Note: Descriptions are shown in the official language in which they were submitted.
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HIGH DENSITY PERFORATING GUN
SYSTEM PRODUCING REDUCED DEBRIS
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The invention relates generally to the design of perforating tools for
use
in creating perforations in wellbores to improve the flow of fluids from the
wellbore.
2. Description of the Related Art
[0002] Perforation guns are used within wellbore holes to increase
the
permeability of the formation surrounding the wellbore. In general,
perforation
guns producing greater numbers of perforations are considered to be more
effective than those producing fewer perforations. It is therefore often
desired to
maximize the number of penetrating jets within a segment of the wellbore. This
may be difficult, however, because there are limitations relating to placement
of
the charges used for perforation. Standard shaped charges have an outer
housing formed of metal or another material that encloses the high explosive
charge. The shaped charge holder has openings that have typically circular
perimeters. When packing the charges in an adjoining manner in the charge
tube, interstitial spaces are unavoidably left between the neighboring charges
as
a result their shape. This packing results in "dead spaces," that is, areas
from
which no perforating product, i.e., no jets, is/are provided, between the
charges,
and limits the density with which the charges can be packed.
[0003] There are a number of known styles and designs for perforation guns.
There are, for example, strip guns that include a strip carrier upon which are
mounted a number of capsule charges. The capsule charges are individually
sealed against corrosive wellbore fluids. Also known are hollow carrier guns
that
have a sealed outer housing that contains unencapsulated shaped charges. In
each case, the shaped charges are arranged such that they will detonate in a
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radially outward direction to form a specific pattern of perforations.
[0004] An alternative perforation gun design is described in U.S. Patent No.
5,619,008 to Chawla et al. In this design, a two-layer liner serves to sheath
discontinuous loadings of explosive material. The liner is configured with
indentations that are each aligned with an individual loading of the explosive
material. Upon detonation of the loadings of explosive material, these
indentations act in the manner of a shaped charge, creating a directed jet of
liner
material. The indentations have a circular perimeter and are spaced apart from
one another, leaving significant "dead space" between them. Following
detonation and any resulting perforation, the housing that surrounds the
charges
is not completely destroyed and forms debris. This debris is undesirable, both
because it must be removed by wireline or by other means in a secondary
operation, and because it may clog the perforations that are formed by the
perforation operation, thereby making the perforations less effective and
sometimes necessitating repeat perforation operations. The Chawla et al.
invention thus suffers from problems relating to both "dead space" and debris
creation.
[0005] The present invention addresses the problems of the prior art.
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SUMMARY OF THE INVENTION
[0006] The present invention provides a perforating device that
produces
multiple perforating penetrators from a single high explosive charge. In one
embodiment, the perforating module has a central rod with a surrounding
cylinder of high explosive. The cylinder of high explosive is contained within
a
liner having formed indentations. The liner may be of any suitable material,
such
as a non-explosive material including, for example, an elemental metal or
alloy, a
composite, a ceramic, a thermoplastic or thermo set polymer, or the like.
Finally,
a cylindrical outer cover is disposed about the liner. In one embodiment, the
indentations are linearly contiguous to one another. In another embodiment,
the
indentations each have a perimeter that is triangular, square, hexagonal, or
octagonal and are disposed in an adjoining fashion to one another.
[0007] In operation and as a result of detonation of the explosive material,
the
module forms penetrators of liner material that propagate into the formation
in a
direction that is, in one embodiment, substantially perpendicular to the
longitudinal axis of the wellbore. The module thus is capable of providing a
relatively dense shot pattern with little or no "dead space" between the
locations
from which the penetrators are formed. This results in an effective
perforation of
a wellbore segment.
[0008] During the detonation, the constituent components of the
module,
including in some embodiments the high explosive, the liner, and the outer
cover, are largely destroyed. As a result, the amount of debris resulting from
the
detonation is reduced or eliminated, as compared with the amount of debris
produced by many conventional perforation devices.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] For greater understanding of the invention, reference is made to the
following detailed description of the embodiments of the present invention,
taken
in conjunction with the accompanying drawings in which reference characters
designate like or similar elements throughout the several figures of the
drawings.
[0010] Figure 1 is a side, cross-sectional view of a wellbore containing an
exemplary perforation system constructed in accordance with the present
invention.
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[0011] Figures la and lb illustrate a pair of alternative constructions for
perforation systems constructed in accordance with the present invention.
[0012] Figure 2 is a side, cross-section depiction of a single
perforation
module of the perforation system shown in Figure 1.
[0013] Figure 3 is an exterior view of the module shown in Figure 2.
[0014] Figure 4 is a detail view of a portion of the liner of an exemplary
perforation module showing further details concerning the indentations.
[0015] Figure 5 is a detail view of a portion of the liner of an
exemplary
perforation module showing an alternative shape for the indentations.
[0016] Figure 6 is a side cross-section of the portion of liner shown in
Figure
5, taken along lines 6-6.
[0017] Figure 7 depicts an exemplary shot pattern that is created
by the
perforation module shown in Figures 2 and 3.
[0018] Figure 8 illustrates an alternative embodiment for a perforation module
in accordance with the present invention having triangular indentations.
[0019] Figure 9 illustrates a further alternative embodiment for a perforation
module in accordance with the present invention having square indentations.
[0020] Figure 10 depicts a portion of the surface of the liner of a
perforation
module that utilizes octagonal indentations.
[0021] Figures 11-14 illustrate an exemplary initiation sequence for a single
penetrator of a perforation module in accordance with the present invention.
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DETAILED DESCRIPTION OF THE INVENTION
[0022]
The present invention relates to devices and methods for
perforating wellbores. The present invention is susceptible to embodiments of
different forms. There are shown in the drawings, and herein will be described
in
detail, specific embodiments of the present invention with the understanding
that
the present disclosure is to be considered an exemplification of the
principles of
the invention, and is not intended to limit the invention to that illustrated
and
described herein.
[0023] Figure 1 illustrates an exemplary perforation system 10 that is
configured in accordance with one embodiment of the present invention. The
perforation system 10 is disposed within a wellbore 12 that has been drilled
through the earth 14 and a hydrocarbon-bearing formation 16. Portions of the
wellbore 12 are cased by a steel casing 18 that is secured within the open
wellbore hole by cement 20.
[0024] The hydrocarbon-bearing formation 16 contains two oil-bearing strata
22, 24, which are separated by a layer of water 26. A layer of water 28 also
separates the lower oil stratum 24 from a stratum of gas 30. It is noted that
this
arrangement of strata in formation 16 is presented only by way of example and
that those skilled in the art will recognize that the actual composition and
configuration of formations varies.
[0025] The
perforation system 10 is disposed into the wellbore 12 on a
conveyance string 32. The conveyance string 32 may be of any known
construction for conveying a tool into a wellbore, including a drill pipe,
wireline,
production tubing, coiled tubing, and the like. The perforation system 10
includes one or more perforating modules that are used to perforate portions
of
the surrounding formation 16. In the described embodiment, there are three
perforating modules 34, 36, 38 that are secured to one another in series.
There
may, of course, be more or fewer than three modules, depending upon the
desired length of wellbore to be perforated. Additionally, it is pointed out
that
there may be intermediate sections of tubing, or subs 37 (see Figure la)
interposed between the individual modules 34, 36, and 38, to provide a desired
spacing therebetween. In practice, the subs 37 are desirably non-explosive. If
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desired, the modules 34, 36, and 38 may alternatively be secured to one
another
so as to form an unbroken, contiguous series of modules. Figure lb illustrates
a
further alternative perforation system arrangement wherein the perforation
modules 34, 36, and 38, of the system are interconnected directly to one
another
in series.
[0026] An exemplary individual module 40 is depicted in Figures 2 and 3. The
module 40 is representative of each of the three modules 34, 36, and 38 shown
in Figure 1. As will be described in further detail below, the module 40
creates a
plurality of perforating penetrators from a single explosive charge. The
penetrators travel in a direction substantially normal or orthogonal to the
longitudinal axis of the wellbore. Advantageously, this arrangement may
significantly increase shot density and simultaneously reduce the amount of
debris left in the wellbore, relative to many conventional perforation
systems. In
one embodiment, the module 40 includes a support member such as a central
rod 42 having upper and lower axial ends 44, 46. The upper and lower axial
ends 44, 46 are provided with threaded connections, as is known in the art, so
that they may be secured to the conveying string 32 (see Figure lb) or to an
adjoining module. The central rod 42 is composed of a central load bearing
portion 41 and an outer detonation layer 43. The load-bearing portion 41 of
the
central rod 42 may be a section of pipe, rod or other load bearing structure.
In
one embodiment, the load-bearing portion 41 of the central rod 42 is formed of
steel. In another embodiment, if the perforation device 10 is not to be
withdrawn
from the wellbore 12 after detonation, the load-bearing portion 41 of the
central
rod 42 is formed of a frangible or combustible material that will be readily
destroyed during the detonation of the perforating device 10. Ceramic is just
one
example of a suitable frangible material.
[0027] The detonation layer 43 comprises, in this embodiment, a primasheet of
a type known in the art for initiation of detonations. The load-bearing
portion 41
of the central rod 42 may also contain an axial passage 48 along its length to
contain electrical wiring (not shown) that is necessary for initiation of the
detonation layer 43 which, in turn, results in detonation of the body 50 of
high
explosive material. The detonation layer 43 may be initiated with a control
signal
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either manually or utilizing some preprogrammed device. For example, suitable
initiating systems can include using electrical signals transmitted from the
surface via wiring (not shown) in the axial passage 48 to initiate detonation
cord
(not shown) disposed within the axial passage 48, by increasing hydraulic
pressure in the wellbore, or by the dropping of a drop bar (not shown) into
the
axial passage 48, as is used conventionally with tubing conveyed perforation
guns. Other initiating systems can utilize timers or well bore parameter
sensitive
devices (e.g., pressure, temperature, depth, etc.). Initiation systems for
detonating perforating guns are known in the art and will not be discussed in
further detail.
[0028] Surrounding the central rod 42 is a substantially unitary body 50 of
high
explosive material that explosively forms the perforating penetrators using
the
liner 52. Suitable high explosive materials may include, for example,
conventionally-employed high explosives such as RDX, HMX and HNS. While
the size of the module is not a critical aspect thereof, it may be convenient
to
configure the module 40 such that it is a cylinder about 12 inches in length
and
about 4.5 inches in diameter. However, the length and diameter may be varied
according to the dimensions of the wellbore 12 or other factors. A tube 51 of
cardboard or a similar material is disposed between the central rod 42 and the
high explosive body 50.
[0029] The liner 52 surrounds the body 50 of high explosive and is configured
to form a plurality of perforating penetrators. The penetrators formed by the
liner
52 may travel in a direction generally perpendicular to the longitudinal axis
of the
wellbore, although modifications in direction may also be achieved in other
embodiments of this invention. In one embodiment, the liner 52 may be, in this
embodiment, a cylindrical and non-explosive liner formed of a metal, such as,
for
example, tantalum. Alternatively, the liner 52 may be made from extruded
copper, tungsten, steel, depleted uranium, aluminum, or another elemental
metal
or alloy. In other embodiments blends of elemental metals or alloys with
materials such as lead, graphite, and zinc stearate may also be employed. In
still other embodiments blends or alloys of aluminum with either titanium or
hafnium may be used. Additionally, a frangible material may be used to form
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the liner 52 in order to further reduce the likelihood that the formed
penetrator
will plug the perforation created in the surrounding formation. Such may
include,
for example, the use of pressed, sintered metallic powders, such as those
described in U.S. Patent No. 6,012,392,
and metal/matrix composites.
[0030] The size, shape, velocity and other characteristics of the perforating
penetrators formed by the liner 52 may be controlled, in part, by adjusting
the
surface contours of the liner 52. In one embodiment, a plurality of linearly
contiguous indentations 54 is formed into the liner 52. As used herein, the
phrase "linearly contiguous" means that the perimeters of every indentation
shares at least one common side with an adjacent indentation. In some
embodiments a majority of each indentation is linearly contiguous with
adjacent
indentations, and in other embodiments essentially all of each indentation is
linearly contiguous with adjacent indentations. In one embodiment, each
indentation 54 has an axis that is substantially perpendicular to the exterior
surface of the liner 52, where such exterior surface is substantially parallel
to the
longitudinal axis of the wellbore. In other embodiments such indentation axis
may be significantly greater or less than ninety degrees to the exterior
surface of
the liner 52 and/or to the longitudinal axis of the wellbore, in order to
direct the
penetrators in a specific direction, according to the purposes and goals of
the
perforation operation.
[0031] Figure 4 depicts further details concerning one embodiment of the
indentations 54. In this embodiment, each indentation 54 has a hexagonal outer
perimeter 56 and therefore adjoins a neighboring indentation 54 on each of its
six sides, i.e., all of its six sides are linearly contiguous with neighboring
indentations 54. Because of this fact, there are no "dead spaces" between the
indentations 54 from which it is inferable that there is no area from which a
penetrator is not, or could not be, transformed. A small linear ridge 58 is
formed
at each of the adjoining contact areas of the neighboring indentations 54. A
hexagonal shape for the perimeter 56 of the indentations 54 is one possible
arrangement, which may offer the additional benefit that, by approximating the
shape of a circle, a penetrator that is relatively radially uniform is, upon
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detonation of the body 50 of high explosive, developed therefrom.
Additionally,
the hexagonal shape of the perimeter 56 permits relatively closer packing of
the
indentations 54 to form an adjoining, interlocking honeycomb effect. As a
result,
the "dead space," that is unavoidable when indentations having circular
perimeters are employed, is thereby greatly reduced or eliminated. A further
advantage of the honeycomb arrangement of the indentations 54 is that the
perforations created may, as a result, be spaced equally in all directions,
that is,
in circumferential, axial, vertical, and horizontal directions, such as to
significantly
reduce the possibility of failure of the surrounding casing 18 upon
perforation. A
high density of perforations may therefore be achieved from the use of such
linearly contiguous and interlocking indentations that cover essentially the
entire
outer surface area of the module 40. For example, a pattern of hexagonal
indentations that are two inches in diameter, i.e., hexagons that can be
inscribed
within a two-inch diameter circle, may in some embodiments generate a shot
pattern of 51 perforations per linear foot of the wellbore from the surface of
a
4.5-inch diameter module 40. In contrast, a similarly sized, conventional
carrier-
type perforating gun, using conventional shaped charges, will typically
provide
only about 18 perforations per linear foot. Thus, this embodiment illustrates
a
capability to increase the perforated area by a factor of three. The size and
number of hexagonal indentations 54 may be varied, depending upon factors
such as the diameter of the module 40 relative to the size of the annular
space
between the perforation system 10 and the casing wall 18; the properties of
the
formation in which the perforation gun is being used; the presence or absence
of
fluid in the annular space; the selection of liner material and explosive; and
the
like. Those skilled in the art will be able to determine optimal
configurations
based upon such skill and with, at most, routine experimentation to ensure
success.
[0032] Figures 4, 5 and 6 show additional possible configurations for the
liner
to enable formation of effective penetrators therefrom. As illustrated
therein, the
indentations 54 each define a cavity 60. While the perimeter of the
indentations
may influence the shape of the cavity 60, it is not necessarily determinative
thereof. Thus, in certain embodiments the shape of the cavity 60 may be of a
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generally conical or pyramidal configuration, as shown in Figure 4, or of a
generally spherical or parabolic configuration, as depicted in Figures 5 and
6.
The cavity 60 provides a formation distance for a penetrator to form. The
cavity
60 provides an apex 62, i.e., point of greatest indentation, opposite the
opening
defined by perimeter 56. In this embodiment, the cavity 60 has six equal
planar
triangular sides 70. The sides 70 adjoin one another along junction lines 72,
forming a cavity 60 that is symmetrical along certain axes. The indentations
54
may be formed into the essentially planar liner 52 by stamping, forging or by
other known means. Thereafter, the sheet may be formed into a cylinder by
bringing opposing ends together and then welding or otherwise connecting the
ends. The high explosive body 50 may then be cast into the space between the
liner 52 and the inner cardboard tube 51.
[0033] An alternative method for forming the high explosive body 50
is by
pressing a billet to a desired length and diameter, and then machining the
billet
to match the hexagonal indentations 54 at the outer surface of the liner 52. A
long axial hole is then drilled into the center of the billet and sized to
accommodate the tube 51. As those skilled in the art are aware, a billet of
high
explosive is a mass of high explosive material that has been pressed or cast
into
cylindrical shape. Pressed billets can be machined to a desired shape, while
cast billets are formed to the desired shape, such as, in this case, a
cylinder with
an axial passage thereth rough.
[0034] Figure 5 illustrates an alternative design for the indentations 54,
here
designated 54'. The indentations 54' still have a hexagonal perimeter 56.
However, the side surfaces defining the cavity 60 are smooth and rounded. In
side cross-section, the cavity 60 forms a dome-like cap or parabola, as
Figures
5 and 6, respectively, depict. The radius and apex of each dome-like cavity 60
depend upon the liner thickness and desired formation distance, with the goal
that a penetrator may be transformed therefrom that is optimal for creating a
large perforation in the wellbore casing 18. In alternative embodiments, other
cavity shapes, such as a conical shape, may be employed.
[0035] Circumferentially surrounding the liner 52 is a cover 64 that protects
the
liner 52 and other parts of the module 40 from the harsh wellbore environment.
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In one embodiment, the cover 64 is a generally cylindrical construction having
planar inner and outer surfaces. The cover 64 may be formed of, for example, a
thermoplastic or thermoset polymer that is resistant to high wellbore
temperatures. The cover 64 may be relatively thin, having a thickness of, for
example, just 0.05 inch, and light in weight, such that it will not unduly
interfere
with the creation of the penetrators from the indentations 54 or 54'. In some
embodiments, an elemental metal or alloy, composite material, thermoplastic or
thermoset polymer, or glass, for example, may be used to form the cover 64.
The cover 64 overlies the adjoining ridges 58 between neighboring indentations
54 or 54' (see Figure 6). There is a space disposed between the cover 64 and
the ridges 58 to permit the indentations 54, 54' to fully develop into
penetrators
upon detonation. Such space may be relatively small, for example, about 5 mm.
Air, at atmospheric pressure, may be trapped within the cavities 60 of the
indentations 54, 54' between the cover 64 and the outer surface of the liner
52.
The distance between the apex 62 of each indentation 54 or 54' and the outer
cover 64 provides a stand-off for each indentation 54 or 54' such that a
penetrator can more fully develop prior to contact with the well casing 18
(see
Figure 1).
[0036] Upper and lower end caps 66, 68 (see Figure 3) are secured to the
cover 64 and liner 52 of the module 40 and serve to help encapsulate and
protect the contents of the module 40, particularly the explosive body 50,
from
fluids within the wellbore 12 prior to detonation.
[0037] In operation, the perforation system 10 is lowered into the wellbore 12
until the modules 34, 36, 38 of the perforation system 10 are aligned with the
desired strata 22, 24, and 30, respectively, of the formation 14. The modules
34,
36, 38 of the perforation system 10 are then detonated to create penetrators
that
perforate the casing 18, cement 20 and formation 14. Following perforation of
the formation 14, the remains of the perforation system 10 may be removed from
the wellbore 12 by pulling upwardly on the conveyance string 32. It is
anticipated
that, in many embodiments, the perforation modules 34, 36, 38 will be
substantially or totally consumed in the detonation.
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[0038] During detonation of the perforation modules 34, 36, 38, directional
penetrators are formed by the indentations 54, 54'. Because the mechanism of
the creation of this type of directional explosively formed penetrator (EFP)
is well
known in the art, it will not be described here in any detail. It is noted,
however,
that the detonation sequence of each module 34, 36, 38, begins at the top end
proximate to the central rod 42 and proceeds simultaneously in axially
downward
and radially outward directions. Each liner indentation 54, 54', when acted
upon
by the advancing detonation wave, forms a robust EFP, which is particularly
well
suited for making large and shallow perforation holes in sandy or soft
formations.
While conventional shaped charges form a relatively fast-moving, low mass jet
that accomplishes the perforation, followed by a relatively slow-moving slug
that
thereafter carries the mass of the remaining charge liner but does not take
part
in the actual perforation, the EFP penetrator of the present invention carries
essentially all of the mass of the liner 52 forming the indentation 54 or 54'.
This
means that the liner mass effectively forms part of the penetrator and takes
an
active part in the perforation, increasing the relative effectiveness thereof.
In one
embodiment it has been found that the perforations that result from
indentations
54 or 54' having hexagonal perimeters very closely approximate those created
from indentations having circular perimeters.
[0039] Figure 7 illustrates an exemplary shot pattern that may be formed upon
detonation of the perforation module 40 within a section 80 of the wellbore
12.
Figure 7 depicts the sidewall of the wellbore section 80 in cylindrical
projection
with the upper end of the section 80 depicted as line 82 and the lower end of
the
section 80 shown as line 84. The illustrated wellbore section 80 has a length
(L)
of approximately one foot. There are fifty-one (51) perforations 86 disposed
within the wellbore section 80, which have been created by penetrators formed
from the indentations 54 or 54' of the perforation module 40. In practice,
those
skilled in the art frequently desire perforations having diameters, as
measured at
the inner surface of the well casing, ranging from about 10 to about 22 mm,
but
larger or smaller perforations may alternatively be obtained by simply varying
the
size of the indentations. It is noted that the fifty-one (51) perforations 86
are
arranged in six horizontal rows 88a, 88b, 88c, 88d, 88e, and 88f of eight
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perforations 86 each. Adjacent rows 88 of perforations 86 are shown herein as
horizontally staggered from one another, such that perforations 86 in one row
are located diagonal to, i.e., offset diagonally in relation to, perforations
86 in
adjacent rows. For example, referring to Figure 7, perforation 86b in row 88b
is
located diagonal to penetrations 86a and 86c in row 88a. This staggered
pattern
is frequently advantageous. Because the penetrations 86 are more densely
concentrated than perforations from conventional shaped charge perforation
devices, the staggered arrangement may help to avoid overlapping of adjacent
perforations. This is desirable because, if there were numerous such overlaps,
the resultant effect of a linear cut in the casing 18 could theoretically
produce a
casing failure, such as a casing collapse. The staggered arrangement may
therefore desirably avoid such an undesirable event. In another embodiment,
some of the indentations may be configured of a material that does not
suitably
form penetrators, in order to reduce the number of penetrators and, therefore,
the number or density of perforations obtained thereby. Such an embodiment
may be acceptable in certain applications, wherein relatively increased
amounts
of post-detonation debris are not problematic.
[0040] Alternative to indentations having hexagonal perimeters, other
perimeter shapes may be selected, desirably such that the perimeters may be
adjoined in a linearly contiguous fashion. For example, the indentations may
be
configured to have triangular, square, or octagonal perimeters. Figures 8 and
9
illustrate alternative embodiments wherein such triangular and square
perimeter
indentations, respectively, are used. Figure 8 depicts an exemplary
perforation
module 90 having triangular perimeter indentations 92. As may be seen, the
triangular perimeter indentations are located in an adjacent manner such that
each of the three sides of a given perimeter borders a side of a neighboring
perimeter. Thus, "dead space" between the indentations 92 has thereby been
eliminated.
[0041] Figure 9 depicts an exemplary perforation module 94 having square
perimeter indentations 96. These indentations 96 are arranged in several
horizontally-disposed rows, e.g., 98a, 98b, 98c. Adjacent rows of indentations
96 are staggered relative to one another, i.e., offset by half a square, such
that
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indentations 96 in each row are located with their apices diagonal to the
apices
of indentations 96 in the adjacent row.
[0042]
It will be understood by those in the art that each perimeter shape will
impart some effect on the configuration of the cavity formed by an
indentation,
and therefore of the penetrator that will be formed from collapse of the
cavity as
a result of detonation. Factors such as the fabrication method, and
capabilities
and limitations thereof, of the liner wherein the indentations are formed, and
the
material of which the liner is composed, will desirably be taken into account
when selecting the perimeter shape and associated packing parameters. For
example, triangular and square perimeter indentations may, because of their
shape, not collapse as readily during detonation as do hexagonal perimeter
indentations in a perforation module wherein all materials and detonation
factors
are the same. However, modification of such factors may, in some
embodiments, offset such disadvantages or even turn such a tendency into an
advantage.
[0043] Figure 10
depicts a portion of an exemplary liner surface for a
perforation module wherein octagonal perimeter indentations are used. As may
be seen in Figure 10, octagonal perimeter indentations cannot completely cover
a given area without leaving some "dead space" between the indentations. In
this aspect, their use may be less advantageous, in some embodiments, than
the use of hexagonal, square or triangular-shaped indentations. However,
octagonal perimeter indentations may more readily approximate the collapse
sequence and penetrator transformation of indentations having a circular
perimeter, and thus may obtain an advantage over triangular and circular
perimeter indentations in certain embodiments. Figure 10 depicts a liner
surface
section 100 having a plurality of octagonal perimeter indentations 102 that
adjoin, i.e., are linearly contiguous to, one another at four of their eight
sides
104. The remaining four sides 106 of the octagonal perimeter indentations 102
define square areas 108 as interstitial spaces. If desired, the interstitial
square
areas 108 may themselves be indented, in the manner of square indentations 96
(see Figure 9), to provide for additional formed penetrators.
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[0044] Turning now to Figures 11 through 14, an exemplary initiation
sequence is illustrated for a single formed penetrator from a perforation
module
40. Figure 11 is a cross-sectional view of the indentation 54 prior to
detonation
of the perforation module 40. The indentation 56 is formed in liner 52 that
surrounds the high explosive body 50. In this embodiment a thermoplastic cover
64 surrounds liner 52. The module 40 is disposed within a section of wellbore
casing 18 surrounded by cement 20. Fluid 57 resides in the annular space that
is between the casing 18 and the radially exterior portion of the cover 64.
Figure
12 depicts the beginning portion of the detonation wherein the material
forming
metallic liner 52 has begun to collapse or coalesce within the space formerly
occupied by the cavity 60 of indentation 54. The cover 64 atop the indentation
54 has begun to bow outward and thin out. In Figure 13, the detonation process
has progressed to the point where a generally spherical penetrator 110 has
been
formed from the material making up the liner 52. The casing 18 and fluid 57
are
essentially sheared through by the penetrator 110. Figure 14 depicts an
advanced stage of the detonation with the penetrator 110 now in a primarily
plastic phase and perforating the cement 20 on its way to the formation (not
shown).
[0045] In summary of the foregoing description, those skilled in the art will
appreciate that the design of the perforation system 10 thus provides a number
of advantages over conventional perforation systems. Included among these,
first, is the fact that the linearly contiguous packing of the indentations
combined
with the unitary body of high explosive produces a greater number of
perforating
penetrators over a given axial length of a module 40 and reduced amount of
"dead space," as compared with conventional perforation systems using shaped
charges and indentations that are physically separated and/or have circular
perimeters. The greater number of penetrators results in a desirably greater
density in the post-detonation perforation shot pattern. Second, the invention
provides for a substantial reduction in debris formed during the perforation
operation. And third, the perforation module 40 may be created or manufactured
and customized relatively easily, without the need for time-consuming
placement
and orientation of individual shaped charges, as with conventional systems.
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CA 02649728 2008-10-17
WO 2008/019173 PCT/US2007/066787
[0046] Those skilled in the art will recognize that numerous modifications and
changes can be made to the illustrative designs and embodiments described
herein and that the invention is limited only by the claims that follow and
any
equivalents thereof.
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