies power to the next perforating gun 910 in the string. The firing switch in the perforating gun 910 is instructed to close its pass switch, and thus power is sent down the string until it reaches the lowest firing switch in the string. The lowest of the firing switches is then instructed to close its pass switch and ramp up the pulse width modulation controlled voltage until the voltage applied to the igniter equals the downhole line voltage. The surface voltage is then ramped up until the igniter has been initiated. Power is then cut by the surface panel so opening all pass switches. The firing switches are then all sequentially powered-up again by connecting the input line to the lower pin, except for the last firing switch in the string, which does not connect power to its lower pin. The lowest firing switch is commanded to open its detonator shorting switch, close the two detonator line switches and ramp up the pulse width modulation controlled voltage until the voltage applied to the associated detonator 904 equals the downhole line voltage. The surface voltage is then ramped up until the detonator has been initiated. The PWM circuitry is included because the detonator switches were instantaneously closed, as there is already a voltage at the firing switch 912, there is a risk the detonator would draw sufficient current to cause a brown-out (low supply voltage induced reset) of the firing switch. To avoid this, as described above, the firing switch 912 includes pulse width modulation circuitry arranged to build up voltage on the detonator over a short time, so enabling the surface system to increase the surface voltage to keep pace with, and compensate for, voltage drops over the wireline.

(39) Once the first device 900 has been fired, the same process can be used to fire any of the remaining perforating guns. As each of the switches has been allocated an address, it is possible for the surface panel to send a fire signal to whichever of the addressable firing switches is required. Also, because the detonation of a perforating gun does not flood the adjacent guns, it may be possible to skip a device in the firing sequence, for example in the event of a misfire of a detonator.

(40) Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those skilled in the art that the invention lends itself to many different variations not specifically illustrated herein.

(41) Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.