U.S. patent application number 10/723713 was filed with the patent office on 2005-05-26 for perforating gun with improved carrier strip.
Invention is credited to Ludwig, Wesley N..
Application Number | 20050109501 10/723713 |
Document ID | / |
Family ID | 34592349 |
Filed Date | 2005-05-26 |
United States Patent
Application |
20050109501 |
Kind Code |
A1 |
Ludwig, Wesley N. |
May 26, 2005 |
Perforating gun with improved carrier strip
Abstract
A perforating gun includes a plurality of charge containers and
an elongate carrier strip. Each charge container may be mounted
within a hole in the carrier strip or in a hole in a mounting
bracket secured to the carrier strip through substantially
continuous contact between an outer surface of the charge carrier
and an inner surface of the mounting hole. One or more relief holes
are positioned longitudinally adjacent to each mounting hole, with
a longitudinal spacing between a perimeter of the relief hole and a
perimeter of the mounting hole being less than the width between a
respective hole and the edge of the carrier strip or mounting
bracket.
Inventors: |
Ludwig, Wesley N.; (Katy,
TX) |
Correspondence
Address: |
Browning Bushman, P.C.
Suite 1800
5718 Westheimer
Houston
TX
77057
US
|
Family ID: |
34592349 |
Appl. No.: |
10/723713 |
Filed: |
November 26, 2003 |
Current U.S.
Class: |
166/55 ;
175/4.6 |
Current CPC
Class: |
E21B 43/117 20130101;
E21B 43/119 20130101 |
Class at
Publication: |
166/055 ;
175/004.6 |
International
Class: |
E21B 029/10 |
Claims
1. A perforating gun for perforating a well, comprising: a
plurality of charge containers for containing charges to be
detonated to perforate the well; an elongate carrier strip having a
centerline along its length and a transverse axis along its width,
the carrier strip defining longitudinally extending, laterally
opposing edges; a plurality of charge container mounting holes in
the carrier strip, each charge container supported on the carrier
strip through substantially continuous contact between an outer
surface of the charge container and an inner surface of the
mounting hole; a pair of webs each defined between a respective
mounting hole and a respective adjacent edge of the carrier strip,
each web having a web width between the mounting hole and
respective adjacent edge; and a relief hole positioned
longitudinally adjacent each mounting hole, with a longitudinal
spacing between a perimeter of the relief hole and a perimeter of
the mounting hole less than each web width, such that the charge
container has less resistance to outward yielding at a location
adjacent the relief hole than at locations adjacent the webs during
a substantially uniform radially outward loading of the detonating
charge container against the mounting hole.
2. A perforating gun as defined in claim 1, wherein the relief hole
is longitudinally spaced from the mounting hole by a deformable
relief section bridging the mounting hole and the relief hole for
yielding generally toward the relief hole in response to detonation
of the charge container.
3. A perforating gun as defined in claim 2, wherein the
longitudinal spacing between the perimeter of each relief hole and
a perimeter of each respective mounting hole is less than 50% of
either web width.
4. A perforating gun as defined in claim 1, further comprising: a
threaded connection between each mounting hole and respective
charge container, for removably supporting each charge container on
the carrier strip.
5. A perforating gun as defined in claim 1, further comprising:
another relief hole longitudinally opposite the relief hole with
respect to the mounting hole.
6. A perforating gun as defined in claim 1, wherein the carrier
strip has a substantially uniform width between the opposing edges
of the carrier strip extending longitudinally between the plurality
of mounting holes.
7. A perforating gun as defined in claim 1, further comprising:
each relief hole is generally circular and has a diameter greater
than 50% of a diameter of the respective mounting hole.
8. A perforating gun as defined in claim 1, wherein the relief hole
is an elongate slot extending longitudinally with respect to the
respective mounting hole.
9. A perforating gun as defined in claim 1, further comprising: a
plurality of relief holes longitudinally arranged to one side of a
respective mounting hole with a longitudinal spacing between the
perimeter of any two relief holes being less than 25% of either web
width.
10. A perforating gun as defined in claim 1, wherein the relief
hole intersects the mounting hole, such that the outer surface of
the charge container is substantially unsupported by the mounting
hole at the intersection.
11. A perforating gun for perforating a well, comprising: a
plurality of charge containers for containing charges to be
detonated to perforate the well; an elongate carrier strip having a
centerline along its length and a transverse axis along its width,
the carrier strip defining longitudinally extending, laterally
opposing edges; a plurality of charge container mounting holes in
the carrier strip, each charge container supported on the carrier
strip by a threaded connection between an outer surface of the
charge container and an inner surface of the mounting hole; a pair
of webs each defined between a respective mounting hole and a
respective adjacent edge of the carrier strip, each web having a
web width between the mounting hole and respective adjacent edge;
and at least two relief holes longitudinally opposite one another
with respect to the mounting hole, each relief hole having a
perimeter longitudinally spaced from the mounting hole less than
50% of either web width, such that the charge container has less
yielding resistance at locations adjacent the relief holes than at
locations adjacent the webs during a substantially uniform radially
outward loading of the detonating charge container against the
mounting hole.
12. A perforating gun as defined in claim 11, wherein each relief
hole is longitudinally spaced from the mounting hole by a
deformable relief section bridging the mounting hole and the relief
hole for yielding generally toward the relief hole in response to
detonation of the charge container.
13. A perforating gun as defined in claim 11, wherein the carrier
strip has a substantially uniform width between the opposing edges
of the carrier strip extending longitudinally between the plurality
of mounting holes.
14. A perforating gun as defined in claim 11, further comprising:
each relief hole is generally circular and has a diameter greater
than 50% of a diameter of the respective mounting hole.
15. A perforating gun as defined in claim 11, wherein at least one
relief hole is an elongate slot extending longitudinally with
respect to the respective mounting hole.
16. A perforating gun as defined in claim 11, further comprising:
one or more additional relief holes longitudinally arranged with
respect to at least one of the relief holes with a longitudinal
spacing between the perimeter of any two longitudinally spaced
relief holes being less than 25% of either web width.
17. A perforating gun as defined in claim 11, wherein one or more
relief holes intersect the mounting hole, such that the outer
surface of the charge container is substantially unsupported by the
mounting hole at the intersection.
18. A perforating gun for perforating a well, comprising: a
plurality of charge containers for containing charges to be
detonated to perforate the well; an elongate carrier strip having a
centerline along its length and defining longitudinally extending,
laterally opposing edges; a plurality of charge container mounting
holes in the carrier strip, each charge container supported on the
carrier strip through substantially continuous contact between an
outer surface of the charge container and an inner surface of the
mounting hole; a pair of webs each defined between a respective
mounting hole and a respective adjacent edge of the carrier strip,
each web having a web width between the mounting hole and
respective adjacent edge; and a generally circular relief hole
having a diameter greater than 50% of a diameter of a respective
mounting hole, the relief hole having a perimeter longitudinally
spaced with respect to a perimeter of the respective mounting hole
less than 50% of either web width to define a deformable relief
section bridging the mounting hole and the relief hole for yielding
generally toward the relief hole in response to detonation of the
charge container, such that the charge container has less yielding
resistance at locations adjacent the relief section than at
locations adjacent the webs during a substantially uniform radially
outward loading of the detonating charge container against the
mounting hole.
19. A perforating gun as defined in claim 18, further comprising: a
threaded connection between each mounting hole and respective
charge container, for removably supporting each charge container on
the carrier strip.
20. A perforating gun as defined in claim 18, further comprising:
another relief hole longitudinally opposite the relief hole with
respect to the mounting hole.
21. A perforating gun as defined in claim 18, wherein the carrier
strip has a substantially uniform width between the opposing edges
of the carrier strip extending longitudinally between the plurality
of mounting holes.
22. A perforating gun as defined in claim 18, further comprising: a
plurality of relief holes longitudinally arranged to one side of a
respective mounting hole with a longitudinal spacing between the
perimeter of any two adjacent relief holes being less than 25% of
either web width.
23. A perforating gun for perforating a well, comprising: a
plurality of charge containers for containing charges to be
detonated to perforate the well; an elongate carrier strip having
mounting locations for supporting charge container brackets, each
bracket defining longitudinally extending, laterally opposing
edges; a charge container mounting hole in each bracket for
supporting a charge container through substantially continuous
contact between an outer surface of the charge container and an
inner surface of the mounting hole; a pair of webs each defined
between a respective mounting hole and a respective adjacent edge
of the bracket, each web having a web width between the mounting
hole and respective adjacent edge; and a relief hole positioned in
each bracket longitudinally adjacent each mounting hole, with a
longitudinal spacing between a perimeter of the relief hole and a
perimeter of the mounting hole less than each web width, such that
the charge container has less resistance to outward yielding at a
location adjacent the relief hole than at locations adjacent the
webs during a substantially uniform radially outward loading of the
detonating charge container against the mounting hole.
24. A perforating gun as defined in claim 23, wherein the relief
hole is longitudinally spaced from the mounting hole by a
deformable relief section bridging the mounting hole and the relief
hole for yielding generally toward the relief hole in response to
detonation of the charge container.
25. A perforating gun as defined in claim 23, wherein the
longitudinal spacing between the perimeter of each relief hole and
a perimeter of each respective mounting hole is less than 50% of
either web width.
26. A perforating gun as defined in claim 23, further comprising: a
threaded connection between each mounting hole and respective
charge container, for removably supporting each charge container on
the carrier strip.
27. A perforating gun as defined in claim 23, further comprising:
another relief hole longitudinally opposite the relief hole with
respect to the mounting hole.
28. A perforating gun as defined in claim 23, further comprising:
each relief hole is generally circular and has a diameter greater
than 50% of a diameter of the respective mounting hole.
29. A perforating gun as defined in claim 23, wherein the relief
hole is an elongate slot extending longitudinally with respect to
the respective mounting hole.
30. A perforating gun as defined in claim 23, wherein the relief
hole intersects the mounting hole, such that the outer surface of
the charge container is substantially unsupported by the mounting
hole at the intersection.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a perforating gun for perforating
a well, and to an improved carrier strip for carrying detonation
charges to form perforations through which fluids are produced.
More particularly, this invention relates to an improved carrier
strip that resists separation upon firing of the gun.
BACKGROUND OF THE INVENTION
[0002] In the recovery of well fluids, such as oil and gas,
perforating charges are commonly mounted on a strip of metal and
lowered into the well. When the charges reach a desired depth they
are ignited to perforate the casing to enable or enhance production
of oil or gas from the formation. The strips of metal are not
reusable, so their entire cost contributes to the cost of the
operation. To achieve a low cost, the strip is preferably made with
as little material and as simply as possible. Examples of
perforating guns and carrier strips for carrying perforation
charges are disclosed in U.S. Pat. Nos. 6,591,911, 6,216,596,
6,098, 707, 5,701,964, and 5,590,723.
[0003] Perforating charges typically are constructed of a shaped
explosive in a sealed metal container or can that focuses the force
of the explosion into a jet that forms a hole in the well casing
and formation. The charges are designed so that the metal can
eventually breaks into small pieces at the end of the firing
process, after the perforation is formed. At some point in the
process, the metal can acts as a pressure vessel containing much of
the force of the explosion and allowing the expanding gases to exit
the can in a well defined jet through the portion of the can
threaded into the carrier strip. When the metal can starts to break
apart, it exerts large longitudinal or axial forces on the carrier
strip, sometimes causing the mounting hole to elongate or even tear
apart.
[0004] Existing carrier strips typically have larger, threaded
holes to directly screw a charge container into the carrier strip,
along with smaller holes axially spaced from the larger holes,
which are used to mount brackets that position other charges at
various angles relative to the face of the carrier strip. An
example of this type of carrier is illustrated in U.S. Pat. No.
6,591,911. The smaller mounting holes are spaced appreciably from
the larger holes due to geometric constraints, such as the size of
the charges, required room for bending of the primer cord, and room
to mount brackets for any angled charges. The smaller holes are
also generally desired to be sufficiently small not to weaken the
strip.
[0005] The general goal of improving the durability of carrier
strips has been addressed somewhat by U.S. Pat. No. 6,098,707. The
'707 patent discloses a perforating gun comprising a charge
receiving area of a strip having a greater width than intervening
areas of the strip, to provide an increased support surface for
charge units. Although this may provide enhanced durability, it is
not optimal in terms of having both a simplified design and
resistance to downhole separation. Existing carrier strips have not
achieved a high level of simplicity and resistance to separation.
Prior art carrier strips that separate laterally downhole upon
firing of the gun can be difficult and expensive to retrieve to the
surface, and may prevent successful operation of other downhole
equipment.
[0006] A perforating gun is therefore desired having an improved
charge carrier strip that is relatively simple and inexpensive to
manufacture, while having improved resistance to separation during
firing.
SUMMARY OF THE INVENTION
[0007] In one embodiment, a perforating gun including a plurality
of charge containers are supported on an elongate carrier strip
having a plurality of mounting holes, with each charge container
being supported on the carrier strip through substantially
continuous contact between the charge container and the mounting
hole. A pair of webs is defined between each mounting hole and
adjacent edges of the carrier strip. A relief hole is positioned
longitudinally adjacent to each mounting hole, with the spacing
between a perimeter of the relief hole and a perimeter of the
mounting hole being less than each web width. As a result of this
relief hole positioning, the carrier strip desirably provides less
resistance to outward yielding of the charge container at a
location adjacent the relief hole than at locations adjacent to the
web. When the perforating gun is detonated, there is a
significantly reduced likelihood of the elongate strip separating
laterally, thereby avoiding problems with portions of the strip
dropping in the hole and not being retrieved with upper portions of
the elongate strip.
[0008] In some embodiments, the relief hole is longitudinally
spaced from the mounting hole to form a deformable relief section
which yields toward the relief hole in response to detonation of
the charge carrier. The longitudinal spacing between a perimeter of
the relief hole and a perimeter of the respective mounting hole may
be less than 50% of either web width. Relief holes are preferably
provided on longitudinally opposite sides of the mounting hole, and
may have a circular or slot configuration. In other embodiments, a
relief hole may alternatively intersect the mounting hole to
further decrease resistence to outward yielding of the charge
container. A plurality of relief holes may also be provided on one
or both sides of the mounting hole to further encourage
longitudinal, rather than lateral, splitting of the carrier strip.
The elongate strip is less likely to laterally separate upon firing
of the gun due to the presence of the relief holes, even though
each charge container is directly mounted to the carrier strip by a
threaded connection. In alternate embodiments, the charge container
may be pressed into a mounting hole in the carrier strip to provide
the substantially continuous contact between an outer surface of
the charge container and an inner surface of the mounting hole. The
carrier strip may have a substantially uniform width between the
opposing edges of the carrier strip, thereby allowing the carrier
strip to be economically manufactured by an extruding
operation.
[0009] In another embodiment, the perforating gun is similarly
provided with an elongate carrier strip and a plurality of charge
containers. Charge container brackets are mounted on the carrier
strip in a conventional manner, with each bracket having laterally
opposing edges and a charge container mounting hole defining a pair
of webs between the mounting hole and the edges of the bracket. A
relief hole is positioned in each bracket longitudinally adjacent a
mounting hole, with a longitudinal spacing between a perimeter of
the relief hole and a perimeter of the mounting hole being less
than the web width. The relief hole or the plurality of the relief
holes in each bracket include the same features and spacings as in
embodiment having the relief hole in the carrier strip. By
minimizing the likelihood of lateral separation of the brackets
upon firing of the gun, portions of a bracket cannot pivot about
the mounting holes, and thereby do not create hooks that may catch
downhole equipment to make removal of the gun difficult.
[0010] A feature of the present invention is that the relief holes
may be provided in the elongate strips or in the mounting brackets
with a nominal increase of cost. A substantial advantage of the
invention is the reduced likelihood of lateral separation of a
perforating gun carrier strip or a mounting bracket upon firing of
the gun, thereby reducing problems associated with retrieving
portions of the perforating gun after firing or having portions of
the gun interfere with other downhole equipment.
[0011] These and further features and advantages of the present
invention will become apparent from the following detailed
description, wherein reference is made to the figures in the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 shows a conventional carrier strip for use in a
perforating gun;
[0013] FIG. 2 shows a charge container for use with the perforating
gun;
[0014] FIG. 3 show a portion of a preferred embodiment of an
improved carrier strip according to the invention;
[0015] FIG. 4 shows another preferred embodiment, wherein relief
holes intersection the mounting holes;
[0016] FIG. 5 shows an embodiment of the carrier strip wherein the
relief holes are slot shaped;
[0017] FIG. 6 shows an embodiment of the carrier strip having slot
shaped relief holes, with inner ends that are substantially
concentric with the mounting hole, resulting in a constant width
relief section;
[0018] FIG. 7 illustrates charge containers secured to the carrier
strip, with slot shaped relief holes similar to those of FIG.
6;
[0019] FIG. 8 illustrates a cross-sectional view of the carrier
taken along section line 1-1 of FIG. 7, to show further details of
one of the charge containers secured to the carrier strip;
[0020] FIG. 9 shows a cross-sectional view taken along section line
2-2 of FIG. 7, to show a section of the carrier strip without a
charge container;
[0021] FIG. 10 shows a perspective view of FIG. 7;
[0022] FIG. 11 illustrates a carrier strip having multiple relief
holes longitudinally arranged on each side of the mounting hole;
and
[0023] FIG. 12 shows a charge container mounted on a bracket, by
substantially continuous contact between the charge container and a
mounting hole through the bracket.
[0024] FIG. 13 illustrates a charge container with its probable
location of failure as mounted on a conventional carrier strip.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] FIG. 1 shows a typical conventional carrier strip 110 for
use in a perforating gun. A strip centerline 113 may be defined as
passing centrally through carrier strip 110 along its length, with
respect to which other features may be described. The carrier strip
110 typically has a generally flattened cross-sectional shape, as
shown in FIG. 9. The carrier strip 110 may include bends, such as
in a spiraling carrier strip (not shown), in which case the strip
centerline 113 will not be straight, and instead may have a
spiraling configuration. The carrier strip 110 has laterally
opposing edges 124.
[0026] A plurality of charge containers 50, conceptually shown in
FIG. 2, may each be positioned within a respective charge container
mounting hole 112 through carrier strip 110. The mounting holes 112
may either provide mere clearance for insertion of the charge
containers 50, in which case a bracket or other support member
(discussed below in connection with FIG. 12) may be used to secure
the charge container 50 to the strip, or the charge containers may
be secured directly to the mounting holes 112, such as with threads
30. The charge container 50 has a first section 41, which typically
is packed with charge material, and a second section 40 press fit
to section 41 to enclose the charge material. A primer cord for
detonating the charge container 50 may be secured at location
152.
[0027] Referring still to FIG. 1, a pair of longitudinally
extending webs 118 are defined between the laterally opposing edges
124 and each mounting hole 112. Other holes 126 are optionally
provided as shown, such as for securing additional brackets
carrying additional charge containers. The other holes 126,
however, are spaced a considerable distance from the mounting holes
112, leaving a large section 109 of strip material between each
mounting hole 112 and other holes 126. The spacing of the mounting
holes, 112 is determined by the spacing of the charges, and is
sufficiently large to accommodate the maximum diameter of the
charges and the bend radius of the primer cord.
[0028] When a charge container 50 is detonated on such a
conventional carrier strip 110, the carrier strip 110 has a
tendency to fail, typically severing the carrier strip 112 into
multiple pieces that are difficult to retrieve from a well. When a
charge container is directly supported from a carrier strip through
substantially continuous contact with the inner wall of the
mounting hole (rather than merely passing through a hole and being
supported by a bracket), the failure mechanism of a conventional
perforating gun carrier strip 110 can be simplified by a two step
failure model. In the first step, as the charge container 50 starts
to expand and before it breaks apart or shatters, pressure is
distributed relatively uniform around the perimeter of the mounting
hole 112. The carrier strip 110 will respond by deforming. The
carrier strip 110 is naturally most easily deformed by the
expansion force in the area of the relatively thin webs 118 of
material defined between the larger mounting holes 112 and the
outer edges 124 of the carrier strip 110 than at the relative large
section 109 of strip material between each mounting hole 112 and
other holes 126. The increased stress causes the charge container
50 to crack at or near the webs 118, preferentially transverse to
the centerline 113 of the carrier strip 110. FIG. 13 shows this
probable line of failure 111 on a charge container 50 positioned on
the strip 110. The line of failure 111 is shown adjacent to webs
118. In the second step, once the container 50 has separated into
substantially two halves, 150, 151, the internal pressure then
separates the halves 150, 151 of the charge container parallel to
the centerline of the strip, generally resulting in a net axial
force elongating the mounting hole 112 along the centerline 113 of
the carrier strip 110. If the metal yields too much before the
energy of the charge is dissipated, the carrier strip 110 will be
broken transverse to the longitudinal axis, and a lower broken
portion of the carrier strip 110 will then be more difficult to
retrieve downhole.
[0029] FIG. 3 shows a portion of a preferred embodiment of an
improved carrier strip 10 according to the invention, in contrast
to the conventional carrier strip 110 shown in FIG. 1. A centerline
13 may be defined as passing centrally through carrier strip 10
along its length, with respect to which other features may be
described, similar to the centerline 113 of FIG. 1. The carrier
strip 10 also typically has a generally flattened cross-sectional
shape, as shown in FIG. 9. The carrier strip 10 may also include
bends, such as in a spiraling carrier strip (not shown), in which
case the centerline 13 need not be straight. The spiraling
configuration may be helical shape, or a regular octagonal
spiraling pattern. The carrier strip 10 may also have straight
sections that are twisted about the centerline 13 at selected
locations, to orient charge containers at different firing
positions. The carrier strip 10 has laterally opposing edges 24, so
that the carrier strip has a uniform width extending
longitudinally. A plurality of charge containers 50 (as in FIG. 2)
may be positioned within respective charge container mounting holes
12 through carrier strip 10.
[0030] Referring again to FIG. 3, the mounting holes 12 should
provide substantially continuous contact between an outer surface
31 of the charge container 50 and an inner surface 22 of the
mounting hole 12, to secure the charge container 50 to the carrier
strip 10. The charge containers 50 are preferably secured directly
to the mounting holes 12, such as with a threaded connection
between threads 30 on the charge container and threads 33 on the
inner surface 22 of the mounting hole 12. Alternatively, the charge
containers 50 may be press fit into a mounting hole 12 to directly
support the charge container 50 by providing the substantially
continuous contact between the outer surface 31 and inner surface
22. A pair of longitudinally extending webs 18 are defined between
the laterally opposing edges 24 and each mounting hole 12. Other
holes 26 are still optionally provided as shown, such as for
securing additional brackets carrying additional charge containers
50.
[0031] One or more relief holes 14 are also included with the
carrier strip 10, however, which typically have relatively large
diameters and are positioned more closely to the mounting holes 12.
The carrier strip 10 in FIG. 3 therefore has a relatively narrow
section 16 of strip material between each mounting hole 12 and
respective relief hole 14. This narrow section 16 may be referred
to as a relief section 16. Because there is substantially
continuous contact between an outer surface 31 of the charge
container 50 and an inner surface 22 of the mounting hole 12, the
charge container 50 when detonated will attempt to expand uniformly
outwardly against the mounting hole 12. The relief section 16 will
provide significantly less resistance to outward yielding of the
charge container 50 than either of the webs 18, because the relief
section 16 has less material than the webs 18. In contrast to the
failure mode of conventional strips described in connection with
FIG. 1, the charge container 50 will instead preferentially split
at a location adjacent each relief hole 14, at relief section 16
along a probable line of failure 11, as shown in FIG. 8. If the
charge container 50 then separates into substantially two halves,
it will exert a transversely outward force on the respective
mounting hole 12, in which case the carrier strip is less likely to
be forcibly separated into two or more pieces. Even if the carrier
strip 10 does split, it will more likely split in the direction of
the longitudinal centerline 13, such as partially splitting along
the centerline 13 at relief section 16.
[0032] The substantially continuous contact between an outer
surface 31 of the charge container 50 and an inner surface 22 of
the mounting hole 12 is very important. That contact supports the
charge container 50 so that it preferentially yields at locations
adjacent to the relief holes 14, rather than unpredictable at some
arbitrary other location. This substantially continuous contact may
be provided by either the press fit connection or threaded
connection between the charge container 50 and mounting holes 14,
as described above. The substantially continuous contact is not
provided, however, in certain prior art embodiments, such as those
carrier strips discussed above having mere loosely fitting
clearance holes, and whereby the charge containers are secured by
brackets. Some minor clearance may be possible with the present
invention, but it would be less than the amount of expansion the
charge container would endure prior to yielding. Typically, any
such clearance would need to be less than one or two thousandths of
an inch between the charge container and mounting hole.
[0033] The relief section 16 should provide less resistance to
yielding than the webs 18, to achieve the results intended. In
embodiments where the relief hole 14 has a relatively large
diameter and is extremely close to the mounting hole 12, it can be
reasonably concluded upon visual inspection that the relief section
16 should provide less resistance to yielding than the webs 18,
according to the invention. Due to a number of variables affecting
yield resistance, however, such as the distance between a relief
hole 14 and a mounting hole 12, and the diameter of the relief hole
12, it is desirable to construct a carrier strip 10 according to
certain predefined parameters. At a minimum, a spacing between the
perimeter of each relief hole and the perimeter of respective
mounting hole should be less than the width of either web 18. In
preferred embodiments, this spacing is less than 50% and preferably
less than 25% of a width of either web 18. Additionally, the
diameter of the relief hole 14 is preferably greater than 50% of
the diameter of the respective mounting hole, and in more preferred
embodiments is about 70% of the diameter of the respective mounting
hole.
[0034] For example, in a carrier strip having a width of 1.146
inches, a mounting hole having a diameter of 0.625 inches, spaced a
center-to-center distance of 0.562 inches from a relief hole having
a diameter of 0.438 inches would result in a spacing of
approximately 0.031 inches between perimeters of the mounting hole
and relief hole (i.e. the narrowest width of the relief section 16
would be 0.031 inches). Each web width would be 0.260 inches. Thus,
the diameter of the relief hole 14 would be slightly more than 70%
of the diameter of the mounting hole 12, and the spacing between
the perimeters of each relief hole and respective mounting hole is
less than 12%.
[0035] In other preferred embodiments, as illustrated in FIG. 4,
the relief hole 14 may be positioned so closely to the mounting
hole 12 that the two holes 12, 14 intersect. The inner surface 22
of the mounting hole 12 thus sufficiently extends circumferentially
to support the charge container 50 with substantially continuous
contact between the inner surface 22 of the mounting hole 12 and an
outer surface 31 of the charge container 50. In contrast to the
embodiment of FIG. 3, however, there is an opening in the surface
22 at intersection 17. Because there is no relief section, there is
little or no resistance to outward yielding of the charge container
50 adjacent the relief hole 12, as compared with locations adjacent
the webs 18. As with the embodiment of FIG. 3 having the relief
section 16, the embodiment of FIG. 4 will thus allow the charge
container 50 to preferentially fail along a generally longitudinal
break line.
[0036] The relief holes are preferably circular, as in FIG. 3,
because a circular shape is generally least expensive to
manufacture. For example, the relief holes may be manufactured by
stamping the carrier strip with a circular die, or by passing a
rotating machine bit through the carrier strip 10. In other
embodiments, however, the relief holes need not be circular. FIGS.
5 and 6 illustrate embodiments of the carrier strip 10 in which the
relief holes are slots 14. As in FIG. 3, the relief holes or slots
14 shown do not intersect the mounting hole 12, although in other
embodiments they might. Instead, a relief section 16 again bridges
the mounting hole 12 and relief holes 14, to deform more readily
than the webs 18. The slots 14 in FIG. 5 have semi-circular ends
17, such as might be created using a circular-profile bit during a
milling operation. The slots 14 in FIG. 6 instead include curved
inner ends 19 that are substantially concentric with the mounting
hole 12, resulting in a constant width relief section 16 that is
possibly easier to yield. Other potential ways of making the relief
holes include laser cutting and water-jet cutting.
[0037] FIG. 7 illustrates charge containers 50 secured to the
carrier strip 10 and having substantially continuous contact with
the mounting hole 12. The carrier strip 10 shown happens to have
slot-shaped relief holes 14, although the choice of relief hole
shape generally does not affect how charge containers 50 are
inserted and secured to the mounting hole 12, i.e., the relief
holes 14 could have any shape within the guidelines set forth
above. The relief holes 14 could even intersect the mounting hole
12 as described in conjunction with the embodiment of FIG. 4,
provided there were sufficient threads 33 on the inner surface 22
of the mounting holes 12 in FIG. 4 to secure the charge containers
50, via threads 30.
[0038] FIG. 8 illustrates a cross-sectional view taken along
section line 1-1 of FIG. 7, to show further details of one of the
charge containers 50 secured to the carrier strip 10 with threads
30. The section view shows the generally flattened shape of the
carrier strip 10. Webs 16 are also visible. FIG. 9 shows a
cross-sectional view taken along section line 2-2 of FIG. 7, to
show a section of the carrier strip 10 without a charge container
50. FIG. 10 show a perspective view of FIG. 7, where again the
relief holes 14 are shown as slots, but may have other shapes.
[0039] In some embodiments, a plurality of relief holes may be
longitudinally arranged to one side of a respective mounting hole
with a longitudinal spacing between the perimeter of any two relief
holes being less than 25% of either web width. FIG. 11 illustrates
a carrier strip 10 having 2 relief holes 14, 15 longitudinally
arranged on each side of the mounting hole 12. Relief sections 16
are provided for the same purpose as in other embodiments. Although
strip material at locations 21 are similar in appearance to relief
sections 16, they have much less influence on yielding of the
charge container 50 than do the relief sections 16. Instead, the
purpose of additional relief holes are to promote preferential
failure in a direction generally along centerline 13. If the charge
container 50 desirably separates into substantially two halves near
the relief sections 16, the two halves will tend to pull the strip
10 laterally apart. The additional relief holes 15 thus allow
greater yielding and energy absorption along the centerline 13.
[0040] As mentioned above, the invention may also be applied to a
perforating gun in which a bracket or other support member is used
to secure the charge container 50 to the strip. FIG. 12 shows a
charge container 50 mounted in such a bracket 220, by substantially
continuous contact between the charge container 50 and a mounting
hole 212 through the bracket 220. Relief holes 214 are shown spaced
slightly from the mounting hole to define relief sections 216,
although in some embodiments the relief holes 214 may intersect
with the mounting hole 212 as described in connection with other
embodiments. Instead of the charge container 50 being directly
supported on the carrier strip discussed above, the bracket 220 is
instead secured to the carrier strip, such as with bracket mounting
members passing through mounting holes 210, which align with holes
26. When charges are mounted on the brackets, separation of the
carrier strip during detonation of the charge containers 50 is
generally not the primary concern. Instead, the invention helps
ensure the bracket 210 does not fail in a transverse direction at
webs 218 between the mounting hole 212 and bracket edges 224. If
the bracket 220 were to fail, pieces of the bracket 220 that remain
attached to the carrier strip might pivot, creating hooks that
could catch on downhole equipment and make removal of the
perforating gun difficult. As before, the spacing between
perimeters of the relief holes 214 and the mounting hole 212 is
less than the spacing between bracket edges 224, and the mounting
hole 212, i.e., less than a width of webs 218, to provide less
resistance to yielding at locations adjacent the relief holes 214
than locations adjacent the webs 218.
[0041] While preferred embodiments of the present invention have
been illustrated in detail, modifications and adaptations of the
preferred embodiments may occur to those skilled in the art. It is
to be expressly understood, however, that such modifications and
adaptations are within the scope of the present invention as set
forth in the following claims.
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