Patent Publication Number: US-11047195-B2

Title: Perforating gun

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 15/088,677, filed Apr. 1, 2016, which claims priority from U.S. Provisional Application Ser. No. 62/142,313, filed on Apr. 2, 2015, the entire disclosure of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to devices and method for perforating a subterranean formation. 
     BACKGROUND 
     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. Perforations are usually made using a perforating gun loaded with shaped charges. The gun is lowered into the wellbore on electric wireline, slickline, tubing, coiled tubing, or other conveyance device until it is adjacent to the hydrocarbon producing formation. Thereafter, a surface signal actuates a firing head associated with the perforating gun, which then detonates the shaped charges. Projectiles or jets formed by the explosion of the shaped charges penetrate the casing to thereby allow formation fluids to flow through the perforations and into a production string. 
     Conventionally, a perforating gun is assembled by affixing a detonating cord to one or more shaped charges disposed along a charge tube. In many cases, the detonating cord is wrapped external to the charge tube and fed through a hole in the charge tube opening. Aside being time consuming, conventional gun assembly methods sometimes damage the detonating cord. 
     Thus, there exists a need for devices that are less time consuming to assemble and less susceptible to damage. In other aspects, there exists a need for improved locking mechanisms and electrical grounding for such devices. The present disclosure addresses these and other needs of the prior art. 
     SUMMARY 
     In aspects, the present disclosure provides a perforating gun that includes a carrier tube and a charge tube assembly. The carrier tube includes a bore and at least one groove formed along an inner surface. The charge tube assembly is disposed in the bore of the carrier tube and includes a charge tube, an alignment end plate, an insertion end plate, a retention member, shaped charges, and a detonating cord. The charge tube has a plurality of shaped charge openings, a plurality of post openings, a first end, and a second end. The alignment end plate is connected to the first end of the charge tube. The insertion end plate is connected to the second end of the charge tube. The shaped charges are disposed in each of the shaped charge openings. Each shaped charge has a post projecting out of one post opening. The detonating cord is connected to each of the projecting posts. 
     In one embodiment, the retention member has at least one anchor segment connected to the alignment end plate and a radially outward segment that extends beyond an outer diameter of the alignment end plate in an extended position. The radially outward segment may be compressible smaller than an inner diameter of the carrier tube in a retracted position. 
     In another embodiment, the retention member may be a wire. The wire may have a hooked anchor segment fixed within the first opening on the end face, a coiled flexure segment at least partially fixed within the second opening on the end face, and a radially outward segment between the hooked anchor segment and the coiled flexure segment. The radially outward segment extends beyond an outer diameter of the alignment end plate in an extended position and is compressible to a second smaller diameter in a retracted position. The wire is configured to bias the radially outward segment against a surface defining the groove and form a metal-to-metal contact with the carrier and with the alignment end plate. 
     In another embodiment, the retention member is a fixed split retention member having a fixed end connected to the alignment end plate and a free end, the fixed split retention member being disposed in a first groove of the carrier tube. This embodiment also includes a free split retention member disposed in a second groove of the carrier tube. 
     It should be understood that examples of 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 
       For detailed understanding of the present disclosure, references should be made to the following detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, in which like elements have been given like numerals and wherein: 
         FIG. 1  schematically illustrates a side sectional view of a perforating gun according to one embodiment of the present disclosure; 
         FIGS. 2A-2B  schematically illustrate isometric end views of an alignment end plate for a perforating gun according to one embodiment of the present disclosure; 
         FIG. 3  schematically illustrates an isometric end view of an open slot for an alignment end plate for a perforating gun according to one embodiment of the present disclosure; 
         FIG. 4  schematically illustrates an isometric end view of an insertion end plate for a perforating gun according to one embodiment of the present disclosure; 
         FIG. 5  schematically illustrates a fixed split retention member disposed in a carrier tube according to the present invention; and 
         FIGS. 6A-B  isometrically illustrates a elastically deformable retention member according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to devices and methods for facilitating the assembly and enhancing the reliability of wellbore perforating tools. 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. 
     Referring now to  FIG. 1 , there is shown one embodiment of a perforating gun  100  in accordance with the present disclosure. For ease of discussion, devices such as shaped charges and detonating cords have been omitted. The perforating gun  100  may include a carrier  102  that is shaped to receive a charge tube assembly  104 . In one arrangement, the charge tube assembly  104  includes an alignment end plate  106 , a charge tube  108 , an insertion end plate  110 , and retention members  112 ,  114 . 
     Referring now to  FIG. 2A , there is shown a section of the charge tube assembly  104  that includes a fixed retention member  112  and the alignment end plate  106 . The fixed retention member  112  provides selective biasing engagement between the alignment end plate  106  and the carrier  102  ( FIG. 1 ). In one non-limiting arrangement, the fixed retention member  112  may be formed as an elastically deformable ring and may be compressed to a reduced diameter state. For example, the ring may be formed of a resilient material (e.g., spring steel) and may include a cut or split. The split allows the fixed retention member  112  to flex diametrically inward when compressed. The alignment end plate  106  may be a tubular member such as a collar that is fixed to a first end  116  of the charge tube  108  with a fastener  118 . However, the alignment end plate  106  may also be formed integral with the charge tube  108 . As shown in  FIG. 2B , the alignment end plate  106  may include an alignment key  122  shaped and sized to mate with an alignment groove (not shown) of the carrier  102  ( FIG. 1 ) during assembly. 
     Referring back to  FIG. 2A , the fixed retention member  112  may be connected to the alignment end plate  106  using a connector  130 . The connector  130  may be a screw, rivet, pin or other element that fixes the fixed retention member  112  to a face  132  of the alignment end plate  106 . In one embodiment, the connector  130  prevents relative axial movement between the alignment end plate  106  and the fixed retention member  112 , but allows some relative rotational movement. The connector  130  may be attached to a first end  134  of the fixed retention member  112 . The fixed retention member  112  has a free end  136  that is not permanently fixed to the face  132  of the alignment end plate  106 . Instead, the free end  136  may include a profile  138  that hooks into a post  140  formed on the face  132 . As used herein a “profile” is a surface shaped in a desired manner. The post  140  may be any protrusion or feature that allows selective engagement with the free end  136 . While the connector  130  and the post  140  are both shown as screws, it should be understood that these may be different structural elements. 
       FIG. 2A  shows the fixed retention member  112  in a relaxed and diametrically expanded state.  FIG. 2B  shows that the fixed retention member  112  has been compressed to a diametrically contracted state. The fixed retention member  112  is held in this diametrically contracted state by the connection of the free end  136  and the post  140 . 
     Referring now to  FIG. 3 , there is shown a section of the charge tube assembly  104  that includes the alignment end plate  106  and the charge tube  108 . In one embodiment, the charge tube first end  116  and the alignment end plate  106  may include an open slot  150 . As used herein, the term “open slot” refers to an opening that is, at least initially, not bound on all sides. That is, the open slot extends from a location axially inward of the first end  116  all the way to the face  132  of the alignment end plate  106 . In some embodiments, tabs  152 ,  154  may be formed along the open slot  150 . For instance, a tab  152  may be used to form a protective ramp that allows a detonating cord  20  to enter the charge tube  108  without encountering a sharp edge. The tab  154  may be formed as a bendable element that can be deformed to block a portion of the open slot  150  after the detonating cord  20  has been installed in the charge tube  108 . Additionally, an opening  156  may be formed to allow wiring to run between the inside and the outside of the charge tube  108 . 
     The arrangement of the insertion end plate  110  ( FIG. 1 ) and the charge tube  108  is similar in many aspects to the  FIG. 3  arrangement. Referring now to  FIG. 4 , there is shown a section of the charge tube assembly  104  that includes the insertion end plate  110  and the charge tube  108 . In one embodiment, the charge tube second end  160  ( FIG. 1 ) and the insertion end plate  110  may include an open slot  150 . In some embodiments, tabs  152 ,  154  may be formed along the open slot  150 . The slot  150  and tabs  152 ,  154  are similar in design to those discussed in connection with  FIG. 3 . 
     Referring now to  FIGS. 2B and 4 , in contrast to the alignment end plate  106 , the insertion end plate  110  does not have an alignment key and is not fixed to the free retention member  114 . Rather, the free retention member  114  effectively “floats” in an annular groove  162  ( FIG. 1 ) or recess formed on an inner surface of the carrier  102 . Like the fixed retention member  112 , the free retention member  114  may be formed as a split annular ring. In one arrangement, the free retention member  114  may be formed of a resilient material (e.g., spring steel) that has a relaxed diametrically expanded size. The split allows the fixed retention member  112  to flex diametrically inward. 
     For a better understanding of the co-action among the several features described above, the assembly of the perforating gun  100  will be discussed. 
     As best shown in  FIG. 1 , the charge tube  108  may include a plurality of shaped charge openings  30  for receiving the shaped charges  32  that are shown in  FIG. 3 . The shaped charges  32  each have a post  34  that project through post openings  35  formed in the charge tube  108 . The detonating cord  20  may be affixed to the shaped charges  32  by being seated firmly within a groove of the post  34 . In one non-limiting embodiment, the post  34  may mate with an external clip  42 . A non-limiting example of the external clip  42  is described in U.S. patent application Ser. No. 11/759,126, which is incorporated herein in its entirety. 
     Referring to  FIG. 3 , after the detonating cord  20  has been affixed within the groove of the shaped charge posts  34 , the detonating cord  20  may be inserted into the bore of the charge tube  108  via the open slot  150  of the charge tube  108  and the alignment end plate  106 . It should be noted that the open slot  150  allows a lateral insertion of the detonating cord  20  as opposed to an axial insertion. That is, an end of the detonating cord  20  does not have to be inserted into the charge tube  108 . Rather, the detonating cord  20  may be slid laterally into the charge tube  108  while the portion of the detonating cord  20  entering the charge tube  108  is parallel with the long axis of the charge tube  108 . Thus, the detonating cord  20  does not have to bend, which reduces the likelihood of kinking. 
     It should be appreciated that the first tab  152  provides a smooth surface on which the detonating cord  20  may lie. Further, the first tab  152  may form a physical barrier between the shaped charges  32  and the detonating cord  20 . This physical barrier may act as a shield that prevents at least some of the energy associated with the detonating of the detonating cord  20  from impacting and damaging the shaped charge  32 . The second tab  154  may be bent or otherwise deformed to obstruct at least a portion of the open slot  150 . Thus, the second tab  154  may act as a retaining element that keeps the detonating cord  20  from inadvertently falling out of the charge tube  108 . 
     As noted previously, the charge tube assembly  104  may include other devices that have not been shown. For example, electrical wiring (not shown) may be installed in the bore of the charge tube  108 . Wiring that may need to exit the charge tube  108 , such as ground wire (not shown) may be fed through the opening  156 . In the case of ground wires (not shown), these wires may be fed through the opening  156  and fixed to the fastener  118 . The ground wire (not shown) may be used to provide an electrical connection with the electric detonator (not shown). 
     Referring to  FIG. 1 , the final assembly of the perforating gun  100  may include installing the retention members  112 ,  114 . The free retention member  114  may be installed in the groove  162  of the carrier  102 . Referring to  FIGS. 2A ,B, the fixed retention member  112  may be attached to the alignment end plate  106  by attaching the connector  130  to the first end  134  of the fixed retention member  112 . To facilitate the installation, the free end  136  of the fixed retention member  112  is hooked to the post  140 . Thus, the fixed retention member  112  is held in a reduced diametrical state. 
     Referring to  FIGS. 1 and 2A ,B, thereafter, the charge tube assembly  104  may be inserted into the carrier  102 . The reduced diameter fixed retention member  112  is generally the same diameter as the alignment end plate  106  (e.g., +/−10% difference) to facilitate entry and assembly. The charge tube assembly  104  is inserted axially until the alignment key  122  is secured within the keyway of the carrier. The charge tube assembly  104  may be rotated as needed to align the alignment key  122  with the alignment groove (not shown) formed in the carrier  102 . This alignment steps aligns the shaped charges  32  with scallops (not shown) formed along the carrier  102 . Thereafter, the charge tube assembly  104  may be inserted until the second end  160  is next to the free retention member  114 . 
     Referring to  FIGS. 1, 2A , B and  5 , to complete assembly, the free end  136  of the fixed retention member  112  is released from the post  140 , which allows the fixed retention member  112  to revert to an expanded diametrical condition. The fixed retention member  112  expands into a locking relationship with a groove  184  formed on an inner surface of the carrier  102 . The diameter of the groove  184  is sized such that the fixed retention member  112  remains partially compressed within the groove  184  and therefore applies a biasing spring force at the fastener  130 . This force is transferred to the alignment plate  106 , which is pushed into engaging contact with an inner surface  186  of the carrier  102 . 
     It should be appreciated that the charge tube  104  nests between the two retention members  112 ,  114 . Thus, the retention members  112 ,  114  cooperate to axially align the charge tube  104  relative to the carrier  102 . It should be appreciated, however, that the retention members  112 ,  114  have different interaction with the charge tube  104 . The retention member  112  is fixed to and moves with the charge tube  104 . When seated in the groove, the retention member  112  can function as a seating surface for the charge tube  104  or act as a hanger from which the charge tube  104  can be suspended to some degree. The retention member  114  can function as only a seating surface because it is not connected to the charge tube  104 . In certain embodiments, the retention member  112 ,  114  are axially spaced such that the retention member  112  never bears the full gravitational weight of the charge tube  104 . 
     Referring to  FIGS. 2A ,B and  5 , it should also be appreciated that the retention member  112  can help maintain continuous physical contact between the carrier  102  and the alignment end plate  106 . As noted previously, a ground wire (not shown) may be attached to the alignment end ring  106  at the fastener  118  as part of an electrical circuit. The biasing force of the retention member enables positive contacting engagement between the fixed retention member  112  and the inner surface  186  of the carrier  102  and between the alignment end ring  106  and the inner surface  186  of the carrier  102 . Thus, these contacting surfaces may be used to form an electrical circuit used to operate the perforating gun  100 . 
     Referring now to  FIGS. 6A-B , there is shown another embodiment of a retention member  112  in accordance with the present disclosure. In this embodiment, the alignment end plate  106  does not have an open slot. As before, the retention member  112  provides selective biasing engagement between the alignment end plate  106  and the carrier  102  ( FIG. 1 ). 
     Referring to  FIG. 6A , in one non-limiting arrangement, the retention member  112  may be formed as an elastically deformable clip, rod or coil. As shown, the retention member  112  is illustrated as a continuous length of wire having several shaped segments. For example, the retention member  112  may be formed of a resilient material (e.g., spring steel) and shaped to have a flexure segment  190 , a first anchor segment  192 , and a second anchor segment  194 . The flexure segment  190  generate a biasing force that pushes one or more arcuate projecting segments  196  radially beyond the outer diameter of the end plate  106 . By biasing, it is meant that the projecting segments  196  are biased in the radially outward direction, but can be compressed to a radially retracted state. The flexure segment  190  may have one or more arcuate cup segments  197  that are shaped to receive a jaw of pliers (not shown) during removal of the retention member  112 . The first and second anchor segments  192 ,  194  are shaped to engage complementary openings  200 ,  202  formed in an end face of the end plate  106 , respectively. As used herein, an end face means a surface that is transverse to a long axis of the charge tube. An end face can also be considered as a terminal surface of the end plate  106  that is perpendicular to an outer circumferential surface of the end plate  106 . The endplate  106  also includes an opening  205  that is positioned adjacent to the cup segment  197 . The openings  200 ,  202  may be through holes, blind holes, bores, grooves, cavities or any other features that can receive the anchor segments  192 ,  194 . 
     Referring to  FIG. 6B , in one non-limiting embodiment, the first anchor segment  192  may be formed as a hook  210  (e.g., a “J” shaped end). The opening  200  may be formed as a through hole in which the hook  210  latches. The second anchor segment  194  may be include a flexure segment  212  and a finger segment  214 . The flexure segment  212  may be a segment that can adjust the spring force generated by the retention member  112 . For instance, as shown, the retention member  112  is made of a continuous length of wire. Thus, the flexure segment  212  is a segment of coiled wire that allows more or less bending or deflection in the retention member  112 . In other embodiments, the flexure segment may be a series of folds, twists, etc. The second opening  202  may include a cavity for  216  receiving the button shaped segment  212  and a groove  218  for receiving the finger segment  214 . 
     It should be appreciated that the retention member  112  of  FIGS. 6A and 6B  may lock the charge tube assembly  108  into a suitable groove formed in the carrier  102  ( FIG. 1 ), which eliminates the need for a separate snap ring. Such suitable grooves are shown in  FIG. 1  as grooves  184  and  162 . The retention member  112  may be attached prior to assembly. At this time the radially projecting segment  196  is biased to the extended position and has a extended radial length. When the charge tube assembly  104  is inserted into the carrier  102 , the radially projection segment  196  is radially compressed smaller than an inner diameter of the carrier tube  102  in a retracted and slides along the inner surface of the carrier tube  102 . Thus, during assembly, the resilient retention member  112  acts like a ratchet and the charge tube assembly  102  can be simply pushed into the carrier  102 . When the retention member  112  snaps into and seats within the groove (e.g., groove  184  of  FIG. 1 ), the retention member  112  provides a positive grounding mechanism for the electrical circuit used to fire the perforating gun. It should be noted that the retention member  112  is biased radially outward and pressed against a surface defining the groove  184  ( FIG. 1 ). Because of the bias or spring force, a metal-to-metal contact is maintained between the carrier  102  and the retention member  112  and the retention member  112  and the alignment end plate  106 . This is in contrast to a snap ring, which merely floats in a groove and does not maintain a positive grounding mechanism. 
     To remove the retention member  112  one jaw of the pliers (not shown) can be inserted into the opening  205  and the other jaw of the pliers (not shown) may wedge against an inner surface  209  of the end plate  106 . Thus, when the pliers&#39; jaws (not shown) are closed, the cup segment  197  is pulled radially inward, which allows the retention member  112  to be freed from the groove  220  of the carrier  102 . 
     It should be noted that the teachings of the present disclosure are not limited to the specific perforating guns illustrated in the figures. For instance, the charge tube and detonator cord may be arranged using an internal and external weave, which would eliminate the need for clips. More generally, the present teachings may be applied to any perforating gun that uses a telescopically arranged carrier tube and charge tube. 
     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.