Shaped charge having metal coated high density metal powder liner

Abstract

 A shaped charge (24) for an oilwell perforator includes a liner (28) which is formed of a metal powder. The metal powder has particles (34) thereof which are coated with a second metal (36). The metal powder (34) may be tungsten, and the particles may be coated with metals such as copper, lead, molybdenum, tin, nickel or silver. The resulting liner content by weight may be between approximately 95 and 100% tungsten.

Description

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to explosive shaped charges and, in an embodiment described herein, more particularly provides an oilwell perforator having a metal coated high density metal powder liner.

[0002] Oilwell perforators are used to perforate casing or liner lining a wellbore, to thereby provide a path for production, or injection, of fluids therethrough. In order to achieve an acceptably deep perforation tunnel in hard rock having high density and high compressive strength, it is generally recognized that it is desirable to form a liner of an oilwell perforator from a relatively dense material.

[0003] In general, deep penetrating oilwell perforators have liners made of partially sintered metal powder, or blends of various metal powders. If different metal powders are used, extreme care must be taken to prevent segregation of the different powders. This segregation may be due to different particle shapes, densities and sizes in the different powders. A liner made of segregated metal powders is undesirable because it will not form an appropriately shaped metal jet when the perforator is detonated.

[0004] A metal powder having a suitably high density for use in a deep penetrating perforator is made up of tungsten metal particles. Unfortunately, the tungsten particles in the powder are relatively hard, and so the particles do not readily adhere together when the powder is pressed into a liner shape. The ability of a pressed metal powder to resist deformation prior to being partially or fully sintered is known as the "green" strength of the pressed powder.

[0005] A sufficiently high green strength is required for handling and other manufacturing processes. A present solution to the problem of low green strength in liners made from tungsten powder is to blend the tungsten powder with other metal powders which, although they may be less desirable in some respects than tungsten for use in deep penetrating perforators, enhance the green strength of the pressed metal powder. Due to the presence of the other metal powders in the liner, segregation problems occur and the tungsten content of the liner is reduced to less than about 95% of the liner by weight.

[0006] Therefore, it may be seen from the foregoing that it would be desirable to provide a perforator with a liner that has an increased proportion of tungsten or other high density metal therein and which has a reduced tendency for segregation of metal powders therein, but which has sufficient green strength.

SUMMARY OF THE INVENTION

[0007] In carrying out the principles of the present invention, in accordance with an embodiment thereof, a shaped charge is provided which includes a liner formed from metal coated high density metal powder. A method of using the shaped charge as a perforator in a well is also provided.

[0008] In one aspect of the present invention, a perforator is provided which has a liner formed of a metal powder wherein particles thereof are coated with another metal. The metal powder may be tungsten and the metal coating may be, for example, copper, lead, molybdenum, tin, nickel or silver. The metal coating enhances the green strength of the liner and significantly reduces the possibility of segregation of the metals as opposed to a mere blending of metal powders.

[0009] In another aspect of the present invention, a perforator is provided which has a liner formed of a tungsten powder wherein particles thereof are coated with a less dense metal. Nevertheless, the liner has an increased proportion of tungsten therein, and therefore has an increased density as compared to conventional liners with tungsten powder therein, and the metal coating permits the tungsten powder particles to be pressed into a liner shape with sufficient green strength.

[0010] These and other features, advantages, benefits and objects of the present invention will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of a representative embodiment of the invention hereinbelow and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 

FIG. 1 is a schematic cross-sectional view of a method of oilwell perforating embodying principles of the present invention;

FIG. 2 is an enlarged scale cross-sectional view of an oilwell perforator embodying principles of the present invention, the perforator being usable in the method of FIG. 1; and

FIG. 3 is an enlarged scale cross-sectional view of a metal coated metal powder particle of the perforator of FIG. 2.

DETAILED DESCRIPTION

[0012] Representatively illustrated in FIG. 1 is a method 10 which embodies principles of the present invention. In the following description of the method 10 and other embodiments of the invention described herein, directional terms, such as "above", "below", "upper", "lower", etc., are used for convenience in referring to the accompanying drawings. Additionally, it is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., without departing from the principles of the present invention.

[0013] In the method 10, a perforating gun 12 is conveyed into a wellbore 16 and positioned opposite a formation or zone 14. As depicted in FIG. 1, the gun 12 is conveyed on a tubular string 18, but other conveyances, such as wireline, etc., may be used.

[0014] The perforating gun 12 is fired, detonating shaped charges known to those skilled in the art as perforators within the gun, and forming perforations 20 extending from the wellbore 16 and into the zone 14. Fluid may now be flowed between the wellbore 16 and the zone 14. However, it is to be clearly understood that principles of the present invention may be incorporated in other methods in which fluid flow between a wellbore and a zone is not the intended or actual result. For example, shaped charges may be used in wells to perforate tubing, provide detonation transfer between guns, etc.

[0015] Referring additionally now to FIG. 2, a perforator 24 embodying principles of the present invention is representatively illustrated. The perforator 24 may be used in the method 10 in the gun 12, or may be used in other methods. Additionally, aspects of the perforator 24 described herein may be incorporated into other types of shaped charges, without departing from the principles of the present invention.

[0016] The perforator 24 includes an outer case 26, an inner liner 28 and an explosive material 30 retained between the case and liner. The liner 28 is formed from a fully or partially sintered metal coated high density pressed metal powder. For example, the metal powder may be tungsten, with particles thereof coated with one or more of copper, lead, molybdenum tin and silver. Of course, other metal powders and other metal coatings may be used without departing from the principles of the present invention. In FIG. 3 is representatively illustrated a metal powder particle 34 with a metal coating 36.

[0017] The liner 28 has a content by weight of approximately 95% to less than 100% tungsten. Preferably, the tungsten content by weight is greater than 90%, but less than 100%. This content of tungsten produces a liner which has enhanced performance in creating a metal jet that forms a deep perforation tunnel.

[0018] The present applicants have solved the problem of low green strength in high tungsten content pressed metal powders by coating the tungsten powder particles with relatively ductile metal, such as copper, lead, molybdenum, tin, silver, nickel etc. Thus, the metal coated metal powder adheres well when pressed and has a sufficient green strength for a perforator liner, even though it has a high tungsten content.

[0019] The present applicants have also solved the problem of segregation between metals in a powdered metal liner having more than one metal therein. Specifically, by providing the high density metal powder particles with a metal coating, the metals are unable to segregate due to their different shapes, densities, size, etc.

[0020] It is to be clearly understood that other metals and combinations of metals may be used without departing from the principles of the present invention. For example, the powder metal particles in the liner 28 may be other than tungsten and may be a combination of metals, and the metal coating may be other than copper, lead, molybdenum, tin, nickel or silver and may be a combination of metals. Additionally, it is not necessary for the metal coating to be less dense or more ductile as compared to the metal powder particles.

[0021] Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to these specific embodiments, and such changes are contemplated by the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims.

Claims

1. A shaped charge, comprising: an outer case; an inner liner; and an explosive material retained between the case and the liner, and wherein the liner is formed of a first metal powder including particles of the first metal which are coated with a second metal.

2. A shaped charge according to Claim 1, wherein the first metal is tungsten, and wherein the amount of tungsten is preferably greater than 95%, but less than 100%, by weight of the liner.

3. A shaped charge according to Claim 1 or 2, wherein the second metal is copper, lead, molybdenum, tin, nickel or silver.

4. A shaped charge according to Claim 1, wherein the first metal has a density greater than that of the second metal.

5. An oilwell perforator for use in forming perforations extending outwardly from a wellbore, the perforator comprising: a liner including a first metal powder having particles thereof coated with a second metal.

6. A perforator according to Claim 5, wherein the liner has a tungsten content by weight of approximately 95% to less than 100%.

7. The perforator according to Claim 5 or 6, wherein the first metal has a density greater than that of the second metal.

8. A perforator according to Claim 5 or 6, wherein the second metal is copper, lead, molybdenum, tin, nickel or silver.

9. A perforator according to Claim 5, 6, 7 or 8, further comprising an outer case and an explosive material retained between the case and the liner.

10. A method of perforating a well, the method comprising the steps of: conveying a perforating gun into the well, the gun including a perforator as claimed in any of claims 5 to 9; and firing the perforator, thereby forming a perforation in the well.

11. A perforator according to Claim 8, wherein the first metal is tungsten.

Drawing