Note: Descriptions are shown in the official language in which they were submitted.
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ASYMMETRIC SHAPED CHARGES AND METHOD FOR MAKING ASYMMETRIC
PERFORATIONS
BACKGROUND
TECHNICAL FIELD
[0001] Embodiments of the subject matter disclosed herein generally relate
to
shaped charges and associated perforations made in the casing of a well, and
more
specifically, to methods and systems for generating an asymmetric jet of
material for
perforating the casing to obtain a desired perforation profile.
DISCUSSION OF THE BACKGROUND
[0002] In the oil and gas field, once a well 100 is drilled to a desired
depth H
relative to the surface 110, as illustrated in Figure 1, and the casing 102
protecting
the wellbore 104 has been installed and cemented in place, it is time to
connect the
wellbore 104 to the subterranean formation 106 to extract the oil and/or gas.
This
process of connecting the wellbore to the subterranean formation may include a
step
of plugging a previously fractured stage of the well with a plug 112, a step
of
perforating a portion of the casing 102, corresponding to a new stage, with a
perforating gun string 114 such that various channels 116 are formed to
connect the
subterranean formation 106 to the inside of the casing 102, a step of removing
the
perforating gun assembly, and a step of fracturing the various channels 116 of
the
new stage. These steps are repeated until all the stages are fractured.
[0003] During the perforating step for a given stage, perforating guns
115i of
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the perforating gun string 114 are used to create perforation clusters in the
horizontal
multistage hydraulically fractured unconventional well 100. Clusters are
typically
spaced along the length of a stage 140 (a portion of the casing that is
separated with
plugs from the other portions of the casing), and each cluster comprises
multiple
perforations (or holes) 130. Each cluster is intended to function as a point
of contact
between the wellbore 104 and the formation 106. After each stage 140 is
perforated,
a slurry of proppant (sand) and liquid (water) is pumped into the stage at
high rates
and then, through the perforation holes 130, into the formation 106, with the
intent of
hydraulically fracturing the formation to increase the contact area between
that stage
and the formation. A typical design goal is for each of the clusters to take a
proportional share of the slurry volume, and to generate effective fractures,
or
contact points, with the formation, so that the well produces a consistent
amount of
oil cluster to cluster and stage to stage.
[0004] In typical wells, the distribution of the slurry and proppant
between the
various clusters is not uniform. There can be more slurry deposited near the
toe end
140A of the stage 140, resulting in a toe biased stage, or more deposited near
the
heel end 140B of the stage 140, resulting in a heel biased stage. Sometimes,
the
clusters may not take appreciable amounts of slurry at all. Size, shape,
distribution,
and uniformity of perforation holes may contribute to this treatment
nonuniformity.
[0005] The perforation geometry is typically a round hole 130, as shown in
Figure 2, punched at a 90 degree angle to the well axis X. During the
fracturing
treatment, holes that are taking fluid and sand may erode to new shapes 132,
as the
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sand wears against the perforation hole while turning from moving down the
well and
into the perforation hole. This process is exaggerated if only a few of the
holes in the
stage are taking the slurry, and the eroded holes continually take more fluid,
thus
propagating the effect even further as the eroding hole 132 becomes much
larger
than all of the other holes 130 in the stage.
[0006] Constant Entry Hole or Equal Entry Hole (CEH or EEH) charges have
proven to be very beneficial in this application. Baseline conventional shaped
charges 150 (Figure 3 shows two shaped charges of the gun 115i, one 150
oriented
downward and one 152 upward) tend to create a much larger hole 151 in the
short
water gap G1 when the gun 115i rests on the low-side 102A of the casing 102
and a
much smaller hole 153 in the high-side 102B of the casing 102 through the
longer
water gap G2. This means that the water gap negatively affects the size of the
holes
made in the casing by the shaped charges. The larger holes 151 take more fluid
than the smaller holes 153, and they erode over time, resulting in the large
holes
taking eventually all of the fluid. CEH charges promote more uniform
distribution of
fluid, and allow the overall reduction of the nominal hole size, which further
enables
high-density perforation techniques.
[0007] One mechanism to promote a more equal distribution of the slurry
into
the hole is the SAN DIQ system, belonging to the assignee of this application,
in
which the perforation charges with CEH or Constant Entry Hole design are
angled
toward the toe so as to create a perforation which might more readily accept
fluid
and sand with less erosion, and with a lower pressure drop. Field results have
been
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promising, with lower pressure drops observed during treatment, and hinting
that the
discharge coefficient might be higher than with systems having shaped charges
with
no angle.
[0008] Shaped charges which create slots have also been used to create
noncircular perforation tunnels. These charges have been used in arrangements
where the slot was perpendicular to the well axis (as shown in Figure 2 for
slot 132)
for the purpose of plug and abandonment (channel finding), and at an angle to
the
axis for fracturing in vertical wells (Saber jet technology). The slots have
been
generated through nonuniformity in the casing, or as a modular linear charge
that
has been shortened for use in perforating guns. Slot based charges have the
disadvantage that the resultant jet is spread over a broad area, resulting in
extreme
sensitivity to the water gap in the pressurized well. Slot creating
perforators
therefore would create a large variation in the hole size in the horizontal
wells, which
would be disadvantageous for this application. Further, slot perforators have
not
been developed in systems where the slots are oriented in line with the well
axis so
as to provide beneficial proppant and fluid transport from the well to the
formation
during hydraulic fracturing operations.
[0009] Thus, there is a need to form slots into the casing, to control an
orientation of the slots along the casing, and to design shaped charges that
would
achieve these results on a consistent basis.
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SUMMARY
[0010] According to an embodiment, there is a shaped charge for making an
asymmetrical perforation into a casing. The shaped charge includes a case
extending along a symmetry axis X and having a back wall and an open end; an
explosive material located within the case; a liner located within the case,
over the
explosive material; a booster material; and an asymmetrical feature. The
asymmetrical feature is selected to generate an asymmetrical perforation into
the
casing.
[0011] According to another embodiment, there is a liner for covering an
explosive material in a case of a shaped charge. The liner includes a metallic
powdered material, a binder that holds together the metallic powdered
material, and
an insert located partially within the metallic powdered material. The liner
has a
concave shape.
[0012] According to still another embodiment, there is a shaped charge for
making an asymmetric perforation in a casing of a well. The shaped charge
includes
a case extending along a symmetry axis X and having a back wall and an open
end,
an explosive material located at the back wall of the case, a liner located
within the
case, over the explosive material, and a booster material located in a channel
formed in the back wall of the case. The liner includes a metallic powdered
material;
a binder that holds together the metallic powdered material; and an insert
located
partially within the metallic powdered material. The liner has a concave
shape.
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[0013] According to yet another embodiment, there is a gun for perforating
asymmetrically a casing of a well. The gun includes a gun carrier; and a
shaped
charge located inside the gun carrier and having a liner placed over an
explosive
material, where the liner includes a metallic powdered material; a binder that
holds
together the metallic powdered material; and an insert located partially
within the
metallic powdered material. The liner has a concave shape.
[0014] According to another embodiment, there is a method for making a
shaped charge that is capable of making an asymmetric perforation into a
casing.
The method includes providing a case that extends along a symmetry axis X and
has
a back wall and an open end; making a channel through the back wall;
installing a
booster material into the channel; adding an explosive material to the back
wall of
the case; forming a liner; and placing the liner within the case, over the
explosive
material. The shaped charge has an asymmetrical feature selected to make the
asymmetric perforation into the casing.
[0015] According to another embodiment, there is a gun for perforating a
casing in a well. The gun includes a gun carrier and an asymmetric shaped
charge
located inside the gun carrier. The shaped charge has an asymmetrical feature
selected to make an asymmetric perforation into the casing.
[0016] According to another embodiment, there is a casing that was
perforated with an asymmetrical shaped charge. The casing includes a round
wall;
and an elongated perforation formed in the round wall with the shaped charge.
A
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longitudinal axis x2 of the elongated perforation extends along a desired
direction as
a result of using the asymmetrical shaped charge.
[0017] According to another embodiment, there is a method for making an
asymmetrical perforation in a casing. The method includes lowering a gun into
the
casing of a well; firing an asymmetric shaped charge located inside a gun
carrier of
the gun; and forming the asymmetrical perforation in the casing due to the
asymmetric shaped charge.
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BRIEF DESCRIPTON OF THE DRAWINGS
[0018] The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate one or more embodiments and, together
with the
description, explain these embodiments. In the drawings:
[0019] Figure 1 illustrates a well and associated equipment for well
completion
operations;
[0020] Figure 2 illustrates various holes formed in a casing due to shaped
charges;
[0021] Figure 3 illustrates how the size of the holes made in the casing is
influenced by the water gap between the casing and the gun;
[0022] Figure 4 illustrates an asymmetrical shaped charge having a tilted
liner;
[0023] Figure 5 illustrates an asymmetrical shaped charge having an
asymmetrical channel and booster material;
[0024] Figure 6 illustrates an asymmetrical shaped charge having two
asymmetrical channels;
[0025] Figure 7 illustrates an asymmetrical shaped charge having an
explosive material with a varying characteristic;
[0026] Figure 8 illustrates an asymmetrical shaped charge having an insert;
[0027] Figure 9 illustrates an asymmetrical shaped charge having an insert
with a window;
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[0028] Figure 10 illustrates an asymmetrical shaped charge having an
insert
attached to a liner;
[0029] Figure 11 is a top view of the asymmetrical shaped charge having
the
insert attached to the liner;
[0030] Figure 12 illustrates the distribution of the initiation points;
[0031] Figure 13 illustrates an asymmetrical shaped charge having an
asymmetrical case;
[0032] Figure 14 is a flowchart of a method for making an asymmetrical
shaped charge;
[0033] Figure 15 illustrates a liner having an insert completely embedded
into
the liner;
[0034] Figure 16 illustrates a liner having an insert asymmetrically
embedded
into the liner;
[0035] Figure 17 illustrates a liner having an insert flush with a surface
of the
liner;
[0036] Figure 18 illustrates a liner having an insert and a certain
profile;
[0037] Figures 19A to 19D illustrate various perforations that may be made
in
a casing with one or more of the shaped charges discussed herein;
[0038] Figure 20 is a flowchart of a method for making a liner as
illustrated in
one of the Figures 15-18; and
[0039] Figure 21 illustrates a gun that has one or more of the shaped
charges
discussed herein.
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DETAILED DESCRIPTION
[0040] The following description of the embodiments refers to the
accompanying drawings. The same reference numbers in different drawings
identify
the same or similar elements. The following detailed description does not
limit the
invention. Instead, the scope of the invention is defined by the appended
claims.
The following embodiments are discussed, for simplicity, with regard to a
perforating
gun used for perforating a casing in a well. However, the embodiments
discussed
herein may be used for guns in another context.
[0041] Reference throughout the specification to "one embodiment" or "an
embodiment" means that a particular feature, structure or characteristic
described in
connection with an embodiment is included in at least one embodiment of the
subject
matter disclosed. Thus, the appearance of the phrases "in one embodiment" or
"in
an embodiment" in various places throughout the specification is not
necessarily
referring to the same embodiment. Further, the particular features, structures
or
characteristics may be combined in any suitable manner in one or more
embodiments.
[0042] According to an embodiment, a shaped charge includes a case, an
explosive material, a liner, and a booster material. The explosive material is
sandwiched between the case and the liner and the booster material is in
contact
with the explosive material, at one edge of the explosive material. At least
one of
these elements of the shape charge is made to be asymmetrical regarding a
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longitudinal axis (symmetry axis) of the shaped charge. In one variation,
although all
the above elements of the shaped charge are symmetrical relative to the
symmetry
axis, one or more inserts are added to one or more of these elements and the
insert
is made asymmetrical. For example, the insert may be asymmetrical in shape
relative to the longitudinal axis. However, in one application, the insert may
have a
symmetrical shape, but asymmetrical properties, i.e., different physical
properties as,
for example, a melting point, impedance, etc. In one application, the insert
is made
of an inert material, i.e., a material that does not explode, ignite, or burns
under
natural conditions. These possible implementations of an asymmetrical shaped
charge are now discussed.
[0043] A shaped charge 400 is illustrated in Figure 4 as having a case 402.
Case 402 may be made of any material that is strong enough to resist when the
explosive material explodes. For example, the case may be made of steel or a
metal. The case may take any shape, for example, conical, cylindrical,
spherical,
hemispherical, bell-shaped, parabolic or hyperboloid. Figure 4 shows the case
402
having a cup shape, with a solid back wall 404 having a channel 406 in which
the
booster material 430 is located. The back wall 404 is also called herein a
closed
end. A pedestal 405, which is attached to the back wall 404 (made either
integrally
or separately of the pedestal) is used to attach the shaped charge to a
carrier (not
shown) in the gun and affix the detonation cord. The channel 406 may extend
through the pedestal 405, along the symmetry axis X. The back wall 404
continues
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with a side wall 408 that is shaped as a cup. A top 409 of the case 402 is
open. For
this reason, this part of the case is called an open end.
[0044] An explosive material 410 is placed inside the cup shaped case 402.
The explosive material 410 is typically packed inside the case 402 by micro-
forging
or other methods. The explosive material may be a high explosive material,
like
NONA, ONT, RDX, HMX, HNS, BRX, PETN, CL-20, HNIW, PYX, TATB, TNAZ,
HNIW, or other known explosive. The liner 420 covers the explosive material
410
and keeps it inside the case 402. The liner 420 may be made of a reactive or
an
inert material, e.g., metal particles mixed with a light glue, so that the
liner appears
like a metallic sheet.
[0045] The booster material 430 is placed at the bottom of the case 402, in
the
channel 406. The booster material 430 is connected to a detonation cord 440,
which
initiates the detonation of the booster material 430. The booster material
includes a
detonation material, which may be the same as the explosive material 410 or
different. When the gun is fired, the gun detonator is first detonated, which
initiates
the detonation cord 440. The detonation cord 440 initiates the booster
material 430.
The detonation of the booster material 430 starts the explosion of the
explosive
material 410. Thus, in the embodiment of Figure 4, there is a single
initiation point,
at the interface between the booster material 430 and the explosive material
410.
The explosive material 410 is then initiated, which generates a detonation
wave.
The detonation wave collapses the liner 420 and melts it at the same time,
resulting
in a jet of material, which is expelled from the case 402 through the open end
409
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with a high energy. If the arrangement of the elements shown in Figure 4 is
symmetrical relative to the longitudinal axis X (the terms "longitudinal axis
X" and
"symmetry axis X" are used herein interchangeably), then the jet has
substantially a
circular cross-section and would generate substantially a circular hole in the
casing
of the well.
[0046] However, in the embodiment of Figure 4, the liner 420 is not made
to
be symmetrical to the longitudinal axis X. As shown in the figure, the case
402
extends along the longitudinal axis X up to a height having the coordinate x1.
One
side 420A of the liner 420 extends to a height having the coordinate x2 (which
may
be the same or smaller than x1) and the opposite side 420B of the liner 420
extends
to a height having the coordinate x3, which is different from coordinate x2.
This
means that the liner 420 is tilted relative to the case 402 and the symmetry
axis. If
the symmetrical reference position 422 of the traditional liner relative to
the
symmetry axis X is considered to correspond to a zero angle, the tilted novel
liner
420 can make any non-zero angle 9 with the reference position. In one
application,
it is possible that the liner has its own symmetry axis X' and the entire
liner is tilted
so that the symmetry axis X' makes the non-zero angle 9 with the symmetry axis
X.
However, in another embodiment, only a portion of the liner is tilted while
the
remaining part of the liner is not tilted, so that the liner itself has no
symmetry axis.
Irrespective of how the non-symmetrical liner is implemented, the non-symmetry
of
the liner would also make the explosive material 410 to be not symmetric
relative to
the longitudinal axis X.
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[0047] In another embodiment illustrated in Figure 5, the explosive
material
410, the liner 420, and the case 402 are all symmetrical relative to the
longitudinal
axis X. However, the booster material 430 is not symmetrical. Figure 5 shows
that
the channel 506 is formed to extend along a longitudinal axis X", which makes
a
non-zero angle a with the symmetry axis X. Note that in the embodiment of
Figure
4, the longitudinal axis X and the axis X" would have been coincident if axis
X"
would have been shown there. In other words, the channel in Figure 5 has a
longitudinal axis X", which makes a non-zero angle with the symmetry axis X.
This
means that the booster material fires along an axis that is not the symmetry
axis X.
In one application, the booster material fires toward a side wall 408 of the
case 402.
[0048] As previously discussed, the booster material 430 constitutes the
initiation point for the explosive material. Due to the asymmetry of the
booster
material, the propagation of the detonation front becomes also asymmetrical
inside
the explosive material 410 while inside the case 402, which results in the
expelled jet
being non-symmetrical. As will be discussed later, by controlling the
asymmetry of
the shaped charge, the expelled jet is expected to form a key hole shape in
the
casing or a slot with a desired orientation relative to a longitudinal axis of
the casing
of the well.
[0049] In one embodiment, it is possible to combine the asymmetric
features
shown in Figures 4 and 5, i.e., to have a shaped charge with a tilted liner
and the
booster material oriented away from the symmetry axis X of the case.
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[0050] According to another embodiment, as illustrated in Figure 6, the
channel 606 is physically offset from the symmetry axis X, with a given
distance d.
In this way, the channel 606 is asymmetrically positioned relative to the
symmetry
axis X and/or the case 402, so that the generated jet is expected to form a
key hole
or slot shape into the casing of the well. In still another embodiment, the
channel
606 axis X" may make a non-zero angle with the symmetry axis X, similar to the
embodiment shown in Figure 5, except that the channel 606 is also offset from
the
symmetry axis X. In yet another embodiment, one or more additional channels
606'
may be formed in the base wall 404, also offset from the symmetry axis X. The
additional channel 606' extends along its own longitudinal axis X¨, which may
be
parallel to axis X" of channel 606, or they may make a non-zero angle. In one
application, the two channels 606 and 606' are located asymmetrically relative
to the
symmetry axis X, as shown in Figure 6. In still another application, one of
the
channels 606 and 606' is oriented to have the longitudinal axis parallel to
the
symmetry axis X while the other channel makes a non-zero angle with the
symmetry
axis X. Any other variation of these arrangements that achieves a non-
symmetrical
jet may be used, for example, combining one or both of the embodiments
illustrated
in Figures 4 and 5 with this embodiment.
[0051] According to another embodiment, which is illustrated in Figure 7,
the
explosive material 410 is made to have at least two different volumes 712 and
714
that differ from each other in one characteristic. The volumes may have any
shape,
may be the same or different, as long as an asymmetry in the generated jet is
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achieved. The characteristic may be the chemical composition, density,
electrical
impedance, strength, thermodynamic stability, etc. This embodiment may be
combined with one or more of the previously discussed embodiments to further
control the asymmetry of the generated jet.
[0052] In another embodiment, as illustrated in Figure 8, an insert 800 is
added to the shaped charge to achieve the desired asymmetry. The insert 800
may
have any shape, may be made of ferrous, inert or composite materials, may have
any thickness and may be positioned anywhere inside the explosive material 410
as
long as it generates an asymmetry in the detonation wave, to obtain a
controlled
asymmetrical jet. Although the insert 800 is shown in Figure 8 as being placed
in
one half of the case 402, it is possible to place the insert to extend in both
halves of
the case. Also, the thickness of the insert does not have to be constant as
illustrated
in the figure. The insert 800 is not placed to separate the explosive material
410
from the booster material 430.
[0053] In one variation of the embodiment of Figure 8, the insert is
attached to
the case 402, either as insert 810 to the wall 408, or as insert 820 to the
back wall
404. In still another application, an insert 830 may be placed inside the
channel 406.
In one embodiment, one or more of the inserts 800, 810, 820, and 830 may be
located inside the case 402. One or more of the inserts 800, 810, 820, and 830
may
have a window 802 cut into it, as illustrated in Figure 9, which shows a top
view of
the shaped charge 400. Th inserts discussed herein may be combined in any way.
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[0054] In another variation of the embodiment of Figure 8, the insert may
be
attached to the liner 420 as illustrated in Figure 10 (see element 1000). The
insert
1000 may be made of metal, ceramic, polymer or other materials. Similar to the
embodiments of Figures 8 and 9, the insert 1000 may have any shape, thickness
or
may have a window. The insert 1000 may directly deposited on the liner with a
3D
printer. In one application, the insert 1000 is achieved by painting the back
of the
liner 420 with a thick bead substance, for example, glyptol, glue, epoxy, or
other
polymers. In still another application, the insert 1000 may be a pocket of air
or air
trapped within a printed or foamed material. The insert 1000, similar to the
insert
800, may be attached to only a sector of the liner 420, or all around the
liner as
illustrated in Figure 11, which shows a top view of the liner. While Figures
10 and 11
shows the formation of the insert 1000 on the back of the liner, i.e., between
the liner
and the explosive material 410, it is also possible to form the insert on top
of the
liner, on the opposite side of the explosive material. Note that the various
asymmetric features discussed in the previous embodiments may be combined in
any way.
[0055] For any of the above discussed embodiments, if two inserts 1200 and
1210 are used, they may be distributed inside the case 402 so that an angle )3
between the two inserts is in the range of 165 to 195 , as illustrated in
Figure 12. In
this way, a variable initiation profile in the initiation section (i.e.,
booster material) of
the shaped charge is obtained, which is responsible for the generation of an
asymmetric detonation wave front, which ultimately results in the asymmetric
jet.
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This asymmetric jet then creates the key hole and/or slots in the casing of
the well.
The inserts discussed above can be made, not only of metallic, polymer or
plastic
materials, but also from ceramic, e.g., silica sand.
[0056] In still another embodiment, as illustrated in Figure 13, it is
possible to
make the case 402 to be asymmetrical. The wall 408 is made to have a part 408A
having a first shape and another part 408B having a different shape. The shape
is
directly associated with the volume of explosive material 410 held by the
respective
part. For example, Figure 13 shows the part 408A of the wall being shaped to
hold
less explosive material 410 than the wall part 408B. The same is true for the
parts
404A and 404B of the back wall. Note that channel 406 still extends along the
former symmetry axis X, which is not a symmetry axis for this embodiment.
[0057] The liner 420 has a smaller part 422 that corresponds to the
smaller
volume of explosive material hold by the part 408A of the lateral wall 408 and
a
larger part 424 corresponding to the part 408B. Thus, for the embodiment shown
in
Figure 13, each of the case 402, the liner 420, and the explosive material 410
are
asymmetrical relative to the symmetry axis X. In one modification of this
embodiment, it is possible to make the liner 420 and the explosive material
410
symmetrical relative to an axis X' parallel to symmetry axis X. Further, in
another
modification, it is also possible to tilt the liner, or to implement any of
the
asymmetries discussed above with regard to Figures 4-12.
[0058] A method for manufacturing an asymmetrical shaped charge 400 (as
shown in any of the Figures 4-13) is now discussed with regard to Figure 14.
In step
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1400, a case 402 is provided. The case 402 may have a symmetry axis X, which
is
also a longitudinal axis. However, the case may also be asymmetric. In step
1402,
the channel 406 is made into the back wall 404 of the case 402. The channel
406
may be made along the symmetry axis X, inclined relative to this axis, or
offset from
the symmetry axis. If the channel 406 is made offset from the symmetry axis X,
it
may also be made to extend along an axis X" that is parallel to the symmetry
axis X,
or axis X" makes a non-zero angle with the symmetry axis X. In one embodiment,
more than one channel 406 is formed into the back wall 404 of the case 402, so
that
all these channels are asymmetrically distributed relative to the symmetry
axis X.
[0059] In step 1404, the booster material 430 is placed into the channel
406
by any known method. If more than one channel 406 is formed, the channels may
be distributed as illustrated in Figure 12, to achieve a desired angle between
the
initiation points. In step 1406, the explosive material 410 is added to the
interior of
the case 402. The explosive material can be added by any known means. The
explosive material 410 may be made to be uniform or not. If the explosive
material is
not uniform, at least one characteristic of the explosive material may vary
inside the
case, as discussed above with reference to Figure 7. In one application,
another
material may be inserted at specific locations inside the case to vary the
characteristic (e.g., density, explosive strength, flammability) of the
explosive
material. The another material may be the insert 800 or 1000 discussed above,
or
even air or another inert material. The explosive material 410 may be made to
be
symmetrical or not relative to the symmetry axis X. The symmetry refers to the
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volumetric distribution of the explosive material, or to at least another
characteristic
(as discussed above) of the explosive material.
[0060] In step 1408 the liner 420 is formed. The liner may be formed by
injection mold, 3D print, machined, cast, extrusion, stamping, mold,
microforge, etc.
The liner 420 may be made to be symmetric relative to the symmetry axis X or
not.
In one embodiment, one side of the liner is made larger than the other side of
the
liner, as illustrated in Figure 13. In one application, the liner is shaped as
a trumpet
for directing the explosive energy to a desired location. In optional step
1410, an
insert 1000 may be attached to the liner as illustrated in Figure 10.
Alternatively, an
insert 800 may be added to the explosive material 410 or the case 402 as
illustrated
in Figure 8. In still another application, the insert may be added to the
channel 406,
to make the entire shaped charge asymmetrical, as shown in Figure 8. Step 1410
may be performed at any time during the method, depending where the insert is
placed. Finally, in step 1412 the liner is attached to the case so that the
shaped
charge is ready to be used.
[0061] In the above discussed embodiments, the asymmetry of the shaped
charge has been added to one of the elements of the shaped charge. However, it
is
possible to introduce an asymmetry into the structure of the liner itself.
Thus, the
next embodiments discuss these possibilities. Figure 15 shows a liner 420
disposed
symmetrically around the symmetry axis X. However, different from the previous
embodiments, an insert 1500 is located completely within the liner 420, i.e.,
no face
or edge of the insert 1500 is facing the explosive material 410 or the ambient
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the shaped charge 400. The insert 1500 may be made of the same materials as
the
inserts 800 and 1000, and it may be manufactured by forging, molding, or
printing.
The insert 1500 may be symmetric relative to the symmetry axis X, extends
along
the liner 420, but not over the entire liner so that a central portion 426 of
the liner 420
has the insert and a peripheral portion 428 of the liner is free of the
insert. Thus, in
this embodiment, both the liner 420 and the insert 1500 are symmetrical
relative to
the symmetry axis X, but the asymmetry of the shaped charge is achieved
because
the insert does not extend over the entire liner.
[0062] The liner 1500 (and other liners illustrated in other figures) may
have a
generally concave shape. The concave shape may be symmetrical or not relative
to
the symmetry axis X. The concave shape may be implemented in many ways, for
example, as a trumpet, cone, bell, hemispherical, etc. The liner 420 includes
at least
one type of powdered metal 1502. The metal may be copper, tin, nickel,
tungsten,
lead, molybdenum or a combination of these materials. The metallic powder is
held
together with a binder 1504. The binder can be a glue, polymer or other
material. In
one application, the liner is machined from a solid piece of material. In
another
application, the liner is printed, forged, or molded.
[0063] In another embodiment illustrated in Figure 16, an insert 1600 is
located only in one portion of the liner and not in an opposite portion. Thus,
the
asymmetry of the shaped charge is achieved in this embodiment because of the
location of the insert within the liner. The asymmetry shown in either Figure
15 or
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Figure 16 may be combined with any of the previously discussed asymmetries of
the
shaped charge.
[0064] The embodiment of Figure 17 is similar to that of Figure 16, except
that
a face 1700A of the insert 1700 is fully exposed either to the ambient or to
the
explosive material 410, i.e., a face of the insert is flush with a front or
back face of
the liner 420.
[0065] The embodiment illustrated in Figure 18 shows the liner 420 having
the
insert 1800 distributed according to any of the embodiments of Figures 15-17,
but an
angle y between the symmetry axis X and an arm of the liner is between 20 and
40 ,
or between 100 and 120 .
[0066] Any of the configurations discussed above achieves a jet of material
that is not symmetrical. Based on experiments performed by the inventors, one
or
more of these asymmetrical configurations may generate the following holes in
a
casing. Figure 19A shows a part of a casing 1902 that extends along a
longitudinal
axis X2, which coincides with the longitudinal axis X1 of the well. A slot
1910 is
formed in the casing with one of the above shaped charge configurations. The
slot
1910 extends along the longitudinal axis X1 due to the orientation of the
asymmetry
of the shaped charge. The slot 1910 is defined as having a middle portion 1912
that
has the largest size along an axis Y1 perpendicular to the longitudinal axis
X1, and
two end portions 1914 and 1916 that narrow when moving away from the middle
portion 1912.
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[0067] Figure 19B shows a key hole perforation 1920 formed in the casing
1902. The key hole perforation 1920 is defined as having a head portion 1922
that is
substantially circular, and a tail portion 1924, that has a decreasing size.
The key
hole perforation 1920 was made so that it extends along the X2 axis, with its
head
portion closer to a heel of the casing (when the casing is used in a
horizontal well) so
that the pumping of the slurry does not erodes substantially this portion. In
this
embodiment, the shaped charge is selected to have the longitudinal axis X2 of
the
key hole aligned with the longitudinal axis X1 of the casing.
[0068] By changing the orientation and/or location of the asymmetry in the
shaped charge, it is possible to control the position of the longitudinal axis
X2 of the
slot 1910 or key hole 1920. For example, as shown in Figure 190, four key
holes
1930-1 to 1930-4 are formed so that their head portions are substantially
superimposed and their tails are distributed as the spokes of a wheel. For
obtaining
such a configuration, four different shaped charges are used. After the first
key hole
1930-1 is made with a first shaped charge, the gun is moved so that a second
shaped charge is aligned with the head portion of the first key hole. As the
second
shaped charge is rotated relative to the first shaped charge, i.e., the
initiation point(s)
of the first shaped charge are angularly offset from the initiation point(s)
of the
second shaped charge, the second shaped charge forms the second key hole 1930-
2. The process continues until all four shaped charges are fired and the
configuration shown in Figure 190 is obtained. More or less than four shaped
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charges may be fired at the same location of the casing for obtaining a star
configuration or a triangle configuration, or other configurations.
[0069] Figure 19D shows a configuration in which a slot 1940 and two key
holes 1950-1 and 1950-2 are formed to have a common area 1942. Similar to the
embodiment of Figure 190, more or less shaped charges may be used to obtain
different perforation configurations.
[0070] For all the embodiments discussed herein, while the asymmetric
shaped charges may be attached to the gun carrier to be perpendicular to the
longitudinal axis of the casing, it is also possible to have the shaped
charges
installed with a non-zero angle relative to the axial direction of the casing.
In one
embodiment, it is possible that some asymmetrical shaped charges are
perpendicular to the longitudinal direction of the casing while the other
asymmetrical
shaped charges are tilted to the axial direction. Further, in one application
it is
possible to combine traditional, symmetrical, shaped charges with one or more
of the
novel asymmetrical shaped charges discussed above.
[0071] One advantage of making key hole perforations is that it can be made
in a consistent manner. Traditional slot charges are very sensitive to the
water gap
and pressure, and will produce suboptimal results in downhole conditions. The
key
hole perforation produced with the asymmetrical shaped charge discussed above
has a consistent hole size, with the key hole extending the opportunity for
sand
placement.
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[0072] Another possible advantage is that the traditionally eroded holes
tend
to be shaped like a key hole, so that by directly producing a key hole
perforation, it is
likely to be less eroded by the sand placement.
[0073] In one embodiment, the perforations will be a tapered slot,
generated
by a slot producing charge being held at an angle within the gun body
(generally
tilted toe-ward, but could be either way) so that the travel distances for the
various
parts of the jet are not symmetric, which will result in a narrowing slot.
[0074] A method for making the liner shown in Figures 15-18 is now
discussed
with regard to the flowchart illustrated in Figure 20. In step 2000, the
material for an
insert 1500, 1600, 1700 or 1800 is selected. In step 2002, the insert is made
into the
desired shape. Any known method that is used for making the liner may be used
to
form the insert. Then, in step 2004, the insert is positioned at one of the
positions
shown in Figures 15-18, inside the material of the liner, and in step 2006 the
material
of the liner is pressed (other methods may be used) to create the liner. Note
that at
least a first face of the insert is fully embedded within the liner as
illustrated in any of
the embodiments of Figures 15-18. In one embodiment, at least a second face of
the insert is partially, if not totally embedded within the liner. In some
embodiments,
more than two faces (even all the faces) of the insert are fully embedded into
the
liner. In still another embodiment, only one face is not fully embedded into
the liner.
[0075] A gun having one or more of the shaped charged discussed with
regard to Figures 4-20 is illustrated in Figure 21. Gun 2100 includes a gun
carrier
2110 that houses one or more shaped charges 400. The gun carrier may be shaped
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as a cylinder and may be sealed from the casing of the well. A first shaped
charge
400 has its symmetry axis X making a non-zero angle with a radial axis Y,
which is
perpendicular on the longitudinal axis L of the gun carrier. However, a second
shaped charge 400 is shown having its symmetry axis X making a zero angle with
the radial axis Y. Any number of shaped charges 400 may be positioned within
the
gun carrier. In one embodiment, traditional shaped charges 150 (discussed with
regard to Figure 3) are mixed up with the asymmetrical shaped charges 400.
[0076] The disclosed embodiments provide methods and systems for
generating a slot or key hole perforation into a casing of a well, by using at
least a
shaped charge that has an asymmetrical feature. It should be understood that
this
description is not intended to limit the invention. On the contrary, the
exemplary
embodiments are intended to cover alternatives, modifications and equivalents,
which are included in the spirit and scope of the invention as defined by the
appended claims. Further, in the detailed description of the exemplary
embodiments, numerous specific details are set forth in order to provide a
comprehensive understanding of the claimed invention. However, one skilled in
the
art would understand that various embodiments may be practiced without such
specific details.
[0077] Although the features and elements of the present exemplary
embodiments are described in the embodiments in particular combinations, each
feature or element can be used alone without the other features and elements
of the
embodiments or in various combinations with or without other features and
elements
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disclosed herein.
[0078] This written description uses examples of the subject matter
disclosed
to enable any person skilled in the art to practice the same, including making
and
using any devices or systems and performing any incorporated methods. The
patentable scope of the subject matter is defined by the claims, and may
include
other examples that occur to those skilled in the art. Such other examples are
intended to be within the scope of the claims.
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