BACKGROUND

1. Field of Invention

[0001] The invention relates generally to a method and system for perforating a wellbore. More specifically, the present invention relates to a liner for a shaped charge having inner and outer layers.

2. Description of Prior Art

[0002] Perforating systems are used for the purpose, among others, of making hydraulic communication passages, called perforations, in wellbores drilled through earth formations so that predetermined zones of the earth formations can be hydraulically connected to the wellbore. Perforations are needed because wellbores are typically lined with a string of casing and cement is generally pumped into the annular space between the wellbore wall and the casing. Reasons for cementing the casing against the wellbore wall includes retaining the casing in the wellbore and hydraulically isolating various earth formations penetrated by the wellbore. Sometimes an inner casing string is included that is circumscribed by the casing. Without the perforations oil/gas from the formation surrounding the wellbore cannot make its way to production tubing inserted into the wellbore within the casing.

[0003] Perforating systems typically include one or more perforating guns connected together in series to form a perforating gun string, which can sometimes surpass a thousand feet of perforating length. The gun strings are usually lowered into a wellbore on a wireline or tubing, where the individual perforating guns are generally coupled together by connector subs. Included with the perforating gun are shaped charges that typically include a housing, a liner, and a quantity of high explosive inserted between the liner and the housing. When the high explosive is detonated, the force of the detonation collapses the liner and ejects it from one end of the charge at very high velocity in a pattern called a jet that perforates the casing and the cement and creates a perforation that extends into the surrounding formation. Each shaped charge is typically attached to a detonation cord that runs axially within each of the guns.

.SUMMARY OF THE INVENTION

[0004] Disclosed herein is an example of a perforating gun that includes a gun body and a shaped charge in the gun body. In this example the shaped charge is made up of a charge case and a liner in the charge case, where the liner has an inner layer and an outer layer made of a material with a lower density and that is more ductile than a material in the inner layer. In one example, the inner layer includes tungsten and the outer layer includes aluminum. In one embodiment, the liner is frustoconically shaped. The inner and outer layers may be formed by cold pressing metal particles. A plurality of shaped charges may be included with the perforating gun, where a detonation cord couples with each of the shaped charges. In one example, further provided with the perforating gun is explosive in the charge case underneath the liner, wherein detonating the explosive inverts and discharges the liner from the charge case to form an elongate metal jet having a generally curved outer lateral periphery, wherein the jet perforates the gun body and deposits a slug on an inner surface of the gun body that blocks a flow of debris from inside of the gun body. In one example embodiment, the slug is formed substantially from material making up the inner layer.

[0005] Also provided herein is a perforating system, where the system includes an annular perforating gun selectively inserted within a wellbore and a shaped charge in the perforating gun. In this example the shaped charge is made up of a charge case having an opening and a substantially curved outer periphery adjacent the opening, and a frustoconically shaped liner inserted into the opening of the charge case that is made up of an inner layer having an outer surface covered by an outer layer that is more ductile than the inner layer. In one example, the perforating system further includes an explosive in the charge case under the liner. The inner layer can optionally be made from tungsten cold pressed into shape. The outer layer can optionally be made from aluminum that is cold pressed into shape.

[0006] Further disclosed herein is a method of reducing debris from being discharged from a perforating gun while perforating a wellbore. In one example the method includes providing a perforating gun with a shaped charge made from a charge case, a liner in the charge case that has an inner layer and a ductile lower density outer layer, and an explosive in the charge case under the liner. The method further includes disposing the shaped charge in the wellbore and detonating the explosive to create an explosion that inverts the liner and expels the liner from the charge case to form a metal jet that perforates a sidewall of the perforating gun and deposits a slug on an inner surface of the perforating gun that restricts debris from exiting the perforating gun. The inner layer can include tungsten particles and softer metal particles that are cold pressed into a frustoconical shape. Optionally, the outer layer includes aluminum particles that are cold pressed into a frustoconical shape.

.BRIEF DESCRIPTION OF DRAWINGS

[0007] Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:

[0008] FIG. 1 is a side sectional view of an example embodiment of a shaped charge in accordance with the present invention.

[0009] FIG. 2 is a side sectional view of the shaped charge of FIG. 1 in a perforating gun in accordance with the present invention. [0010] FIG. 3 is a side sectional view of an example embodiment of a perforating system having the perforating gun of FIG. 2 and disposed in a wellbore in accordance with the present invention.

[0011] FIG. 4 is a side sectional view of an example embodiment of the perforating gun of FIG. 2 while the shaped charges are detonating in accordance with the present invention.

[0012] FIG. 5 is a side sectional view of an example embodiment of the perforating gun of FIG. 2 after the shaped charges have detonated and in accordance with the present invention.

[0013] While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.

.DETAILED DESCRIPTION OF INVENTION

[0014] The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout.

[0015] It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the improvements herein described are therefore to be limited only by the scope of the appended claims.

[0016] Figure 1 shows in a side sectional view one example embodiment of a shaped charge 10 for use in downhole perforating operations. The shaped charge 10 includes a shaped charge case 12, wherein a forward portion of the outer periphery of the case 12 is substantially cylindrical that has an opening 13 on one end. The end of the cylindrical portion away from the opening 13 transitions into a frustoconical shape, whose radius diminishes with distance away from the opening 13. Further in the example of Figure I, a cavity 14 is formed within the case 12 that extends from the opening 13, through the cylindrical portion, and into the frustoconical portion. A frustoconical liner 16 is shown set in the cavity 14, also having a cavity and opening, wherein the opening of the liner 16 substantially aligns with the opening 13 in the case 12 and where a closed end of the liner 16 is directed away from the opening 13. High explosive 18 fills the portion of the cavity 14 between the liner 16 and the walls of the cavity 14. On a rear 19 of the case 12 opposite the opening 13, shown is a detonating cord 20 for initiating detonation of the explosive 18. As is known, a shock wave propagates along the length of the detonating cord 20 that initiates detonation of a booster 22. In the example of Figure 1, the booster 22 is an amount of explosive disposed in a passage 23 axially formed through the rear 19 of the case 12 between the detonating cord 20 and a rear wall of the cavity 14. The liner 16 is shown made up of multiple layers, which in the example of Figure 1 include an inner layer 24 is on a side of the liner 16 opposite the high explosive; and an outer layer 26 that covers the outer surface of the inner layer 24 and has an outer surface in contact with the high explosive 18.

[0017] Figure 2 shows in side sectional view one example of a perforating gun 28 with embodiments of the shaped charges 10 set in an a perforating gun body 30. In the example of Figure 2, the shaped charges 10 are shown "phased," that is having their respective openings 13 directed radially outward at various angles with respect to an axis A _x of the body 30 of the perforating gun 28. In the example of Figure 2, the body 30 is a substantially annular member in which the shaped charges 10 are spaced in an axial direction within the sidewalls of the body 30. The detonating cord 20 extends within the body 30 and into contact with each of the shaped charges 10.

[0018] Figure 3 depicts in a side sectional view examples of shaped charges 10 incorporated into a perforating system 34. In this example, multiple perforating guns 28 are mounted end to end to form a perforating string 36 shown suspended on a wireline 38. The wireline 38 extends from a surface truck 40, from which control commands to the perforating string 36 may be transmitted through the wireline 38. The wireline 38 also provides a means for raising and lowering the perforating string 36. From the surface truck 40, the wireline 38 threads through a wellhead assembly 42 and into a borehole 44 shown under the wellhead assembly to suspend the perforating string 36 therein. In the example of Figure 3, the shaped charges 10 are being initiated and the ensuing detonations form perforations 46 in the formation 48 that surrounds the borehole 44. The phasing of the shape charges 10 provides for perforations 46 to be disposed at multiple angular locations around the borehole 44. As is known, detonating the explosive 18 not only expels the liner 16 from within the charge case 12 but also inverts the liner 16 and forms metal jets 50 shown exiting the charge cases 12 and forming openings 52 through side walls of the gun body 30.

[0019] Referring now to Figure 5, shown is one example of a perforating gun 28 at a time after the jets 50 have exited the side wall of the gun body 30. In one example, the outer layer 26 of the liner 16 is made from a material that is more ductile and less dense than the inner layer 24. An advantage of a ductile less dense outer layer 26 is that slugs 54 may be deposited on the inner surface of the gun body 30 and adjacent the openings 52. The slugs 54 can extend over the opening 52 to restrict or block debris from flowing from the gun body 30 during and subsequent to the step of perforating. As such, an advantage in addition to the enhanced performance realized by having liner 16 with two or more layers is the reduced amount of debris left in a wellbore during a step of perforating.

[0020] Example materials for the outer layer 26 include aluminum, copper, silver, gold, nickel, combinations thereof, and other ductile materials. Example materials for the inner layer 24 include tungsten, tungsten alloys, and other materials less ductile than the outer layer 26. In one example, the inner and outer layers 24, 26 are formed separately using a ram and die process, wherein metal particles are deposited within a die and a correspondingly shaped ram is inserted into the die under pressure while rotating to cold form each of the layers 24, 26. The ram and die arrangement may also be used for forming the composite liner 16, wherein the outer layer 26 is placed in the die, and the inner layer 24 is on the ram portion of the tooling.

[0021] In one example, the stresses employed by the ram and die assembly during fabrication of each specific layer are about 50% of that used in forming a typical cold form liner having a single layer. In one example, the stresses involved in forming the composite layer 16 when combining the inner and outer layers 24, 26 are about 85% of that employed while forming a currently known single layer liner. Advantages of using the less dense more ductile outer layer 26 include a weight savings of the shape charge 10 over a liner having a single layer totally formed from a higher density material. Moreover, the weight savings is not offset by a reduction in performance, in contrast, performance is enhanced by use of the composite layer liner 16 described herein. In another example, the thickness of each of the inner layer and outer layer 24, 26 is about one millimeter by making the total thickness of a liner to be about 2 millimeters, which is comparable to most liners currently in use. [0022] The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. For example, instead of wireline, the perforating string can be deployed on tubing, slickline, or any other currently known or later developed conveyance means. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.