Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02421671 2003-03-11
Title
[0001] Shaped-Charge Liner With Precursor Liner
Field of the Invention
[0002] The present invention is concerned with explosive shaped-charges,
and more particularly town improved liner for use in such shaped-charges, an
improved shape charge which is especially useful in a well pipe perforating
gun, and a method for making them.
Background of the Invention
[0003] The use of shaped-charges for perforating the tubing, pipes, or
casings used to line wells such as oil and natural gas wells and the like, is
well-known in the art. For example, U.S. Pat. No. 3,128,701, issued Apr. 14,
1964 to J. S. Rinehart et al, discloses a shaped-charge perforating apparatus
for perforating oil well casings and well bore holes.
(0004] Generally, shaped-charges utilized as well perforating charges
include a generally cylindrical or cup-shaped housing having an open end and
within which is mounted a shaped explosive which is configured generally as
a hollow cone having its concave side facing the open end of the housing.
The concave surface of the explosive is lined with a thin metal liner which,
as
is well-known in the art, is explosively drwen to hydrodynamically form a jet
of
material with fluid-like properties upon detonation of the explosive and this
jet
of viscous material exhibits a good penetrating power to pierce the well pipe,
its concrete liner and the surrounding earth formation. Typically, the shaped-
charges are configured so that the liners along the concave surfaces thereof
define simple conical liners with a small radius apex at a radius angle of
from
about 55 degrees to about 60 degrees. Other charges have a hemispherical
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apex fitted with a liner of uniform thickness.
[0005] Generally, explosive materials such as HMX, RDX, PYX, or HNS
are coated or blended with binders such as wax or synthetic polymeric
reactive binders such as that sold under the trademark KEL-F. The resultant
mixture is cold- or hot-pressed to approximately 90% of its theoretical
maximum density directly into the shaped-charge case. The resulting
shaped-charges are initiated by means of a booster or priming charge
positioned at or near the apex of the shaped-charge and located so that a
detonating fuse, detonating cord or electrical detonator may be positioned in
close proximity to the priming charge.
[0006] The known prior art shaped-charges are typically designed as either
deep-penetrating charges or large-diameter hole charges. Generally, shaped-
charges designed for use in perforating guns contain 5 to 60 grams of high
explosive and those designed as deep-penetrating charges will typically
penetrate concrete from 10 inches to over 50 inches. Large-diameter hole
shaped-charges for perforating guns create holes on the order of about one
inch in diameter and display concrete penetration of up to about 9 inches.
Such data have been established using API RP43, Section I test methods.
Summary of the Invention
[0007] The disclosed embodiments of the present invention addresses a
liner for a shaped-charge made up of two liner components and a method for
making a shaped-charge using such a liner. In the preferred embodiments,
each liner component has a convex outer surface, a concave inner surface,
an apex having a center, a mouth portion of the liner component opposite the
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apex of the liner component, and a skirt portion terminating in a circular
skirt
edge at the mouth portion of the liner component. The first liner component is
made of a first material and has an opening at the center of its apex. The
second component is made of a second material and a portion of the second
component is within the opening at the center of the apex of the first
component.
[0008] The first material and the second material include different
materials. In one embodiment, the first material has a greater density than
the
second material. In another embodiment the second material has a greater
sound speed than the first material. In the more preferred embodiments, the
first material comprises a metal and most commonly the first material is
selected from the group of copper, copper alloy, aluminum, aluminum alloy,
tin, tin alloy, lead, lead alloy, powdered' metal, powdered metal within a
polymeric base, and sintered metal. By comparison, the second material is
may be made from a similar set of materials or compacted or hardened
explosive, but more preferably comprises aluminum or copper alloy or
powdered metal in a polymeric base. In the most preferred embodiment the
first material comprises copper alloy and the second material comprises
aluminum.
(0009] In the described embodiments, each of the first and second
components has a liner angle. In the more preferred embodiment the second
component has a liner angle which is no more than, about 15 degrees greater
than the liner angle of the first component. In alternative embodiments, the
liner angle of the second component is less than the liner angle of the first
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component. The first and second components each also have a liner height.
In the preferred embodiments, liner height of the second component is no
more than about the liner height of the first component. The circular skirt
edges of first and second components each have a diameter. In the presently
most preferred embodiment the circular skirt edge of the second component
has a diameter of between about 0.30 inches and about 0.45 inches. It is also
preferred that the ratio of the diameter of the circular skirt edge of the
second
component to fhe diameter of the circular skirt edge of the first component is
between about 0.05 and about 0.35 and more preferably between about 0.10
and about 0.25.
[0010] The more preferred shape for the second component is an
approximately conical shape. The more preferred approximate shapes for the
first component are selected from the group consisting of hemispherical,
parabolic, ellipsoidal, flattened parabolic, and hyperbolic. For both it is
highly
preferred that each component be radially symmetric about the central axis
passing through the apex.
[0011] The present disclosure also addresses a method for making a
shaped-charge. The preferred method . starts by forming a first liner
component of a first material wherein the first liner component has an apex
and an opening at the center of the apex. A second liner component is
formed of a second material wherein the second material is not identical to
the
first material. A housing is provided which contains explosive material. The
first component and the second component are assembled into the housing
acting together to line the explosive material. The components are
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assembled so that a portion of the second component is within the opening at
the center of the apex of the first component.
[0012] In various embodiments, the action of forming the liner components
may comprise drawing or molding the liner components among a number of
possible forming methods. In the most preferred embodiments, the two liner
components are joined, although they may be joined before, during, or even
after assembly into the housing.
[0013] The action of joining may include fitting a portion of the second
component within the opening in the apex of the first component. This may
involve pressing the second component into the opening of the apex of the
first component until an interference fit is attained between the two
components. In an alternative embodiment, the second component could
have a lip around its mouth, in which case the action of fitting would include
inserting the second component into the opening of the apex of the first
component until the lip of the second component catches the edge of the
opening of the first component. In another alternative, the first component
could also have a recess around the opening and the lip of the second
component could fit into the recess around the opening in the apex of the
first
component.
[0014] Finally, in the preferred embodiments the two components may be
attached at the intersection of the opening of the apex and the portion of the
second component. Attaching could be accomplished by applying an
adhesive coating, by soldering, by welding, or by other methods disclosed
herein. These forms of attachment could be accomplished alone or in
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combination with each other and could occur before, during, or after assembly
into the shaped-charge.
Description of the Drawings
[0015] The invention, together with further advantages thereof, may best
be understood by reference to the following description taken in conjunction
with the accompanying drawings in which:
[0016] Figure 1 is a cross-sectional diagram illustrating an assembled
shaped-charge including a primary liner having a flattened parabolic apex with
a conical precursor liner.
[0017] Figure 2 is a cross-sectional diagram illustrating an assembled
shaped-charge including a primary liner having a hemispherical apex with a
conical precursor liner.
[0018] Figure 3 is a cross-sectional diagram illustrating a flat-bottom cone
primary liner having a flattened parabolic apex with a conical precursor
liner.
[0019] Figure 4 is a cross-sectional diagram illustrating a hemi-cone
primary liner having a hemispherical apex with a conical precursor liner.
[0020] Figure 5 is a cross-sectional diagram illustrating an assembled
shaped-charge including a primary liner having a hemispherical apex with a
larger conical precursor liner.
[0021] Figure 6 is a cross-sectional diagram illustrating an ellipsoidal
primary liner with a conical precursor liner.
[0022] Figure 7 is a cross-sectional diagram illustrating an assembled
shaped-charge including a flat-bottom cone primary liner having a flattened
parabolic apex with a hemispherical precursor liner.
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Detailed Description
[0023] One factor influencing performance of shaped-charges in large well
bores is the presence of fluid in the annulus between the perforating gun
carrying the charges and the casing. The presence of fluid in this area
significantly affects the formation of the jet tip, particularly in "big hole"
perforators, but also in perforators in general (where shaped-charges are the
perforators or perforating devices carried on the perforating guns). The fluid
has a mushrooming effect on the jet tip which causes it to create a large
entry
hole in the first string of casing. While this may be desirable for single
string
completions where big holes are sought, there are situations where wells are
completed in zones with multiple strings of casings, or it is necessary to
establish fluid communication through multiple strings. When this situation
occurs, it is desirable to obtain a large hole in all of the casing strings.
Having
fluid in the annulus makes this more difficult, because the mushroomed jet tip
expends most of its energy getting through the fluid and creating a large hole
in the first string, and there is very little energy left to perforate
subsequent
strings.
[0024] The present disclosure suggests a method to remove well bore fluid
from the path of a shaped-charge jet in order to reduce the effect it has on
the
jet tip. The reduction of the mushrooming effect caused by the fluid enables
the shaped-charge designer to spread out the jet's energy so that it can be
used more effectively to create large holes through multiple strings of casing
when shooting across fluid gaps. The shaped-charge designer may
alternatively be able to create a larger hole in a single string when shooting
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across fluid gaps or even a deeper penetration of the formation after shooting
across fluid gaps. This is most preferably accomplished by using a precursor
liner and a primary liner both pressed in the same housing. In the most
preferred embodiment, the primary liner is similar or equivalent to a standard
big hole shaped charge Finer. The precursor liner is pressed into the booster
end (or apex end) of the primary liner to form an initial very fast moving jet
to
open a path through the fluid of the well bore annulus. The jet from the
primary liner moves at a slower rate of speed and thus follows the path made
through the fluid by the precursor resulting in reduced effects from the well
bore fluid.
(0025] A particular class of big hole liner incorporates the use of an
opening, preferably circular, at the center of the apex of the liner. The
opening at the apex is especially useful in "big hole" applications, as it
enhances entrance hole performance, although there typically is a trade off in
terms of loss of penetration. When assembled in a shaped-charge under the
present disclosure, the primary liner has the apex opening, and the precursor
liner is fit within the apex opening. The precursor liner and primary liner
may
also be viewed as components of a single overall shaped-charge liner which
are joined together by any of a number of means. The liners are in theory
usable separately, but when placed together in the shaped-charge act
together to line the explosive charge. The two liners (or liner components as
they are also referred to herein) most typically interact at the apex opening
of
the primary liner.
[0026] A number of potential approaches may be used to join the two liner
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components at the apex opening. One preferred method involves the use of
an interference fit between the mouth of the precursor liner and the walls of
the opening in the primary liner. Another method could involve the addition of
a lip to the mouth of the precursor liner such that the lip is too large to
pass
through the apex opening in the primary liner, while the rest of the precursor
liner is able to pass through. The precursor liner could also sit atop the
primary liner. This could be done by forming a recess in the top of the convex
outer portion of the main liner and setting the precursor liner in the recess.
In
this instance, "glue" could again be used to keep the precursor liner in place
or the confinementlcompression between the explosive powder and the
primary liner could be the fixing mechanism. An additional alternative could
employ welding or soldering the border between the precursor liner and the
primary liner.
[0027] In an alternative embodiment, the precursor liner may not be
pressed all the way onto the primary liner, leaving a portion of the precursor
liner extending above the opening in the primary liner. One approach to this
alternative would be to have an interference fit where the mouth of the
precursor liner is somewhat larger than the opening in the apex of the primary
liner such that as the precursor liner is pressed in the two are interference
fit
at a circumference of the precursor liner below the mouth of the precursor
liner. Alternatively the precursor liner could be inserted to the desired
point
and one of the other attachment methods described above or below could be
used to join the two components together into the overall liner.
[0028] The most preferred approach is to have a close fit (without being an
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interference fit) and applying an adhesive coating to keep the two components
of the overall liner (individually the primary liner and the precursor liner)
together. The coating is most preferably an adhesivelpaint sold under the
trademark Glyptol, preferably an adhesive selected from an epoxy material
compatible with the explosive material, and generally comprises an adhesive.
The coating may be a single layer either of adhesive alone or adhesive in
combination with graphite. The coating may also be more than one layer, with
a layer as described above and additional layers contributing to other
properties, such as improving the moisture barrier . characteristics, or
improving the slight amount of time the coating acts as to dynamically confine
the explosive gases which are the product of detonation. The coating as a
whole is preferably no more than twice the thickness of the liner around the
opening in the apex, more preferably less than or about the thickness of the
liner around the opening of the apex, and most preferably between about 5-
10% of the thickness of the liner around the opening of the apex. This tends
to place the thickness of the coating within the range of about 0.002 inches
to
about 0.05 inches. The coating may also be employed even when other
methods should maintain relative position (such as the use of a lip or
interterence fit or other methods understood by those of skill in the art). In
this
case the adhesive properties of the coating may provide additional
assistance, and the coating may also help to improve the seal between the
liners, preventing potential salting out of explosive material through the
component interface (the interface between the primary liner component and
the precursor liner component).
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[0029] The primary liner component is preferably made from a metal strip
or sheet, more preferably from a metal selected from the group of copper,
copper alloy, aluminum, aluminum alloy, tin, tin alloy, lead, and lead alloy,
and
most preferably made of copper alloy. In alternative processes, the liner may
be made from a powdered metal within a polymeric base which is molded (for
example injection molded) into the form of a liner. The liner could also be
made from a sintered metal, possibly with other material components, which
is cast or molded into a desired shape. These alternative processes would
typically be manufactured using a molding or casting process.
[0030] The precursor liner component may be made from similar materials
and using similar processes. However, in the preferred embodiment, the
precursor liner is made from a material which is less dense than the material
used in the primary liner component. Alternatively, the precursor liner
component may be made from a material with a greater sound speed, where
the sound speed is the speed at which an acoustic shockwave travels through
the liner material. In either event, these properties assist the precursor
liner in
traveling more quickly than the primary liner following the detonation of the
charge. This helps to promote the travel of the jet formed by the precursor
liner into the fluid preceding the jet formed by the primary liner. A
preferred
material for the precursor liner component is aluminum, but a lighter brass or
even a CLG-80 powdered metal are preferred alternative materials. Another
less preferred alternative would involve making the precursor liner out of a
hardened or compacted explosive. This could create an exploding precursor
jet to push a path through the fluid. It might also have a lower density or
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higher sound speed than the primary liner component. For either liner
component, when the word material is used in the present disclosure it is
intended to refer to blends and composites as well as more simple elemental
materials. Basically, it represents the stuff out of which a liner component
is
formed.
[0031] The preferred method for making the liner components calls for
drawing the chosen material (preferably from a flat state) into a concave
shape radially symmetric about a central axis passing through and
perpendicular to the center of the apex, where radial symmetry about an axis
is intended to describe concentricity about such axis within any plane defined
perpendicular to such axis and intersecting such axis. In this process the
center of the material is drawn down to form the apex while the perimeter of
the material forms a skirt portion terminating in a circular skirt edge at the
mouth of the liner. Depending on the desired apex shape and other factors,
the draw may be done in a single step or may be done in several steps. For a
hemispherical apex, a single step draw is preferable. The drawing process
may result in creation of a slight necking point in the material, where the
thickness is slightly reduced generally in the area near the transition from
the
skirt portion to the apex portion of the liner. Multiple step draws tend to
leave
several necking points near each radial transition, but these are generally
smaller and less well defined: Multiple step draws are preferable when the
desired apex profile is parabolic such as the more complex flattened parabolic
apex described in this disclosure:
[0032] The primary liner component will typically use an opening in the
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apex to locate andlor hold the precursor Finer component. Preferably, a punch
is used to punch the opening in the apex centered on the central axis. This
preferably occurs in the same sequence as the drawing process to increase
reliability of the central axis for the punch being identical to the central
axis for
the draw. Other alternatives to the use of a punch to create the hole include
drilling, honing, sawing, or chemically etching.
[0033] The draw is preferably done from a sheet of material, but may also
be performed on pre-cut and sized discs or other shaped blanks. At the
conclusion of the draw, either preferably as a final step in the drawing
process
using the drawing tools, or as a separate step, any excess flat material from
the sheet or blank outside of the circular skirt edge forming the mouth of the
liner must be removed. Additionally, in some embodiments, following removal
of any excess flat material, an additional step may be undertaken to trim the
height of the liner to a desired size.
[0034] In an alternative method of manufacture, the liner components of
the present invention may be manufactured by spinning a sheet of material
into a concave shape radially symmetric about a central axis, having an apex
centered on the central axis and a mouth at the opposite end from the apex;
wherein a portion of the material forms the apex and a portion of the material
forms a skirt portion terminating in a circular skirt edge at the mouth of the
liner. Following the spinning process there must be a removal of any excess
material outside the circular skirt edge forming the mouth. Where an opening
in the apex is desired, this may be accomplished by the use of a punch or
drill, after the completion of the spinning process. Other methods of
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manufacture may also be contemplated by those of skill in the art as
appropriate to the material of choice, such as sintering, casting, molding,
compositeing, and the like.
[0035] Figure 1 is a cross-sectional diagram illustrating one specific
embodiment of the present invention. Figure 1 is a cross-section of a
shaped-charge 10 having a primary liner 50 with a flattened parabolic apex 54
and a precursor liner 70 with a conical apex 74. The shaped-charge 10
includes a housing 12 having an outer wall 14, an inner wall 16, a base 18,
and a mouth 20 opposite the base 18. Within the housing is contained a
shaped explosive 28 mounted on the inner wall 16 of the housing 12 and
having an open concave side facing the mouth 20 (or mouth portion) of the
housing.
[0036] The housing 12 also contains a chamber 22 to hold an initiation
charge 24. The initiation charge 24 preferably is actually larger than chamber
22 and flows into the area housing the main shaped explosive 28. In the
illustrated embodiment, the initiation charge actually overlaps the precursor
liner. One alternative may modify the shape of the standard shaped-charge
housing to allow sufficient initiation charge without having the charge
overlap
the precursor liner.
[0037] One of the simpler approaches to change the position of the
initiation charge is to angle the cavity where the initiation charge generally
sits
while preserving the minimum diameter. This would bring the initiation charge
line away from the precursor liner. In addition increasing the angle of the
inner wall of the case above the cavity by increasing the minimum diameter
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would also lower the initiation charge line. Another way to change the level
is
by manipulating how much powder is actually poured into the charge. Finally,
a two-step pressing process could be employed in which the initiation charge
is shaped to reflect the conical (or other) shape of the precursor liner.
During
this pressing the shape could potentially be offset to allow some amount of
air
or preferably some amount of the main explosive to be between the initiation
charge and the precursor liner. While an alternative, it may be less desirable
to pre-form the initiation charge after it was poured into the case due to the
additional process steps and complexity of manufacture.
[0038] The initiation charge 24 is triggered by an explosive member,
preferably a linear explosive member linking and initiating several shaped-
charges, contained at least in part within primer container 26 attached to the
base 18 of housing 12.
[0039] The primary shaped-charge liner component 50 (also referred to as
the primary liner) has a concave inner surface 51, a convex outer surface 52,
an apex 54 (or apex portion), and a mouth opposite the apex 54 (illustrated
here contiguous to mouth 20 of housing 12). The apex 54 has a center at a
point where the apex 54 intersects the central axis 53 about which the
shaped-charge liner is radially symmetric. The embodiment illustrated in
Figure 1 further includes an opening 56 at the center of the apex 54. The
liner 50 also includes a skirt portion 60 terminating in a circular skirt edge
62
at the mouth of the liner on the opposite end of the liner from the apex 54.
The liner 50 lines the concave side of the shaped explosive 28 leaving an
open space 30 between the concave inner surface 51 of the liner and the
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mouth 20 of the housing.
[0040) The precursor shaped-charge liner component 70 (also referred to
as the precursor liner) has a concave inner surface 71, a convex outer surface
72, an apex 74 (or apex portion}, and a mouth opposite the apex 74
(illustrated here contiguous to opening 56 of primary liner 50). The apex 74
has a center at a point where the apex 74 intersects the central axis 53 about
which both the primary liner 50 and the precursor liner 70 are radially
symmetric. The precursor liner 70 also includes a skirt portion 80 terminating
in a circular skirt edge 82 at the mouth of the liner on the opposite end of
the
liner from the apex 74. The combined liner components 50 and 70 work
together to line the concave side of the shaped explosive 28 leaving an open
space 30 between the concave inner surface 51 of the primary liner and the
mouth 20 of the housing.
[0041) The main shaped explosive 28 is bounded by the housing inner wall
16, the initiation charge 24, the convex outer surface 52 of the primary liner
50, and the convex outer surface 72 of the precursor liner 70.
[0042) In the embodiment illustrated in Figure 1, the primary liner 50 is
drawn multiple steps. The transition between the skirt portion 60 and the
apex portion 54 of the liner 50 is roughly defined as the transition from a
straighter, although not necessarily completely straight, skirt section 60
from
the skirt edge 62 of the liner 50 to the more curved (having a shorter radius
of
curvature) apex portion 54 of the finer 50. With the more complex curve of
this embodiment, the transition is a transition region of gradually decreasing
radius of curvature, which may decrease stepwise or in an approximately
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curvilinear fashion. In a simpler curved liner such as Figure 2 below, the
primary liner may be drawn in a single step and have a necking point near the
transition between the skirt portion and the apex portion of the liner. For
the
embodiment of Figure 1, the transition between the skirt portion 60 and the
apex portion 54 of the liner 50 is roughly defined as the transition from a
straighter, although not necessarily completely straight, skirt section 60
from
the skirt edge 62 of the liner 50 to the more curved (having a shorter radius
of
curvature) apex portion 54 of the liner 50. With a more complex curve, the
transition is a transition region of gradually decreasing radius of curvature,
which may decrease stepwise or ideally in a curvilinear fashion. The
transition point 64 identified in the drawing of Figure 1 is illustrative, but
is not
intended to be correct to scale.
[0043] For the purposes of this disclosure a "liner angle" may be defined
for a liner component. If a section is taken on a plane through a liner or
liner
component which includes the central axis and intersects the apex of the liner
and a straight line is drawn tangential to the skirt portion of the liner on
each
side. The lines should intersect at a point below the apex of the liner (or
exactly at the apex of the liner in the case of a perfect cone) and define an
angle between them. This angle represents the liner angle for the liner or
liner component.
[0044] For the embodiment described in Figure 1, the liner angle for the
primary component is preferably within the range of 10 degrees to 150
degrees, more preferably within the range of 35 degrees to 75 degrees, and
most preferably within the range of 50 degrees to 55 degrees. For the
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embodiment described in Figure 1, the liner angle for the precursor
component is preferably within the range of 10 degrees to 150 degrees, more
preferably within the range of 20 degrees to 75 degrees, and most preferably
within the range of 35 degrees to 55 degrees. It is also preferable that the
liner angle for the precursor liner be no more than 15 degrees more than the
liner angle for the primary liner. It is more preferable that the liner angle
for
the precursor liner be between about 15 degrees less and about 5 degrees
more than the liner angle for the primary liner. In the present described
embodiment, it is most preferable that the liner angle for the precursor liner
be
less than the liner angle for the primary liner. Similar to the deep-
penetrating
advantages provided by conical liners over the more curvilinear big hole
liners, it is believed that steeper liners (smaller liner angles) for the
precursor
liners will travel faster thus helping to promote the travel of the jet formed
by
the precursor liner into the fluid preceding the jet formed by the primary
liner.
[0045] For the purposes of this disclosure a "liner height" may be defined
for a liner component. If measurement is taken along the central axis from the
opening or lowest apex of the liner component to the point on the axis where
a plane defined by the circular skirt edge of the liner intersects the axis,
this
measurement represents the liner height for the liner or liner component.
[0046] For the embodiment described in Figure 1, the liner height for the
primary component is preferably within the range of 0.25 inches to 3.0 inches,
more preferably within the range of 0.5 inches to 2.0 inches, and most
preferably within the range of 0.75 to 1.25 inches. For the embodiment
described in Figure 1, the liner height for the precursor component is
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preferably within the range of 0.125 inches to 1.5 inches, more preferably
within the range of 0.125 inches to 0.5 inches, and most preferably within the
range of 0.2 inches to 0.4 inches. These represent specific heights for a
specific embodiment, but as is understood by those of skill in the art,
charges
may be scaled up or down depending on the proposed or desired end use.
There are also preferred ratios for the height of the liners. It is preferable
that
the liner height for the precursor liner be less than '/2 the liner height for
the
primary liner. It is more preferable that the liner height for the precursor
liner
be less than about 113 of the liner height for the primary liner, and most
preferable that the liner height for the precursor liner be between 1/5 and
1/3
of the liner height for the primary liner.
[0047] Figure 2 is a cross-sectional diagram illustrating a distinct specific
embodiment of the present invention. Figure 2 is a cross-section of a
shaped-charge 110 having a primary liner 150 with a hemispherical apex 154
and a precursor liner 170 having a conical apex 174. The shaped-charge 110
includes a housing 112 having an outer wall 114, an inner wall 116, a base
118, and a mouth 120 opposite the base 118. Within the housing is contained
a shaped explosive 128 mounted on the inner wail 116 of the housing 112
and having an open concave side facing the mouth 120 (or mouth portion) of
the housing.
[0048] The housing 112 also contains a chamber 122 to hold an initiation
charge 124. The initiation charge 124 is triggered by an explosive member
contained at least in part within primer container 126 attached to the base
118
of housing 112.
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[0049] The primary shaped-charge liner 150 has a concave inner surface
151, a convex outer surface 152, an apex 154 (or apex portion), and a mouth
opposite the apex 154 (illustrated here contiguous to mouth 120 of housing
112). The apex 154 has a center at a point where the apex 154 intersects the
central axis 153 about which the shaped-charge liner is radially symmetric.
The embodiment illustrated in f=figure 2 further includes an opening 156 at
the
center of the apex 154. The liner 150 also includes a skirt portion 160
terminating in a circular skirt edge 162 at the mouth of the liner on the
opposite end of the liner from the apex 154. The liner 150 lines the concave
side of the shaped explosive 128 leaving an open space 130 between the
concave inner surface 151of the liner and the mouth 120 of the housing.
[0050] The precursor shaped-charge liner 170 has a concave inner surface
171, a convex outer surface 172, an apex 174 (or apex portion), and a mouth
opposite the apex 174 (illustrated here contiguous to opening 156 of primary
liner 150). The apex 174 has a center at a point where the apex 174
intersects the central axis 153 about which both the primary liner 150 and the
precursor liner 170 are radialiy symmetric. The precursor liner 170 also
includes a skirt portion 180 terminating in a circular skirt edge 182 at the
mouth of the liner on the opposite end of the liner from the apex 174. The
2o combined liner components 150 and 170 line the concave side of the shaped
explosive 128 leaving an open space 130 between the concave inner surface
151of the primary liner and the mouth 120 of the housing.
[0051] The shaped explosive 128 is bounded by the housing inner ~niall
116, the initiation charge 124, the convex outer surface 152 of the primary
CA 02421671 2003-03-11
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liner 150, and the convex outer surface 172 of the precursor liner 170.
[0052] For the embodiment described in Figure 2, the liner angle for the
primary component is preferably within the range of 10 degrees to 150
degrees, more preferably within the range of 35 degrees to 65 degrees, and
most preferably within the range of 42 degrees to 47 degrees. For the
embodiment described in Figure 2, the liner angle for the precursor
component is preferably within the range of 10 degrees to 150 degrees, more
preferably within the range of 20 degrees to 90 degrees, and most preferably
within the range of 20 degrees to 50 degrees. For this embodiment and some
other embodiments, it is also preferable that the liner angle for the
precursor
liner be no more than 15 degrees more than the liner angle for the primary
liner. It is more preferable that the liner angle for the precursor liner be
between about 15 degrees less and about 10 degrees more than the liner
angle for the primary liner.
[0053] For the embodiment described in Figure 2, the liner height for the
primary component is preferably within the range of 0.25 inches to 3.0 inches,
more preferably within the range of 0.5 inches to 2.0 inches, and most
preferably within the range of 1.0 inches to 1.35 inches. For the embodiment
described in Figure 2, the liner height for the precursor component is
preferably within the range of 0.125 inches to 1.5 inches, more preferably
within the range of 0.125 inches to 0.5 inches, and most preferably within the
range of 0.2 inches to 0.4 inches. These represent specific heights for a
specific embodiment, but as is understood by those of skill in the art,
charges
may be scaled up or down depending on the proposed or desired end use.
CA 02421671 2003-03-11
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There are also preferred ratios for the height of the liners. With the
embodiment of Figure 2 in mind, it is preferable that the liner height for the
precursor liner be less than 2/3 the liner height for the primary liner. It is
more
preferable that the liner height for the precursor liner be less than 112 of
the
liner height for the primary Finer, and most preferable that the liner height
for
the precursor liner be between 114 and 1/2 of the liner height for the primary
liner:
[0054] The liner illustrated in Figure 3 is made up of a relatively straight
conical section in the skirt transitioning into a flattened parabolic apex,
where
the apex comprises a flattened parabola that is radially symmetric about the
central axis passing through the center of the apex. The parabolic apex is
blended in a curvilinear fashion to a simple truncated conical section that
extends to the opening of the case. This type of liner allows an increased
standoff for the parabolic section while minimizing the amount of explosive
material necessary to fill the case. The conical section allows this standoff
while maintaining a solid boundary between the explosive and the cavity
within the shaped-charge. The precursor liner illustrated is approximately a
simple cone where the mouth of the precursor liner is contiguous to the
opening in the apex of the primary liner. The various methods of coupling the
two liner components at or about the opening in the primary liner are
addressed above and equally apply for this embodiment.
[0055] In the described example of Figure 3, the opening at the center of
the apex of the primary liner has a diameter of about 0.375 inches and the
circular skirt edge has a diameter of about 1.9 inches. In this example the
CA 02421671 2003-03-11
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ratio of the diameter of the opening to the diameter of the circular skirt
edge is
about 0.2. Preferably the ratio of the diameter of the opening to the diameter
of the circular skirt edge is between about 0.05 and about 0.35 and more
preferably the ratio of the diameter of the opening to the diameter of the
circular skirt edge is between about 0.10 and about 0.25. In the specific
examples disclosed herein the opening at the center of the apex preferably
has a diameter of between about 0.30 inches and about 0.45 inches. In the
preferred embodiment, this ratio equally applies to the ratio of the diameter
of
the circular skirt edge of the mouth of the precursor liner to the circular
skirt
edge of the mouth of the primary liner.
[0056) In the described example of Figure 4; the opening at the center of
the apex of the primary liner has a diameter of about 0.36 inches and the
circular skirt edge has a diameter of about 2.45 inches. In this example the
ratio of the diameter of the opening to the diameter of the circular skirt
edge is
about 0.15. Similarly the ratio of the diameter of the circular skirt edge of
the
mouth of the precursor liner to the circular skirt edge of the mouth of the
primary liner is about 0.15. in both Figure 3 and Figure 4, the size of the
opening in the apex also approximates the size of the mouth of the precursor
liner and thus the ratio of the mouth of the primary liner to the apex opening
of
the primary liner approximates the ratio of the mouth of the primary liner to
the
mouth of the precursor liner.
[0057) The hemi-cone primary liner illustrated in Figure 4 allows a larger
apex and tends to distribute more explosive material directly behind the apex
section. Again, the embodiment illustrated in Figure 4 incorporates a simple
CA 02421671 2003-03-11
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cone for the precursor liner.
[0058] In one alternative embodiment illustrated in Figure 5, it may be
desirable to have a more substantial precursor component resulting in a larger
apex opening in the primary liner and corresponding larger mouth in the
precursor liner. Similarly, the relative liner heights of the two liners may
also
approach one end of the most preferred spectrum.
[0059] For the embodiment described in Figure 5, the liner angle for the
primary component is preferably within the range of 10 degrees to 150
degrees, more preferably within the range of 35 degrees to 65 degrees, and
most preferably within the range of 42 degrees to 47 degrees. For the
embodiment described in Figure 5, the liner angle for the precursor
component is preferably within the range of 10 degrees to 150 degrees, more
preferably within the range of 30 degrees to 100 degrees, and most preferably
within the range of 40 degrees to 60 degrees. For this embodiment and some
other embodiments, it is also preferable that the liner angle for the
precursor
liner be no more than 15 degrees more than the liner angle for the primary
liner. It is more preferable that the liner angle for the precursor liner be
between about 15 degrees less and about 15 degrees more than the finer
angle for the primary liner (within about 15 degrees of the liner angle for
the
primary liner).
[0060] For the embodiment described in Figure 5, the liner height for the
primary component is preferably within the range of 0.25 inches to 3.0 inches,
more preferably within the range of 0.5 inches to 2.0 inches, and most
preferably within the range of 1.0 inches to 1.35 inches. For the embodiment
CA 02421671 2003-03-11
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described in Figure 5, the liner height for the precursor component is
preferably within the range of 0.125 inches to 1.5 inches, more preferably
within the range of 0.25 inches to 1.0 inches, and most preferably within the
range of 0.6 inches to 0.8 inches. These represent specific heights for a
specific embodiment, but as is understood by those of skill in the art,
charges
may be scaled up or down depending on the proposed or desired end use.
There are also preferred ratios for the height of the liners. With the
embodiment of Figure 5 in mind, it is preferable that the liner height for the
precursor liner be less than the liner height for the primary liner. It is
more
preferable that the liner height for the precursor liner be less than 2/3 of
the
Liner height for the primary Finer, and most preferable that the liner height
for
the precursor liner be between 113 and 213 of the liner height for the primary
liner.
[0061] Ln the described example of Figure 5, the opening at the center of
the apex of the primary liner has a diameter of about 0.675 inches and the
circular skirt edge has a diameter of about 2.45 inches. In this example the
ratio of the diameter of the opening to the diameter of the circular skirt
edge is
about 0.275. Similarly the ratio of the diameter of the circular skirt edge of
the
mouth of the precursor liner to the circular skirt edge of the mouth of the
primary liner is about 0.275. Preferably the ratio of the diameter of the
opening to the diameter of the circular skirt edge is between about 0.10 and
about 0.45 and more preferably the ratio of the diameter of the opening to the
diameter of the circular skirt edge is between about 0.20 and about 0.35.
[0062] While the embodiments particularly addressed above reflect the use
CA 02421671 2003-03-11
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of an approximately hemispherical apex finer and .of a flattened parabolic
apex
liner as primary liners, one of skill in the art will recognize that the
benefits of
the proposed invention could also apply in other shapes of liners, for example
simple conical liners, slightly modified conical liners which take the form of
ellipsoids (partial 3-dimensional ellipses) or have ellipsoidal apexes (for
example the primary and precursor liner illustrated in Figure 6), liners with
hyperbolic apexes, liners with truncated apexes, other shapes familiar to
those of skill in the art. For any of the shapes described herein, when an
apex is described as having a particular shape it is recognized that the shape
is approximate and may involve some degree of eccentricity, deviation, or
transitioning, both as a matter of design and as a matter of manufacture. The
shape is intended to provide insight into the basic pattern being followed and
is not intended to be a precise description of the physical outcome. In any
event, the liners are preferably radially symmetric about the central axis
passing through the center of the apex. While the disclosure herein refers to
concave and convex surfaces to describe the general orientation of the
surface within the context of the object, the use of convex and concave are
not intended to imply a requirement that the surface be smooth or curvilinear.
[0063] Returning to the embodiment described in Figure 6, (briefly
introduced above) the liner angle for the primary component is preferably
within the range of 10 degrees to 150 degrees, more preferably within the
range of 25 degrees to 55 degrees, and most preferably within the range of 37
degrees to 43 degrees. Far the embodiment described in Figure 6, the liner
angle for the precursor component is preferably within the range of 10
CA 02421671 2003-03-11
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degrees to 150 degrees, more preferably within the range of 20 degrees to 75
degrees, and most preferably within the range of 35 degrees to 55 degrees.
For this embodiment and some other embodiments, it is also preferable that
the liner angle for the precursor liner be no more than 15 degrees more than
the liner angle for the primary liner. It is more preferable that the liner
angle
for the precursor liner be within about 15 degrees of the liner angle for the
primary liner.
[0064] For the embodiment described in Figure 6, the liner height for the
primary component is preferably within the range of 0.25 inches to 3.0 inches,
more preferably within the range of 0.75 inches to 2.0 inches, and most
preferably within the range of 1.20 inches to 1.50 inches. For the embodiment
described in Figure 6, the liner height for the precursor component is
preferably within the range of 0.125 inches to 1.5 inches, more preferably
within the range of 0.125 inches to 0.5 inches, and most preferably within the
range of 0.2 inches to 0.4 inches. These represent specific heights for a
specific embodiment, but as is understood by those of skill in the art,
charges
may be scaled up or down depending on the proposed or desired end use.
There are also preferred ratios for the height ~f the liners. With the
embodiment of Figure 6 in mind, it is preferable that the liner height for the
precursor liner be less than 'h the liner height for the primary liner. It is
more
preferable that the liner height for the precursor liner be less than about
113 of
the liner height for the primary Liner, and most preferable that the liner
height
for the precursor liner be between 1/5 and 1/3 of the liner height for the
primary liner.
CA 02421671 2003-03-11
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[0065] In the described example of Figure 6, the opening at the center of
the apex of the primary liner has a diameter of about 0.375 inches and the
circular skirt edge has a diameter of about 2.50 inches. In this example the
ratio of the diameter of the opening to the diameter of the circular skirt
edge is
about 0.15. Similarly the ratio of the diameter of the circular skirt edge of
the
mouth of the precursor liner to the circular skirt edge of the mouth of the
primary liner is about 0.15. Preferably the ratio of the diameter of the
opening
to the diameter of the circular skirt edge is between about 0.05 and about
0.35
and more preferably the ratio of the diameter of the opening to the diameter
of
the circular skirt edge is between about 0.10 and about 0.25.
[0066] While the precursor liners shown in the examples have been simple
cones, more complex shapes could be employed as described above or as
illustrated in Figure 7. Alternatively, even a simple button or disk could be
employed for the precursor liner, however, such an instance makes
particularly favorable the choice of a material for such liner which is less
dense or has a greater sound speed than the material making up the primary
liner.
[0067] The embodiments addressed above involve an open shaped
charge, i.e. one without a cover. This type of shaped-charge is typically used
2o within a perforating gun or tubing, which provides protection from direct
exposure to the downhole pressure and environment. Alternative shaped-
charges have covers that cooperate with the housing to protect each
individual charge from direct exposure to the downhole environment. While
not specifically addressed here, the benefits of the present invention would
CA 02421671 2003-03-11
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equally apply to such covered charges, as would be recognized by one of skill
in the art.
[0068] Although only a few embodiments of the present invention have
been described, it should be understood that the present invention may be
embodied in many other specific forms without departing from the spirit or the
scope of the present invention. Therefore, the present examples are to be
considered as illustrative and not restrictive, and the invention is not to be
limited to the details given herein, but may be modified within the scope of
the
appended claims along with their full scope of equivalents.
