Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
HIGH ENERGY SEVERING TOOL WITH PRESSURE BALANCED
EXPLOSIVES
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a patent cooperation treaty (PCT)
application that
claims priority to U.S. Patent No. 9,4315,170, entitled "High Energy Severing
Tool With
Pressure Balanced Explosives," filed September 18, 2015, which is a
continuation-in-part
application that claims priority from U.S. Patent No. 9,4315,170, entitled
"Drill Collar
Severing Tool," filed January 26, 2015.
STATEMENT REGARDING FEDERAL RESEARCH OR DEVELOPMENT
[0002] Not applicable.
FIELD
[0003] The present invention relates to the earthboring arts. More
particularly, the
present invention relates, generally, to methods and devices for severing
drill pipe, casing
and other massive tubular structures by the remote detonation of an explosive
cutting
charge.
BACKGROUND
[0004] Deep well earthboring for gas, crude petroleum, minerals and
even water or
steam requires tubes of massive size and wall thickness. Tubular drill strings
may be
suspended into a borehole that penetrates the earth's crust several miles
beneath the drilling
platform at the earth's surface. To further complicate matters, the borehole
may be turned
to a more horizontal course to follow a stratification plane.
[0005] The operational circumstances of such industrial enterprise
occasionally present
a driller with a catastrophe that requires him to sever his pipe string at a
point deep within
the wellbore. For example, a great length of wellbore sidewall may collapse
against a drill
string and cause the drill string to wedge tightly in the well bore.
Thereafter, the wedged
drill string cannot be pulled from the well bore and, in many cases, cannot
even be rotated.
A typical response for salvaging the borehole investment is to sever the drill
string above
the obstruction, withdraw the freed drill string above the obstruction, and
return to the
wellbore with a "fishing" tool to free and remove the wedged portion of the
drill string.
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[0006] The
drill string weight, which is bearing on the drill bit and necessary for
advancement into the earth strata, is provided by a plurality of specialty
pipe joints having
atypically thick annular walls. In the industry vernacular, these specialty
pipe joints are
characterized as "drill collars." A drill control objective is to support the
drill string above
the drill collars in tension. Theoretically, only the weight of the drill
collars bears
compressively on the drill bit. With a downhole drilling motor, which is
configured for
deviated bore hole drilling, the drill motor, bent sub and drill bit are
positioned below the
drill collars. This drill string configuration does not rotate in the borehole
above the drill
bit. Consequently, the drill collar section of the drill string is
particularly susceptible to
borehole seizures and because of the drill collar wall thickness, is also
difficult to cut.
[0007] When
an operational event, such as a "stuck" drill string, occurs, the driller may
use wireline suspended instrumentation that is lowered within the central,
drill pipe flow
bore to locate and measure the depth position of the obstruction. This
information may be
used to thereafter position an explosive severing tool within the drill pipe
flow bore.
[0008]
Typically, an explosive drill pipe severing tool comprises a significant
quantity,
800 to 1,500 grams (12,345 grains to 23,149 grains) for example, of high order
explosive,
such as RDX (1,3,5-Trinitro-1,3,5-triazinane), HMX (1,3,5,7-Tetranitro-1,3,5,7-
tetrazocane) or HNS (hexanitrostilbene). The explosive powder is compacted
into high
density "pellets" of about 22.7 grams to about 38 grams (350 grains to 586
grains) each.
The pellet density is compacted to about 1.6 gm./cm3 to about 1.65 gm./cm3
(404.6
grains/inch3 to 417.3 grains/ inch3) to achieve a shock wave velocity greater
than about
9144 meters/second (30,000 ft/sec), for example. A shock wave of such
magnitude provides
a pulse of pressure in the order of 2.8 X 104 MPa (4 X 106 psi). It is the
pressure pulse that
severs the pipe.
[0009] In
one form, the pellets are compacted, at a production facility, into a
cylindrical
shape for serial, juxtaposed loading at the jobsite as a column in a
cylindrical barrel of a
tool call" _____________________________________________________________ idge.
Due to weight variations within an acceptable range of tolerance between
individual pellets, the axial length of explosive pellets fluctuates within a
known tolerance
range.
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[0010] Extreme well depth is often accompanied by extreme hydrostatic
pressure.
Hence, execution of the drill string severing operation may be required at
hydrostatic
pressures above 206.94 MPa (30,000 psi). Such high hydrostatic pressures tend
to
attenuate and suppress the pressure of an explosive pulse to such degree as to
prevent
separation.
[0011] One prior effort, by the industry, to enhance the pipe severing
pressure pulse
and to overcome high hydrostatic pressure suppression has been to detonate the
explosive
pellet column at both ends simultaneously. Theoretically, simultaneous
detonations at
opposite ends of the pellet column will provide a shock front from one end
colliding with
the shock front from the opposite end within the pellet column at the center
of the column
length. On collision, the pressure is multiplied, at the point of collision,
by about 4 to 5
times the normal pressure cited above. To achieve this result, however, the
detonation
process, particularly the simultaneous firing of the detonators, must be timed
precisely in
order to assure collision at the center of the explosive column.
[0012] Such precise timing is typically provided by means of mild
detonating fuse
and special boosters. However, if fuse length is not accurately cut or
problems exist in the
booster/detonator connections, the collision may not be realized at all and
the device will
operate as a "non-colliding" tool with substantially reduced severing
pressures.
[0013] The reliability of state-of-the-art severing tools is further
compromised by
complex assembly and arming procedures required at the well site. With those
designs,
laws and regulations require that explosive components (detonator, pellets,
etc.) must be
shipped separately from the tool body. Complete assembly must then take place
at the
well site under often unfavorable working conditions.
[0014] Finally, the electric detonators utilized by many state-of-the-art
severing tools
are vulnerable to stray electric currents and uncontrolled radio frequency
(RF) energy
sources, thereby further complicating the safety procedures that must be
observed at the
well site.
SUMMARY OF THE INVENTION
[0015] The pipe severing tool of the present invention comprises an outer
housing of
such outside diameter that is compatible with the drill pipe flow bore
diameter intended
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for use. Distinctively, the housing wall is extremely thin (e.g. 0.028 in.)
and vented to the
surrounding exterior environment for interior/exterior pressure equalization.
Accordingly,
the only material limitation on the housing is sufficient wall strength to
withstand the
rigors of well descent.
[0016] Another consequence of equalizing the interior housing pressure
with the
exterior well bore pressure is the design freedom to use a thin wall metallic
tube to house
the main load explosive charge. Furthermore, for a given external housing
diameter, a
larger internal diameter is available for explosive loading and, therefore, a
greater quantity
of explosive per unit length of housing. Synergistically, the shock value of
an explosive
detonation is exponentially increased by an increased explosive quantity,
often by the cube.
[0017] Vented housing exposure of the main load explosive to downhole
fluids, such
as water and petroleum based drilling fluids, is enabled by the use of fluid
impermeable
binders, such as Teflon or any other suitably hydrophobic polymer, which can
be
combined with formulations of HMX and other military grade explosives.
Explosives of
such formulations have been discovered to absorb well fluids at very low rates
of
deterioration. Little or no explosive energy is lost to well fluid exposures
that occur in the
order of an hour, which is usually more than an adequate time to accurately
position a
cutting tool for detonation.
[0018] The lower end of the present invention housing tube can be
closed by a sliding,
overlap assembly with a nose plug. The nose plug can be secured by screw
threads to a
tubular load rod. The housing tube upper end can be closed by a sliding,
overlap assembly
with a top carrier plug. However, the tubular load rod is threaded into the
inside face of
the top carrier plug and extends along the housing tube axis for substantially
the full length
of the housing tube.
[0019] A first bi-directional booster can be secured within the bore of
the load rod
tube at the top carrier plug. A first mild detonation cord can be housed along
the length of
the load rod tube bore, from the first booster to a second bi-directional
booster at the nose
plug end of the load rod tube. A third bi-directional booster can be secured
in the top
carrier plug for initiating a second mild detonation cord. The length of a
second mild
detonation cord can be laid in the trough of a helical flute that can be
formed on the
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surface of a timing spool. Opposite ends of the second detonation cord can be
disposed
within detonation proximity of third and fourth bi-directional boosters. In a
first
embodiment of the invention, the first and second detonation cords are of
identical length.
In another embodiment of the invention, the first, second, or both detonation
cords may
be pre-shrunk.
[0020] A pellet of initiating explosive (i.e., booster explosive) can be
positioned
within a socket in the top carrier plug. between the first and third bi-
directional boosters.
A thin, fluid impermeable bulkhead can be used to separate the initiating
explosive from
the first and third bi-directional boosters, to isolate the booster pellet
from the downhole
well fluid environment of the main lower explosive housing.
[0021] The timing spool is a substantially cylindrical body element, which
can have
an axial bore and a helical surface flute about the cylindrical axis. The
timing spool can
be secured to the load rod by rod penetration through the axial bore of the
spool. An
upper axial sleeve extension from the spool body can abut the top carrier plug
inside face
to secure a spacial separation of the spool from the booster carrier. A lower
axial sleeve
extension from the spool body can support the fourth bi-directional booster
and can serve
as a limit stop for a stack of washer-shaped primary explosive pellets, which
can be
aligned along the length of the load rod. A coil spring can be compressed
between an
inside face of the nose plug and a terminal pellet in the column of the main
load explosive
to bias the column tightly against the lower sleeve extension.
[0022] Those of skill in the art of oilfield explosives will appreciate a
characteristic of
the invention that allows the bi-directional boosters and detonation cord to
be transported
while assembled with the housing tube structure, as a unit, by traditional
carriers. The
main load explosive material and the explosion initiating booster pellet are
removed from
the assembly for isolated transport. The housing tube, bi-directional boosters
and
detonation cord, in operational assembly, are in compliance with standard
transport
regulations. At the site of use, the main load explosive pellets and
initiating booster may
be quickly inserted.
[0023] The invention assembly and loading sequence includes a separation of
the
housing tube and nose plug, as a unit, from the booster carrier and load rod.
Measured
quantities of military grade explosive material, such as HMX, RDX and HNS that
can be
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blended with a fluid impervious binder of polymer material that inhibits fluid
penetration
of, or absorption by, the explosive material, is pressed into annular disc
shaped pellets
that can have a central aperture with an inside diameter that can be slightly
greater than
the load rod diameter. The outside diameter of the pellets corresponds to the
inside
diameter of the housing tube. A multiplicity of such pellets can be aligned in
a column
along the length of the load rod, with the first pellet engaging the distal
end of the lower
axial sleeve of the timing spool and in detonation proximity with the fourth
bi-directional
booster.
[0024] With the predetermined number of main load explosive pellets in
place along
the load rod length, the housing tube and nose plug are repositioned over the
column of
the main load pellets. Threading the nose plug onto the load rod compresses a
coil spring
against the lower-most main load pellet. The thin wall housing tube remains
free of axial
compression.
[0025] An embodiment of the present invention includes an apparatus for
severing a
length of pipe, which can comprise a tubular housing having an internal bore
and a
plurality of bi-directional boosters, and one or more vents in the housing to
substantially
equalize fluid pressure within the bore with fluid pressure outside of the
tubular housing.
The apparatus can include a first detonation cord that can have a first length
between a
first bi-directional booster and a second bi-directional booster of said
plurality of bi-
directional boosters. In addition, the apparatus can comprise a second
detonation cord that
can have a first length between a third bi-directional booster and a fourth bi-
directional
booster of said plurality of bi-directional boosters. The embodiment of the
apparatus can
include a main load explosive material, positioned in the tubular housing and
located
between the second bi-directional booster and the fourth bi-directional
booster of the
plurality of bi-directional boosters; a fluid impermeable material that can be
mixed with
the main load explosive material; and an initiating booster explosive that can
be used for
simultaneously initiating the first and the third bi-directional boosters of
the plurality of-
bidirectional boosters.
[0026] In an embodiment, the main load explosive material can be pressed
into a
plurality of annular pellets, and the plurality of annular pellets can be
compressed to a
pressure corresponding to an expected detonation environment pressure.
Conesponding
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to the expected detonation environment pressure may entail either matching or
exceeding
the expected detonation environment pressure or, alternatively, if the
expected detonation
environment pressure is in excess of the pressure required to compress the
explosive
material to its maximum possible density, simply applying sufficient pressure
to achieve
said maximum possible density.
[0027] In an embodiment of the apparatus, the tubular housing can further
comprise a
tubular loading rod that can be used for penetrating a central aperture of the
plurality of
annular pellets. The annular pellets can be aligned along the tubular loading
rod, between
the second and the fourth of the plurality of bi-directional boosters. In an
embodiment, the
fourth of the plurality of bi-directional boosters can be disposed within
detonation
proximity of the main load explosive material.
[0028] In an embodiment of the apparatus for severing a length of pipe, the
tubular
loading rod can comprise a central bore, and the first bi-directional booster
and the
second bi-directional booster of the plurality of bi-directional boosters can
be disposed
within the central bore, at respectively opposite ends of the first detonation
cord. In an
embodiment, a first resilient bias can be positioned within said tubular
loading rod,
between a second end plug and the second of the plurality of bi-directional
boosters, and
the first resilient bias can bias the first bi-directional booster and the
second bi-directional
booster and the first detonation cord toward the pellet of initiating booster
explosive.
[0029] In an embodiment, the third bi-directional booster and the fourth bi-
directional
booster of the plurality of bi-directional boosters can be disposed at
respectively opposite
ends of the second detonation cord. An intermediate portion of the second
detonation cord
can be located between the third and the fourth of the plurality of bi-
directional boosters,
wherein the intermediate portion is wound about a timing spool. In an
embodiment, the
timing spool can comprise a cylindrical body and a helical flute formed on the
surface of
the body, about an axis thereof.
[0030] In an embodiment of the present invention, the apparatus can further
comprise
a first end plug and a second end plug for enclosing an internal bore between
opposite
ends of the tubular housing. The first end plug can comprise an initiating
booster cavity,
wherein the initiating booster cavity can hold the initiating booster
explosive. The
apparatus can further comprise a firing head that can be secured to the first
end plug, and
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the firing head can comprise a detonator that can be disposed within
detonation proximity
of the initiating booster explosive. In an embodiment, a second resilient bias
can be
positioned between the second end plug and the plurality of annular pellets.
[0031] In an embodiment, the tubular loading rod can comprise a structural
wall
surrounding or about the central bore, wherein the structural wall can be
penetrated by an
aperture, for example, between the second bi-directional booster and a portion
of the
plurality of annular pellets.
[0032] An embodiment of the present invention includes a method of severing
a pipe,
which comprises the steps of enclosing opposite ends of a tubular housing,
venting the
tubular housing to substantially equalize fluid pressure within the tubular
housing to the
fluid pressure outside of the tubular housing, and placing a first bi-
directional booster, a
second hi-directional booster, a third hi-directional booster, and a fourth hi-
directional
booster within the tubular housing. The steps of the method can continue by
connecting a
first detonation cord with a first length between the first hi-directional
booster and the
second bi-directional booster. In this embodiment, the method can include
connecting a
second detonation cord with a first length between the third hi-directional
booster and the
fourth hi-directional booster. The steps of the method can further continue by
combining
a main load explosive material and a fluid impermeable material into a
mixture, and
loading the mixture into the tubular housing, between the second and fourth bi-
directional
boosters. The method steps can conclude by positioning the tubular housing and
the
mixture inside of a pipe, and simultaneously initiating the ignition of the
second and the
fourth bi-directional boosters.
[0033] In an embodiment, the steps of the method can include the step of
pressing the
mixture into a plurality of annular pellets, wherein the step of pressing the
mixture further
comprises compressing the plurality of annular pellets to a pressure
corresponding to an
expected detonation environment. In an embodiment, the step of loading the
mixture into
the tubular housing can further comprise aligning the plurality of annular
pellets in a
column between the second bi-directional booster and the fourth hi-directional
booster of
the plurality of hi-directional boosters.
[0034] In an embodiment, the method can further include the step of
penetrating a
central aperture of the plurality of annular pellets with a tubular loading
rod, wherein the
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step of placing the first bi-directional booster, the second bi-directional
booster, the third
bi-directional booster, and the fourth bi-directional booster, of the
plurality of bi-
directional boosters, can further include placing the first bi-directional
booster of the
plurality of bi-directional boosters within one end of a central bore of the
tubular loading
rod and placing the second bi-directional booster of the plurality of bi-
directional boosters
within the central bore at an opposite end of the tubular loading rod.
[0035] The method steps of placing the first, the second, the third, and
the fourth of
the plurality of bi-directional boosters can further include placing the first
bi-directional
booster of the plurality of bi-directional boosters within detonation
proximity of an
initiating booster explosive, and in the same or another embodiment, placing
the third bi-
directional booster of the plurality of hi-directional boosters within
detonation proximity
of said initiating booster explosive.
[0036] In an embodiment, the step of connecting a second detonation cord
can
include wrapping the second detonation cord about a timing spool, and
positioning
opposite ends of the second detonation cord in detonation proximity of the
third bi-
directional booster and the fourth bi-directional booster, of the plurality of
bi-directional
boosters.
[0037] Other embodiments of the present invention can include an apparatus
for
severing a length of pipe, wherein the apparatus can comprise a tubular
housing that
includes an internal bore and at least one vent, wherein the at least one vent
can be usable
for equalizing fluid pressure within the internal bore to fluid pressure
outside of the
tubular housing; and a first end cap, positioned on a first distal end of the
tubular housing,
that is usable to close a first distal end of the internal bore, with an
initiating booster
explosive located in the first end cap. The apparatus can further comprise a
second end
cap positioned on a second distal end of the tubular housing and usable to
close a second
distal end of the internal bore. In addition, the apparatus can include a
loading tube
positioned within the tubular housing and connecting the first end cap with
the second
end cap, wherein the loading tube comprises a central bore and extends through
a timing
spool, and wherein a first bi-directional booster is positioned within the
central bore of
the loading tube, proximate to the first end cap and in detonation proximity
to the
initiating booster explosive. In this embodiment of the apparatus, a second hi-
directional
9
booster can be positioned within the central bore of the loading tube and
proximate to the
second end cap, and a first detonation cord can be positioned within the
loading tube,
between the first and the second bi-directional boosters. In this embodiment,
a second
detonation cord can have a first length between the third bi-directional
booster and the
initiating explosive booster, and a main load explosive material can be
positioned within
the tubular housing, between the second end cap and the third bi-directional
booster, for
ignition and use in severing the length of a pipe or other tubular. In an
embodiment, the
main load explosive can be pressed into a plurality of annular pellets, and
the loading tube
can extend through the plurality of annular pellets. The annular pellets can
be aligned
along the loading tube, between the second bi-directional booster and the
third bi-
directional booster.
[0038] In an embodiment, the apparatus can include a second detonation
cord that is
helically wound about the timing spool body. The second detonation cord can
extend
from the bi-directional booster, through the timing spool, to connect to the
initiating
booster explosive through an aperture in the first end cap.
[0039] An alternative embodiment of the present invention eliminates
the use of the
timing spool and a second detonation cord. Progression of a detonation front
along the
column of the main load explosive pellets may be retarded by a select number
of timing
discs that can be fabricated from a low impedance material, such as Teflon or
other
suitable polymer, that can be positioned along the load rod, between the
adjacent main
load explosive pellets. Similar results can be obtained by blending the
formulation of the
main load explosive with micro bubbles, which can reduce the detonation front
velocity.
[0040] Such an alternate embodiment can include an apparatus for
severing a length
of pipe that includes a tubular housing that includes an internal bore and at
least one vent,
wherein the at least one vent can be usable for equalizing fluid pressure
within the internal
bore to fluid pressure outside of the tubular housing; and a first end cap,
positioned on a
first distal end of the tubular housing, that is usable to close a first
distal end of the internal
bore, with an initiating booster explosive located in the first end cap. The
apparatus can
further comprise a second end cap positioned on a second distal end of the
tubular housing
and usable to close a second distal end of the internal bore. In addition, the
apparatus can
include a loading tube positioned within the tubular housing, between the
first end cap
Date Recue/Date Received 2022-02-08
and the second end cap. The loading tube can include a first bi-directional
booster
positioned within the loading tube and in detonation proximity to the
initiating booster
explosive, a second bi-directional booster positioned within the loading tube
and
proximate to the second end cap, and a detonation cord positioned within the
loading tube
and between the first bi-directional booster and the second bi-directional
booster. The
detonation cord can provide a detonation ignition time interval between
ignition of the
first bi-directional booster and ignition of the second bi-directional
booster. A third bi-
directional booster can be located within the first end cap and in detonation
proximity to
the initiating booster explosive. In this embodiment, a blend of explosive
material and
fluid impermeable material can be compressed into a plurality of annular
explosive pellets,
and a first column of the plurality of annular explosive pellets can comprise
a first quantity
of explosive material aligned along the loading tube, from the second bi-
directional
booster toward a detonation wave collision point. A second column of the
plurality of
annular explosive pellets can comprise the first quantity of explosive
material aligned
along the loading tube, from a third bi-directional booster toward the
detonation wave
collision point, and a detonation wave retarding material that can be usable
for retarding
the progress of a detonation wave along the second column by a time interval
corresponding to a detonation wave time interval along the first column.
[0041] In an embodiment, the apparatus can include a fluid barrier
positioned in the
first end cap, between the tubular housing and the initiating booster
explosive, to isolate
the initiating booster explosive from fluid within the housing. The detonation
wave
retarding material can comprise one or more annular discs of polymer material
that can be
distributed among the plurality of annular explosive pellets, wherein the
polymer material
can be Teflon. In an embodiment, the detonation wave retarding material can
comprise
glass micro-balloons that can be blended with the explosive material and the
fluid
impermeable material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] The advantages and further features of the invention will be
readily appreciated
by those of ordinary skill in the art as the same becomes better understood by
reference to
the following detailed description when considered in conjunction with the
accompanying
drawings in which like reference characters designate like or similar
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elements throughout.
[0043] FIG. 1 is a sectional view of the present invention as assembled for
operation.
[0044] FIG. 2 is a lower end view of Fig. 1.
[0045] FIG. 3 is a sectional view of the second embodiment of the
invention.
[0046] FIG. 4 is a sectional view of the third embodiment of the invention.
[0047] FIG. 5 is a sectional view of the fourth embodiment of the
invention.
[0048] FIG. 6 is a sectional view of a fifth embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0049] Before explaining selected embodiments of the present invention in
detail, it is
to be understood that the present invention is not limited to the particular
embodiments
described herein and that the present invention can be practiced or carried
out in various
ways. 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 describe 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.
Moreover, in the specification and appended claims, the terms -pipe", -tube",
"tubular",
"casing", "liner" and/or "other tubular goods" are to be interpreted and
defined
generically to mean any and all of such elements without limitation of
industry usage.
[0050] Embodiments of the present invention relate, generally, to methods
and
devices for severing drill pipe, casing and other massive tubular structures
by the remote
detonation of an explosive cutting charge. Referring to the FIG. 1, a cross-
sectional view
of the present invention is shown that includes a tubular outer housing 10,
which is
secured at an upper distal end to a top carrier plug 12. The outer housing 10
has an
internal bore 11 that is closed at its lower end by a nose plug 14 (also shown
in Fig. 2).
Notably, the housing 10 interior is vented to the exterior by the use of
tubular wall
apertures 16.
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[0051] The upper end of the housing bore 11 is closed by a firing assembly,
which
can comprise a top carrier plug 12 and a firing head 26, as shown. An internal
cavity 20 in
the top carrier plug 12 is formed to receive a pellet of initiating booster
explosive 22.
Thin, fluid pressure bulkheads 24 are shown, for example as fluid barriers,
that can be
positioned across the initiating booster cavity bottom to isolate the
initiating booster
explosive 22 from the well fluid and pressure environment that can occupy the
interior
bore of the housing 10 due to the apertures 16 (i.e., vents).
[0052] The upper end of the top carrier plug 12 can include an internally
threaded
socket 18, as shown in Fig. 1. The socket 18 can receive the firing head 26
that positions
a detonator 28 in detonation proximity of the initiating booster explosive 22.
Detonation
proximity is that distance between a particular detonator and a particular
receptor
explosive within which ignition of the detonator will initiate a detonation of
the receptor
explosive.
[0053] The loading rod 30 can be secured to the top carrier plug 12 by
threads, and
the loading rod 30 can project from the inside face 32 of the plug 12, along
the housing
axis. The opposite distal end of the loading rod 30 can be threaded into a
socket 15 in
the nose plug 14.
[0054] The upper end of the loading rod 30 can penetrate an axial bore
through and
along the length of a generally cylindrical timing spool body 34. The
cylindrical surface
of the timing spool body 34 can be formed with a helically wound flute 36.
Opposite ends
of the timing spool body 34 can be formed as reduced outside diameter sleeves
38 and 39.
The upper sleeve 38 can be usable for spacing the spool body 34 from the top
carrier plug
12. The lower sleeve 39 can be usable for spacing the spool body 34 from the
uppermost
main load explosive pellet 40 and can provide structural support for a hi-
directional
booster 48. Bi-directional boosters 42, 44, 46, 48 may additionally be self-
supporting
through compression prior to loading within housing 10 or loading rod 30.
[0055] As shown in Fig. 1, the length of a first detonation cord 43 is
housed within
the central bore of the loading rod 30 and links the first bi-directional
booster 42 with the
second bi-directional booster 44. The first bi-directional booster 42 is
housed within the
upper end of the bore of the loading rod 30 and within detonation proximity of
the
initiating booster explosive 22. The second hi-directional booster 44 is
housed near the
13
lower distal end of the bore of the loading rod 30 and against the resilient
bias of a coil
spring 50, also positioned within the bore of the loading rod 30. The coil
spring 50
maintains a compressive contact between the first and second bi-directional
boosters and
the first detonation cord 43. A slit is cut into the structural wall of the
loading rod 30,
adjacent the second bi-directional booster 44, to provide an ignition
initiation window 52
between the second bi-directional booster 44 and the adjacent main load
explosive pellets
40. A larger coil spring 54 surrounds the lower end of the load rod 30 to
apply a resilient
bias between the nose plug 14 and the end-most main load explosive pellet 40.
[0056] In the embodiment shown in Figure 1, a third bi-directional
booster 46 can be
secured within an aperture 13 (shown in Fig. 3) that penetrates the transverse
wall 32 (i.e.,
inside face wall) of the top carrier plug 12 to position the third bi-
directional booster 46
in detonation proximity of the initiating explosive 22. As further shown in
the embodiment
of the present invention shown in Fig. 1, a fourth bi-directional booster 48
can be secured
to the lower timing spool sleeve 39. The third and fourth bi-directional
boosters 46 and 48
can be linked by a second mild detonation cord 45, which has substantially the
same length
as the first mild detonating cord 43. However, the intermediate length of the
second
detonation cord 45 is wound about the flutes 36 on the timing spool 34
surface.
[0057] The distal end of the nose plug 14 can be tapered back from a
central boss 56
to provide flexure clearance for the two or more centralizers 58, as shown by
Fig. 2, which
are used for centralizing the high energy severing tool within a tubular
and/or the wellbore.
Each centralizer 58 can be secured by a pair of fasteners, such as machine
screws 60, to
provide resistance against rotation of the centralizers about the tool axis.
[0058] It should be understood that the tool assembly, as described
above, may be
safely transported by traditional media with the bi-directional boosters 42,
44, 46, and 48
in place and the detonation cords 43 and 45 positioned between the respective
bi-
directional boosters. However, in transport, no main load explosive material
40 and/or
initiating booster pellets 22 are present within the housing 10 assembly.
[0059] Annular pellets of main load explosive material 40 can be formed
from
explosive material, such as RDX, HNX or HNS, which is mixed with a fluid
impermeable
material, such as Teflon or other polymer as a binder. Approximately 22.7
gms. to 38
gms. (350 grains to 586 grains) of such explosive material is pressed into an
annular disc
14
Date Recue/Date Received 2022-02-08
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of an outside diameter that is less than the inside diameter of the housing 10
and a central
aperture diameter that is greater than the outside diameter of the loading rod
30.
Preferably, the annulus shaped pellets are compacted to a pressure
corresponding to an
expected detonation environment pressure.
[0060] As previously stated, the apparatus may be safely transported to the
well site
of use with the bi-directional boosters and the detonation cord in place. The
main load
pellets 40 and initiation booster explosive pellet 22 are transported
separately.
[0061] Final assembly of the complete severing tool normally occurs on the
drilling
rig floor at the well site. The housing tube 10 and nose plug 14, as an
integral unit, are
withdrawn from the top carrier 12 and loading rod 30,
[0062] The required number or plurality of main load pellets 40 can be
aligned in a
column with the pellet central aperture around the loading rod 30, and the
first pellet
abutting the lower spool sleeve 39. Then, the threaded socket 15 of the nose
plug 14 can
be screwed onto the lower distal end of the loading rod 30, thereby
compressing the load
rod spring 50 against the second bi-directional booster 44 and the outer
larger spring 54
against the main load explosive pellet 40 assembly.
[0063] With the main load explosive pellets aligned in a column over the
loading rod
30, the housing 10 can be secured to the top carrier plug 12. Next, the pellet
of initiating
booster explosive 22 can be inserted into the internal cavity 20, and the
firing head 26 can
be screwed into the socket 18 of the top carrier plug 12 to position the
detonator 28 within
detonation proximity of the pellet of initiating booster explosive 22.
[0064] As assembled, the tool can be secured to the end of a suspension
string and
lowered into the well bore, along the well pipe flow bore. When positioned at
the required
location, the initiating booster explosive 22 is detonated to start a pair of
parallel ignition
sequences that meet at the central collision point.
[0065] The second embodiment of the invention, illustrated by Fig. 3,
differs from
Fig. 1 mainly by the omission of the third bi-directional booster 46. As shown
in Figure 3,
the first detonation cord 43 is positioned between the first bi-directional
booster 42 and
the second bi-directional booster 44, and the second detonation cord 45
connects the
fourth bi-directional booster 48 to the initiating booster explosive 22. As
shown, the
upper distal end of the second detonation cord 45 is secured within an
aperture 13, thereby
positioning the end of the second detonation cord 45 within detonation
proximity of the
pellet of initiating booster explosive 22. The intermediate length of the
second detonation
cord 45, between the aperture 13 and the bi-directional booster 48, is wrapped
about the
flutes 36 of the timing spool body 34.
[0066] A third embodiment of the invention, as shown by Fig. 4, omits
the use of a
timing spool body 34, a second detonation cord 45, and a fourth bi-directional
booster 48
by inserting timing washers 70 between explosive pellets 40 in the upper
portion of the
main load explosive column. As shown, this embodiment includes a detonation
cord 43
positioned between the first bi-directional booster 42 and the second bi-
directional booster
44, with the third bi-directional booster positioned proximate to the
initiating booster
explosive 22.
[0067] In this third embodiment of the invention, a first column of
main load
explosive pellets 40, collectively comprising a predetermined quantity of
explosive
material and a fluid impermeable material, is aligned along the loading rod
30, between
the second bi-directional booster 44 and a detonation wave collision point. A
second
column of main load explosive pellets 40, also collectively comprising the
predetermined
quantity of explosive material, is aligned along said loading rod 30, from
detonation
proximity with the third bi-directional booster 46 to said detonation wave
collision point.
However, also progressing along the second column from the third bi-
directional booster
46 toward said detonation wave collision point is a number of pellet shaped
timing
washers 70 that are distributed among the main load explosive pellets 40. Each
timing
washer 70 retards the progress of the explosive shock front as it advances
along the second
explosive column from the third bi-directional booster 46 toward the
detonation wave
collision point. Suitable fabrication materials for such timing washers
include numerous
polymers, such as Teflon . The total elapsed time between detonation of the
first bi-
directional booster 48 and the second bi-directional booster 44 corresponds to
the total
retardation time that must be incurred by the timing washers 70. As many of
the timing
washers 70 are provided in the second main load explosive column as is
necessary to
substantially match the time interval for a detonation wave to travel along
the first
detonation cord 43, from the first bi-directional booster 42 to the second bi-
directional
16
Date Recue/Date Received 2022-02-08
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booster 44, so the two primary explosive shock waves, arising from the same
quantity of
explosive material in both columns, will collide at the detonation wave
collision point.
[0068] As a variant of Fig. 4, the embodiment shown in Fig. 5 provides
glass micro-
bubbles that can be blended with the explosive material of the second column
along with
the fluid impermeable material. Such micro-bubbles are known to retard the
shock wave
advance through explosive material. In this example, the micro-bubble blended
pellets 41
comprise the second column of main load explosive. As in the second example,
however,
the same quantity of explosive material is provided for both columns.
[0069] As a further variant, the embodiments depicted in Figs. 4-5 may be
constructed without an outer housing. Fig. 6 depicts a variant of Fig. 5, with
the housing
and corresponding housing apertures removed from the apparatus such that the
compressed pellets are directly exposed to the well environment. It can be
appreciated by
those of ordinary skill in the art that the embodiment in Fig. 4 may be
similarly
constructed without a housing.
[0070] Numerous modifications and variations may be made of the structures
and
methods described and illustrated herein without departing from the scope and
spirit of
the invention disclosed. Accordingly, it should be understood that the
embodiments
described and illustrated herein are only representative of the invention and
are not to be
considered as limitations upon the invention as hereafter claimed.
17
