US 3346056 A
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Description (OCR text may contain errors)
Oct. 10, 1967 I F. o. BOHN 3,346,056
HOLLOW CARRIER GUN Filed May 24, 1965 INVENTOR. FLOYD O. BOHN I VBZM/IZVW ATTORNEY United States Patent 3,346,056 HOLLOW CARRIER GUN F 0. Bohn, Houston, Tex., assiguor to Dresser Industries, Inc., Dallas, Tex., a corporation of Delaware Filed May 24, 1965, Ser. No. 458,222 3 Claims. (Cl. 1754.6)
ABSTRACT OF THE DISCLOSURE The length of a shaped charge extends substantially the entire diameter of the space inside a hollow carrier body, and a booster cap extends into an aperture in the wall of the carrier from the outside and has a portion extending externally therefrom to receive the Primacord which extends along the outer surface of the hollow carrier body.
This invention relates to lined shaped charge perforating guns and more particularly, to a hollow carrier type gun for use in small diameter tubing.
Lined shaped charges are used extensively by the petroleum industry for perforating operations. Generally speaking, there are two common types of carriers or guns used to properly position the shaped charges in the well borehole. These are the hollow carrier type gun and the capsule type gun. In the hollow carrier type gun, all of the charges are positioned within a generally cylindrical enclosed tubing. The explosive forces are retained within the tube and all residual parts resulting from the detonation of the lined shaped charges also remain in the gun. Therefore, no junk is left in the well. In the capsule type gun the lined shaped charge has its own pressure resistant housing. In some of the capsule type guns, the carrier for the charges is also expendable, however, in other types of capsule guns the carrier is retrievable and the only junk remaining in the hole is that left by the individual shaped charges. Accordingly, for many operations the hollow carrier type gun is preferred. However, since in hollow carrier type guns the charges are contained within a pressure resistant housing the length of the shaped charge is usually less than a corresponding diameter capsule type charge.
In addition, the diameter of tubing has been decreasing and the problem of size of the gun used in the well is becoming more acute. For example, today in throughtubing or small diameter tubingless completions, the common sized tubing used has an outside diameter of 2%" and a nominal inside diameter of 2%". Moreover, in the through-tubing completion practice, there may be one or more landing nipples having a seating surface for packers which have a reduced inside diameter. For instance, 2%"
. in 2%" tubing, 1 in'2%" tubing, etc. Retrievable perforator guns that go down through the tubing also have to be brought back out of the well without damaging the seating surface of the nipple. As mentioned, the explosive forces resulting from the detonation of theshaped charges is contained by the body of the hollow carrier gun and the guns swell. The swelling of the gun body is in localized spots opposite the flank of the charge. Knobby guns, which result from the localized swelling, decrease annular clearance and increase the hazards in running. In addition, there is often a burr resulting from the jet piercing through the gun body. This burr also increases the diameter of the gun. In the example above given where the inside diameter of a landing nipple is 2%" and has a sealing surface which it is desirable not to mar, the producing companies have a rule that no hollow carrier gun exceeding 2 may be used and it is further specified that the gun may not exceed 2 after 3,34%,fi56 Patented Oct. 10, 1967 firing. Therefore, the size of the gun body is of prime importance.
The purpose of the present invention is to effectively use the available space in a hollow carrier gun body thereby to permit the design and manufacture of shaped charges with superior performance characteristics.
It has been customary in hollow carrier guns to have the Primacord which is customarily used as the detonating means for shaped charges, to extend inside the gun barrel at the axial rear end of the booster in the charge. Accordingly, the Primacord takes up an inproportionately large part of the available space inside the hollow carrier gun. Effort-s have been made to place the Primacord at the side of the booster of the charge, however, trials of charges in which the Primacord has been placed on the side rather than at the axial rear end have been ineflicient and inconsistent.
The demand for elimination of gun debris in boreholes has led to increased use of retrievable gun bodies of thin walled steel tubing. In such guns the Wall of the guns must withstand the explosive force of the shaped charge and the Primacord. The inside diameter of the gun body limits the length of the shaped charge and consequently, the depth of the penetration of the charge. The gun body must be retrieved through established restrictions. In current designs, expansion of the gun body is such that definite clearances between the outside diameter of the gun body and the minimum inside diameter are provided.
It is an object of the present invention to more effectively use the space inside a hollow carrier gun by removing the detonating means from Within the body of the hollow carrier gun.
It is another object for small diameter hollow carrier guns to increase the effective size of the charge by fully utilizing the space available.
In accordance with the present invention, the Primacord used for detonating the charges is removed from inside the housing and placed tangent to the outer periphery. The shaped charges use-d in the improved hollow car-rier type gun have a booster portion extending into the wall of the hollow carrier type gun so that the detonating forces of the Primacord will properly excitate the shaped charge. By moving the shaped charge over against the wall of the hollow carrier type gun and actually having a portion of it in the wall of the hollow car-rier type gun, the depth of the shaped charge is increased; therefore, the angle of the cavity may be decreased, increasing the jet resulting from the detonation of the charge, accordingly increasing the depth of penetration obtainable with the shaped charge.
As previously mentioned, the diameter of a hollow carrier has to be substantially smaller than the smallest diameter it encounters in entering the well because of swelling resulting from the detonation of the charge withbe used for swelling.
Accordingly, it is a further object to use expendable detonating means located outside the hollow carrier gun body so that the diameter of the gun on coming out of the well does not exceed predetermined maximums.
Other objects and objects relating to details of manu' facture and use will be more fully apparent from the detailed description about to follow, taken in conjunction with the single figure in the drawing showing a cross section of improved hollow carrier type gun of the present invention.
Referring now to the drawing, it can be seen that the hollow carrier gun of the present invention is comprised of a length of hollow open-ended tubing which forms a gun body 10, the length of the tubing will depend upon the number of charges which it is desired that the gun will carry. Since the present gun is designed as an expendable gun and the shaped charge will shoot through the body, the tubing forming the gun body may be thin walled tubing of tnild or heat treated steel. However, as previously explained, the debris from the charge will remain inside the gun enabling the gun and debris resulting from the detonation of the charges to be retrieved from the Well. A closure closes each end of the tubing making the inside of the gun body pressure resistant. The upper closure 12 has means enabling the hollow carrier gun to be attached to a cable so that it may be properly positioned in the borehole, as is well known in the art. The bottom closure 14 is provided with a space 16, the purpose of which will be described subsequently. Means are provided to seal around each closure. They may take the form of an O-ring 17 illustrated or other suitable sealing means. Means are also provided to secure the closure to the tubing.
A plurality of counterbore apertures 18 are positioned along the length of the tubing 10. These may be in either spiral arrangement or may be vertically aligned.
A plurality of shaped charges 20' are positioned inside the tubing. Each shaped charge 20 is formed of a case 22 which is so designed that it will fit inside the tubing 10. The case 22 is generally cup-shaped and provided with an axial aperture 24 at its lower end. A block of explosive 26 normally used in forming a shaped charge such as RDX or cyclonite, is positioned inside the casing 22. The block of explosive 26 has a cavity 28 in its front face. A suitable liner 30 covers the face of the cavity as is well known in the art. The shaped charge 20 is formed in accordance with convention-a1 methods, except for the fact that the casing 22 is not provided with a booster as is customary. As can be seen, the length of the case 22 without the booster is equal to the diameter of the inside of the body. Therefore, the charge utilizes all available space. By so doing, the included angle of the cavity 28 may be decreased to permit the formation of the longest jet and subsequently, the deepest penetration available for a shaped charge of such caliber.
The shaped charges 20 are positioned in a carrier strip 32 which has a number of apertures 33, which positions the charges opposite the apertures 18 in the body 10.
A plurality of booster caps 34, one for each shaped charge 20, are positioned in each of the apertures 18. The booster cap is formed of a round stepped end 36 which is matingly engaged and sealed by appropriate sealing means 37 with the counterbore apertures 18. The end of the booster cap extends into the axial aperture 24 in the case 22 of the shaped charge 20. The stepped round end 36 of each booster cap 34 is provided with a hole 38 in which is positioned a charge of explosive 40 forming the booster for the main body of the explosives of the shaped charge.
, The hole 38 is limited in depth so that a fluid resistant bulkhead 41 is formed. The booster 40 is actually in contact with the end of the explosive 26 of the shaped charge 20. The booster cap 34 has an annular extension 42 extending from the round stepped end 36.
A length of Primacord 44 extends from the space 16 in the bottom closure 14 through each of the annular extensions 42 of the booster caps 34. An electrically fireable pressure resistant blasting cap 46 is located in the space 16 of the end closure 14 and a pair of wires 48 extend from it to the cable and thence to the surface to the firing control, as is well known in the art.
Accordingly, firing of the blasting cap 46 will ignite the Primacord 44 which will in turn detonate the booster 40 through the bulkhead 41. The detonation of booster 40 detonates the block of explosive forming the shaped charge 20. The explosive force developed by the shaped charge will disintegrate the liner 30 and form a particle laden jet which will penetrate the Wall of the tubing and then further penetrate the steel casing of the well bore, the
cement sheath and cause a hole to be formed in the formation. The detonation of the Primacord 44 will break the annular extension 42 of the booster cap 34 into small pieces.
Since the shaped charges are contained within the hollow carrier gun, any residue left from the detonation of the shaped charges 20 will be retained in the hollow carrier gun. Although the hollow carrier gun of the present invention may be formed of thin walled tubing and will swell as a result of the detonation of the shaped charges, nevertheless, in view of the fact that the space occupied by the Primacord 44 on entry of the shaped charge gun int-o the well has now been eliminated. The overall diameter of the hollow carrier of the gun body will not be such as to hang up as it is being retrieved from the well, and the only residue which will be left in the well will be the finely disintegrated portions of the annular extension of the booster cap which will be so minor as not to be of any significance.
l. A hollow carrier gun for lined shaped charges for use in perforating small diameter tubing, said gun comprising:
a gun body formed of a length of hollow, open-ended tubing having counterbore apertures spaced apart along its length, a closure sealingly engaged with each end of the tubing; a shaped charge carrier strip inside said body, said carrier strip having apertures aligned with said apertures in said body, a plurality of shaped charges in said apertures of said carrier strip, each shaped charge formed of a generally cupshaped case designed to fit inside of the gun body and having an axial aperture aligned with the opposing aperture in said gun body; a block of high explosive in said case having a lined cavity in its front face; a plurality of booster caps, one for each shaped charge, each booster cap formed of a round, stepped end sealingly engaged with the counterbore aperture in the body and engaging the axial aperture in the case of the shaped charge; a booster in the end of said booster cap contacting the block of explosive of the shaped charge, an annular extension extending from the round stepped end; a Primacord passing through the annular extension of each booster cap, and ignition means attached to the end of the Primacord.
2. A hollow carrier gun for lined shaped charges for use in perforating small diameter tubing, said gun comprising:
a gun body formed of a length of hollow, open-ended tubing, a plurality of counterbore apertures along the length of the body, a closure sealingly engaged with each end of the tubing; a plurality of shaped charges inside said body, each shaped charge formed of a generally cup-shaped case designed to fit inside the body and aligned with said aperture, the case having an axial aperture at its small end; a block of high explosive in said case having a cavity in its front face; a plurality of booster caps, one for each shaped charge, each booster cap formed of a round, stepped end sealingly engaged with the counterbore aperture in the ,body and engaging the axial aperture in the case of the shaped charge; a booster in the end of said booster cap contacting the block of explosive of the shaped charge, an annular extension extending from the round stepped end; a Primacord passing through the annular extension of each booster cap, ignition means attached to the end of the Primacord.
3. A hollow carrier gun for lined shaped charges for use in perforating small diameter tubing, said gun comprising:
a hollow gun body, a plurality of apertures along the length of the body; a plurality of shaped charges inside said body, each shaped charge formed of a generally cup-shaped case designed to fit inside the body, having an axial aperture at its small end; the axial aperture of the case aligned with an opposing aperture in the gun body; a block of high explosive in said case having a lined cavity in its front face; a plurality of booster caps, one for each shaped charge, each booster cap engaged with the aperture in the gun body and the axial aperture in the case of the shaped charge; a booster in the end of said booster cap contacting the block of explosive of the shaped charge, an annular extension extending from the booster cap external of said body; a Primacord passing along the outside of said body and through each annular extension, ignition means attached to the end of the Primacord.
' References Cited UNITED STATES PATENTS Harcus 1754.6
McKee 175--4.6 X
Castel 175-46 Meddick 1754.6
CHARLES E. OCONNELL, Primary Examiner.
D. H. BROWN, Examiner.