Note: Descriptions are shown in the official language in which they were submitted.
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Thi6 .invention reLates to explosive devices used for selec-
tiuely severing metal or the like, and in a specific aspect,
relates to a method and apparatus for explosively effec~ing the
in situ cutting of dri.ll collars at a selected downhole location.
: 5 In the drilling of oil and gas wells, the drill string some-
times becomes fouled and obstructed so as to become stuck in the
well bore several hundred ~eet b~low ground level. On occasion,
attempts to free the drill string result in loss of substantial
, parts, or even possibly all, of the drill stem. In many such
cases, it ha5 been the practice, where the size and natur~ o
~ . the drilliny rig permi.tted, to lower a suitable.cuttiny tool
into the drill string to the.looation whe e the ouling exists,
and to there cut through or sever the drill stri~g, preferably
at a c.ollar, in order to free at least the upper portion of the
string. ~On some:occasions~ where the drill pipe is large in
: diame~er, attempts to saver the s~ring at a selected location
:~have been carried out usiny an explosive charge. Wi-th relatively
smaller diametqr drill pipe, it has been ~ound difficult to lower
, a su~ficient amount of explosive to the locus of the ouling to
efect dis.enyagement of the free upper section o~ the string
from.~ha~obstructed lower section~ This is especially true when
i~ is sought to seuer the drill string by cut~ing through a drill
1. .
. collar/ since thes0 coupling elements in the string ~ave a sub-
.
~ stantially ~reater wall thickness than the thickness of ~he drill
i . . . .
~ 5 pipe sections.
.. . . .. , . .. . ~ . . ~ , ..
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In some ins~ances, the large amount of explosive resuired,
and the ~elatively small diameter of the tubing/ prevent the
elongated cartridge or houslng carrying the explosive from
traversing bends or angulations in the tubing string of the
sort which are frequently encountered in operational drilling.
Even where larger amounts of explosive are susceptible to utili-
æation, shoclc ~aves are fre~uently generated upon detonation
which axe of sufficient magnitude and are sufficiently widely
dispersed that undesirable damage is caused to s.urrounding struc- .
ture~ `
On other occasions during oil and gas well drilling, blow-outs
can occur in which drilling fluia is lost at the location o the
blow-out unless cementing can be efected at that location to
alle~iate.the blow-out by plugging the well. At times, it is
possible to perforate a drill collar at the location of the blow~
outt~ and~to squeeze a sufficient amount of cement through it to
alIeviate the blow-out. :Sometimes, however, drill collar perfor-
:ation~in ~his manner does not permit a sufficient quantity o
,
cement to be squeezed through the perforations and in~o the
: 20. annulus to effecti~ely overcome the blow-out. In such instances,
it would be desirable to in some way se~er or cut through the
. drill collar to~a suficient degree to permit an adequate quantity
.of cement to be ~orced through the collar at a high enough rate
.
to permit the well to be plugged.
.:~ 2:5 ~ .The present invention is a method and apparatus for efficiently
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and selectively severing thick-walled tubing at a selected
location. The tool used can be effectively placed in a Fipe
of relatively small inside diameter, and whether the pipe be
straight, or curved and bent to some extent.
Broadly described, the tubing severing apparatus of the
invention comprises a housing in which are contained a pair
of discrete explosive charges which are aligned along the
axis of the housing. The housing is transversely dimensioned
to facilitate its insertion in a pipe or tubing to be severed
at a selected location. The explosive charges include adja-
cent, facing end portions toward the center of the surround-
ing housing, which end portions define between them an air
gap or space serving as an explosive-free open space~ A
small part of these end portions of the two charges can be
in point or tangential contact with each other, provided
only that the air gap or space between the main bodies o~
the two charges is maintained. Preferably, the end portions
of the two charges are oE a generally convex or conical con-
figuration, and are in tangential contact with each other at
the apices of the cover. In another embodiment of the
invention the facing end portions of the two discrete charges
may be~spaced sllghtly from each other. Means are provided
for detonating the charges at the opposite ends thereof so
tha~ the detonation waves are propagated axially within the
housing and collide at the location of the adjacent, opposed
ends o~ the two charges which deEine the air gap or space.
In utilizing the apparatus of the invention for
,
severing a downhole drill string, the housing containing the
explosive charges arranged in the manner described is placed
30~ upon the end of a suitable wire line carrying electrioal ~-
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~onductoxs appropriate to effect detonation of the charges
when a power source at the surface~is activated. The
apparatus is then lowered on the wire line to the desired
depth within the drill string which is to be severed.
Detonation of the two explosive charges at the distally
disposed ends thereof, as they are located in opposite
ends of the housing, is then substantially simultaneously
initiated.
An advantage of the tubing cutter apparatus of the
invention is that a relatively small amount of explosive
charge can be used to selectively sever or cut through
relatively thick pipe or tubing at a precisely selected
downhole location with total control being effected from
the surface.
An object of the invention is to provide a compact
drill collar cutting apparatus which can be easily lowered
into a drill string without being blocked or obstructed
by bends or departures from linearity occurring over the
length of the drill string.
An additional object of the invention is to provide a
tubing cutter apparatus which concentrates and selectively
.
directs the force generated by the explosion of a rela
tively small amount of high explosive in such a way that a
thick tubing, such as a d~ill collar, can be cleanly cut
through at a selected location.
Another advantage of the invention is that the
cutting apparatus of the invention concentrates and
directs the force developed upon detonation of explosive
1: .
charges in such manner that a thick drill collar may be
; 30 cleanly cut through along a transverse plane without the
force developed in the course of such cutting severely
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damaging or injuriously affecting an adjacent formation
surrounding the bore hole.
In the drawings Eorming a part of this disclosure:
Figure 1 is a schematic illustration of apparatus
incorpora~ing the concepts of the present invention;
Figure 2a is a vertical sectional view taken along the
axial center line of the lower portion of a downhole tool
incorporating a drill collar cutter construc~ed in
accordance with the present invention;
Figure 2b is a vertlcal sectional view taken along the
axial center line of the upper portion of the downhole
tool illustrated in Figure 2a, and constituting a vertical
continuation of the structure shown in Figure 2a;
Figure 3 is a plan view of a truncated cone explosive
cartridge of the type used in the drill collar cutter
device illustrated in Figures 2a and 2b;
Figure 4 is a sectional view taken along line 4-4 of
Figure 3;
FI~gur~e 5 is a~plan view of a conical explosive
; 20 cartridge of the~type utilized in the drill collar cutter
` device illustrated in Figures 2a and 2b;
Figure 6 is a sectional view taken along line 6~6 of
Figure 5;
Fiyure 7 is an electrical wiring diagram illustrating
the manner in wh~ich the detonator elements used in the
::
cutting apparatus are electrically interconnected.
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Referring initially to Figure 1 of the drawings,
the principal or basic concepts utilized in the construction
of the apparatus and practice of the method of the invention
are schematically illustrated. One of the most important
applications and usages of the apparatus of the invention is
in a downhol environment where it is desired to sever a
drill string by explo~ively cutting through a drill collar.
In Figure 1l a drill string 10 includes drill pipe sections
12 and 14 in~erconnec~ed by a relatively thick drill collar
16 in conventional array. The drill string is, of course,
disposed in a bore hole (not shown)O In most cases, the drill
collar 16 is located at a substantial distanca below the
surface near the location where fouling of the string has
occurred, or where it is desired to eject cement throu~h a
severed drill collar.
The dri.ll collar cutter apparatus of the present
invention is designated generally by reference numeral 18
and is placed in the selected downhole by lowering the
apparatus into the seri.ally interconnected drill pipe sections
on a wire line. In a preferred method of practicing the
invention, the wire line utilized will incl~de a cable head
at its lower end to which the apparatus of the present invention ; .
can be aktached, and will further include suitable electri.cal
conductors for conducting an electrical current from the
surface of the lower end of the wire line and through the
cable head to certain electrical.ly fired detonator devices .~
forming a portion of a preferred embodiment of :
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the drill collar cutter tool o~ the invention.
In Figure l, electrical conductors 20 and 22 are shown
.connected to a pair of detonator devices 26 and 28. The deto-
nator aevices 26 and 28 are mo~nted centrally within ~ooster
charges 30 and 32, respectively, which are placed ~ithin the
respecti~e dis-tally disposed end~ o a pair o axially spaced,
cylindricall~ configured sleeves or housings 34 and 36~ The
housings 34 and 36 are intexconnected in spaced, axial alignment
. by means of a connecting coupling 3B which telescopes over the
proximate, facing ends of the housings. Alternatively, the
housings 34 and 36 ma~ be interconnected i.n a single or unitary
cylind~.ical structure in which the cylindrical wall o~ the
housing extends continuously between the locations o~ the booster
charges 30 and 32t and the coupling 38 is eliminated.
.
Positioned within the housing 34 ad~acent the booster charye
30, and ~illing a majox portion of this housin~, is a ~irst main
high explo.slve charge 40. The high explosive charge 40 terminates
at its end which is adjacent ~he coupling 3~ in a conically shaped
end portion 42 which points toward the housing 36. A conical cap
43 of a rigid material can be piaced over the end portion 42 of
the charge. In similar ~ashion, a second main chaxge 44 of high
explosive is positioned adjacent the ~ooster charge 32 within the
housing 3~ an~ fills a major portion of this housing. The main
'
~xplosi~e char~e 44 terminates atits end adiacent the coupling 38
in a conically shaped end portion 46 located within a ri~id
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conical cap 47 which preferably contacts the tip of the
cap 43 over the end portion 42 of'''the main explosive
charge 40.
It will be noted that the point of contact of the
conical end portions 42 and 46 of the main charges 40 and
44 is immediately opposite and centrally disposed with
- respect to the coupling 38, and can be said to lie in
a transverse plane extending through this coupling and
' through the concentrically positioned drill collar 16.
.'- 10 Stated differently, the point of contact of the end por-
tions 42 and 46 of the explosive charges 40 and 44 lies
~ in a plane which projects normal to the axis of the drill
'. string, as well as to the aligned axes of the housings 34
and.36. It will also be noted that caps 43 and 47 extend
between and s'eparate the charges 40 and 44.
: In the operation of the schematically illustrated '.
~ apparatus in carrying out the method of the invention, the
apparatus 18 is emplaced by lowering it on the end of a ~
' .wire line in the manner hereinbefore described, so that it
: 20 is positioned opposite the drill collar 16 to be severed.
~ - The contacting conical ends 42 and 46 o:E the main explo-
.
sive charges 40 and 44 thus are located in a transverse
plane extending through the drill collar~ With the ':~
apparatus in position, the detonator devices 26 and 28
are electrically actuated by closure of a suitable switch
located at the surface to thereby close the electrical
circuit to the detonators 26 and 28. Either D~ or AC
current may be utilized for detonation. Upon initiation
of detonation~, the booster charges 30 and 32 associated
30~ with~:the detonator devices 26 and 28r respectively,
.
are caused to explode, and they in twrn initia~e explosion o the
main charges 40 and 44. It will be perceived that the ex~lo~ion
of the main charges 40 and 44 is caused to be initiated or ori~i
nated at their di~tally located or remote ends-, or in any arrange-
ment, at points located equidistantly from the respéctive conical
ends 42 and 46.
As the main charges 40 and 44 explode, the detonation waves
generated thereby collide at the locus of the cone-shaped end
portions of the explosive charges, and there form an extremely
high pressure zone around the cones in the middle section of the
cutter apparatus. This high pressure is focused into a planar
wa~e w~ich acts perpendicular to the direction of propagation oE
th~ original detonation waves. Tha planar wave acting trans~ersely
across the apparatus exerts very high pressure which severs or
.
; lS blows away the coupling 38 and, upon impacting upon the interior
~' o~ the drill collar 16, exerts a greater pressure on this element
than th~ yield strength of the s~eel o~' which it i5 made. 'rhis
action causes the drill collar to separate or be severed. rrhe
tubing severing appaxatus o the invention is particularl~ useful
and advantageous in its ability to cut thxough pipe or tubing
having a wall thickness exceeding two inches, and to sever tubing
characteri2ed by an outside diame~er to inside diameter ratio
exceeding 2.
Figures 2a and 2b o the drawings illustrate in section a
:: i
~.5 dQwnhole tool which~incorporates a preferred embodiment o~ a
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drill collar cu~cter constructed in accordance with the invention.
.. The collar cutter per se is designated generally by ref~rence
. numeral 50, and is illustrated in Figure 2a. The upper portion
of an adapter 52 and a wire line cable head 54 to which the
adapter ls connected are shown in Figure 2b.
The drill collar cutter apparatus 50 includes an elongated
cylindrical tubing 5G. The lower end of the tubing 56 is closed
. by a bull plug 58 secured in the tubing by cap s~rews 60 and
sealingly engaged therewith by means of O-ri~gs 62. The bull
plug 58. is provided with a central or axial cavity 64 which pro-
jects downwardly into the plug from the upper end thereof and
communicates with a transverse passageway 66 which projects
r~diall~ into ~he bull plug ~rom the outer periphery thereo~.
A peripheral, axially extending groove 68 is formed along the
iS outer side of the bull plu.g 58 parallel to the cavity 64, and
. :
: projects ~rom the uppèr side of the bull plug to a point o--.-
communication wi.th the transverse passageway 66. The upper side
of ~he bull plug 5~ at which th~ central cavity 64 opens prefer-
~ ably includes a ~rusto-conicàl protuherance configured to mate
with a ~rusto-conically shaped cavity formed in.a high explosive
cartridge~hereinafter descri~ed.
.At the uppsr end of the tube 56, the tube is closed by a
. mandril end plug 72. The mandxil end plug 72 is retained in
;~ : : : . .
the tube 56 b~ cap~screws 74, and is sealed agaLnst the tube by
;~ 25 O-rings 76. ~ c~rcwm~erential ~lange 78 is formed around ~he
.: : ~ . :
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outer periphery of the upper end portion o~ the mandril end plug
72 and bears against the upper end of the 'cu~e 56~ Above the
flange 78, an externa1ly threaded neck portion 80 of thé ~lug
. 72 projects into and ~hreadedly engages an internally threaded
;- 5 female box cavity or socket 81 in the lQwer end of ~he adapter
5~.
The lower end o~ the mandril end plug 72 is a centrally
.
located frusto~conical protuberance 82 which extends downwardly.
~; in the tube 56, and is substantially identical in confi~u.ration
to the frusto-conical protuberance 70 at the upper end o.~ the
bull plug 58. An axial or central cavity 84 extends into t.he.
mandril end plug 72 from the apex or lowermost portion of the
protuberance 82, and communicates with an elongated axial bore
86 which extends through the end plug frDm the upper end thereof.
:~i5 ~A t:ransverse passa~eway 88 pro~ects radially inwardly from one
side of~the plug 72~to intersect and communicate with the axial
bore 86 at a location immediately above the axial ca~ity 840
The tran5verse passageway 88 registers with a relief or groove
90 ~ormed in an axial direction along the outqr periphery o the
end plug 7Z, and terminating in the lower end face of ~he end
plllg'.
For the purpose of initiating detonation of the high explo-
sive charges used in the apparatus of the invention, a pair of
; electrica~L conductors 94 and 96 (see Figure 2b) extend downwardly
~through an~axial b~re 9~8 in the~adapter 5Z and through the axial
.
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bore 86 in the.end plug 72 to the intersectLon of the transverse
passageway 88 with '_he axial bore 86. At this location, the
conduc~or 94 and another electrical conductor 100 extend out
throug~ the transverse passageway and pxoject downwardly through
S the groove 90 along the side of the tubi~g 56 to the lower end
; thereQf. There the conductors 94 and 100 enter the groove 68
in the bull plu~ 58 and are then led through the transverse
passageway 66 into.the axial cavity 64 in the bull plug. The
conductor 96 is connected at its lowex end to a detonator element
106 which is pO5 i~i.oned in the cavity 84 with its lower end
flll~h with the lower end of the ~rusto-conical protuberance 82.
In similar fashion, the lower ends of the conductors 94 and 100
are connected t~ a detonator element 108 which i5 positioned in
the cavity 64 and has its upper end flush with the upper end of
` 15 the frusto-conical protubexance 70 at the upper end of the bull
.
j :plug 58. A short:conductor 109 is connected between the deto-
nator elen~ent 106 and the conductor 100 so that. the detonator
elements are wi.red in series, as ~hown in Figure 7.
For the purpose of completing the electrical circuit neces-
sary ~o electrical firing of the detonating elements 106 and 108,
:~ the conductors 94 and 96 are made part of an electrlcal circui~
extending to the surface of the earth where a power source and
switch are located fo.r energizing and closing the circuit. Al-
hough the structure o~ ap~aratus ~acili~ating the downhole
. .
:: 25 : :e~tension o~ the conductors 94 and 96 is well understood in the
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art, this is accomplished in the lllustrated embodiment of the
invention by connection of the conductors in an ap,ropriate
~ashion to the lower end of a cable head 54 suspended,upon the
lower end of a conventional wire line. The adapter 52 ha.s an
- 5 internally threaded female bo~. lL0 formed in the upper end
thereof and communicating with the'open upper end of an axial
; cavity 112 in the adapter. The cavity 112 in turn communicates
with the axial bore 98 whlch extends downwardly in the adapter
to khe end plug 72. The box 110 threadedly receives an exter--
nally threaded pin~ formed on the lower end of the cable headk~
' '54.
~ ~ ~f
The lower'end o the pin ~t~ abuts the upper end of a spring~
cup 116 which is constxucted of a dielectric or electrically non-
oonductive materlal and i5 seated in the cavity 112. The conductor
,~15 9~ is extended around,the outer side of ~he spring cup 116 and is
,
. suitably groundecl ~o the metallic wall of the adapter 52. ~ small
' opening 118 is formed in the bottom o~ the spring cup 116 and
funct.ions to permit extension into the interior o~ the spring'cup
of the conductor 94. Inside the sprin~ cup 112, ~he insulation
20, is remo~ed from the end p~rtion o~ the conductor 94, and ~he bare
~,
conduc~or is connected to a helical spxing 120.,
' The spring 120 unctions to resiliently urge or bias a con-
tactor plate 1~2 upwardly into contact with a contact head 124
,~ .. . .
's~cured to the lower end of a flexi~le electrical conductor ele-
~5; ment~126 forming~a part~of the cable head 54. The conductor
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element 126 is enclosed within a tube 128 of an insulator
ma~erial, and the tube is in turn enclosed in a braided
shield 130 of conventional construction. The entire cable
head 54 as thus constructed is o~ conventional construc-
tion and is attached to the lower end of a wire line (not
shown).
The force required for severing a drill collar or
other tubular member at a selected location when the drill
collar surrounds the cutter apparatus 50 is developed by
detonation of explosive charges positioned within the tube
56 between the bull plug 58 and the mandril end plug 72.
For purposes of discussion, the explosive charges utilized
will be referred to generally as an upper explosive charge
134 and a lower explosive charge 136~ It should be
pointed out that though ~ortions of the two explosive
charges and the surrounding tube 56 have been broken away
and not shown in Figure 2a in order to afford clarity of
illustration, and sufficient compactness in the drawing,
the upper and low~r explosive charges 134 and 136 are
preferably 5ubstantially identically shaped and sized so
as to develop substantially equal explosive forces when
they are fir.ed.
Each of the explosive charges 134 and 136 consists of
a plurality of trancated explosive cartridges 138, and a
conical cartridge 140r The configuration of these
respective high explosive cartridges is more clearly and
specifically illustrated in Figures 3-6.
It will be perceived in referring to Figures 3 and 4,
which
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show one of the truncated cartridges 138, that this stxucture
includes the body o~ a suitable high explosive material which
is formed to have a generally cylindrical outer periphery 142
. intersected by a pair of subs.tantially parallel, axially .spaced
5 plana- end faces 144 and 146~ Extending between the end faces
144 and 146 at one side of the cartridge 138 is a peripheral
groove 148 which exte.nds parallel to the axis of the tube 56
and functions to pass the electrical conductors 94 and 100 as
they are extended down one side of the tube for connection to the
lower detonator element 108 ~see Figure 2a). ~ frusto-conical
cavity ~50 is ~ormed in the planar end face 146 of each truncated
cartridge 13a; and a truncated protuberance or projection 152
. cQmplementary in con~iguration to the cavity lSO is formed upon
and projec~s out~o~ the planar end face 144. It will be per-
~lS ceived in reerring ~ Figure 2a that the described configuration
; of the kruncated cartridges 13R permits them to be stacked in
nestLng relationship within the tube 56, with the 10~7ermost. car-
tridge in the lower high explosive charge 136 nestably receiving
the cpmplementary ~rusto~conical projection 70 at the upper end
,
of the bull plug 58, and the uppermost cartr.idge in the upper
hiyh explosive charge 134 nestably receiving the downwardly pro-
jecting complementary frusto conical protuberance 82 formed on
the lower end of the mandxil end plug 72.
` At the proximate or:centxally disposed ends of the uppPr
~5 and lower hlgh explosive charges 134 and 136, respec~ively, each
.
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of these charges includes a conical explosive cartridge 140.
The appearance of each of the conical car~ridges 1~ is illus-
trated in detail in Figures 5 and 6. Each o~ the conical car-
tridges 140 is characterized in having a cylindrical outer
; 5 peripheral surface 154 which is grooved along one side by a
peripheral groove 156 extendin~ parallel to the axis of the tube
56. The groove 156 projects from a planar end face ~58 defining
a rusto-conlca~ cavity 160 to a generally conical face I62 on the
opposite side of the cartridge ~rom the end face 158~ The face
162 of the conical cartridge 140 is preferably of parabolic cross-
sect~onal configuration.
It will be noted in referring to E'igure 2a that the conical
.
cartridges 140 carried at the lower end o~ the upper high explo-
sive chargé 134 and the upper end of the lower high explosive
i.~S ~ charge 136~ace each other with the apices o the conical sur-
.
faces 162 in immediate proxi~ity to each other. In a preferxed
construction of the invention, a hollow metallic ~a~ 164 is
poslt~oned o~er the respective parabolica~ly conEigured sur~aces
162 of ~he conical cartridges 14Q, and the metallic caps cc~tact
~20 each other at a point which lies in the axis of the tube S6. The
caps 164 are preferably constructed o~ thin copper plate. It will
ba perceived that the described arrangement of the high explosive
charges in~the upper charge 134 and lower charge 136 is such that
an air~space ,or ~ap 166 exists between the main bGdies of both
Z5 ~: these high explos1ve~charges~ and is that air space whlch surrounds
, ~ . l
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~37~l~3
the parabolica]ly shaped generally conical surfaces 162
at the facing sldes of the conical cartridges 140.
The types of high explosive material used in the
charges 134 and 136, and specifically in both the trun-
cated cartridges 138 and the conical cartridges 140, can
vary widely. ~xamples of suitable high explosives are
those described in U.S. Patent 3,865,436 to Dorrough and
Brown issued February ll, 1975. The explosives ~DX
~Cyclotrimethylenetrinitramine, Hexahydro-l, 3, 5-Trinitro-
5-Triazine, Cyclonite, Hexogen, T4~ and COMP B ~Cyclotol)
are preferred.
In typical construction of the drill collar cutter
apparatus 50l the tube or housing in which the explosives
are located will have an outside diameter of from 1 1/2
inches up to about 2 l/2 inches. The overall length of
the explosive used will be from about 10 inches to about
20 inchesr such dimensions depending, of course, upon the
; ~ drill pipe diameter and the drill collar thickness.
In the operation of the drill collar cutting apparatus
illustrated in Figures 2~6, a switch is closed at the sur-
Eace to complete the electrical circuit extending downhole
through the wlre line cable head 54 and adapter 52 to the
detonator elements 106 and 108. As previously indicated,
either alternatlng or direct current can be used to elec~
trically fire the detonator elements. When the detonator
elements 106 and 108 are exploded, detonation of the high
explosive charges 134 and 136 is substantially simultaneously com-
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menced. As the explosi~n o~ these charges,proceeds, detonation
waves are developed and propa~ated toward the center o~, the tu~e
56, and these waves converge and collide at the location where the
- metallic caps 164 capping the conical cartrid~es 140 are in con-
' 5 tact~ A zone o~ extremely hiyh pressurè is developed at this
location and is focused into a planar shock wave acting perpen-
dicular to the direction of propagation of the colliding original
detonation waves, A tremendous pressure is developed within thè
tubing 56 at this location, and acts ~ransversely o~ the tubing
and perpendicular to the axis thereof. This pressure quic}cly rup-
tures the tube 56 and impinges upon the,internal wall o~ a sur-
xounding drill collar in the manner p'reviously described. The
pxessure is of suf~icient magnitude ~hat: it exceeds the yield
strength o~ the steel drill collar and severance of th~ drill
~ "'t;-15 collar is thereby effe~ted.
Although a pre~erred embodiment of the invention ha~ beenherein
described in order to provide exemplary illustration o~ the basic
principles which underlie ~he invention, it will be understood that
'various changes and innovations in khe depicted and described struc-
~ture can be e~ec~ed without departure from th~ basic principles
which underlie the invention.' Changes and innovations o~ this type
are therefore deemed to be circumscribed hy the spirit and scope of
~ the~in~ention, except;as the s~le may be necessarily limi~Pd by the
'~ ; ' appended claims~Qr reasonable equivalents thereof.
~ What is ciaimed ~i~s: ' '
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