Note: Descriptions are shown in the official language in which they were submitted.
"~~ WO 95/09966 217 2 0 4 7
PCT/US93I09685
METHOD AND APPARATUS FOR DOWNHOLE ACTIVATED
WELLBORE COMPLETION
Field of the Invention
This invention relates to completing a well
traversing earth formation in a borehole and more
particularly to detonating a fluid flow device by means of
a pressure wave to open communication between casing pipe
and an earth formation.
Hackcrround 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.
Additionally, when completing horizontal borehole
sections in a well, whether cased or in open holes, it is
often a problem getting perforating apparatus into the
horizontal section because the gravity factor may not be
sufficient to assist in running the equipment and friction
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2172047
between the equipment and borehole walls or pipe further
hinders such operations. For this same reason it is
difficult in many cases to run casing into such a well, and
when casing is installed, the typical bow spring
centralizers are ineffective and it is difficult to center
the casing in the borehole in order to cement the casing.
Accordingly, it is an object of the present
invention to provide a method and apparatus for opening a
fluid flow path between casing and the formation in a
wellbore which overcomes or avoids the above noted
limitations and disadvantages of the prior art.
It is a further object of the present invention
to provide a method and apparatus for perforating a
wellbore wherein a casing string is centered in the
wellbore to provide for effective cementing of the casing
even when installed in a horizontal borehole, and also
where perforating charges are directed into the formation
without penetrating a casing pipe.
It is yet another object of the present invention
to provide a method and apparatus for perforating a
wellbore wherein perforating charges are conveyed into the
wellbore on a pipe string and are detonated by a pressure
wave or pulse which is produced by equipment run into the
wellbore separately from the pipe string.
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 positioning explosive charges in a wellbore
wherein the charges are arranged to be detonated by a
pressure or shock wave, and also positioning a pressure
wave producing device in the wellbore which device is
separated from the charges.
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Additionally, the charges are placed in
extendable pistons mounted in a casing string and the
pressure wave producing device is run into the casing
string in a separate operation. The casing may also then
be cemented before the charges are detonated. By placing
the charges in pistons extendable from the casing string,
the charges are directed into the formation without passing
through the casing and/or cement.
In one embodiment, the system comprises a piston
for being mounted in an opening in the peripheral wall of
the pipe and for extending generally radially outwardly
from the pipe to contact the wall of the wellbore wherein
the piston includes an explosive device therein. A
deploying device rploys the piston from a retracted
position which is generally within the maximum exterior
profile of the pipe to an extended position wherein the
piston extends generally radially from the opening to
contact the wall of the wellbore. A detonation device is
then positioned in the wellbore for detonating the
explosive device in the piston while the piston is in its
deployed position against the wall of the formation so as
to perforate the formation by an explosive proximate to the
formation. The piston when extended serves to center the
pipe in the borehole and is substantially clear of the
inner bore of the pipe to render the bore of the pipe full
open.
$r~ef 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.
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21 ~~'Q~7
Figure 2 is an enlarged cross-sectional end view
of the casing taking 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
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 centralizes piston having a detonation 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 centralizes 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 wave
generating device positioned in the casing by means of a
pipe string.
Figures 7 and 8 show cross-sectional views of a
wellbore having an alternative system for producing a
pressure wave in a casing string for detonating perforating
charges.
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
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WO 95/09966 PCT/US93/09685
~:1~ ~2~41
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
hydrocarbon-bearing zone. With a long span of contact
within a pay _>ne, it is likely that more of the
hydrocarbon present will be produced. Unfortunately, there
are adjacent zones which have fluids such as brine that may
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
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WO 95/09966 PCT/US93/09685
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 inj ected
into the annular free space to set the casing 60. The
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
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section of casing.
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
casing 60 is run into the wellbore with the centralizers 50
retracted as illustrated in Figure 3 which allows substan-
tial 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. However, as will be discussed
below, the bulbous portions 80 are utilized in some embodi-
ments especially in smaller diameter casings such is often
used in horizontal holes when they are cased. It should
also be recognized that the bulbous portions 80 are rounded
to slide better along the walls of the wellbore and that
the casing string 60 will include collar sections 90 that
will extend out radially farther than the bulbous portion
(see Figure 3). Thus, the collar sections 90
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WO 95/09966 217 2 0 4 7 PCT~S93/09685 ,~,
present the maximum outer profile of the casing string even
when the bulbous portions are present. 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
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. In
addition, the activator may be run into the casing string
on the end of a pipe string such as a drill pipe or coiled
tubing wherein force is applied to the pipe string and thus
to an activation device to engage and push out or extend
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2112041
the pistons 50.
The centralizers or pistons may take many forms
and shapes as is illustrated in United States 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 bore-
hole. 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 portion 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 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 18 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
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WO 95/09966 PCT/US93I09685
217247
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
centralizer 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
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
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2172047
position as shown in Figure 4. As the piston 12 is illus-
trated 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
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 .
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 deploy
ing force on the inner end of each piston to overcome
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WO 95/09966
217 2 0 4 7 PCT~S93/09685 "m
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
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
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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
25 of the initiator plug extends slightly into the bore of
the casing for purposes to be described so that it is
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.
As noted above with respect to Figures 1 to 3,
the centralizers 50 are initially arranged in the retracted
position so that the casing 60 can be run into the well
without the drag and interference of the centralizers 50
extending outwardly. The snap ring 29 is engaged within
the retaining groove 33 to hold the piston in the retracted
position until the piston 12 is moved outwardly. Once the
casing 60 is positioned in the wellbore for permanent
installation, the pistons 12 are deployed to the extended
position. A deploying arrangement as will be discussed
below, provides a deploying force on the inner end of each
piston 12 to overcome the resistance of the snap ring 29 in
retaining groove 33 and cause the snap ring 29 to move into
the snap ring groove 31 as the outer surface of piston 12
expands the snap ring outwardly. The deploying force
further moves the piston 12 radially outwardly through the
bore of button 14 so that the snap ring 29 rides over the
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outer surface of piston 12 to engage the locking groove 32
and thereby secure the piston in an extended position.
When extended, the inner end of the piston and the rounded
end face 25 of the initiator plug 19 are substantially
clear of the casing bore to render the casing fully open
for running tools or equipment therethrough. The term full
open bore within the context of oil field terminology,
encompasses a situation such as the present wherein for all
practical purposes equipment can be moved through the bore
of a pipe unrestrictedly. In the present situation, the
rounded end 25 of the plug 19 is designed to encroach into
the bore approximately .14 inches. When the piston is
extended, this encroachment is further reduced when the
deploying device 82 forces the piston outwardly and
slightly deforms the rounded end face 25 of the plug 19.
Any equipment which would be passed through a casing string
bore would readily pass this end portion 25 when the
centralizers are extended.
As illustrated in Figure 2 and 3, the casing 60
and centralizers 50 are selected based on the size of the
wellbore W so that the pistons 12 may fully extend to the
extended position and contact the borehole wall around most
of the casing 60. Accordingly, during deployment of the
piston 12 the deploying force is expected to move the
piston 12 to its fully extended position wherein the snap
ring 29 will snap into the securing groove 32 as the piston
12 moves to the fully extended position. The securing
groove 32 has square edges so that the snap ring rides deep
within the groove to prevent the snap ring from being
expanded and thus to prevent the piston 12 from retracting
back into the casing 60.
At about the same time that the snap ring 29
engages the securing groove 32, the outwardly tapered
enlarged edge 39 of the piston 12 engages the chamfered
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edge 41 of the button 14 to stop the outward movement of
the piston 12. Accordingly, once the snap ring 29 snaps
into the securing groove 32, the piston 12 cannot extend
outwardly farther and cannot be retracted.
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
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. A shaped charge 58 is positioned in the
canister 46 with a conical depression and metal liner 59 in
the distal end of the face of the shaped charge facing
outwardly.
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21~~Q4~
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 or cup 64.
The shell 64 is held in place within the recess 62 by means
of a thread locking compound press fit 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 fonaed between the recesses 62 and 66. The
rupture disc 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 air space 70, a primary charge comprised
of a layer of lead azide 72, and a base charge comprised of
a layer of RDX explosive 74. 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 or a layer of a mixture of lead
styphanate can be placed over lead azide.
An alternative arrangement of rupture disc in
Figure 5 includes a circular groove 61 formed inwardly into
the plug 19 on either side of the 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 provides initiation reliability to the pressure wave
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WO 95109966 PCT/US93/09685
217~2~4:7
detonation process. 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
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.
The plug 19 at the inner end of the piston 12 is
arranged so that it extends slightly into the interior bore
of the casing string so that as the deploying device 82
passes the plug 19, the rounded surface 25 guides the
deploying device past the plug 19. The plug 19 is of a
material soft enough to be slightly deformed by the passage
of the deploying plug and also is sized so that the rubber
seal portion 81 at the rear of the deploying plug is
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WO 95/09966 PCT/US93/09685
deformable to a certain extent to permit its passage. The
plug 19 is arranged so that the deformation of the curved
outer surface 25 does not rupture the rupture disc portion
68 which is formed between the outer cavity 66 and the
inner cavity 62 of the detonating device. It is also
noted, that the explosive material 72 is spaced away from
the end of the plug 19. Thus the passage of the deploying
device 82 through the interior bore of the casing 60 will
not cause sufficient distortion of the plug 19 to bring the
rupture disc 68 into contact with the explosive material
72. 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 might 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 device present within the system
thus far described to initiate the explosive 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
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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 prf~ent 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
be produced.
In the initial installation of the casing within
the wellbore, it is important to note that the centralizers
which are not extended permit the casing to be rotated and
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WO 95/09966 2 1 ..7 2 0 4 7 PCT/US93/09685
reciprocated to work past tight spots or other
interferences in the hole. These retracted centralizers 50
also do not interfere with the fluid path through the
casing string so that fluids may be circulated through the
casing to clear cuttings from the end of the casing string.
Also the casing interior can be provided with fluids that
are less dense than the wellbore fluids, in the annular
space, causing the casing string to float. Clearly, the
centralizers 50 of the present invention permit a variety
of methods for installing the casing into its desired
location in the wellbore.
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 sufficient
pressure head against the affect of formation pressure to
avoid a blowout situation. While the production string is
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WO 95/09966 PCT/US93/09685
~~ ~~2~41
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
already in place to prevent a blowout, so that the casing
and production string can be 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 within the detonator shell 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. I-: 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
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WO 95/09966 PCTIUS93/09685
2172047
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. The perforating head
normally utilizes a detonator actuated by electrical,
mechanical, or hydraulic means. 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 thereby initiate the detonating cord. Alternatively,
a wireline can be used to operate the perforating head or
otherwise initiate the detonating cord. Once the
detonating cord is initiated, it results in the development
and propagation of a pressure wave within the pipe string
76. This pressure wave is then communicated through the
fluid in the pipe 76 and 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 the disc 68 in the plug 19. This
rupture of disc 68 will sequentially initiate 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 without the provision of an air space 70 in the shell
64 by locating powders adj scent to the ruptured disc 68 .
The amount of pressure required to rupture the disc is
increased when the air space is eliminated, so that the
powder contacts the disc; however, detonation does take
place. It is believed that the principle behind the
detonation is an adiabatic compression within the shell 64
which is sufficient to initiate the powders 72, 74 therein.
Therefore, it appears to only be necessary to generate
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WO 95/09966 PCT/US93/09685
2172047
sufficient pressure within the interior of the casing bore
to cause the ruptured disc 68 to rupture which will thereby
initiate the detonator housed within 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 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 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 solid
pipe 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.
Referring now to Figures 7 and 8 of the drawings,
an alternative system for detonating the perforators
includes a pumpdown arrangement for positioning a
detonating cord within the interior of a casing string. An
important feature of this centralizing and perforating
system is that the perforators are not functionally armed
when they are installed in the casing string, nor when they
are positioned in the borehole, in that an initiating
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WO 95!09966 PCT/US93/09685
2172041
source is not provided. A means is thus provided for
initiating the perforators after they are located within
the wellbore. In this embodiment, a detonating cord is
again provided to generate a pressure wave which in turn
ruptures the protective membrane or disc 68 on the end of
the plug 19 within the perforating cylinder 12, with such
rupturing of the membrane causing the detonator explosives
to fire. Firing of the detonator explosives will initiate
firing of the shaped charge. The detonating cord 104 is
carried in a housing 94 which is attached to a displacement
plug 96. The plug 96 may be pumped down behind cement
being injected into the annulus to isolate the casing
string from the formation. The detonating cord 104 is
shown in Figure 7 coiled up within the housing 94 which is
releasably attached to the pumpdown plug 96. An electrical
wireline or the like 98 which is attached to the housing 94
is pulled into the casing string through a stuffing box
(not shown) at the surface. Once the displacement plug 96
and housing 94 reaches the bottom of the casing string, it
lands in a seat 102 whereupon a pressure increase in the
casing is registered at the surface to indicate that the
plug has seated at the bottom of a casing string in the
seat 102 and sealed off the end of the casing at least
partially. The seat 102 provides a latching mechanism (not
shown) for holding the seated plug 96 in place. Such
displacement plugs and latching mechanisms are commonly
used in cementing operations. Thereafter the wireline 98
is pulled upwardly as shown in Figure 8 to release the
housing 94 from the displacement plug 96. The detonating
cord 104 which is positioned within the housing and which
is attached to the displacement plug 96 is then pulled out
behind the upwardly moving housing 94 a sufficient distance
to ensure that the detonating cord is positioned within the
pipe string opposite the centralizer/perforators which are
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". WO 95/09966 PCT/US93/09685
~~~~047
to be activated by a pressure wave. The upper end of the
detonating cord is attached within the housing 94 to an
electrically operated detonator (not shown) on the end of
the electric wireline 98. When the displacement plug 96
lands at the bottom and we know that all the cement in the
pipe string is displaced, 24 to 48 hours is given for the
cement to set up. After the cement has set up, an
electrical current is passed from the surface through the
wireline 98 for detonating cord detonation. Firing of the
detonating cord generates a pressure wave within the casing
pipe 60 which in turn impinges upon the rupture disc or
membrane 68 in the end of piston 12 to fire the detonating
mixtures 72, 74 within the detonator cup. This detonation
in shell 64 passes energy through the opening 48 within: the
carrier 46 to initiate the shaped charge 58 within the
cylinder 12. This in turn causes the shaped charge 58 to
penetrate into the formation F and to develop a
communication path between the interior of the casing
string and the formation.
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 95/09966 PCT/US93/09685
2112p47
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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