Note: Descriptions are shown in the official language in which they were submitted.
CA 02149154 2004-07-13
EXPENDABLE EBW FIRING MODULE FOR DETONATING
PERFORATING GUN CHARGES
BACKGROUND
This invention relates to perforating gun detonation apparatus, and more
particularly to exploding bridgewire (EBW) detonators and safe circuits for
firing such
EBW detonators. A' conventional electric detonator of the kind in general use
by
wireline service companies for use in oil and gas well perforating activities
typically
contains a bridgewire embedded in an ignition mix, plus a primer charge and a
base
charge. The primer charge is a sensitive explosive, usually lead azide and the
base
charge is the same explosive material used in detonating cord and shaped
charges,
usually RDX or HNS. When sufficient current is applied through the detonator
leads
to the bridgewire it ignites the ignition mix, which in turn ignites the
primer charge.
The exploding primer charge causes the base charge to detonate.
The main drawbacks of such electric detonators are:
1. They contain sensitive primary explosives, and must be handled carefully
to avoid accidental initiation by mechanical impact; and
2. They are easily fired electrically, requiring only the application of 0.5 A
or less for a few milliseconds. Accordingly, they are particularly
susceptible to any source that could provide this power accidentially, such
as electric welding equipment, radio transmitters, cathodic protection
systems and faulty rig machinery and equipment. To protect against such
spurious electrical power, all possible equipment and machines that could
produce such stray power often had to be shut down for extended periods,
and the wellhead and rig structure monitored for stray voltages.
By contrast, Exploding Bridgewire (EBW) detonators contain no primary
explosive, which makes them insensitive to initiation by mechanical impact and
therefore
safer to handle than conventional detonators. In addition, they are immune to
initiation
CA 02149154 2004-07-13
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by the external power sources usually on the welt or rig site. However, to
fire an EBW
detonator successfully requires the use of a specialized electronic circuit.
That electronic
circuit can pick up spurious AC, radio frequency (RF) and DC voltages from the
many rig
sources named above, including lighting strikes that can accidentally cause
the EBW
detonator to be fired.
Accordingly, it is necessary to design the electronic firing circuits for EBW
detonators to include safety circuits for isolating the detonator firing
circuit from such
spurious voltages to prevent accidental detonation of the perforating gun
charges.
SUMMARY OF INVENTION
In one aspect of the invention there is provided a compact expendable EBW
firing module, for use in connection with a conventional perforating gun
system
deployed from a surface into a well at a well site, including a source of DC
power at the
surface to be supplied to the perforating gun system through a wireline cable
interconnected thereto, without requiring any additional perforating gun
hardware, the
firing module comprising: a high-voltage multiplier circuit (37) for
multiplying a first
voltage related to the voltage received from the DC power source by a
predetermined
multiple to generate a second DC voltage capable of detonating an EBW
detonator; a
firing circuit (30) for receiving the second DC voltage from the multiplier
circuit for
application to the EBW detonator; and an electronic safety circuit (35)
coupled to the
2 0 multiplier (37) so that it will be interposed between the DC power supply
at the surface
and the multiplier circuit for preventing unintentional activation of the
multiplier circuit by
stray ACIRF and DC voltages present at the well site, the expendable module
being
adapted for mounting directly in the interior housing of a conventional
pertorating gun
system directly adjacent the EBW detonator without protection from the
perforating gun
2 5 charge blast, characterized in that the multiplier has an AC input and in
that the safety
circuit comprises means (66, 68) for converting DC voltage in the safety
circuit to AC
voltage for input to the multiplier circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the manner in which the above-recited principles and features of
30 the invention are attained can be understood in detail, a more particular
description of
the invention may be had by reference to specific embodiments thereof which
are
illustrated in the accompanying drawings, which drawings form a part of this
specification.
In the drawings:
CA 02149154 2004-08-23
- 3 -
Fig. 1 is an illustrative drawing showing a wireline perforating tool disposed
in a
wellbore and utilizing the expendable EBW firing module according to the
present
invention.
Fig. 2 is a block diagram showing the major assemblies of. the wireline
perforating tool utilizing the expendable EBW firing module according to the
present
invention.
Fig. 3 is a detailed schematic diagram of the preferred embodiment of the
expendable EBW firing module according to the present invention.
Fig. 4 is a detailed schematic diagram of another embodiment of the expendable
EBW firing module according to the present invention.
Fig. 5 is a vertical diagrammatic view, partly in cross-section, of a wireline
perforating gun system utilizing the expendable EBW firing module in
accordance with
this invention.
Fig. 6 is a cross-sectional view of one embodiment of protective packaging for
the expendable EBW firing.module.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figs. 1 and 2, a wireline perforating gun system 10, including
the
expendable EBW firing module 24, is shown disposed in a borehole 14 that has
been
drilled in earth formation 12. The perforating gun tool 10 is shown spaced
adjacent
steel casing 16 that has been set in the borehole 14 adjacent a formation of
interest 13.
The tool 10 is supported by a conventional signal- or multi-conductor wireline
cable 18
that travels over a sheave 26 and is spooled onto a winch drum 28. The
perforating
tool 10 is raised and lowered in the borehole 14 by the action of the cable
drum 28 and
the "spoofing out" of the cable 18 to Power the gun system 10 in the borehole,
or the
"spooling in" of cable 18 to raise the perforating gun system 10 in the
borehole 14.
Depth measurements are made from the travel of the wireline cable 18 as it
passes
over the sheave 26 and communicated to the surface control equipment 30 via
cable or
conductor 32. Electrical power for operating the perforating gun system 10,
including
the necessary control signals for firing the tool, are applied through cable
18 from the
control equipment 30. The performing gun system 10 includes a perforating gun
21~g~.~~
WO 95/24608 PCT/US94/10275
section 20, an electronic bridge wire (EBW) detonator and booster section 22,
the
expendable EBW firing module 24 according to the present invention cooperating
with
the EBW section and a cablehead 25 interconnected to the cable 18 and the
control
panel 30. As will hereinafter be described in greater detail, and as more
particularly
shown in Fig. 2, the expendable EBW firing module 24 comprises a safety
circuit 35,
a voltage multiplier circuit 37 and a firing circuit as more particularly
shown in Fig.
3. The expendable EBW firing module 24 receives DC power for operating the EBW
and booster section 22 for firing the perforating gun system 20 from a DC
power
supply 40 disposed in the surface control equipment 30 transmitted via the
single- or
mufti-conductor cable 18 and cablehead 25.
Referring now to Figs. 1, 2and 3, the operation of the preferred embodiment
of the expendable EBW firing module 24 will be described in detail. DC
electrical
power is applied from the DC power supply 40 in the surface equipment 30
through
the cable 18 and cablehead 25 to the input of the safety circuit 35. The DC
power
(200 VDC) is applied to one side of a surge voltage protector (SVP) 41, the
SVP 41
rated at 600 volts. The SVP will conduct and connect the input of circuit 35
directly
to ground potential (the perforating gun housing) at 48 in the event of an
applied
voltage surge in excess of 600 VDC, such as in the case of a lightning strike
nearby
to the perforating gun system 10 or other DC power interference at the well
site.
The 200 VDC applied across the SVP 41 is also applied across a resistor 44 and
a series connected LED 46, a capacitor bank 50-50' and to the positive side of
a diode
52. The capacitor bank 50-50' appears as an open circuit to DC power, but will
react
with radio frequency (RF) and AC power as a low impedance path to shunt any
RF/AC
applied as an input to the circuit 35 to ground at 48. While the capacitor
bank 50-50'
is shown comprising several capacitors in series, the capacitor bank could be
repleced
with a single capacitor that is rated the same as the combined capacitance of
the bank
50-50'. Resistor 44 acts as a bleed resistor for the capacitor bank 50-50',
and as a
current limiting resistor for the LED 46. The fuse 42 is rated at 125 mA and
any
significant stray RF or AC voltage will cause a current in excess of the
rating of fuse
42 which will blow the fuse and disable the circuit. Such AC and/or RF inputs
might
WO 95/24608 PCT/U594/10275
-5-
be caused by adjacent power generating machinery, radio transmitters, radar
equipment, faulty rig wiring or equipment or other like sources that may be
present at
the well site. The LED will conduct when any current is flowing through
resistor 44,
and is particularly useful as a power indicator when testing the circuit on
the surface
prior to lowering the perforating tool into the well bore.
As power is applied to the circuit 35, the diode 52 conducts and applies the
DC
voltage to the anode of the SCR 58. As soon as the voltage across the Zener
diodes
56 and 56' reaches 150 VDC; the SCR 58 is switched on and acts as a basic
"short
circuit" to permit current to pass without offering any significant impedance.
The SCR
58 thus acts as a "switch" to sharply turn "on" when 150 VDC appears across
the
anode and gate legs of the SCR. This acts as a safety feature to prevent other
stray
DC voltages under 1S0 VDC, such as may be caused by a welding machine or other
DC machinery at the well site, from passing through to the voltage multiplier
circuit
37 and activating it. The resistor 60 is a bias resistor to achieve positive
shut-off of
the SCR when the applied voltage is removed from the anode.
The remaining components of the safety circuit 35 comprise a self-triggering
multivibrator circuit for applying an AC input signal to the voltage
multiplier circuit
37 as will hereinafter be further described. The heart of the multivibrator
circuit are
the pair of transistors 66 and 68, the collectors of each of which are
connected as an
input to the multiplier circuit 37 through conductors, 80 and 78,
respectively. The
resistors 62 and 64 are current limiting resistors, and resistors 70 and 72
act as biasing
resistors for the base inputs 66' and 68' of the transistors 6b and 68,
respectively. The
capacitors 74-74' and 76-76' couple the bases 66' and 68' of each transistor
to the
collector of the other transistor. The output of the multivibrator circuit is
an
approximate sine wave that is applied to the input of the voltage multiplier
circuit 37
via conductors 78 and 80.
The voltage multiplier circuit 37 is a conventional stacked voltage doubter
circuit that will receive an input of 200 VAC and multiply the voltage by a
predetermined value, in this case eight, and generate an output of 1600 VDC
applied
through diode 99 and input resistor 104, to resistor 100 in parallel with
capacitor 102
WO 95/24608 PCT/US94I10275
-6-
of the firing circuit 39. The resistor 100 is a bleed resistor for the
capacitor 102 while
resistor 104 acts as a current limiting resistor. In series with resistor 104
is another
SVP 106, which is rated at 1500 VDC, and which will conduct when capacitor 102
has
reached a voltage of 1500 VDC to apply the 1500 VDC in a time interval of 1
uSec ,
to the output of the firing circuit 39 to the EBW and booster in 22 for
actuating the
EBW and firing the perforating guns. A resistor 108 is placed in parallel with
SVP
106 between the output of the circuit 39 and the capacitor 102 for acting as a
bleed
resistor for capacitor 102 and to permit direct voltage reading across the
firing storage
capacitor 102 for testing purposes. During testing at the surface prior to the
time the
expendable EBW firing module24 is attached into the circuit of the perforating
gun
system 10, a load resistor (or a dummy EBW) may be tied to the output leads of
the
firing circuit 39 and the rated 200 VDC applied to the input of the safety
circuit 35.
A test voltmeter may also be attached across the output leads of the circuit
39 and a
measurement of the voltage appearing across capacitor 102 may be made to
verify that
the circuit is functioning properly. The inductor 54 functions to protect the
multivibrator circuit described above from large voltage spikes that may be
conducted
through the grounding connections of the tool when the capacitor 102 is
discharged.
This protection is only necessary during testing, since the expendable EBW
firing
modulewill be damaged beyond repair upon actual detonation of the EBW and the
firing of the perforating guns.
Referring now to Figs. 1, 2 and 4, the operation of another embodiment of the
expendable EBW firing module24 will be described in detail. DC electrical
power is
applied from the DC power supply 40 in the surface equipment 30 through the
cable
18 and cablehead 25 to the input of the safety circuit 35'. The DC power (200
VDC)
is applied to one side of a surge voltage protector (SVP) 141, the SVP 141
being rated
at 600 volts, and functioning in the same manner as SVP 41 in the circuit of
Fig. 3 as
hereinabove described to conduct and connect the input of circuit 35 directly
to ground
potential (the perforating gun housing) at 148 in the event of an applied
voltage surge
in excess of 600 VDC, such as in the case of a lightning strike nearby to the
perforating gun system 10 or other DC power interference at the well site.
2~~~~.~4
t'~'~' ; WO 95/24608 PCTIUS94/10275
_7_
The 200 VDC applied across the SVP 141 is also applied, across a capacitor 150
and to a fuse 142. The capacitor 150 appears as an open circuit to DC power,
but
will react with radio frequency (RF) power to create a low impedance path to
shunt RF
power applied as an input to the circuit 35 to ground at 48. Diodes 152 and
153
S conduct and apply the DC power to an AC voltage shunt circuit comprising
capacitor
144, and cascaded transistors 146 and 149: AC current will pass through the
capacitor
144 and be applied to the base of the first transistor 146 via lead 147,
causing the
transistor to conduct. When transistor 146 conducts, the second transistor 149
is
switched on, causing the applied voltage to be shunted to ground. With an AC
voltage
of abou~ 30 V and 60 Hz, enough current will flow through the transistor 149
to blow
the fuse 142, thus disabling the circuit. Such AC and/or RF inputs might be
caused
by adjacent power generating machinery, radio transmitters, radar equipment,
faulty
rig wiring or equipment or other like sources that may be at the well site.
Resistors
156 and 157 act as current limiting resistors to prevent the activation of the
IC 158
until approximately 130 VDC has been applied from power supply 40. The Zener
diodes 169, 170 and 171 act to prevent voltages below approximately 150 VDC
from
being passed~to the voltage multiplier circuit 37'.
The resistors and capacitors 159, 160, 161, 162, 163 and 164 form other
resistive and capacitance values for biasing the selected IC circuit 158 and
to preselect
the frequency and the pulse width of the generated pulse signal train for
applying AC
triggering pulses to the to transistor 168 as will hereinafter be further
described. The
pulse train output of the IC circuit 158 is applied through current limiting
resistor 165
to the base of transistor 168 which conducts on the occurrence of each pulse.
A Zener
diode 166 is interconnected between the base and emitter of the transistor 168
to
prevent an overvoltage appearing thereacross. The transistor 168 acts as a
switch
only to rapidly pulse the current through the inductor 172. The rapidly rising
and
collapsing electromagnetic fields in inductor 172 caused by the pulsed current
therethrough generate a series of high-voltage spikes, which act as the input
of the
stacked voltage doubter circuit as hereinabove described.
PCTIUS94I10275
WO 95/24608
_g_
The voltage multiplier circuit 37 is a conventional stacked voltage doubter
circuit that will receive the output across inductor 172 and multiply this
voltage by a
predetermined multiplier factor to generate an output of 1600 VDC applied
through
diode 199 as an input to resistor 204, and to resistor 200 in parallel with
capacitor 202
of the firing circuit 39'. The resistor 200 is a bleed resistor for the
capacitor 202 while
resistor 204 acts as a current limiting resistor. In series with resistor 204
is another
SVP 206, which is rated at 1500 VDC, and which will conduct when capacitor 202
has
reached a voltage of 1500 VDC to apply the 1500 VDC in a time interval of 1
uSec
to the output of the firing circuit 39' to the EBW and booster in 22 for
actuating the
EBW and firing the perforating guns. A resistor 208 is placed in parallel with
SVP
206 between the output of the circuit 39 and the capacitor 202 for acting as a
bleed
resistor for capacitor 202 and to permit direct voltage reading across the
firing storage
capacitor 202 for testing purposes.
During testing at the surface prior to the time the expendable EBW firing
module 24 is attached into the circuit of the perforating gun system 10, a
load resistor
(or a dummy EBW) may be tied to the output leads of the firing circuit 39 and
the
rated 200 VDC applied to the input of the safety circuit 35. A test voltmeter
may also
be attached across the output leads of the circuit 39 and a measurement of the
voltage
appearing across capacitor 202 may be made to verify that the circuit is
functioning
properly. The inductor 154 functions in the same manner as inductor 54 as
hereinabove described in connection with Fig. 3 for protecting the IC circuit
158 from
large voltage spikes that may be conducted through the grounding connections
of the
tool when the capacitor 202 is discharged. As described above, this protection
is only
necessary during testing, since the expendable EBW firing modulewill be
damaged
beyond repair upon actual detonation of the EBW detonator.
''~ ': WO 95/24608 PCT/US94J10275
-9-
Components for the circuits described above are given in the following table:
Table 1
Component Values
Ref. No. Component
$ 41, 141 SVP 600 VDC
42 Fuse 125 ma
142 Fuse 100 ma
50, 50' Capacitor, 47 uF
52, 152, 153, 86, 87, 88, 89, 90, Diode 1N4249 1000 V, 1
91, A
92, 93, 99, 186, 187, 188,189,
190,
191 & 199
54, 154 Inductor, 1000 uH
56, 56' Zener diode, 75 V
5g SCR, MCR100-6
60 Resistor, 10 K
62, 64 24.9 K
66, 68 Transistor, MJE13007
70, 72 . Resistor 464 K
74, 74' 76 & 76' Capacitor, 0.001 uF
82, 83, 84, 85, 86, 94, 95, 96, Capacitor, 0.01 uF
97, 98,
164, 182, 183, 184, 194, 195,
196 & 198
100, 200 Resistor, 390 M
102 Capacitor, 0.32 uF, 2000
V
202 Capacitor, 0.27 uF, 2000
V
104, 202 Resistor, 150 K
106, 206 SVP, 1500 VDC
108, 208 Resistor, 390 M
144 Capacitor, 0.01 uF
146, 149 & 168 Transistor, MPSA42
156 Resistor, 30 K
157 Resistor, 36 K
158 Integrated Circuit (IC)
~ TL494
159 Resistor, 10 K
160 Resistor, 45.3 K
162 Capacitor, 1 uF
163 Resistor, 37.4 K
165 Resistor, 1K
166, 169, 170 & 171 Zener diode, 51 V
172 Inductor, 50 mH
t~
PCTIUS94/10275
WO 95!24608
-10-
Referring now to Figs. 1, 2 and 5, a portion of the perforating gun system 10
is shown comprising a portion of the perforating gun section 20, showing the
typical
perforating shaped charges 225 supported by a charge carrier (not shown for
simplicity)
distributed vertically in the gun section 20. A hollow nose plug 20' is shown
attached
S to the lower end of the perforating gun section 20 by means of a threaded
connection
21. An electrical power conductor from cablehead 25 (Figs: 1 and 2) and a
primacord
225 interconnecting the shaped charges 235 terminate below a bulkhead 227 at
the end
of the gun section 20. The expendable EBW firing module 24 is connected to the
power conductor (+) and to the gun section body for ground (-), and the EBW
and
booster 22 are connected to the primacord. A pair of conductors 228 and 230
connect
the output of the firing circuit 39 of the expendable EBW firing module 24 to
the EBW
22. When the expendable EBW firing module 24 detonates the EBW to set off the
shaped charges 235 of the perforating gun section 20, the force of the EBW and
booster charge 22 blast will substantially destroy the module 24. When the
perforating
gun is returned to the surface, the gun section 20 will be replaced, new
charges 235
loaded, and a new expendable EBW firing module 24 and EBW and booster charge
22
mounted and interconnected for firing the perforating charges as hereinabove
described.
Of course, the expendable EBW firing module 24 and the associated EBW 22
may be mounted either below the gun section 20 as shown in Fig. 5, or above
the gun
section as preferred. If a second gun section is being carried in the
perforating gun
system for perforating multiple formation vertical intervals, a second
expendable EBW
firing module24 may be attached to the electrical power conductor 226 for the
second
device with the (+) and (-) terminals reversed and the second circuit 24 will
fire upon
the application of a negative DC power input.
The circuits 35, 37 and 39 that make up the expendable EBW firing module 24
are mounted on a single circuit board and comprise a size of approximately 5
inches
by 5/8 inches, and may be packaged in a selected packaging material for
protecting the
expendable module during transit and handling. Fig. 6 shows an example of such
packaging, in wick the module 24 is shown comprising a single circuit board
250 upon
which is mounted electrical circuit components such as shown at 252 is encased
in a
s
2~~J~.a
!~''°sW0 95/24608 PCTJUS94110275
-11-
plastic resin materail 254. The plastic resin material 254 may also comprise
any other
selected packaging material that will serve the necessary purpose of
protecting the
circuit board 250 and components 252, such as a plastic tubing "shrink-
wrapped" onto
the circuit board or mounted within a heavier plastic tubing. A pair of
conductors 256
and 258 would extend from the module 24 for attaching the module to the power
input
cord 226 (Fig. 5) and the tool housing and for interconnection to the EBW and
booster
charge section 22.
Numerous variations and modifications may be made in the structure herein
described without departing from the present inevntion. Accordingly, it should
be
claerly understood that the forms of the invention herein described and shown
in the
figures of the accompanying drawings are illustrative only and are not
intended to limit
the scope of the invention.
