U.S. patent application number 16/656239 was filed with the patent office on 2020-02-13 for method of blasting.
This patent application is currently assigned to ORICA INTERNATIONAL PTE LTD.. The applicant listed for this patent is ORICA INTERNATIONAL PTE LTD.. Invention is credited to Rodney Wayne APPLEBY, Richard John GOODRIDGE, David Olaf JOHNSON, Thomas M MILLER.
Application Number | 20200049476 16/656239 |
Document ID | / |
Family ID | 44904523 |
Filed Date | 2020-02-13 |
![](/patent/app/20200049476/US20200049476A1-20200213-D00001.png)
United States Patent
Application |
20200049476 |
Kind Code |
A1 |
GOODRIDGE; Richard John ; et
al. |
February 13, 2020 |
METHOD OF BLASTING
Abstract
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.
Inventors: |
GOODRIDGE; Richard John;
(Redhead, AU) ; APPLEBY; Rodney Wayne;
(Springfield Lakes, AU) ; JOHNSON; David Olaf;
(Aurora, CO) ; MILLER; Thomas M; (Evergreen,
CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ORICA INTERNATIONAL PTE LTD. |
Singapore |
|
SG |
|
|
Assignee: |
ORICA INTERNATIONAL PTE
LTD.
Singapore
SG
|
Family ID: |
44904523 |
Appl. No.: |
16/656239 |
Filed: |
October 17, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13696519 |
Jan 4, 2013 |
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PCT/US2011/035706 |
May 9, 2011 |
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16656239 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F42D 1/05 20130101; F42D
1/055 20130101; F42B 3/113 20130101 |
International
Class: |
F42D 1/05 20060101
F42D001/05; F42D 1/055 20060101 F42D001/055; F42B 3/113 20060101
F42B003/113 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 2010 |
AU |
2010901993 |
Claims
1. An explosive booster comprising: a working explosives charge
that is a secondary explosive; a confined explosives charge
disposed in an elongate tubular member that is embedded in and
surrounded by the working explosives charge, wherein the confined
explosives charge is a secondary explosive dosed with a heat
transfer medium; a power supply; a laser diode coupled to the power
supply and configured to emit light; a lens that focuses light
emitted by the laser diode directly onto a portion of the confined
explosive charge; a transceiver configured to receive wireless
command signals sent from blast control equipment; a control
circuit coupled to the power supply and in signal communication
with the transceiver and the laser diode, wherein the control
circuit is configured to process received wireless command signals
and activate the laser diode in response to a specific wireless
command signal; and a common housing in which each of the
transceiver, the control circuit, and the laser diode reside.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of copending application
Ser. No. 13/696,519, filed on Jan. 4, 2013, which is a national
phase of PCT International Application No. PCT/US2011/035706 filed
on May 9, 2011, which claims the benefit under 35 U.S.C. .sctn.
119(a) to Patent Application No. 2010901993, filed in Australia on
May 7, 2010, all of which are hereby expressly incorporated by
reference into the present application.
[0002] 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 TO INVENTION
[0003] In commercial blasting operations a bulk or packaged
explosive is generally required to be initiated according to a
predetermined blast design that specifies 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 OF THE INVENTION
[0004] Accordingly, in one embodiment the present invention
provides an initiation device for initiation of an explosives
charge, which comprises:
[0005] a transceiver for receipt of wireless command signals;
[0006] a control circuit for processing of wireless command signals
received by the transceiver;
[0007] and
[0008] a light source that is suitable for initiation of the
explosives charge and that is activated by the control circuit.
[0009] 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.
[0010] The invention also provides a method of blasting using the
initiation device of the invention, and a blasting system
comprising the initiation device and associated blast control
equipment.
[0011] As will be explained, the present invention combines
wireless communication capability with light initiation of an
explosives charge. This combination is believed to provide
significant improvements over known blasting methodologies and
componentry.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The FIGURE shows the device of the invention (1), having
transceiver (2) for receiving wireless command signals (5), as well
as a control circuit (3) for processing the wireless command
signals (5) received by the transceiver (2), a light source (4),
which is suitable for initiating explosive charge (6) by light
(4A), discharged from the light source (4). The control circuit (3)
comprises an integrated circuit (not shown) for preprogramming with
a time delay to allow precise control of activation of the light
source (4) when a wireless command FIRE signal is received by the
transceiver (2).
DETAILED DISCUSSION OF THE INVENTION
[0013] 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 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.
[0014] 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.
[0015] The control circuit will also typically include some form of
timing mechanism to allow 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.
[0016] 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.
[0017] 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.
[0018] 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 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.
[0019] 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.
[0020] 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.
[0021] 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.
[0022] 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.
[0023] A further possibility might involve the use of an aerial
system 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.
[0024] 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", the contents of which are incorporated by reference.
[0025] 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.
[0026] 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 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 license is likely to be required.
[0027] 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
downhole unit may need to be respected.
[0028] 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 downhole componentry.
[0029] 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.
[0030] 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: [0031] Simplified design for
receipt of wireless command signals. [0032] 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. [0033] 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. [0034] 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.
[0035] 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.
[0036] 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 "Initiation of explosives materials", the contents of
which are incorporated herein by reference. The latter stipulates
use of an optic fibre to convey light but this is not essential in
accordance with the present invention.
[0037] Accordingly, in this embodiment the invention provides a
detonator free blasting system which comprises:
[0038] a working explosive charge;
[0039] a confined explosives charge; and
[0040] 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.
[0041] 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.
[0042] 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. However, 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.
[0043] 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.
[0044] 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.
[0045] 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.
[0046] A typical tubular member of circular cross-section useful in
the present invention generally has an internal diameter of about 2
to about 5 mm, for example about 3 mm, and a length of up to about
110 mm, for example from 20 to 110 mm. 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 30 mm,
whereas for pentolite the minimum length will be about 90 mm (for
an internal diameter of about 3 mm).
[0047] 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
polymeric materials.
[0048] 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.
[0049] 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 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.
[0050] 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 .mu.m.
[0051] 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 .mu.m to 5.0 mm
[0052] 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
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 1450 nm.
[0053] 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 O-ring may be used to grip the exposed end
of the fibre optic and to prevent leakage of gas.
[0054] 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.
[0055] 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.
[0056] 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. 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.
[0057] 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.
[0058] 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.
[0059] 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.
[0060] 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
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.
[0061] 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.
[0062] 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.
[0063] 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.
[0064] 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.
[0065] 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 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.
[0066] 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 .mu.m but preferably in the order of 6 to 100 .mu.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.
[0067] 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.
[0068] 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.
[0069] 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.
[0070] 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 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.
[0071] 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.
[0072] 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.
[0073] 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.
[0074] 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.
[0075] 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.
[0076] 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 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.
[0077] Many modifications will be apparent to those skilled in the
art without departing from the scope of the present invention
[0078] 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.
[0079] 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.
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