Abstract:
A perforating gun having a charge case with a boss element partially circumscribing Optionally the pair of bosses may be included that are substantially symmetric about the axis of the charge case. Forming a shaped charge with such a charge case allows for gun strips to be formed with increased web material between adjacent shape charges in the gun strips. The increased web material provides for a more structurally sound gun tube, especially when dealing with high density charges. Notches may be provided in the gun tube on the outer radius of the holes formed to receive the shape charges, the notches are to be aligned with the bosses on the outer periphery of the shaped charge case. This also may orient the charge cases so they are pre-aligned for ready connection to an associated detonation cord.

Description:
BACKGROUND 
   1. Field of Invention 
   The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a perforating system. Yet more specifically, the present invention relates to a shaped charge having a modified boss for use in a perforating gun system. 
   2. Description of Prior Art 
   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 completed by coaxially inserting a pipe or casing into the wellbore. 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. 
   Perforating systems typically comprise one or more perforating guns strung together, these strings of guns can sometimes surpass a thousand feet of perforating length. In  FIG. 1  an example of a perforating system  4  is shown. For the sake of clarity, the system  4  depicted comprises a single perforating gun  6  instead of a multitude of guns. The gun  6  is shown disposed within a wellbore  1  on a wireline  5 . The perforating system  4  as shown also includes a service truck  7  on the surface  9 , where in addition to providing a raising and lowering means, the wireline  5  also provides communication and control connectivity between the truck  7  and the perforating gun  6 . The wireline  5  is threaded through pulleys  3  supported above the wellbore  1 . 
   Perforating guns typically include a cylindrical gun strip  16  coaxially housed within a gun body  14 . Shaped charges  8  are provided within the gun strip  16  and aimed generally perpendicular to the axis of the wellbore  1 .  FIG. 2  provides an example of a shaped charge  8  that includes a housing  18 , a liner  22 , a quantity of high explosive  24  inserted between the liner  22  and the housing  18 , and a booster charge  26  adjacent the base of the high explosive  24 . 
   The shaped charges  8  are typically connected to a detonating cord  27  which is affixed to the shaped charge  8  by a case slot  25  proximate to the booster charge  26 . Igniting the detonation cord  27  creates a compressive pressure wave along its length that initiates the booster charge  26  that in turn ignites the high explosive  24 . When the high explosive  24  is detonated, the force of the detonation collapses the liner  22  and ejects it from one end of the charge  8  at very high velocity in a pattern called a “jet”  12 . The jet  12  perforates the casing and cement lining the wellbore  1  and creates a perforation  10  that extends into the surrounding formation  2 . 
   Shaped charges  8  also include a boss  20  protruding outward from the case  18  perpendicular to the axis A SC  of the case  18 . The boss  20  fully circumscribes the case  18  outer circumference. A perspective example of the gun strip  16  is provided in  FIG. 3  illustrating holes  28  formed through the gun strip  16  for receiving shaped charges  8  therein. The shaped charge  8  is inserted into the hole  28  until the boss  20 , whose outer diameter extends past the hole  28  outer diameter, contacts the outer surface of the gun strip  16 . Thus the boss  20  supports the shaped charge  8  in the gun strip  16  and vertically aligns the shaped charge  8  in the gun strip  16 . However, because the boss  20  is generally planar but the gun strip  16  outer diameter is curvilinear, the entire radius of the boss  20  does not lie above the hole  28 , but instead the hole  28  outer diameter is shaped to accommodate the shaped charge  8  placement. Accordingly although the shaped charge  8  outer diameter is substantially circular, the typical gun tube  16  hole  28  is not. This can be a problem in certain perforating guns employing a “high density” shot pattern. For example,  FIG. 3  illustrates an example of a gun tube  16  having high density shot pattern wherein adjacent holes  28  are sufficiently close that a web portion  30  between the holes  28  is too narrow to provide adequate structural support. 
   SUMMARY OF INVENTION 
   Disclosed herein is a perforating gun with a first shaped charge having a charge case, a liner, and explosive disposed between the liner and charge case. The perforating gun also includes an annular gun strip, a first boss on the charge case partially circumscribing the charge case outer periphery, a first hole formed through the side of the gun strip, and a landing on the gun strip and adjacent the hole formed to mateingly cooperate with the first boss. A second boss may optionally be provided on the charge case partially circumscribing the charge case outer periphery. The respective ends of the first and second boss may, in one embodiment, be substantially equidistant from one another. The lengths of the first and second boss may range from about 10% to about 30% of the charge case circumference. The length of the first and second boss may be about 20%. A second landing may be included on the gun strip and adjacent the hole formed to mateingly cooperate with the second boss. The charge case has an open end and a closed end, and an axis extending through the open and closed ends, the charge case being substantially symmetric about the axis. The gun strip may include a second hole in the gun strip adjacent to the first hole, a web defined by the portion of the gun strip body between the first hole and the second hole, a landing on the gun strip on the second hole perimeter, the landings being disposed away from the web. The web dimensions comprise structural integrity sufficient for a high density perforating gun. The perforating gun may further comprise a detonation cord coaxially extending through the gun strip, and a cord slot formed on the bottom end of the charge case formed for attachment with the detonation cord, the first boss and landing formed to align the cord slot with the detonation cord when inserted into the hole. The landing may comprise notches configured to mate with the respective ends of the first boss and a planar section between the notches. 
   Also disclosed herein is a method of forming a wellbore perforating device comprising, (a) providing a shaped charge with a first boss that partially circumscribes the shaped charge outer periphery, (b) providing a gun strip with a first hole and a first landing formed adjacent the hole edge, the landing configured to cooperatively mate with the first boss, (c) inserting the shaped charge into the gun strip hole, and (d) cooperatively mating the first boss with the first landing. The shaped charge in the method may further include a second boss partially circumscribing the shaped charge outer periphery and the gun strip may further include a second landing configured to cooperatively mate with the first boss, the method further comprising cooperatively mating the second boss with the second landing. The perforating device may further comprise a second shaped charge having a boss partially circumscribing its outer periphery, a second hole, a landing formed adjacent the second hole configured to cooperatively mate with the boss of the second shaped charge, and a web portion defined between the first and second hole, wherein the landings are disposed away from the web. The web dimensions are sufficient for use in a high density perforating gun application. The method may further comprise deploying the perforating device within a wellbore and initiating detonation of the shaped charges. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     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: 
       FIG. 1  is partial cutaway side view of a prior art perforating system in a wellbore. 
       FIG. 2  illustrates a cutaway view of a shaped charge. 
       FIG. 3  is a perspective view of a gun strip with holes for shaped charges. 
       FIG. 4  is a side view of an embodiment of shaped charge case. 
       FIG. 5  is an overhead view of an embodiment of shaped charge case. 
       FIG. 6  is a perspective view of a gun tube formed to receive a shaped charge case formed in accordance with the present disclosure. 
       FIGS. 7 and 8  are respectively perspective and axial views of an embodiment of a gun strip with shaped charges. 
   

   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 
   The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. This invention may, however, be embodied 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 the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. For the convenience in referring to the accompanying figures, directional terms are used for reference and illustration only. For example, the directional terms such as “upper”, “lower”, “above”, “below”, and the like are being used to illustrate a relational location. 
   It is to be understood that the invention 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 of the invention 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 invention is therefore to be limited only by the scope of the appended claims. 
     FIG. 4  is a side view of an embodiment of a charge case  32  for use in a shape charge of a perforating system. The case body  34  is a container-like structure having a bottom  33  sloping upward with respect to the axis A x  of the charge case  32 . The charge case  32  as shown is substantially symmetric about the axis A x . In the embodiment shown, the case  32  transitions into the upper portion  35  where the case  32  outer surface slope steepens. The upper portion  35  also has a profile oblique to the axis A x . Extending downward from the bottom portion  33  is a cord slot  36  having a pair of tabs  37 . The tabs  37  are configured to receive a detonating cord therebetween and are generally parallel with the axis A x  of the charge case  32 . 
   A crown portion  41  defines the portion of the case body  34  extending from the upper terminal end of the upper portion  35 . The upper most portion of the crown portion  41  defines the opening of the charge case  32  and lies in a plain that is largely perpendicular to the axis A x . In the embodiment shown, the crown portion  41  has an outer surface extending generally parallel with the axis A x . A boss element  38  is provided on the outer surface of the crown portion  41 . The boss element  38  is an elongated member whose elongate section partially circumscribes a portion of the outer peripheral radius of the crown portion  41 , and thus partially circumscribes the outer circumference of the charge case  32 . In the embodiment shown, the boss element  38  cross section is largely rectangular and extends outward from the outer radius of the charge case  32 . 
     FIG. 5  provides an overhead view looking along the axis A x  of the charge case  32  and through its opening. In this embodiment, two boss elements ( 38 ,  39 ) extend outward from the outer radius of the charge case  32  and along a portion of its outer radius. The boss elements ( 38 ,  39 ) may each extend from about 10% to about 30% of the charge case  32  circumference. In one embodiment, the bosses ( 38 ,  39 ) each extend approximately 20% of the charge case  32  circumference. 
     FIG. 6  illustrates a perspective view of an example of a gun strip  40  combineable with the charge cases  32  of  FIGS. 4 and 5 . The gun strip  40  illustrated is an annular member provided with holes  42  configured to receive the charge cases  32  therein. Landings ( 43 ,  48 ) are formed in the gun strip  40  on the gun strip  40  body adjacent the outer circumference of the holes  42 . In the embodiment of  FIG. 6 , the landings ( 43 ,  48 ) comprises notches ( 44 ,  45 ,  46 ,  47 ) configured to cooperatively mate with respective ends of the bosses ( 38 ,  39 ). The landings ( 43 ,  48 ) may also optionally provide a planar surface (rather than the angular outer surface of the gun strip  40 ) in the region of the gun strip  40  between the notches ( 45 ,  45 , and  46 ,  47 ). The cooperative mating between the bosses ( 38 ,  39 ) and the landings ( 43 ,  48 ) orients the shape charge  32  within the gun strip  40  without mechanically affixing the charge case  32  to the gun strip  40 . The cooperative mating restricts charge case  32  radial movement within the holes such that the charge case is maintained in alignment until it is mechanically affixed or otherwise fastened to the gun strip  40 . 
   Provided in  FIG. 7  is a perspective view of the charge cases  32  formed in accordance with the present disclosure and positioned within a gun strip  40 . As shown, the ends of the boss  38  are received within the notches ( 44 ,  45 ) of the landing  43 . The cooperative mating between the boss  38  and boss  39  and the landings ( 43 ,  48 ) provides a novel manner of seating the charge case  32  within the gun strip  40 . 
   For the purposes of discussion herein, a high density shot typically has at least 10-12 shaped charges per linear foot of perforating gun. In some instances however high density shots may include guns having as few as 6 shots per linear foot. Referring again to  FIG. 6 , the gun strip  40  provides an example of a high density configuration. As is the case in high density guns, first and second holes ( 42 ,  49 ) are disposed so that their respective peripheries are proximate to one another thereby leaving a relatively narrow strip of gun strip material between the holes. The placement of these holes ( 42 ,  49 ) defines a web  50  which comprises the gun body material between these two adjacent holes ( 42 ,  49 ). As noted above, certain high density configurations result in a web lacking sufficient structural integrity to support charges within the particular gun strip. However, another advantage of the charge case disclosed herein is realized by configuring the holes such that the respective landings are disposed on the hole periphery away from the web  50 . In the embodiment of  FIG. 6 , the landings of the holes ( 42 ,  49 ) are disposed at roughly 90° or more from the midpoint of the web  50 . Since the bosses ( 38 ,  39 ) are aligned with the landings ( 43 ,  48 ) the bosses ( 38 ,  39 ) are therefore also away from the web  50 . Accordingly, use of the embodiments described herein results in a gun tube having web dimensions producing sufficient structural integrity, even in the case of a high density configuration. 
     FIG. 8  provides a view looking along the axis of the gun strip  40  having multiple charge casings  32  disposed therein. In this view, a detonation cord  52  is shown coupled with the tabs  37  and cord slot  36  of the respective charge casings  32 . The respective cord slots  36  of each charge case  32  are aligned for receiving the detonation cord  52  therethrough. Aligning the cord slots  36  to readily receive the detonation cord greatly increases the ease of attaching the perforating cord  52  to each charge case  32 , thereby significantly reducing the time required to assemble a perforating gun. The alignment of each of the cord slots  36  of the charge casings  32  in the gun strip  40  is accomplished by an appropriate placement of the boss of each charge case, and the landings in which the charge case  32  is cooperatively mated with. The cord slot  36  alignment described above can be accomplished in conjunction with forming a high density perforating gun and can also be accomplished for charge cases used in applications that are not high density. Thus use of the boss and/or landings described herein is useful for forming high density perforating guns and for pre-aligning charge cases so their respective cord slots may readily receive a detonation cord. 
   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. 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.