Note: Descriptions are shown in the official language in which they were submitted.
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Description
Spiral Or Wave Strip Perforating System
Technical Field
The present invention relates to through tubing
perforation guns used to support explosive charges in a
borehole to form perforations through which water,
petroleum or minerals are produced.
Background Art
This invention is an improvement to prior art
phased, through tubing, perforating systems in that it
allows for widely varied phasing (i.e., orientation of
multiple directional charges at various angles) while
allowing for retrieval of the carrier. Prior art phased
capsule perforating systems may be generally classified
into three categories: (1) the phased frangible base
strip (US 4,951,744); (2) the retrievable base strip with
frangible retaining means (US 5,095,999); and (3) the
phased expendable link (US 5,241,891).
The disadvantages of the first category (illustrated
in Figure 1 of the drawings) is that the shattered pieces
of the base strip are not retrieved from the well leaving
a substantial amount of debris. As a result, one cannot
determine if all the charges detonated properly. Also,
since the base strip shatters after firing the gun, the
strip must be brittle and thereby could break when it is
not desirable (e.g. upon conveying in the well).
The disadvantage of the second category (illustrated
in Figure 2 of the drawings) is that the base strip is
composed of a heavy gauge steel bar that limits possible
= phasing (normally + 45 degrees, -45 degrees) and that
distorts (when the shaped charges are fired) to make
retrieval difficult. Also, since only a relatively weak
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breakable clip retains the capsule charge to the base
strip, it may break when it is undesirable (e.g. upon
conveying into the well) . The advantage of this system is
that it permits some simple phasing (two rows at +/- 45
degrees typically), and the strip is rugged and
retrievable.
The disadvantages of the third category (illustrated
in Figure 3 of the drawings) are that more debris is left
in the well and that the system is weak (the pins and
links often break when they hit obstructions in the
tubing), resulting in use only for simple perforating
operations. The main advantage of the third category is
that very flexible phasing is possible. This high degree
of phasing of the capsules is significant to well
productivity in many formation types.
Co-pending application PCT/US95/15230 discloses a
perforating gun carrier with a slotted configuration and
interior dimensions to enable capsule orientation at
selected phases between 0 and 360 degrees. The carrier
has a frangible seam that fractures upon detonation to
form two retrievable strips, each supported by the
conveyance sub for retrieval. The seam is a narrow
bridge, formed by slotting the carrier partially, with a
cross-sectional area that shatters upon detonation of the
shaped charges. The remaining cross-sectional area and
strength of each strip is sufficient to assure retrieval
after detonation. The strips are preferably nonplanar,
arcuate or a segment of a circle in cross section. When
the capsule charges are arrayed around many phases, by
attaching both front and rear portions of the capsule
charges to the nonfrangible regions of the carrier,
detonating cords are used for detonation.
Disclosure of Invention
The general object of the invention is to provide a
gun for well perforating that overcomes the various
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disadvantages of the prior art devices with a carrier
that produces perforations in a wide degree of patterns,
including a 360 degree phase relationship, that does not
fragment and that is therefore removable from the well.
This object is achieved also with a perforating gun
having an elongated mounting having a spiral or selected
wave, or non-linear, zig-zag form as seen in a plan view,
with an outer surface diameter sized for convenient
insertion and removal from a well. The mounting strip
has a series of openings spaced in intervals for mounting
capsule explosive charges in a phased relationship
between 0 and 360 degrees. The cross-sectional area of
the mounting strip around each opening is selected to
prevent fragmentation of the carrier upon detonation of
the charges. The mounting strip is preferably metallic
with a selected amplitude and wave length.
In each opening is an explosive capsule with a
hollow cap with a nose for attachment to one of the
openings. The cap has an annular, interior thread with
a thread run-out of selected width. The explosive
capsule has a hollow body having an open end with
exterior threads and a width less than the width of the
thread run-out in the cap to permit free spinning of the
body in the cap after thread makeup for convenient
threading and connection with the detonating cord.
Certain exemplary embodiments may provide a
perforation gun for carrying a plurality of explosives
connecting by a detonating cord to perforate a section
of a well in a selected pattern, comprising: an
elongated, spiraled strip having an outer diameter
sized for convenient entry and removal from a well; a
series of openings spaced in internals along a length
of the spiraled strip to serve as mounts for the
explosives to be arranged in an angular phase
relationship to correspond with said selected
perforation pattern in the well; the cross-sectional
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area of the strip around each opening being selected
to prevent fragmentation of the carrier upon
detonation of the charges; whereby the spiraled strip
is capable of being positioned in the well, the
explosives detonated to create perforations in the
selected pattern and the spiraled strip retrieved from
the well.
The above as well as additional objects,
features, and advantages of the invention will become
apparent in the following detailed description.
Description of the Drawings
The novel features believed characteristic of the
invention are set forth in the appended claims. The
invention itself however, as well as a preferred mode of
use, further objects and advantages thereof, will best
be understood by reference to the following detailed
description of an illustrative embodiment when read in
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conjunction with the accompanying drawings, wherein:
Figure 1 illustrates a prior perforating gun of the
type that utilizes a frangible base strip;
Figure 2 is a prior art perforating gun of the type
utilizing a retrievable base strip with frangible
retaining means;
Figure 3 is a prior art perforating gun having multi
phased expendable links;
Figure 4 illustrates the preferred embodiment of the
present invention in a frontal view;
Figure 5 is a side elevational view of the Figure 4
embodiment;
Figure 6 is a view of the Figure 4 embodiment shown
from the top within a casing to be perforated to
illustrate the shaped charge orientations and
perforations in the casing and geological formation;
Figure 7 is a phase diagram showing the phase
relationship of the capsule charges in the Figure 4
embodiment;
Figure 8 is a fragmentary, enlarged view of the
carrier of the Figure 4embodiment to illustrate the
mounting means and strip configuration;
Figure 8-A is a cross-sectional view as seen looking
along the corresponding lines and arrows of Figure 8;
Figure 9 illustrates one capsule charge of the type
used in the preferred embodiment of Figure 4;
Figure 9-A is an enlarged, fragmentary view taken
from Figure 9; and
Figure 10 is a plan or frontal elevational view of
an alternative embodiment of the mounting means shown in
the plane of the paper.
Description of the Invention Referring initially to Figures 1-3 of the
drawings,
which illustrate three prior art perforating guns, the
perforating gun 11 of Figure 1 utilizes a frangible base
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strip 13 having plural surfaces 15, 17 upon which are
mounted a plurality of capsule charges 19 oriented at
different angles or phases to perforate a well in more
than one direction. The base strip 13 is constructed of
a material as explained in the specification of U.S.
Patent No. 4,951,744 to shatter into a multitude of very
small pieces in response to detonation of the capsule
charges, allowing the resulting debris from the base
strip to fall ideally below the perforating zone, to
prevent obstruction of the flow of oil or gas from the
perforated well. The material of the base strip 13 is
strong enough to avoid breakage during impact with an
obstruction when travelling downward in the borehole.
A retrievable base strip that will not shatter when
the charges detonate, and that may be retrieved from the
well, is disclosed in U.S. Patent 5,095,999. Here, the
charges are retained on the base strip by support rings
that will shatter into a multitude of pieces, allowing
the charges to fall to the bottom of the well. This
configuration of perforating gun is illustrated in Figure
2 of the drawings and is taken from U.S. Patent
5,095,999. A nonfrangible strip 21 is retrievable from
the well after detonation of the capsule charges 23 upon
ignition of the detonating cord 25. The capsule charges
23 are retained on the base strip 21 by a plurality of
support rings 26 that shatter upon detonation of the
capsule charges.
Another prior art perforating gun is shown in U.S.
Patent No. 5,241,891 and in Figure 3, wherein the
explosive charges 27 are mounted on link carriers 29, and
are detonated by ignition of the detonating cord 31.
This configuration of perforating gun occupies a small
diameter similar to prior art guns in the well while
enabling multi-phase orientation of the charges and
retrieval from a well.
Referring now to Figure 4 of the drawings and the
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preferred embodiment of the present invention, the
numeral 33 designates a perforating gun for well
perforating having an elongated, spiraled mounting strip
35 having an outer diameter sized for convenient
insertion and removal from a well that contains
geological formations that are to be perforated to
enhance the production of petroleum or other minerals.
The spiral strip 35 is manufactured by utilizing the
capabilities of a multiple axis laser milling machine on
drawn-over-mandrel (DOM) tubing. The laser mill must
have at least the X-axis and rotational capabilities in
order to slit the spiral strip. Four (4) strips are
manufactured from each full round tube started. The tube
is left partially connected until all spiral slits are
made over the length of the tube. The partial connection
points are later broken apart to yield four (4) separate
strips. The threaded holes on the strip are then
completed on conventional machine centers.
The perforating gun 33 -has at its upper end a
connector 37 for mounting on a conveyance sub (not shown)
to raise or lower and position the gun at the selected
elevation in the well adjacent to the geological
formation to be perforated. The strip 35 is connected to
a lower end of connector 47 with a plurality of fasteners
39 that may be socket head set screws or the equivalent.
Secured to the connector 37 is an electrical means 41
(see Fig. 5) adapted to supply electrical energy to a
detonating cord 43.
The exterior surface of the strip 35 is cylindrical
about a longitudinal axis (not shown) and is formed of a
selected metal that forms a helical band with a pitch in
a range of 12 to 24 inches. As shown in_the cross-
sectional view of Figure 8A, a suitable thickness t for
the strip is 0.125 inches and the circumferential width
W 1.25 inches. At the lower end of the strip is
connected a strap 45 to which may be secured a second
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spiraled strip 47. There are a series of openings in the
spiraled strip 35 to serve as mounts for a plurality of
explosive capsules 49. These openings are spaced in
intervals along the length of the spiral strip so that
they are arranged in a phase relationship to correspond
with the selected perforation pattern in the well.
As shown in Figure 9, each of the explosive capsules
49 has a cap 51 having a threaded nose 53 that engages
the threads 55 of the strip 35. The cross-sectional area
of the strip around or adjacent each opening is selected
to prevent fragmentation of the strip 35 upon detonation
of the charge, taking into account the strength of the
material used to form the strip, which in the preferred
embodiment is a strong, ductile and flexible material
such as 1018 steel or 304 stainless steel. The cap 51 is
hollow with an interior cavity 57 to receive an explosive
charge and terminate in an angular interior thread 59
having a thread runout 61, as may be better seen in the
enlarged, fragmentary view of Figure 9A.
The thread runout 61 is wider than the threads 63
that are formed on the exterior of the open end of a
hollow body 64 that partially contains the previously
described explosive charge. The open end of the hollow
body also has a seal 65 in an annular groove 67 to
prevent contamination and degradation of the explosive
charge. The opposite end of the hollow body 63 has a
slot 69 to receive the detonating cord 43 shown in
Figures 4 and 5, which is adjacent a heat-sensitive
firing pin 71 that will detonate the explosive inside the
capsule. A slot 73 receives a retainer clip 75 (see Fig.
8) of conventional configuration to secure the detonating
cord in its position adjacent to firing pin 71.
Referring now to Figure 10 of the drawings (and an
alternate embodiment of the present invention) the
numeral 101 designates drawn-over-mandrel (DOM) tube
shown in the plane of the paper (not a true plan or
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frontal elevational view) from which four (4) non-linear
zig-zag mounting strips can be manufactured from each
full round of tube with the use of a multiple axes laser
milling machine. One such strip 103 is shown with a
plurality of apertures 105 over its non-linear zig-zag
length, having edges 107, 109 defined by slitting the
tubing 101 with the laser mill. The laser mill must have
rotational capabilities in order to slit the tubing 101
and form the non-linear zig-zag strip.
The tube is left partially connected until the non-
linear zig-zag slits are made over the length of the
tube. The partial connection points are later broken
apart to yield four (4) separate non-linear zig-zag
strips. The apertures 105 on the strip are then threaded
and completed.
In the Figure 10 embodiment, the tube 101 is shown
as if it were cut longitudinally and rolled into the
plane of the paper, appearing to be a rectangle. The
circumference is marked in degrees ill at the bottom of
the tube. The degrees are used to define the edges 107,
109 of the strip 103 and their geometric shape. The
dotted lines 113 are imaginary lines that are used in
designing the shape of the strip 103 and do not appear
physically on the tube. The strip 103 is described as
being non-linear and in a zig-zag pattern.
Another way to define the strip 103 shape is with
reference to wave forms. The strip 103 has a wave form
comprised of a first triangular wave having a half wave
length 11 and an amplitude al. This wave intersects and
is continued by a second wave having a half wave length
12 and an amplitude aa. The waves can have a variety of
forms such as triangular (as shown), square, rectangular
or sinusoidal to provide some examples. The waves can be
repeating or identical or may have differing lengths and
amplitudes as shown.
The wave form is selected to provide the requisite
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pattern of apertures 105 in which to mount shaped charge
capsules and to maximize the number of strips 103 that
may be cut from the tube 101. By cutting the strip 103
from the tube 101, the shaped charges, when mounted in
apertures 105 are arranged in a segment of a cylinder (or
arc of a circle in a range of preferably 90-120 degrees)
to match the cy'lindrical shape of the wall in the well to
be perforated. The apertures 105 are preferably spaced
from one another in a range of 12 to 24 inches.
In the preferred example of Figure 10, the material
is the same as that indicated for the spiral strip of
Figure 4, with a thickness of 0.125 inches. The
dimensions for a successful strip are:
1v
W = 1.25 inches
11 = 6 inches
12 = 12 inches
D = 3 inches
d = 0.5 inches
al = 45 degrees
a2 = 45 degrees
It should be apparent from the foregoing that an
invention having significant advantages has been
provided. The spiral strip 35 of Figure 4 can be
configured to enable the orientation of explosive
capsules in a wide variety of selected patterns, one of
which is shown in Figure 6 in which the strip 35 is used
to position the explosive capsule 49 and others like it
to form perforation 77 through the metal casing 79 and
into the geological formation 81. This pattern has a
phase relationship as shown in Figure 7 wherein the
perforation 77 is indicated by the corresponding point at
zero degrees. Moreover, the configuration of the spiral
strip, when constructed as indicated above, prevents it
from fragmenting or major distortion that would prevent
its retrieval from a wellbore after the explosive
capsules are detonated. The spiral may be considered to
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be a three dimensional and continuous wave in a
cylindrical boundary.
The non-linear or waved strip 103 of Figure 10 is an
alternate way to achieve many of the advantages of the
spiral strip of Figure 4. It is especially advantageous
when the pattern perforations need not extend 360
degrees. Since plural strips can be formed of one tube
107, manufacturing efficiencies are obtained.
While we have shown our invention in only two of its
forms, it is not so limited but is susceptible to various
changes and modifications without departing from the
spirit thereof.
A
