Note: Descriptions are shown in the official language in which they were submitted.
- 1 -
Method of blasting
The present invention relates to a device for initiation of an explosives
charge, to a blasting
system including the device and to a method of blasting using the device. The
invention is
believed to have particular utility in commercial blasting operations, such as
in mining and in
oil and gas wells.
Background
In commercial blasting operations a bulk or packaged explosive is generally
required to be
initiated according to a predetermined blast design that specifics the time
and sequence of
initiation as between individual charges in a blast. In this context the bulk
or packaged
explosive is responsible for fracturing rock etc ¨ it is the "working" or main
explosives
charge. This explosives charge is itself typically initiated by firing of a
smaller explosives
charge that is invariably provided under heavy confinement in the form of a
cartridged
detonator. The detonator is in signal communication with blast control
equipment that is
responsible for its firing. There is a continuing need to enhance the
performance of
commercial blasts by the development of blasting methodologies and componentry
used.
The present invention seeks to contribute in this regard.
Summary
Certain exemplary embodiments provide an initiation device for initiation of
an explosives
charge, which comprises: a transceiver for receipt of wireless command
signals; a control
circuit for processing of wireless command signals received by the
transceiver; and a light
source that is suitable for initiation of the explosives charge and that is
activated by the
control circuit, wherein the control circuit comprises a timing mechanism to
allow precise
control of activation of the light source when a fire command is received by
the transceiver,
wherein the light source discharges through a focussing lens directly into or
onto the
explosives charge; and wherein the explosive charge is a secondary explosive
material dosed
with a heat transfer medium.
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Accordingly, in one embodiment there is provided an initiation device for
initiation of an
explosives charge, which comprises:
a transceiver for receipt of wireless command signals;
a control circuit for processing of wireless command signals received by the
transceiver; and
a light source that is suitable for initiation of the explosives charge and
that is activated by the
control circuit.
In use this initiation device will be operatively associated with an
explosives charge that is
capable of being initiated by the light source. Thus, in another embodiment
there is provided
an explosive device comprising an initiation device in accordance with the
invention and an
associated explosives charge, the explosives charge being provided and being
adapted to be
initiated by the light source.
Also provided is a method of blasting using the initiation device of the
invention, and a
blasting system comprising the initiation device and associated blast control
equipment.
As will be explained, certain embodiments combine wireless communication
capability with
light initiation of an explosives charge. This combination is believed to
provide significant
improvements over known blasting methodologies and componentry.
Detailed discussion of certain embodiments
The initiation device used in the present invention includes a transceiver and
the function of
this is to receive wireless communication signals sent from blast control
equipment. The
device can therefore be controlled remotely without the need for physical
connections (e.g.
wires) to convey command signals required in a blasting operation. Preferably,
the
transceiver has the capability for two-way communication so that such things
as diagnostic
and status checks can be conducted prior to a blast being initiated. The use
of wireless
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communication in blasting operations is known in the art and transceivers
useful in the
present invention are known and available, or they may be made by the
adaptation of known
componentry.
The initiation device also includes a control circuit. The basic function of
this is to process
wireless command signals received by the transceiver and, subject to receipt
of a suitable
command signal, to activate the associated light source. In practice the
control circuit is
likely to have additional functional capability and will be responsive to a
variety of wireless
command signals received by the transceiver.
The control circuit will also typically include some form of timing mechanism
to allow
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precise control of activation of the light source when a FIRE command is
received by the
transceiver. The control circuit will invariably be an integrated circuit.
Such circuits are well
known in the art. They are used for example in electronic detonators in order
to control
detonator functionality and timed initiation. One skilled in the art would
therefore be familiar
with the design of and componentry required in such circuits.
The initiation device also includes a light source and the function of this is
to cause initiation
of an explosives charge into or onto which light from the light source is
discharged. The light
source used in a particular device will be selected based on the type of
explosives charge to
.. be initiated ¨ appropriate pairing of the light source and explosives
charge is important to
implementation of the present invention. Typically, the explosive charge will
have been
sensitised in some way to render it susceptible to initiation by a given light
source. The light
source may discharge directly into/onto the explosives charge or light from
the source may be
delivered to the explosives charge by a suitable wave guide, such as an optic
fibre or by direct
irradiation with or without a focussing lens.
An important characteristic of the present invention is that each initiation
device has its own
light source and in use this will typically be located in a borehole (or well
hole or the like).
The light source is controlled by the control circuit of the device. The
device is under the
(wireless) control of blast control equipment but otherwise the device is self-
governing. This
means for example that a single firing command can be sent to an array of
initiation devices
with the devices then being able to implement firing independently in
accordance with the
time delay programmed into the firing circuit. This allows increased control
and reliability.
This arrangement also allows a burning front to be achieved in a blast field
in which a
particular initiation device or devices has/have been (light) initiated whilst
other initiation
devices are in the process of timing down to (light) initiation.
This arrangement should be contrasted with a system in which a single
(centralised) light
source is used to deliver light through individual fibre optics to multiple
points of intended
initiation. This arrangement offers only crude control since a single light
source is used to
initiate multiple initiation events and this light source can only be either
on or off. Optical
switches would be required to control the transmission of light over
individual fibre optics
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and this adds to operating complexity and cost. There may also be reliability
issues with this
type of system since there exists the possibility that a fibre optic may be
damaged by
detonation of charges in proximity before or during light transmission by the
fibre optic. The
approach used in the present invention does not suffer these drawbacks.
In an embodiment of the invention the initiation device includes a single
transceiver and a
plurality of associated control circuits and light sources. In this embodiment
the transceiver
has the capability of directing multiple independent control circuits and
light sources
associated with those control circuits. This allows a number of control units
(and light
sources) to be loaded in the same blasthole with all control circuits being in
communication
with a single transceiver. This enables each control circuit/light source to
initiate an
associated explosive charge at independent delay times whilst maintaining a
burning front. In
other words this embodiment allows multi-decking of a blasthole using the same
transceiver,
noting here that the down-hole componentry (control circuits and light
sources) are
independently powered. In this embodiment the transceiver may be provided at
the surface at
ground level although it is possible depending upon the nature of the wireless
commands to
the transceiver that it is positioned below ground in the blasthole.
In accordance with the invention wireless command signals are sent from blast
control
equipment to the transceiver of an initiation device. One or more mechanisms
may be relied
upon to ensure suitable transmission and receipt of the command signals.
In one embodiment the transceiver may need to be physically positioned so that
wireless
command signals can be received directly. For example, in this case, the
transceiver may
need to be provided at the top of a blasthole. In this case communication may
take place
using standard radio frequency transmission systems and protocols.
In another embodiment the transceiver may be positioned below ground level
with wireless
command signals being transmitted through the ground via low frequency
signals. Low
frequency communication is common through the mining industry and a number of
systems
to control blasting already exist.
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extending from the transceiver
to a point at which the wireless command signals can be received. For example,
if the
initiation device is positioned down a borehole, an aerial may extend from the
transceiver
along the length of the borehole to the surface.
In yet another embodiment of the present invention direct communication
between blast
control equipment and one or more initiation devices is not necessary for
successful
implementation. This embodiment involves indirect communication between these
components by the formation of a low powered network in which one or more
initiation
devices act to relay a wireless command signal to a particular initiation
device even if that
device is out of range or otherwise unable to receive the wireless command
signal directly. In
this embodiment one or more initiation devices that is/are not intended to act
on a wireless
command signal relay the signal to one or more initiation devices that is/are
intended to act
on the command signal. It will be appreciated that in this embodiment the
initiation devices
will also have the ability to transmit wireless command signals. Formation of
a cross-
communicating network in this way can extend the range over which a wireless
command
signal may be effective. This approach is disclosed in International Patent
Publication No.
WO 2006/076777 entitled "Wireless detonator assemblies, and corresponding
networks".
A clear advantage of using a network of initiation devices to ensure
communication of
command signals over a blast field is that if a communication "connection" to
a particular
device is lost, it may be possible to re-route the communication pathway
around the lost
connection thereby maintaining operability. The system may also be configured
to diagnose
communication problems thereby allowing corrective action to be taken. This
should be
contrasted with conventional direct communication systems where loss of a
single
communication pathway will usually bring down the whole system.
Another advantage of employing a low powered network to facilitate
communication of
wireless command signals is that the network has the potential to allow two-
way
communication. In this case a transceiver having two-way communication
capability is used.
This allows for example an initiation device to send information to blast
control equipment
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on the current status of a network of the devices and for the blast control
equipment to
communicate to individual initiation devices timing protocols and firing
commands. Thus,
the control, timing and firing of a blast can be carried out using a remote
(wireless) system
with two-way communication allowing a blast operator to assess the status and
performance
of the blasting system before committing to a fire command. This adds an extra
level of
safety to a blasting operation. A further advantage is that the network is low
powered and, as
such, it should not interfere with other communications systems in operation
at a blast site.
Further, being a low powered network, no special operating licence is likely
to be required.
In the initiation device the transceiver is required to be in signal
communication with the
control circuit. The two components may be provided together, for example in a
single
housing, or they may be separate but suitably connected for signal
communication for
example, by wire, wireless or optical communication means. Likewise, the
control circuit is
required to be in signal communication with the light source in order to
activate the light
source as necessary. The control circuit and light source can be provided
together, for
example within the same housing, or they may be separate but suitably
connected. The
initiation device will also require a power supply to power the transceiver,
control circuit and
light source. The power supply may be physically associated with the device,
or a
component thereof, but this is not essential. In this regard safety
requirements and regulations
concerning the provision of a power supply on a dovvnhole unit may need to be
respected.
The power supply may be conventional in design, such as a low voltage battery
(possibly
located with the light source component) or a supercapacitor charged from a
battery. In the
latter case the supercapacitor may be charged using a battery provided at the
surface with the
supercapacitor provided as part of the dovvnhole componentry.
In another embodiment, one or more components of the device may be powered by
less
conventional means. For example, it may be possible to use environmental
means, such as
solar power. Other possibilities may exist depending upon how the present
invention is
implemented in practice. It may be desirable however for the device of the
invention to
function without the need to use a conventional power source such as a
battery.
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It will be appreciated from the preceding paragraphs that the transceiver
functionality and the
light source may be physically separated from each other (the control circuit
can be
associated with either). Thus, the transceiver could be located at or above
ground level and
the light source (the firing functionality of the device) provided adjacent or
on top of an
explosives train (of working explosives) in a borehole. This offers a number
of advantages as
follows:
= Simplified design for receipt of wireless command signals.
= The transceiver can be used to transmit blast performance data during and
possibly
after a blast. For example, if the transmitter and control unit are connected
via wires,
the wire could be used to measure VOD in the hole via a change in resistance
and this
information transmitted back to the control centre.
= The size of the down-hole componentry may be reduced and this will be
beneficial for
small bore applications. In this regard current solid state lasers may be of
very
compact design.
= As noted, it may be possible for a single transceiver, for example located
at the
surface, to control the activation of a number of down-hole firing units by
having
multiple output points which allow connection of a number of units. This would
be
beneficial for holes in which there are multiple detonators, for example,
multi decked
holes.
The explosives charge that is light initiated in accordance with the present
invention may be
used to initiate an associated "working" or main explosives charge. In this
case the light
initiated explosives charge is relatively small but selected to nevertheless
be effective in
detonating the main explosives charge. In this case the light initiated
explosive charge may be
provided under heavy confinement as per a conventional cartridge detonator.
Light can be
delivered into the cartridge direct or via a fibre optic.
In another embodiment the light initiated explosives charge is used to
detonate an associated
main explosives charge but the arrangement is detonator free. In this case the
light explosive
charge is provided in direct contact with at least part of the main charge or
the two may be
separated by a membrane that does not influence detonation of the main
explosives charge.
This approach is described in International Patent Publication No. WO
2008/113108 entitled
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"Initiation of explosives materials". The latter stipulates use of an optic
fibre to convey light
but this is not essential in accordance with the present invention.
Accordingly, in this embodiment the invention provides a detonator free
blasting system
which comprises:
a working explosive charge;
a confined explosives charge; and
an initiation device in accordance with the present invention, wherein the
initiation device is
provided to deliver light to the confined explosives charge and the confined
explosives
charge is adapted to be initiated by that light and wherein initiation of the
confined explosives
charge causes initiation of the working explosive.
In accordance with this embodiment the working explosives charge is initiated
by detonation
of the confined explosives charge. In turn initiation of the confined charge
is caused by
irradiation of the confined explosive by a suitable light source. Thus, the
working explosive
is initiated without using a conventional detonator device.
In accordance with this embodiment initiation is achieved by irradiating the
confined charge
until ignition of it occurs. The confined charge is confined such that this
initial ignition
propagates to full detonation. The confined charge and working charge are
provided relative
to one another such that detonation of the confined charge causes initiation
of the working
charge. In an embodiment of the invention a portion of the confined charge and
a portion of
the working charge may be in direct contact. Ilowever, in other embodiments
this may not be
essential provided that the intended operative relationship between the
charges is retained.
For example, in certain embodiments, the charges may be separated by a
membrane, or the
like. In this case the membrane, or the like, may be included for ease of
manufacture; the
membrane (or like) does not influence detonation of the working charge.
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The working explosives charge that is used is generally a secondary explosive
too. The
blasting system of the invention may therefore be free of primary explosives.
The working
explosives charge may be the same as or different from the light initiated
explosives charge.
When the charges are of the same explosives material the invention may be
implemented by
suitable confinement of a portion of the bulk explosive.
An important aspect of this embodiment is the way in which the confined
explosives charge
is confined since it has been found that the geometry of the confinement is
critical to the
successful detonation of the working explosive. Thus, the confined explosive
charge should
be confined in such a manner to contain initial ignition of the confined
charge and to allow
subsequent propagation to full detonation. A variety of confinement means
(geometry and
material) may be employed in implementation of the embodiment of the present
invention.
In one embodiment the confined explosive charge may be confined in an elongate
tubular
member. Usually, this will be of circular cross-section, although this is not
mandatory.
When an elongate tubular member is used, the internal diameter of the tubular
member
should be greater than the critical diameter for the explosive being confined.
When the
confined explosive charge is strongly confined, for example, when the
confinement means is
made of a metal, the internal diameter of the tubular member may be up to 3
times larger than
the critical diameter for the explosive being confined.
A typical tubular member of circular cross-section useful in the present
invention generally
has an internal diameter of about 2 to about 5mm, for example about 3mm, and a
length of up
to about 110mm, for example from 20 to 110mm. The length of the tubular member
required
for transition of the confined explosives charge will vary as between
different types of
explosive. For example, for PETN the minimum length of the tubular member will
be about
30mm, whereas for pentolite the minimum length will be about 90nun (for an
internal
diameter of about 3nun).
The confinement means may take on other geometries. Thus, spherical or conical
confinement means may be used. Examples of suitable materials for the
confinement means
include metals and metal alloys, for example aluminium and steel, and high
strength
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polymeric materials.
For the purposes of illustration, in the following, the invention will be
described in
connection with a tubular elongate member of circular cross-section as
confinement means.
5
Typically, the working explosives charge is provided in (direct) contact with
a portion of the
confined explosives charge. When the confined explosives charge is confined in
an elongate
tubular member the requisite contact may be achieved via an end of the tubular
member in
which the confined portion is confined (that end being remote from the end of
the tubular
10 member to which laser light is delivered through the fibre optic).
When other geometries of
confinement means are employed it is important that at least a portion of the
confined
explosive charge is in contact with the working explosive.
In an embodiment a fiber optic may be used to communicate light from the light
source to the
confined explosives charge. This can be done by providing one end of the
(exposed) fibre
optic in contact with, or embedded in, the confined explosive charge. Thus,
one end of the
fibre optic may be inserted into an end of the tubular member in which the
explosive charge
is confined. The fibre optic will usually have a diameter of from 50 to 400
pm.
In a related embodiment of the present invention the exposed end of the fibre
optic may be
provided adjacent to but not in contact with the (external surface of the)
confined explosive
charge. It has been found that providing a gap (of air) between the end of the
(exposed) fibre
optic and the confined explosive charge has an effect on heat transfer to the
confined
explosive and thus on the delay time between when laser light is discharged
through the fibre
optic and when the confined explosive is initiated. More specifically, it is
believed that the
gap acts as an insulator that facilitates efficient heat transfer to the
confined explosive by
minimizing/avoiding reverse conduction effects. Preferably, the exposed end of
the fibre
optic is provided at a short distance away from the surface of the confined
explosive in the
tubular member. Typically, this short distance is from 5 pm to 5.0mm
The fibre optic is of conventional design and is provided with a layer of
cladding. This may
be removed at one end of the fibre optic when the fibre optic is being
positioned relative to
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the confined explosive provided in the tubular member. The characteristics of
the fibre optic
will be selected based on amongst other things the wavelength of laser light
to be
communicated to the confined explosive. By way of example the wavelength is
typically
from 780 to 1450nm.
The exposed end of the fibre optic is usually held in an appropriate position
relative to the
confined explosive by means of a suitable connector. An 0-ring may be used to
grip the
exposed end of the fibre optic and to prevent leakage of gas.
In other embodiments it is not necessary to use a fibre optic to communicate
light from the
light source to the confined explosives charge. This may simplify design and
manufacture,
and be more economical. In one such embodiment it may be possible to
communicate light
directly from the light source to the confined explosives charge. Here the
outlet of the light
source would be provided in very close proximity or even touching the confined
explosive
charge. For example, the "window" of a laser diode may be provided adjacent to
or in contact
with the explosive charge. In another embodiment a lens may be used to focus
light from the
light source onto the explosive charge. For example, it may be possible to
replace the
"window" portion of a laser diode with a (sapphire) lens that focuses light
emitted from the
diode onto the explosive. This approach may enhance efficiency.
The working explosives charge that it is desired to detonate is generally
provided in (direct)
contact with at least a portion of the confined explosives charge. Typically,
this contact will
occur at the end of the tubular member in which the confined explosive is
confined remote
from the end of the tubular member associated with the fibre optic. Depending
upon the form
in which the explosive charge is provided, the explosives charge may also
surround the
tubular member in which the confined explosive is confined. In other words the
tubular
member may be embedded in the explosives charge.
In a related embodiment the explosives charge that is to be light initiated
takes the form of a
booster, for example a pentolite booster. In this case the confined explosives
charge,
preferably PETN or pentolite, is provided in an elongate tubular member that
is embedded in
the booster. The booster may be designed accordingly to accommodate the
tubular member.
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Thus, the tubular member may be provided and secured in the booster in a
suitable well, as is
the case for detonator initiated boosters. Otherwise, conventional boosters
may be used to
implement this embodiment.
Alternatively, in another related embodiment of the invention, the pentolite
booster may be
cast around and with a suitable tubular member. In this case it may be
possible to implement
the invention using a one-piece booster comprising a shell/casing and an
integrally formed
tubular member extending into a cavity defined by the shell/casing. Suitable
explosives
material(s) may then be cast into the shell/casing and tubular member.
These embodiments of the present invention relating to the booster may have
practical
application in seismic exploration where (pentolite) boosters are used to
generate signals
(shock waves) for analysis to determine geological characteristics in the
search for oil and gas
deposits. The present invention thus extends to use of this embodiment of the
invention in
seismic exploration.
It is also possible for the working explosives charge to take the form of a
length of detonating
cord. In this case the end of the detonating cord is typically provided in
direct contact with at
least a portion of the confined explosives charge. Any suitable retainer or
connector may be
used to ensure that this direct contact is maintained prior to use. Initiation
of the detonating
cord aside, the detonating cord may be used in conventional manner.
Instantaneous
detonation of detonating cord across multiple blastholes could prove
advantageous in pre-
split and tunnel perimeter blasting operations. In another embodiment the
detonating cord
may itself be used to initiate a booster, for example a booster comprising an
emulsion
explosive. In this case one end of the detonating cord will be embedded in the
booster
explosive with the other end of the cord being available for light initiation
in accordance with
the present invention.
In another embodiment the confined and working explosives charges may be an
emulsion
explosive material. Conventional emulsion explosive material may be used in
this regard. In
this embodiment a portion of the emulsion explosives material may be confined
in a suitable
elongate tubular member and immersed/embedded in the working charge emulsion.
In this
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embodiment (and for all others) the nature and dimensions of the means used
for confinement
may be manipulated in order to optimise implementation of the invention.
In another embodiment the light initiated explosives charge may itself be
adequate to achieve
the desired blast outcome. For example, the explosives charge deployed in a
suitable device
configuration may be adequate to perforate a well casing in oil or gas
exploration.
The explosives charge to be initiated by light and the light source are
selected based on the
required outcome and the two must be paired accordingly. Examples of light
sources that
may be used include solid state lasers, laser diodes, LEDs and other
electronic light sources.
Compact design and low power consumption are desirable characteristics for the
light source.
By way of example a 1-10 W power laser may be suitable for use in the
invention. The laser
wavelength may be within the near infra-red region and indeed this is
preferred, although
other wavelengths may be used. A fibre optic and/or lens may be required to
channel and
focus the laser output, although direct irradiation of the explosives charge
would be preferred
as this would simplify overall design.
Usually, the light initiated explosive is a secondary explosive material, such
as PETN, tetryl,
RDX, HMX, pentolite, and the like. The use of PETN or pentolite tends to be
preferred. It is
possible however that the explosives charge is a conventional emulsion
explosive, such as a
water-in-oil emulsion explosive, or a water-gel explosives material.
Depending upon the characteristics of the light source and explosives charge,
it may be
necessary to dose the explosives charge with a heat transfer medium to enhance
coupling of
the light energy irradiated from the light source and the explosive charge.
Typically, the heat
transfer medium is a light absorbing material that has an absorption band in
the wavelength
of the light being used. Examples of heat transfer media include carbon black,
carbon
nanotubes, nanodiamonds and laser dyes. Such materials are known in the art
and are
commercially available.
In an embodiment of the invention it may be possible to use a conventional
camera flash to
initiate an explosives charge. It is known for example that unpurified single
wall carbon
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nanotubes (SWCNT) can be caused to ignite when light is applied to them from a
standard
camera flash. This is believed to be due to oxidation of iron nanoparticle
catalysts that are
present at the ends or on the surface of the nanotubes.
The flash initiation reaction is not particularly violent since only small
regions of the
nanotubes seem to show reaction. However, if nano-magnesium and/or nano-iron
is mixed
with nano-iron particles a more intense and violent reaction can result with
significant
amounts of heat being given off Typically, the particle size for the iron and
magnesium
particles will be 2 to 4000 pm but preferably in the order of 6 to 100 p.m.
The reaction may
be a thermite reaction with the formed oxide. The additional heat associated
with that
reaction may enable initiation of an explosives charge dosed with the
nanotubes, or a blend of
nano-iron and nano-magnesium particles. It is possible that the same effect
may be achieved
using a high intensity LED or laser rather than a camera flash.
In the same way, other additives that serve as a thermal source and that
actively take part in
detonation reactions may be included in the confined explosive. Such materials
include
nitrated nanomaterials, silicon nanowires and other optically sensitive fuels.
The amount of
such materials may be up to 10% by weight of the confined explosives charge.
Such
materials may be used together with a heat transfer medium, or alone. The use
of one or
more heat transfer media and/or optically sensitive materials may allow
detonation to be
achieved with irradiation energies orders of magnitude lower than when such
media and/or
materials are not used.
The invention also relates to a method of blasting using an initiation device
in accordance
with the invention. In this case the light source of the device is provided in
operative
association with an explosive charge that is adapted to be light initiated by
the light source
used in the device. The method comprises the transmission of a suitable
wireless command
signal to the device, the command signal being received by the transceiver and
processed by
the control circuit. The control circuit activates the light source and this
causes the
explosives charge to be initiated. The explosives charge is typically
associated with and
causes initiation of an associated working explosives charge.
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The invention further provides a blasting system comprising an initiation
device in
accordance with the invention and blast control equipment that is adapted to
transmit wireless
command signals to the device.
5 The present invention may have particular use in the Oil & Gas (O&G)
industry. Possible
applications within this industry include use in the completion of O&G wells,
specifically the
initiation of explosives within perforation guns. Perforation guns are used in
the final stage
(completion) of an O&G well to break through the concrete (and/or other
materials) casing
laid down during the well making process. A further purpose of the perforation
gun is to
10 fracture the formation holding the oil in order to stimulate oil and/or gas
flow. This may
happen whether the well casing is intact or not. Perforation of O&G wells is
generally carried
out by specialized personnel through dedicated service companies, although
other
arrangements are possible.
15 The presence of primary explosives (amongst other things) in the
perforation gun firing train
means that once the explosive train is established on (or near) an O&G well
working platform
a range of activities must cease, resulting in a significant loss of
productivity from the well.
Removing primary explosives from this environment thus provides a tangible
economic
benefit in addition to the substantial safety advantage inherent in secondary
(vs. primary)
explosives. The present invention enables direct photo-initiation of secondary
explosives and
this will remove this hazard and allow a significantly wider range of
activities to continue.
A further application in the O&G industry is the use in exploration for O&G
through seismic
surveys. Explosives are important sources of seismic energy used to uncover
underground
geologic features able to retain O&G. Seismic surveys entail burying of one or
more
explosives charges to pre-determined depths (e.g. shot-holes) in arrays of
particular design.
Geophone (or other measuring devices) arrays of are also established to detect
reflected (as
well in some cases direct) seismic energy. The explosives are then initiated,
measurements of
resultant (including background) seismic energy are recorded and analysis is
performed to
visualize relevant geologic features.
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Explosive arrays are generally relatively large, consisting of 10's, 100's or
even 1000's of
individual charges. These charges are generally deployed by relatively small
teams of people
and a significant time can elapse between loading the first and last charges
giving rise to long
periods where live explosives are left in shot-holes. Further delays can arise
due to technical
activities surrounding a survey including, but not limited to, establishing
the firing train,
measurement array or other related activities. Even further delays may be
caused by non-
specific issues including scheduling of staff/equipment, weather or other
seasonal issues.
Taken together, these delays (and others not specified) result in potentially
long explosive
sleep-times, i.e. explosives deployed before initiation. Seismic survey
applications can result
in longer sleep times than most other explosive applications making the
removal of primary
explosives particularly preferable in that context.
As noted the present invention allows the use of primary explosives materials
to be avoided.
One of the safety benefits of this in seismic exploration is that the overall
sensitivity to
detonation by non-specific means is significantly reduced. This is
advantageous during the
survey as it reduces the possibility of an unintended detonation. It is also
important following
completion of the survey as it is accepted that a certain proportion of
charges deployed will
fail to detonate. This proportion can be up to 10% depending on local
conditions but is
generally considerably lower. Due to the hazards involved in recovering
misfired charges,
many are left in place and are abandoned. The presence of highly sensitive
primary
explosives in these deployed charges means that shock, or another event, can
lead to
unintended detonation by non-specific stimulus. The chances of this are
significantly reduced
if the present invention is employed in order to avoid the use of primary
explosives.
Notwithstanding the reduced sensitivity of secondary explosives to a wide
range of stimuli,
the photo-initiation system will fire only in response to a specific stimulus.
Proven, secure
systems to generate this stimulus exist and include, but are not limited to
electronic systems,
able to generate a fire, no fire or disarm signals. It is highly unlikely that
the fire signal will
be generated in the environment of an abandoned charge by chance.
A further advantage of removal of primary explosives is environmental, in that
many widely
used primary explosives include highly toxic and environmentally stable
compounds. One
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example of this is the wide use of lead azide in detonators - the azide
component is a highly
toxic poison and lead is a recognized environmental pollutant that cannot be
broken down by
any natural process. Whilst many secondary explosives are classed as
recalcitrant pollutants,
natural mechanisms do exist in nature for their efficient degradation with
biodegradation
reported for all secondary explosives in wide use.
Many modifications will be apparent to those skilled in the art without
departing from the
scope of the present invention
Throughout this specification and the claims which follow, unless the context
requires
otherwise, the word "comprise", and variations such as "comprises" and
"comprising", will be
understood to imply the inclusion of a stated integer or step or group of
integers or steps but
not the exclusion of any other integer or step or group of integers or steps.
The reference in this specification to any prior publication (or information
derived from it), or
to any matter which is known, is not, and should not be taken as an
acknowledgment or
admission or any form of suggestion that that prior publication (or
information derived from
it) or known matter forms part of the common general knowledge in the field of
endeavour to
which this specification relates.
