Note: Descriptions are shown in the official language in which they were submitted.
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ENERGY CONTROLLING DEVICE
FIELD OF THE INVENTION
100021 The present invention relates generally to perforating tools used in
downhole
applications, and more particularly to a device for controlling the use of
explosive energy
of an explosive charge in a perforating gun in a wellbore.
BACKGROUND OF THE INVENTION
[0003] An apparatus, such as a perforating gun, may be lowered into a well and
detonated to form fractures in the adjacent formation. After the perforating
gun
detonates, fluid typically flows into the well and to the surface via
production tubing
located inside the well.
[0004] Typically, perforating guns (which include gun carriers and shaped
charges
mounted on or in the gun carriers) are lowered through tubing or other pipes
to the
desired well interval. Shaped charges carried in a perforating gun are often
phased to fire
in multiple directions around the circumference of the weilbore. When fired,
shaped
charges create perforating jets that form holes in surrounding casing as well
as extend
perforations into the surrounding formation.
[0005] It may be necessary to control the amount of energy (e.g., reduce or
focus)
released by the explosive charge. For example, in some cases, it may be
advantageous to
rupture the hollow carrier (or other hollow chamber or sealed enclosure)
without
penetrating the surrounding casing and/or penetrating the well formation.
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SUMMARY OF THE INVENTION
[0006] Accordingly, the present invention provides an
apparatus capable of influencing explosive energy during
wellbore applications. In one embodiment, a cap or other
interfering element may be arranged proximate to an
explosive charge prior to detonation. The size and
positioning of the element with respect to the explosive
charge may be manipulated to achieve an optimum explosive
orientation.
[0007] The element utilized by the present invention may
be a ring having a bore therethrough for directing the
explosive energy of the charge upon detonation. Further,
the charge cap may include an area having a thinner wall
than the rest of the cap. In operation, the thicker
portion of the cap absorbs some of the explosive energy of
the charge and the thinner portion (or opening)
conducts/directs the explosive energy. The exact thickness
of the "absorbing" volume of the cap and the thickness of
the "conducting" volume of the cap may be determined and
selected to achieve a particular result.
An aspect of the invention relates to an
apparatus for use in a wellbore comprising: an explosive
charge; and at least one element capable of influencing the
explosive energy released by said explosive charge upon
detonation.
Another aspect of the invention relates to an
apparatus for use in a wellbore comprising: an explosive
charge for insertion into a perforating gun; and at least
one element capable of influencing the explosive energy
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released by said explosive charge upon detonation, said
element having walls defining at least one cavity for
directing explosive energy, said element being positioned
between said explosive charge and said perforating gun.
A further aspect of the invention relates to a
method of controlling explosive energy in a wellbore
comprising the steps of: providing a perforating gun
containing one or more explosive charges; positioning at
least one element between said explosive charge and said
perforating gun, said element being capable of influencing
explosive energy released by said explosive charge upon
detonation; and detonating one or more of said explosive
charges.
BRIEF DESCRIPTION OF THE DRAWINGS
(0008] A more complete appreciation of the invention and
many of the attendant advantages thereof will be readily
obtained as the same becomes better understood by reference
to the following detailed description when considered in
connection with the accompanying drawings; it being
understood that the drawings contained herein are not
necessarily drawn to scale; wherein:
[0009] Figure 1 is an enlarged cross-sectional view of
an embodiment of a shaped charge.
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[0010] Figure 2A is a profile cross-sectional view of an embodiment of a
perforating gun.
[0011] Figure 2B is a axial cross-sectional view of an embodiment of the
perforating gun
of Figure 2A.
[0012] Figure 3 is a profile view of an embodiment of a perforating gun string
being run
downhole in a cased wellbore.
[0013] Figure 4A is a profile view of an embodiment of a perforating gun
string being
detonated in a cased wellbore.
[0014] Figure 4B is a profile view of an embodiment of a perforating gun
string being
detonated in an open wellbore.
[0015] Figures 5A-6B are axial views of multiple embodiments of the
perforating gun of
the present invention.
[0016] It is to be noted, however, that the appended drawings illustrate only
typical
embodiments of this invention and are therefore not to be considered limiting
of its
scope, for the invention may admit to other equally effective embodiments.
DETAILED DESCRIPTION OF THE INVENTION
[0017] 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.
[0018] In the specification and appended claims: the terms "connect",
"connection",
"connected", "in connection with", and "connecting" are used to mean "in
direct
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connection with" or "in connection with via another element"; and the term
"set" is used
to mean "one element" or "more than one element". As used herein, the terms
"up" and
"down", "upper" and "lower", "upwardly" and downwardly", "upstream" and
"downstream"; "above" and "below"; and other like terms indicating relative
positions
above or below a given point or element are used in this description to more
clearly
described some embodiments of the invention. However, when applied to
equipment and
methods for use in wells that are deviated or horizontal, such terms may refer
to a left to
right, right to left, or other relationship as appropriate.
[0019] Referring to Figure 1, a shaped charge (10) includes an outer case (12)
that acts as
a containment vessel. Common materials for the outer case (12) include steel
or some
other metal. The main explosive charge (16) is contained inside the outer case
(12) and is
sandwiched between the inner wall of the outer case (12) and the outer
retaining surface
(20). A primer column (14) is a sensitive area that provides the detonating
link between
the main explosive charge (16) and a detonating cord (15), which is attached
to the rear
of the shaped charge (10).
[0020] To detonate the shaped charge (10), a detonation wave traveling through
the
detonating cord (15) initiates the primer column (14) when the detonation wave
passes
by, which in turn initiates detonation of the main explosive charge (16) to
create a
detonation wave that sweeps through the shaped charge (10).
[0021] Referring to Figure 2, a plurality of shaped charges (10) may be
conveyed
downhole via a hollow carrier gun (30). The shaped charges (10) may be non-
capsule
charges since the shaped charges are protected from the environment by the
hollow
carrier (30), which is typically sealed. The hollow carrier (30) may also
include a
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plurality of recesses (32) formed in the outer wall. The recesses (32) are
typically
localized areas where the wall thickness of the carrier (30) is reduced to
optimize overall
system function. Within the hollow carrier (30), a loading tube (40) is
positioned. The
loading tube (40) includes a plurality of openings (42) proximal, for
receiving and
mounting the shaped charges (10). The openings (42) of the loading tube (40)
are
typically aligned with the recesses (32) of the hollow carrier (30).
[0022] Referring to Figure 3, a series of hollow carrier guns (50A) and (50B)
may be
assembled to form a perforating gun string (50) having a desired length. An
example
length of each gun (50A and 50B, respectively), may be about twenty feet. To
make a
perforating gun string (50) of a few hundred feet or longer, several guns may
be
connected together in series by adapters (52). Each of the adapters (52)
contains a
ballistic transfer component, which may be in the form of donor and receptor
booster
explosives. Ballistic transfer takes place from one gun to another as the
detonation wave
jumps from the donor to the receptor booster. At the end of the receptor
booster is a
detonating cord that carries the wave and sets off the shaped charges in the
next gun.
Examples of explosives that may be used in the various explosive components
(e.g.,
shaped charges (10), detonating cord (15), and boosters) include RDX, HMX,
HNS,
TATB, and others.
[0023] Generally, once assembled, the gun string (50) is positioned in a
wellbore (60)
that is lined with casing (62). A tubing or pipe (64) extends inside the
casing (62) to
provide a conduit for well fluids to wellhead equipment (not shown). A portion
of the
wellbore (60) is isolated by packers (66) set between the exterior of the
tubing (64) and
the interior of the casing (62). The perforating gun string (50) may be
lowered through
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the tubing or pipe (54) on a carrier line (70) (e.g., wireline, slickline, or
coiled tubing).
Once positioned at a desired wellbore interval, the gun string (50) is fired
to create
perforations in the surrounding casing and formation (as shown in Figure 4A).
[0024] In another embodiment, as shown in Figure 4B, the gun string (50)
includes one
or more sealed carriers (30). In alternative embodiments, the gun string (50)
may include
one or more sealed chambers (or other sealed enclosures), each chamber housing
one or
more explosive charges therein. The pressure within the gun carrier (30) is
lower than
the pressure in the target wellbore interval. The sealed gun string (50) is
positioned in an
open wellbore (100). The perforating gun string (50) may be lowered through
the open
wellbore (100) on a carrier line (70) (e.g., wireline, slickline, or coiled
tubing). Once
positioned at a desired wellbore interval, the gun string (50) is fired to
create holes or
ruptures in the sealed carrier (30) while not substantially damaging the
surrounding.
Upon detonation of the one or more explosive charges and subsequent rupturing
of the
carrier (30), a fluid surge will be formed toward the carrier thus generating
a transient
underbalanced condition in the wellbore interval. This transient underbalance
condition
may be utilized to clean perforation tunnels in the surrounding formation, to
remove filter
cake from the walls of the wellbore, or to otherwise remove debris from the
wellbore
interval. Moreover, by rupturing the carrier, trapped pressurized gas in the
sealed bore of
the carrier may be released.
[0025] In other embodiments, the sealed perforating gun string (50) may be
deployed in a
cased wellbore and may be used to perforate the sealed carriers and the casing
simultaneously to create a transient underbalanced condition to surge clean
the
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perforation tunnels in the formation and remove wellbore debris from the
target well
interval. This will effectively increase productivity of the well.
[0026] The explosive energy released and the resulting perforation achieved by
detonating the guns discussed above may be a function of the physical size and
geometrical arrangement of the explosive charges. An embodiment of the present
invention is directed at controlling this explosive energy release.
[0027] Referring to Figures 5A-6B, a cap or other interfering element (80) may
be
arranged proximate the charge (10) to absorb a portion of the energy. The size
and
particular arrangement of the cap (80) with respect to the charge (10) may be
determined
to achieve an optimum explosive state for a selected result. For example, by
controlling
the explosive energy release of a charge, the amount of debris released into
the wellbore
and excessive deformation of the perforating gun may be limited.
[0028] The charge cap (80) of the present invention may also be used to direct
or
otherwise focus the explosive energy release to achieve a particular result.
For example,
the cap (80) may be sized and arranged to focus the explosive energy in a
charge to break
debris into small enough fragments such that the debris does not hider
productivity of the
well.
[0029] The charge cap (80) of the present invention may be used in various
perforating or
other explosive well operations. For example, the charge cap (80) may be used
to direct
and control explosive energy released by charges in a conventional perforating
gun (30)
used to perforate a formation and/or a casing and a formation. In another
example, the
charge cap may be used to direct and control explosive energy released by
charges in a
sealed chamber (e.g., carrier or other sealed enclosure) to rupture the
chamber but not
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damage the surrounding casing. In this way, the charges may be used to
generate a
transient underbalance condition to clean debris from the perforation tunnel.
[0030] Figures 5A and 5B illustrate embodiments of the charge cap (80) of the
present
invention connected to a shaped charge (10). The charge cap or other
interfering element
may be designed to fit between the arms (10A) of the explosive charge (10).
This
embodiment of the present invention is ideal for use with shaped charges
capable of
fitting relatively snugly within the internal compartment of the loading tube
(40).
[0031] In one embodiment, the charge cap of the present invention has a
section designed
to absorb explosive energy (88A) and another section designed to conduct
and/or direct
explosive energy (88D). In one embodiment, the section of the charge cap (80)
designed
to absorb explosive energy (88A) is designed to engage an inner surface (101)
of one or
more arms (10A) of the explosive charge. In one embodiment, the section of the
charge
cap (80) designed to conduct and/or direct explosive energy (88D) forms a
central portion
of the charge cap.
[0032] In one embodiment, the section of the charge cap designed to absorb
explosive
energy (88A) may be composed of a relatively thick and/or dense material
particularly
suited to absorb explosive energy. Further, the section of the charge cap
designed to
conduct and/or direct explosive energy (88D) may be composed of a thinner
and/or less
dense material than that used by the absorbing section (88A). In this manner,
the charge
cap allows for maximum effectiveness with regard to the disbursement of
explosive
energy upon detonation. The exact thickness and/or density of each section
(88A and
88D, respectively) of the charge cap may be determined and selected to achieve
any
number of desirable results.
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[0033] In one embodiment, one or more walls (82) of the charge cap may define
one or
more cavities (84) capable of directing explosive energy. Such cavities may
have any
number of orientations and/or configurations designed to achieve particular
results. For
example, one or more cavities provided by the present invention may have a
generally
conical or cylindrical configuration designed to direct explosive energy in a
particular
manner. It being understood that these are example configurations only, not to
be taken
in a limiting sense. A ring element having a bore therethrough may also be
utilized for
directing the explosive energy of the charge upon detonation.
[0034] Figures 6A and 6B illustrate embodiments of a charge cap (80) connected
to a
shaped charge (10). In these embodiments, the shaped charge and charge cap are
mounted in a jacket (86) and for insertion into a loading tube (40). The
loading tube may
hold a plurality of shaped charges (10), each having a charge cap (80). The
loading tube
is loaded into a gun carrier (30). The gun carrier (30) may have a scallop
(32) formed on
the outer surface for alignment with each shaped charge (10).
[0035] In one embodiment, the charge cap (80) of the present invention is
designed to
engage the outer surfaces (102) of the charge arms (10A) of the explosive
charge (10).
Further, the charge cap may be utilized in conjunction with a jacket (86) in
order to allow
the charge cap/charge/jacket combination to be conveniently mounted within the
loading
tube. This feature of the present invention allows smaller explosive charges
to be
successfully mounted within loading tubes having larger diameters. As
discussed above,
the present invention may utilize any number of charge cap arrangements and/or
configurations as needed to achieve a particular result. Further the thickness
and/or
density of the materials comprising each section of the charge cap may be
varied. A ring
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element having a bore therethrough may also be utilized for directing the
explosive
energy of the charge upon detonation, as discussed above.
[0036] In some embodiments, the charge cap (80) may be fabricated from a
material that
stays together sufficiently such that the cap does not exit the ruptures in
the gun. This
way the cap can be removed from the well with the gun and does not hinder well
productivity. In other embodiments, the charge cap (80) may be fabricated from
a
highly-frangible material such that the cap breaks into sufficiently small
fragments so as
not to hinder well productivity even if the fragments exit the gun. For
example, the
charge cap may be fabricated from plastic, polymer, metal, cellulose, rubber,
or other
suitable material.
[0037] Although the invention has been described with reference to specific
embodiments, this description is not meant to be construed in a limited sense.
Various
modifications of the disclosed embodiments, as well as alternative embodiments
of the
invention, will become apparent to persons skilled in the art upon reference
to the
description of the invention. It is, therefore, contemplated that the appended
claims will
cover such modifications that fall within the scope of the invention.
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