CA1107193A - Method and apparatus for severing tubing - Google Patents

Abstract

METHOD AND APPARATUS FOR SEVERING TUBING
Abstract of the Disclosure Apparatus for severing tubing along a generally transverse plane through the tubing wall, and including two confined ex-plosive charges aligned axially with the tubing wall and termi-nating at opposed, proximal ends facing each other across a space disposed in such transverse plane. A portion of the opposed ends of the charges can contact each other, provided the main bodies of the two charges are spaced at the location of the plane of desired severance. Detonation devices are dis-posed at the distal or remote ends of the charges for originating detonation of the charges at such distal ends.
The apparatus is employed by emplacing the confined charges in the tubing to be severed with the charges positioned on opposite sides of, and terminating with their proximal ends substantially at, the plane in which the desired severance is to be effected. The charges are then simultaneously exploded by concurrently initiating the explosion of each at points sub-stantially equidistantly spaced from the desired plane of severance.

Description

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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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1~0~3 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 . -3-.,: ~ : ~ .

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 ~-~7~5~3 ~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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~7~3 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.

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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 - 1 0- , , . :
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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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~3 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 ' -14-7:~3 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 .' .

~7~3 -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 -,; .' ~

~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-i .
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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: ' ' - . : .

Claims (30)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A drill collar cutter apparatus for severing a drill collar in a downhole environment consisting essentially of:
an elongated tubular housing;
lowering means connected to one-end of said housing for lowering said housing in a drill string;
first explosive charge means in said housing, said first explosive charge means having a first end and a generally convex second end;
second explosive charge means in said housing in axial alignment with said first explosive charge means, said second explosive charge means having a first end and a generally convex second end, said first and said second explosive charge means being positioned within said tubular housing means such that the generally convex second ends of said first and said second explosive charge means are in adjacent opposed relationship and said generally convex second ends cooperate to define and maintain an explosive-free open space between said first and said second explosive charge means;
a first detonator element at said first end of said first charge means; and a second detonator element at said first end of said second explosive charge means.

2. A drill collar cutter apparatus as defined in claim 1 wherein the second end of each of said explosive charge means comprises a metallic cap having a convex surface with the convex surfaces of the caps contacting each other to further define said explosive-free space around the locus of contact within said tubular housing.

3. A drill collar cutter apparatus as defined in claim 2 wherein said lowering means comprises a wire line.

4. A drill collar cutter apparatus as defined in claim 2 and further characterized as including electrical circuitry connected to said detonator elements for electrically firing the detonator elements and comprising electrical conductors extending through said lowering means for powering and controlling the circuitry from the surface.

5. A drill collar cutter apparatus as defined in claim 2 wherein each of said first and second charges comprises:
a conically configured explosive cartridge having its apex comprising said convex second end of the respective charge.

6. A drill collar cutter apparatus as defined in claim 5 wherein each of said first and second charges comprises:
a plurality of nestable explosive cartridges stacked axially in said tabular housing in internested array and including one nestable cartridge in contact with the base of the conically configured cartridge; wherein each of said nestable cartridges comprises a body of explosive having a cylindrical outer peripheral surface mated to the inside diameter of said tubular housing;
a pair of spaced, parallel planar end surfaces inter-secting the peripheral surface;
a cavity extending into one of said end surfaces; and a protuberance complementary in configuration to said cavity and projecting from the other of said end surfaces for registering engagement with the cavity of an adjacent nestable cartridge.

7. A drill collar cutter apparatus as defined in claim 6 wherein each of said conically configured cartridges includes:
a parabolic surface comprising the convex second end of one of said charges; and a surface defining a cavity on the opposite side of the respective conically configured cartridge from said parabolic surface.

8. A drill collar cutter apparatus as defined in claim 6 and further characterized as including plugs closing opposite ends of said tubular housing and each including a projection extending into, and mating with, the cavity in an adjacent one of said nestable cartridges, said plugs each defining a cavity extending axially in said tubular housing and receiving one of said detonator elements.

9. A drill collar cutter apparatus as defined in claim 6 wherein each of said first and second explosive charge means defines groove means adjacent said tubular housing and extending parallel to the axis thereof for receiving said electrical conductors extended from said lowering means to one of said detonator elements.

10. A drill collar cutter apparatus as defined in claim 6 wherein each of said cartridges is peripherally grooved, and said cartridge grooves define with said housing a conductor passageway for receiving electrical conductors extended from said lowering means to one of said detonator elements.

11. Tubing cutting apparatus consisting essentially of a tubular housing having an upper end and a lower end;
a first explosive charge confined in the upper portion of the housing and terminating in a convex end portion adjacent the center of the housing;

a second explosive charge confined in the lower portion of the housing and terminating in a convex end portion adjacent the center of the housing;
an explosive-free space at the center of the housing adjacent the convex ends of the first and second charges;
and means for detonating both of the explosive charges at locations spaced axially in the housing from the center thereof.

12. The method of severing a tubular member along a plane extending normal to the axis thereof consisting essen-tially of configuring two explosive charges as elongate bodies terminating in protuberant, convexly shaped end portions;
confining the two charges in an enclosing, elongate housing sized for insertion in the tubular member with the elongate bodies in longitudinal alignment, and with the convexly shaped end portions in adjacent opposed relationship wherein said convexly shaped end portions cooperate to define and maintain an open space between said charges within said housing;
positioning the housing inside the tubular member with the convexly shaped end portions substantially in the desired plane of severane of the tubular member; and simultaneously detonating the charges by initiating the explosion thereof at points therealong substantially equidistant from the convexly shaped end portions.

13. The method of claim 12 wherein said convexly shaped end portions are in tangential contact with each other.

14. The method defined in claim 13 wherein in configuring said explosive charges, each body is assembled by nesting a plurality of separate explosive cartridges in a stack with adjacent cartridges having registering protuberances and cavities.

15. Apparatus for severing a tube along a plane extending generally transversely through the walls of said tube, said apparatus consisting essentially of;
two explosive charges each of said charges having distal end and a proximal end;
two detonation means for simultaneously initiating detonation of said charges at said distal ends thereof; and housing means for confining and aligning said two charges within the interior of said tube; wherein said two charges are axially positioned within said housing means such that said proximal ends are effectively placed in adjacent opposed relationship and cooperate to define and maintain an explosive-free air space between said charges within said housing means and said distal ends are spaced axially in said housing means from said air space; and wherein one of said detonation means is positioned at each said distal end so that upon initiation detonation waves propagate axially through each of said charges within said housing means to collide at said air space and sever the walls of said tube along a plane extending generally transversely through said air space and said walls.

16. The apparatus of claim 15 wherein each of said charges defines an electrical conductor-receiving passage-way with said housing; and said detonation means comprises detonator elements contacting the respective distal ends of the respective charges; and an electrical circuit including electrical conductors extending through; said passageways and connected to said detonator elements.

17. The apparatus of claim 15 wherein said detonation means comprises a pair of electrically actuatable detonator elements.

18. The apparatus of claim 15 being further comprised of means connected to said housing to facilitate gravity emplacement of said housing within said tube.

19. The apparatus of claim 15 wherein at least one of said charges comprises a plurality of stacked, internested explosive cartridges.

20. The apparatus of claim 15 wherein said proximal ends of said charges are in contact at a point along the longitudinal axis of said housing.

21. The apparatus of claim 20 wherein each of said proximal ends of said charges is parabolically configured.

22. The apparatus of claim 21 wherein at least one of said charges comprises a plurality of stacked, internested explosive cartridges.

23. The apparatus of claim 20 wherein each of said charges includes a plurality of internested explosive cartidges serially stacked; and a conical explosive cartridge in contact with one of said internested cartidges and having a parabolic face forming one of said proximal ends.

24. The apparatus of claim 23 being further comprised of a metal cap registering with said parabolic face and having a complementary parabolic configuration thereto.

25. Apparatus for severing thick-walled tubing from a location within the interior of said tubing said apparatus consisting essentially of:
an elongated housing transversely dimensioned to facilitate insertion of said housing into the interior of said tubing;

two explosive charges confined and axially aligned within said housing each of said charges having a distal end and a proximal end, and positioned within said housing such that said proximal ends are effectively placed in adjacent opposed relationship and cooperate to define and maintain an explosive-free air space between said charges within said housing and said distal ends are spaced axially in said housing from said air space;
two caps each said cap covering one of said proximal ends and having a configuration complimentary to said proximal end; and two detonation means each said detonation means positioned at each said distal end for simultaneously initiating detonation of said charges at said distal ends thereof so that detonation waves propagate axially through each of said charges within said housing means to collide at said air space and sever the walls of said tubing along a plane extending generally transversely through said air space and said walls.

26. The apparatus of claim 25 wherein said proximal ends are convex and said caps are convex.

27. The apparatus of claim 25 wherein the apices of said caps are in contact.

28. The apparatus of claim 27 wherein said detonation means comprises a pair of electrically actuatable detonator elements, each of said elements contacting one of said distal ends.

29. The apparatus of claim 28 further comprising means connected to said housing to facilitate gravity emplacement of said housing within the interior of said tubing.

30. The apparatus of claim 29 wherein said tubing is a drill string.