Note: Descriptions are shown in the official language in which they were submitted.
W O 95/09969 ~ ~ ~ ~ b 4 6
PCT/US93/09683
FLUID ACTIVATED DETONATING SYSTEM
~i.eld of the Invention
This invention relates a fluid activated
detonating system and more particularly to detonating an
explosive device by producing a sudden pressure wave or
pulse.
Background of the Invention
In the process of establishing an oil or gas
well, the well is typically provided with an arrangement
for selectively excluding fluid communication with certain
zones in the formation to avoid communication with
undesirable fluids. A typical method of controlling the
zones with which the well is in fluid communication is by
running well casing down into the well and then sealing the
annulus between the exterior of the casing and the walls of
the wellbore with cement. Thereafter, the well casing and
cement may be perforated at preselected locations by a
'perforating device or the like to establish a plurality of
fluid flow paths between the pipe and the product bearing
zones in the formation. Unfortunately, the process of
perforating through the casing and then through the layer
of cement dissipates a substantial portion of the energy
from the perforating device and the formation receives only
a minor portion of the perforating energy.
Perforating in wellbores is typically
accomplished by the use of perforating guns which usually
employ shaped charges or bullets. The guns are usually
positioned in the wellbore on a tubing string or suspended
from a cable. Detonating the explosive in the gun is
sometimes accomplished by initiating a detonating cord
which is positioned adjacent a shaped charge. Various
electrical, hydraulic and mechanical systems are employed
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to initiate the detonating cord. The detonating systems
which are now used in this industry have many safety '
drawbacks especially when electrical energy is used to
initiate the process. Accordingly, it is an object of the
present invention to provide a new and improved system to
initiate an explosive device.
It is a further object to provide a system to
safely initiate an explosive device at a remote location
as, for example, in a wellbore.
Additionally, it is an object of the present
invention to provide a method and apparatus for perforating
a wellbore which overcomes or avoids the above noted
limitations and disadvantages of the prior art.
It is yet another object of the present invention
to provide a method and apparatus for detonating explosive
charges by a pressure wave or pulse.
Summary of the Invention
The above and other obj ects and advantages of the
present invention have been achieved in the embodiments
illustrated herein by the provision of an apparatus and
method for detonating an explosive charge by means of a
pressure pulse or shock wave, and additionally by
positioning a~pressure pulse generating device in proximity
to but spaced from the explosive charge.
Additionally, the charges may be placed in the
walls of a casing string in a wellbore and a pressure pulse
generating device is run into the casing string in a
separate operation.'
In one embodiment, an explosive detonator is
arranged in a housing having a rupture means in
communication with a fluid environment so that when the
rupture means is subjected to a sufficient pressure and
ruptures, a detonator is subjected to a sudden pressure
wave which initiates the detonator.
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In another embodiment, the system comprises an
explosive device mounted in an opening in the peripheral
wall of a pipe. An initiation device is then positioned in
the wellbore for detonating the explosive device.
According to another aspect, the invention is an
improved detonator device adapted for detonation by a
predetermined pressure generated from a remote source when
the detonator is in contact with a fluid environment. The
detonator device, which is conveniently mountable adjacent
to an explosive charge, such as a shaped charge explosive
of the type described hereinabove, comprises a housing
which contains a base charge of a detonating explosive and
a priming charge of a heat sensitive explosive adjacent to
the base charge. The housing adjacent the priming charge
is sealed from the fluid environment by a rupturable
membrane or rupturable disc. Optionally, the detonator may
include an open volume between the priming charge and the
rupturable disc. Generation of a pressure pulse from any
convenient pulse generator, such as, for example, a
detonating cord, at any remote location within the fluid
and the subsequent sudden impact of the pulse on the
rupturable disc reliably initiates the priming charge.
brief Description of the Drawings
Figure 1 is a cross-sectional view of a wellbore
traversing earth formations with a casing string arranged
therein and spaced from the walls of the wellbore by a
plurality of downhole activated pistons which are shown
being activated to an extended position and which embody
features of the present invention.
Figure 2 is an enlarged cross-sectional end view
of the casing taken along lines 2-2 in Figure 1, wherein
the centralizers are shown extended to center the casing
string in the wellbore.
Figure 3 is a cross-sectional end view similar to
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Figure 2 prior to the casing being centralized and with the
downhole activated centralizers in the retracted position.
Figure 4 is an enlarged cross-sectional view of
a centralizer piston having a detonator device and shaped '
charge positioned therein, with the piston shown in a
retracted or running-in position relative to the casing
wall.
Figure 5 is an enlarged cross-sectional view of
the centralizer piston of Figure 4 in an extended position
wherein the outer end of the piston is in contact with an
earth formation.
Figure 6 is a cross-sectional view of a wellbore
showing a casing centralized in a borehole by pistons in an
extended position and further showing a pressure pulse
generating device positioned in the casing by means of a
pipe string.
Figures 7 and 8 show alternative detonation
devices for detonating an explosive in response to a
pressure pulse.
Detailed Description of the Preferred Embodiments
Referring first to Figure 1 of the drawings, a
wellbore W is shown having been drilled into the earth
formations such as for the exploration and production of
oil and gas. The illustrated wellbore W includes a
generally vertical section A, a radial section B leading to
a horizontal section C. The wellbore has penetrated
several formations, one of which may be a hydrocarbon-
bearing zone F. Moreover, the wellbore W was drilled to
include a horizontal section C which has a long span of
contact with the formation F of interest, which may be a
A
hydrocarbon-bearing zone. With a long span of contact
within a pay zone, it is likely that more of the ,
hydrocarbon present will be produced. Unfortunately, there
are adj acent zones which have fluids such as brine that may
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get into the production stream and thereafter have to be
separated from the hydrocarbon fluids and disposed of at
additional costs. Accordingly, fluid communication with
such adjacent zones is preferably avoided.
To avoid such communication with nonproduct-
bearing zones, wellbores are typically cased and cemented
and thereafter perforated along the pay zones. However, in
the highly deviated portions of a wellbore such as the
radial section B and the horizontal section C of the
wellbore, the casing tends to lay against the bottom wall
of the wellbore, thereby preventing cement from encircling
the casing and leaving a void for wellbore fluids such as
brine to travel along the wellbore and enter the casing far
from the formation from which it is produced. In the
illustrated wellbore W, a casing string or liner 60 has
been run therein which is spaced from the walls of the
wellbore by a plurality of downhole activated pistons
generally indicated by the number 50, which serve to
centralize the casing. The downhole activated pistons or
centralizers 50 are retracted into the casing 60 while it
is being run into the wellbore as is illustrated by the
centralizers 50 in Figure 1 which are ahead of an activator
or pusher 82. Once the casing 60 is suitably positioned,
the centralizers 50 are deployed to project outwardly from
the casing as illustrated behind the activator or in
Figure 1. The centralizers 50 move the casing from the
walls of the wellbore if the casing 60 is laying against
the wall or if the casing is within a predetermined
proximity to the wall of the wellbore W. This movement
away from the walls of the wellbore will thereby establish
an annular free space around the casing 60. The
centralizers 50 maintain the spacing between the casing 60
and the walls of. the wellbore W while cement is injected
into the annular free space to set the casing 60. The
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pistons, however, are latched in an extended position and
will thereby maintain the casing 60 centered even if the
casing is not cemented.
The centralizers 50 are better illustrated in
Figures 2 and 3 wherein they are shown in the extended and
retracted positions, respectively. Referring specifically
to Figure 2, seven centralizers 50 are illustrated for
supporting the casing 60 away from the walls of the
wellbore W although only four are actually shown contacting
the walls of the wellbore W. It should be recognized and
understood that the centralizers work in a cooperative
effort to centralize the casing 60 in the wellbore W. The
placement of the centralizers 50 in the casing 60 may be
arranged in any of a great variety of arrangements. In
particular, it is preferred that the centralizers 50 be
arranged to project outwardly from all sides of the
periphery of the casing 60 so that the casing 60 may be
lifted away from the walls of the wellbore W no matter the
rotational angle of the casing 60. It is also preferred
that the centralizers 50 be regularly spaced along the
casing 60 so that the entire length of the casing 60 is
centralized. The distance between centralizers and their
radial orientation on the casing will vary depending upon
the circumstances of a particular completion. For example,
it is conceivable that the centralizers may be provided
only in one radial orientation, or only at the ends of a
section of casing. In Canadian Patent Number 2,117,086
(laid open 1 April, 1993).
various arrangements are shown for mounting centralizer
pistons in the wall of a pipe string.
Referring again to Figures 2 and 3, the seven
illustrated centralizers 50 are evenly spaced around the
casing 60. As the casing is centralized, an annular space
70 is created around the casing within the wellbore. The
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casing 60 is run into the wellbore with the centralizers 50
retracted as illustrated in Figure 3 which allows
substantial clearance around the casing 60 and permit the
' casing 60 to follow the bends and turns of the wellbore W.
Such bends and turns particularly arise in a highly
deviated or horizontal hole. With the centralizers 50
retracted, the casing 60 may be rotated and reciprocated to
work it into a suitable position within the wellbore.
Moreover, the slim dimension of the casing 60 with the
centralizers 50.retracted (Figure 3) may allow it to be run
into wellbores that have a narrow dimension or that have
narrow fittings or other restrictions.
In Figures 2 and 3 and in subsequent figures as
will be explained below, the centralizers 50 may present
small bulbous portions 80 on the outside of the casing 60.
It is preferable not to have any dimension projecting out
from the casing to minimize drag and potential hangups
while moving the string. The outward projection of the
retracted centralizers 50 being within the maximum outer
profile of the casing string 60 is believed to minimize any
problems of running the casing.
Referring again to Figure 1, a deploying device
or pusher 82 which moves from the top of the casing to its
bottom end is shown positioned within the horizontal curved
section B of the casing string. The deploying device 82 is
sized to push the pistons 50 from a retracted to an
extended position. It is noted that the centralizers or
pistons 50 behind or to the left of the pusher 82 are in an
extended position having been engaged by the tapered nose
portion 85 of the pusher. The tapered portion 85 engages
. the inner ends of the pistons and pushes them outwardly as
the piston travels until the body portion 83 has passed the
piston whereupon the piston will be fully extended and
locked into an extended position as will be hereinafter
1 WO 95!09969 ~ ~' ~ ~ ~~ ~ ~ PCT/US93I09683
described. The centralizers in front of the pusher 82 are
still in a retracted position and consequently the
horizontal portion C of the casing in front of the pusher
is shown lying on the bottom side of the borehole. The
upper vertical section A and radial section B are shown
centered in that the pistons 50 have been deployed to an
extended position. The activator device shown in Figure 1
is a pumpable activator or deploying device having a tail
pipe 81 which extends rearwardly from the main body portion
83 and seals the rear end of the device to the inside of
the casing so that the device may be pushed down through
the casing 60 by the application of hydraulic pressure.
The centralizers or pistons may take many forms
and shapes as is illustrated in Applicants' U.S. Patent
No. 5,228,518" _ In the
present application, the piston or centralizer 50 is shown
in Figures 4 and 5 as including an explosive charge for
perforating formations in the borehole. Referring first to
Figure 4, the centralizer 50 has a cylindrical or
substantially cylindrical barrel portion or piston 12 which
is slidably received in a bore in button 14. The button 14
is threadedly received within a tapped hole 16 which
extends transversely through the wall of casing 60. A
bulbous or rounded outer portion 80 extends outwardly
slightly beyond the outside wall of the casing 60 but only
to provide an adequate seat for the button 14 in thin wall
smaller diameter casing and is constructed so that the
outer extension of the bulbous poxtion 80 does not exceed
the maximum profile of the pipe string which would normally
be represented by the outside diameter of collars 90 in the
casing string. The button 14 has a shoulder 17 formed at
the base of the bulbous outer portion 80 that provides a
surface for seating within a mating recessed surface at the
outer end of the threaded hole 16 in the casing wall. The
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shoulder 17 forms a vertical surface on the button which
fits against the mating vertical surface at the outer end
of hole 16. An O-ring 118 is arranged within a groove on
the shoulder 17 to provide a seal between the shoulder 17
and a vertical face at the end of hole 16. The button 14
is arranged so that its inner end does not extend into the
interior of the casing 60. The piston 12 is arranged for
axial movement through the button 14 from a retracted
position (Figures 3 and 4) to an extended position (Figures
2 and 5). The piston 12 and the button 14 are mounted into
casing 60 so that their axis are collinear and directed
radially outwardly with respect to the axis of the casing
60. The piston 12 includes a plug 19 secured in an
interior bore or passageway 18 in the piston by screw
threads 22. An annular sealing ring 21 is positioned
between the plug 19 and the inner end of piston 12. The
piston 12 shown in Figures 4 and 5 also serves as a housing
for a perforating device. The plug 19 is called an
initiator plug in that it carries a device for initiating
detonation of a shaped charge in the piston. The plug 19
does not fill the entire passageway 18 but is rather
approximately the thickness of the casing 60. The plug 19
further includes a rounded inner end face 25 and a flat
distal end face 24. The rounded surface 25 on the inner
end of plug 19 is provided for facilitating the use of a
deploying device to push the centralizes 50 into an
extended position.
The distal end 28 of the piston 12 may be
chamfered or tapered inwardly to ease the installation of
the piston 12 into the button 14. The piston 12 is mounted
in a central bore in the button 14 which is preferably
coaxial to the opening 16 in the casing 60 and is held in
place by a snap ring 29. The snap ring 29 is located in a
snap ring groove 31 milled in the wall of the interior bore
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WO 95/09969
of the button 14.
Piston 12 includes two radial piston grooves 32
and 33 formed in the exterior cylindrical surface of the
piston 12. The first of the two piston grooves is a
circumferential securing or locking groove 32 which is
positioned adjacent the inner end 27 of piston 12 to be
engaged by the snap ring 29 when the piston is fully
extended. The second of the two grooves is a
circumferential retaining groove 33 positioned adjacent the
distal end 28 of the cylinder 12 to be engaged by the snap
ring 29 when the piston is in the retracted or running
position as shown in Figure 4. As the piston 12 is
illustrated in Figure 5 in the extended position, the snap
ring 29 is engaged in the radial locking groove 32.
The snap ring 29 is made of a strong resilient
material arranged to expand into the snap ring groove 31
when forced outwardly and to collapse when unsupported into
the grooves 32 and 33 when aligned therewith. The snap
ring 29 is resilient as noted above so that it can be
deflected deep into the snap ring groove 31 to slide along
the exterior of the piston 12 and allow the piston 12 to
move from the retracted position to the extended position.
The snap ring 29 must also be strong to prevent the piston
12 from moving unless a sufficient activation force is
applied to the piston 12 to deflect the snap ring 29 out of
the retaining groove 33 into the snap ring groove 31 to
permit the piston 12 to move through the snap ring to the
extended position. The piston grooves 32 and 33 have a
shape that in conjunction with the snap ring 29 allows the
piston 12 to move in one direction but not the other. In
the direction in which the snap ring 29 allows movement,
the snap ring 29 requires an activation or deploying force
of a certain magnitude before it will permit the piston 12
to move. The magnitude of the activation or deploying
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force depends on the spring constant of the snap ring 29,
the relevant frictional forces between the snap ring 29 and
the piston 12 , the shape of the piston groove, and other
factors. A particular arrangement of snap ring and grooves
is shown in greater detail in Canadian Patent Number
2,117,086 (laid open 1 April, 1993).
Once the casing 60 is positioned in the wellbore
for permanent installation, the pistons are deployed to the
extended position. The deploying method provides a
deploying force on the inner end of each piston to overcome
the resistance of the snap ring in the retaining groove 33
and cause the snap ring 29 to ride up and out of the
retaining groove 33 whereupon the snap ring 29 is pushed up
into the snap ring groove 31 within the button 14. This
allows the piston to move out into the annular space of the
wellbore. Once the piston encounters the wellbore wall, it
will then lift the casing off of the wellbore to centralize
the casing until such time as the snap ring 29 aligns with
and expands into the locking groove 32. The pistons should
be of such a length that the pistons can be fully deployed
to the locking groove 32 while giving the maximum amount of
centralization. Once the pistons are fully deployed, the
inner surface 25 on the plug 19 will be substantially clear
of the casing bore for all practical purposes, and the
casing bore should be substantially full opened.
The button 14 further includes a sealing
arrangement to provide a pressure tight seal between the
piston 12 and the button 14. In particular, the button 14
includes two O-rings, 34 and 36, which are positioned on
either side of the snap ring 29 in O-ring grooves 37 and
38, respectively. The O-rings 34 and 36 seal against the
exterior of piston 12 to prevent fluids from passing from
one side of the casing wall to the other through the bore
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of the button 14. The O-rings 34 and 36 must slide along
the exterior of the piston 12 passing the piston grooves 32
and 33 while maintaining the pressure tight seal.
Accordingly, it is a feature of the preferred embodiment
that the spacing of the O-rings 34 and 36 is such that as
the piston 12 moves through the bore of the button 14 from
the retracted position to the extended position, one of the
O-rings 34 or 36 is in sealing contact with a smooth
exterior surface of the piston 12 while the other may be
opposed to one of the piston grooves 32 and 33.
The piston 12 further includes an outwardly
tapered enlarged diameter peripheral edge 39 on its inner
end 27, which edge 39 is larger than the bore in button 14
that receives the piston 12. Thus the edge 39 serves as a
stop against the button 14 to limit the outward movement of
the piston 12. The inside face of button 14 includes a
chamfered edge 41 for engaging the outwardly tapered
peripheral edge 39 on the piston when the inner end 27 of
the piston is approximately flush with the inner end face
of the button 14. Therefore, while the extended piston 12
is recessed into the button 14 and clear of the interior
bore of the casing 60, the inwardly facing rounded surface
of the initiator plug extends slightly into the bore of
the casing for purposes to be described so that it is
25 substantially clear of the bore to render the casing bore
fully open to permit passage of the deploying device 82 or
other similar device such as packers or the like that would
be passed through the bore of a casing string.
Still referring to Figure 4, the inner bore 18 of
the piston 12 is shown having a shaped charge insert
installed therein. The shaped charge insert includes a
cup-shaped canister or carrier 46 which is sized to be
press fit into the bore 18 of the piston 12. A locking
compound is used to hold the canister 46 in the bore cavity
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of the piston. The carrier 46 is nested against a shoulder
47 in the piston bore 18, the shoulder 47 being the end of
the threads 22 which are cut in the bore 18 of the piston
' at its inner end to receive plug 19. An ignition hole 48
is formed in the inner wall 49 of the cup-shaped carrier
46. A thin metal foil 51 is placed over the outer surface
of hole 48 facing the plug 19. At the distal end of the
piston 12, an outer end cap 54 is fitted within a recessed
shoulder 55 and is held in place by its press fit and a
locking compound. The shaped charge 58 is positioned in
the canister 46 with a conical depression and metal liner
59 in the distal end facing outwardly.
The opposite inner end of the piston 12 has the
plug 19 enclosing the inner end. The plug 19 has a
cylindrical recess 62 which is formed from the inner side
of the plug 19 for receiving a detonator shell 64. The
shell 64 is held in place within the recess 62 by means of
a thread locking compound or the like. On the rounded
outer surface 25 of the plug 19 and central to the plug 19,
a recess 66 is formed in the outer wall surface 25 opposite
the recess 62 on the interior of the plug 19. The recess
66 may be for example 3/16 inch in diameter and
approximately .040 inches deep to leave an integral rupture
disc portion 68 formed between the recesses 62 and 66. The
rupture disc 66 may be on the order of .0275 inches thick.
The shell 64 which is assembled within the recess 62 has
provided within its interior bore a detonating system which
is comprised of an optional air space 70, a primary charge
of lead azide 72, and a base charge of RDX explosive 74.
. 30 The fluid actuated detonator described above is
particularly useful when incorporated into a holder with
the explosive charge with which it is to be employed, such
as the shaped charge 58 in centralizer pistons 12 shown in
Figures 4 and 5. As so incorporated, the rupture disc 68
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of the detonator is concealed from accidental activation.
An alternative embodiment of the detonator in its most
basic form is shown in Figures 7 and 8. The detonator
comprises a generally tubular shell 64 which is closed at
its bottom end. At least one base charge 74 of a
detonating explosive composition is located in 'the bottom
of the shell as shown, and a priming charge 72 of a heat
sensitive explosive composition is located adjacent to the
base charge. The embodiments shown in Figures 7 and 8
include an open volume 70 between the priming charge 72 and
the rupture disc 68. In this application, the space
between the top surface of the priming charge 72 and the
rupture disc 68 is optional and can be any distance from
about 0 to 279 mm (0 to 11 inches). Rupture disc 68 may be
adapted by any suitable means known in the art to seal the
end of the tubular shell 64. Typical base charges that can
be used are pentaerythritol tetranitrate (PETN),
cyclortrimethylene trinitramine (RDX), cyclotetramethylene
tetranitramine (HMX), picrylsulfone, nitromannite,
trinitrotoluene (TNT), hexanitrostilbene (HNS), lead azide,
and the like. Covering the base charge is a priming charge
72 that can be flat as shown or tapered and embedded in the
base charge. Typical priming charges are of lead azide,
lead styphanate, diazodinitrophenol, mercury fulminate and
nitromannite. Mixtures of diazodinitrophenol/potassium
chlorate, nitromannite/diazodinitrophenol and lead
azide/lead styphanate also can be used. A separate layer
of lead styphanate or a layer of a mixture of lead
styphanate can be placed over lead azide. The tubular
shell 64 and the rupture disc 68 can be aluminum,
magnesium, brass or any metal, plastic, or other suitable
material.
The detonator of Figure 7 is shown having an
explosive charge 96 which represents a booster charge or a
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main charge to be detonated by the detonating charge in
shell 64. A housing 94 extending upwardly from shell 64
contains a fluid medium 99 which serves as a transmission
means for conveying a pressure wave or pulse to the rupture
disc 68. In Figure 8 the fluid medium 99 is contained in
a housing 98 which has a lower detonator portion to house
detonator shell 64. The lower end of the detonator portion
of housing 98 has an extension 104 which securably receives
a detonating cord 97. Crimps 105 may be provided to hold
the cord 97 within the lower end 104 of housing 98 in
proximity to the detonator shell 64.
In the detonator arrangement of Figures 4 and 5
the rupture disc includes a circular groove 61 formed
inwardly into the plug 19 from the recess 66. This groove
61 can be formed on either or both sides of the rupture
disc 68. In order to accommodate this groove 61, the
rupture disc 68 is made thicker so as not to unnecessarily
weaken the integrity of the barrier 68 that protects the
detonator shell 64. By undercutting the circular groove or
rim 61 around the circumference of the rupture disc 68, the
disc 68 will yield more predictably than by relying solely
on normal yield of the metal between the recesses 66 and
62. This in turn improves initiation reliability. Also,
a thicker disc 68 can be provided between the recesses 66
and 62 to protect the detonator from inadvertent activation
by movement of a piston activating or extending device 82
through the casing bore.
In Figure 5 of the drawings, the centralizing
piston 12 is shown having been moved to an extended and
locked position wherein the distal end 28 of the piston is
in contact with the bore hole wall. A deploying device 82
such as is shown in Figure 1 has been moved through the
interior bore of the casing string to contact the outer
surface 25 of plug 19 on the inner end of the piston. As
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the deploying device 82 passes the position in the casing
string where the cylinder is positioned, the cylinder is
forced outwardly with sufficient force to override the
restraining effect of the snap ring 29 in the retaining
groove 33. This overriding force causes the snap ring to
move upwardly and expand outwardly into the groove 31 as it
expands over the outer surface of the piston 12. The
piston continues its movement until the tapered enlarged
portion 39 on piston 12 abuts the mating chamfered surface
41 on the button 14 whereupon the piston 12 is positioned
so that the snap ring 29 retracts into the locking groove
32 to hold the extended cylinder 12 in a predetermined
fixed position. At this point, the deploying device 82
(Figure 1) will have passed the extended piston 12 and
proceeded downwardly through the casing string. Once the
piston is extended and locked in its predetermined fixed
position as shown in Figure 5, the perforating apparatus is
now in a position to permit perforation of the formation
which the wellbore traverses. It is noted, that
alternatively the pistons 12 may be extended by the
application of hydraulic pressure to the interior of the
casing pipe string which provides a force that impinges on
the inner end of the piston to move the pistons outwardly.
It is to be noted that one particular advantage
of the apparatus described herein is that the centralizing
piston and a button 14 which guides the piston, when
provided, may be assembled within the casing string at some
time just before the casing is run into the wellbore W.
Accordingly, the handling of the casing pipe up to the
point that it is being installed in the wellbore is not
subjected to the danger which would be caused by having the
explosive devices installed during shipping and handling of
the casing prior to its installation. It is also to be
noted that there is no means present within the system thus
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far described to accidentally initiate the detonator device
within the piston so that such handling in the
configuration described above is considered safe and will
not unnecessarily endanger the personnel who are installing
the devices in the casing or installing the casing within
the wellbore.
Referring now to Figure 6 of the drawings, the
casing 60 is shown having been run into a well. The
centralizers are shown having been extended by means of a
pumpable activator device 82 such as shown in Figure 1 or
by the application of hydraulic pressure to the casing
string at the surface. This is accomplished by closing a
valve at the base of the casing string and applying the
necessary activation or deploying force required to move
the pistons from the retracted position to the extended
position. Accordingly, pumps or other pressure generating
mechanism would provide the necessary deploying force for
the pistons.
Once the casing has been centralized within the
wellbore, an annulus of cement can be injected and set
around the entire outer periphery of the casing, over some
appropriate interval of casing, to seal the casing from the
formation. As suggested by the present invention, the
casing string with the centralizer system as described is
arranged so that in those portions of the wellbore where it
is desired to have a centralizing only function for the
centralizers, the centralizers are not configured so as to
provide a perforating function. However, within a zone
opposite formation F as shown in Figure 6, where it is
desirable to open the casing to permit the recovery of
fluids from the formation into the casing string and to
perforate the formation, the centralizers are of the
embodiment shown in Figures 4 and 5 which include a shaped
charge device or the like for perforating the formation to
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be produced.
Once the casing 60 is in a suitable position, the
centralizers are deployed to centralize the casing. As
discussed above, there are several methods of deploying the
centralizers. Once the pistons are all deployed and the
snap rings have secured them in the extended fixed position
projecting outwardly toward the wall of the wellbore, the
cement may be inj ected by well known techniques into the
annulus formed by the centralizing of the casing within the
borehole.
The cement around casing 60 may be allowed to set
while the production string is assembled and installed into
the casing. It is important to note that at this point in
the process of establishing the well, the casing and
wellbore are sealed from the formation. Accordingly, there
is as yet no problem with controlling the pressure of the
formation or with loss of pressure control fluids into the
formation. In a conventional completion process, the
perforation string is assembled to create perforations in
the casing adjacent to the hydrocarbon bearing zone.
Accordingly, high density fluids are provided in the
wellbore and the production string to maintain a suf f icient
pressure head against the affect of formation pressure to
avoid a blowout situation. While the production string is
assembled and run into the well some of the wellbore
fluids, in an overbalance condition, may be forced into the
formation. Accordingly, the production string must be
installed quickly to begin producing the well once the well
has been perforated. However, with the present invention,
such problems are avoided. Once the casing is set in
place, the production string may be assembled and installed
in the casing before the casing is opened and perforation
of the formation is performed. If the production string is
already in place in the well, adequate surface controls are
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WO 95/09969 PCT/US93/09683
already in place to prevent a blowout, so that the casing
and production string may contain a fluid in an
underbalanced condition. Thus, production may begin when
communication is established with the formation, such as by
perforation. Accordingly, the well is brought on-line in
a more controlled manner.
Figure 6 shows an apparatus and system for
initiating the detonators 64 (Figure 5) in the pistons, in
order to fire the shaped charges and penetrate the
,formation. A small diameter pipe string such as production
tubing 76 or coiled tubing is run into the interior of the
casing string after the centralizers 50 are extended. The
casing may or may not be cemented in place. A detonating
cord 84 may be pre-installed in the lower end of the tubing
string 76 and run into the well with the tubing string.
Alternatively, the tubing string may be located in the
casing string and then the detonating cord is run into the
tubing string. In the latter case, in order to set the
detonating cord 84 in place, the bottom of the tubing
string could be provided with a latching mechanism 93.
After the tubing 76 is run into the casing string, a sinker
bar with detonating cord trailing behind, can be lowered
into the tubing string and latched inside of the tubing.
Alternatively, a device can be pumped to the latch 93 with
a detonating cord trailing. A perforating head 89 would be
run at the trailing, upper end of the detonating cord 84 to
provide a means for initiating the detonating cord. Once
the tubing is run, a production packer 86 can be set. At
this time a sinker bar 91 can be dropped which would strike
the perforating head and initiate the detonating cord.
Alternatively, an electrical wireline could be connected
with the detonating cord or perforating head in order to
initiate the detonating cord. A hydraulically actuated
detonating head is also available for initiating the
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WO 95/09969 PCT/US93/09683
detonating cord 84.
The detonating cord shown is initiated by
dropping a latch bar 91. Once the detonating cord is
initiated, it results in the development and propagation of
a pressure pulse or wave within the fluid environment which
exists within the pipe string 76. This pressure wave is
then communicated through the fluid in the pipe 76 and the
fluid in casing 60 to the plug 19 at the inner end of the
cylinders 12. If necessary, the pipe string 76 may be
centered in the casing by means of conventional
centralizers 78. Centering the pipe string 76 in the
casing string may be important in view of the importance of
propagating a pressure wave to the cylinders 12 on all
sides so that the force of this pressure wave is sufficient
to rupture membrane or disc 68 in the plug 19. This
rupture of disc 68 sequentially initiates the powders 72
and 74 within the shell 64 positioned in the plug 19.
Tests have shown that initiation of the detonator will take
place reliably without the provision of an air space 70 in
the shell 64. The amount of pressure required to rupture
the disc is increased when the air space is eliminated:
however, detonation does take place satisfactorily. It is
believed that the principle behind the detonation is an
adiabatic compression within the shell 64 which is
sufficient to initiate the primary charge 72. Therefore,
it appears to only be necessary to generate sufficient
pressure within the interior of the casing bore to cause
the ruptured disc 68 to rupture which will thereby initiate
the detonator in the shell 64. When a shaped charge is
present in the piston 12, initiation of the detonator is
communicated through the opening 48 within the carrier 46
to detonate the shaped charge 58. This detonation produces
a penetrating force that is directly applied to the
formation F so that all the outwardly directed energy of
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WO 95/09969 PCT/US93/09683
2~~2Q46
the shaped charge is applied to perforation and fracturing
of the formation.
In the configuration shown in Figure 6, the
smaller diameter pipe 76 housing the detonating cord, may
be provided with slots or holes in the outside walls
thereof to facilitate transmission through the resident
fluid environment of the pipe and casing of a pressure wave
emanating from the detonating cord to the perforating
cylinders 12. However, experiments have shown that a
pressure wave may be propagated through the walls of a
solid pipe 76 which is sufficient to initiate the
detonators within the plug 19 on the cylinders 12. The
system shown in Figure 6 with a production packer 86 set in
place will permit the completion to take place with an
under-balanced fluid in the pipe string, so that upon
perforation of the formation F formation, fluids may be
readily received into the casing string through the now
open cylinder 12 and from there into the production tubing
76 for conveyance to the surface.
In the process of perforating the formation as
described in the present invention, it is noted that the
word "penetrating" is used to describe the process for
opening a communication path into the formation. The
reason that penetrating the formation is desirable is that
the permeability of porous reservoir rock is usually
reduced or plugged near the wellbore due to the leakage of
drilling fluids into the first few inches of rocks
surrounding the wellbore. This reduces permeability near
the wellbore and is referred to as skin damage. In the
present perforating technique, the shaped charges are not
designed to punch a hole in the casing as in a normal
perforating system, but rather to establish communication
with the reservoir rock and to penetrate the rock itself
with a fracturing and penetrating blast that extends
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WO 95109969 PC'~'/US93/09683
communication beyond the skin damage. Whereas normal
shaped charges in a perforating system are positioned
within the casing string and must therefore progress
through the fluids within the casing string, the steel
casing string wall, and then into the skin damaged portion
of the reservoir. In the present system the shaped charge
is positioned directly against the formation and thus a
much greater portion of the energy developed by the shaped
charge is applied to the formation rock itself.
It is readily appreciated that various other
techniques could be developed for providing the placement
of a detonating cord into the interior of either a casing
pipe string or a production string in order to initiate the
pressure wave described herein for detonating the
perforation devices. For example, the detonating cord
could be pumped in behind a pumpable plug or the like to
position the detonating cord into a horizontal reach of
pipe. In a vertical or nearly vertical pipe section,
gravity would be sufficient to lower a detonating cord
weighted on its lower end, into a pipe string. In
addition, other methods could be used to develop a pressure
wave for initiating the shaped charge. Also, it is readily
seen that a variety of detonators might be used to initiate
the explosion of the shaped charged within the centralizing
cylinder 12. Therefore, while particular embodiments of
the present invention have been shown and described, it is
apparent that changes and modifications may be made without
departing from this invention in its broader aspects and
therefore the aim in the appended claims is to cover all
such changes and modifications as fall within the true
spirit and scope of this invention.
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