Abstract:
A shaped charge assembly for use in a perforating gun that further comprises a charge carrier, and gun housing. The charge carrier substantially encapsulates the closed portion of the shaped charge and extends from the outer periphery of the shaped charge to the inner diameter of the associated gun housing. Encapsulating the shaped charge substantially reduces the introduction of debris into the wellbore resulting from detonation of the perforating gun shaped charges. The charge carrier can include a multiplicity of shaped charges therein.

Description:
RELATED APPLICATIONS 
     This application claims priority from co-pending U.S. Provisional Application No. 60/730,624, filed Oct. 27, 2005, the full disclosure of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to the field of oil and gas production. More specifically, the present invention relates to a non-frangible shaped charge system. Yet more specifically, the present invention relates to a perforating gun system that after detonation of its associated shaped charges minimizes wellbore gun fragments produced during well perforations. 
     2. Description of Related 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, 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. 
     Perforating systems typically comprise one or more perforating guns strung together, these strings of guns can sometimes surpass a thousand feet of perforating length. 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. 
     Due to the high force caused by the explosive, the shaped charge and its associated components often shatter into many fragments that exit the perforating gun into the fluids within the wellbore. 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. Therefore, there exists a need for an apparatus and a method for conducting perforating operations that can significantly reduce fragmentation of shaped charges. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention involves a shaped charge assembly comprising, a gun housing, a shaped charge housed within the gun housing, and a charge carrier disposed in the space between the gun housing and the shaped charge. The charge carrier fills at least a portion of the volume between the outer periphery of the shaped charge and the gun housing. The combined volume of the charge carrier and the shaped charge can range from about 20% to about 80% of the total empty volume of the gun housing inner space; the free volume within the gun housing can range from about 80% to about 20% of the total empty volume of the gun housing inner space. Optionally, the combined volume of the charge carrier and the shaped charge can be about 65% of the total empty volume of the gun housing inner space. In the optional embodiment, the free volume within the gun housing can be about 35% of the total empty volume of the gun housing inner space. 
     In one embodiment of the present device, the shaped charge has an open end, and the shaped charge assembly further comprise a gap in the region between the open end of the shaped charge and the gun housing. An explosive can be disposed within the shaped charge, wherein the charge carrier maintains the structural integrity of the shaped charge upon detonation of the explosive. Moreover, the shaped charge assembly can further comprise a multiplicity of shaped charges. A multiplicity of bores may be disposed on the charge carrier formed to receive the multiplicity of shaped charges. The bores may be arranged perpendicular to the axis of the charge carrier and disposed at substantially the same radial location about the axis of the charge carrier. In another embodiment, each bore may be arranged perpendicular to the axis of the charge carrier and spaced about the axis of the charge carrier at multiple radial locations. Also, the bores may form a spiral pattern along the outer surface of the charge carrier. 
     Each shaped charges may have an open end and wherein each shaped charge assembly may further comprise a gap in the region between each of the open ends and the gun housing. An explosive may be further included within each shaped charge, wherein the charge carrier maintains the structural integrity of each shaped charge upon detonation of the explosives. 
     An orienting weight can optionally be included with the charge carrier. Also, the charge carrier may comprise at least two modular segments. The modular segments may be configured in a phased arrangement. In one alternative embodiment of the shaped charge assembly, the charge carrier may be comprised of interconnected strands. 
     Also included with the present disclosure is a shaped charge assembly comprising, a gun housing, a shaped charge housed within the gun housing where the shaped charge includes a casing, a liner within the casing, and explosive between the casing and the liner. This embodiment of a shaped charge assembly includes a charge carrier disposed in the space between the gun housing and the shaped charge, wherein the charge carrier circumscribes the outer surface of the casing and minimizes fragmentation during detonation of the explosive. Here the combined volume of the charge carrier and the shaped charge can range from about 20% to about 80% of the total empty volume of the gun housing inner space and the free volume within the gun housing may range from about 80% to about 20% of the total empty volume of the gun housing inner space. Optionally in this embodiment, the combined volume of the charge carrier and the shaped charge may be about 65% of the total empty volume of the gun housing inner space and the free volume within the gun housing can be about 35% of the total empty volume of the gun housing inner space. The shaped charges of this embodiment can be a phased arrangement, further the shaped charge assembly may additionally comprise an orienting weight. 
     The charge carrier may optionally comprise at least two modular segments and can also be comprised of interconnected strands. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  depicts a perspective cross sectional view of one embodiment of a charge carrier. 
         FIG. 2  illustrates a perspective view of one embodiment of the present invention. 
         FIGS. 3   a  and  3   b  portray perspective views of embodiments of a charge carrier. 
         FIGS. 4   a  and  4   b  depict alternative embodiments of the structure of a charge carrier. 
         FIG. 5  illustrates a segmented embodiment of a charge carrier. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings herein,  FIG. 1  depicts a cross sectional view of one embodiment of the present invention in a perspective aspect. As shown, this embodiment comprises a gun housing  10 , a shaped charge  18 , a charge carrier  16 , and an optional orienting weight  14 . As is known, strategic placement of the orienting weight  14  in combination with positioning the shaped charges  18  in a predetermined arrangement, can orient the perforating system  6  within the wellbore thereby creating desired perforations within the wellbore. In the embodiment of  FIG. 1 , the gun housing  10  shown is an elongated member having a substantially cylindrical cross section. For the purposes of the disclosure herein, the gun housing  10  can include both a gun body or a gun tube, or any other structure capable of holding, housing, and/or positioning shaped charges  18  therein. However the shape of the gun housing  10  is not limited to cylindrical cross sections, but can include other shapes, such as ones having multifaceted planar sides as hexagons, octagons, and the like. Alternatively, a gun tube (not shown) may be included with the shaped charge assembly and housed coaxially within the inner radius of the gun housing  10 . 
     As shown, the shaped charge  18  is housed within the inner radius of the gun housing  10  and oriented perpendicular to the length of the gun housing  10 . The shaped charge  18  comprises a charge casing  34 , explosive  32 , and a liner  30 . The device disclosed herein can be used with any type of shaped charge  18 , either “off-the-shelf” or manufactured to specific size, shape, or performance specifications. The charge casing  34  is comprised of a base section  36  and walls  38 . The walls  38  form a generally tube-like section extending up and away from the outer circumference of the base section  36 . The space between the walls  38  and the base section  36  is formed to receive the explosive  32  and the liner  30 . Preferably the base section  36  has a bowl-shaped inner periphery such that its inner and outer surfaces curve parallel to the axis  42  of the base section  36  as the surfaces travel away from the axis  42 . The walls  38  and the base section  36  meet approximately at the point where the inner surface of the charge casing  34  is substantially parallel to the axis  42 . The base section  36  further includes a booster charge  20  for initiation of the explosive  32  within the charge casing  34 . 
     The shaped charge  18  of  FIG. 1  is oriented within the gun housing  10  such that the open end  19  of the charge casing  34  points to the optional scallop  12  that is formed on the outer surface of the gun housing  10 . As is known, the presence of the scallop  12  reduces the amount of gun housing material that the detonating charge must penetrate, thereby enhancing the performance of the shaped charge perforation penetration. 
     The charge carrier  16  of the embodiment of  FIG. 1  occupies at least a portion of the space between the inner surface of the gun housing  10  and the charge casing  34 . Also, the charge carrier  16  substantially circumscribes the outer surface of the charge casing  34  at its base and along its length, but the charge carrier does not extend into the region above the open end  19  of the shaped charge. A gap  21  exists between the open end  19  of the shaped charge  18  and the inner radius of the gun housing  10  to enable formation of the shaped charge jet as it exits the shaped charge  18 . Additionally, in the embodiments that do not include an orienting weight  14 , the charge carrier  16  could occupy the space where the orienting weight  14  resides. 
     The free volume of the embodiment of  FIG. 1 , i.e. the volume within the inner circumference of the gun housing  10  not occupied by the shaped charge  18 , charge carrier  16 , or orienting weight  14 , can range from about 20% to about 80% of the total empty volume of the gun housing inner space. The free volume of the perforating system  6  can be occupied by ambient air, pressurized air, or some other gas at ambient or pressurized conditions. The substance that occupies the free space is not limited to gases, but can include other low-density matter. The solid volume, i.e. the total volume of the charge carrier  16  and shaped charge  18  (and optionally the orienting weight  14 ), can occupy the remaining space within the gun housing  10 , and thus can range from about 80% to about 20% of the total empty volume of the gun housing inner space. 
     In one embodiment of the present device, the free space volume occupies around 35% of the total empty volume of the gun housing inner space. This embodiment thus provides for a volume of the charge carrier  16  and shaped charge  18  (and optionally the orienting weight  14 ) to be around 65% of the total empty volume of the gun housing inner space. These volume ratios of free space/solid volume are not dependent upon the number of shaped charges  18  within the charge carrier  16 , but are applicable to charge carriers  16  having any number of associated shaped charges  18 , even those having as little as one shaped charge  18 . 
     The charge carrier  16  should be capable of confining the shaped charge  18  during its detonation, thus the charge carrier material should have sufficient structural integrity to avoid being shattered or fragmented during operation. One criterion for choosing a proper material is to chose materials whose density exceeds 19 g/cc. Thus suitable materials include metals such as steel, aluminum, nickel, brass, copper, and other ductile metals to name but a few. The material selection is not limited to metals, but can also include sand, cementitious materials, water, wood, plastics, and polymeric materials. Moreover, the charge carrier  16  material need not be uniform, but can be comprised of a combination of two or more different types of materials. For example, the charge carrier  16  can be comprised of different strata of materials where the materials differ along its height. Also, high tensile bands (not shown) could be inserted within the bores  17  to provide a strengthening buffer around the shaped charges  18 , while the remaining portion of the charge carrier  16  could be of a lower strength and subsequently lower density than the bands. It should be pointed out that the charge carrier  16  need not be solid but instead could have a design with multiple voids formed therein. An example might be a substrate comprised of multiple strands or weblike links structurally interconnected. More specific examples include a honeycomb structure  16   a  as shown in  FIG. 4   a  and an accordion structure  16   b  as shown in  FIG. 4   b.    
     In the embodiment depicted in  FIG. 2  is shown in a perspective exploded view. In  FIG. 2  the charge carrier  16  is shown having bores  17  formed therein perpendicular to the axis  28  of the charge carrier  16 . The bores  17  extend through the charge carrier  16  and are profiled to match the profile of the walls  38  and base section  36  of the charge casing  34 . Accordingly the bores  17  engagingly receive the shaped charges  18  within their inner periphery. While the bores  17  shown are aligned at roughly the same radial location on the charge carrier  16 , the bores  17  can be formed at any radial location on the carrier  16 . As with many perforating systems, the shaped charges  18  can be “phased” such that they are positioned within the perforating system  6  to detonate at multiple radial locations around the charge carrier  16 . The specific shaped charge phasing is dependent on the particular application of the perforating system  6  and thus many phasing scenarios are available. Also shown in  FIG. 2  included with the perforating system  6  are connectors  22  for connecting the adjacent segments of the perforating system  6 . Also shown is a stop ring  24  that is used in securing the charge carrier  16  into a proper orientation so that the shaped charges  18  are aligned with their respective scallops  12 . 
     Adjacent bores  17  must have a sufficient amount of charge carrier material between them for withstanding the detonation force of the explosive to thereby prevent fragmentation of the charge carrier  16 . The distance between adjacent bores  17  depends on the type of material used in forming the charge carrier  16 . A charge carrier  16  formed from materials having low yield strength will require more material between adjacent bores  17  than a carrier  16  made from a material having high yield strength. Those skilled in the art can determine the required distance with regard to each specific material used in manufacturing the charge carrier  16  without undue experimentation. Likewise, a certain amount of charge carrier  16  material must be present between the end of the charge carrier  16  and the outermost shaped charge  18  for bolstering the resiliency of the charge carrier end to prevent fragmentation during detonation of the shaped charge  18 . How much material is required depends on the physical properties of the material—this also can be determined by those skilled in the art. 
     Impedance barriers  26  can be formed on the charge carrier  16  between each bore  17 . The impedance barriers  26  are troughs cut or formed perpendicular to the axis  28  of the charge carrier  26 . These troughs can simply be air filled voids existing between the bores  17 , or can be filled with shock absorbing material such as cotton, rubber, polymeric compositions, plastics, cork, felt, or like materials. The existence of the impedance barriers  26  serves to eliminate shock wave interference that can be transmitted from one shaped charge  18  to an adjacent shaped charge  18 . 
     Additional embodiments of the charge carrier ( 16   a ,  16   b ) are illustrated in  FIGS. 3   a  and  3   b . With respect to  FIG. 3   a , the charge carrier  16   a  has a hexagonal cross section where the outer periphery is comprised of planar sides  15  connected at their respective ends. Bores  17  are formed within the sides  15 , and can be placed in any pattern depending on the design requirements of the particular perforating system  6 . Also, the embodiment of  FIG. 3   a  is not limited to six sided members, but can include any number of planar sides  15 . With regard now to the embodiment of  FIG. 3   b , here a charge carrier  16   b  is illustrated with associated bores  17  arranged in a spiral pattern along its length. Other slot patterns include a helical arrangement, multiple spirals, staggered, high density, or any other know known or later developed slot arrangement. 
       FIG. 5  illustrates one embodiment of a charge carrier  16   a  comprised of modular segments ( 42   a ,  42   b ,  42   c ). Here the segments ( 42   a ,  42   b ,  42   c ) each have a bore  17   a  (shown in a dashed outline) formed through its upper face  44 . As shown, each bore  17   a  has a shaped charge  18  with charge casing  34  disposed within. The lateral sides  46  of each segment ( 42   a ,  42   b ,  42   c ) are curved and formed to fit inside of a gun tube or gun body. The distal sides  48  of the segments ( 42   a ,  42   b ,  42   c ) are generally planar. Each segment is preferably affixed to each adjacent segment either by pins (not shown), welding, or any other type of fastening means suitable for securing the segments. Although the segments ( 42   a ,  42   b ,  42   c ) of  FIG. 5  are shown in a phased configuration, the segments ( 42   a ,  42   b ,  42   c ) can be aligned such that their respective shaped charges  18  could be fired in a straight line. It should be pointed out that the volume values discussed above are applicable to each individual segment, or the segments as a whole. For example, the combined volume of the segment  42   a  and its corresponding shaped charge  18  can range from about 80% to about 20% of the total empty volume of the inner space of the portion of the gun housing occupied by the segment  42   a . Accordingly the free volume that occupies the space between the segment  42   a  and its corresponding shaped charge  18  thus ranges from about 20% to about 80% of the total empty volume of the inner space of the portion of the gun housing occupied by the segment  42   a . Similarly, the combined volume of all segments ( 42   a ,  42   b ,  42   c ) and their respective shaped charges  18  can occupy from about 80% to about 20% of the total empty volume of the inner space of the portion of the gun housing occupied by these segments ( 42   a ,  42   b ,  42   c ). Thus resulting in a free volume between the segments ( 42   a ,  42   b ,  42   c ) and their corresponding shaped charges  18  to range from about 20% to about 80% of the total empty volume of the inner space of the portion of the gun housing occupied by the segment  42   a . Moreover, the embodiment of  FIG. 5  includes a solid volume to free volume ratio of 65% to 35%, for individual segments and when combined as a whole. 
     While detonation of the shaped charges  18  of the perforating system  6  disclosed herein results in some damage to the component parts, the fragmented parts are contained within the gun housing  10 . Accordingly when the perforating system  6  is retrieved from the wellbore after use, either no debris, or a negligible amount of debris, remains within the borehole. Thus use of the present device substantially reduces the threat of clogging due to fractured component per. 
     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, the invention described herein is applicable to any shaped charge phasing as well as any density of shaped charge. Moreover, the invention can be utilized with any size of perforating gun. 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.