Patent Publication Number: US-11649703-B2

Title: Preferential fragmentation of charge case during perforating

Description:
BACKGROUND 
     After drilling the section of a subterranean wellbore that traverses a formation, individual lengths of relatively large diameter metal tubulars are typically secured together to form a casing string that is positioned within the wellbore. This casing string increases the integrity of the wellbore and provides a path for producing fluids from the producing intervals to the surface. Conventionally, the casing string is cemented within the wellbore. To produce fluids into the casing string, hydraulic opening or perforation must be made through the casing string, the cement and a short distance into the formation. 
     Perforations are created by detonating a series of shaped charges located within the casing string that are positioned adjacent to the formation. One or more charge carriers are loaded with shaped charges that are connected with a detonating device, such as detonating cord. The charge carriers are then connected within a tool string that is lowered into the cased wellbore at the end of a conveyance such as a tubing string, wireline, slickline, or coiled tubing. The charge carriers are positioned in the wellbore with the shaped charges adjacent to the formation to be perforated. Upon detonation, each shaped charge creates a jet that blasts through a scallop or recess in the carrier. Each jet creates a hydraulic opening through the casing and the cement and enters the formation forming a perforation. 
     When the shaped charges are detonated, numerous metal fragments are created due to, among other things, the disintegration of the metal casings of the shaped charges. These fragments often fall out or are blown out of the holes created in the carrier. As such, these fragments become debris that is left behind in the wellbore. It has been found that this debris can obstruct the passage of tools through the casing during subsequent operations. This is particularly problematic in the long production zones that are perforated in horizontal wells as the debris simply piles up on the lower side of such wells. The debris can also get trapped in pumps, impellers, and other down hole tools causing failures in subsequent operation and non-productive time (NPT). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These drawings illustrate certain aspects of some of the embodiments of the present disclosure and should not be used to limit or define the method. 
         FIG.  1    is an elevation view of a wellsite as an example environment in which a perforating gun and method according to this disclosure may be implemented. 
         FIG.  2    is a perspective view of one example of a perforation gun assembly including a charge carrier for mounting a plurality of shaped charges at predetermined firing orientations. 
         FIG.  3    is a perspective view of the shaped charge according to one configuration wherein a plurality of voids are embodied as holes formed in the parent material of the charge case, and a plurality of inclusions comprise the remaining parent material between the voids. 
         FIG.  4    is a cross-sectional side view of the shaped charge having the charge case configuration of  FIG.  3   . 
         FIG.  5    is a top view of the charge case detailing the example hole configuration of  FIG.  4   . 
         FIG.  6    is an enlarged view of the cross-sectional portion of the shaped charge generally indicated in  FIG.  4   . 
         FIG.  7    is an enlarged view of the cross-sectional portion of the shaped charge with an alternative configuration of holes. 
         FIG.  8    is a perspective view of the shaped charge according to another example configuration wherein the holes are radially staggered along the periphery of the charge case. 
         FIG.  9    is a top view of the charge case according to the  FIG.  8    configuration. 
         FIG.  10    is a perspective view of the shaped charge according to another example configuration having holes that are non-circular. 
         FIG.  11 A  is a diagram of a spallation of a charge case at time 0. 
         FIG.  11 B  is a diagram of the spallation of the charge case at time 6 microseconds. 
         FIG.  12    is a top view of an alternative example configuration of a charge case where pieces of a hardened material are embedded within a parent material of the charge case. 
         FIG.  13    is a top view of an alternative example configuration wherein the inclusions comprise localized regions where the parent material has had its physical properties altered to provide stress concentrations for the purpose of controlled fragmentation. 
         FIG.  14    is a chart summarizing the fragments of flange (rim) debris of a charge case without any voids, over a number of experimental runs. 
         FIG.  15    is a chart summarizing the fragments of flange (rim) debris of a charge case having the arrangement of voids generally depicted in  FIG.  3   . 
     
    
    
     DETAILED DESCRIPTION 
     Disclosed herein are perforating apparatus and methods for preferential fragmentation of charge cases during perforating. The various apparatus may include a perforating gun or system, an assembly of the perforating gun or system, and may have a charge case that provides preferential fragmentation according to this disclosure. To the user, certain features of the perforating system may look and function similar to other systems, but with internal differences in the charge case. By incorporating inclusions and voids into the charge case, a perforating operation may create controlled debris, and leave acceptable sized material in the well bore that can easily pass through pumps, impellers and other down hole tools. The voids and inclusions may be concentrated along the periphery where larger fragments are more likely to occur in a conventional charge case. In some examples, the charge case includes a mounting flange on its periphery for mounting to a charge carrier. Voids may be formed in the vicinity of the mounting flange in an effort to minimize or eliminate fragments larger than a target rim debris length. 
     The number and size of fragments of a charge case above a certain target rim debris length may accordingly be reduced or eliminated so that any fragments do not appreciably interfere with downhole equipment. Broadly, the preferential fragmentation is achieved by forming the charge case with particular arrangement of voids and inclusions around the periphery. These voids and inclusions may be introduced during manufacturing using cost-effective manufacturing operations. The voids can be created, in at least some embodiments, by forming holes in the flange such as by machining, stamping, forging, casting, or other suitable manufacturing processes. The voids in other embodiments can be created by displacing the parent material of the charge case with a foreign (e.g. hardened) material. 
     Inclusions in other embodiments can be created by a method of material processing that result in a micro-effected area that results in the controlled condition of the charge case rim. Various methods of heat treatment to provide hardening or embrittlement are possible. Lasers, for example, are a suitable option, and may be the most practical option for high-volume shaped charge case manufacturing. A laser may be used for heat treating or etching of the surface to induce localized embrittlement of material that forms the preferred fragmentation of the charge case. 
       FIG.  1    is an elevation view of a wellsite  10  as an example environment in which a perforating gun and method according to this disclosure may be implemented. The wellsite  10  is depicted by way of example as an offshore wellsite. However, those of ordinary skill in the art will appreciate that aspects of this disclosure are also well suited to use with other types of wellsites, including land-based oil and gas drilling and production. The offshore wellsite  10  includes a semi-submersible platform  12  centered over a submerged oil and gas formation  14  located below sea floor  16 . A subsea conduit  18  extends from a deck  20  of the semi-submersible platform  12  to a wellhead installation  22  that includes subsea blow-out preventers  24 . The platform  12  has a hoisting apparatus  26  and a derrick  28  for raising and lowering pipe strings such as work sting  30 . The work string  30  may be used as a conveyance for a perforating gun in this case, although any suitable conveyance may be used depending on the situation, such as a wireline, slick line, tubing string, or coiled tubing. 
     A wellbore  32  extends through the various earth strata of the formation  14 . The wellbore  32  may be drilled with any given wellbore path using directional drilling techniques as necessary, resulting in any number of wellbore sections that deviate from vertical. In this example, the wellbore  32  has a generally vertical portion from the sea floor  16  and a horizontal section below that. It should be noted, however, by those skilled in the art that the debris retention perforating guns of the present invention are equally well-suited for use in other well configurations including, but not limited to, inclined wells, wells with restrictions, non-deviated wells and the like. 
     A wellbore casing  34  is cemented within a wellbore  32  by cement  36 , which lines and reinforces the wellbore  32 . The tubular work string  30  may provide various tools involved in perforating, such as a plurality of perforating guns  38 , along with electrical power and signal communication pathways. To perforate the casing  34 , the work string  30  may be lowered through casing  34  until the perforating guns  38  are positioned as desired relative to the formation  14 . Thereafter, the shaped charges within the string of perforating guns  38  are sequentially fired, either in an uphole to downhole or a downhole to uphole direction. Upon detonation, the liners of the shaped charges form jets that create a spaced series of perforations extending outwardly through the casing  34 , cement  36  and into the formation  14 . These perforations allow fluid communication between the formation  14  and the wellbore  32 . 
     The work string  30  includes a retrievable packer  44  that may be sealingly engaged with casing  34  in vertical portion of the wellbore  32 . At the lower end of work string  30  is the gun string including the plurality of perforating guns  38 , a ported nipple  46  and a time domain fire device  48 . In the illustrated embodiment, perforating guns  38  are preferably internally oriented perforating guns which allow for increased reliability in orienting the shaped charges to shoot in the desired direction or directions. Examples of perforating gun components and assemblies thereof, including various shaped charge configurations for reducing fragments, are further disclosed below along with associated methods. 
       FIG.  2    is a perspective view of one example of a perforation gun assembly  100  including a charge carrier  110  for mounting a plurality of shaped charges  120  at predetermined firing orientations. The charge carrier  110  in this example includes a generally cylindrical structural tube having a plurality of mounting holes  112 , each for receiving one of the shaped charges  120 . Two of the shaped charges  120  are mounted to the charge carrier  110  in their respective mounting holes  112  in the figure. Another one of the shaped charges  120  on the left side of the figure is shown aligned for insertion into the respective mounting hole  112 , and its features are further referenced for purpose of discussion. 
     Each shape charge  120  includes a charge case  122  that can contain an explosive charge. Each charge case  122  has an initiation end  124  where a detonation cord may attach to detonate the explosive charge, and a discharge end  126  opposite the initiation end  124  where liner material is jetted when the explosive charge is detonated. The charge case  122  may be generally round, and regardless of shape, may define an axis  125  that passes centrally through the charge case  122  from the initiation end  124  to the discharge end  126 . The charge case  122  narrows toward the initiation end  124 , where it is received into the respective mounting hole  112  in the charge carrier  110 . The charge case  122  may be formed with a plurality of voids and inclusions on its periphery (not shown), examples of which are provided in subsequent figures and discussed below. 
     Each mounting hole  112  may receive one of the shaped charges  120 . However, not every mounting hole must be used in any given perforating operation. The selection of mounting holes in which to position a shaped charge  120  may depend, in part, on the desired firing pattern. The spacing of the mounting holes  112  can vary significantly according the firing pattern desired for a particular formation. It is common for the shaped charges  120  to be placed in an angular pattern; although, a single straight line of shaped charges  120  may be appropriate in some circumstances as well. The number of shaped charges  120  per linear foot of the charge carrier  110  is another criterion. It is common for a well engineer to specify between four to six charges per foot of charge carrier, for example. 
     In any given configuration of a perforating gun assembly according to this disclosure, a retention feature may be provided for each mounting hole that engages the charge case to retain the respective shaped charge received within the mounting hole. Such a retention feature may be any feature that engages the charge case on its periphery to retain the charge case withing the mounting hole. The retention feature may engage the charge case on its periphery near the discharge end. The retention feature may provide interference between the charge case and the mounting hole to prevent the charge case from coming out of the mounting hole, such as a tab on the charge carrier that engages a flange at the periphery. 
     One non-limiting example of a retention feature shown in the  FIG.  2    configuration includes one or more tabs  114  adjacent the mounting hole  112  that cooperate with a flange  128  on the periphery of the charge case  122 . More particularly, this example has two tabs  114  at the mounting hole  112  spaced at 180 degrees apart; however, any number of tabs  114  could be used at any of a variety of different angular spacings. The flange  128  projects radially outwardly from the periphery of the charge case  122  to provide a structure that can cooperate to secure the charge case  122  to the charge carrier  110 . The flange  128  also extends circumferentially along at least a portion of the periphery of the charge case  122 , and is interrupted in this example by two clearance portions, embodied here as opposing flats  130  spaced at 180 degrees apart. An aspect of the retention feature in this example is that the charge case  122  may be inserted axially into the respective mounting hole  112  on the charge carrier  110 , oriented as shown, so the tabs  114  on the mounting hole initially clear the flange  128  at the flats  130 . Then, the charge case  122  may be rotated (e.g., 90 degrees) so that the flange  128  is captured behind the tabs  114 , thus retaining the charge case  122  by interfering with removal of the charge case  122  from that mounting hole  112 . A detonation cord may then be coupled to the charge case at the initiation end  124 . This can reduce the likelihood of the charge case  122  rotating to a position where the tabs  114  and flats  130  are again adjacent. 
     In any given configuration, the periphery of the charge case  122  may be formed with a plurality of inclusions of a material interspersed with a plurality of voids of that material. Different example configurations of these inclusions and voids are shown in subsequent figures as discussed below. In some embodiments, the material may be a parent material of the charge case  122 , and the voids may be holes formed in the charge case. In other embodiments the voids may be particles of another material that displace the parent material. Generally, these inclusions and voids may cause the charge case to preferentially fragment so that the perforating operation creates controlled debris, and leaves acceptable sized material in the well bore that can easily pass through pumps, impellers and other down hole tools. To the observer, the perforating system may look and function in a way that is comparable to current systems in many respects, such as how the charges may be electrically connected within a perforating system and fired, and their explosive capacities. 
       FIG.  3    is a perspective view of the shaped charge  120  according to one configuration wherein a plurality of voids are embodied as holes  132  formed in the parent material of the charge case  122 , and a plurality of inclusions  134  comprise the remaining parent material between the voids (holes  132 ). The parent material may be a steel or other structural material suitable for containing an explosive charge and mounting to a charge carrier. For example, the overall shape of the charge case  122  with a generally round exterior  136  and a concave interior  138  (see  FIG.  4   ) for receiving an explosive material may initially be cast, stamped, forged, machined, or a combination thereof, from the parent material. The charge case  122  also includes an upper ridge  140 , which is radially inward of the flange  128  and extends axially beyond the flange  128  toward the discharge end  126  of the charge case  122 . 
     Certain features of the charge case  122  such as the flange  128  and/or holes  132  may be formed in the same manufacturing step of forming the overall round, concave shape of the charge case  122  or from separate manufacturing steps. For example, although it may be possible to form the flange  128  and/or the holes  132  on the periphery of the charge case  122  by an initial casting or forging, the flange  128  and the holes  132  more typically may be formed in a subsequent manufacturing step such as by machining them into the charge case  122 . 
     The placement, orientation, geometry, and other aspects of the holes  132  in combination with other aspects of the charge case  122  may be selected to facilitate preferential fragmentation of the charge case  122  upon detonation of the shaped charge. The holes  132  in this example are arranged in a single ring of holes that are radially equidistant from the central axis  125  of the charge case  122 . The holes  132  extend axially, parallel with the central axis  125  of the charge case  122 . The holes clip at least a portion of the upper ridge  140  in this example, as well as extending into the flange  128 . Thus, the holes  132  serve as discontinuities in the structure of both the flange  128  and the upper ridge  140 . This facilitates preferential fragmentation of the charge case on the periphery in the vicinity of the flange  128  and upper ridge  140 , and especially at the discharge end  126  of the charge case  122  where larger fragments may otherwise occur. Toward the detonation end  124 , the charge case  122  may fragment into sufficiently large particles, because of the case thickness and mass that these larger particles stay in the gun after detonation. The flange  128  near the discharge end breaks up into smaller particles that can fall out of the gun but, without the arrangements of inclusions and voids disclosed herein, may still be large enough to cause issues as they pass through pumps, impellers and other down hole tools. Therefore, the inclusions and voids in the case help create extra-small case debris that avoids or at least reduces such issues. 
       FIG.  4    is a cross-sectional side view of the shaped charge  120  having the charge case configuration of  FIG.  3   . A shaped explosive charge  50  is disposed within the concave interior  138  of the charge case  122 . Within the concave interior  138 , there is also a booster  52  at the initiation end  124 . The booster  52  is generally configured to aid in transferring the explosive detonation from a detonating cord  54  to the shaped explosive charge  50 . The booster  52  may be triggered by the detonating cord  54  at the detonation end  124 . A passageway may be formed in a base  142  of the charge case  122  for receiving the detonating cord  54  and retaining the detonating cord  54  in a configuration for passing the explosive detonation from the detonating cord  54  to the booster  52  and to the shaped explosive  50  within the charge case  122 . A liner  56  is disposed within the charge case  122  over the explosive charge  50 . 
       FIG.  5    is a top view of the charge case  122  detailing the example hole configuration of  FIG.  4   . There are a plurality of holes  132  of substantially equal circumferential spacing from each other along the periphery of the charge case  122 . Each hole  132  is at substantially the same radius “R” from the central axis  125  of the charge case  122 . In this example, the radius “R” positions each hole  132  so that it overlaps with the ridge  140  and the flange  128 . The diameter of the holes  132  extends outside the flats  130  of the opposing portions of the flange  128 . For evenly spaced holes  132 , the center-to-center arc length between holes can be calculated or estimated, such as by 2πR divided by the number of holes  132 . The arc length of material between holes  132  (which is less than the center-to-center arc length) can represent the length of the material inclusion  134  between adjacent holes  132 . In one or more examples, an angular spacing of the voids (in this case, holes  132 ) along the periphery is between 65 to 135% of a target rim debris length in response to detonation of the shaped charge. In one or more examples, the target rim debris length is less than about 10 mm. In other examples, the target rim debris length is less than about 10 mm. In some examples, the voids and inclusion are configured so that the charge case  122  fragments into pieces of less than 10 mm virtually every time (e.g., in at least 95% of detonations). 
       FIG.  6    is an enlarged view of the cross-sectional portion of the shaped charge  120  generally indicated at 5 in  FIG.  4   . The holes  132  penetrate the periphery of the charge case  122  at the discharge end  126 , including at least a portion of the flange  128 , in an axial direction. As drawn here, the holes  132  do not pass fully through the charge case  122  nor through the flange  128  in particular (i.e., the holes  132  are not through holes in this example). However, the holes  132  may alternatively pass through the flange  128  in one or more embodiments. The explosive charge  50  has a high point  58  within the charge case  122 , which in this example is a vertex or point at  58  where the explosive charge  50  meets the interior of the charge case  122 . The explosive charge  50  has a height “H” within the charge case  122  in an axial direction from high point  58  at the discharge end  126  to the initiation end. In at least one range of examples, the holes  132  on the periphery are to a depth of between 0.050 to 0.150 inches below the high point  58  that defines the height H of the explosive charge  50 . Thus, the holes  132  axially extend past/below the high point  58  of the explosive charge  50 , thus overlapping with the explosive charge  50 . This overlap helps to ensure that the explosive charge  50 , when detonated, will cause the charge case  122  to yield and preferentially fragment in the vicinity of the holes  132 . 
       FIG.  7    is an enlarged view of the cross-sectional portion of the shaped charge  120  with an alternative configuration of holes  232 . The holes  232  may have a similar placement with respect to the flange  128  as the holes  132  in  FIG.  5   , except the holes  232  in  FIG.  6    taper radially inwardly in an axial direction toward the initiation end of the charge case. An initial portion of each hole  232  is a generally cylindrical portion  233 . Below the cylindrical portion  233  is a tapered portion  234 , which converges at a lowermost point  235  in this example. This tapered portion  234 , which may be generally conical in the case of a circular cross-section hole, helps create a stress concentration to facilitate preferential yielding and fragmentation at the holes  232 . 
       FIG.  8    is a perspective view of the shaped charge  120  according to another example configuration wherein the holes  132  are radially staggered along the periphery of the charge case  122 . That is, instead of all of the holes  132  being at substantially the same radius from the center of the charge case  122 , the holes alternate between two different radiuses along the flange  128 . 
       FIG.  9    is a top view of the charge case according to the  FIG.  8    configuration. The radially staggered holes  132  can effectively be regarded as two sets of holes, including a first set of holes  132 A at a first radius R1 and a second set of holes  132 B at a second radius R2 that is less than the first radius. The spacing between holes  132  of the two sets of holes  132 A,  132 B is substantially uniform in this example. 
     In another example configuration, rather than uniformly spaced holes or other voids, the voids could instead comprise multiple clusters of voids, wherein a spacing between the voids in each cluster is less than a spacing between adjacent clusters. Also, there may be a trade-off between the number of holes and the size of the holes in terms of promoting fragmentation. The number of holes could be increased and the size of each hole correspondingly decreased to achieve a desired fragmentation upon detonation. 
       FIG.  10    is a perspective view of the shaped charge  120  according to another example configuration having holes  232  that are non-circular. In this example, the holes  232  are generally square or rectangular in cross-section. However, any of a variety of different non-circular hole shapes including linear, symmetrical and even asymmetrical hole shapes are possible. The non-circular holes  232  in this configuration have a similar hole placement to the round holes in  FIG.  3   . However, any non-circular hole shape can be combined with other features disclosed herein. For example, non-circular holes may be positioned in any of a variety of arrangements including but not limited to the radially-staggered hole arrangement in  FIG.  8   . Non-circular holes may also go only part way through the casing and not be through holes. Non-circular holes may also be tapered just as the circular holes are tapered in the example of  FIG.  7   . 
       FIGS.  11 A and  11 B  are diagrams of a spallation of a charge case at different points in time, at a selected time interval apart (e.g., 6 microseconds apart).  FIG.  11 A  shows the Density at time 0.  FIG.  11 B  shows the density at time 6 microseconds. These images of case density show the spallation of flange debris caused by the shock wave created by the detonation of the shaped explosive charge  50 . Without the presence of voids and or inclusions in the flange, larger flange debris is created. With the introduction of voids and or inclusions into the flange as discussed above, spalling flange material is broken up into small fragments due to the size and location of voids and or inclusions. 
     In the preceding example configurations illustrated in the figures, the voids of the material were holes in the parent material of the charge case, which is a structural material, and the inclusions of the material were the remaining structural parent material (e.g., steel) between the holes.  FIGS.  12  and  13    illustrate alternative embodiments wherein the charge case is formed of a parent material, and the parent material is interspersed with inclusions having properties dissimilar to that of the parent material (no holes or scoring are required). 
       FIG.  12    is a top view of an alternative example configuration of a charge case  222  where hardened particles  84  are embedded within a parent material  85  of the charge case  222 . The hardened particles  84  may be separately formed, foreign particles of a dissimilar material embedded in the parent material  85  during manufacturing (e.g. molding or casting). For example, the parent material  85  of the charge case may be a steel, and the particles of hardened material  84  could be a carbide, stone, polycrystalline diamond, or other particular other than the parent material that are embedded in the parent material  85  during forming of the charge case  222 . These pieces of hardened material  84  may displace the parent material, and create failure initiation sites during detonation. The hardened particles may have an irregular shape as depicted, although round hardened particles or other shapes are also within the scope of this disclosure. 
     The hardened material  84  may thus further contribute to fragmentation as compared with a hole or empty space in the parent material. The properties of the hardened material  84  differ from the parent material  85 . In some cases, the hardened material  84  be harder, stronger, and/or tougher than the parent material  85 , so that it deforms differently than the parent material  85  of the charge case in response to an applied stress. The hardened material  84  may also be irregular in shape. The hardened material properties and/or irregular shape may introduce a greater probability of discontinuities and stress concentrations along the periphery. This may still allow sufficient strength prior to detonation, but may facilitate fragmentation of the parent material of the charge case  222  upon detonation. 
       FIG.  13    is a top view of an alternative example of a charge case  322  wherein the inclusions comprise localized regions  86  and/or  87  where the parent material  85  has had its physical properties altered to provide stress concentrations for the purpose of controlled fragmentation. A laser  400  may be applied to the parent material  85  to create embrittled, high stress shapes (e.g., linear or other shapes) that may score the rim of the charge case to facilitate the desired fragmentation. The depicted shapes of localized regions  86  and/or  87  are just two example of local alteration of properties that could be present, e.g. a generally round shape like localized regions  86  or a scored/linear shape like localized regions  87 . In this example, the localized regions  86  and/or  87  are being formed on the parent material by laser-hardening using a laser  400 . (Other embrittlement methods may also be used without a laser.) The laser  400  may be used to form the localized regions  86  and/or  87  directly into the parent material  85  at spaced-apart locations as shown. The laser  40  may be used to form such a pattern of localized regions  86  and/or  87  along all or at least a portion of the flange  128 . 
       FIGS.  14  and  15    illustrate the efficacy of an embodiment wherein the voids comprise holes in the periphery of a charge case.  FIG.  14    is a chart summarizing the fragments of flange (“rim”) debris of a charge case without any voids, over multiple experimental runs tested and averaged. The number of fragments recovered was between 4 and 10 fragments per charge case. The average length of fragments recovered was about 15 mm.  FIG.  15    is a chart summarizing the fragments of flange (rim) debris of a charge case having the arrangement of holes generally depicted in  FIG.  3   . In this case, there were very few (0 to 1) fragments recovered. Of these, the average length was 12 mm in length. With the voids included in the charge case, flange debris mass was reduced by 89%. 
     Accordingly, the present disclosure may provide apparatus and method for preferential fragmentation of charge cases during perforating. The number of large fragments may be reduced or eliminated below a certain target rim debris length, with the rest of the charge case disintegrating into smaller or insignificant fragments. Broadly, the preferential fragmentation is achieved by selecting creating voids and inclusions around the periphery. The voids can be created by machining holes or displacing the parent material of the charge case with a foreign (e.g. hardened) material. The methods/systems/compositions/tools may include any of the various features disclosed herein, including one or more of the following statements. 
     Statement 1. A shaped charge for a downhole perforating gun, comprising: a charge case having an initiation end and a discharge end, the charge case including a periphery formed of a plurality of inclusions of a material interspersed with a plurality of voids of the material; an explosive charge disposed within the charge case; and a liner disposed within the charge case over the explosive charge. 
     Statement 2. The shaped charge of Statement 1, further comprising: a mounting flange along the periphery of the charge case for mounting the shaped charge on a charge carrier, wherein the voids are each at least partially on the flange. 
     Statement 3. The shaped charge of Statement 1 or 2, wherein the material is a parent material of the charge case, the voids of the material comprise holes formed on the periphery of the charge case, and the inclusions comprise the parent material remaining on the periphery of the charge case between the holes. 
     Statement 4. The shaped charge of Statement 3, wherein the holes penetrate the periphery of the charge case in an axial direction from the discharge end toward the initiation end without passing fully through the charge case. 
     Statement 5. The shaped charge of Statement 4, wherein the holes taper radially inwardly in an axial direction toward the initiation end of the charge case. 
     Statement 6. The shaped charge of Statement 4 or 5, wherein the holes have a non-circular cross-section. 
     Statement 7. The shaped charge of Statement 3, wherein the explosive charge has a height within the charge case in an axial direction from the initiation end toward the discharge end, and wherein the holes on the periphery are to a depth of between 0.050 to 0.150 inches below the height of the explosive charge. 
     Statement 8. The shaped charge of any of Statements 1 to 7, wherein an angular spacing of the voids along the periphery is between 65 to 135% of a target rim debris length in response to detonation of the shaped charge. 
     Statement 9. The shaped charge of any of Statements 1-8, wherein the target rim debris length upon detonation of the shaped charge is less than 15 mm. 
     Statement 10. The shaped charge of any of Statements 1-9, wherein the voids are radially staggered along the periphery. 
     Statement 11. The shaped charge of any of Statements 1-10, wherein the voids comprise multiple clusters of voids, wherein a spacing between the voids in each cluster is less than a spacing between adjacent clusters. 
     Statement 12. A shaped charge for a downhole perforating gun, comprising: 
     a charge case having an initiation end and a discharge end, the charge case including a periphery formed of a parent material interspersed with a plurality of inclusions of dissimilar material properties; an explosive charge disposed within the charge case; and a liner disposed within the charge case over the explosive charge. 
     Statement 13. The shaped charge of Statement 12, wherein the inclusions comprise a plurality of spaced apart hardened particles embedded in the parent material. 
     Statement 14. The shaped charge of Statement 12 or 13, wherein the inclusions comprise spaced apart regions of local hardening formed in the parent material. 
     Statement 15. A method of perforating a well, comprising: interspersing a plurality of inclusions and voids of a material along a periphery of a charge case for a shaped charge with an explosive material disposed within the charge case; disposing the shaped charge downhole in a well; and detonating the shaped charge to preferentially fragment the charge case along the periphery between the inclusions. 
     Statement 16. The method of Statement 15, further comprising: spacing the plurality of inclusions along the periphery such that the charge case is fragmented into multiple fragments of less than 15 mm each. 
     Statement 17. The method of Statement 15 or 16, further comprising: forming the voids of the material by forming holes in a parent material of the charge case, wherein the inclusion comprise a remaining parent material along the periphery of the charge case. 
     Statement 18. The method of any of Statement 15-17, further comprising: producing hydrocarbon fluid through one or more perforations in the well formed by detonating the shaped charge. 
     Statement 19. A perforating gun, comprising: a plurality of shaped charges each including a charge case having an initiation end, a discharge end, and a periphery formed of a plurality of inclusions of a material interspersed with a plurality of voids of the material; and a charge carrier having a plurality of mounting holes each for receiving one of the shaped charges, each mounting hole comprising a retention feature engaging the charge case for retaining the received shaped charge within the mounting hole. 
     Statement 20. The perforating gun of Statement 19, wherein each charge case further comprises a mounting flange along the periphery of the charge case, wherein the voids are each at least partially on the flange, and wherein the retention feature on the charge carrier retains the charge case by engagement with the flange. 
     Statement 21. The perforating gun of Statement 19 or 20, wherein an angular spacing of the voids along the periphery is between 65 to 135% of a target rim debris length in response to detonation of the shaped charge. 
     Statement 22. The perforating gun of any of Statements 19-21, wherein the explosive charge has a height within the charge case in an axial direction from the initiation end toward the discharge end, and wherein the voids comprise holes on the periphery that are to a depth of between 0.050 to 0.150 inches below the height of the explosive charge. 
     For the sake of brevity, only certain ranges are explicitly disclosed herein. However, ranges from any lower limit may be combined with any upper limit to recite a range not explicitly recited, as well as, ranges from any lower limit may be combined with any other lower limit to recite a range not explicitly recited, in the same way, ranges from any upper limit may be combined with any other upper limit to recite a range not explicitly recited. Additionally, whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range are specifically disclosed. In particular, every range of values (of the form, “from about a to about b,” or, equivalently, “from approximately a to b,” or, equivalently, “from approximately a-b”) disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values even if not explicitly recited. Thus, every point or individual value may serve as its own lower or upper limit combined with any other point or individual value or any other lower or upper limit, to recite a range not explicitly recited. 
     Therefore, the present embodiments are well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present embodiments may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Although individual embodiments are discussed, all combinations of each embodiment are contemplated and covered by the disclosure. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present disclosure.