Abstract:
A shaped charge includes a casing; a liner located within an opening of the casing; and an explosive located in the region between the casing and the liner, wherein at least one of the liner and the explosive comprises an intermetallic mixture comprising boron and a reactant metal. The reactant metal is one selected from the group consisting of Ti, Mg, Zr, Mo, and a combination thereof. A method for perforating in a well includes positioning a perforating gun in the well, wherein the perforating gun includes a shaped charge that includes: a casing; a liner located within an opening of the casing; and an explosive located in the region between the casing and the liner, wherein at least one of the liner and the explosive includes an intermetallic mixture that contains boron and a reactant metal; and detonating the shaped charge in the well.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The application claims priority of the U.S. Provisional Application No. 61/427,647 filed on Dec. 28, 2010. The disclosure of this provisional application is incorporated by reference in its entirety. 
     
    
     BACKGROUND OF INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates generally to shaped charges for perforating, particularly shaped charges having reactive liners. 
         [0004]    2. Background Art 
         [0005]    After a well has been drilled and casing has been cemented in the well, perforations are created to allow communication of fluids between pay zones in the formation and the wellbore. Shaped charge perforating is commonly used, in which shaped charges are mounted in perforating guns that are conveyed into the well on either an electric line (e.g., a wireline) or tubing (e.g. production tubing, drill pipe, or coiled tubing). 
         [0006]      FIG. 1  shows that, after a well  11  is drilled, a casing  12  is typically run in the well  11  and cemented to the well  11  in order to maintain well integrity. After the casing  12  has been cemented in the well  11 , one or more sections of the casing  12  that are adjacent to a formation zone of interest, otherwise referred to as a “target zone,” may be perforated to allow fluids from the target zone  13  to flow into the well for production to the surface or to allow injection fluids to be applied into the target zone  13 . To perforate a casing section, a perforating device, such as a perforating gun  15 , may be lowered into the well  11  to a desired depth, such as at a depth corresponding to the target zone  13  in the surrounding formation  16 . Next, one or more shaped charges  20  are fired to create holes in the casing  12  and to create perforations into the target zone  13  of the formation  16 . Production fluids in the target zone  13  can then flow through the fractures, through the perforation in the casing, and into the wellbore. 
         [0007]    A shaped charge for a perforating device typically includes an energy source located within a shaped charge casing and enclosed with a liner. Energy sources typically include explosive materials. Liners may be made of metals, alloys and/or ceramics. The liner is shaped, such that upon detonation of the explosives, the energy that is released converts the liner material into a directional perforating jet that penetrates the well casing and the adjacent formation to create perforation tunnels. The perforation tunnels allow formation fluids to communicate with the wellbore. In some instance, residual liner material can coat the pores in the perforation tunnel walls and can be harmful to the permeability in the perforation tunnels. On the other hand, these liner materials that are converted into the shaped charge jet can offer an opportunity to enhance the performance characteristics of shaped charges. 
         [0008]    In recent years, shaped charges with reactive liners have been developed. The reactive liners are made of reactive materials that can generate additional heat and/or pressure inside the perforation tunnels. Such secondary events can improve the performance characteristics of the shaped charges. For example, a reactive liner composition may include a reactive metal or a reactive metal mixture, such as Al, Ti, Mg, an intermetallic mixture (e.g., Al and Ni), or a thermite mixture (e.g., Al and a metal oxide), that can generate substantial heat inside the newly created perforation tunnels. 
         [0009]    The term “thermite” refers to a pyrotechnic composition that comprises a metal powder and a metal oxide. Thermite mixtures can undergo exothermic oxidation-reduction reactions, known as thermite reactions. Most thermite reactions are not explosive in nature, but are characterized by a large energy release in the form of extremely high heat. Aluminum (Al) is among the most common powders used in thermite compositions. Examples of Al-containing thermite compositions include Al/Fe 2 O 3 , Al/Fe 3 O 4 , and Al/CuO, which are at present incorporated into shaped charge liners. 
         [0010]    Thermite reactions generally are more energetic than intermetallic reactions owing to the amount of energy released by the Al oxidation reaction. A major disadvantage related to the incorporation of thermite-type mixtures into shaped charge liners, however, is that the only available method involves the separate addition of each component into the powder mixture used to generate the liners. For example, Al powder and Fe 2 O 3  powder must separately be added into the liner powder mixture. After detonation of the shaped charges, the Al powder and Fe 2 O 3  powder in the penetration jets then need to find each other before the thermite reactions can take place. Thus, the reaction rate may be hindered by the Al and Fe 2 O 3  particles having to “find” each other in order to react, and it is likely that some Al and Fe 2 O 3  remain un-reacted. 
         [0011]    An intermetallic composition consists of two or more metallic elements. Some intermetallic compositions can undergo exothermic reactions upon activation. Such exothermic intermetallic reactions may be used for perforating applications. For example, WO 2005/035939, entitled “Improvements in and Relating To Oil Well Perforators,” by Leslie Bates and Brian Bourne, discloses uses of intermetallic reaction systems in shaped charge liners. Specifically, WO 2005/035939 discloses the use of Al/Ni and Al/Pd intermetallic compositions in shaped charge liners to enhance performance. 
         [0012]    In addition to uses with a metal oxide, as in a thermite mixture, aluminum can also react with various reagents to produce heat. For example, U.S. Pat. No. 7,393,423 B2, entitled “Use of Aluminum in Perforating and Stimulating a Subterranean Formation and other Engineering Applications,” issued to Liquing Liu in 2008, discloses the use of Al in liners, based on various oxidation reactions. 
         [0013]    U.S. Patent Application Publication No. 2009/0078144 Al, entitled “Liner for Shaped Charges,” by Lawrence Behrmann and Wenbo Yang, discloses the use of a variety of energetic metals, including Ti, Mg, and Al, in liners. The Astro Silver™ charges from Schlumberger Technologies (Houston, Tex.) also contain Ti as an energetic material in the liner. These types of shaped charges depend on the reactive elements in the liners to interact with either the explosive decomposition products or materials external to the perforating gun, such as water or the reservoir rock/fluids. 
         [0014]    These reactive liners all provide enhancements to shaped charge perforation characteristics. There remains, however, a need to improve upon shaped charge technology and achieve further improvements in shaped charge performance characteristics. 
       SUMMARY OF INVENTION 
       [0015]    One aspect of the invention relates to shaped charges. A shaped charge in accordance with one embodiment of the invention includes a casing; a liner located within an opening of the casing; and a region containing explosive between the casing and the liner, wherein at least one of the liner and the explosive comprises an intermetallic mixture comprising boron and a reactant metal. 
         [0016]    One aspect of the invention relates to perforating guns. A perforating gun in accordance with one embodiment of the invention includes a shaped charge that includes a casing; a liner located within an opening of the casing; and an explosive located in the region between the casing and the liner, wherein at least one of the liner and the explosive comprises an intermetallic mixture comprising boron and a reactant metal. 
         [0017]    One aspect of the invention relate to methods for manufacturing a shaped charge. A method in accordance with one embodiment of the invention includes obtaining an intermetallic mixture comprising boron and a reactant metal; and preparing a shaped charge comprising a casing; a liner located within an opening of the casing; and an explosive located in the region between the casing and the liner, wherein at least one of the liner and the explosive incorporates intermetallic mixture comprising boron and a reactant metal. 
         [0018]    One aspect of the invention relates to methods for perforating a well. A method in accordance with one embodiment of the invention includes: positioning a perforating gun; and detonating the shaped charge in the well, wherein the perforating gun includes a shaped charge that includes a casing; a liner located within an opening of the casing; and an explosive located in the region between the casing and the liner, wherein at least one of the liner and the explosive comprises an intermetallic mixture comprising boron and a reactant metal. 
         [0019]    Other aspects and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0020]      FIG. 1  shows a perforation operation of the prior art, illustrating a perforation device disposed in a well. 
           [0021]      FIG. 2  shows a cross-sectional layout of a shaped charge in accordance with one embodiment of the invention. 
           [0022]      FIG. 3  shows a cross-sectional layout of a shaped charge in accordance with one embodiment of the invention. 
           [0023]      FIG. 4  shows a cross-sectional layout of a shaped charge in accordance with one embodiment of the invention. 
           [0024]      FIG. 5  shows a cross-sectional layout of a shaped charge in accordance with one embodiment of the invention. 
           [0025]      FIG. 6  shows a cross-sectional layout of a shaped charge in accordance with one embodiment of the invention. 
           [0026]      FIG. 7  shows a cross-sectional layout of a shaped charge in accordance with one embodiment of the invention. 
           [0027]      FIG. 8  shows a method for manufacturing a shaped charge in accordance with one embodiment of the invention. 
           [0028]      FIG. 9  shows a method for perforating a well in accordance with one embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    Embodiments of the invention relate to shaped charges and methods for using such shaped charges. Specifically, embodiments of the invention relate to shaped charges that use boron intermetallic reactions to enhance the performance of the shaped charges. The following description concerns a number of embodiments and is meant to provide an understanding of the invention. The description is not in any way meant to limit the scope of any present or subsequent related claims. 
         [0030]    As noted above, various approaches have been used to enhance the performance of shaped charges, such as the use of reactive liners. Several types of reactive liners have been attempted based on different exothermic reactions that occur after the explosives have been detonated. These secondary reactions include thermite reactions, intermetallic reactions, etc. These exothermic reactions can generate a large amount of heat, which elevates the temperature in the perforation tunnel and expands any gases that are present from the explosive decomposition. This in effect can create pressures that generate cracks in the walls of the perforation tunnels. These reaction systems can also be incorporated with other components that produce gaseous byproducts, which in combination with the elevated temperature can enhance the fracturing effects. 
         [0031]    Some reactive liners contain reactive metals that can react with external components, such as components in the formation or the decomposition products of the explosives. When a shaped charge is fired, the explosives or propellants generate decomposition products that mainly contain CO 2  and water vapor. Both CO 2  and water may oxidize reactive metals (e.g., aluminum, titanium, magnesium, or boron). Therefore, if a liner contains such a reactive metal (e.g., Al, Ti, Mg, or B), the secondary reaction would generate heat to achieve greater energy release, and hence result in better performance characteristics. 
         [0032]    Although boron is generally more energetic than Al when applied to such oxidation reactions and could potentially be used as an energetic additive to enhance explosive or propellant performance, boron is not commonly used in such systems. Instead, aluminum is more commonly applied in these types of applications. Boron is not commonly used with propellants and explosives owing to complications encountered during boron oxidation. For example, boron oxidation in the presence of water will form HBO 2 , which hinders subsequent oxidation, leading to a slower reaction rate and an incomplete reaction (i.e. some boron remains unreacted). 
         [0033]    Boron may also be used in thermite reactions. For example, the B/CuO thermite reaction can generate 738.1 Cal/g of heat. However, boron is also not as commonly used as aluminum in thermite mixtures for the same reasons—i.e., in the presence of water, the reaction rates may be slow and reaction completion may significantly be impacted. In addition, there exist limitations related to the manner by which the metal and metal oxide components are incorporated into a reactive liner—they must be added as separate powder components. After detonation of the shaped charges, this condition requires that these components would need to “find” each other either in the jet or perforation tunnel for the thermite reactions to occur. 
         [0034]    In contrast, embodiments of the invention use boron in intermetallic reactions. Boron-type intermetallic reactions are attractive because they do not rely on oxygen-boron interactions, thus, allowing one to use boron without the concern of adverse oxidation effects impacting the reaction rates. In addition, unlike thermite reactions, boron intermetallic components can be incorporated as alloyed powders, metal-coated boron powders, or boron-coated metal powders, and, therefore, these components are ready to react and need not find each other after detonation of the shaped charges. 
         [0035]    As used herein, the term an “intermetallic mixture” means a system comprising two metal components that can react to generate a substantial amount of heat. A boron-type intermetallic mixture is one having boron as one of the metal components. The other metal component in a boron-type intermetallic mixture may be referred to as a “reactant metal.” The term “intermetallic mixture” as used herein may include a system the two components are physically separated in two different parts of a shaped charge, e.g., liner and explosive. These “separated” system will also be referred to as an “intermetallic mixture” in this description because they will become a mixture once the shaped charge is fired. Furthermore, an “intermetallic mixture” in the examples described herein comprise two components—boron and a reactant metal. However, one skilled in the art would appreciate that one can also use three or more components in an intermetallic mixture without departing from the scope of the invention. 
         [0036]    In the following description, boron and the reactant metal may be used in the form of powders and/or particles. For clarity, the description may use “powders” in a broad sense to include “particles.” Specifically, in this description wherever “powder” is mentioned, one may substitute this with “particle” or use both “powder” and “particle.” 
         [0037]    Although aluminum is more favorable as a component in thermite mixtures or as a reactive metal for oxidative reactions, boron is actually better for intermetallic reactions because boron-type intermetallic reactions typically release more energy (i.e. are more exothermic) than the Al-type intermetallic reactions. For example, the average ΔH for boron and titanium intermetallic reactions (B+Ti→TiB; 2B+Ti→TiB 2 ) is −4.02 kJ/g, whereas ΔH (3Al+2Ni→Ni 2 Al 3 )=−1.42 kJ/g. 
         [0038]    In addition, many other metals can be used with boron in the boron-type intermetallic reactions. The following Table 1 lists some intermetallic mixtures that can produce substantial heat and the energies that are released from such intermetallic reactions. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Reactants 
                 ΔH (KJ/g) 
                 Reactants 
                 ΔH (KJ/g) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 4B + C     
                 −1.28 
                  2B + Ta 
                 −1.03 
               
               
                   
                 6B + Ce  
                 −1.65 
                     4B + Th 
                 −0.79 
               
               
                   
                 2B + Cr     
                 −1.28 
                     B + Ti 
                 −2.73 
               
               
                   
                 2B + Hf  
                 −1.68 
                     2B + Ti 
                 −5.52 
               
               
                   
                 6B + La  
                 −2.34 
                 2B + U 
                 −0.62 
               
               
                   
                 2B + Mg 
                 −2.00 
                 4B + U 
                 −0.87 
               
               
                   
                 6B + Mg 
                 −1.05 
                  B + V 
                 −2.24 
               
               
                   
                 2B + Mn 
                 −1.23 
                 2B + V 
                 −2.81 
               
               
                   
                 2B + Mo 
                 −0.82 
                     5B + 2W 
                 −0.35 
               
               
                   
                 2B + Nb     
                 −2.19 
                 6B + Y 
                 −0.65 
               
               
                   
                 6B + Sm 
                 −0.97 
                  2B + Zr 
                 −2.86 
               
               
                   
                 6B + Si  
                 −0.32 
               
               
                   
                   
               
             
          
         
       
     
         [0039]    All these reactant metals may be used in embodiments of the invention to participate in intermetallic reactions with boron to produce substantial amounts of heat. As can be seen from Table 1, some of these reactant metals (e.g., La, Mg, Nb, Ti, V, and Zr) can produce more heat than others. However, the costs for these reactant metals would be a factor to consider. Therefore, one may select the types of reactant metals based on the desired effects and/or purposes. For example, the intermetallic mixtures in accordance with embodiments of the present invention may include Ti/B, Mg/B, Zr/B, Mo/B, etc. 
         [0040]    The intermetallic mixtures usually require relatively high temperatures (typically &gt;1000 K) to initiate the intermetallic reactions. Therefore, the components of an intermetallic mixture may be mixed together without much concerns of dangers or degradation over long term storage. This is advantageous, as compared to thermite mixtures. 
         [0041]    Therefore, in accordance with embodiments of the invention, the components of an intermetallic mixture to be used in a shaped charge can be either mixed into the same part or different parts of a shaped charge. For example, in accordance with some embodiments of the invention, boron and the reactant metal may be mixed into a powder blend used for making a liner, or one of he components may be mixed in with the explosive and the other in the liner. 
         [0042]      FIG. 2  shows a cross-section view of a shaped charge  20  according to one embodiment of the invention. Shaped charge  20  includes a liner  22  and a casing  24 , forming a cavity. An explosive  26  is enclosed within the cavity. Furthermore, an explosive primer  28  is located at the base of the cavity to enhance the detonation transfer from the detonating cord (not shown). The liner  22  is converted into the shaped charge jet upon detonation of the explosive, and it also helps retain the explosive  26  in the cavity of the casing  24 . 
         [0043]    Explosive  26  may contain any suitable explosive materials known in the art, such as RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), FINS (hexanitrostilbene), HMX (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane), PETN (pentaerythritol tetranitrate), TATB (triaminotrinitrobenzene), and/or PYX (2,6-bis picrylamino-3,5-dinitropyridine). 
         [0044]    In accordance with some embodiments of the invention, boron and the reactant metal in an intermetallic mixture may be included in a liner. In this configuration, the boron metal and the other metal may be included in the liner in several manners: (i) both are added as separate powders or separate particles; (ii) the reactant metal is coated on granules of boron, or vice versa; and (iii) boron and the reactant metal are made into an alloy. 
         [0045]      FIG. 3  illustrates one embodiment of the invention, in which both boron and the reactant metal are added to the liner as powders and/or particles.  FIG. 3  shows a schematic illustrating a cross-section view of a liner  22  and an explosive  26  of a shaped charge  20 . Liner  22  may contain a mixture of boron powders/particles  30  and the reactant metal powders/particles  32 . The reactant metal powders/particles  32 , for example, may be Ti, Mg, Zr, Mo, etc. In an alternative embodiment, one may also put the powders and/or particles of boron and the reactant metals in the explosive, instead of the liner. 
         [0046]      FIG. 4  illustrates one embodiment of the invention, in which boron particles are coated with the reactant metal before they are added to a liner.  FIG. 4  shows a schematic illustrating a cross-section view of liner  22  and explosive  26  of a shaped charge  20  according to one embodiment of the invention. Liner  22  contains intermetallic particles  40 , which are boron particles  42  coated with the reactant metal coatings  44 . The reactant metal coatings  44  may be Ti, Mg, Zr, Mo, etc. One skilled in the art would appreciate that the coated particles may also comprise the reactant metal as the core and boron as the coating. 
         [0047]      FIG. 5  illustrates one embodiment of the invention, in which both boron and the reactant metal are added to a liner as an alloy.  FIG. 5  shows a schematic illustrating a cross-section view of liner  22  and explosive  26  of a shaped charge  20  according to one embodiment of the invention. Liner  22  may contain reactant metal-B alloy powders/particles  50 . The reactant metal-B alloy powders/particles  50  may include Ti/B, Mg/B, Zr/B, Mo/B alloy, etc. 
         [0048]      FIGS. 6 and 7  illustrate other embodiments of the invention, in which boron and the reactant metal are added to separate parts of a shaped charge. In these embodiments, the boron and the reactant metal are not in a “mixture” in a strict sense. Nevertheless, the term an “intermetallic mixture” as used herein intends to include these situations, where boron and the reactant metal are deposited in different parts of a shaped charge. Even though they are in different parts of a shaped charge, these components will be mixed and form a “mixture” once the shaped charge is fired. 
         [0049]      FIG. 6  shows a schematic illustrating a cross-section view of liner  22  and explosive  26  of a shaped charge  20  according to one embodiment of the invention. Liner  22  may contain boron powders/particles  60  and explosive  26  may contain reactant metal powders/particles  62 . The reactant metal powders  62  may include Ti, Mg, Zr, Mo, etc. After the charge is initiated boron powders  60  and metal powder  62  may be mixed together in the penetrating jet. 
         [0050]    An alternative embodiment to the one shown in  FIG. 6  is illustrated in  FIG. 7 , which shows a schematic illustrating a cross-section view of liner  22  and explosive  26  of a shaped charge  20  according to one embodiment of the invention. Explosive  26  may contain boron powders  70  and liner  22  may contain reactant metal powders  72 . The reactant metal powders  72  may include Ti, Mg, Zr, Mo, etc. After the charge is initiated boron powders  70  and metal powder  72  may be mixed together in the penetrating jet. 
         [0051]    Some embodiments of the invention relate to methods of manufacturing a shaped charge of the invention as described above.  FIG. 8  shows a method  80  in accordance with one embodiment of the invention. As shown, method  80  include the step of selecting a reactant metal for use with boron in an intermetallic mixture (step  81 ). Then, one decides how these components are to be incorporated into a shaped charge (step  82 ). For example, boron and the reactant metal may be incorporated into the shaped charge as separate powers in a liner or in separate parts (liner and explosive) of a shaped charge. In this case, there is no need to process these two components prior to incorporating them into a shaped charge. Alternatively, boron and the reactant metal may be pre-processed into an alloy or coated particles, as described above. Then, the intermetallic components are used to prepare a shaped charge containing the intermetallic components (step  83 ). 
         [0052]    One skilled in the art would appreciate that the method  80  shown in  FIG. 8  is for illustration only. Many variations and modifications to these procedures are possible without departing from the scope of the invention. For example, one may purchase a pre-manufactured alloy or coated particles from a commercial source. In this case, steps  81  and  82  would not be necessary. 
         [0053]    Perforating devices, such as perforating guns, using shaped charges that incorporate boron-type intermetallic reactions according to embodiments of the invention may be used in perforating operations. For example,  FIG. 9  shows a method  90  of perforating a formation in accordance with embodiments of the invention. As shown, the method  90  include the step of locating a perforating gun in a wellbore (step  91 ), wherein the perforating gun contains a shaped charge that has a boron-type intermetallic mixture in accordance with embodiments of the invention illustrated above. Once the perforating gun is in the wellbore at the desired zone (depth), the shaped charge may be fired to create perforations in the well casing and/or nearby formation. (step  92 ). 
         [0054]    Advantages of embodiments of the invention may include one or more of the following. Embodiments in accordance with the invention described here may incorporate all the reactive elements into the shaped charge itself, resulting in a more robust and reliable reaction system. Fore example, shaped charges of the invention may provide faster reaction rates by allowing one to tailor the reactants using either metal-coated B particles or metal-B alloy, such as Ti—B alloy, particles where the reactants are incorporated together. Furthermore, B may be incorporated into the AstrosSilver shaped charge technology since the Ti—B reaction may enhance the energetic characteristics. 
         [0055]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.