Abstract:
Disclosed herein is a shaped charge assembly for use in a perforating gun. The shaped charge assembly includes a shaped charge combined with a longitudinal spine extending along a portion of a perforating gun barrel. The shaped charge can be secured to the spine with a retaining shell. A bushing is included between the outer radius of the casing the retaining shell. The bushing serves to absorb shock during detonation of the shaped charge and to help in orienting the shaped charges.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to an apparatus that connects perforating guns. Yet more specifically, the present invention relates to a perforating gun connector utilizing corresponding tapered ends to facilitate connections thereof. Yet even more specifically, the present invention relates to an automated method of connecting perforating guns with a perforating gun connector.  
         [0003]     2. Description of Related Art  
         [0004]     Perforating guns 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 completed by coaxially inserting a pipe or casing into the wellbore, and the casing is retained in the wellbore by pumping cement into the annular space between the wellbore and the casing. The cemented casing is provided in the wellbore for the specific purpose of hydraulically isolating from each other the various earth formations penetrated by the wellbore.  
         [0005]     Included with the perforating guns 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”. The jet penetrates the casing, the cement and a quantity of the formation.  
         [0006]     Due to the high force caused by the explosive, the shaped charge often shatters into many fragments that exit the perforating gun into the fluids within the wellbore  5 . These fragments can clog as well as damage devices such as chokes and manifolds, thereby restricting the flow of fluids through these devices and possibly hampering the amount of hydrocarbons produced from the particular wellbore  5 . Therefore, there exists a need for an apparatus and a method for conducting perforating operations that reduces fragmentation of shaped charges and also provides a manner of retaining fragments of shaped charges produced during the perforation sequence.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     The present invention involves a shaped charge assembly comprising a casing for a shaped charge, the casing can have a generally tubular shape with open on one end and closed on the other. A base is formed on the closed end and walls extending away from the outer edge of the base terminating on the open end thereby forming a space on the inside of said walls and the base. The space should be capable of receiving an amount of explosive. Also included with the present invention is a spine disposed adjacent to the casing having a recess formed therein to receive the casing. The spine and recess can be capable of retaining substantially all of the casing fragments produced during detonation of the explosive. The shaped charge assembly of the present invention can further comprise a retaining shell releasably securable to the spine. The retaining shell should be coaxially circumscribing the casing when secured to the spine.  
         [0008]     The shaped charge assembly can further comprise a first set of threads formed on the spine formed to mate with a corresponding second set of threads formed on the retaining shell. Further, a bushing can be included with the present invention that is coaxially disposed between the case and the retaining shell. The shaped charge assembly of claim  1 , wherein the thickness of the walls decreases with distance from the base to the open end of the case. The thickness of the bushing can vary to accommodate varied orientations of the casing. Optionally, the present invention can include at least one other shaped charge assembly as well as a gun body capable of retaining the shaped charge assembly.  
         [0009]     With regard to the gun body, the spine can extend along a portion of the length of the gun body, wherein the presence of the spine and the casing are capable of producing an asymmetric radial weight distribution around the axis of the gun body. Optionally, the edges of the base can be substantially curvilinear and the thickness of the base can exceed the thickness of the walls thereby producing a crucible shaped casing. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0010]      FIG. 1  depicts a cross sectional view of one embodiment of the present invention.  
         [0011]      FIG. 2  illustrates one embodiment of the present invention within a wellbore.  
         [0012]      FIG. 3  illustrates one embodiment of the present invention within a wellbore. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0013]     With reference to the drawings herein, in  FIG. 1 a  cross sectional view of one embodiment of a shaped charge assembly  10  of the present invention is shown. The shaped charge assembly  10  of  FIG. 1  comprises a case  12 , a spine  16 , a retaining shell  14 , and a bushing  18 . As is well known, when assembled these components are preferably positioned and used within a gun body  22 . For the purposes of reference and not to serve as any limitation of the scope of the present invention, a dashed line is included with  FIG. 1  representing an axis  42  of the shaped charge assembly  10 . As will be described herein, it is preferred that many of the components of the shaped charge assembly  10  be bisected by the axis  42  in the embodiment of  FIG. 1 .  
         [0014]     The case  12  is comprised a base  24  and walls  25 , where the walls  25  are generally a tube-like section that extend up and away from the outer circumference of the base  24 . The space  28  between the walls  25  and the base  24  is formed to receive explosive  32  and a liner  30 . Preferably the base  24  is shaped similar to a bowl in that it has inner and outer surfaces that curve parallel to the axis of the base  24  as the surfaces travel away from the axis  42 . The walls  25  and the base  24  meet approximately at the point where the inner surface of the case  12  is substantially parallel to the axis  42 . It is also preferred that the thickness of the base  24  and the walls  25  be roughly the same at the region where they meet. However, the thickness of the walls  25  can decrease as the walls  25  approach the open end  26  of the case  12 .  
         [0015]     Rounding the outer surface of the base  24  combined with decreasing the thickness of the walls  25  results in a generally crucible shaped case  12 , this enhances the fit between the case  12  and the recess  17  formed in the spine  16 . Further, the generally curvilinear shaped of the base  24  also helps to equalize the forces that are subjected to the case  12 , this helps to reduce fragmentation of the case  12  during detonation of the explosive. This shape also works to produce fragments that are more uniform in size. Both of these effects result in minimization of metal fragments escaping the gun body  22 . However the present invention can accommodate a case  12  made from any one of a number of different shapes, such as one that has a largely rectangular cross section, a hemispherical shape, or a cross section where the inner and outer surface have different cross sections, such as an outer surface with a rectangular cross section and an inner surface having rounded edges, or vice versa.  
         [0016]     As illustrated in a cross sectional view in  FIG. 1 , the spine  16  of one embodiment of the present invention has a generally curved outer surface  38  formed to fit a portion of the inner surface  40  of the gun body  22 . Preferably the spine  16  should be somewhat hemispherical so that when situated within the gun body  22  its mass coupled with the base  24 , retaining shell  14 , and the bushing  18 , will produce an eccentric moment of inertia around the axis of the gun body  22 . While the outer surface  38  of the spine  16  has mostly the same radius along its circumference, the shape of the spine&#39;s  16  inner surface  37  varies along its circumference. The shape of the inner surface  37  surrounding and proximate to the axis  42  is largely curved and forms a recess  17 . The shape of the recess  17  should closely match the shape of the outer surface of the base  24  such that a majority of the base  24  can be positioned within the recess  17 .  
         [0017]     A ledge  44  is positioned at the outer edge of the recess  17 , the contour of the ledge  44  is primarily perpendicular to the axis  42 . When viewed from the axis, the ledge  44  has a generally annularly shaped surface with a radius that extends from the terminal edge of the recess  17  up to the threaded portion  46 . As can be seen in  FIG. 1 , the length of the ledge  44  should be able to accommodate the ends of both the retaining shell  14  and the bushing  18  when they are positioned coaxially around the case  12 . The threaded portion  46  of the spine  16  is mostly parallel with the axis  42  having threads  49 , such as National “N” threads, formed along its surface. The length of the threaded portion  46  will depend on the particular size of shaped charge assembly  10  involved as well as the type of threads used, but the length should be sufficiently long to ensure a tight and secure coupling of the threads  50  of the retaining shell  14  with the threaded portion  46 . An annularly shaped shoulder  48  connects the inner surface  37  of the gun body  22  with the threaded portion  46 . The shoulder  48  circumscribes the threaded portion  46  and preferably has a surface that is largely parallel to the surface of the ledge  44 . However the shape and contour of the shoulder  48  is not critical, but can be any shape. The shoulder  48  though should have a large enough radius to provide sufficient material so that when the threads  49  are formed on the threaded portion  46  the spine  16  can still structurally support the addition of the retaining shell  14 .  
         [0018]     When viewed along the axis  42 , the bushing  18  is has a mostly annular cross section. While the outer radius of the bushing  18  is preferably constant along its length, its inner radius can vary in size to match the contour of the outer radius of the casing  12 . In the embodiment of the present invention shown in  FIG. 1 , the outer radius of the casing  12  decreases as it approaches the open end  26 . Since it is desired that the inner radius of the bushing  18  closely circumscribe the outer surface of the casing  12 , the inner radius of the bushing  18  is shown to correspondingly decrease proximate to the open end  26 , while the outer radius remains relatively constant. Thus the thickness of the bushing  18  increases along its length from the ledge  44  towards the open end  26 . However the shape of the inner radius is not limited to that shown in  FIG. 1 , but can be of any contour, but it should closely match the contour of the outer radius of the particular casing  12  included with the present invention—which as noted above can be of various types.  
         [0019]     As previously noted, threads  50  on the outer circumference of one edge of the retaining shell  14  are included to mate with the threads of the threaded portion  46 . The corresponding threads ( 49  and  50 ) provide a means of releasably attaching the retaining shell  14  to the spine  16 , either by hand or with the aid of an associated tool. A retaining lip  15  is provided on the inner radius of the retaining shell  14  on the side opposite the threads  50 . The retaining lip  15  extends inward towards the axis  42  from the inner radius of the retaining shell  14  having a surface that is generally at an angle oblique from the axis  42 . Similarly, a beveled edge  19  is provided on the outer surface of the bushing  18  such that when the retaining shell  14  and the bushing  18  are assembled within the shaped charge assembly  10 , the angle of the beveled edge  19  is substantially the same as the angle of the retaining lip  15 . The combination of the retaining lip  15  and the beveled edge  19  provide a means of enabling the retaining the bushing  18  within the shaped charge assembly  10  when the retaining shell  14  is secured to the shaped charge assembly  10 . It is believed it is well within the scope of those skilled in the art to design and implement adequate dimensions and angles for both the retaining lip  15  and the beveled edge  19  without undue experimentation.  
         [0020]     It should be noted that the inner radius of the retaining shell  14  increases along its length such that its width is smaller proximate to its threaded end than proximate to the retaining lip  15 . This increase in radius combined with a constant outer radius of the bushing  18  produces an annular void  55  between the bushing  18  and the retaining shell  14 . As will be described in more detail below, the presence of the annular void  55  introduces shock absorption capabilities to the shaped charge assembly  10 , thereby reducing fragmentation.  
         [0021]     In operation of the preferred embodiment of the present invention, the shaped charge assembly  10  is assembled, then combined with a gun body  22 , and integrated into a perforating gun  8 . As is known in the art, the perforating gun  8  is inserted into a wellbore  5  preferably by a wireline  6 . The perforating gun  8  can also be inserted into the wellbore  5  and lowered to the spot where perforations are desired. The perforating gun  8  can be tethered by a slickline, by tubing, or any now known or later developed insertion/suspension technique or devices. Once the surface personnel have determined that the perforating gun  8  has been lowered to the region where perforations are to be conducted, perforating operations can be commenced. Generally perforating is initiated by sending a signal down the wireline  6  from the surface to the perforating gun  8 . As is well known, initiators (not shown) within the perforating gun  8  receive that surface signal and in turn transfer a detonative force though the detonation cord  34  that in turn initiates detonation of the explosive  32  within the shaped charge assembly  10 . Detonation of the explosive  32  collapses the liner  30  and transforms the solid liner into a metal jet  11  that exits the wall of the gun body  22  and penetrates the inner surface of the wellbore  5 . The metal jet  11  pierces the inner surface of the wellbore  5  thereby producing perforations  9  in the formation  12  that surrounds the wellbore  5 .  
         [0022]     During detonation of the shaped charge assembly  10  of the present invention the likelihood of fragments of the case  12  entering the wellbore  5  after detonation of the explosive  32  is highly reduced over prior art shaped charges. The improved size and shape of the case  12  combined with shock absorbing capabilities of the annular void  55  result in less fragmentation of the case  12 . The annular void  55  can provide an air gap having shock absorbing qualities that greatly reduces the shock absorbed by the case  12 . Providing alternate devices to absorb shock serves to decrease the shock realized by the case  12  thus reducing the fragmentation of the case  12 . Furthermore, with regard to the fragmentation that does occur, the presence of the spine  16  combined with the retaining shell  14  serves to contain the fragments of the case  12  well within the gun body  22  and not allow them to enter the wellbore  5  where the fragments might likely cause clogging or congestion problems.  
         [0023]     The spine  16  also can aid in orientation of the perforating gun  8  in which it is integrated. The eccentric loading of the spine  16  produces an asymmetric mass distribution axis (not shown) of the gun body  22 . This is important when the perforating gun is in deviated section  7  of the wellbore  5 , such that when allowed to rotate about its axis, the gravitational pull on the gun body  22  will attempt to orient it such that the spine  16  is located proximate to the lowermost portion  21  of the wellbore  5 .  
         [0024]     The components of the present invention should have the capability of withstanding downhole conditions, such as high pressures and temperatures, as well as the ability to withstand attach by corrosive agents. Accordingly steel is a suitable material for the components of the present invention.  
         [0025]     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, other materials, such as rubber, elastomeric objects, foam, or other shock absorbing substances can be installed within the annular void  55 . 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.