US 3268016 A
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Description (OCR text may contain errors)
2 Sheets-Sheet 1 Filed June 11, 1964 W////a/77 7: J56
ATTORNEY Aug. 23, 1966 w. T. BELL 3,
SHAPED CHARGE APPARATUS Filed June 11, 1964 2 Sheets-Sheet 2 INVENTOR.
ATTO/P/VEV a 3,268,016 1C6 Patented Aug 23, 1966 3,268,016 SHAPED CHARGE APPARATUS William T. Bell, Houston, Tex., assignor to Schlumberger Well Surveying Corporation, Houston, Tex., a corporation of Texas Filed June 11, 1964, Ser. No. 374,414 2 Claims. (Cl. 175--4.51)
This invention relates to perforating apparatus and, more particularly, pertains to new and improved perforating apparatus employing shaped explosive charges.
Shaped charges are widely and effectively used as perforating devices in well bore completions. Usually a shaped charge intended for such a purpose includes a block of explosive material which has a conical recess in its front face. This recess receives -a liner having a suitable thickness and composition so that upon detonation of the explosive material, the explosive shock wave traveling toward the liner eventually collapses the liner and a high velocity perforating jet is formed along the axis of the recess. Because of the high velocity and energy content of the perforating jet it is capable of penetrating the wall' of the casing lining the well bore, the cement sheath surrounding the casing and the earth formations therebeyond. It has been of concern recently that the perforating jet in the penetration of the casing or the forming of an entry hole also tends to extrude the material of the casing about the penetration or entry hole into the bore of the casing thereby forming a burr or projection which can be objectionable. The reason for extrusion of the metal is the high radial pressures exerted on the casing while the hole is being formed. The burr is objectionable since it interferes with the sealing action of a ball sealer which is used in fracturing operations to isolate Zones.
It is, therefore, an object of the present invention to provide new and improved apparatus for perforating in a well bore whereby there is no burr formed on the entry hole through the casing.
This and other objects of the invention are obtained by producing an explosive force or perforating jet with a forward, high speed penetrating portion and a rearward portion forming a slug traveling at an appreciably lower velocity. In the present invention the slug is formed with a transverse dimension sufficient to peen or impact the periphery of an entry hole formed by the leading end of the perforating jet. The slug is subsequently removed from the hole by action of the fluids flowing from the formations.
The novel features of the present invention are set forth with particularity in the appended claims. The present invention both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description when taken in conjunction with the accompanying drawings in which:
FIG. 1 is a longitudinal view of expendable shaped explosive charge perforating apparatus constructed in accordance with the present invention and shown disposed in a well bore;
FIG. 2 is a longitudinal view of carrier shaped explosive charge perforating apparatus constructed in accordance with the present invention;
FIG. 3 is a view in longitudinal cross section of a shaped explosive charge perforating apparatus constructed in accordance with the present invention;
FIGS. 4-7 are views representing various stages or conditions existing at sequential times during the operation of the shaped charge of FIG. 2.
In FIG. 1 of the drawings, there is illustrated a casing in a well bore 11 which traverses earth formations 12. A column of cement 13 is disposed between the casing and well bore. Shaped charge apparatus 14 can be suspended in the casing in any usual manner and includes anumber of fluid-tight shaped charge capsules 18 which are attached to a rigid retrievable carrier 19 as rods or a strip. Blasting cord 20 for detonation of the charges is connected to an electric blasting cap 21 which can be electrically ignited in the usual manner from the surface by wires and a power source (not shown).
At suitable locations positioning devices 15 are attached to the carrier 19. Positioning devices 15, for example, can be housings with portions 16 brought into contact with the casing wall by means of properly located spring biased arm members 17. The housing portions 16 are aligned relative to the capsules so as to bring the forward faces of the shaped charge capsules 18 into or nearly into contact with the wall of the casing. To do this, of course, requires the suitable positioning of arms 17 relative to the carrier 19 and capsules 18.
In FIG. 2, a retrievable, re-usable steel housing carrier 14a is illustrated wherein shaped charges 18a are disposed within the fluid-tight interior 22 of the housing. Port hole covers 23 through which a perforating jet may pass are located adjacent the forward end of each charge. Carrier 14a has permanent magnets 23a aligned relative to the port hole covers so as to bring the port hole covers 23 into proximate contact with the wall of the casing.
It will be appreciated that the positioning devices as heretofore described can be interchanged so long as the fuction of bringing a portion of the shaped charge apparatus into proximate contact with the wall of the casing is achieved.
In FIG. 3 of the drawing, a shaped charge 18 is comprised of a hollow container 24 of generally conical form which receives, in close interfitting relation, an explosive charge 25. A cover 26 is provided for the container to form a sealed capsule shaped charge 18. The container and cover may be constructed of any fluid-tight, frangible material such as cast iron, glass or the like. The container 24 can be attached to a strip 19, for example, in any suitable manner for positioning in a well bore. As illustrated in FIG. 3, the forward portion of the shaped charge is disposed in proximate contact with casing 10. Positioning means 15 assures the proximate contacting position of the capsules with the casing. It will be understood from the following description how the invention applies to the carrier apparatus of FIG. 2.
In the charge explosive 25 is a hollowed out or conically shaped forward end 27 which receives a closely fitting conical liner 28 constructed, for example, of copper with a suitable thickness or a bi-metal liner. The charge explosive 25 may be detonated in a suitable manner as by the blastiing cord 20 disposed at the rear end of the explosive charge 25, the blasting cap being detonated in a usual manner by the electric blasting cap 21.
In operation, the blasting cord 20 is detonated and it, in turn, deton-ates the rear end of the explosive charge 25 through booster explosive 29. Thus, an explosive shock wave is generated in charge 25 which progressively collapses the liner 28 and developes a perforating jet. The shock wave, which travels from left to right, sweeps along the liner from its apex 30 to its base 31. The resulting pressures produced on the liner are so large that the liner behaves as a perfect fluid and the pressures cause the walls of the liner to collapse and move inwardly at high velocities. As shown in FIG. 4, the collapsing liner retains practically a conical shape and an inner part of the cone or liner is squeezed out from the inner apex of the liner and forms a leading jet portion 32 which travels to the right of a point P (FIGS. 3 and 4). To the left behind the moving apex point P is found a portion 33 of collapsed liner forming a slug of metal from the outer part of the liner. In other words, the metal of the liner divides into two parts with the dividing surface between these two parts being a cone lying somewhere between the inner and outer surface of the original liner. Further explanation of formation of a perforating jet, if desired, may be found in the article entitled A New Approach Toward Elimination of Slug in Shaped Charge Perforating in March, 1958 issue of Journal of Petroleum Technology.
In the present invention, the liner 28 is provided with a disk-like internal appendage 34 disposed within the explosive material 25 along a plane perpendicular or transverse to the longitudinal axis through the charge. This appendage to the apex of the liner remains in its characteristic form in the slug in the trailing end of the perforating jet without materially affecting the forward or leading portion of the perforating jet. Hence, as shown in FIG. 5, the high speed leading portion of the perforating jet initially produces the entry hole 36 in the casing and a penetration 37 into the earth formations which extends through the casing and cement sheath while a large slug portion follows at a lower speed. As shown in FIG. 5, the formation of entry hole 36, a burr 38 is formed. A moment later, as shown in FIG. 6, the energy of the forward end of the jet is expended in fully forming the penetration 37 in the earth formations 12 and the trailing slug portion 33 (which has coalesced to a solid) enters the entry hole 36. The disc portion 34 of the liner, which is larger in size than the entry hole 36 in the casing, remains substantially intact as a part of the slug. As shown in FIG. 7, the momentum of the slug 33 causes the disc portion 34 to peen the protruding burr portion 38 formed by the forward end of the perforating jet and the disc portion 34 of the slug breaks off from the body of the slug. While the body of the slug enters the penetration 37 it has been found that with the usual liner arrangement, this body is removed from the penetration when the fluids from the formations are permitted to flow.
It will be appreciated that the essence of this invention is the formation of a slug with a particular portion thereof arranged to react with a burr produced on a casing Wall to eliminate the burr.
While a particular embodiment of the present invention has been shown and described, it is apparent that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.
What is claimed is:
1. Shaped charge apparatus for use in a cased well bore comprising: means for positioning said apparatus in proximate contact with the wall of a casing; explosive means in said apparatus having a forward shaped recess arranged relative to said positioning means for facing the Wall of a casing; liner means for said forward recess; means for detonating said explosive means thereby to cause a perforating jet to form along a perforating axis, said liner having an apex portion shaped in a direction transverse to such an axis, said apex portion being arranged to form a slug portion greater in dimension than the dimension of an entry hole formed upon penetration of a casing by such a perforating jet.
2. Shaped charge apparatus comprising: explosive means in said apparatus having a forward shaped recess; means for detonating said explosive means to cause a perforating jet to form along a perforating axis; and liner means for said forward recess including a solid rearward apical portion received therein and extending transversely across said perforating axis a distance greater than the dimen sion of an entry hole formed by the resulting perforating jet.
References Cited by the Examiner UNITED STATES PATENTS 2,308,006 1/1943 Hendrickson. 2,779,278 1/1957 Klotz 102-20 2,946,283 7/1960 Udry l02-20 3,064,571 11/1962 True 1022l.8 3,077,834 2/1963 Caldwell 10224 BENJAMIN A. BORCHELT, Primary Examiner. SAMUEL FEINBERG, Examiner.
V. R. PENDEGRASS, Assistant Examiner.