Abstract:
A perforating tool includes a charge holder connected to a work string and a perforator fixed in a charge holder disposed along the work string. The perforator includes a cylindrical case, an explosive material, a metal cap, and a detonating cord. The case has a bulkhead at a first end, an open mouth at a second end, and an interior volume. The first end includes a post having a slot. The explosive material is disposed in the interior volume. The metal cap covers the open mouth of the case and has a disk section defined by a separator ring. The separator ring has a structurally weakened zone that encircles the disk section. The detonating cord is received in the slot of the post.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Application Ser. No. 62/237,302, filed Oct. 5, 2015, the entire disclosure of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to devices and methods for subsurface perforating. 
       BACKGROUND 
       [0003]    Hydrocarbons, such as oil and gas, are produced from cased wellbores intersecting one or more hydrocarbon reservoirs in a formation. These hydrocarbons flow into the wellbore through perforations in the cased wellbore. A number of wellbore tubulars may be used in a wellbore in addition to casing. Such tubulars including liners, production tubing, and drill pipe. In some situations, it may be desirable to sever a portion of a wellbore tubular. For example, a drill pipe may become stuck in a wellbore. Removal of the drill pipe may require cutting the drill pipe into two sections. In another example, pipe may need to cut during well abandonment. 
         [0004]    The present disclosure addresses the continuing need for perforators useful for subsurface operations that may take place during the construction, completion, workover, and/or de-commissioning of a well. 
       SUMMARY 
       [0005]    In aspects, the present disclosure provides a perforator for perforating a wellbore tubular in a wellbore. The perforator may include a cylindrical case having a bulkhead at a first end, an open mouth at a second end, and an interior volume; an explosive material disposed in the interior volume; and a cap covering the open mouth of the case, the cap having a disk section defined by a separator ring having a reduced strength zone that encircles the disk section, wherein an outer circumference of the cap form a seat for receiving an edge of the open mouth. 
         [0006]    In aspects, the present disclosure provides a perforating tool for perforating a wellbore tubular in a wellbore. The perforating tool may include a charge holder connected to a work string and a perforator fixed in a charge holder disposed along the work string. The perforator may include a cylindrical case having a bulkhead at a first end, an open mouth at a second end, and an interior volume, wherein the first end includes a post projecting therefrom, the post having a slot; an explosive material disposed in the interior volume; and a metal cap covering the open mouth of the case, the cap having a disk section defined by a separator ring, the separator ring having a structurally weakened zone that encircles the disk section. A detonating cord may be received in the slot of the post. 
         [0007]    In aspects, the present disclosure also provides a method for perforating a wellbore tubular in a wellbore. The method may include the step of forming a work string by connecting a charge holder connected to the work string, disposing a detonating cord along the work string, and fixing a perforator in the charge holder. The method may also include the steps of conveying the work string into the wellbore; positioning the perforator in the wellbore tubular; and firing the shaped charge by detonating the detonating cord. 
         [0008]    It should be understood that certain features of the invention have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will in some cases form the subject of the claims appended thereto. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    For detailed understanding of the present disclosure, references should be made to the following detailed description taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein: 
           [0010]      FIG. 1  illustrates an isometric side sectional view of a perforator in accordance with one embodiment of the present disclosure; 
           [0011]      FIG. 2  illustrates an isometric view of the  FIG. 1  perforator; 
           [0012]      FIG. 3  illustrates a schematic side view of a well tool that uses the  FIG. 1  perforator; and 
           [0013]      FIG. 4  illustrates a well in which perforators according to the present disclosure may be used. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The present disclosure relates to devices and methods related to subsurface activity such as casing perforating, casing removal, completion, fishing operations to remove wellbore tubulars, etc. The present disclosure is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the present disclosure with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure, and is not intended to limit the disclosure to that illustrated and described herein. 
         [0015]    Referring to  FIGS. 1 and 2 , there is sectionally shown one embodiment of a shaped charge  10  in accordance with the present disclosure. The shaped charge  10  is designed to generate a large diameter projectile for puncturing, cutting, and/or severing a wellbore structure. The shaped charge  10  may include a case  12  and a cap  14 . The case  12  may be formed as a cylindrical body  16  with a mouth  18  that is covered by the cap  14 . A quantity of explosive material (not shown) may be disposed inside an interior volume  52  of the case  12 , e.g., RDX, HMX and HNS. 
         [0016]    The cap  14  is configured to generate a large diameter perforator which acts as a projectile that punctures, severs, cuts through, or otherwise perforates an adjacent structure. In one embodiment, the cap  14  includes a disk section  20  defined by a separator ring  22 . An outer circumference  24  of the cap  14  may include a lip  26  in which an edge of the case  12  seats. The cap  14  has a face  28  that is formed of the surfaces defining the disk section  20  and the outer circumference  24 . The face  28  may be configured to contact the wellbore structure to be cut or have a predetermined stand-off or spacing from an adjacent surface. 
         [0017]    The disk section  20  contains the material which forms the perforator. The cap  14  and/or disk section  20  may be formed from a powdered metal mixture that is compressed at high pressures to form a solid mass in the desired shape. A high density metal may be included in the mixture in order to achieve the desired effect from the explosive force. Common high density metals used include copper and tungsten, but other high density metals can also be used. The mixture of metals typically contains various other ductile metals being combined within the matrix to serve as a binder material. Other binder metals include nickel, lead, silver, gold, zinc, iron, tin, antimony, tantalum, cobalt, bronze, molybdenum and uranium. 
         [0018]    The disk section  20  may be generally flat and circular, but other geometric shapes may also be used (e.g., square or triangular). As used herein, the term “flat” is used as a contrast to a conical shape. However, in some embodiments, the flat disk section  20  may use a convex or concave arch to provide pressure integrity. The separator ring  22  is a portion of the cap  14  that is defined by a structurally weakened or reduced strength zone  24  that allows the disk section  20  to separate from the cap  14  when the explosives (not shown) inside the case  12  are detonated. A variety of mechanisms may be used to form the separator ring  22  in embodiments where the cap  14  is a single integral body. For example, a groove may be formed into the cap  14 . Alternatively, as shown, a fold may be formed into the cap  14 . The fold or groove may be “V” shaped, “U” shaped, sinusoidal, a square shape, a rectangular, or any other shape having curved or straight sides that are suited for weakening the zone  24 . In other embodiments, the separator ring  22  may have a reduced wall thickness section formed while the cap  14  is manufactured. In still other embodiments, the material at the separator ring  22  may be treated chemically to reduce strength. In yet other embodiments, the cap  14  may be an assembly of two or more discrete components; e.g., the disk section  20  may be a separate element. 
         [0019]    Referring to  FIG. 3 , there is shown a portion of a perforating tool  40  disposed in a wellbore  42 . The perforating tool  40  includes a shaped charge  10  fixed in a charge holder  60  and positioned to be in intimate contact with a wellbore tubular  44 . The charge holder may be a tube, strip, plate, or other structure that is shaped and configured to point the shaped charge  10  such that the disk section  20  can travel radially outward toward the wellbore tubular  44 . By intimate contact, it is meant that at least a portion of the face  28  ( FIG. 2 ) is in physical contact with the wellbore tubular  44 . In embodiments, it may be desirable to have the face  28  parallel with the surface of the wellbore tubular  44 . Thus, a majority of the disk section  20  has a surface that is parallel with the surface of the wellbore tubular  44  or, simply, the disk section  20  is substantially parallel with the wellbore tubular  44 . When positioned as desired, a suitable firing system may be used to detonate the shaped charge  10 . For instance, in one non-limiting embodiment, a detonating cord  46  may be used to detonate the explosive material (not shown) inside the shaped charge  10 . Upon detonation, the disk section  22  breaks free of the cap  14  along the separator ring  22  and is propelled against the surface of the wellbore tubular  44 . Once free of the cap  14 , the disk section  20  functions as a perforator that cuts through the wellbore tubular  44 . 
         [0020]    In one non-limiting arrangement, the perforating tool  40  may be configured such that the shaped charge  10  is in physical contact with wellbore fluids. However, the explosive material inside the case  12  is isolated from contact with such liquids and gases as noted previously. In such embodiments, the charge holder  60  may be a strip or frame that does not enclose the charge holder  60 . Also, the detonating cord  46  may be insulated in a pressure tubing  47  that protects the energetic material of the detonating cord  46  from exposure to the ambient wellbore environment (e.g., drilling fluids, fluid pressure, temperature, formation fluids, gases, etc.). Thus, the explosive material of the detonating cord  46  and the shaped charge  10  do not physically contact fluids in the wellbore such as liquids (e.g., drilling fluids, water, brine, liquid hydrocarbons) or gases (e.g., natural gas, etc.). A detonator (not shown) may be used to detonate the detonating cord  46 , which then fires the shaped charge  10 . 
         [0021]    The teachings of the present disclosure may be used in connection with a variety of shaped charge configurations. As shown in  FIG. 1 , the case  12  may be configured as an encapsulated shaped charge. That is, the case  12  may include an unperforated bulkhead  50 . By “unperforated,” it is meant that there are no openings or passages through the case  12 . A post  54  formed at the bulkhead  50  may include a channel  56  for receiving the detonating cord  46  and/or a booster material (not shown). However, the channel  56  may be “blind” in that it does not extend and communicate with the interior  52 . Further, the engagement of the outer circumference  24  and the case  12  may also be fluid tight. Thus, the interior volume  52  of the shaped charge  10  may be hydraulically isolated from the ambient wellbore conditions. However, a conventional case, which has a channel, passage, or bore that does communicate with the interior of the case  12  may also be used. 
         [0022]    Referring to  FIG. 4 , there is shown a well construction and/or hydrocarbon recovery facility  100  positioned over a subterranean formation of interest  102 . The facility  100  can include known equipment and structures such as a rig  106 , a wellhead  108 , and casing or other wellbore tubular  44 . A work string  112  is suspended within the wellbore  104  from the rig  106 . The work string  112  can include drill pipe, coiled tubing, wire line, slick line, or any other known conveyance means. The work string  112  can include telemetry lines or other signal/power transmission mediums that establish one-way or two-way telemetric communication. A telemetry system may have a surface controller (e.g., a power source)  114  adapted to transmit electrical signals via a cable or signal transmission line  116  disposed in the work string  112 . To perforate or sever equipment in the wellbore  104 , the work string  112  may include a downhole tool  120  that as a perforating tool  122  that includes one or more shaped charges according to the present disclosure. 
         [0023]    In one mode of use, the perforating tool  122  is positioned at a location  56  such that at least a portion of the face  28  ( FIG. 2 ) of the shaped charge(s)  10  ( FIG. 1 ) is in physical contact with the wellbore tubular  44 . The wellbore tubular  44  may be casing, liner, drill string, production tubing, etc. In some embodiments, a positioning tool  124  may be used to position the perforating tool  122  inside the wellbore tubular  44 . The positioning tool  122  may include arms, vanes, or other extendable elements that can contact an adjacent structure and push to the shaped charge  10  ( FIG. 1 ) of the perforating tool  122  into contact with the wellbore tubular  44 . The positioning tool  122  may use metal springs, inflatable packers, bladders, hydraulic fluid, or other mechanism to bias the extendable members into the extended position. Next, a firing signal from the controller  114  is used to detonate the shaped charge  10 . Upon detonation, the disk section  20  ( FIG. 2 ) cuts through the wellbore tubular  44  in a manner discussed previously. 
         [0024]    The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope of the invention. It is intended that the following claims be interpreted to embrace all such modifications and changes.