Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR DETONATING AN EXPZOSIVE CHARGE
The present invention relates to an apparatus for
perforating a tubular member extending into a wellbore
Once a well bore has been drilled, utilizing the
conventional technique of a drilling string with a drill
bit secured to the lower free end, the well is completed
by positioning a casing string within the well bore.
This increases the integrity of the well bore and
provides a path to the surface for the produced fluids.
The casing string is normally made up of individual
lengths of relatively large diameter metal tubulars
secured together by any suitable means, for example screw
threads or welds. Conventionally, the casing string is
cemented to the well face by circulating cement into the
annulus defined between the casing string and the well
face. The cemented casing string is subsequently
perforated to establish fluid communication between the
formations of interest, those containing hydrocarbons,
and the interior of the casing string. Perforating has
conventionally been performed by means of lowering a
perforating gun, having at least one shaped charge
positioned within a carrier, down inside the casing
string and then firing the charge via wireline control
from the surface of the earth. A perforating gun may be
constructed to be of any length. The perforating gun is
lowered within the casing on wireline or tubing to a
point adjacent the zone of interest and the shaped
explosive charge is detonated to penetrate or perforate
both the casing and the formation. This establishes
fluid communication between the cased well bore and the
zone of interest. The resulting perforations extend
through the casing, cement, and a short distance into the
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formation. The perforating gun is either removed from
the well bore or dropped to the bottom thereof. The
formation is then often stimulated by any one of a number
of well-known means to enhance production of hydrocarbons
~5 therefrom. ~
Examples of the known perforating devices can be
found in U. S. Patent Nos. 4,538,680 to Brieger et al;
4,619,333 to George; 4,768,597 to Lavigne et al;
4,790,383 to Savage et al; 4,911,251 to George et al;
5,287,924.to Burleson et al; 5,423,382 to Barton et al;
and 6,082,450 to Snider et al. All of these relate to
perforating guns which are lowered within a casing string
carrying explosive charges which are detonated to
perforate the casing outwardly. This had the advantage
of leaving the inside of the casing relatively
unobstructed since debris and ragged edges would be
outwardly directed by the detonations of the charges.
In the late 1990s, successes were found with casing
conveyed perforating guns in which the guns and control
lines were attached to the outside of the casing. One
disadvantage of this approach is that the externally
conveyed elements are subject to damage during normal
run-in operations. A second disadvantage is the
perforations leaving ragged shards extending inwardly
causing obstructions on the inside of the casing.
PCT application PCT/US00/05774, to Snider et al,
describes another attempt to perforate a tubular from the
outside. This differs from the above mentioned
perforating from the outside of the casing in that Snider
et al propose a perforating gun separate from and
exterior to the.casing to be perforated. When the Snider
et al perforating gun is detonated, portions of the gun
act in a manner similar to shrapnel to perforate the
casing string. This is not a satisfactory solution to
the problem of perforating tubulars in that it raises the
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possibility of a very ragged perforating which could
easily destroy the structural integrity of the casing
string, particularly in view of the fact that it utilizes
portions of the casing itself to perforate the side of
~5 the casing furthest from~the perforating gun. This can
also result in a ragged inner surface of the casing which
could damage or prevent passage of downhole tools and
instruments. Perforating a casing from the inside raised
this consideration to a much lesser degree.
Frequently a well penetrates multiple zones of the
same formation and/or a plurality of hydrocarbon bearing
formations of interest. It is usually desirable to
establish communication with each zone and/or formation
of interest for injection and/or production of fluids.
Conventionally, this has-been accomplished in any one of
several ways. One way is to use a single perforating gun
which is conveyed by wireline or tubing into the well
bore and an explosive charge fired to perforate a zone
and/or formation of interest. This procedure is then
repeated for each zone to be treated and requires running
a new perforating gun into the well for each zone and/or
formation of interest. One alternative is to have a
single perforating gun carrying multiple explosive
charges. This multiple explosive charge gun is conveyed
on wireline or tubing into the well and, as the gun is
positioned adjacent to each zone and/or formation of
interest, selected explosive charges are fired to
perforate the adjacent zone and/or formation. In another
alternative, two or more perforating guns, each having at
least one explosive charge, are mounted spaced apart on a
single tubing, then conveyed into the well, and each gun
is selectively fired when positioned opposite a zone
and/or formation of interest. When the select firing
method is used, and the zone and/or formation of interest
are relatively thin, e.g. 15 feet or less, the
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perforating gun is positioned adjacent the zone of
interest and only some of the shaped charges carried by
the perforating gun are fired to perforate only this zone
or formation. The gun is then repositioned, by means of
'5 the tubing, to another zone or formation and other shaped
charges are fired to perforate this zone or formation.
This procedure is repeated until all zones and/or
formations are perforated, or all of the shaped explosive
charges detonated, and the perforating gun is retrieved
to the surface by means of the tubing.
However, the necessity of tripping in and out of the
well bore to perforate and stimulate each of multiple
zones and/or formations is time consuming and expensive.
In view of this, multiple zones and/or formations are
often simultaneously stimulated, even though this may
result in certain zones and/or formations being treated
in a manner. more suitable for an adjacent zone and/or
formation. .Thus a need exists for apparatus and
processes.to perforate casing which is positioned within
a well bore which eliminates the need to run perforating
equipment in and out of the well when completing multiple
zones and/or formations.
Disadvantages of the presently known methods of
perforating are several, including: the perforating
device itself may need to be retrieved; and the cabling
systeins.to convey signals to the charges must be carried
outside or inside the tubulars, either subjecting the
cabling system to damage and/or taking up space.
Protective means, such as wraparound metal protectors,
armored cable housings, or grooved casing couplings, must
be used to avoid damaging externally mounted cabling
systems, explosive charges and their respective
detonating means. In order to perforate the adjacent
formation, internally conveyed or mounted perforating
systems necessarily also perforate the tubluar within
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which they are conveyed which in certain instances, such
as when trying to relieve annular pressure, is
undesirable.
Accordingly, it is an object of the present invention
to provide an improved apparatus for perforating a
tubular member extending into a wellbore, which overcomes
the aforementioned drawbacks.
In accordance with the invention there is provided an
apparatus for perforating a tubular member extending into
l0 a wellbore, comprising:
at least one explosive charge in contact with the
wall of said tubular member;
for each explosive charge, a detonation device
arranged to detonate the explosive charge; and
l5 ~ a remote Control station in wireless and cable-less
communication with the detonation device whereby a signal
from said control station causes said detonation device
to detonate the respective explosive charge.
The present invention will now be described, by way
20 of example, with reference to the accompanying drawings
in which:
Figure 1 is a side elevation, partially in section,
of an embodiment of the invention utilizing explosive
charges attached to a tubing wall;
25 Figure 2 is a detailed section through one of the
shaped charges of the present invention;
Figure 3 is a side elevation of an embodiment of the
invention utilizing external ribs containing the
explosive charges;
30 Figure 4 is a side elevation of an embodiment of the
invention utilizing an explosive linear strip;
Figure 5 is a block level schematic diagram of the
programmable interface and detonation device; and
Figure 6 is a detail plan view of the exploding
35 bridgewire detonation device of the present invention.
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The method and apparatus of the present invention is
described in an embodiment for perforating a tubing
string and the adjacent formation without the need for
conventional perforating guns and their related extensive
~5 downhole wiring or cables. The described apparatus can
best be described as a "self-perforating" production
tubular or casing. What this means is at least one
portion of the tubing making up the production tubing
and/or casing itself carries the perforating charges, all
necessary apparatus to control detonation and, after
detonation, production continues through the n,ow
perforated tubing or casing.
Turning now to the drawings, as seen in Figure 1, a
tubular 10 is provided with an outside surface 12, a
tubular wall 14, and an inside surface 16. Explosive '
charges and their associated detonators 18 are attached
to the outer surface of the wall, preferably in blind
bores 20. In wells, where space is~at a premium, this
embodiment allows the explosive charges to be set close
~ to flush with the outside surface l2 thereby lessening
the danger of damage to the explosive charges and their
detonators during running of the tubular downhole.
The self-perforating tubing or~ casing of the present
invention is made from standard tubular materials having
~5 . coaxial outside and inside surfaces with a closed wall
extending therebetween. At least one explosive charge is
mounted in direct contact with the outside surface of the
wall of the tubular. This contact may be a mechanical
connection, such as, by adhering the explosive charges to
the outside surface of the tubular; but preferably is by
drilling receiving blind bores in the wall of the tubular
and fixing the explosive charges into the respective
blind bores; or
by bracketing, banding, clamping or by the use of
adhesives the explosive charges to the outside surface of --
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the tubular. The tubular itself may also be modified in'
other ways to carry the explosive charges. An example is
to add one or more ribs to the outside of the tubular,
preferably in a helical spiral around the outside
surface. The explosive charges may then be placed within
the ribs. Prefabricated, molded plastic sleeves could
also be used to carry the explosive charges. Such
sleeves could be made to attach to the outside surface of
the tubular, for example.in a clamping manner or as~
' shrink wrap, and could be provided with additional
features, such as molded channels to allow circulation of
well fluids, for example cement slurry, through the
annular space between the casing and the well bore.
Figure 2 shows a cross section through an explosive
charge 18 in accordance with the first embodiment. The
tubular 10 is first prepared by boring a series of blind
bores 20 about the circumference. These bores 20 can be
in set geometric patterns, randomly spaced, aligned'
vertical rows, circumferential bands, etc. in accordance
with the desired plan for perforating. The shaped
explosive charges 18 are secured in their respective-
blind bores 20 by any known means, such as threading or
affixing the explosive charge into the blind bore with an
adhesive material. The explosive charges 18 are then
connected to their respective detonating means (not
shown) for single, multiple, sequential, etc. detonation
in accordance with the plan for perforating. The
detonating means are in wireless/cableless contact with
control means (also not shown) at the surface. When the
explosive charge 18 is detonated, it will shear a plug 22
(shown in phantom) from wall 14. This amounts to no-jet
perforating.
This preferred method to perforate the pipe string
uses an explosive charge to open a hole from outside to
inside to create a flow path between the inside and
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outside of the pipe. A second explosive charge can, if
so desired, be used to perforate outwardly through the
annular space, which may be cement filled, into the
formation or zone of interest. The present method can be
~5 considered "plugging" in that an explosive charge is set
in contact with the casing wall, or in a partially
penetrating blind bore drilled into the casing wall, and
detonation of that explosive charge creates a stress
riser that shears a steel "plug" out of the casing wall
leave a hole of known geometry and size without burrs or
splatter inside the casing that can block or damage
equipment being run in the hole.
A key feature of the present system is the slim
. overall profile which does not increase borehole size
requirements.
A collar, sleeve or coating of a diameter greater
than that of the casing and with channels) cut helically
on its exterior surface can be used to provide protected
clearance for the charge, receiver, and controller while
~ allowing clearance for flow of fluids and slurries, for
example cement,.past the collar. A hole or holes can be
partially drilled into the collar from the outside to
provide a site for a stress riser when the perforating
charge is ignited without substantially affecting the
pressure rating of the casing string.
In Figure 3, a tubular 24 has an outside surface 26
and one or more ribs 28 wrapped around and secured to the
outside surface. A plurality of explosive charges 30 are
placed in recesses in the ribs 28 to lie against.the .
outer surface 26. This embodiment maintains full
strength of the tubular, as the wall is without the blind
bores of the embodiment of Figure 1, but has a slightly
larger profile. However, the ribs 28 can be used to
advantage by directing flow during casing running and
cementing operations.
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The embodiment of Figure 4 utilizes a linear strip or
shaped explosive charge 32 placed on and winding
helically about the outside surface 34 of the tubular 36
oriented to shoot outward into the cement and/or
'5 formation. Such helically arranged linear strip charges
provides a channel for flow and exposes a greater surface
area of rock/sand to be perforated, as compared to
conventional "button" or conical shaped charges. The
flexible strips may be oriented in a variety of patterns.
Explosive strips may be constructed so that the force of
the explosion is highly directional. When explosive
linear strips are used, it is advisable to place them on
the outside surface of the outermost tubing string, such
as the casing, so that the force.is directed outward and
the structural integrity of the casing is not
compromised. This is an important new advantage of the
subject system.
With all of the above-mentioned embodiments of the
present invention, the use of shaped explosive charges
allows a controlled and directed explosive force thereby
allowing use as a means to open holes to release annular
pressure without damaging internal tubulars.
Figure 5 shows a schematic of the detonation device
of the present invention including a wireless receiver
38; digital s,igna~ processing logic and control 40;
exploding bridge wire 42; high voltage supply 44~ and
energy storage and trigger means 46. A coded wireless
signal from the control at the surface will be received
by receiver 38, the digital signal processed by the
associated micro processor based logic 40 and, if the
'code designates that the respective explosive charge is
to be detonated, sends a signal to the trigger means 46
which will supply high voltage to explosive bridge wire
42 to trigger detonation of the respective explosive
charge,
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Among the advantages of this system are: the coded
r signal allows selective detonation of the explosive
charges individually, in sequence, in patterns, etc., and
the wireless signal does not transmit the power to
initiate detonation of the explosive charge thereby
reducing the risk of accidental detonation of the
explosive charge.
Figure 6 shows a detail of an explosive bridge wire
42, which can be compared to a printed circuit board 48
with the bridge portion 50 of the circuit 52 overlying an
aperture 54, thus bridge. The bridge 50 has dimensions
smaller than the rest of the circuit 52, so that, upon
application of power to the circuit 52, the bridge 50
will flash vaporize creating enough energy to cause
~ detonation of the nearby explosive charge 18.
The explosive charge is in communication with a
detonation device which receives signals, via a
programmable logic interface, to detonate the explosive
charge. The explosive charges may be programmed and/or
wired to fire independently of each other, or several may
be linked together, in parallel or in series, to fire
together. One explosive charge or several explosive
charges may be connected to a single detonator. The
detonator is typically conveyed into the well as an
attachment to the casing/tubing, but it may be remote,
such as at the surface.
The present invention has one or more antenna (not
shown) embedded in the well casing to facilitate wireless
communication with the surface. Embedding antennas into
the casing and adding instrumentation to the casing
allows all wells thus equipped to have increased
capabilities for monitoring and/or further processing.
Embedding antennas into the casing avoids irregular
inside surface topography and its related problems. This
allows normal inside casing well operations to be
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performed in an unhindered fashion. The embedded antenna
resides in a relief area machined into the inside of each
connection. It is generally circular in shape, but could
have substantially any shape or form including, but not
~5 limited to, a single wire, a loop of wire, or a coil of
looped wire. The antenna forms an electrically isolated
area from the casing itself. The antenna can be designed
to work with any frequency or communication protocol
specified by the user. Many communication protocols and
10, practical techniques exist for wireless communication
through an empty or partially filled wave guide. The
well bore casing. would be such a wave guide. The antenna
can be designed to work within any size of well casing.
The antenna design, coupled with a properly designed
15 transceiver unit, would allow more than one antenna to be
embedded into the well casing, if so desired.
Build up of trapped annular pressure is a major
threat when constructing subsea wells. In a conventional
subsea well, there is no opportunity to vent trapped
20 annular pressure. Conventional perforating equipment
cannot be used. since such equipment would also perforate
the inner most tubular, which is intended to be a
pressure barrier. The use of the subject self-
perforating casing provides the capability for
25 selectively perforating an outer casing string while
leaving the innermost string in tact thereby providing a
flow path for~venting of pressure in an outward direction
form the annular space in the formation.
.The use of an explosive strip charge allows
30 perforation of much increased surface area of rock/sand
compared with the usual circular (hole) charge. The
explosive strip charge may be axially or circular or
spiral oriented with chosen pitch. The.use of an
explosive~strip charge in conventional (internal to pipe)
35 perforating is not possible because such a charge would
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cut a path along the casing, significantly decreasing the
structural strength of the casing. Because the proposed
strip charge lies outside the pipe, it is designed
specifically to not reduce the structural strength of the
'5 casing, while cutting a strip of large surface area along
the bore wall surface.
The use of molded plastic ribs attached to the
outside of the casing allows fluids and slurries, for
example cement, to be pumped around and be directed by
the ribs. Either straight or spiral crests on the ribs
hold the. explosive charges in place and enclose means.
used to connect the explosive charges to their respective
detonating devices.
The method for producing exploding bridgewire
detonators uses both standard and nonstandard circuit
board manufacturing techniques. Previous techniques to
produce exploding bridgewires have used extremely fine
wires of gold, copper, or other conductive material
joined to conductors by a variety of known methods. The
present method replaces the previous fine wires and
attachment techniques with etched or plated circuit board
traces. The exploding bridgewire trace is in contact
with a small mass of low density explosive consisting of
PETN, RDX, HMX or other secondary explosive to begin the
detonation process. This small mass of. low density
explosive is in contact with a larger mass of high
density explosive to complete the initiation process.
As a high voltage pulse is passed through the
exploding bridgewire trace, the trace is vaporized and
sends a shock wave into the low density explosive,
initiating detonation. The low density explosive in turn
initiates the larger mass of high density explosive to
complete the detonation train. The output from this
secondary charge can then be used to initiate larger
masses of explosives. Additionally, the initial mass of
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low density explosive may be in contact with the final
mass of high density explosive to be used iri an explosive
device.
The circuit board trace for the exploding bridgewire
~5 is shown in Figure 6. In the figure a wider trace that
acts as a~conductive path narrows down to the trace
shown, the narrow trace acts as the exploding bridgewire.
Variations in lengths, widths and thicknesses of the
trace provide for tailoring of voltage and energy
requirements for initiating the explosive. Variations of
the trace sizes, types of explosives in.contact with the
traces, and densities of explosives are all considered to
be pertinent to the method described.
The subject explosive bridge wire detonating system
is a major improvement over the previously widely used
primacord for detonation. The board can be built to
withstand high operating temperatures, where primacord
cannot be used because of its instability. The subject
explosive bridge wire detonating system also provides a
way to make selective perforating with conventional guns
much cheaper and easier to operate. The digitally
operated controller and downhole battery power source
provide easy selectivity for the system which enables the
perforator to be constructed safely offsite and run in
the hole without having to wait for a complete well
evaluation, improving safety and saving rig time. In
completion intervals that may be impacted by gas and
water contact within a producing interval, the
selectivity allows the system to be run into and cemented
in the well before log evaluation is completed because
the spacing of the charges would preferably overlap
beyond,the potential completion intervals.
The linear perforating charge increases the amount of
formation exposed for completion. The linear charge is an
outwardly directed jet perforator that is designed to
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penetrate the formation with a high velocity jet, not by
expansion of gas. Also, the linear explosive charge can
be used in combination with the above discussed
"plugging" explosive charges and can be fired
~5 sequentially, e.g., first plugging holes in the casing
and then firing the linear charge.
The coded, wireless signal sent downhole 'in the
present invention is used only to arm the explosive
charges. The power to initiate the explosive charge
comes from a battery positioned downhole as a part of the
detonating system.
The present apparatus requires a control station and
a wireless and cableless means for communicating between
the~control station and the detonation device. Any
wireless or cableless communication method may be used
including, but not restricted to, radio waves, infrared
waves, acoustic waves, optical light waves, seismic
waves, magnetic waves, or combinations thereof. Wireless
signals are conveyed using the tubular string wall as a
waveguide. Alternatively, a ball containing a
transponder may be dropped downhole, sending signals to
the controllers for the detonators as it passes them. If
a "smart ball" or transponder is used, signals may vary
as the smart ball progresses thus allowing only selected
~5 explosive charges to detonate.
The use of the subject apparatus varies only slightly
if the tubular is production tubing or if it is casing.
When perforating as part of a production tube or tubes,
the perforating device is attached as part of the tool
string and lowered into a well bore in the typical manner
in which production tubulars are run into a well. The
tubular(s) to which perforating devices) are attached
are placed within the tubing string such that, when the
tubing string is in place, the perforating devices) are
adjacent to predetermined zones to be perforated. The
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explosive charges are detonated, as described above, by
means of wireless and cableless communication. Once the
perforation operation is complete, one may begin to
produce or inject liquids, gases, or a combination.
thereof through the production tubing string or, if
desired, through the production casing string.
When the self-perforating tube is a portion of the
casing, the subject method varies only slightly. In the
casing scenario the self-perforating casing is made part
of the casing string and the casing string is set such
that the at least one self-perforating casing is set
adjacent a predetermined zone to be perforated. The
self-perforating casing and its external charges are
cemented into the well bore. Detonation of the explosive
charges then takes place as previously described.
When tubing is run inside casing, an annular space is
formed between the outside surface of the tubing and the
insidevsurface of the casing. A pressure differential
typically builds up in this annular space. Trapped
annular pressure is a major threat to the mechanical
integrity of certain wells, such as subsea wells. It is
not desirable to perforate the innermost production
tubing in such wells, for the purpose of relieving this
pressure since the innermost tubing is used as a barrier
to prevent escape of well fluids. Conventional
perforating equipment has the disadvantage of perforating
both the tubing as well as the casing. The apparatus and
method of the present invention have the further
advantage of allowing one to selectively perforate an
outer casing to relieve (vent) annular pressure during
the operating life of the well. Explosive charges may be
placed on the casing or on the outside wall of an outer
production tubing string. By use of directional
explosive charges, all force may be directed outward, so
that only the outer strings are perforated, allowing
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annular pressure to vent, while the integrity of the
inner production strings is maintained intact to provide
the desired barrier.
The present invention may be subject to many
~5 modifications and changes without departing from the
sprit or essential characteristics thereof. The
described embodiments should therefore be considered in
all respects as illustrative and not restrictive of the
scope of the present invention, as defined by the
appended claims, without departing from its spirit or
scope as set forth herein.
