U.S. patent application number 09/394792 was filed with the patent office on 2002-02-14 for perforating devices for use in wells.
Invention is credited to ASELTINE, CLIFFORD L., ASELTINE, MARGARET LYNN, BROOKS, JAMES E., JACOBY, JEROME J..
Application Number | 20020017214 09/394792 |
Document ID | / |
Family ID | 26796932 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020017214 |
Kind Code |
A1 |
JACOBY, JEROME J. ; et
al. |
February 14, 2002 |
PERFORATING DEVICES FOR USE IN WELLS
Abstract
The perforating device for use in completing a well includes a
case, an explosive charge contained in the case, and a generally
bowl-shaped liner. The liner is positioned adjacent the explosive
charge and has non-uniform thickness along its length. The liner
further includes a protruding portion near its tip. In another
configuration, the liner includes a hole near its tip to expose a
portion of the explosive charge.
Inventors: |
JACOBY, JEROME J.; (GRASS
VALLEY, CA) ; BROOKS, JAMES E.; (MANVEL, TX) ;
ASELTINE, CLIFFORD L.; (HOUSTON, TX) ; ASELTINE,
MARGARET LYNN; (HOUSTON, TX) |
Correspondence
Address: |
JEFFREY E GRIFFIN
SCHLUMBERGER TECHNOLOGY CORPORATION
14910 AIRLINE ROAD
P O BOX 1590
ROSHARON
TX
775831590
|
Family ID: |
26796932 |
Appl. No.: |
09/394792 |
Filed: |
September 13, 1999 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60100233 |
Sep 14, 1998 |
|
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Current U.S.
Class: |
102/307 |
Current CPC
Class: |
F42B 1/028 20130101 |
Class at
Publication: |
102/307 |
International
Class: |
F42B 001/00; F42B
001/02 |
Goverment Interests
[0002] The United States Government has rights in this invention
pursuant to Contract No. W-7405-ENG-48 between the U.S. Department
of Energy and the University of California, for the operation of
Los Alamos National Laboratory, and pursuant to CRADA No.
LA93C10074, "Advanced Down-Hole Perforating Technologies," between
Schlumberger Perforating and Testing Center and Los Alamos National
Laboratory.
Claims
What is claimed is:
1. A perforating device for use in completing a well, comprising: a
case; an explosive charge contained in the case; and a generally
bowl-shaped liner positioned adjacent the explosive charge and
having non-uniform thickness along its length, the liner further
including a protruding portion near its apex.
2. The perforating device of claim 1, wherein initiation of the
liner produces a perforating jet having a bulged portion in which
gas is encapsulated to enhance a size of the bulged portion.
3. The perforating device of claim 1, wherein the protruding
portion includes a generally nipple-shaped protrusion into the
explosive charge.
4. The perforating device of claim 1, wherein the protruding
portion includes a generally conical-shaped protrusion into the
explosive charge.
5. The perforating device of claim 1, wherein the liner has a first
section that is generally parabolic and a second section that is
generally conical
6. The perforating device of claim 5, wherein the liner thickness
increases gradually in the generally parabolic section and
increases in steps in the generally conical section.
7. The perforating device of claim 5, wherein the generally
parabolic section has an increasing radius of curvature with
increasing distance from its center axis.
8. The perforating device of claim 1, wherein the liner has a
segment that increases in thickness with distance from the liner's
apex.
9. The perforating device of claim 1, wherein the liner increases
in thickness along its length.
10. The perforating device of claim 1, wherein step increases in
thickness are formed at predetermined locations in the liner.
11. The perforating device of claim 10, wherein the step increases
in thickness are formed on the convex surface of the liner.
12. The perforating device of claim 10, wherein the step increases
in thickness are formed on the concave surface of the liner.
13. The perforating device of claim 1, wherein the liner is divided
into a segment that increases in thickness with increasing distance
from the liner's apex and a segment that decreases in thickness
with increasing distance from the liner's apex.
14. A perforating device for use in a well, comprising: a case; an
explosive charge contained in the case; and a liner positioned
adjacent the explosive charge and having a hole near its apex to
expose the explosive charge.
15. The perforating device of claim 14, wherein the explosive
charge includes a cavity adjacent the liner hole.
16. The perforating device of claim 15, wherein the cavity is
generally bowl-shaped.
17. The perforating device of claim 15, wherein the cavity is
generally conical-shaped.
18. A method of creating a large diameter perforation using a
perforator comprising: forming a liner having variable thickness
along its length; and firing the detonator to collapse the liner to
form a thick perforating jet.
19. The method of claim 18, wherein the liner increases in
thickness with increasing distance from its apex.
20. The method of claim 18, further comprising forming a protruding
portion in the liner.
21. The method of claim 18, wherein collapse of the liner forms a
perforating jet having a bulged portion that encapsulates gas to
increase a size of the bulged portion.
22. The method of claim 18, further comprising forming a hole in
the liner near its apex.
23. The method of claim 22, wherein the liner is contacted to an
explosive charge, the method further comprising forming a cavity in
the explosive adjacent the liner hole.
24. A well completion apparatus comprising: a perforating gun; and
a shaped charge perforator positioned in the gun, the shaped charge
perforator having an explosive charge and a generally bowl-shaped
liner that has a thickness that increases with distance from its
apex.
25. The apparatus of claim 24, wherein the liner further includes a
protruding portion near its apex.
26. The apparatus of claim 25, wherein the protruding portion
includes a generally nipple-shaped bump.
27. The apparatus of claim 25, wherein the protruding portion
includes a generally conical-shaped portion.
28. The apparatus of claim 24, wherein the liner has step increases
in thickness along its length.
29. The apparatus of claim 24, wherein the liner includes a hole
near its apex.
30. The apparatus of claim 29, wherein the explosive charge has a
cavity formed adjacent the liner hole.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority under 35 U.S.C.
.sctn. 119(e) to U.S. Provisional Patent Application Serial No.
60/100,233, entitled "Perforating Devices Used in Wells," filed
Sep. 14, 1998.
BACKGROUND
[0003] The invention relates to perforating devices for use in
wells.
[0004] Perforating devices have been used by the oil-well service
industry for many years to complete oil and natural gas wells. When
wells are drilled into deep rock formations, they are cased to
prevent the surrounding rock, sand, and water from invading the
wellbore and interfering with the production of oil or natural gas.
A typical casing material is high-strength steel pipe. In
completing a well, a perforating device having an array of
perforators (which may be shaped charge perforators) is lowered
downhole into the well in a perforating gun. When the gun is at the
correct depth in the well the perforators are fired, sending shaped
charge jets outward first through the side of the gun, then through
the fluid between the gun and the casing, through the well casing,
and finally into the oil-bearing or natural gas-bearing rock. The
resulting holes in the well casing allow the oil or natural gas to
flow into the well and to the surface. What remains of the gun may
be withdrawn from the well after the perforators have been
fired.
[0005] The downhole formation adjacent the well may have many
different characteristics. As examples, the formation may include
competent rock that contains oil, gas or a loosely consolidated
sand containing hydrocarbons. These types of formations govern the
kind of perforators that are needed to complete the well. In the
first case a perforator is needed that produces a large depth of
penetration so that the maximum amount of rock is exposed to the
hole in the well casing. In the latter case a perforator is needed
that makes as large a hole in the well casing as possible so that
gravel can be pumped through the hole to form a gravel pack, and
depth of penetration is a secondary consideration. Penetrators used
to create such large holes are sometimes referred to as big hole
penetrators.
[0006] A shaped charge perforator may include a liner, a case to
contain the liner, a high explosive, and some mechanism to initiate
the detonation of the explosive. Typical materials for the case
include steel or zinc. Typical liner materials include wrought
materials such as copper, zinc, and various alloys or pressed
powder including a mixture of copper, lead, and tungsten. An often
used initiation mechanism includes a detonating cord that is
positioned onto an opening at the rear of the perforator. Since the
gun is typically withdrawn from the well after the perforators are
fired, there is a constraint on the amount of explosive in the
perforators. Furthermore, since perforators are used in large
numbers every year, cost is a very important factor--both materials
cost and manufacturing cost.
[0007] One way of manufacturing liners includes deep drawing a
metal sheet into various shapes, such as conical, hemispherical
shapes, and parabolic. Because ease of manufacture is an important
consideration, these deep-drawn liners have approximately uniform
thickness that approximates the uniform thickness of the original
metal sheet. In order to be deep drawn, the liner material must be
very ductile, so copper is often the material of choice. Other
reasons for favoring copper are that copper has good penetration
properties and copper is comparatively inexpensive.
SUMMARY
[0008] In general, according to an embodiment, a perforating device
for use in completing a well includes a case, an explosive charge
contained in the case, and a generally bowl-shaped liner positioned
adjacent the explosive charge and having non-uniform thickness
along its length. The liner includes a protruding portion near its
apex.
[0009] Other features of the invention will become apparent from
the following description and from the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a diagram of a shaped charge perforator according
to an embodiment of the invention that has a liner with a
nipple-shaped protrusion.
[0011] FIGS. 2A-2F illustrate the jet formation and penetration of
the gun and well fluid upon activation of the shaped charge
perforator of FIG. 1.
[0012] FIG. 3 is a diagram of a shaped charge perforator according
to another embodiment of the invention that has a liner with a
conical-shaped protrusion.
[0013] FIG. 4 is a diagram of a shaped charge perforator according
to yet another embodiment that has a liner with a nipple-shaped
protrusion.
[0014] FIG. 5 is a diagram of a shaped charge perforator according
to a further embodiment that has a liner with a shallow
protrusion.
[0015] FIGS. 6A-6D illustrate the jet formation and penetration of
the gun and well fluid when the shaped charge perforator of FIG. 5
is activated.
[0016] FIGS. 7A-7C are diagrams of shaped charge perforators
according to yet further embodiments of the invention.
[0017] FIG. 8 is a diagram of a perforating string incorporating an
embodiment of the invention.
DETAILED DESCRIPTION
[0018] In the following description, numerous details are set forth
to provide an understanding of the present invention. However, it
will be understood by those skilled in the art that the present
invention may be practiced without these details and that numerous
variations or modifications from the described embodiments may be
possible.
[0019] A perforating device according to some embodiments of the
invention includes a shaped charge perforator adapted to form a
perforating jet that makes a relatively large hole in the
surrounding well casing during well completion.
[0020] Referring to FIG. 1, a perforating device according to an
embodiment of the invention includes a shaped charge perforator 8
having a liner 10 and an explosive charge 20, both contained in a
case 30 (which can be made of steel, for example). A dotted line L
through the center of the shaped charge perforator 8 generally
represents the axis of symmetry of the liner 10 and explosive 20. A
detonating cord (not shown) may be positioned in an opening 31
located generally at the rear of the case 30. The outer surface 30A
of the case 30 may be formed to fit into a holding apparatus inside
a perforating gun (such as the gun shown in FIG. 7).
[0021] The liner 10 may include a powder that is a mixture of
copper and lead or some other high-density material, including tin,
zinc, aluminum, tungsten, nickel, silver, gold, tantalum, or a
metal alloy. Further, solid liners may be used. Using the standard
techniques of pressing metal powders, virtually any shape liner can
be made. Typically, the assembly of perforators is done by pressing
the drawn liner 10 into a pre-made case 30, into which the correct
amount of explosive charge 20 has been poured. The explosive charge
20 may optionally be pressed into a shape to accept the liner 10
prior to the liner being pressed into the final assembly. The liner
10 may be made slightly oversized to ensure a tight fit within the
case 30. This tight fit of the liner 10 and explosive charge 20 in
the case 30 helps keep the entire perforator device intact during
shipment, assembly into the gun, and lowering of the gun down the
well into a firing position.
[0022] The case 30 may be generally axially symmetric (with respect
to the axis L) except at the surface 31, which represents a slot in
the rear end of the case where the detonating cord (not shown) is
in contact with the explosive charge 20. The inner surface 30B of
the case 30 defines the shape of the main explosive 20 and the
liner 10. Upon initiation of the perforating device 8, the case 30
acts to confine the main explosive 20.
[0023] The liner 10 of the perforating device 8 has a generally
bowl-like or semi-hemispherical shape. The generally bowl-like
shape of the liner 10 aids in producing a perforating jet pattern
upon firing that creates an entrance hole in the surrounding well
casing having a relatively large diameter (a "big hole"). Other
liner shapes can also create big holes, including liners that are
generally conical-shaped, parabolic-shaped or tulip- or
trumpet-shaped. According to an embodiment, the thickness of the
liner 10 may vary according to its distance from the center axis
L.
[0024] The liner 10 also includes a protruding portion 11 that is
formed generally near the apex or tip (represented generally as 25)
of the bowl-shaped liner 10. The protruding portion 11 according to
the illustrated embodiment is generally nipple-shaped, having a
slight groove 11B on the inner surface 10B of the liner 10 (the
concave surface facing away from the gun). On the outer surface 10A
of the liner 10 (the convex surface facing the main explosive
charge 20), a generally rounded bump or hill-shaped portion 11A is
formed that is integral with the liner 10. Thus, as illustrated,
the protruding portion 11 juts out into the explosive charge 20
from the rest of the liner 10.
[0025] The liner 10 in the illustrated embodiment is separated into
several sections (represented by S.sub.i-j), each generally
symmetrical about its center axis L. However, it is contemplated
that the liner 10 need not be generally symmetrical about its
center axis L in other embodiments. In the embodiment of FIG. 1,
the multiple segments S of the liner 10 may each have different
curvatures. For example, a section S.sub.12-13 may be generally
parabolic or hyperbolic in shape, whereas the next section
S.sub.13-14 may be generally conical in shape. The section
S.sub.12-13 (defined between edges 12 and 13) is adjacent and
integrally connected to the nipple-shaped portion 11. In the
illustrated embodiment, the section S.sub.12-13 may be connected to
the nipple-shaped portion 11 at an angle that is nearly
perpendicular to the axis L. In section S.sub.12-13, the radius of
curvature of the liner 10 may increase with increasing distance
from its center axis L. Further, in the section S.sub.12-13, the
thickness of the liner 10 may gradually increase with distance away
from the apex of the liner 10. At edge 13, the generally parabolic
section S.sub.12-13 of the liner 10 joins a generally conical
section S.sub.13-14 that gradually increases in thickness from edge
13 to edge 14. At edge 14, the section S.sub.13-14 is connected to
another generally conical section S.sub.14-15. Further, at edge 14,
a step increase in thickness occurs from section S.sub.13-14 to
section S.sub.14-15. In the section S.sub.14-15, the liner 10 also
gradually varies in thickness between edges 14 and 15. At edge 15,
another step increase in thickness is formed between the sections
S.sub.14-15 and S.sub.15-16. In the section S.sub.15-16, the liner
10 may continue to increase in thickness until it reaches edge 16,
where the liner 10 beings to decrease in thickness in the last
section S.sub.END. Thus, the generally bowl-shaped liner 10 has a
thickness that increases from near its tip to the edge 16 with
several step increases formed in the liner 10 at predetermined
locations. The step increases may be formed on the outer surface
10A (the convex surface) of the liner 10.
[0026] Although, the embodiment of FIG. 1 includes a liner having a
thickness that increases with distance from a center axis, other
embodiments may include a liner in which the thickness may have
other variations.
[0027] Due to the protruding portion 11 and the varying liner
thickness, the liner 10 of the illustrated embodiment increases the
formation of a thick jet such that an entrance hole with increased
diameter may be created in the surrounding well casing. The
nipple-shaped portion 11 enables the collapsing liner 10 to
encapsulate some of the explosive gases during the jet formation
process while the increasing thickness of the parabolic or
hemispherical section of the liner 10 causes the formation of a
relatively thick jet. The encapsulated gas increases the diameter
of the jet over what it would otherwise be if the gas were not
encapsulated.
[0028] Because the liner has increasing radius of curvature with
increasing distance from the center axis L, a narrow, pointed jet
tip can be formed, which creates a relatively small opening in the
gun tube. Thus, during the initial collapse of the liner, a sharp
tip is formed in the perforating jet to make a small hole in the
gun tube. Having small holes in the gun tube prevents debris from
falling into and contaminating the wellbore. However, to create
large holes in the casing, a perforating jet with a large bulge is
needed. To accomplish this, the variable thickness liner is used in
which the thickness increases with increasing distance from the
apex of the liner. By having step increases in thickness at
predetermined locations in the liner, an extended bulge in the
perforating jet can be created. Further, by encapsulating a bubble
of explosive gases, the diameter of the resulting perforating jet
is also increased. Thus, embodiments of the invention may have the
advantage of being able to create large holes in the surrounding
casing while creating small holes in the gun tube.
[0029] In the illustrated embodiment, the explosive charge 20 may
also generally be bowl-shaped, and its thickness may be selected to
be thicker near the tip (indicated generally as 21) and decreases
in thickness gradually to 22, and further gradually decreases
thickness to 23. The inner surface 20B of the explosive charge 20
has an indented portion 20C that mates with the surface 11A of the
nipple-shaped portion 11 of the liner 10.
[0030] At its outer surface 20A (the convex surface contacting the
inner surface 30B of the case 30), the explosive charge 20 may have
a slanted segment 24 formed between a segment 25 that is coupled to
the primer cord (not shown) and the main body of the explosive
charge 20. When the explosive charge 20 is initiated, a detonation
wave starts in the segment 25 and sweeps in a forward direction.
The slanted segment 24 assists the detonation wave in turning the
corner from the segment 25 to the main body of the explosive charge
20. The configuration of the slanted segment 24 may vary with the
type of explosive charge used, since the ability of the detonation
wave of different types of charges to turn corners may be
different. The segment may be made smaller in those explosives that
are more sensitive, such as HMX (C.sub.4H.sub.8N.sub.8O.sub.8), and
larger in those explosives that are less sensitive, such as TATB
(C.sub.6H.sub.6N.sub.6O.sub.6).
[0031] The formation and penetration of the perforating jet from
the liner 10 of FIG. 1 is illustrated in FIGS. 2A-2F, which
represent snap-shots of the shaped charge formation and penetration
at different times. In all of these figures, a section 40
represents the wall of the perforating gun that holds the multiple
perforators during well completion, and well fluid outside the
perforating gun wall 40 is generally represented as 50. The well
casing (not shown) is to the right of the well fluid 50. When the
explosive charge 20 is detonated, the detonation pressure creates a
wave that collapses the liner 10. Material from the collapsed liner
10 flows along stream lines to form a perforating jet (such as the
jet 42). In FIG. 2A, shortly after detonation of the explosive, the
nipple-shaped portion 11 has collapsed to form a short slug 17. As
seen in FIGS. 2B-2F, the slug 17 moves very slowly compared to the
rest of the collapsing liner 10. In FIG. 2B, the liner 10 begins to
collapse, starting with section S.sub.12-13. In FIG. 2C, the
collapsing liner 10 forms a perforating jet 42. Also, a portion of
the slug 17 begins to break apart into particles. The liner 10
continues to collapse in FIGS. 2D-2F, with the liner collapsing
into the jet 42 in generally the following order: beginning with
the protruding portion 11 and followed by the sections S.sub.12-13,
S.sub.13-14, S.sub.14-15, S.sub.15-16, and the end portion
S.sub.END.
[0032] As shown in FIG. 2D, the explosive gases are encapsulated
within the perforating jet 42 generally at 19 during the
perforating jet formation process. In FIG. 2E, most of the liner 10
has collapsed (with the section SEND remaining) and the perforating
jet 42 has penetrated most of the way through the perforating gun
wall 40. In FIG. 2D, the tip 46 of the perforating jet 42 is
relatively sharp to create a smaller opening in the gun wall 40. In
FIG. 2F, section S.sub.END has collapsed into the perforating jet
42, which in FIG. 2F has perforated all the way through the wall 40
and into the well fluid 50.
[0033] The function of the last section of the liner (section SEND)
is illustrated in FIGS. 2E and 2F. Being generally thinner than its
neighboring section S.sub.15-16, the section S.sub.END of the liner
leads its neighboring portions slightly; that is, its collapse
speed is slightly higher than its neighboring portions. As a
result, the section SEND of the liner adds material to the trailing
portion of a bulged portion 44 shown in FIG. 2F.
[0034] On the other hand, if the thickness of the liner 10 were
constant, collapse of the liner from edge 12 in FIG. 1 to edge 16
would produce a thin jet forward of point 19 in FIG. 2D. This thin
jet would produce a small-diameter hole in well casings (not
shown). However, if there was a single step increase in thickness
in the liner, for example at edge 14, then there would be a bulge
in the resulting jet at some position before point 19 in FIG. 2D.
In like manner, a series of step increases in thickness along the
liner 10 will produce a corresponding series of bulged portions. By
spacing these steps according to predetermined distances and
varying the magnitudes of the thicknesses, the bulged portions may
be made to merge with one another producing a thick, extended and
generally cylindrical segment traveling rapidly through the well
fluid as shown (44) in FIG. 2F. This thick jet produces the
increased diameter holes in the well casing which give this
perforator design its superior performance.
[0035] The perforating gun is generally not centralized inside the
casing, causing the individual jets to penetrate varying amounts of
wellbore fluid before penetrating the casing. The portion of the
jet that eventually penetrates and produces a hole in the casing
(which may be made of steel, for example) therefore varies
according to the amount of fluid it encounters. This causes
typically larger hole diameters for gun clearances that are 0-1
times the diameter of the shaped charge and smaller holes for
clearances that are typically greater than the diameter of the
shaped charge. The maximum hole diameter in the casing is produced
by timing the location of the maximum bulge in the jet (enhanced by
the encapsulated explosive gases) so that it just starts
penetrating the casing.
[0036] Referring to FIG. 3, a perforator 80 according to another
embodiment has a liner 110 with a protruding portion 111 that is
generally conical-shaped. Thus, instead of the nipple-shaped
portion 11 having a rounded bump 11A that is used in the liner 10
of the embodiment of FIG. 1, the liner 110 of the FIG. 3 embodiment
uses a more pronounced protrusion in the general form of a cone
111A. A corresponding deep groove 111B may also formed on the
concave surface 110B of the liner 110.
[0037] The liner 110 of FIG. 3 also may have the varying thickness
feature of the liner 10 of FIG. 1. As with the liner 10, the liner
110 in the FIG. 3 embodiment also may have step increases occurring
at edges 14 and 15 (or at other predetermined locations). The rest
of the perforator 80, including the case 130 and the explosive
charge 120, are substantially similar in structure except for where
the explosive charge 120 mates with the protruding portion 111 of
the liner 110 in FIG. 3 and a slight difference in the shape of the
outer surface of the case 130. The collapse of the conical-shaped
portion 111 into a slow-moving slug of the perforating jet is
essentially the same as in FIGS. 2A-2D.
[0038] Referring to FIG. 4, a perforator 180 according to yet
another embodiment includes a shaped charge liner 210 in which the
step increases in thickness are on the inner surface 210B of the
liner 210 (the concave surface), in contrast to the steps formed in
the outer surface 10A in the liner 10 of FIG. 1. The protruding
portion 211 of the FIG. 4 embodiment is substantially the same as
the protruding portion 11 of the FIG. 1 embodiment. Within each
section S.sub.12-13, S.sub.13-14, S.sub.14-15, and S.sub.15-16, the
thickness of the liner 210 also gradually increases with distance
from the liner's apex, much like the thickness variation in the
FIG. 1 liner 10. The function of the section S.sub.END, which
decreases in thickness, is described above. The collapse and jet
formation of this third embodiment is essentially the same as that
described in FIGS. 2A-2F.
[0039] Referring to FIG. 5, a perforator 280 according to a further
embodiment includes a shaped charge liner 310 in which the
nipple-shaped protruding portion 11 of the FIG. 1 liner 10 has been
replaced with a protruding portion 311 having a general shape of a
very shallow cone. Thus, to create the slight protruding portion
311, a slight bump 311A is formed on the outer surface 310A of the
liner 310 and a corresponding slight groove 311B is formed on the
inner surface 310B of the liner 310. The liner 310 also is
configured to have varying thicknesses along its length. Again, the
other components in the perforator 280, such as the explosive
charge 320 and the case 330, may be substantially the same as the
corresponding components in the perforator 8 of the FIG. 1
embodiment. The formation of the jet from the liner in FIG. 5 is
shown in FIGS. 6A-6D, which are snapshots of the liner collapse
process at about the same times as FIGS. 2A-2D, respectively. As
illustrated, because of the slight protruding portion 311 used, a
slug is not created during the collapse of the liner 310 in the
FIG. 5 embodiment. Thus, formation of a slow-moving slug is not
essential to the process of encapsulating explosive gases into the
perforating jet 342.
[0040] Referring to FIG. 7A, 7B, and 7C, perforators according to
further embodiments include shaped charge liners each with a hole
generally in the apex of the liner. FIG. 7A shows a shaped charge
380 having a liner 510, an explosive 520, and a case 530, and FIG.
7B shows a shaped charge 480 having a liner 610, explosive 620, and
case 630. In each of the shaped charges 380 and 480 an unlined
shaped cavity region 540 (FIG. 7A) and 640 (FIG. 7B) in the
explosive (520 and 620) is located near the apex of the liner (510
and 610). The effect is similar to the shaped charges of FIGS. 1-5,
in that gases are encapsulated in the jet, forming a bulge that
produces larger holes in the casing. The advantage of these
embodiments is that it is easier to manufacture. FIG. 7A shows an
embodiment with a conical shaped cavity 540, FIG. 7B shows an
embodiment with a generally bowl-shaped cavity 640, and FIG. 7C
shows a shaped charge 580 with a liner 710, explosive 720, and a
case 730 having generally the same geometry (liner with a hole in
the apex) but without the shaped explosive cavity. Table 1 shows
experimental results of the effect of having unlined shaped
explosive cavity near the apex of a liner with a hole in it. The
experimental results summarized in Table 1 are for the shaped
charges 480 and 580 of FIGS. 7B and 7C according to experimental
embodiments.
1TABLE 1 Water Casing diameter produced by Casing diameter produced
by clearance shaped charge 480 shaped charge 580 .95" 1.24" 1.17"
1.65" 1.11" 1.11"
[0041] Each data entry represents the average of more than 30 shots
created by shaped charges according to the experimental
embodiments. There is an apparent beneficial increase in hole size
of about 6% at the 0.95" water clearance. (The effect was seen to
be slightly more than 6% increase when the small explosive cavity
was lined with a thin copper liner.) Note that the effect is
localized--the encapsulation of the explosive gas increases the
casing hole diameter only with water clearances of about 1 inch or
less. For clearances larger than that, the bulge is expended by
penetrating the water and is gone by the time the jet penetrates
the casing. That is why the hole diameters produced by shaped
charges according to experimental embodiments are about the same at
1.65" of water clearance.
[0042] Referring to FIG. 8, an exemplary perforating string 404
that can incorporate embodiments of the invention is positioned in
a wellbore 414. The perforating string 404 is lowered down in the
wellbore 414 adjacent a pay zone 402 that contains oil or gas in a
formation 400. The wellbore 414 is cased by casing 416 that is held
in place by a cement layer 418. The perforating string 404 is
carried by a tubing 406 (which can be, for example, a coiled
tubing). Alternatively, the perforating string 404 can be carried
by a wireline. The tubing 406 is connected to a firing head 408,
which is in turn connected to a perforating gun 410. The
perforating gun 410 contains shaped charges 420, which are
detonated by a detonating cord connected to the firing head 408 and
the shaped charges 420. The shaped charges 420 are designed to
create perforations in the adjacent casing 416, cement layer 418,
and pay zone 402 having relatively large hole diameters. The types
of shaped charge perforators that can create such big-hole
perforations include the shaped charges described in FIGS. 1-7
above. In the embodiments described, perforators of different sizes
may be used, such as 35-mm, 43-mm, or 64-mm perforators.
[0043] Perforations having a hole of a relatively large diameter
are particularly advantageous for use in controlling sand flow into
the wellbore 414 from the surrounding pay zone 402. After
perforations 412 are created through the casing 416 and the cement
418 into the adjacent pay zone 402, the perforating string 404 can
be removed and equipment to perform gravel packing can be lowered
into the wellbore 414 to pack gravel into and around the big-hole
perforations 412. The gravel acts as a filter to prevent sand from
flowing while still allowing flow of well fluids. Big-hole
perforations can also be used in other applications.
[0044] While the invention has been disclosed with respect to a
limited number of embodiments, those skilled in the art will
appreciate numerous modifications and variations therefrom. For
example, the particular embodiment chosen to manufacture a
particular shaped charge depends upon manufacturing techniques
available at any given time. It is intended that the appended
claims cover all such modifications and variations as fall within
the spirit and scope of the invention.
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