US3128701A

US3128701A - Shaped charge perforating apparatus

Info

Publication number: US3128701A
Application number: US750657A
Authority: US
Inventors: John S Rinehart; Robert D Cocanower
Original assignee: Western Company of North America
Current assignee: Western Company of North America
Priority date: 1958-07-24
Filing date: 1958-07-24
Publication date: 1964-04-14
Anticipated expiration: 1981-04-14

Description

April 14, 1964 FIG.3

LINER THICKNESS (PERCENT OF LINER DIAMETER) April 14, 1964 Filed July 24, 1958 J. s. RINEHART ETAL SHAPED CHARGE PERFORATING APPARATUS 2 Sheets-Sheet 2 FIG.4

SPECIFIC I GRAVITY OF LINER METAL OR ALLOY United States Patent Ofilice 3,128,701 SHAPED CHARGE PERFORATING APPARATUS John S. Rinehart, Cambridge, Mass., and Robert D. Cocanower, Dallas, Tex., assignors to The Western Company of North America, a corporation of Delaware Fiied July 24, 1958, Ser. No. 750,657 3 Claims. (Cl. 102-20) This invention relates to an improved device for perforating oil well casings and well bore holes. More particularly, the invention relates to an explosive jet charge which is capable of efiectively perforating an oil well casing without leaving a slug or carrot of metal in the resulting hole to thereby obstruct the flow of oil or gas into the perforation.

Shaped charges, capable of producing an explosive jet, have been employed in recent years to perforate oil Well bore hole casings. In general, these charges have been characterized by a shaped explosive charge housed in a container having one open end at which the explosive provides a concave surface facing the casing at the point to be perforated. This concave surface is normally lined with a metallic liner which seals off the open end of the charge container. This metallic liner has been made conventionally of copper or steel or other high melting metal or alloy. Such liners have been reasonably suitable for oil well operations except for one serious drawback. Liners of copper and steel and other such high melting metals are prone to leave a metal plug or carrot in the hole formed in the earth by the explosive jet. This plug or carrot usually lodges about one-third of the Way into the hole made by the jet and substantially blocks oif the other two-thirds of the hole. This means that as much as two-thirds of the possible oilor gas producing area penetrated by the jet is obstructed and the flow of oil or gas from this area is prevented. This phenomenon is such a common occurrence that carroting has been considered by the oil recovery industry to be inherent in the use of shaped charges.

It is accordingly an object of the present invention to provide an improved apparatus for perforating the casing of an oil well borehole.

It is another object of the invention to provide an apparatus capable of perforating an oil well borehole casing Without producing a metallic slug or carrot in the hole formed in the surrounding earth formation.

It is also an object of the present invention to provide a shaped explosive charge liner which does not produce a slug or carrot in the penetrated earth formation.

It is an additional object of the invention to provide a novel process of perforating oil well borehole casings employing the novel apparatus and liner of the invention.

The above enumerated objects, as well as other objects, together with the advantages of the invention, will be readily comprehended by persons skilled in the art upon reference to the present description, taken in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a longitudinal cross-section of one preferred form of the apparatus of the invention showing the parts;

FIGURE 2 is a cross-section of a hole produced in the earth formation surrounding a well borehole casing by a prior art device employing a shaped charge concave liner of copper or steel, with the hole partially blocked by the inherent carrot which frequently forms;

.50-50 mixtures, is also quite suitable.

3,128,701 Patented Apr. 14, 1964 FIGURE 3 is a cross-section of a hole produced in the earth formation surrounding a well borehole casing by an apparatus in accordance with the present invention without the formation of a slug or carrot of metal from the shaped charge liner; and

FIGURE 4 is a diagram showing the desired relationship of liner thickness to density of the metal composing the liner in the device of the present invention.

The objects of the present invention are accomplished by employing a concave charge liner, such as that shown by 15 in FIG. 1 of the drawings, which is composed of a metal or alloy capable of melting or being substantially completely liquefied at the temperature produced by the compression resulting from the detonation of the explosive charge. The discovery that a liner composed of a metal or alloy which will melt at temperatures reached upon detonation will not produce a slug or carrot, constitutes an essential feature of the invention. This feature of the invention will be characterized and explained in greater detail hereinbelow.

In order to describe the apparatus and concave liner of the invention more clearly, reference is made to FIG. 1 of the accompanying drawings illustrating one preferred embodiment of the apparatus of the invention. This is done by way of illustration only and is not to be regarded in any way as a limitation in the scope of the invention. FIG. 1 illustrates a longitudinal crossection of a shaped explosive jet charge gun 10. The gun comprises a housing 11, composed of any material capable of protecting the shaped explosive charge from damage in handling. The housing material is preferably composed of a soft metal, such as lead or zinc, which gives increased confinement to the explosive detonation. Other materials have been employed in devices of this kind and it is not contemplated that the nature of the housing material shall be limited. The housing 11 shown contains a centrally located ignition opening 12 which is desirably equipped for service with a fuse of a suitable material, such as the well know Primacord fuse containing PETN (pentaerythrityl tetranitrate) or RDX (cyclotrimethylenetrinitramine) explosive. Communicating with the ignition opening 12, is an explosive booster charge 13 positioned adjacent to the opening 12. Packed adjacent to the booster charge 13 within the confines of the housing 11 is the main shaped mass of explosive charge 14. The nature of the shaped explosive charge may vary, but a detonating explosive which is preferably of high density, such as a pressed or cast solid organic nitrate or nitro-compound, is generally suitable. Compressed PETN is one suitable material and compressed or cast blends of PETN with TNT, for example, in Similarly, RDX is a suitable explosive as are its high density mixtures with TNT, one suitable blend consisting of parts of RDX and 20 parts TNT. These explosive materials are suitable since they possess high strength and upon detonation produce a high velocity, reaching maximum velocity -very rapidly. The booster charge 13 may be composed of the same explosive as the main shaped charge or other explosives Well known to the art may be employed.

The foregoing components of the embodiment illustrated by FIG. 1 do not per se constitute essential features of the present invention. These foregoing components have been employed in one form or other in prior art devices designed to perforate borehole casings. An essential feature which permits accomplishing the objects of the invention is the character of the concave metallic liner which seals off the open end of the housing 11 and the shaped explosive charge 14. As illustrated in FIG. 1, the concave liner 15 has a setolt 1.6 from the open end of the housing 11. This setotf is frequently employed in devices of this type to obtain the full benefits of the so-callecl Munroe effect.

The liner 15 in accordance with this invention is composed of a metal or alloy having a melting point low enough to substantially melt at the temperatures produced by the compression caused when the shaped explosive charge 14 is detonated. The specific temperature obtained under the conditions of compression resulting from detonation will depend somewhat upon the specific metal or alloy of which the liner 15 is composed. In general, however, it is contemplated that to obtain the benefits of the invention, i.e., freedom from slugging or carroting, the metal or" which the liner is composed shall have a melting point of not more than about 500 C. This melting point range is substantially less than the melting points of metals which have been employed in the conventional prior art devices of this type. Prior employed retals, such as copper and steel, have melting points of about 1082 and 1539 (3., respectively. The high melting points of these prior metals, being vastly greater than those of the low melting metals and alloys contemplated tor use in the liners of the present invention, prevent any substantial melting of the liner metal upon detonation of the shaped charge. The difference in results obtained is illustrated by FIGS. 2 and 3 of the drawings. FIG. 2 illustrates what happens in the penetration hole produced when a liner of copper or steel is employed, whereas FIG. 3 illustrates the penetration hole produced when a liner of metal or alloy melting below about 500 C. is employed. As shown in the two figures, the earth formation is penetrated to form a hole 21. In the case of FIG. 2, illustrating the use of a copper or steel liner, a carrot 22 is formed whereas no such carrot is formed in FIG. 3 employing the liner of the present invention. The carrot 22 efi'ectively obstructs a substantial portion of a penetration hole as shown at 23.

It is desirable that the low melting metal or alloy comprising the liner 15 have a tensile strength of between about 3,000 and 13,000 p.s.i. and a hardness of between about 5 and 22 on the Brinnel scale.

Although the liner 15 illustrated in FIG. 1 is in the form of a cone having an angle (oz) of about 60, other angles such as between about and 80 and other shapes may be employed. The difference in angle and shape of the liner may be varied according to the dimensions of the perforation which one desires to produce. These variations are well known to those skilled in the art. Other shapes which may be employed include pyramidal, hemispherical, parabolic, etc.

Illustrative of the various metals and alloys which may be employed in forming the concave liner are those disclosed by the examples which follow. It should be understood, however, that this is done solely by way of example and is intended neither to delineate the scope of the invention nor limit the ambit of the appended claims. In the examples which follow, and throughout the specification, the quantities of metals are expressed in terms of percent by weight, unless otherwise specified.

EXAMPLES zinc-1.6% lead)melting (7) Leadantimony alloy lead-40% antimony)melting point, 270 C.

(8) Bismuth solder (40% bismuth, 40% lead, 20% tin)--melting point, 111 C.

In addition to those specific metals and alloys disclosed in the foregoing examples, other low melting metals, and binary, ternary and quaternary alloys of bismuth, lead, tin, cadmium, indium, etc., may be employed, provided the metal or alloy is capable of melting at the compres sion temperatures reached upon detonating the shaped explosive charge. it is characteristic of these metals and alloys to flow under high pressure or load which is related to their thermodynamic property of melting at a low temperature.

An additional important feature of the liner of the shaped charge of the present invention is its thickness. in prior apparatus of the present type, it has been considered necessary that to have a charge giving satisfactory performance and penetration, the mass of the liner in front of the shaped explosive charge must remain substantially constant from metal to metal. Thus, for aluminum, a relatively low density metal, the liner must be relatively thick. For higher density metals, such as copper and steel, it has been considered necessary that the liner be thinner. Thus, for an aluminum liner, having a specific gravity of 2.7, it has been considered necessary that the thickness of the liner be from about 2% to 6% of its diameter. For a steel liner, having a specific gravity of 7.85, it has been considered necessary that the liner thickness be from about 1 to 3% of the liner diameter. For copper liners, having a specific gravity of about 8.95, it is standard practice for the thickness of the liner to be about 1.5% of the liner diameter. Following these standard teachings of the prior art, one would contemplate that for a liner of lead, in accordance with the present invention, having a specific gravity of about 11.35, the thickness should be about 1% of the liner diameter. However, unexpectedly, we have discovered that when the liner is composed of a low melting metal or alloy these teachings of the prior art regarding liner thickness have been found to produce unsatisfactory results. We have discovered that a liner of lead having a thickness of about 1% of the liner diameter does not provide satisfactory penetration. We have discovered that when employing the low melting metals, it is essential that the thickness of the liner must be much greater in relation to the density of the metal to provide satisfactory results. Thus, for example, in the case of a lead liner in accordance with the present invention, it is necessary that the liner thickness be from about 2% to 6%, with best results being obtained at a thickness at about 4.0%. Thicknesses of the low melting liners (in terms of percent thickness of liner diameter) compared with the specific gravity of the metal is set forth in the diagram of FIG. 4 of the accompanying drawing. As set forth in the diagram, the low melting point liners contemplated for use in the present invention should have a thickness expressed in terms of percent of the liner diameter falling within the area delineated by the points ABCD. Optimum results are obtained by values expressed by the line EF.

While we do not propose to be bound to any explanation as to how our invention succeeds in accomplishing its objects, we believe that when employing a low melting point metal liner it must be sufliciently massive to prevent breakthrough of the explosion products until the metallic jet has had a chance to form. Good results are not obtained with liners which are too thick because the velocity of collapse is not sufliciently great. Thus, if the benefits and high penetrating power of the shaped explosive charge is to be obtained employing a low melting metallic liner, it is necessary that the liner be of a thickness within the range prescribed by the points ABCD of FIG. 4 of the drawings. This concept of thickness of the liner applies only to the low melting point metallic liners of the invention.

Listed in the table below for each of the foregoing examples is the corresponding specific gravity, desired liner thickness range and optimum liner thickness value.

Table Thickness of liner Actual thickness for (percent of liner liner 1.25 inches in Example Specific diameter) diameter N o. gravity Desired Optimum Desired Optimum range value range value The value of the apparatus and liner of the invention is applicable to shaped charges for oil well penetration as distinguished from shaped charges intended for military purposes. Shaped charges intended for oil well penetration are characterized by having a shaped explosive charge distributed over a length which is less than two times its diameter.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is:

*1. A well borehole casing perforating apparatus comprising a closed container capable of being inserted into a well borehole comprising a housing having an open end and containing a shaped high-order explosive charge and a low melting metallic concave liner sealing the open end of said housing, said low melting metallic concave liner being composed of a metal having a melting point of not more than about 500 C., the surface area of said liner in contact with said explosive charge being such that said liner will disintegrate upon detonation of said explosive charge, said liner having a thickness to diameter ratio within the area delineated by the points ABCD of FIG. 4 of the attached drawings and which will produce a resulting perforation which is free from the presence of a metallic slug.

2. A well borehole casing perforating apparatus comprising a closed container capable of being inserted into a well borehole comprising a housing having an open end and containing a shaped high-order explosive charge and a low melting metallic concave liner sealing the open end of said housing, said low melting metallic concave liner being comprised of a metal having a melting point of not more than about 500 C., the surface area of said liner in contact with said explosive charge being such that said liner will disintegrate upon detonation of said explosive charge, said liner having a thickness to diameter ratio which is substantially that represented by the line EF of FIG. 4 of the attached drawings and which will produce a resulting perforation which is free from the presence of a metallic slug.

3. A well bore hole casing perforating apparatus comprising a closed container capable of being inserted into a well borehole comprising a housing having an open end and containing a shaped high-order explosive charge and a low melting metallic concave liner sealing the open end of said housing, said low melting metallic concave liner being substantially lead, the surface area of said liner in contact with said explosive charge being such that said liner will distintegrate upon detonation of said explosive charge, said liner having a thickness to diameter ratio of about 4%.

References Cited in the file of this patent UNITED STATES PATENTS 2,605,703 Lawson Aug. 5, 1952 2,667,836 Church et al Feb. 2, 1954 FOREIGN PATENTS 693,164 Great Britain June 24, 1953 OTHER REFERENCES American Institute of Mining and Metallurgical Engineers, Technical Publication No. 2158, Class A. Mining Technology, 1947, pages 1-13, Behavior of Metal Cavity Liners in Shaped Explosive Charges by George B. Clark and Walter H. Bruckner.

Claims

1.A WELL BOREHOLE CASING PERFORATING APPARATUS COMPRISING A CLOSED CONTAINER CAPABLE OF BEING INSERTED INTO A WELL BOREHOLE COMPRISING A HOUSING HAVING AN OPEN END AND CONTAINING A SHAPED HIGH-ORDER EXPLOSIVE CHARGE AND A LOW MELTING METALLIC CONCAVE LINER SEALING THE OPEN END OF SAID HOUSING, SAID LOW MELTING METALLIC CONCAVE LINER BEING COMPOSED OF A METAL HAVING A MELTING POINT OF NOT MORE THAN ABOUT 500*C., THE SURFACE AREA OF SAID LINER IN CONTACT WITH SAID EXPLOSIVE CHARGE BEING SUCH THAT SAID LINER WILL DISINTEGRATE UPON DETONATION OF SAID EXPLOSIVE CHARGE, SAID LINER HAVING A THICKNESS TO DIAMETER RATIO WITHIN THE AREA DELINEATED BY THE POINTS ABCD OF FIG. 4 OF THE ATTACHED DRAWINGS AND WHICH WILL PRODUCE A RESULTING PERFORATION WHICH IS FREE FROM THE PRESENCE OF A METALLIC SLUG.