US 2782715 A
Description (OCR text may contain errors)
United States Patent ,2,782,715 WELL IERFORATOR John J. Udry, South Gate, Calif., assignor, by mesne assignments, to Borg-Warner Corporation, Vernon, Calif., a corporation of Illinois y Application October 5, 1951, SerialNo. 249,838
` 4 Claims. (Cl. '10'2-20) This invention relates in general to well perforators, and more particularly to improvements in explosive shaped charge means for perforating well casings and Ythe surrounding earthA 'formations of well boreholes.
In the usual employment of :a plurality of shaped 'charges for perforation of Huid-filled Well casings, the shaped charges arec'on'tained in suitable fluid-tight, thick- Walled, cylindrical, steelhousings which lare adapted to be lowered into vthe Well borehole to be perforated. In Suchapparatus the shaped charges are usually posi- 'tioned at longitudinally spaced intervals throughout the length of the interior bore of the housing, with their perforating axes "directed laterally thereof in alignment with suitable ports formed in the carrier walls, the ports being initially 'closed by suitable, relatively thin, lluidtight port seals. Y
It is known that, in general, the perforating power of the shaped charge is a function 4of the quantity of the high explo'sive materialfin ythe Ycharge and the maximum diameter of the conical cavity 'in the forward end of the charge. The penetrating 'power is also aifected by the so-called stand-off distance of the shaped charge, the stand-off distance being the optimum axial distance from the shaped 'charge to the 'surface of the body to be perforated thereby. It is further known that the presence of 'any solid body on the perforating axis of the shaped charge, at 'a distance lfrom the charge less than the optin'iuml stand-ofi, interferes with the perforating jet issuing from 'the charge When detonated, in such manner as to materially impair its perforating characteristics and penetrating power. c
The 'optimum 'stand-oit distance of the shaped charge increases with yincrease of the diameter of the shaped charge cavity, and to vsome extent with increase of the quantity of the explosive. Therefore, it becomes apparent that the size and stand-off of a shaped charge as heretofore constructed, and hence the penetrating power thereof, is limited by the inside diameter of the housing 'in which it is contained, which in turn is limited by the inside diameter of the borehole in which it is t'o be employed.
It is therefore an object of this invention to provide a shaped charge perforatin'g device having increased pene- 'trating power. v
It is another object of this invention to provide a shaped charge perforating unit` having increased penetrating power for a given overall si'z'e.
t is a further 'object of this invention to furnish a shaped charge unit capable of eicient performance under conditions Where 'the stand-off `distance is less than the conventional optimum stand-off distance.
It is la :still further-object of the invention to provide a .shaped charge unit for thepurpose herein described having-.a 4stand-olf vdistance which is less critical than that I'of the shaped .charges heretofore employed for such Purpose., Y
It is another object of the invention to provide a 2,78Z.,7 l 5 Patented Feb. 26, 19,57
shaped charge unit having reduced length relative to diameter without resultant reduction in penetrating power, whereby shaped charges of increased penetrating power can be contained in housings of given inside diameters.
The objects of this invention are laccomplished in general, by employing a compounded, shaped charge comprising an approximately annular shaped primary or main charge of high explosive material having a coaxial, frusto-conical opening or passage extending therethrough, and an approximately cylindrical, shaped booster charge of high explosive material having a conical cavity in one end thereof and positioned coaxially within the smaller end of. the truste-conical opening of the primary charge, with the conical cavity facing in the same direction as the said opening, together with a suitable detonator 'for the booster charge. The inner surfaces of bothvthe conical cavity of the booster charge and the frusto-conic'al opening through the primary charge are preferably lined with a relatively thin layer of metal.
Referring to the drawing, the invention is there illustrated in connect-ion with a perforator such as is used for oil Well casing and formation perforation, and comprises an elongated tubular housing 10 having a coaxial bore 1i, the cylindrical wall of which is provided with one or more laterally directed, threaded ports or openings as shown at 12. Where a plurality of such ports are employed together With a plurality of shaped charge uni-ts, as hereinafter described, they may be positioned in suitable longitudinally spaced-apart arrangement, as shown and disclosed in the copending application of Lindsay et al, Serial No. 106,567, now Patent No. 2,707,917, dated May l0, i955. The explosive shaped charge unit of this invention is formed and contained in a relatively thin-walled housing or shell formed with a cylindrical forward end portion 15, a tapering intermediate portion 16, and a cylindrical base extension 17, which may have a reduced rear end boss extension 18 for positioning in a circular recess Ztl formed in the inside surface of the Wall of the body AIii and diametrically opposite port 12. The housing or shell 14 may be made of any suitable material, preferably a relatively light frangible material such as plastic. A charge retainer l21, comprising a tapered, tubular member of suitable resilient material, such as rubber or the like material, and constructed and operated in a manner similar to that more fully described in the beforementioned copending application, is provided to engage at one end thereof the inner surface of rim 22 of the cylindrical portion 15 of the shell and also at the other end thereof the inner edge portion of the annular opening of port l2, thereby to retain the boss 1S in engagement with recess 2t) and to support the forward end in coaxial alignment with the port 12, A port plug or seal member 23, which may be made of copper, brass, aluminum, or the like material, is threaded, fluidtight, into port 12 and is formed with a relatively thin end wall'or diaphragm 24 positioned substantially at the outer dimensional line of cylinder 10 and in alignment with the longitudinal, perforating axis of the shaped charge unit. The tubular body 10, being thick Walled and preferably made of high strength alloy steel, serves to exclude well iiuid from the shaped charge units prior torliring and partially to retain the extraneous explosive forces from the shaped charges, thereby shielding the surrounding well casing or borehole from possible damage.
The primary or main explosive charge of this invention as indicated at 25 comprises a somewhat tapered, tubular or annular shaped body of high explosive material, conforming in exterior contour with the shape of lthe inside surface of the cylindrical and tapered portions l5 and 16, respectively, of the container shell 14, and having an interior, coaxial, forwardly diverging, frusto-conical passage 19 -conforming in shape with the exterior surface of a frusto-conical liner member 26. This explosive body is preferably east or otherwise consolidated or pelletized to proper density, as is well known in the art. The liner 26 may be made of a suitablenon-explosive material preferably having a relatively high density, such as, for example, copper, steel or the like. A booster charge as indicated at 27 is positioned in the rear end opening of 4and in coaxial alignment with the passage 19 formed through the primary shaped charge body 25, and comprises a cylindrical body or pellet 27 of high explosive material contained in a cup member having cylindrical side walls 2S and a forwardly facing conical end wall or liner 30. The walls 23 and 30 may be composed of any suitable material, but preferably of metal such as aluminum, copper or brass, having a thickness in the order of approximately .015. The angles of taper of walls 26 and 30 are not critical, however, and as shown are substantially 411/2I and 90, respectively. The base extension 17 of 4the shell 14 is formed with a transverse opening or passage 32 adjacent the inner or rearward end of the booster charge 27 into which may be inserted a detonator or through which may be threaded an elongated detonating fuse 31, in the manner more fully shown `and described in the applicants copending application Serial No. 220,770, tiled April 13, 1951, or in the hcreinbeforementioned copending application of Lindsay et al., Serial No. 106,567, which applications also illustrate suitable conductor cable supporting means for the apparatus and suitable electrical connections for igniting the fuse. The fuse 31 is preferably of an explosive or detonating type such as, for example, that known commercially as P. E. T. N. plastic covered Primacord, designated as 100 4gin/ft. The fuse is preferably covered throughout its length by a protective rubber tubing 33.
The booster charge 27 preferably should be a high explosive material such as cyclotrimethylenetrinitramine, commonly known as Cyclonite, and more sensitive than that of the primary charge 25, which should also be a high explosive material such as, for example, R. D. X. explosive, which is the trade name of an explosive material which is manufactured by E. I. du Pont de Nemours and Company.
In the operation of the invention, upon the booster if charge 2'7 being tired, an explosive jet will be directed therefrom along the axis of the shaped charge unit toward the target, which initially may be considered as the diaphragm 24 of the port seal 23, thereby opening a hole in the port seal diaphragm in advance of the perforating jet from the main charge 25. The tiring of the booster charge will be closely followed by the tiring of the main charge 25, and its jet will follow the path cleared by the booster jet into impingement with the surrounding well casing or borehole formation. The wall 2b of the booster charge 27 provides a short delay between the tiring of the booster charge and the detonation of the primary shaped charge sufficient to permit the perforating jet from the booster charge to reach and penetrate the port seal lbefore the jet from the primary charge has completely Vfoirned. l
inasmuch as the seal or diaphragm 24 has been opened by the booster charge 27, the full effect of the force of the perforating jet from the main charge 25 will be applied, without interference, to the main target which will be at some point beyond the seal 24, such as somepoint in a well casing or borehole formation, and therefore the effective optimum stand-off of the compounded shaped charge will be greater than that of a single shaped charge 4of conventional form and of substantially the same explosive power.
The present invention additionally makes it possible to increase shooting power by using a larger shaped charge than with other designs because the charge is truncated and thereby shortened, which permits it to be of larger diameter for a given perforator housing inside diameter, and the optimum effective stand-olf distance is not limited to the distance from the main shaped charge body to the port seal, as heretofore, but-is extended by the action of the shaped booster charge, as hereinbefore described, thereby making it possible to place the forward end of the shaped charge unit closer to the inside surface of the housing and the port seal than heretofore possible.
It is to be understood that the foregoing is illustrative only and that the invention is not limited thereby, but may include various modifications and changes made by those skilled in the art without distinguishing'from the scope of the invention as defined in the appended claims.
What is claimed is:
l. In combination with a well perforator in which a shaped chargeY having a forwardly opening concavity is contained within a iiuid-tight housing adapted to be lowered into a well borehole: a support for said shaped charge inside of said housing; a port in said housing in front of said concavity and in axial alignment with the axis of penetration of said shaped charge; a uid seal member closing said port, said seal member being relatively thin at a point in alignment with said axis as compared to the thickness of the adjacent wall of said housing surround,- ing said port and being positioned relative to the forward end of said concavity of said shaped charge at a distance less than the optimum stand-olf distance thereof; a through opening in the rear end of the concavity ofsaid shaped charge; a separate shaped charge positioned in said open/- ing, to the rear of said eoncavity, and coaxial with said shaped charge axis of penetration and facing said seal member, said separate shaped charge being separated from Vthe adjacent portion of said shaped charge by an intermediate, relatively thin wall of non-explosive material; and detonator means positioned adjacent the rear end of said separate shaped charge.
2. In a well perforator adapted to be lowered into a well borehole, the combination of: a fluid-tight housing', a shaped charge having a forwardly opening concavity, a support for said shaped charge inside of said housing; a port in said housing in front of said concavity and in axial alignment with the axis of penetration of said shaped charge; a liuid -seal member closing said port, said seal member being relatively thin at a point in alignment with said 'axis as compared to the thickness of the adjacent wall of said housing surrounding said port and being positioned relative to the forward end of said concavityof said shaped charge at a distance less than the optimum standoff distance thereof; said shaped chargecomprising a main body of explosive material formed with a substantially frusto-coni'cal passage therethrough, a separate shaped explosive charge having aconcave recess formed in one end thereof andpositioned adjacent the inner smaller end portion of said passage, with said recess coaxial with and facing into said passage toward the larger end thereof, a relatively thin Wall of nonexplosive material positioned between and substantially in contact with said separate explosive charge and the adjacent explosive material fat said smaller end of said passage, and detonator means positioned adjacent the end of said separate explosive charge opposite said recess and adapted to detonate said separate explosive charge prior to detonation, through said wall, of said main body of explosive material.
3. In a well perforator adapted to be lowered intoa well borehole, the combination defined by claim 2, wherein said separate shaped explosive charge is composed of an explosive more sensitive than that of said main body of explosive material.
4. ln a well perforator adapted to be lowered into a well borehole, the combination defined by claim 2 with a relatively thin metal liner on the inner surface of said frusto-conieal passage, and a relatively thin metal liner on vthe surface of said concave recess, and wherein said v 6 concave recess has a Wider included angle than that of 2,628,559 .Tasse Feb. 17, 1953 said frusta-conical passage. 2,629,325 Sweetman Feb. 24, 1953 References Cited in the le of this'patent 5 GFOREIGN PATENTS 1 9 78,775 reat Britain Ju y 11, 1 46 .2 413 004 UlTEtD STATES PATENT?) 24 1946 578,995 Great Britain July 19, 1946 or ec. 2,420,201 seavey May 6, 1947 y OTHER REFERENCES 2,440,568 After Apr. 27, 1948 Article entitled: The I et Perforation Pnooess, by W. T. 2,446,640 Davis Aug. 10, 1948 10 Box and R. F. Meiklejohn; published n World Oil, March 2,494,256 Muskat et al. Jan. l0, 1950 1950;Vo1. 130, No. 4, pages 112, 116, 118, 121, 122. 2,513,233 Byers June 27, 1950