Patent Publication Number: US-7721649-B2

Title: Injection molded shaped charge liner

Description:
RELATED APPLICATIONS 
   This application claims priority to and the benefit of co-pending U.S. Provisional Application Ser. No. 60/973,032, filed Sep. 17, 2007, 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 an injection molded shaped charge liner formed from a heavy metal and a binder. Yet more specifically, the present invention relates to a shaped charge liner comprising a mixture of tungsten, copper, and nickel. 
   2. Description of Related Art 
   Perforating guns 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. 
   Shaped charges known in the art for perforating wellbores are used in conjunction with a perforation gun. One embodiment of a traditional shaped charge  5  is illustrated in  FIG. 1 . As shown, shaped charge  5  includes a housing  6 , a liner  10 , and a quantity of high explosive  8  inserted between the liner  10  and the housing  8  where the high explosive  8  is usually HMX, RDX PYX, or HNS. When the high explosive  8  is detonated, the force of the detonation collapses the liner  10  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. 
   Some of the traditional methods of producing shaped charge liners include sintering and cold working. Cold working involves mixing a powdered metal mix in a die and compressing the mixture under high pressure into a shaped liner. One of the problems associated with cold working a liner is a product having inconsistent densities. This is usually caused by migration of either the binder or the heavy metal to a region thereby producing a localized density variation. A lack of density homogeneity curves the path of the shaped charge jet that in turn shortens the length of the resulting perforation. This is an unwanted result since shorter perforations diminish hydrocarbon production. 
   Cold worked liners have a limited shelf life since they are susceptible to shrinkage thereby allowing gaps to form between the liners and the casing in which they are housed. These liners also tend to be somewhat brittle which leads to a fragile product. Liners produced by cold working may slightly expand after being assembled and stored; this phenomenon is also referred to as creep. Even a slight expansion of the shaped charge liner reduces shaped charge effectiveness and repeatability. Additionally, liner density also affects liner performance. Increasing liner density correspondingly increases jet density that in turn deepens shaped charge penetrations. However the cold forming process allows for low density regions in the liner thus resulting in an upper limit on liner density. 
   Sintered liners necessarily involve a heating step of the liner, wherein the applied heating raises the liner temperature above the melting point of one or more of the liner constituents. The melted or softened constituent is typically what is known as the binder. During the sintering or heating step, the metal powders coalesce while their respective grains increase in size. The sintering time and temperature will depend on what metals are being sintered. The sintering process forms crystal grains thereby increasing the final product density while lowering the porosity. Sintering is generally performed in an environment void of oxygen or in a vacuum. However the ambient composition within a sintering furnace may change during the process, for example the initial stages of the process may be performed within a vacuum, with an inert gas added later. Moreover, the sintering temperature may be adjusted during the process, wherein the temperature may be raised or lowered during sintering. 
   Prior to the sintering step the liner components can be cold worked as described above, injection molded, or otherwise formed into a unitary body. However the overall dimensions of a sintered liner can change up to 20% from before to after the sintering step. Because this size change can be difficult to predict or model, consistently producing sintered shaped charge liners that lie within dimensional tolerances can be challenging. Information relevant to shaped charge liners formed with powdered metals is addressed in Werner et al., U.S. Pat. No. 5,221,808, Werner et al., U.S. Pat. No. 5,413,048, Leidel, U.S. Pat. No. 5,814,758, Held et al. U.S. Pat. No. 4,613,370, Reese et al., U.S. Pat. No. 5,656,791, and Reese et al., U.S. Pat. No. 5,567,906. 
   Therefore, there exists a need for a method of consistently manufacturing shaped charge liners, wherein the resulting liners have a homogenous density, have consistent properties between liner lots, have a long shelf life, and are resistant to cracking. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention involves a method of injection molding a shaped charge liner with a metal powder of a first metal, a second metal, and a third metal, where the first metal is about 50%-99% by weight, the second metal is about 1%-40% by weight, and the third metal is about 1%-40% by weight. The first metal density exceeds about 11 gm/cc and may comprise tungsten and the second metal may comprise nickel, copper, and metals whose density is less than about 10 gm/cc, and combinations thereof. The metal powder can be chosen from these listed metals singularly or can come from combinations thereof. The liner may be combined with a shaped charge as a green part without any processing after being molded, combined after debinding the liner, or combined after being sintered. 
   A binder may be included comprising a polyolefine, an acrylic resin, a styrene resin, polyvinyl chloride, polyvinylidene chloride, polyamide, polyester, polyether, polyvinyl alcohol, paraffin, higher fatty acid, higher alcohol, higher fatty acid ester, higher fatty acid amide, wax-polymer, acetyl based, water soluble, agar water based and water soluble/cross-linked. The binder can be chosen from these listed binders singularly or can come from combinations thereof. 
   The present method disclosed herein further comprises forming a shaped charge with the shaped charge liner, disposing the shaped charge within a perforating gun, combining the perforating gun with a perforating system, disposing the perforating gun within a wellbore, and detonating the shaped charge. 
   An alternate method of forming a shaped charge liner is disclosed herein comprising, combining powdered metal with organic binder to form a mixture, passing the mixture through an injection molding device, ejecting the mixture from the injection molding device into a mold thereby forming a liner shape in the mold, and debinding the binder from the liner shape; wherein the liner shape is sintered. The alternate method further comprises placing the liner shape in a vacuum. The alternate method of forming a shaped charge liner may also comprise forming a shaped charge with said shaped charge liner, disposing the shaped charge within a perforating gun, combining the perforating gun with a perforating system, disposing the perforating gun within a wellbore, and detonating the shaped charge. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  depicts a perspective cross sectional view of a shaped charge. 
       FIG. 2  represents in flow chart form an embodiment of a liner forming process. 
       FIG. 3  illustrates a cross sectional view of an injection molding device. 
       FIG. 4  portrays a side view of a liner shape. 
       FIG. 5  is a cut away view of a perforating system with detonating shaped charges. 
       FIG. 6  is a cross sectional view of an embodiment of a shaped charge having a liner formed by the process described herein. 
       FIG. 7  represents in flow chart form an embodiment of a shaped charge case forming process. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present disclosure involves a shaped charge liner and a method of making the shaped charge liner. The method disclosed herein involves a form of metal injection molding wherein metal powders are mixed with binders and the mixture is subsequently injected under pressure into a mold. The binder is then removed during a de-binding process in order to form the final product. 
   With reference now to  FIG. 2 , an embodiment of forming a liner in accordance with the present disclosure is shown in flow chart form. Initially an amount of metal powder is combined with an amount of binder to form a mixture (step  100 ). The amount of metal powder of the mixture can range from about 20% up to about 100%, therefore the amount of binder will range from about 0% to about 80%. The particulate size of the powdered metal can range from about 1 micron to in excess of 70 microns. 
   The powdered metal can be chosen from the list comprising: tungsten, uranium, hafnium, tantalum, nickel, copper, molybdenum, lead, bismuth, zinc, tin, silver, gold, antimony, cobalt, zinc alloys, tin alloys, nickel, palladium, and combinations thereof. Optionally, in place of the powdered metal, other materials such as ceramic, high density polymers, or cementitious materials can be substituted. Another option is to use a coated powder metal, where the coating typically comprises a metal whose hardness is less than that of the particle being coated. 
   The binder can be selected from the list comprising: polyolefines such as polyethylene, polypropylene, polystyrenes, polyvinyl chloride, polyetheylene carbonate, polyethylene glycol, microcrystalline wax, ethylene-vinyl acetate copolymer and the like; acrylic resins such as polymethyl methacrylate, polybutyl methacrylate; styrene resins such as polystyrene; various resins such as polyvinyl chloride, polyvinylidene chloride, polyamide, polyester, polyether, polyvinyl alcohol, copolymers of the above; various waxes; paraffin; higher fatty acids (e.g., stearic acid); higher alcohols; higher fatty acid esters; higher fatty acid amides. Other binder possibilities include: acetyl based, water soluble, agar water based and water soluble/cross-linked; acetyl based binders comprise polyoxymethylene or polyacetyl with small amounts of polyolefin. The use of metal injection molded binders is well known and thus the size of the binder particulate can vary depending on the type of binder and/or the application. Accordingly, choosing a proper binder particulate size is within the scope of those skilled in the art. 
   Upon forming the mixture  22  of the metal powder and binder the mixture  22  is injection molded (step  102 ). One embodiment of injection molding the mixture  22  employs an injection molding device  12 , an example of which is shown in  FIG. 3 . In this embodiment, both the powder  18  and the binder  20  are directed through respective dispensers  14  to a chute  16 , where the chute in turn guides the mixture  22  into the injection molding device  12 . The mixture  22  can be formed within the chute  16 , the injection molding device  12 , or alternatively, the mixture  22  can be formed prior to being directed into the chute  16 . Once inside the injection molding device  12 , the mixture  22  is within the plenum  26  of the injection molding device  12 . Rotation of an auger  24  disposed within the plenum  26  agitates the mixture  22  thereby insuring a uniformity of the mixing of the binder and powder. The auger  24  action also directs the mixture  22  towards an exit port  27  disposed on the side of the injection molding device  12  distal from the chute  16 . Moreover, the auger  24  provides a source of pressure for urging the mixed and homogenous mixture  22  from within the plenum  26  through the exit port  27  and into the inner confines of a mold  28 . Urging the mixture  22  into the mold  28  under pressure forms a liner shape  30  having the constituents of the mixture  22  (step  104 ). 
   One embodiment of a liner shape  30  is shown in  FIG. 4 . It should be pointed out that this liner has but one of the possible shapes that could be formed from the mixture  22  described herein. With regards to an actual liner  10  made in accordance with the method and process described herein, any liner shape could be formed with this process. Shapes such as conical frusto-conical, triangular, tulip and trumpet shape, and parabolic shapes, to name but a few, are considered within the scope and purview of the present invention. 
   Optionally, binder in the liner shape  30  can be removed after the shape  30  is taken from the mold  28 . Removing the binder can be done both chemically, i.e. with solvents or liquids, and thermally by heating the liner shape. Mechanical or chemical debinding can begin with applying to the shape  30  a debinding liquid or solvent (step  106 ). This step involves chemically dissolving the organic binder with the de-binding liquid. Debinding can occur at atmosphere or under vacuum. The debinding solutions for use with the present method include water, nitric acid, and other organic solvents. However any suitable debinding solution can be used with the present method and skilled artisans are capable of choosing an appropriate debinding solution. During debinding, the liner shape  30  can be sprayed with the de-binding liquid or placed in a bath of de-binding solution. 
   After the liner shape  30  is processed with the liquid de-binding solution, the remaining binder is removed during a thermal de-binding process (step  106 ). The thermal de-binding process involves placing the liner shape into a heated unit, such as a furnace, where it is heated at temperature for a period of time. With regard to the de-binding temperature, it should be sufficient to cause it to remove remaining binder within the liner that remains after chemical de-binding and yet be low enough to not exceed the melting point of a metal powder used as part of the liner constituency. It is believed as well within the capabilities of those skilled in the art to determine a proper temperature and corresponding heating time to accomplish this process. 
   An optional sintering process (step  108 ) may be implemented. The shape  30  can be sintered in addition to debinding or sintered without debinding. Sintering comprises placing the liner shape into a furnace at a temperature sufficient to soften the metal particles without melting them. Softening the particles causes particle adhesion and removes voids or interstices between adjacent particles, thereby increasing liner density. 
   In an optional embodiment, the method comprises forming a shaped charge  5   a  using the liner shape  30  formed in the injection molding process, without de-binding, sintering, or otherwise heating or other treatment of the injection molded product. The shaped charge  5   a  comprising the injection molded formed liner can then be included within a perforating system, disposed within a wellbore, and detonated. Such an injection molded part implemented for final use without a debinding step, or other treatment such as sintering or heating, can be referred to as a green part. Thus a green part liner  30  could be used as the final product liner in a shape charge  5   a . Accordingly instead of a liner that had its binder removed during a de-binding process (step  106 ), in an alternative embodiment a shaped charge  5   a  comprising a green part liner  30  can be formed and used as part of a perforating system. An advantage of a green part is because it is not heated, its final dimensions do not change after the injection molding process, unlike products subjected to heating and injection molding. Accordingly the size of the mold  28  could be more accurate in conforming to the required size of the final product. 
   In one embodiment, the injection molded liner has a density ranging from about 15 gm/cc to about 19 gm/cc, in another embodiment the liner density ranges from about 16 gm/cc to about 18 gm/cc, in yet another embodiment the liner density is about 17.6 gm/cc. 
   In one embodiment the liner composition comprises a mixture of a first metal, a second metal, and an optional third metal. The first metal has, in one embodiment, a density greater than about 11 gm/cc, in another embodiment a density greater than about 13 gm/cc, in another embodiment a density greater than about 15 gm/cc, in another embodiment a density greater than about 17 gm/cc, and in another embodiment a density greater than about 19 gm/cc. The second metal has, in one embodiment, a density up to about 10 gm/cc, in another embodiment a density up to about 9 gm/cc, in another embodiment a density up to about 8.8 gm/cc, in another embodiment a density up to about 8.5 gm/cc, and in another embodiment a density greater than 19 gm/cc. The third metal may have a density up to about 10 gm/cc, in one embodiment a density up to about 9 gm/cc, in another embodiment a density up to about 8.8 gm/cc, in another embodiment a density up to about 8.5 gm/cc, and in another embodiment a density greater than 19 gm/cc. 
   The mixture, in one embodiment, comprises from about 50% to about 99% by weight of the first metal, and about 1% to about 50% by weight of the second metal. In another embodiment, the mixture comprises from about 50% to about 98% by weight of the first metal, about 1% to about 40% by weight of the second metal, and about 1% to about 40% by weight of the third metal. In another embodiment, the mixture comprises from about 50% to about 98% by weight of the first metal, about 1% to about 40% by weight of the second metal, and about 1% to about 40% by weight of the third metal. In another embodiment, the mixture comprises from about 60% to about 95% by weight of the first metal and about 5% to about 15% of the second metal, and about 5% to about 15% of the third metal. In another embodiment, the mixture comprises about 92% by weight of the first metal and up to about 8% of the second metal, and up to about 8% of the third metal. The first metal may comprise tungsten, the second metal may comprise nickel, and the third metal may comprise copper. In one embodiment, the liner comprises greater than 97% by weight of tungsten, in another embodiment the liner comprises greater than 97% by weight of tungsten up to about 99% by weight of tungsten. 
   With reference now to  FIG. 5  one embodiment of the final product of the present disclosure is shown combined with a perforating system  32 . The perforating system  32  comprises a perforating gun  36  disposed within a wellbore  42  by a wireline  44 . As shown, the surface end of the wireline  44  is in communication with a field truck  34 . The field truck  34  can provide not only a lowering and raising means, but also surface controls for controlling detonation of the shaped charges of the perforating gun  36 . With regard to this embodiment, the liner  10   a  is made in accordance with the disclosure herein is combined with a shaped charge  5   a  that is disposed in the perforating gun  36 . Also shown are perforating jets  38 , created by detonation of each shaped charge  5   a  thereby creating perforations  41  within the formation  40  surrounding the wellbore  42 . Accordingly the implementation of the more homogenous and uniform liner material made in accordance with the method described herein is capable of creating longer and straighter perforations  41  into the accompanying formation  40 . 
   It should be pointed out that the shaped charge  5   a  of  FIG. 6  has essentially the same configuration as the shaped charge  5  of  FIG. 1 .  FIG. 6  is provided for clarity and to illustrate that shaped charges having the traditional configuration can be formed with a liner  10   a  made in accordance with the disclosure provided herein. Moreover, the formation process disclosed herein can also be applicable for the forming of a charge case or housing. As seen in  FIG. 7 , a process similar to that of  FIG. 2  is illustrated. With regard to the process of  FIG. 7 , a mixture of metal powder and binder is formed (step  200 ). The metal powder used in the formation of a charge case includes the metals used in the liner formation and further comprises steel such as carbon steel and stainless steel and other metals including monel, inconel, as well as aluminum. 
   Also similar to the process of forming a liner, after mixing the shaped charge case components, the mixture is directed to an injection mold (step  202 ). Moreover, the injection mold can be the same as or substantially similar to the injection molding device  12  of  FIG. 3 . The mixture can be formed prior to being placed in the injection molding device or can be formed while in the injection molding device. Steps  204 ,  206 , and  208  of  FIG. 7  are substantially similar to the corresponding steps  104 ,  106 , and  108  of  FIG. 2 . One difference however between formation of the charge case and liner is that the charge case forming step (step  204 ) would require a mold having a charge case configuration instead of a liner shaped mold. Also similarly, the present method can involve producing an injection molded charge case without the de-binding or sintering steps thereby producing a “green part” charge case. While the sintering temperature and time of sintering depends on the constituent metals and their respective amounts, it is within the scope of those skilled in the art to determine an appropriate sintering temperature, time, as well as other furnace conditions, such as pressure and ambient components. 
   The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.