US2699721A - Explosive cutting device - Google Patents

Description

Jan. 18, 19155 R. L.- KLOTZ. JR

'EXPLOSIVE CUTTING DEVICE 3 Sheets-Sheet 1 Filed Feb. 19, 1947 Q i A Mi In w 1 way i f i K a @QC J fi wig a,

IN VEN TOR. 2 058;; J 15%; cza- R. L. KLOTZ. JR

EXPLOSIVE CUTTING DEVICE 7 Jan. 18, 1955 s Sheets-Sheet 2 Filed Feb. 19, 1947 al? W Z INVENTOR k I w 3 Sheets-Sheet 3 DEVICE INVENTOR. 1% w; y 6 %mm./

Jan. 18, 1955 R. L. KLOTZ.

' EXPLOSIVE CUTTING Flled Feb 19 1947 United States Pate t EXPLOSIVE CUTTING DEVICE Robert L. Klotz, Jr., Hazleton, Pa., assignor to Seismograph ServiceCorporation, Tulsa, Okla, a corporation of Delaware Application February 19, 1947, Serial No. 729,656 7 Claims. c1. 102 '2o The present invention relates to improvements in devices adapted to be lowered into a borehole in the earth, such for example, as an oil well, to cut an elongated me tallic element, such as well casing or a drill stern of a stuck drill, tubing, etc, which extends longitudinally of the borehole.

In oil field salvage work, tools are commonly used for cutting casing set in depleted wells to permit salvaging of the casing by removal thereof in sections. Again, in the drilling of oil wells and also shot holes of the character used in seismic exploration work, tools are not infrequently used to cut the drill string or the stems of drill bits which become stuck at the bottoms of partially drilled holes, in order to permit salvaging of the drill strings or parts thereof. Generally speaking, cutting tools of the explosive type have not been satisfactory for work of this type for the reasons that clean cutting without distortion of the uncut sections of the element which it is desired to cut cannot be obtaihed, as belling of the casing or folding of the drill string occurs and furthermore excessive quantities of explosive material, tional capacity of the borehole, would have to be used to effect severance of the element.

It is an object of the present invention, therefore, to provide an improved explosive device which is adapted to-be lowered into a borehole to cut an elongated element extending longitudinally of the borehole and completely obviates the above-mentioned disadvantages.

It is another object of the invention to provide an improved device of the character described which is of simple, .low cost construction, is light in weight, requires a minimum of explosive material to perform a given cutting operation and is easy to handle in the field.

The invention both asto its organization and method of operation together with further objects and advantages thereofwill best be understood by reference to the following specification taken in connection with the accompanyin'g drawings in which:

Figure l is a fragmentary sectional view taken along a vertical section bisecting a borehole in the earths crust, illustrating the manner in which one embodiment of the present invention may be used to cut casing which lines the borehole. V p g Figure 2 isanenlarged fragmentary sectional view illustrating the details of the cutting .device shown in Figure 1;

Figure 3 is a top plan view of the device shown in Figure 1 also showing a section through the well casing;

Figure 4-is a view in full section illustrating a modified housing structure for the cutting device shown in Figure Figure 5 is a sectional view similar to Figure 4, but illustrating a modified form of detonating mechanism;

Figure. 6 is a fragmentary sectional view taken along a vefrticalplane bisecting a borehole beingdrilled in the etrthscrust, illustrating the manner in which a different embodiment of the invention may be employed to cut the stem of a drill bit stuck in the borehole;

, Figure 7 is an enlarged perspective view of the cutting device shown in Figure 6;

Figure 8 is a View in full section illustrating the constructional details of the cutting device shown in Figure 6; and

Figure 9 is a fragmentary detail view partially in section illustrating the arrangement ofthe means for detonating the explosive charge embodied in the cutting device shown in Figure 6.

Referring now to the drawings and more particularly sometimes exceeding the sec- 2,699,721 Patented Jan. 18, 1955 to Figures 1, 2, and 3 thereof, the present invention is there illustrated in its embodiment in a cutting device generally indicated at 12 which is adapted to be lowered by means of a cable 13 into a borehole 10 extending downward from the surface 11 of the earth for the purpose of cutting the casing 9 with which the borehole .10 is lined. As will be evident from the foregoing explanation, casing cutting is. commonly required in the salvaging ofcasing from old non-producing wells of depleted oil fields, as well as other non-producing wells. ,The' usual practice is that of removing thecasing by sections and various types of cutting tools have in the past been employed to perform the casing sectionalizing operation.

In accordance with the present invention and as best illustrated in Figures 2 and 3 of the drawings, a cutting device is provided, which comprises a disc-like body 17 of explosive material having a V-shaped cavity 17a ex,- tending continuously around the outer peripheral edge thereof for directionalizingtoward the casing walls the explosive forces developed upon detonation of the explosive material. This body of explosive material, which may be 60 to per cent blasting gelatin, such, for example, as Seismogel A, manufactured by E. I. du Pont de Nemours Company, Inc., is contained within a sheet metal structure comprising a lower bottom plate 21 of disc-like form uponwhich is mounted a hollow doughnut-shaped element 20 having V-related walls 20c which line the cavity 17a in the body of explosive material. The outer edges of these V-related walls terminate in upper and lower annular parts 20a and 2012 which function as stand-01f means to maintain the outer cavitated edge of the explosive body spaced at least a predetermined distance from the inner wall of the casing 9. The annular part 20a also serves to support a cover 22 which, as best shown in Figure 3 of the drawings, is provided with radially extending locking lugs 22a adapted to be rotated beneath fingers Ztle struck upwardly. from the part 200 to lock the two elementsll) and 22 in assembled relationship. This cover is provided with a conical dome 22b extending upward from the annular part 20a and having a sealed opening 22c at the top thereof through which the circuit conductors 19 leading to the igniter of a detonating cap 18 may extend. This detonating cap is of cartridge form and extends transversely through the explosive body 17, preferably at the exact central axis. It is equipped with the usual igniter or ignition wire which upon energization of a circuit including the conductors 19 is'adapted to detonate the explosive body 17. These wires which may form a part of the lowering cable 13, or alternatively may themselves be used as the means for lowering the cutting device into the borehole 10 to the desired depth, extend to a detonator 14 located at the surface of the earth which maybe of the conventional electric impulse type. Preferably all of the parts 20, 21 and 22 are made of nonsparking metal, such as brass or copper, and have a wall thickness of the order of .075 inch.

For the purpose of protecting the assemblage of ele ments thus far described as making up the explosive unit 16, while it is being lowered into the borehole 10 and the more important purpose of maintaining the disc-like body 17 of explosive material in a' position extending transversely of the borehole, the unit 16 is mounted within an elongated open wire cage 15 which may be of conventional spot welded construction. The side elements 15a of the cage are preferably provided with formed recesses 15b midway between the ends thereof for receiving the spaced edges of the metal parts 20 and 21 to hold the unit 16 in a fixed position within the cage 15. These cageside members; extend around and are spot welded to spacing rings 15c adjacent the upper and lower ends thereof, and the ends are then brought together and welded to complete the cage structure. The upperpointed end of the cage is employed as an anchor point for the lowering cable 13 and the circuit conductors 19 extend loosely from this point to the ignition element of the detonating cap 18 to prevent their being pulled out of the detonating cap. If desired, the conductors may be wrapped around the upper spacing rings to prevent their becoming entangled and possibly broken as the device 12 is lowered into the borehole 10.

In using the described cutting device 12 to cut the casing 9 with which the borehole 10 is lined, the. device -is first lowered by means of the cable 13 to the desired position longitudinally of the borehole, which position is obviously determined by the length of casing to be extracted, following which the detonator 14 is actuated to energize the igniter of the ignition element 18 and thus detonate the explosive material 17. When the charge is 'fired, the element 20 is formed into an annular projectile and propelled by explosive forces through the adjacent segment of the casing 9. Further, the explosive energy is concentrated into a thin expanding annulus and directed laterally outward from the longitudinal axis of the borehole due to the effect of the V-shaped cavity provided entirely around the outer edge of this body. Specifically, cavity 17a causes the well known Munroe effect to occur in that the explosive forces first travel perpendicularly away from the wall surfaces of the cavity 17a, meet and then travel in highly concentrated form radially outward from the center of the explosive body. Due to the sharpness of the explosive impulse and the high degree of concentration of the explosive energy, the casing 9 is cut cleanly around the line of impact of these forces. Thus, belling or bulging of the casing 'at the point of explosion is prevented. Such belling renders extraction of the casing section from the borehole very difiicult. Further, due to the fact that most of the explosive energy is used in the cutting operation, and little energy is expended longitudinally of the hole, a relatively small amount of explosive material, well within the limits imposed by cross sectional area of the casing, is required. The degree of directionalization of the explosive energy is materially enhanced by the described means for maintaining at least a predetermined stand-off distance between the mouth of the cavity 17a and the adjacent inner wall of the casing 9. In general, the stand-off distance as determined by the width of the annular parts 20a and 20b will depend upon the angle of the concavity of the V-shaped cavity 17. For a sixty degree angle between the walls of the cavity 17a (this angle preferably ranges between 45 and 60 degrees depending upon the permissible diameter of the cutting device), the stand-off distance between the mouth of this cavity and the adjacent inner wall of the casing 9 should be at least equal to the thickness of the disk of explosive material.

In order further to enhance the directionalization of the explosive eflFect produced upon detonation of the body 17, the annular chamber between the liner walls 200 and the outer edges of the parts 20a and 20b may be evacuated to a low subatmospheric pressure. This may be accomplished by using a ring 20d to seal off the space immediately in front of the cavity 17a and evacuating this space to a low subatmospheric pressure. It has been found that such evacuation effectively lowers the impedance to wave front propagation during the initial or starting intervals of the wave fronts emanating from the surfaces of the cavity 17 and hence enhances the extent of concentration and the degree of directionalization of the explosive forces developed upon detonation of the explosive body 17.

Referring now more particularly to Figure 4 of the drawin s. the embodiment of the invention there illustrated differs only from that described'above in the type of support employed for the unit 16. While the open wire cage construction illustrated in Figures 2 and 3 of the drawings is entirely satisfactory for shallow work, for dee er work, i. e., casing cutting in deep wells, it is preferable to use a closed or semiclosed container. Thus a conventional torpedo can 24 having a len th about twice the diameter of the hole may conveniently be emplo ed to support the explosive unit 16. This can is equipped with a bail 24a for anchoring the lowering cable 13 and is provided adiacent the top thereof with a transverse bar 24b to which the ignition conductors 19 are anchored. The unit 16 is supported intermediate the ends of the can 24 upon a bed of packing material in the form of clay, sand, gravel. or the like, which fills approximately the lower one-third of the can. The remaining unoccupied space within the can 24 is also preferably filled with packing material in order to increase the over-all weight of the complete assembly. If the device is to be used in liquid filled wells, the top of the can. is preferably covered and sealed to prevent fluid entry into the can. Sealing may, if desired, be accomplished by filling the upper third of the can with warm melted 'tar' or-an equivalent sealing compound havlng a low melting point. The purpose of closing and seallng .the..can..24 is -to prevent liquid from fiowing'into the stand-off zone and forcing'its way into the chamber in which the explosive material 17 is disposed. Aside from the differences just pointed out, the device illustrated in Figure 4 of the drawings is identical in construction and mode of operation with that shown in Figures 1, 2 and 3 of the drawings and described above.

The embodiment of the invention illustrated in Figure 5 of the drawings differs from that shown in Figure 4 only in the use of a different type of detonating mechanism. Specifically, a torpedo bumper type of detonating mechanism is employed in the Figure Seenstruction to fire the cap or ignition element 18a and thus eliminate the necessity for extending circuit conductors from the cutting device to the top of the borehole. In brief, this mechanism comprises an upwardly spring biased firing pin 26 adapted to be struck a hammer blow by a firing plunger 27 which is slidably supported within a tube 28 projecting upwardly from the dome of the cover 22. Normally, the lower end of the plunger 27 is maintained away from the top of the firing pin 26 by means of a light coil spring 29 which is telescoped over the plunger 27 and extends between the head 27a of this plunger and the flanged upper end 28a of the tube 28.

In the operation of this firing mechanism, a weight (window weights are commonly used) is lowered into the borehole after the cutting device 12 is in position and such weight is dropped a short distance to engage the head 27a of the plunger 27. This plunger in moving downward strikes the firing pin 26 to ignite the detonating cap and thus detonate the explosive charge 17. From this point on, the cutting device functions in the exact manner explained above with reference to the embodiment of the invention illustrated in Figures 1, 2, and 3 of the drawings.

Referring now more particularly to Figures 6 to 9, inclusive, of the drawings, the present invention is there illustrated in its embodiment in a cutting device 30 particularly adapted for use in cutting drill string or the stem 31a of a drill bit 31 which has become stuck at the bottom of a borehole 32 in the process of being drilled into the earths crust. As will be understood, the drill bit 31 is carried at the lower end of a drill string 33 which extends upward and out of the borehole 32 to have rotary motion imparted thereto by the usual driving mechanism of a conventional rotary rig schematically illustrated at 34. In accordance with conventional practice, the drill string 33 is sectionalized in character, being comprised of a number of sections 33a which are added section by section as the depth of the borehole increases.

In brief, the cutting device 30 comprises an explosive cutting unit 35 which is supported within an elongated open Wire cage 36 having rings 37 and 38 at the top and bottom ends thereof for receiving the drill string 33. As best shown in Figures 7, 8, and 9 of the drawings, the cutting unit 35 comprises an annular body of explosive material 39 having a center opening for receiving the drill string and stem 31a of the drill and having a continuous V-shaped cavity 39a around the inner edge thereof for directionalizing toward the drill stem 31a the explosive forces developed upon detonation thereof. The explosive material, such, for example, as per cent gelatin, manufactured by E. I. du Pont de Nemours and Company, Inc., is confined within a sheet metal structure, which comprises annular top and bottom plates 40 and 41, an edge ring42 and an inner doughnut-shaped element 43. The latter element is provided with annularly related walls 43:: which closely line the V-shaped cavity 39a of the explosive body 39 and terminate in annular parts 43b and 430 which act as stand-off means for maintaining the mouth of the cavity spaced at least a predetermined dis- 1 39a which may be evacuated to enhance the degree of directionalization and concentration of the explosive forces developed upon detonation of the material 39in the manner explained above.

Here also, the angle defined by the V-related walls may range from 45 to 60 degrees and all metal parts of the unit 35 are preferably formed of brass or copper to reduce the likelihood of inadvertent detonation of the material 39.

For the purpose of detonating the explosive materlal 39, an ignition element in the form of a length of Primacord 45 is wrapped around the outer edge of this body in contact therewith within the ring 42. The ends of the Primacord 45 are brought out through an openlng 40a in the plate 40 and extend into contact with a detonatmg cap schematically indicated at 46 mounted upon .the plate 40 at the upper side thereof. This cap is. equtpped with the usual ignition elements which may be electr cally energizedfrom a remote point over a pair of circuit conductors 47. Specifically, these conductors may form a part of a cable for lowering the cutting devlce 30 into the borehole 32 and are connected at the surface 'of the earth to a detonator 14a of the conventional electric impulse type.

In employing the cutting device 30 to cut the drill stern 31a of the bit 31 located at the bottom of the borehole 32, the upper section 33a of the drill string is uncoupled from that portion of the drill string 33 disposed in the borehole, following which the cutting device 30 is telescoped over the upper end of the drill string with this str ng extending through the aligned openings in the cutting unit 35' and'the upper and lower cage rings 37 and 38. The cable may now be used to lower the device 30 into the borehole 32 by sliding the same downwardly along the drill string 33 until it comes to rest against the enlarged head of the drill bit 31. With the device 30 in this position, the cutting unit 35 thereof obviously surrounds the stern 31a of the bit. Accordingly, by utilizing the detonator 14a to energize the ignition element of the cap 46 over the circuit conductors 47, the Pri'macord 45 may be ignited to effect detonation of the explosive material 39. In this regard itwill be understood that the characteristics of Primacord' are such that the explosive material 39 is almost instantaneously ignited at all points around the outer perimeter of the explosive body. The resulting diiectionalized explosive forces developed in a manner which will be clearly apparent from the above explanation, are all directed inwardly toward the drill bit stem 31a and-have the effect of cleanly shearing this stem into two parts. It will be noted that due to the annular construction of the cutting unit 35 the explosive forces strike the stem 31:; simultaneously from all directions'so that twisting or distortion of the unsevered portions of the stem is minimized. After the stem 31a is thus divided into two parts, the drill string 33 may be readily withdrawn from the borehole 32 and the drill stem segment remaining at the end thereof removed. Obviously, the borehole may be extended to a lower depth by drilling around the stuck bit 31 in the usual manner.

From the foregoing explanation, it Will be understood that the present invention affords a reliable and economical solution to the problem of cutting an elongated metallic element such, for example, as casing or the stern of a drill bit, disposed at substantial depths in a borehole in the earth. Not only are the devices illustrated in the drawings and described above of simple and economical construction, but they also are very easy to use and their action to produce the desired results is instantaneous.

While different embodiments of the invention have been described, it will be understood that various modifications may be made therein which are Within the true scope and spirit of the invention as defined in the appended claims.

I claim:

1. Apparatus for severing an elongated element extending longitudinally of a borehole in the earth, comprising a disk-like body of explosive material having a cavity extending around one edge thereof for directionalizing toward said elongated element the explosive forces developed upon detonation of the material, a metal structure providing a liner for said cavity and including means providing a sealed stand-ofif space between said cavity and the adjacent surface of said elongated element, means for lowering said structure and body of explosive material into the borehole to position said cavity opposite said elongated element at the desired point of severance therealong, said last-named means including a plurality of side members and spacing rings defining an open wire cage of substantial length which substantially fills the borehole, means for positioning said metal structure intermediate the ends of said side members with said disk-like body of explosive material in a position extending transversely of said borehole as said cage is lowered into said borehole, and means for detonating said explosive material from the earths surface.

2. Apparatus for severing an elongated element extending longitudinally of a borehole in the earth, comr bers and spacing prising a disk-like body of ,Iexplosive material having a cavity extending around one edge thereof for directionali'zingfto'ward saidelongated elementtheexplosive forces developed upon detonation of the material, asheet metal structure completely enclosing said body of explosive material and provided with a liner for said cavity, said structure also including means cooperating with said-linerto provide a sealed annular stand-01f space between said cavity and the adjacent surface of said elongated element, means for lowering said structure and body of explosive material into the borehole to positionsaid cavity opposite said elongated element at the desired point of severance therealong, said last-named means including a plurality of side members andspacing rings defining a disposable open wire cage of substantial length which substantially fills theborehole, means for positioning said metal structure intermediate the ends of said side members with. said disk-like body of explosive material in a position extending transversely of said borehole as said cage is lowered into said borehole, and means for detonating said explosive material from the earthTs surface. 7

3. Apparatus for severing an elongated element extending longitudinallyof a borehole in the earth, comprising a disk-like, body of explosive material having a cavity extending around one edge thereof for directionalizing toward said elongated element the explosive forces developedupon detonation of the material, a sheet metal structure completely enclosing said body of explosive material andprovided with a liner for said cavity-,.s'aid.struc-' ture also including means cooperating with said liner to provide a sealed annular stand-off space between said cavity and the adjacent surface of said elongated element, means for lowering said structure and body of explosive materialinto-the borehole to position said cavity opposite said elongated element at the desired point of severance therealong, said last-named means including a plurality of side members connected at their ends to a pair of spacing rings to define a disposable open wire cage of substantial length which substantially fills the borehole, said side members having recesses intermediate the length thereof adapted to receive the spaced edges of said metal struc ture for positioning said structure with said disk-like body of explosive material in a position extending transversely of saidborehole as said cage is lowered into said'bor'ehole, a .de'tonating cord extending at least part way aroundthe non-cavitied edge of said disk-like body of explosive material within said metal structure, and means for.detonat-' ing. said cordfrom the earths surface, thereby to detonate said explosive material.

4. Apparatus for severing an element of a drill string extending longitudinally of a borehole in the earth and disposed at approximately the center of the borehole, comprising an annular body of explosive material having a center opening for receiving said element and provided with a cavity around the inner edge thereof for directionalizing toward said element the explosive forces developed upon detonation of said explosive material, a metal structure providing a liner for said cavity and including means providing a sealed stand-off space between said cavity and the adjacent surface of said element, means for lowering said structure and body of explosive material into the borehole to position said cavity opposite said element at the desired point of severance therealong, said last-named means including a plurality of side memrings defining an open wire cage of substantial length which substantially fills the borehole, means for positioning said metal structure intermediate the ends of said side members with said annular body of explosive material in a position extending transversely of said borehole as said cage is lowered into said borehole, and means for detonating said explosive material from the earths surface.

5. Apparatus for severing an element of a drill string extending longitudinally of a borehole in the earth and disposed at approximately the center of the borehole, comprising an annular body of explosive material having a center opening for receiving said element and provided with a cavity around the inner edge thereof for directionalizing toward said element the explosive forces developed upon detonation of said explosive material, a sheet metal structure completely enclosing said body of explosive material and provided with a liner for said cavity, said structure also including means cooperating with said liner to provide a sealed annular stand-off space between said into the borehole to'position-said cavity opposite saidelement at the desired point of severance therealong, said 'la'st-named'm'e'ans including aplurality of side members and spacing rings defining a disposable open wire cage, the intermediateportions of said side members being positioned adjacent the walls of said borehole and said spacing rings loosely embracing saiddrill string, means for positioning said metal structure intermediate the ends of said side members with said annular body of explosive material in a position extending transversely of said borehole as said. cage is lowered into said borehole, and means for detonating said explosive material from the earths surface.

6. Apparatus for severing an element of a drill string extending longitudinally of a borehole in the earth and disposed at approximately the center of the borehole, comprising an annular body of explosive material having a center opening for receiving said element and provided with a cavity around the inner edge thereof for directionalizing toward said element the explosive forces developed upon detonation of said explosive material, a sheet metal structure completely enclosing said body of explosive material and provided with a liner for said cavity, said structure also including means cooperating with said liner to provide a sealed annular stand-off space between said cavity and the adjacent surface of said element, means for lowering said structure and body of explosive material into the borehole to position said cavity opposite said element at the desired point of severance therealong, said last-named means including a plurality of side members having intermediate portions positioned adjacent the walls of said borehole and terminating in converging end portions, a pair of spacing rings connecting the end portions of said side members to define a disposable open Wire cage, said spacing rings being adapted loosely to embrace said drill string, means for positioning said metal structure intermediate the ends of said side members with said annular body of explosive material in a position extending transversely of said drill string as said cage is lowered into said borehole, and means for detonating said explosive material from the earths surface.

7. Apparatus for severing an element of a drill string extending longitudinally of a borehole in the earth and disposed at approximately the center of the borehole, comprising an annular body of explosive material having a center opening for receiving said element and provided with -a'bavity arounduheinner edge thereof for directionalizi ng toward said "element ,the explos'ive forcesdevelopedjupon Wdetonation of said explosive materiaLfQa metal's'tructure completely enclosing said body of ex plosive materialand pr'ovided with a liner forsaid cavity, saidjistruc'ture'also including means cooperatirig'with said liner to providejf'a sealed annular stand-off space between said cavity and the adjacent surface of said element, means for lowering said structure and body of explosive material 'into the borehole to position said cavity opposite said element at the desired point of severance therealong, said last-named means including a plurality of side members and spacing rings defining a disposable open wire cage, the intermediate portions of said side members being positioned adjacent the walls of said borehole and said spacing rings being adapted loosely to embrace said drill string, said side members having recesses in the intermediate portions thereof adapted to receive the spaced edges of said metal structure for positioning said structure with said annular body of explosive material in a position extending transversely of said borehole as said cage is lowered into said borehole, a detonating cord extending at least part way around the outer non-cavitied edge of said annular body of explosive material within said metal structure, and means for detonating said cord from the earths surface, thereby to detonate said explosive material.

References Cited in the file of this patent UNITED STATES PATENTS 215,408 Swett May 13, 1879 2,080,875 Pitzer May 18, 1937 2,138,603 Johnson Nov. 29, 1939 2,399,211 Davis Apr. 30, 1946 7 2,407,093 Mohaupt Sept. 3, 1946 2,415,814 Davis Feb. 18, 1947 2,494,256 Muskat et al. Jan. 10, 1950 2,543,057 Porter Feb. 27, 1951 2,587,243 Sweetrnan Feb. 26, 1952 2,587,244 Sweetman Feb. 26, 1952 OTHER REFERENCES The Sh aped Charge by Torrey in the Explosives Engineer, July-August, 1945, pages 161163. (Copy in Div. 70.)

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