Note: Descriptions are shown in the official language in which they were submitted.
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SEISMIC EXPLOSIVE SYSTEM
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to an explosive
system for seismic charges which is safe from detonation by
radio frequency (RF) signals and electrostatic discharge
(ESD).
DESCRIPTION OF THE PRIOR ART
The current art of explosive seismic exploration
relies on fast-acting electric detonators that typically
function in less than 1 millisecond, and up to 1,000
detonators may be fired essentially simultaneously by a
relatively low-voltage capacitor discharge. Because of
their fast action, seismic electric detonators rely on a
very sensitive primary explosive like lead styphnate, lead
azide and diazodinitrophenol (DDNP). These seismic electric
detonators can never be considered totally safe because they
may be actuated by electrostatic discharge or stray voltage
and are also susceptible to actuation by stray current and
distant lightning strikes.
Accordingly, for safety reasons, seismic charges
are currently shipped from the factory without detonators,
and the detonators and charges are assembled and combined in
the field. Of course, assembly of the charges and
detonators in the field presents safety problems since RF
signals and electrostatic discharge can cause detonation as
the charges are being field-assembled.
An example of an exploding bridge wire (EBW)
detonator is illustrated in U.S. Patent No. 4,777,878. An
EBW detonator may, for example, employ a two electrode
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arrangement in the detonator and have an exploding bridge
conductor between the two electrodes. The exploding bridge
is located at one end of a column of explosive material used
in the device. Within the column of explosive and spaced a
distance away from the exploding bridge portion of the
detonator is a shock reflector element on an inert but
relatively dense material having a high shockwave impedance.
The cooperative action of the exploding bridge and the shock
reflector intensifies the shockwave propagated through the
explosive and causes a detonation because of this
intensification.
Exploding foil initiator (EFI) detonators have
also been available, and one such detonator is illustrated
in U.S. Patent No. 6,752,083, which is owned by the assignee
of the present application. An EFI detonator includes an
electrically conductive metal foil which is connected to a
source of current. The metal foil includes a narrow neck
section that explodes or vaporizes when a high current is
discharged quickly through the neck section. The exploding
neck section of the foil shears a small flier from a disk
that is disposed in contact with the foil. The flier
travels or flies through a barrel to impact a secondary
explosive, e.g., dynamite, to initiate a detonation.
Because EBW and EFI detonators contain only
secondary explosives (e.g. HNS, Nona, and RDX), and require
very high power to function, they are known to offer safety
against electrostatic discharge, stray current and even
lightening strike hazards. These detonators also have
extremely short function times that meet or surpass the
standard seismic requirement of less than 1 millisecond.
The disadvantage of this technology is the requirement of
very high voltages, e.g., over one thousand volts, and
extremely high currents, usually over one thousand amps to
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activate these devices. The required voltage and current
need only be applied for a very short period of time, e.g.,
1-2 microseconds and is typically accomplished by the
discharge of a high-voltage capacitor into a low-inductance
firing circuit.
A new technology which can operate at lower
voltages and currents but still provide very good safety is
to use semiconductor bridges (SOB) in place of the metal
foil bridge of the EFI. SCB's can be used in two ways.
They can be placed in direct contact with sensitive
pyrotechnic and primary explosives in which case their use
offers only a slight improvement over typical hot-wire low-
voltage detonators because they are still susceptible to
stray voltages, currents and ESD. However, the SCB can also
be used to replace the metal foil bridge in a slapper type
detonator. When used this way with only secondary
explosives the resulting detonator is ESD safe. When an SOB
slapper detonator is also coupled to an addressable switch,
then the whole assembly becomes safe from stray voltages and
currents and ESD.
Addressable switch technology has been
commercially available in the mining and blasting industry
for several years. Each of these systems incorporate an
addressable switch to isolate the firing circuit of the
detonator from the lead wire input until the detonator has
been properly addressed and then armed. All systems capable
of firing multiple detonators also have built in firing
circuit diagnostic capability allowing the identification of
detonators that are not properly attached to the firing
circuit.
The U.S. Department of Defense and the U.S.
Department of Transportation consider it unsafe to transport
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or store explosive charges which have been assembled with
initiation systems without additional safety precautions.
Initiation systems that rely on primary explosives must have a
shutter that physically isolates the primary explosive from the
rest of the explosive train so that even if the primary explosive
accidentally detonates it will not initiate the main charge. It
is also required that these shutter devices require two
independent signals or actions to arm, i.e. to couple the primary
explosive component to the initiation circuit. If a an explosive
device containing primary explosive in its initiation chain has
such a shutter requiring two independent signals to arm and
another independent signal to fire, then such a device is
considered safe to transport and store with its initiation system
installed. For initiation systems that do not contain primary
explosives it is not required to have a physical barrier,
shutter, that interrupts the initiation chain. Rather in these
systems it is acceptable to require just two independent signals
to arm the device and a third signal to fire the device. These
signals can be mechanical or electrical. A further restriction
on such non-primary systems is that at signal of at least 500
volts is required to fire the device.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present
invention, a seismic explosive package is provided which
comprises a seismic charge, and an addressable switch for use in
selecting that seismic charge for detonation. A seismic
explosive package according to one embodiment of the present
invention further comprises a fireset which is interposed between
the addressable switch and the seismic charge. The fireset is
for receiving a firing voltage via the addressable switch and for
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using the firing voltage to produce an actuation voltage. In one
embodiment, the actuation voltage may be formed by increasing the
magnitude of the firing voltage, and the fireset may, for
example, comprise a voltage multiplier for increasing the
magnitude of the firing voltage. A seismic explosive package
according to one embodiment of the present invention further
comprises a Detonating Device, which comprises a secondary
explosive. The Detonating Device may, for example, may be either
an EBW detonator, an EFI detonator or a Semiconductor Bridge
(SOB) Slapper Detonator, which is interposed between the fireset
and the seismic charge. The actuation voltage from the fireset
is sufficient to cause the Detonating Device to detonate, which
in turn detonates. the seismic charge.
In accordance with another embodiment of the present
invention, a system for detonating seismic explosives is provided
which comprises a plurality of explosive devices, as described
above. The plurality of explosive devices may be deployed in
desired patterns at spaced intervals at or near the earth's ,
surface, and a system according to one embodiment of the present
invention may further comprise a base unit having a computer and
a power supply for providing selection, firing and trigger
signals to the plurality of explosive devices. The base unit
selects an explosive device for detonation by providing a
selection signal to the addressable switch associated with that
explosive device. The base unit also provides the firing signal
via the addressable switch to the fireset in the selected
explosive device. When a trigger signal is received from the
base unit by the fireset, the actuation voltage is presented to
the Detonating Device. This actuation voltage causes detonation
=
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of the Detonating Device which in turn causes detonation of the
seismic charge.
According to another embodiment of the present
invention, there is provided an explosive package for use in
seismic exploration that requires a first arming signal, a second
arming signal, and a firing signal to be detonated, comprising: a
seismic charge; an addressable switch that receives the first
arming signal and the second arming signal, the addressable
switch being responsive to the first arming signal, the first
arming signal being for use in selecting the seismic charge for
detonation, the second arming signal being passed on to a fireset
based on a response of the addressable switch to the first arming
signal; the fireset being responsive to the second arming signal
and being 'operatively coupled to the addressable switch for
receiving a firing signal via the addressable switch and for
producing an actuation voltage at its output based on the firing
signal; and a Detonating Device which is operatively coupled to
the output of the fireset for detonating the seismic charge upon
presentation of the actuation voltage to the Detonating Device.
According to still another embodiment of the present
invention, there is provided a system for use in seismic
exploration, comprising: a plurality of explosive packages
wherein each said explosive package requires a first arming
signal, a second arming signal, and a firing signal to be
detonated and wherein each said package comprises: a seismic
charge; an addressable switch which receives the first arming
signal and the second arming signal, the addressable switch being
responsive to the first arming signal and being operatively
coupled to said seismic charge, the second arming signal being
passed on to the fireset based on a response of the addressable
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switch to the first arming signal; a fireset which is responsive
to the second arming signal and which is operatively coupled to
the addressable switch for receiving a firing signal via the
addressable switch and for producing an actuation voltage at its
output based on the firing signal; and a Detonating Device which
is operatively coupled to the output of the fireset for
detonating the seismic charge upon presentation of the actuation
voltage to the Detonating Device.
According to yet another embodiment of the present
invention, there is provided a system for use in seismic
exploration, comprising: a) a base unit comprising a computer and
a power supply for providing selection signals, firing signals
and trigger signals; b) a plurality of explosive packages located
at spaced locations along the earth's surface, which each
explosive package requires a first arming signal, a second arming
signal, and a firing signal to be detonated and wherein each
explosive package comprises: (i) a seismic charge; (ii) an
addressable switch which is responsive to the first arming
signal, the addressable switch passing the second arming signal
on to a fireset based on a response of the addressable switch to
the first arming signal; (iii) thefireset which receives the
second arming signal from the base unit via the selected
addressable switch and which produces an actuation signal at its
output; and (iv) a Detonating Device which is operatively coupled
between the output of the fireset and the seismic charge for
receiving the actuation signal and for detonating the seismic
charge upon receipt of said actuation signal.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
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FIG. 1 is a pictorial drawing illustrating a system for
use in seismic exploration in accordance with one embodiment of
the present invention.
FIG. 2 is .a schematic diagram in partial block diagram
form illustrating an explosive device in accordance with one
embodiment of the present invention for use in seismic
exploration.
DESCRIPTION OF SPECIFIC EMBODIMENTS
It will be appreciated that the present invention may
take many forms and embodiments. In the following description,
some embodiments of the invention are described and numerous
details are set forth to provide an understanding of the present
invention. Those skilled in the art will appreciate, however,
that the present invention may be practiced without those details
and that numerous variations and modifications from the described
embodiments may be possible. The following description is thus
intended to illustrate and not to limit the present invention.
In this specification and the appended claims: (a) the
term "Detonating Device" means a device which contains only
secondary explosives and which when detonated causes a seismic
charge to detonate. Examples of a Detonating Device include EBWs,
EFIs and SBC slapper detonators; and (b) two items are "operative
coupled" if they are directly connected or connected through an
intermediate device.
With reference first to FIG. 1, there is illustrated a
system 100 in accordance with the present invention for use in
seismic exploration. System 100
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comprises base unit 102 which includes a computer and a
power supply for providing selection, firing and trigger
signals to explosive packages 101(1), 101(2) . 101(n), where
n represents the number of explosive packages that are
arranged in a predetermined pattern at or near the earth's
surface. Each of the explosive devices 101(1), 101(2),
.101(n) are constructed as illustrated in FIG. 2 and
described below. Base unit 102 utilizes the computer
therein to generate a selection signal or signals to select
which explosive package 101(1) will be detonated. Following
selection of the explosive package 101(i) to be detonated,
base unit 102 generates a firing signal which is received by
the selected explosive device 101(1). The receipt of a
trigger signal by the selected explosive device causes
seismic charge in the selected explosive device to be
detonated.
Referring now to FIG.1 and 2, the structure and
operation of each explosive package 101(i) for i =1,
2, ...n of FIG. 1 is illustrated. Explosive package 101(i)
comprises seismic charge 204 which may, for example, be
dynamite. Explosive package 101(i) also comprises
addressable switch 201 which, when selected by the selection
signals from base unit, permits a firing signal to be
presented to fireset 202 which is operatively coupled to the
addressable switch 201. The output of fireset package 102
is operatively coupled to Detonating Device 203, which in
turn is coupled to seismic charge 204.
In operation, explosive package 101(1) is coupled
to base unit 102 by appropriate cabling 103, and base unit
102 provides selection, firing and trigger signals to
explosive package 101(i) via cabling 103. A selection
signal is first provided which selects the addressable
switch associated with seismic charge 204 in explosive
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package 101(i) for detonation. Thereafter, a firing signal
is provided by base unit 102 and this firing signal may, for
example, be a voltage between 300 and 500 volts.
Addressable switch 201, which has been selected, allows the
firing voltage to be presented to fireset 202 which uses the
firing voltage to charge a capacitor to produce an actuation
voltage. The fireset may, for example, also comprise
circuitry for increasing the magnitude of the firing voltage
from base unit 102 to produce the actuation voltage. This
increase in firing voltage may, for example, be necessary
when the Detonating Device is an EBW or EEI detonator and
may be accomplished by using a voltage multiplier circuit in
fireset 202. Such voltage multiplier circuitry is well known
to those skilled in the art. The output of fireset 202 is
operatively coupled to the input of Detonating Device 203,
and when base unit 102 provides a trigger signal to the
selected explosive device, the actuation voltage, which is
present at the output of fireset 202, is presented to
Detonating Device 203. Detonating Device is thus detonated
which in turn detonates seismic charge 204.
An explosive package 101(i) which is made in
accordance with the present invention has an advantage over
the prior art in that all explosive devices for use in a
particular seismic operation may be assembled in a factory
as opposed to being assembled in the field. Factory
assembly of explosive package 101(1) should not only be
cheaper, but also safer than the field assembly of seismic
charges which is currently practiced.
An explosive package in accordance with the
present invention may also be safely transported and stored
while assembled with its own circuitry for initiation; which
is of great advantage to the seismic exploration industry.
Such devices have not previously been used or available to
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the seismic exploration community and are possible only by
coupling several dissimilar technologies together to form a
new invention. This invention couples direct initiation of
secondary explosive via EBW, EFI or SOB Slapper technology
with the use of addressable switch technology and a seismic
charge to create a seismic explosive system with an
initiation train requiring two independent arming signals,
and an independent firing signal, and an initiator
(detonator) that requires more than 500 volts to function.
Such a system is safe from accidental initiation due to
commonly encountered stray voltages, currents, electrostatic
discharge and simple human errors.
It will be appreciated by those skilled in the art
that the explosive devices 101(1), 101(2), . . .101(n) may
be arranged in any pattern which the user deems appropriate
for the seismic exploration task at hand. A plurality of
the explosive devices may, for example, be arranged in
series with one another and the series connection of
explosive devices may be arranged in parallel with one
another. It will also be appreciated by those skilled in
the art that the present inventive concept may be used in a
detonator package for downhole operation, e.g., for
detonating a perforating gun, jet cutter, propellant or
other downhole device.
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