Patent Publication Number: US-6702039-B2

Title: Perforating gun carriers and their methods of manufacture

Description:
This application claims the benefit of U.S. Provisional Application No. 60/279,996, filed Mar. 30, 2001, and U.S. Provisional Application No. 60/345015, filed Oct. 29, 2001. 
    
    
     FIELD OF THE INVENTION 
     The subject matter of the present invention relates to perforating gun carriers and their methods of manufacture. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a typical shaped charge, loading tube, and perforating gun carrier. 
     FIG. 2 is a perspective view of a typical shaped charge and loading tube. 
     FIG. 3 is a perspective view of a loading tube being inserted into a perforating gun carrier. 
     FIG. 4 is a perspective view of a perforating gun carrier made by machining longitudinal grooves into the outer surface of the carrier. 
     FIG. 5 is a perspective view of a perforating gun carrier made by machining spiral grooves into the outer surface of the carrier. 
     FIGS. 6 a - 6   f  are side views of exemplary embodiments of perforating gun carriers having machined grooves. 
     FIG. 7 is a perspective view of flat sheet metal stock used in an embodiment of the electric resistance weld manufacture of a perforating gun carrier. 
     FIG. 8 is a perspective view of a high strength perforating gun carrier made by an embodiment of the electric resistance weld manufacturing method. Recesses are milled into the gun carrier. 
     FIG. 8 a  is a cross-sectional view of the gun carrier of FIG. 8 taken along the line a—a. 
     FIG. 9 is a perspective view of a high strength perforating gun carrier made by an embodiment of the electric resistance weld manufacturing method. Grooves are extruded from the gun carrier. 
     FIG. 9 a  is a cross-sectional view of the gun carrier of FIG. 9 taken along the line a—a. 
     FIG. 10 is a perspective view of flat sheet metal stock used in an embodiment of the electric resistance weld manufacture of a perforating gun carrier. Grooves have been extruded from the sheet metal stock. 
     FIG. 11 is a perspective view of a high strength perforating gun carrier made by an embodiment of the electric resistance weld manufacturing method. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 1-3 provide an illustration of a typical shaped charge, loading tube, and perforating gun carrier used for perforating a well casing. Typical shaped charges for use in perforating guns are discussed in U.S. Pat. No. 4,724,767 to Aseltine issued Feb. 16, 1988; U.S. Pat. No. 5,413,048 to Werner et al. issued May 9, 1995; U.S. Pat. No. 4,669,384 to Chawla et al. issued Jun. 2, 1987; and again in U.S. Pat. No. 5,597,974 to Voreck, Jr. et al. issued Jan. 28, 1997. Each of the above mentioned disclosures are incorporated by reference into this specification. 
     A typical shaped charge  1  includes a case  10 , a main body of explosive material  12 , which in the past has been, for example, RDX, HMX, PYX, HTX, or HNS packed against the inner wall of the case  10 , a primer  13  disposed adjacent the main body of explosive  12  that is adapted to detonate the main body of explosive  12  when the primer  13  is detonated, and a liner  14  lining the primer  13  and the main body of explosive material  12 . The liner  14  acts to maintain the shape of the explosive to assure proper propagation of the detonation. A detonating cord  20  contacts the case  10  of the shaped charge  1  at a point nearest the apex of the liner  14  of the charge. When a detonation wave propagates within the detonating cord  20 , the detonation wave will detonate the primer  13 . When the primer  13  is detonated, the detonation of the primer  13  will further detonate the main body of explosive  12  of the charge  1 . In response to the detonation of the main body of explosive  12 , the liner  14  will form a jet that will propagate along a longitudinal axis of the shaped charge  1 . 
     One or more shaped charges  1  are housed within a loading tube  22  or loading strip for transport. The loading tube  22  can house the shaped charges  1  at desired orientations, or in a linear fashion. A jacket  24 , if used, both secures the shaped charges  1  to the loading tube  22  and to maintains the orientation of the shaped charges  1 . Once the loading tube  22  is ready for delivery downhole, a perforating gun carrier  30  is used to carry the loading tube  22  and housed shaped charges  1 . 
     In one conventional use, the shaped charges  1  and jackets  24  are inserted into the loading tube  22  until the jackets  24  shoulder against the loading tube shoulders  23 . Once all of the shaped charges  1  are secured, the loading tube  22  is inserted into the interior of a perforating gun carrier  30 . The gun carrier  30  then transports the shaped charges  1  downhole to the desired depth of perforation. 
     Upon detonation, the jets from the shaped charges  1  pierce the perforating gun carrier  30 , the well casing and the formation penetrated by the wellbore. When the jets pierce the gun carrier  30 , they generate circular, jagged pieces of metal (“burrs”) that may extend beyond the surface of the gun carrier  30 . To minimize any increase in overall diameter of the gun carrier  30 , recesses (“scallops”)  32  are milled into the outer surface of the gun carrier  30 . By aligning the shaped charges  1  such that the generated jets penetrate the recesses  32 , the resulting burrs effect on the overall diameter of the gun carrier  30  is reduced by the depth of the recesses  32 . 
     As shown in FIG. 4, one embodiment of the present invention provides a method of minimizing any increase in overall diameter of the gun carrier  30  resulting from the burrs generated by the shaped charge jets. In this method, grooves  34  are machined into the gun carrier  30  by extruding the gun carrier  30  through dies in either a cold-working or a hot-working process. The width and angles of the grooves  34  are extruded to match the desired gun pattern. The grooves  34  are located where the jets of the shaped charges  1  are intended to exit the gun carrier  30 . 
     In the embodiment shown in FIG. 4, the grooves  34  extend longitudinally along the length of the gun carrier  30 . However, the grooves  34  can be extruded in alternate patterns such as helical or spiral, for example. FIG. 5 illustrates spiral grooves  34  extending along the length of the gun carrier  30 . Further, as shown in FIGS. 6 a - 6   e,  the grooves  34  may be extruded in any number of geometries. As examples, FIG. 6 a  provides beveled edge grooves, FIG. 6 b  provides dove tail shaped grooves, FIG. 6 c  provides curved grooves, FIG. 6 d  provides flat grooves, FIG. 6 e  provides v-shaped grooves, and FIG. 6 f  provides radiused corner grooves. 
     With reference to FIGS. 7-9, an embodiment of the manufacture of alloy steel tubing for use as a perforating gun carrier  40  is detailed. The alloy steel tubing is manufactured by the electric resistance weld (ERW) method. Flat sheet metal stock  42  of the alloy steel is first rolled into a hollow tube  43 . Subsequently, the ends  42   a,    42   b  of the sheet metal stock  42  are welded using ERW techniques to complete the tube  43 . Finally, the hollow tube  43  is stretched and reduced, and heat treated (quenched and tempered). The end result is an alloy steel tube  43  for use as a perforating gun carrier  40  that has strength and toughness characteristics similar to heat treated alloy steel tubing produced by either a “hot finished” or “cold drawn” process, and has low wall thickness variations similar to plain carbon steel tubing manufactured by the ERW method. 
     Typically, to complete the manufacture of the high strength, uniform thickness perforating gun carrier  40 , recesses  44  (shown in FIG. 8) are machined into the outer surface of the gun carrier  40 . The recesses  44  are formed on the outer surface of the gun carrier  40  by conventional milling. In an alternate embodiment, shown in FIG. 9, grooves  46  are formed on the outer surface of the gun carrier  40  by the extrusion process detailed above. 
     As best seen in FIGS. 8 a  and  9   a , cross-sectional views taken along the lines  8 A and  9 A of FIGS. 8 and 9, respectively, the wall thickness T, less the depth of the recess d, is the web thickness t. It is the web thickness t that the shaped charge jet must pass through when the shaped charge detonates. Because the wall thickness T of the high strength, uniform thickness perforating gun carrier  40  is substantially uniform, the recesses  44  can be machined into the wall of the carrier  40  to more consistently generate a uniform web thickness t. A uniform web thickness t provides more consistent shape charge performance, allowing the shaped charge to be more effectively optimized for highest performance. 
     If the high strength, uniform thickness perforating gun carrier  40  is being used as a deep penetrator perforating gun carrier, it is not necessary to have machined recesses or grooves in the carrier wall through which the shaped charge jet. In such instances, the objective is to provide maximum hole size in the casing that is shot. It is desirable to have a minimum of the jet material absorbed by the wall of the gun carrier  40  to provide a maximum of jet material to strike the wellbore casing. Clearly, variations in the wall thickness T can have an adverse effect on the performance of the shaped charge. If the wall thickness T is too thick, some of the high energy portion of the jet must be used to penetrate the gun carrier  40 , resulting in a smaller casing entrance hole. Likewise, if the wall thickness T is too thin, some of the smaller portion of the jet survives the penetration of the gun carrier  40  and enters the casing, also resulting in a smaller casing entrance hole. Thus, in deep penetrator applications, specific importance is placed on the perforating gun carrier  40  having a low variation in wall thickness T. 
     FIGS. 10 and 11 illustrate yet another embodiment of the manufacture of alloy steel tubing for use as a perforating gun carrier  40 . As above, the alloy steel tubing is manufactured by the ERW method. However, in this embodiment, grooves  42  are extruded from the flat sheet metal stock  42  prior to rolling into a hollow tube  43 . 
     EXAMPLE 1 
     The following example compares the performance of gun carriers made from conventional hot finished mechanical tubing with the performance of the high strength, uniform wall thickness gun carriers  40  made by the ERW method discussed above. For purposes of illustration, the gun carriers in the example have a wall thickness T of 0.500 inches and a recess depth d machined to 0.280 inches. It should be noted that the example applies equally to embodiments of gun carriers  40  having grooves  46  extruded by the methods detailed above. 
     1) Conventional hot finished gun carrier. Conventional gun carriers are made from hot finished mechanical tubing. The wall thickness T of a conventional gun carrier has a variance of approximately 10 percent. Thus, in the present example, the resulting thickness T ranges between 0.450 inches and 0.550 inches. The recess depth d of 0.280 inches is machined with a variance of 0.010 inches. The resulting range of the recess depth d is between 0.270 and 0.290 inches. Thus, the web thickness t that the shaped charge jet must shoot through varies between 0.160 inches and 0.280 inches. The variance range of the web thickness t is 0.120 inches. 
     2) Alloy Steel ERW Gun Carrier. By contrast, the high strength, uniform wall thickness gun carrier  40  manufactured by the ERW method discussed above has a wall thickness T having a variance of approximately 4 percent. The resulting thickness T ranges between 0.480 inches and 0.520 inches. The recess depth d is again machined to 0.280 inches with a variance of 0.010 inches. Thus, the web thickness t that the shaped charge jet must shoot through varies between 0.190 inches and 0.250 inches. The variance range of the web thickness t of 0.060 inches is half the range of the conventional gun carrier web thickness t. 
     The above discussed data of Example 1 is provided in tabular form in Table I below. 
     
       
         
           
               
             
               
                 TABLE I 
               
             
            
               
                   
               
               
                 Conventional v. ERW Gun Carrier Web Thickness 
               
            
           
           
               
               
               
            
               
                   
                 Conventional Carrier 
                 Allow Steel ERW Carrier 
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                 Thickness (T) (in.) 
                 0.500 
                 0.500 
               
               
                 T Range (in.) 
                 0.450-0.550 
                 0.480-0.520 
               
               
                 Recess Depth (d) (in.) 
                 0.280 
                 0.280 
               
               
                 d Range (in.) 
                 0.270-0.290 
                 0.270-0.290 
               
               
                 Web Thickness (t) 
                 0.160-0.280 
                 0.190-0.250 
               
               
                 Range (in.) 
               
               
                 Variance Range (in.) 
                 0.120 
                 0.060 
               
               
                   
               
            
           
         
       
     
     Another embodiment of manufacture of alloy steel tubing for use as a perforating gun carrier  40  utilizes the ERW method of manufacture described above. However, in this embodiment, after heat treating (quenching and tempering), the material of the hollow tube  43  is cold worked through the drawn over mandrel or cold drawing process to further increase the strength of the material. Subsequently, the material of the hollow tube  43  is stress relieved or tempered to generate a high level of toughness. 
     In addition to improving the strength and toughness of the material, the subsequent cold working and stress relieving also increases the uniformity of the OD and ID dimensions of the perforating gun carrier  40 . The associated highly uniform bending moments of inertia enable the gun carrier  40  to be used in gun strings which must be aligned or oriented in a bent wellbore without adversely turning the gun string out of orientation. 
     Once again, the manufacture of the high strength perforating gun carrier  40  is completed by machining recesses  44 , or grooves  46 , into the outer surface of the gun carrier  40 . 
     EXAMPLE 2 
     The following example compares the performance of high strength, uniform thickness gun carriers made from: 1) The ERW process without subsequent cold working and stress relieving; and 2) The ERW process with subsequent cold working and stress relieving. 
     1) ERW Process Without Subsequent Cold Working and Stress Relieving. As detailed in Example 1, the high strength gun carrier  40  made by the ERW process has a wall thickness T of 0.500 inches with a variance of 4 percent. The resulting thickness T ranges between 0.480 inches and 0.520 inches. The recess depth d is again machined to 0.280 inches with a variance of 0.010 inches. Thus, the web thickness t that the shaped charge jet must shoot through varies between 0.190 inches and 0.250 inches. The variance range of 0.060 inches is half the range of the conventional gun carrier web thickness t. 
     2) ERW Process With Subsequent Cold Working And Stress Relieving. The high strength, uniform wall thickness gun carrier  40  made by the ERW process with subsequent cold working and stress relieving has a wall thickness T of 0.500 inches with a variance of 2 percent. The resulting thickness T ranges between 0.490 inches and 0.510 inches. The recess depth d is again machined to 0.280 inches with a variance of 0.010 inches. Thus, the web thickness t that the shaped charge jet must shoot through varies between 0.200 inches and 0.240 inches. The variance range of 0.040 inches is one-third the range of the conventional gun carrier web thickness t and two-thirds the range of the ERW process without cold working web thickness. 
     The above discussed data of Example 2 is provided in tabular form in Table II below. 
     
       
         
           
               
             
               
                 TABLE II 
               
             
            
               
                   
               
               
                 ERW Carrier v. Cold Worked ERW Carrier 
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 Alloy Steel 
               
               
                   
                 Conventional 
                 Alloy Steel 
                 ERW Carrier 
               
               
                   
                 Carrier 
                 ERW Carrier 
                 (cold worked) 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                 Thickness (T) (in.) 
                 0.500 
                 0.500 
                 0.500 
               
               
                 T Range (in.) 
                 0.450-0.550 
                 0.480-0.520 
                 0.490-0.510 
               
               
                 Recess Depth (d) (in.) 
                 0.280 
                 0.280 
                 0.280 
               
               
                 d Range (in.) 
                 0.270-0.290 
                 0.270-0.290 
                 0.270-0.290 
               
               
                 Web Thickness (t) 
                 0.160-0.280 
                 0.190-0.250 
                 0.200-0.240 
               
               
                 Range (in.) 
               
               
                 Variance Range (in.) 
                 0.120 
                 0.060 
                 0.040 
               
               
                   
               
            
           
         
       
     
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such are intended to be included within the scope of the following non-limiting claims.