US3021784A - Shaped charge unit for well perforators - Google Patents

Description

Feb. 20, 1962 D. MEDDICK SHAPED CHARGE UNIT FOR WELL PERFORATORS Filed Sept. 2l, 1955 2 Sheets-Sheet 1 Feb. 20, 1962 L.. D. MEDDICK 3,021,784

SHAPED CHARGE UNIT FOR WELL PERFORATORS Filed Sept. 2l, 1955 2 Sheets-Sheet 2 BY al@ United States Patent 3,021,784 SHAPED CHARGE UNKT FOR WELL PERFRATRS Lorrain ll). Meddiclk, Whittier, Calif., assigner, by mesne assignments, to Borg-Warner Corporation, Vernon, Calif., a corporation of Illinois Filed Sept. 21, 1955, Ser. No. 535,586 6 Claims. (Cl. lill- 20) This invention relates generally to well perforators and more particularly to improvements in explosive shaped charges for use in perforating well casings and the surrounding earth formations in well boreholes.

In the employment of shaped charges for making perforations in well boreholes, a number of different apparatuses and arrangements have been developed suitable for lowering one or more ,shaped charges through fluid-filled well casings or earth boreholes to locations therein where perforation is desired, and for the tiring at such locations simultaneously or selectively of the shaped charges. As an example of one type of such apparatus, a so-called shaped charge perforator gun has heretofore been developed which makes provision for the mounting of one or more, and preferably a plurality of shaped charges adjacent one another inside a suitable, liquid-tight, thick-walled cylindrical, steel housing which is adapted to be lowered on a conductor cable into the fluid-containing well borehole and casing to be perforated. In such apparatus, the plurality of shaped charges are usually positioned at suitable, longitudinally spaced-apart intervals throughout the length of the cylindrical housing, with the jet-forming or perforating axes of the shaped charges directed laterally thereof in alignment with suitable ports formed in the housing Walls. The ports are initially closed prior to tiring of the shaped charges by suitable, relatively thin, frangible, replaceable, fluid-tight port seals. Uponring of the shaped charges, usually by means of electrical current passed through the conductor in the before-mentioned conductor cable to suitable detonating means within the housing, the port seals are perforated, destroyed, or otherwise removed from the ports by the shaped charge perforating jets which are of suicient penetrating power to continue on through the fluid in the borehole, through the casing and into the surrounding formations. The cylindrical housing serves initially before ring to exclude borehole liquid from contact with the shaped charges therein and also, upon tiring, to confine therein all of the blast of the shaped charges other than that directed into the perforating jets which are projected through the perforated port openings. Typical examples of the before-described so-called shaped charge perforating gun apparatus in which the device Of the present invention may be used are shown in US. Patent No. 2,707,917, issued May 1o, 1955, to Win H. Lindsay, Jr., et al. and in the copending application of Will H. Lindsay, lr., Serial No. 276,156 led March l2, 1952, now abandoned in favor of' the copending continuation application of Will H. Lindsay, lr., Serial No. 703,676, led December 18. 1957 now U.S. Patent No. 2,926,603, issued March l, 1960.

In oil well perforating operations as hereinbefore mentioned, it is desirable to attain the maximum depth of penetration of perforations laterally through the Well casing and into surrounding formations, together with the use of a minimum explosive charge and with a minimum resultant amount of damage to the cylindrical housing in which the shaped charges are contained. It is also in some cases desirable to attain a maximum size of perforation through the casing and into the surrounding formations, but in some cases and under some conditions it is also desirable to be able to control. the perforation hole sizes obtained between certain specified limits.

Heretofore, the attainment of improved performance of the shaped charges in regard to increase of depth of perforation penetration and increased hole size has usually been at the expense of the use of greater and greater amounts of explosive, with attendant incr-eased damage to the shaped-charge containing housings.

It is, therefore, an object of this invention to provide a shaped charge perforating unit of superior performance characteristics.

It is another object of this invention to provide a shaped charge perforating unit having increased penetrating power for a given amount of explosive charge.

It isa further object of this invention to provide a i shaped charge unit of superior design whereby the perforating jet is of more effective shape and power.

lt is a still further object of this invention to provide a shaped charge construction which will produce larger perforations for a given amount of explosive and in which adjustments may be readily made to vary the perforation hole sizes.

It is a still further object to permit adjustment of the shaped charge in the eld to Vary the size of the produced perforation. I

A still further object of this invention is to provide a shaped charge construction which will permit of its use with a minimum of damage to the containing houslng.

The objects of this invention are attained in general by employing an improved casing for the shaped charge explosive body, the primary constructional feature of which resides in the employment of a plurality of relatively thick, substantially separate, coaxial, metal ring members which closely and firmly encircle a part or all of the portion of the shaped charge which surrounds the jet-forming cavity therein. The reason for obtaining the improved shaped charge performance characteristics in this manner is not entirely understood, but it is thought possibly to result from employing such rings of suicient weight and tensile strength as to provide an effective back-up and connement for the shaped charge, While at the same time permitting rupture of the rings in a progressive, orderly manner from the rearmost one thereof forward therethrough through the plurality of such rings as the detonation wave is propagated forwardly from the detonator through the explosive charge body, in such a manner as to provide at all times a consistant and symmetrical confinement and direction of the gaseous explosive products into the formation of a more perfectly shaped and more powerful perforating jet. Erratic fracture of the entire case at any one instant as otherwise probably occurs is thus prevented by such sepa- In this connection it has also been discovered that a variation in the number of rings employed will result in a variation in the resultant perforated hole size.

These and other objects, advantages and features of novelty of the invention will be evident hereinafter.

In the accompanying drawing wherein a preferred embodiment and the best mode contemplated by the inventor forV carrying out his invention is illustrated:

FIGURE 1 is a longitudinal sectional view illustrating a typical arrangement of the shaped charge structure of this invention utilizing a shaped charge casing having a plurality of separate ring members.

FIGURE 2 is a fragmentary sectional view of an alternative embodiment in whichV the shaped chargeY casing is provided with a plurality of encircling annular grooves formed in the outer periphery thereof.

FIGURE 3 is a fragmentary sectional view of an embodiment alternative to that of FIGURE 2 and in which the annular grooves are formed in the inner surface of the shaped charge casing. FIGURE 4 is a longitudinal sectional view showing a modified embodiment of the invention and illustrating the manner in which the number of reinforcing rings may be varied to control the dimensions of the perforation produced by the shaped charge.

FIGURE 5 is a View, partly in elevation and partly in longitudinal section, of a completely assembled perforator apparatus, illustrating a typical arrangement of the shaped charge devices of this invention.

FIGURE 6 is a cross-sectional view, on an enlarged scale, taken on line 6-6 of FIGURE 5.

Referring first primarily to FIGURE l, the shaped charge apparatus of the invention therein illustrated, incorporates a basic explosive body and coneassembly. This explosive body and cone, which may be pelletized or cast together as is conventional practice, is seated in a separate rearward portion of the case, which may be considered basic for a givenshaped charge body, and need not vary in form as the remaining case parts are assembled or varied.

The before-mentioned basic rearward portion 1 of the case may be formed preferably of a material of substantial tensile strength, such as steel, although diecast zinc, aluminum, Bakelite, or equivalent materials may be used. It consists of a cylindrical rear portion 2 having a frustoconical portion 4 flared outwardly and forwardly therefrom. The basic case 1 is thus of generally conical form about its longitudinal axis, but is bored transversely through the cylindrical rear portion 2 as shown at 5 to receive therethrough an explosive fuse 6, and the case 1 is also internally bored at 7 along its longitudinal axis to form a cylindrically shaped recess to receive a booster charge 9.' Booster charge 9 may be pressed into the bored portion 7 of case 1, but is preferably contained in a metal, cup-shaped container comprising'a thin-walled, cylindrical portion 9a and a relatively thick, annular, rear end closure member 9b which surrounds a thin, central diaphragmed aperture portion 9c. Forward of the booster charge 9 the basic case 2 is formed with a generally frusto-conical interior portion 10 defining a conical seat for the reception of the correspondingly shaped rear end portion of the main explosive shaped charge body 11. vThe explosive charge Abody 11 is formed with a coaxial, forwardly directed concavity or recess 12 of generally conical formand which may have the apical portion rounded as at 13. The concavity or recessed portion 12 is provided with a thin, closely adherent liner 14 of copperv orsimilar material. The shaped charge concavity 12 and liner 14 flare outwardly from the rounded portion 13 near the booster 7, to intersect the inner wall of the case 20 near or within a charge aligner receiving ring 15. Charge aligner receiving ring 15 is formed with an annular recess 16 to provide for the reception therein of the inner end of a suitable charge retainer and aligner member which may be of the type illustrated at 35 in the hereinbefore mentioned copending patent application of Lindsay, Jr., which retainer and aligner member provides for the proper alignment and stand-olf distance -required for the perforating jet when the charge is seated in a gun for firing.

The outer surface of the explosive charge 11 may be, under some circumstances, protected by a thin metallic coating or shell as shown at 17 in the embodiment of FIGURE 4. The shell or coating 17 preferably extends completely around the frusto-conical portion 4a of the shaped charge 11 and cylindrical rear portion 2a in order to provide a conveniently handled, substantially sealed unitary structure.

" Theremainderfof the casing between the VchargeV aligner may be seen in fragmentary form in FIGURE 2. Here the shaped charge casing, generally indicated at 25, includes in one piece the retainer receiving ring portion 26, the annular ring portions 27, and a rear portion 29 corresponding to the basic case portion shown at 2 in FIG- URE 1. The aligner receiving ring 26 and the annular ring portions 27 are, however, formed integrally instead of separately as in the embodiment of FIGURE l. The individually functioning annular portions are then defined by cutting a plurality of annular slots into the external periphery of the casing 25. These slots may extend for only a portion of the casing wall thickness, although preferably they extend almost entirely therethrough, as shown at 35. In some `cases sufficient stress concentration may be provided by grooves of medium` depth.

A relatedalternative embodiment is shown in FIGURE 3, in which slots 31a-3112 inclusive, are cut into the internal surface of a similar case 32 before the shaped charge body 11 is inserted.

In the embodiments of FIGURES 2 and 3, it will be seen that the essential characteristic of the embodiment of FIGURE 1 is preserved. That is, a series of pressurestabilizing annular members is presented to the traveling shock wave, essentially separate so far as their ability to resist rupturing stresses, yet mechanically joined for ease in construction and convenience in handling during assembly.

FIGURE 4 illustrates. the manner in which the number of rings applied about the charge may be varied in the field or elsewhere by the operator, to control the diameter of the hole produced. AIn tests on one embodiment, it has been found possible to vary the hole diameter between about .33 to .75" solely by controlling the number of rings. The hole size increases as the number of such rings is increased.

In this arrangement, the aligning member-receiving ring 15 with recess 16 is identical with the type shown in FIG- URE 1. Rings 34a and 34h are then slipped over the shell 17 encasing charge 11, and as many additional rings 34C, 34d, etc., applied as will produce the hole size desired. Shell 17 is preferably of thin sheet metal, metal foil, or any equivalent sealing material which will form a firm mechanical connection between the explosive charge and the surrounding case structure and which will contain the explosive charge and prevent contamination by atmospheric moisture. This makes itpossible to determine hole size in accordance with the needs of the particular location under the ready control of the operator through the utilization of one basic explosive body or pellet.

Advantages of the hereinbefore described shaped charge construction of this invention and a possible explanation of the reasons therefor, are as follows:

If the case enclosing the shaped charge body is con- Structed of a continuous uninterrupted body, upon detonation of the charge therein the case is ruptured in an irregular and erratic manner, with breaks possibly developing in the case for a considerable distance in advance of the explosive wave. This erratic and irregular manner of rupture of the case possibly results in a comparable irregular and erratic fracture and deformation of the explosive charge ahead of the explosive wave which in turn would result in a similarly nonsymmetrical production of the gaseous products ot the detonation relative to the longitudinal axis of the shaped charge body. This action together with the resultant nonsymmetrical support of the products of the explosion by the surrounding case would thereby result in defective action of the shaped charge.

In the instant embodiment of this invention, however, it is believed that this undesirable action is eliminated by providing a case structure which, as herenbefore described, is composed of a plurality of coaxial, substantially separate, ring members which closely encircle the exterior surface of the shaped charge and which ring members by reason of their being substantially separate are able to rupture successively, one at a time, as the explosive waveprogressesforwardly through the shaped charge body.v A. The result of this action is the insurance that the surrounding case will, for all practical purposes, remain intact around the unexploded portion of the shaped charge body until the explosive wave has progressed forwardly. therepast. The rupture of one ring will not be carried forward into the next forwardly adjacent ring until the pressure therein also reaches the ring-fracturing value. This affords an over-all effect of a series of momentary but appreciable additional periods of confinement for the explosive charge during which a more efficient build-up of pressure and a better form of the body of gaseous products may be maintained, together with an increased rate of detonation of the explosive, which results in the formation of a perforating jet of increased volume and velocity and of superior form.

Another important advantage which resides in the shaped charge construction of this invention is as follows: As a result of the increased eiiiciency of the shaped charge construction of this invention, a reduced amount of explosive may be employed without sacricing any performance characteristics or penetrating power. As a result of this reduction in quantity of explosive, the damage to the housing or so-called shaped charge perforating gun is greatly reduced. The so-called gun damage is found to be still further reduced when the shaped charge case is constructed from a plurality of rings in the manner of the invention herein disclosed. This latter result appears to be due largely to the greater ability of the gun body to absorb a succession of separate lesser shocks and impacts as the rings rupture progressively, as contrasted with its ability to absorb the entire shock of much greater magnitude which occurs when a coventional type of shaped charge case is employed,

Referring to FIGURES and 6, the well perforator apparatus shown has a liquid-tight, thick-walled, cylindrical, steel housing including a tubular section 36. The bottom of the tubular section is closed by a bull plug 37. The top of the tubular section is closed by a cable head 3S coupled to the :op of the tubular section through an intermediate sleeve member 39. A conductor cable 4l), containing an insulated conductor 41, is anchored to the cable head 38 and serves as a means for lowering the perforator apparatus into the well and for conducting electrical ring current to the firing means of the perforator. Typical cable head construction suitable in this connection is illustrated in U.S. Patent No. 2,043,34l to Turechek. The electrical conductor 41 is connected through the cable head 38 and through an insulated electric con- 6 r ductor 42 to an electric detonating cap 43. The cap is secured within the upper end of a tubular fuse terminal union 44, which is in turn supported centrally within the upper end of the housing section 36 by means of a centrally perforated diaphragm 45. A suitable fuse 6, such as the fuse described with reference to FIGURE 1, which is threaded through the rear end portions of the shaped charge units, enters and is crimped into the lower end of the fuse terminal union 44 adjacent to or in contact with the cap 43.

The housingsection 36 has a series of longitudinally spaced, radially directed openings or ports 46 therethrough, each port being enlarged on the outside end by a short counterbore 47 to receive a port seal disc 48. Such series of ports 46 (only two of which are shown in FIGURE 5, duplicate portions thereof having been omitted) may be arranged along the housing in any desired pattern.

A shaped charge unit, such as shown in FIGURE l, having the ring . members 20a, 20b, etc., is mounted opposite each of the ports 46 and positioned so that the jetshaped blast projected from the forward, concave end of the unit will pass through the center of the port. In order to position and accurately maintain each such shaped charge unit in axial alignment with its respective port 46, the inner wall ofthe tubular housing section 36, diametrically opposite each port 46, is provided with suitablel means `to engagean'd support the rear end portion4 of the shaped charge unit. Preferably, such means takes the form of a radially directed, generally cylindrical recess 49, and the rear end portion 2 of the shaped charge case is formed to t Within such recess. The forward end of the shaped charge unit may be supported by any suitable means adapted to hold the rear end of the shaped charge securely seated within the recess 49 and at the same time maintain accurate alignment of the axis of the shaped charge with the center of the port 46. For this purpose, a retainer 5i) may be employed. The retainer is in the general form of a hollow, truncated cone, with end portions 51 and 52 for making telescoping engagement with the annular recess 16 formed within the forward end of the shaped charge unit, and with the inside surface of the inner end portion of the port 46, respectively, and a coaxial, frusto-conical, tubular, interconnecting portion 53 extending between these end portions. The interconnecting portion 53 is preferably of flexible, resilient material, such as rubber, to enable one end portion thereof to be collapsed or telescoped within the other end portion for initial installation of the shaped charge unit within the bore of the tubular housing section 36, as more fully described in the hereinbefore mentioned U.S. Patent No. 2,707,917 to Will H. Lindsay, Jr., et al.

It will be understood that the shaped charge units of FIGURES 2, 3 and 4, and other units in accordance with the invention, may be similarly mounted in a hollow housing in the manner illustrated in FIGURES 5 and 6.

In operation of the apparatus of FIGURES 5 and 6, an electric potential is applied to the conductor 41, which is transmitted down through the conductor cable 40 from the top of the borehole to the cable head, through conductor 42 within the cable head, and through the electric detonator cap 43 to ground. The resultant detonation of the cap in turn detonates the fuse 6, the explosive wave of which travels through the full` length of the fuse from top to bottom at high velocity. This explo- Y sive wave fires the shaped` charge units` in rapid succession. The resultant perforating jets pierce the seal discs 48 and the surrounding well casing and earth formation, thus perforating the Well. t y

It is to be understood that the foregoing is illustrative only and that the invention is not limited thereby, but may include variousmodications and changes made by those skilled in the art without distinguishing from the scope of the invention as4 defined in the appended claims.

. housing, and with a surrounding exterior surface coaxial with the axis of said concavity and extending rearwardly from adjacent the ,forward edge portion of said concavity to the inner end, of the latter, a liner lining the walls of said concavity, afmetal case about saidbody of high explosive material,and means at the rear of said body of high explosive material for detonating the latter, said perforating unit being adapted to fire a perforating jet through a wall of said housing into the surrounding wall of the well, said body of explosive material being adapted to fracture said case and to scatter its fragments forcefully against the inner walls of said housing, the improvement for reducing damage to said housing caused by the scattered fragments of said case which comprises .said metal case having an annular wall portion'disposed about said surrounding exterior surface of said body of high explosive material, said wall portion CQmPISing several substantially separate, solid ring mem.-

bers, said ring members being longitudinally disposed i with adjacent ring members substantially abutting'each` plosive charge vperforating unit mounted in said housing,

said unit including a body of high explosive material formed with a forwardly facing concavity symmetrical about an axis transverse to the longitudinal axis of the housing, and with a surrounding exterior surface coaxial I with the axis of said concavity and extending rearwardly from adjacent `the forward edge portion of said concavityv to the inner end of the latter, a liner lining the walls of said concavity, a metal case about said body of high explosive material, and means at the rear of said body of high explosive material for detonating the latter, said kperforating unit being adapted to re a perforating jet through a wall of said housing into the surrounding wall of the well, said body of explosive material being adapted to fracture said case and to scatter its fragments forcefully against the inner walls of said housing, the improvement for reducing damage to said housing caused by the scattered fragments of said case which comprises said metal case having an annular wall portion disposed about said surrounding exterior surface of said body of high explosive material, said wall portion comprising several thick-walled, high-strength, separate, solid ring members,

.said ring members being longitudinally disposed with ad- K i jacenty ring members substantially abutting each other, lsaidvring members being coaxial with the axis of said concavity and being supported upon and closely encompassing said external surface of said body of high explosive material along its substantially entire longitudinal length, said ring members being adapted to be ruptured successively as the explosive wave progresses forwardly through said body of high explosive material upon detonation of the Vlatter.

3. In .a shaped charge perforating apparatus for use ina well borehole including a liquid-tight, generally cylindrical housing having a longitudinal axis and adapted to be lowered into a well borehole, at least one shaped explosive charge perforating unit mounted in said housing, said unit including a body o-f high explosive material formed with a forwardly facing concavity symmetrical about anY axis transverse to the longitudinal axis of the housing, and with a surrounding exterior surface coaxial with the axis of said concavity and extending rearwardly from adjacent the forward edge portion of said concavity to the inner end of the latter, a liner lining the walls of said concavity, a metal case about, said body of high explosive mate-rial, and means at the rear of said body of high explosive material for detonating the latter, said perforating unit being adapted to lire a per.-

forating jet through a wall of said housing into the surrounding wall of the well, said body of explosive material being adapted to fracture said case and to scatter its fragments forcefully against the inner walls of said housing, the improvement for reducing damage to said housing caused by the scattered fragments of said case which comprises said metal case having an annular wall portion disposed about said ysurrounding exterior surface of said body of high explosive material, said wall portion having a plurality of longitudinally spaced-apart, annular grooves extending laterally through a major portion of its thickness to form several substantially separate, solid ring members, said ring members being Ylongitudinally disposed with adjacent ring members substantially abutting each other, said ring members 4being coaxial with the axis of said concavity and closely encompassing said body of high explosive material along its substantially entrie longitudinalllength, said ring members being adapted to be ruptured successively as the explosive wave progresses forwardly through said body of high explosive material upon detonation of the latter.

4. In a shaped charge perforating apparatus forv use in a well borehole including a liquid-tight, generally cylindrical housing having a longitudinal axis and adapted to be lowered into a well borehold, at least one shaped explosive charge perforating unit mounted in said housing, said unit including a body of high explosive material formed with a forwardly facing concavity sym, metrical about an axis transverse to the longitudinal axis of the housing, and with a surrounding exterior surface coaxial with the axis of said concavity and extending rearwardly from adjacent the forward edge portion of said concavity to the inner end of the latter, a liner lining the walls of said concavity, a metal case about said body of high explosive material, and means at the rear of said body of high explosive material for detonating the latter, and perforating unit being adapted to lire a perforating jet through a wall of said housing into the surrounding wall of the well, said body of explosive material being adapted to fracture said case and to scatter its fragments forcefully against the inner walls of said housing, the improvement for reducing damage to said housing caused by the scattered fragments of said case which comprises a relatively thin sheet metal shell in contact with and extending over said exterior surface, and said metal case having an annular wall portion in contact with and encircling said shell, said wall portion comprising several substantially separate ring members, rsaid ring members being longitudinally disposed. with adjacent ring members substantially abutting each other, said ring members being coaxial with the axis of said concavity and closely encompassing said body of high explosive material along its substantially entire longitudinal length, said ring members being adapted to be ruptured successively as the explosive wave progresses forwardly through rsaid body ofhigh explosive material upon detonation of the latter.

5. In a shaped charge perforating apparatus as delined in claim 3, the further improvement which com- 9 6. In a shaped charge well performing apparatus as 2,792,783 dened in claim 3, the further improvement which com- 2,798,431 prises said plurality of longitudinally' spaced-apart, an- 2,819,673 nular grooves being formed in the :inner periphery 0f said annular Wall portion of said case. 5

324,903 References Cte in the file of this patent UNITED STATES PATENTS 997,992 2,513,233 Byers June 27, 195() 10 1,022,867 2,603,155 Clarke et al Iu'ry 15, 1952 692,741 2,708,408 Sweetman May 17, 1955 1,098,194

1Q Delacour May 21, 1957 Semen et al. July 9, 1957 Cecil et al, Jan. 14, 1958 FOREEGN PATENTS France May 23, 1921 France May 23, 1921 Great Britain Dec. 21, 1945 France Sept. 19, 1951 France Dec. 24, 1952 Great Britain June 10, 1953 France Mar. 2, 1955 UNITED STATES PATENT OFFICE CERTIFICATE 0F CGRRECTION Patent No. 3,021,784 February 20, 1962 Lorrain D. Meddck It is hereby certified that error appears in the above numbered patent requiring correction and that the seid Letters Patent should read as corrected below.

Column 7, line 36, forl "letteN read latter --5 column 8, line 31, for' "entre" read entire same column, line 51, for "and" read said vSigned and sealed this 24th day of July 1962.

(SEAL) Attest:

ERNEST w. swlDER DAVID L. LADD Attesting Officer Commissioner of Patents

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