Abstract:
The present invention provides an apparatus capable of influencing explosive energy during wellbore applications. In one embodiment, a cap or other interfering element may be arranged proximate to an explosive charge prior to detonation. The size and positioning of the element with respect to the explosive charge may be manipulated to achieve an optimum explosive orientation. A ring element having a bore therethrough may be utilized for directing the explosive energy of the charge upon detonation.

Description:
[0001]     This patent application claims priority on a U.S. provisional patent application entitled “Controlling Explosive Energy of Charges for Perforating Guns”, having a Ser. No. 60/594,057 and a filing date of Mar. 8, 2005. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates generally to perforating tools used in downhole applications, and more particularly to a device for controlling the use of explosive energy of an explosive charge in a perforating gun in a wellbore.  
       BACKGROUND OF THE INVENTION  
       [0003]     An apparatus, such as a perforating gun, may be lowered into a well and detonated to form fractures in the adjacent formation. After the perforating gun detonates, fluid typically flows into the well and to the surface via production tubing located inside the well.  
         [0004]     Typically, perforating guns (which include gun carriers and shaped charges mounted on or in the gun carriers) are lowered through tubing or other pipes to the desired well interval. Shaped charges carried in a perforating gun are often phased to fire in multiple directions around the circumference of the wellbore. When fired, shaped charges create perforating jets that form holes in surrounding casing as well as extend perforations into the surrounding formation.  
         [0005]     It may be necessary to control the amount of energy (e.g., reduce or focus) released by the explosive charge. For example, in some cases, it may be advantageous to rupture the hollow carrier (or other hollow chamber or sealed enclosure) without penetrating the surrounding casing and/or penetrating the well formation.  
       SUMMARY OF THE INVENTION  
       [0006]     Accordingly, the present invention provides an apparatus capable of influencing explosive energy during wellbore applications. In one embodiment, a cap or other interfering element may be arranged proximate to an explosive charge prior to detonation. The size and positioning of the element with respect to the explosive charge may be manipulated to achieve an optimum explosive orientation.  
         [0007]     The element utilized by the present invention may be a ring having a bore therethrough for directing the explosive energy of the charge upon detonation. Further, the charge cap may include an area having a thinner wall than the rest of the cap. In operation, the thicker portion of the cap absorbs some of the explosive energy of the charge and the thinner portion (or opening) conducts/directs the explosive energy. The exact thickness of the “absorbing” volume of the cap and the thickness of the “conducting” volume of the cap may be determined and selected to achieve a particular result. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings; it being understood that the drawings contained herein are not necessarily drawn to scale; wherein:  
         [0009]      FIG. 1  is an enlarged cross-sectional view of an embodiment of a shaped charge.  
         [0010]      FIG. 2A  is a profile cross-sectional view of an embodiment of a perforating gun.  
         [0011]      FIG. 2B  is a axial cross-sectional view of an embodiment of the perforating gun of  FIG. 2A .  
         [0012]      FIG. 3  is a profile view of an embodiment of a perforating gun string being run downhole in a cased wellbore.  
         [0013]      FIG. 4A  is a profile view of an embodiment of a perforating gun string being detonated in a cased wellbore.  
         [0014]      FIG. 4B  is a profile view of an embodiment of a perforating gun string being detonated in an open wellbore.  
         [0015]      FIGS. 5A-6B  are axial views of multiple embodiments of the perforating gun of the present invention. 
     
    
       [0016]     It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
       DETAILED DESCRIPTION OF THE INVENTION  
       [0017]     In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.  
         [0018]     In the specification and appended claims: the terms “connect”, “connection”, “connected”, “in connection with”, and “connecting” are used to mean “in direct connection with” or “in connection with via another element”; and the term “set” is used to mean “one element” or “more than one element”. As used herein, the terms “up” and “down”, “upper” and “lower”, “upwardly” and downwardly”, “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly described some embodiments of the invention. However, when applied to equipment and methods for use in wells that are deviated or horizontal, such terms may refer to a left to right, right to left, or other relationship as appropriate.  
         [0019]     Referring to  FIG. 1 , a shaped charge ( 10 ) includes an outer case ( 12 ) that acts as a containment vessel. Common materials for the outer case ( 12 ) include steel or some other metal. The main explosive charge ( 16 ) is contained inside the outer case ( 12 ) and is sandwiched between the inner wall of the outer case ( 12 ) and the outer retaining surface ( 20 ). A primer column ( 14 ) is a sensitive area that provides the detonating link between the main explosive charge ( 16 ) and a detonating cord ( 15 ), which is attached to the rear of the shaped charge ( 10 ).  
         [0020]     To detonate the shaped charge ( 10 ), a detonation wave traveling through the detonating cord ( 15 ) initiates the primer column ( 14 ) when the detonation wave passes by, which in turn initiates detonation of the main explosive charge ( 16 ) to create a detonation wave that sweeps through the shaped charge ( 10 ).  
         [0021]     Referring to  FIG. 2 , a plurality of shaped charges ( 10 ) may be conveyed downhole via a hollow carrier gun ( 30 ). The shaped charges ( 10 ) may be non-capsule charges since the shaped charges are protected from the environment by the hollow carrier ( 30 ), which is typically sealed. The hollow carrier ( 30 ) may also include a plurality of recesses ( 32 ) formed in the outer wall. The recesses ( 32 ) are typically localized areas where the wall thickness of the carrier ( 30 ) is reduced to optimize overall system function. Within the hollow carrier ( 30 ), a loading tube ( 40 ) is positioned. The loading tube ( 40 ) includes a plurality of openings ( 42 ) proximal, for receiving and mounting the shaped charges ( 10 ). The openings ( 42 ) of the loading tube ( 40 ) are typically aligned with the recesses ( 32 ) of the hollow carrier ( 30 ).  
         [0022]     Referring to  FIG. 3 , a series of hollow carrier guns ( 50 A) and ( 50 B) may be assembled to form a perforating gun string ( 50 ) having a desired length. An example length of each gun ( 50 A and  50 B, respectively), may be about twenty feet. To make a perforating gun string ( 50 ) of a few hundred feet or longer, several guns may be connected together in series by adapters ( 52 ). Each of the adapters ( 52 ) contains a ballistic transfer component, which may be in the form of donor and receptor booster explosives. Ballistic transfer takes place from one gun to another as the detonation wave jumps from the donor to the receptor booster. At the end of the receptor booster is a detonating cord that carries the wave and sets off the shaped charges in the next gun. Examples of explosives that may be used in the various explosive components (e.g., shaped charges ( 10 ), detonating cord ( 15 ), and boosters) include RDX, HMX, HNS, TATB, and others.  
         [0023]     Generally, once assembled, the gun string ( 50 ) is positioned in a wellbore ( 60 ) that is lined with casing ( 62 ). A tubing or pipe ( 64 ) extends inside the casing ( 62 ) to provide a conduit for well fluids to wellhead equipment (not shown). A portion of the wellbore ( 60 ) is isolated by packers ( 66 ) set between the exterior of the tubing ( 64 ) and the interior of the casing ( 62 ). The perforating gun string ( 50 ) may be lowered through the tubing or pipe ( 54 ) on a carrier line ( 70 ) (e.g., wireline, slickline, or coiled tubing). Once positioned at a desired wellbore interval, the gun string ( 50 ) is fired to create perforations in the surrounding casing and formation (as shown in  FIG. 4A ).  
         [0024]     In another embodiment, as shown in  FIG. 4B , the gun string ( 50 ) includes one or more sealed carriers ( 30 ). In alternative embodiments, the gun string ( 50 ) may include one or more sealed chambers (or other sealed enclosures), each chamber housing one or more explosive charges therein. The pressure within the gun carrier ( 30 ) is lower than the pressure in the target wellbore interval. The sealed gun string ( 50 ) is positioned in an open wellbore ( 100 ). The perforating gun string ( 50 ) may be lowered through the open wellbore ( 100 ) on a carrier line ( 70 ) (e.g., wireline, slickline, or coiled tubing). Once positioned at a desired wellbore interval, the gun string ( 50 ) is fired to create holes or ruptures in the sealed carrier ( 30 ) while not substantially damaging the surrounding. Upon detonation of the one or more explosive charges and subsequent rupturing of the carrier ( 30 ), a fluid surge will be formed toward the carrier thus generating a transient underbalanced condition in the wellbore interval. This transient underbalance condition may be utilized to clean perforation tunnels in the surrounding formation, to remove filter cake from the walls of the wellbore, or to otherwise remove debris from the wellbore interval. Moreover, by rupturing the carrier, trapped pressurized gas in the sealed bore of the carrier may be released.  
         [0025]     In other embodiments, the sealed perforating gun string ( 50 ) may be deployed in a cased wellbore and may be used to perforate the sealed carriers and the casing simultaneously to create a transient underbalanced condition to surge clean the perforation tunnels in the formation and remove wellbore debris from the target well interval. This will effectively increase productivity of the well.  
         [0026]     The explosive energy released and the resulting perforation achieved by detonating the guns discussed above may be a function of the physical size and geometrical arrangement of the explosive charges. An embodiment of the present invention is directed at controlling this explosive energy release.  
         [0027]     Referring to  FIGS. 5A-6B , a cap or other interfering element ( 80 ) may be arranged proximate the charge ( 10 ) to absorb a portion of the energy. The size and particular arrangement of the cap ( 80 ) with respect to the charge ( 10 ) may be determined to achieve an optimum explosive state for a selected result. For example, by controlling the explosive energy release of a charge, the amount of debris released into the wellbore and excessive deformation of the perforating gun may be limited.  
         [0028]     The charge cap ( 80 ) of the present invention may also be used to direct or otherwise focus the explosive energy release to achieve a particular result. For example, the cap ( 80 ) may be sized and arranged to focus the explosive energy in a charge to break debris into small enough fragments such that the debris does not hider productivity of the well.  
         [0029]     The charge cap ( 80 ) of the present invention may be used in various perforating or other explosive well operations. For example, the charge cap ( 80 ) may be used to direct and control explosive energy released by charges in a conventional perforating gun ( 30 ) used to perforate a formation and/or a casing and a formation. In another example, the charge cap may be used to direct and control explosive energy released by charges in a sealed chamber (e.g., carrier or other sealed enclosure) to rupture the chamber but not damage the surrounding casing. In this way, the charges may be used to generate a transient underbalance condition to clean debris from the perforation tunnel.  
         [0030]      FIGS. 5A and 5B  illustrate embodiments of the charge cap ( 80 ) of the present invention connected to a shaped charge ( 10 ). The charge cap or other interfering element may be designed to fit between the arms ( 10 A) of the explosive charge ( 10 ). This embodiment of the present invention is ideal for use with shaped charges capable of fitting relatively snugly within the internal compartment of the loading tube ( 40 ).  
         [0031]     In one embodiment, the charge cap of the present invention has a section designed to absorb explosive energy ( 88 A) and another section designed to conduct and/or direct explosive energy ( 88 D). In one embodiment, the section of the charge cap ( 80 ) designed to absorb explosive energy ( 88 A) is designed to engage an inner surface ( 101 ) of one or more arms ( 10 A) of the explosive charge. In one embodiment, the section of the charge cap ( 80 ) designed to conduct and/or direct explosive energy ( 88 D) forms a central portion of the charge cap.  
         [0032]     In one embodiment, the section of the charge cap designed to absorb explosive energy ( 88 A) may be composed of a relatively thick and/or dense material particularly suited to absorb explosive energy. Further, the section of the charge cap designed to conduct and/or direct explosive energy ( 88 D) may be composed of a thinner and/or less dense material than that used by the absorbing section ( 88 A). In this manner, the charge cap allows for maximum effectiveness with regard to the disbursement of explosive energy upon detonation. The exact thickness and/or density of each section ( 88 A and  88 D, respectively) of the charge cap may be determined and selected to achieve any number of desirable results.  
         [0033]     In one embodiment, one or more walls ( 82 ) of the charge cap may define one or more cavities ( 84 ) capable of directing explosive energy. Such cavities may have any number of orientations and/or configurations designed to achieve particular results. For example, one or more cavities provided by the present invention may have a generally conical or cylindrical configuration designed to direct explosive energy in a particular manner. It being understood that these are example configurations only, not to be taken in a limiting sense. A ring element having a bore therethrough may also be utilized for directing the explosive energy of the charge upon detonation.  
         [0034]      FIGS. 6A and 6B  illustrate embodiments of a charge cap ( 80 ) connected to a shaped charge ( 10 ). In these embodiments, the shaped charge and charge cap are mounted in a jacket ( 86 ) and for insertion into a loading tube ( 40 ). The loading tube may hold a plurality of shaped charges ( 10 ), each having a charge cap ( 80 ). The loading tube is loaded into a gun carrier ( 30 ). The gun carrier ( 30 ) may have a scallop ( 32 ) formed on the outer surface for alignment with each shaped charge ( 10 ).  
         [0035]     In one embodiment, the charge cap ( 80 ) of the present invention is designed to engage the outer surfaces ( 102 ) of the charge arms ( 10 A) of the explosive charge ( 10 ). Further, the charge cap may be utilized in conjunction with a jacket ( 86 ) in order to allow the charge cap/charge/jacket combination to be conveniently mounted within the loading tube. This feature of the present invention allows smaller explosive charges to be successfully mounted within loading tubes having larger diameters. As discussed above, the present invention may utilize any number of charge cap arrangements and/or configurations as needed to achieve a particular result. Further the thickness and/or density of the materials comprising each section of the charge cap may be varied. A ring element having a bore therethrough may also be utilized for directing the explosive energy of the charge upon detonation, as discussed above.  
         [0036]     In some embodiments, the charge cap ( 80 ) may be fabricated from a material that stays together sufficiently such that the cap does not exit the ruptures in the gun. This way the cap can be removed from the well with the gun and does not hinder well productivity. In other embodiments, the charge cap ( 80 ) may be fabricated from a highly-frangible material such that the cap breaks into sufficiently small fragments so as not to hinder well productivity even if the fragments exit the gun. For example, the charge cap may be fabricated from plastic, polymer, metal, cellulose, rubber, or other suitable material.  
         [0037]     Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limited sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is, therefore, contemplated that the appended claims will cover such modifications that fall within the scope of the invention.