U.S. patent application number 09/949990 was filed with the patent office on 2003-03-13 for drill pipe explosive severing tool.
Invention is credited to Bell, William T..
Application Number | 20030047312 09/949990 |
Document ID | / |
Family ID | 25489797 |
Filed Date | 2003-03-13 |
United States Patent
Application |
20030047312 |
Kind Code |
A1 |
Bell, William T. |
March 13, 2003 |
Drill pipe explosive severing tool
Abstract
A pipe severing tool is arranged to align a plurality of high
explosive pellets along a unitizing support structure whereby all
explosive pellets are inserted within or extracted from a tubular
housing as a singular unit. Electrically initiated exploding wire
detonators (EBW) are positioned at opposite ends of the tubular
housing for simultaneous detonation by a capacitive firing device.
The housing assembly includes a detachable bottom nose that permits
the tool to be armed and disarmed without disconnecting the
detonation circuitry. Because the tool is not sensitive to stray
electrical fields, it may be transported, loaded and unloaded with
the EBW detonators in place and connected.
Inventors: |
Bell, William T.;
(Huntsville, TX) |
Correspondence
Address: |
W. ALLEN MARCONTELL
P.O. BOX 800149
HOUSTON
TX
77280
US
|
Family ID: |
25489797 |
Appl. No.: |
09/949990 |
Filed: |
September 10, 2001 |
Current U.S.
Class: |
166/297 ;
166/55.1 |
Current CPC
Class: |
F42B 3/26 20130101; E21B
17/06 20130101; E21B 29/02 20130101; F42D 1/22 20130101; F42B 3/24
20130101; F42B 3/00 20130101; F42D 3/00 20130101 |
Class at
Publication: |
166/297 ;
166/55.1 |
International
Class: |
E21B 043/11 |
Claims
1. An apparatus for explosively severing a length of pipe having an
internal flowbore, said apparatus comprising: a tubular exterior
housing having an interior barrel extending between opposite distal
ends of the barrel; a plurality of high explosive pellets in axial
alignment and bound together as a singular and independent unit
that may be selectively inserted within said barrel and withdrawn
unexploded therefrom as a single unit; and, electrically initiated
detonation means engaging the explosive pellet unit.
2. An apparatus as described by claim 1 wherein said detonation
means comprises detonators at opposite ends of said pellet
unit.
3. An apparatus as described by claim 1 wherein the detonators
respective to said opposite ends are connected for simultaneous
detonation.
4. An apparatus as described by claim 3 wherein said opposite end
detonators resiliently bear compressively against respective ends
of said pellet unit.
5. An apparatus as described by claim 3 wherein one end of said
exterior housing is selectively detached, with one of said
detonators, from the remainder of said exterior housing for loading
said pellet unit into said barrel.
6. An apparatus for explosively severing a length of pipe having an
internal flowbore, said apparatus comprising: (a) a tubular housing
having an internal barrel space between opposite distal ends for
aligning an axial column of explosive material; (b) detonator
socket housings disposed at opposite ends of said opposite distal
ends; (c) resilient bias means for resiliently translating at least
one socket housing along said barrel space toward the other socket
housing; (d) exploding bridge wire detonators in said socket
housings; and, (e) a capacitive firing device electrically
connected to said exploding bridge wire detonators.
7. An apparatus as described by claim 6 wherein at least one of
said detonator housings may be selectively separated from said
tubular housings while maintaining an electrically conductive
connection with said firing device.
8. An apparatus as described by claim 6 wherein one distal end of
said tubular housing is sealed by a closure means that is
selectively removed from said tubular housing to load a column of
explosive material into said internal barrel, said closure means
including the socket housing respective to said one distal end.
9. An apparatus as described by claim 8 wherein said closure means
further including a guide aperture for aligning said explosive
material within said internal barrel.
10. An apparatus as described by claim 6 wherein the socket housing
respective to said other distal end is resiliently biased along the
length of said internal barrel to compressively confine said column
of explosive material between said socket housings.
11. A method of severing a length of pipe having an internal flow
bore comprising the steps of: assembling a plurality of high
explosive pellets into a singular, columned unit; depositing said
columned unit into a tubular barrel; resiliently engaging at least
one end of said columned unit with detonator means; positioning
said tubular barrel within said flow bore at a predetermined
location along the length of said flow bore; and, electrically
initiating said detonator means.
12. A method of severing a length of pipe as described by claim 11
wherein detonator means engage opposite ends of said columned unit
of high explosive pellets.
13. A method of severing a length of pipe as described by claim 12
wherein opposite end detonator means are simultaneously
initiated.
14. A method of severing a length of pipe as described by claim 11
wherein said plurality of high explosive pellets are unitized in a
column separate from said tubular barrel and inserted in said
tubular barrel as a singular unit prior to positioning said barrel
within said flow bore.
15. A method of severing a length of pipe as described by claim 14
wherein said plurality of pellets are formed for meshed engagement
with unitizing structure whereby said unitizing structure and
meshed pellets are inserted within or removed from said tubular
barrel as a singular unit.
16. A method of severing a length of pipe having an internal flow
bore comprising the steps of: providing a tubular barrel space for
assembling a column of highly explosive material; providing
exploding wire detonators at opposite ends of said tubular barrel
space; providing a capacitive firing device for selectively
igniting said detonators substantially simultaneously; assembling a
column of highly explosive material within said tubular barrel
space; resiliently engaging opposite ends of said explosive
material column with said exploding bridge wire detonators;
positioning said tubular barrel within the internal flow bore of a
pipe at a predetermined location along the length of said flow
bore; and, electrically initiating said detonator means.
17. A method as described by claim 16 wherein said column of
explosive material is assembled externally of said tubular barrel
and positioned into said barrel space as an integral unit;
18. A method of severing a string of pipe extending within a well
bore from a wellhead site, said method comprising the steps of:
providing a severing tool at a wellhead site, said severing tool
having an internal barrel space between opposite distal ends within
a substantially tubular housing; providing exploding bridge wire
detonators at said opposite distal ends; electrically connecting
said exploding bridge wire detonators to a capacitive firing device
for substantially simultaneous ingition of said detonators by said
firing device; delivering said electrically connected severing tool
to a wellhead site; depositing a column of explosive material in
said internal barrel space between said exploding bridge wire
detonators at said wellhead site; positioning said severing tool at
a predetermined location within a string of pipe suspended from
said wellhead site; and, detonating said column of explosive
material by an electrical signal to said capacitive firing
device.
19. A method as described by claim 18 wherein said column of
explosive material is assembled as a singular unit externally of
said barrel space and deposited in said barrel space as a singular
unit.
20. A method as described by claim 19 wherein said column of
explosive material is deposited within said barrel space without
electrically disconnecting either of said detonators.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the earthboring arts. More
particularly, the invention relates to methods and devices for
severing drill pipe, casing and other massive tubular structures by
the remote detonation of an explosive cutting charge.
[0003] 2. Description of Related Art
[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 presents 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 the drill string causing it to wedge tightly in the well
bore. The 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 with a "fishing" tool to free and remove the
wedged portion of drill string.
[0006] 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.
[0007] Typically, an explosive drill pipe severing tool comprises a
significant quantity, 800 to 1,500 grams for example, of high order
explosive such as RDX, HMX or HNS. The explosive powder is
compacted into high density "pellets" of about 22.7 to about 38
grams each. The pellet density is compacted to about 1.6 to about
1.65 gms/cm.sup.3 to achieve a shock wave velocity greater than
about 30,000 ft/sec, for example. A shock wave of such magnitude
provides a pulse of pressure in the order of 4.times.10.sup.6 psi.
It is the pressure pulse that severs the pipe.
[0008] 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
cartridge. 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. Furthermore, the
diameter-to-axial length ratio of the pellets is such that allows
some pellets to wedge in the tool cartridge barrel when loaded. For
this reason, a go-no-go type of plug gauge is used by the prior art
at the end of a barrel to verify the number of pellets in the tool
barrel. In the frequent event that the tool must be disarmed, the
pellets may also wedge in the barrel upon removal. A non-sparking
depth-rod is inserted down the tool barrel to verify removal of all
pellets.
[0009] Extreme well depth is often accompanied by extreme
hydrostatic pressure. Hence, the drill string severing operation
may need to be executed at 10,000 to 20,000 psi. Such high
hydrostatic pressures tend to attenuate and suppress the pressure
of an explosive pulse to such degree as to prevent separation.
[0010] One prior effort by the industry to enhance the pipe
severing pressure pulse and 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 precisily in
order to assure collision within the explosive column at the
center.
[0011] Such precise timing is typically provided by means of mild
detonating fuse and special boosters. However, if fuse length is
not accurate 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.
[0012] 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, 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.
[0013] Finally, the electric detonators utilized by
state-of-the-art severing tools are not as safe from the electric
stray currents and RF energy points of view, further complicating
the safety procedures that must be observed at the well site.
SUMMARY OF THE INVENTION
[0014] The pipe severing tool of the present invention comprises an
outer housing that is a thin wall metallic tube of such outside
diameter that is compatible with the drill pipe flow bore diameter
intended for use. The upper end of the housing tube is sealed with
a threaded plug having insulated electrical connectors along an
axial aperture. The housing upper end plug is externally prepared
to receive the intended suspension string such as an electrically
conductive wireline bail or a continuous tubing connecting sub.
[0015] The lower end of the outer housing tube is closed with a
tubular assembly that includes a stab fit nose plug. The nose plug
assembly includes a relatively short length of heavy wall tube
extending axially out from an internal bore plug. The bore plug
penetrates the barrel of the housing tube end whereas the tubular
portion of the nose plug extends from the lower end of the housing
tube. The bore plug is perimeter sealed by high pressure O-rings
and secured by a plurality of set screws around the outside
diameter of the outer housing tube.
[0016] The tubular portion of the nose plug provides a closed
chamber space for enclosing electrical conductors. The bore plug
includes a tubular aperture along the nose plug axis that is a load
rod alignment guide. Laterally of the load rod alignment guide is a
socket for an exploding bridge wire (EBW) detonator or an exploding
foil initiator (EFI).
[0017] Within the upper end of the outer housing barrel is an inner
tubular housing for a electronic detonation cartridge having a
relatively high discharge voltage, 5,000 v or more, for example.
Below the inner tubular housing is a cylindrical, upper detonator
housing. The upper detonator housing is resiliently separated from
the lower end of the inner tubular housing by a suitable spring.
The upper detonator housing includes a receptacle socket 31 for an
exploding bridge wire (EBW) detonator. The axis for the upper
detonator receptacle socket is laterally offset from the outer
housing barrel axis.
[0018] Preferably, the severing tool structure is transported to a
working location in a primed condition with upper and lower EBW
detonators connected for firing but having no high explosive
pellets placed between the EBW detonators. At the appropriate
moment, the nose plug assembly is removed from the bottom end of
the outer housing and a load rod therein removed. The upper distal
end of the load rod includes a circumferential collar such as a
snap ring. The opposite end of the load rod is visually marked to
designate maximum and minimum quantities of explosive aligned along
the load rod.
[0019] Explosive pellets for the invention are formed as solid
cylinder sections having an axial aperture. The individual pellets
are stacked along the load rod with the load rod penetrating the
axial aperture. The upper distal end collar serves as a stop limit
for the pellets which are serially aligned along the rod until the
lower face of the lowermost pellet coincides with the max/min
indicia marking. A restriction collar such as a resilient O-ring is
placed around the loading rod and tightly against the bottom face
of the lowermost explosive pellet.
[0020] The rod and pellet assembly are inserted into the outer
housing barrel until the uppermost pellet face contiguously engages
the upper detonator housing. The rod guide aperture in the nose
plug is then assembled over the lower distal end of the load rod
and the lower detonator brought into contiguous engagement with the
lowermost pellet face. The assembly is then further compressed
against the loading spring between the inner tubular housing and
the upper detonator housing until abutment between the nose plug
shoulder and the lower distal end of the outer housing tube.
[0021] In the event that the invention severing tool must be
disarmed, all pellets may be removed from the housing barrel as a
singular unit about the load rod. This is accomplished by removing
the lower nose plug which exposes the lower end of the load rod. By
grasping and pulling the load rod from the housing barrel, all
pellets that are pinned along the load rod below the upper distal
end collar are drawn out of the housing tube with the rod.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Relative to the drawings wherein like reference characters
designate like or similar elements or steps through the several
figures of the drawings:
[0023] FIG. 1 is a sectional view of the invention as assembled
without an explosive charge for transport;
[0024] FIG. 2 is a sectional view of the invention with the bottom
nose piece detached from the main assembly housing;
[0025] FIG. 3 is a sectional view of an assembled, explosive pellet
unit;
[0026] FIG. 4 is a sectional view of the invention with the
explosive pellet unit combined with the main assembly housing but
the bottom nose piece detached therefrom;
[0027] FIG. 5 is a sectional view of the invention in operative
assembly with an explosive pellet unit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] Referring to the FIG. 1 cross-sectional view of the
invention 10, a tubular outer housing 12 having an internal bore 14
is sealed at an upper end by a plug 16. The plug 16 includes an
axial bore 18 and an electrical connector 20 for routing detonation
signal leads 22. A boss 17, projecting from the base of the plug,
is externally threaded for the attachment of the desired suspension
string such as an electrical wireline or service tubing.
[0029] An inner housing tube 24 is secured to and extends from the
upper end plug 16 into the internal bore 14 of the outer housing
12. The inner housing tube 24 encloses a capacitive firing
cartridge 26. Below the inner housing 24 is an upper detonator
housing 28. A coil spring 30 links the upper detonator housing 28
to the inner housing tube 24. An exploding bridge wire (EBW)
detonator or exploding foil initiator (EFI) 32 is seated within a
receptacle socket formed in the upper detonator housing 28
laterally of the housing axis. Electrical conduits 34 connect the
capacitive firing cartridge 26 to to the EBW detonator or EFI
32.
[0030] An exploding bridge wire (EBW) detonator comprises a small
quantity of moderate to high order explosive that is detonated by
the explosive vaporization of a metal filament or foil (EFI) due to
a high voltage surge imposed upon the filament. A capacitive firing
cartridge is basically an electrical capacitator discharge circuit
that functions to to abruptly discharge with a high threshold
voltage. Significantly, the EBW detonator or EFI is relatively
insensitive to static or RF frequency voltages. Consequently, the
capacitive firing circuit and EBW or EFI function cooperatively to
provide a substantial safety advantage. An unusually high voltage
surge is required to detonate the EBW detonator (or EFI) and the
capacitive firing cartridge delivers the high voltage surge in a
precisely controlled manner. The system is relatively impervious to
static discharges, stray electrical fields and radio frequency
emissions. Since the EBW and EFI detonation systems are,
functionally, the same, hereafter and in the attached invention
claims, reference to an EBW detonator is intended to include and
encompass an EFI.
[0031] The lower end of the outer housing tube 12 is operatively
opened and closed by a nose plug 40. The nose plug 40 comprises a
plug base 42 having an O-ring fitting within the lower end of the
outer housing bore 14. The plug base 42 may be secured to the outer
housing tube 12 by shear pins or screws 44 to accomodate a straight
push assembly. Projecting from the interior end of the plug base is
a guide tube boss 46 having an axial throughbore 48 and a
receptacle socket 50 for a detonator cap 66.
[0032] Projecting from the exterior end of the plug base 42 is a
heavy wall nose tube 52 having a nose cap 54. The nose cap 54 may
be disassembled from the nose tube 52 for manual access into the
interior bore 56 of the nose tube 52. Detonation signal conductor
leads 58 are routed from the firing cartridge 26, through the upper
detonator housing and along the wall of housing bore 14. A
conductor channel 60 routes the leads 58 through the nose plug base
42 into the nose tube interior 56. This nose tube interior provides
environmental protection for electrical connections 62 with
conductor leads 64 from the lower EBW detonator 66.
[0033] Although the electrical connections of both EBW detonators
32 and 66 are field accessible, it is a design intent for the
invention to obviate the need for field connections. Without
explosive pellet material in the outer housing bore 14, EBW
detonators 32 and 66 are the only explosive material in the
assembly. Moreover, the separation distance between the EBW
detonators 32 and 66 essentially eliminates the possibility of a
sympathetic detonation of the two detonators. Consequently, without
explosive material in the tubing bore 14, the assembly as
illustrated by FIG. 1 is safe for transport with the EBW detonators
32 and 66 connected in place.
[0034] The significance of having a severing tool that requires no
detonator connections at the well site for arming cannot be
minimized. Severing tools are loaded with high explosive at the
well site of use. Often, this is not an environment that
contributes to the focused, intellectual concentration that the
hazardous task requires. Exacerbating the physical discomfort is
the emotional distraction arising from the apprehension of
intimately manipulating a deadly quantity of highly explosive
material. Hence, the well site arming procedure should be as simple
and error-proof as possible. Complete elimination of all electrical
connection steps is most desirable.
[0035] The load rod 70, best illustrated by FIGS. 2, 3 and 4, is
preferably a stiff, slender shaft having an end retainer 72 such as
a "C" clip or snap ring. Preferably, the shaft is fabricated from a
non-sparking material such as wood, glass composite or non-ferrous
metal. Individual high explosive "pellets" 74 are cylindrically
formed with a substantially uniform outer perimeter OD and a
substantially uniform ID center bore. The term "pellets" as used
herein is intended to encompass all appropriate forms of explosive
material regardless of the descriptive label applied such as
"cookies", "wafers", or "charges". The axial length of the pellets
may vary within known limits, depending on the exact weight
quantity allocated to a specific pellet. The pellets are assembled
as a serial column over the rod 70 which penetrates the pellet
center bore. A prior calculation has determined the maximum and
minimum cumulative column length depending on the the known weight
variations. This maximum and minimum column length is translated
onto the rod 70 as an indicia band 76. The maximum and minimum
length dimensions are measured from the rod end retainer 72. The OD
of the end retainer 72 is selected to be substantially greater than
the ID of the pellet center bore. Hence the pellets cannot pass
over the end retainer and can slide along the rod 70 length no
further than the end retainer. When loading the tool with explosive
in the field, the correct quantity of explosive 74 will terminate
with a lower end plane that coincides within the indicia band 76.
An elastomer O-ring 78 constricted about the shaft of rod 70
compactly confines the pellet assembly along the rod length.
[0036] A lower distal end portion 79 of the rod extends beyond the
indicia band 76 to penetrate the guide bore 48 of the bore plug
base 42 when the bottom nose plug 40 is replaced after an explosive
charge has been positioned. This rod extension allows the high
explosive to be manually manipulated as a singular, integrated
unit. In full visual field, the explosive charge is assembled by a
columned alignment of the pellets over the penetrating length of
the rod. When the outside surface plane of the last pellet in the
column aligns within the indicia band 76, the lower end retainer 78
is positioned over the rod and against the last pellet surface
plane to hold the column in tight, serial assembly. Using the rod
extension 79 as a handle, the explosive assembly is axially
inserted into the housing bore 14 until contiguous contact is made
with the lower face of the upper detonator housing 28.
[0037] One of the synergistic advantages to the unitary rod loading
system of the invention is use of lighter, axially shorter pellets,
i.e. 22.7 gms. These lighter weight pellets enjoy a more favoraable
shipping classification (UN 1.4S) than that imposed on heavier, 38
gm pellets (UN 1.4D). In a prior art severing tool, the lighter
weight pellets would be avoided due to "cocking" in the tool barrel
14 during loading. The loading rod system of the present invention
substantially eliminates the "cocking" problem, regardless of how
thin the pelleet is.
[0038] With the explosive assembly in place, the lower end of the
housing is closed by placement of the nose plug 40 into the open
end of the housing. The rod end projection 79 penetrates the guide
bore 48 as the plug base 42 is pushed to an internal seal with the
housing bore 14. To assure intimate contact of the opposite end EBW
detonators 32 and 66 with the respective adjacent ends of the
explosive assembly, the upper detonator housing 28 is displaced
against the spring 30 to accommodate the specified length of the
explosive column. Accordingly, when the nose plug 40 is seated
against the end of the outer housing tube 12, both EBW detonators
are in oppositely mutual compression as is illustrated by FIG. 5.
The severing tool is now prepared for lowering into a well for the
pipe cutting objective
[0039] Presently applied Explosive Safety Recommendations require
the severing tool 10 to be electrically connected to the suspension
string i.e. wireline, etc., before arming ballistically. Ballistic
arming with respect to the present invention means the insertion of
the explosive Pellets 24 into the housing bore 14.
[0040] On those occasions when the severing tool must be disarmed
without discharge, it is only necessary to remove the nose plug 40
and by grasping the rod extension 79, draw the pellets 74 from the
tube bore 14 as a single, integrated item.
[0041] 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 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.
* * * * *