Patent Publication Number: US-8978749-B2

Title: Perforation gun string energy propagation management with tuned mass damper

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of 35 U.S.C. 371 National Stage of and claims priority to International Application No. PCT/US12/56164, filed Sep. 19, 2012, entitled “PERFORATION GUN STRING ENERGY PROPAGATION MANAGEMENT WITH TUNED MASS DAMPER,” which is incorporated herein by reference in its entirety for all purposes. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not applicable. 
     BACKGROUND 
     Wellbores are drilled into the earth for a variety of purposes including tapping into hydrocarbon bearing formations to extract the hydrocarbons for use as fuel, lubricants, chemical production, and other purposes. When a wellbore has been completed, a metal tubular casing may be placed and cemented in the wellbore. Thereafter, a perforation tool assembly may be run into the casing, and one or more perforation guns in the perforation tool assembly may be activated and/or fired to perforate the casing and/or the formation to promote production of hydrocarbons from selected formations. Perforation guns may comprise one or more explosive charges that may be selectively activated, the detonation of the explosive charges desirably piercing the casing and penetrating at least partly into the formation proximate to the wellbore. 
     SUMMARY 
     In an embodiment, a perforation tool assembly comprises a perforation gun, and a mass energy absorber coupled to the perforation gun. The mass energy absorber is configured to alter the propagation of mechanical energy released by firing one or more perforation guns. The mass energy absorber comprises a mass and at least one absorber, and the at least one absorber is disposed between the mass and the perforating gun. 
     In an embodiment, a perforation tool assembly comprises a plurality of perforation guns, and a mass energy absorber disposed between at least two of the plurality of perforation guns. The mass energy absorber is configured to reduce the propagation of mechanical energy across the mass energy absorber. The mass energy absorber comprises a mass and at least one absorber, and the mechanical energy is released by firing one or more perforation guns. 
     In an embodiment, a method of perforating a casing string in a wellbore comprises modeling a wellbore, modeling a perforation tool assembly, wherein the perforation tool assembly comprises at least one perforation gun and a mass energy absorber, simulating firing the at least one perforation gun, designing the mass energy absorber based on the simulating, firing the first perforation gun when the first perforating gun is disposed in a wellbore, and attenuating a mechanical energy that propagates across the mass energy absorber, where the mechanical energy is associated with firing the first perforation gun. 
     In an embodiment, a perforation tool assembly is disclosed. The perforation tool assembly comprises a tool string connector, a perforation gun coupled to the tool string connector, and a structure configured to absorb mechanical energy released by firing one or more perforation guns. The coupling is configured to provide a limited range of motion of the tool string connector relative to the perforation gun. The tool string connector and the perforation gun retain the structure configured to absorb mechanical energy. 
     In an embodiment, a perforation tool assembly is disclosed. The perforation tool assembly comprises a tool string connector having a latch component, a perforation gun having a latch mate that is configured to engage the latch component to couple the perforation gun to the tool string connector, and a mechanical energy absorber configured to absorb mechanical energy released by firing one or more perforation guns. The tool string connector and the perforating gun are configured to provide a limited range of motion of the tool string connector relative to the perforation gun when the mechanical energy absorber is not located between the tool string connector and the perforation gun. The mechanical energy absorber is retained by the tool string connector and the perforation gun. 
     In an embodiment, a method of perforating a casing sting in a wellbore is disclosed. The method comprises placing a perforation gun in a wellbore, placing a mechanical energy propagation management device between the perforation gun and a tool string connector, and coupling the perforation gun to the tool string connector, wherein the perforation gun and the tool string connector are configured to move relative to each other within a limited range of motion. 
     In an embodiment, a perforation tool assembly comprises a perforation gun string; and a mass energy absorber coupled to the perforation gun. The mass energy absorber comprises a mass disposed within a tool body; and at least one spring, where the at least one spring is disposed between the mass and the tool body. 
     In an embodiment, a method of absorbing energy during a perforation event comprises detonating at least one explosive charge in a perforation gun to create a shock wave; transferring the shock wave to a mass energy absorber coupled to the perforation gun, wherein the mass energy absorber comprises: a mass disposed within a tool body, and one or more retaining elements disposed between the mass and the tool body, and wherein the perforation gun and the mass energy absorber are disposed in a perforation gun assembly; inducing movement of the mass based on the transferring of the shock wave; and removing energy from the perforation gun assembly in response to the movement of the mass. 
     These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts. 
         FIG. 1  is an illustration of a wellbore and workstring according to an embodiment of the disclosure. 
         FIG. 2  is an illustration of a perforation tool assembly according to an embodiment of the disclosure. 
         FIG. 3  is an illustration of an exemplary shock load function according to an embodiment of the disclosure. 
         FIG. 4A  is an illustration of a tool string connector and a perforation gun in a first state according to an embodiment of the disclosure. 
         FIG. 4B  is an illustration of the tool string connector and a perforation gun in a second state according to an embodiment of the disclosure. 
         FIG. 5  is an illustration of the tool string connector and a perforation gun in the second state exhibiting a range of motion of the tool string connector relative to the perforation gun according to an embodiment of the disclosure. 
         FIG. 6A  is an illustration of the tool string connector and a perforation gun retaining a first mechanical energy absorbing structure in the first state according to an embodiment of the disclosure. 
         FIG. 6B  is an illustration of the tool string connector and a perforation gun retaining a second mechanical energy absorbing structure in the first state according to an embodiment of the disclosure. 
         FIG. 7A  is an illustration of a mechanical energy absorbing structure viewed from the edge according to an embodiment of the disclosure. 
         FIG. 7B  is an illustration of the mechanical energy absorbing structure viewed from above according to an embodiment of the disclosure. 
         FIG. 8  is an illustration of a mechanical energy absorbing structure viewed from above according to an embodiment of the disclosure. 
         FIG. 9A  is an illustration of a mechanical energy absorbing structure viewed from the edge according to an embodiment of the disclosure. 
         FIG. 9B  is an illustration of a mechanical energy absorbing structure viewed from above. 
         FIG. 10  is an illustration of a mechanical energy absorbing structure viewed from the edge according to an embodiment of the disclosure. 
         FIG. 11  is an illustration of a mechanical energy absorbing structure viewed from above according to an embodiment of the disclosure. 
         FIG. 12  is a flow chart of a method according to an embodiment of the disclosure. 
         FIG. 13  is an illustration of a mass energy absorber according to an embodiment of the disclosure. 
         FIG. 14  is an illustration of a computer system according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It should be understood at the outset that although illustrative implementations of one or more embodiments are illustrated below, the disclosed systems and methods may be implemented using any number of techniques, whether currently known or not yet in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, but may be modified within the scope of the appended claims along with their full scope of equivalents. 
     In recent downhole wellbore servicing practice, perforation tool assemblies have featured increasing numbers of explosive charges, and the overall length of the perforation tool assemblies has increased. Along with this evolution, new problems have been experienced during wellbore servicing operations. These problems may include perforation tool assemblies that separate, leaving a portion of the perforation tool assembly in the wellbore when the workstring is removed from the wellbore after firing the perforation guns. The perforation tool assembly and/or workstring may buckle, deform, or yield. The perforation tool assembly and/or workstring may fail in compression or in a corkscrew buckling mode. In some failures, the perforation tool assembly and/or workstring may become stuck in the wellbore. A packer in the workstring and/or tubing above the perforation tool assembly may be damaged. Yet other failure modes may be experienced. These problems may entail time consuming and expensive fishing operations to capture and retrieve portions of the perforation tool assembly that parted. These problems may delay placing the wellbore on production, thereby incurring financial losses. In a worst case scenario, the wellbore may be lost entirely. 
     It is a teaching of the present disclosure that, in some cases, the cause of these problems experienced during the course of perforating the wellbore may be ascribed to an accumulation of energy in a shock wave, a shock wave peak, and/or a shock load that propagates in a tool body of the perforation tool assembly. This may be referred to as an accumulation of the shock load in a tool body of the perforation tool assembly. As used herein, the term shock load may have a variety of meanings. One meaning is to refer to a mechanical stress caused by detonation of one or more explosive charges that is applied as a force on the perforation tool assembly and/or workstring. To some extent, most of the shock load may comprise a force directed parallel to an axis of the perforation tool assembly and/or workstring. This stress may be applied both downhole and uphole parallel to the axis of the perforation tool assembly and/or workstring. It is understood that in some circumstances, the perforation tool assembly and/or workstring may be curved or arced over one or more segments. In this circumstance, the expression “parallel to an axis” is understood to mean tangent to the arc of the perforation tool assembly and/or workstring at the point of interest. Notwithstanding, a portion of the stress may be directed in other directions such as radial to the perforation tool assembly and/or workstring. 
     As explosive charges in the perforation guns of the perforation tool assembly are detonated, some of the energy released by the detonation propagates in the tool body of the perforation tool assembly, parallel to the axis of the perforation tool assembly. If the activation of the explosive charges progresses parallel to the axis of the perforation gun assembly at about the same speed that the shock wave propagates in the tool body, the energy in the shock wave can accumulate and/or build with each successive detonation, increasing the shock load. In an embodiment, the shock wave may travel down the perforation tool assembly in a compression wave, reflect off the end of the perforation tool assembly, and travel back up the perforation tool assembly as a tensile wave. Some failure modes may be associated with compression waves, and other failure modes may be associated with tensile waves. While descriptions herein refer to a top to bottom detonation sequence of explosive charges and/or perforation guns, it is understood that other detonation sequences are consistent with the present disclosure. 
     Under some circumstances, it may be desirable to create a dynamic underbalance condition in the wellbore immediately following charge detonation. The dynamic underbalance is a transient pressure condition in the wellbore during the perforating operation that allows the wellbore to be maintained at an overbalanced pressure condition prior to perforating. The dynamic underbalance condition can be created using hollow carrier type perforating guns, which consists of an outer tubular member that serves as a pressure barrier to separate the explosive train from pressurized wellbore fluids prior to perforating. The interior of the perforating guns contains the shaped charges, the detonating cord and the charge holder tubes. The remaining volume inside the perforating guns consists of air at essentially atmospheric pressure. 
     Upon detonation of the shaped charges, the interior pressure rises to tens of thousands of psi within microseconds. The detonation gases then exit the perforating guns through the holes created by the shaped charge jets and rapidly expand to lower pressure as they are expelled from the perforating guns. The interior of the perforating guns becomes a substantially empty chamber which rapidly fills with the surrounding wellbore fluid. In some cases, an underbalance subassembly may be incorporated into a perforation gun string that carries no charges itself but which is designed to suddenly open to contribute to the dynamic underbalance condition immediately following charge detonation. Further, as there is a communication path via the perforation tunnels between the wellbore and reservoir, formation fluids rush from their region of high pressure in the reservoir through the perforation tunnels and into the region of low pressure within the wellbore and the empty perforating guns. All this action takes place within milliseconds of gun detonation. In an embodiment, the dynamic underbalance may contribute to the forces in the perforation tool assembly and/or the shock load in the perforation tool assembly. 
     A method and apparatus for mitigating a shock load in a perforation tool assembly is taught herein. In an embodiment, the shock load may be managed in one or more ways. The shock wave may have a portion of its energy frequency shifted to a different frequency by one or more components in the perforation tool assembly. For example, a tool string connector and a perforation gun may be assembled with a nonlinear spring located between them. The tool string may be coupled to the perforation gun so as to provide a limited range of relative motion, for example axial motion of the perforation gun relative to the tool string connector. As the shock wave propagates from the perforation gun to the tool string connector, the nonlinear spring transforms a portion of the shock wave energy to higher order harmonic frequencies. 
     The shock wave may have a portion of its energy absorbed by one or more components in the perforation tool assembly. For example, a tool string connector and a perforation gun may be assembled with a mechanical energy absorbing structure located between them. The tool string may be coupled to the perforation gun so as to provide a limited range of relative motion between the two components, for example axial motion (e.g., free motion) of the perforation gun relative to the tool string connector. When the shock load propagates from the perforation gun to the tool string connector, the perforation gun moves with reference to the tool string connector, and the mechanical energy absorber disposed between the perforation gun and the tool string connector may be configured to absorb at least a portion of the energy. For example, energy from the shock load is consumed in crushing a honeycomb structure or crushing a grooved or fluted ductile metal washer. As another example, the structures may comprise one or more energy mass absorbers where a mass is suspended within a segment of tubing with energy absorbing elements and/or spring members supporting the mass on either end. The mass absorber may be disposed between guns of a multi-gun system to absorb and/or disrupt the transmission of the shock waves along the string. 
     The wellbore and the perforation gun string may be modeled, and a perforation job may be simulated based on the wellbore model and the perforation gun string model. The results of the simulation may be analyzed to adapt the design of the nonlinear spring and/or the mechanical energy absorber to more desirably manage the shock load propagation in the perforation gun string. For more details of modeling shock loads, see U.S. patent application Ser. No. 13/210,303, entitled “Modeling Shock Produced by Well Perforation,” by John Rodgers, et al., and International Application Serial No. PCT/US10/61104, filed 17 Dec. 2010, entitled “Modeling Shock Produced by Well Perforation,” by John Rodgers, et al., which are hereby incorporated by reference in their entirety. 
     Unless otherwise specified, any use of any form of the terms “connect,” “engage,” “couple,” “attach,” or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and also may include indirect interaction between the elements described. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. Reference to up or down will be made for purposes of description with “up,” “upper,” “upward,” or “upstream” meaning toward the surface of the wellbore and with “down,” “lower,” “downward,” or “downstream” meaning toward the terminal end of the well, regardless of the wellbore orientation. The term “zone” or “pay zone” as used herein refers to separate parts of the wellbore designated for treatment or production and may refer to an entire hydrocarbon formation or separate portions of a single formation such as horizontally and/or vertically spaced portions of the same formation. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art with the aid of this disclosure upon reading the following detailed description of the embodiments, and by referring to the accompanying drawings. 
     Turning now to  FIG. 1 , a wellbore servicing system  10  is described. The system  10  comprises servicing rig  20  that extends over and around a wellbore  12  that penetrates a subterranean formation  14  for the purpose of recovering hydrocarbons from a first production zone  40   a , a second production zone  40   b , and/or a third production zone  40   c . The wellbore  12  may be drilled into the subterranean formation  14  using any suitable drilling technique. While shown as extending vertically from the surface in  FIG. 1 , in some embodiments the wellbore  12  may be deviated, horizontal, and/or curved over at least some portions of the wellbore  12 . For example, in an embodiment, the wellbore  12 , or a lateral wellbore drilled off of the wellbore  12 , may deviate and remain within one of the production zones  40 . The wellbore  12  may be cased, open hole, contain tubing, and may generally comprise a hole in the ground having a variety of shapes and/or geometries as is known to those of skill in the art. In an embodiment, a casing  16  may be placed in the wellbore  12  and secured at least in part by cement  18 . 
     The servicing rig  20  may be one of a drilling rig, a completion rig, a workover rig, or other mast structure and supports a workstring  30  in the wellbore  12 , but in other embodiments a different structure may support the workstring  30 . In an embodiment, the servicing rig  20  may comprise a derrick with a rig floor through which the workstring  30  extends downward from the servicing rig  20  into the wellbore  12 . In some embodiments, such as in an off-shore location, the servicing rig  20  may be supported by piers extending downwards to a seabed. Alternatively, in some embodiments, the servicing rig  20  may be supported by columns sitting on hulls and/or pontoons that are ballasted below the water surface, which may be referred to as a semi-submersible platform or rig. In an off-shore location, a casing  16  may extend from the servicing rig  20  to exclude sea water and contain drilling fluid returns. It is understood that other mechanical mechanisms, not shown, may control the run-in and withdrawal of the workstring  30  in the wellbore  12 , for example a draw works coupled to a hoisting apparatus, a slickline unit or a wireline unit including a winching apparatus, another servicing vehicle, a coiled tubing unit, and/or other apparatus. 
     In an embodiment, the workstring  30  may comprise a conveyance  32  and a perforation tool assembly  34 . The conveyance  32  may be any of a string of jointed pipes, a slickline, a coiled tubing, and a wireline. In another embodiment, the workstring  30  may further comprise one or more downhole tools (not shown), for example above the perforation tool assembly  34 . The workstring  30  may comprise one or more packers, one or more completion components such as screens and/or production valves, sensing and/or measuring equipment, and other equipment which are not shown in  FIG. 1 . In some contexts, the workstring  30  may be referred to as a tool string. The workstring  30  may be lowered into the wellbore  12  to position the perforation tool assembly  34  to perforate the casing  16  and penetrate one or more of the production zones  40 . 
     Turning now to  FIG. 2 , a perforation tool assembly  200  is described. In an embodiment, the perforation tool assembly  200  comprises a plurality of perforation guns  202  optionally interconnected by one or more spacers  204  and terminated by a foot  206 . While the perforation tool assembly  200  is illustrated in  FIG. 2  as comprising a first perforation gun  202   a , a second perforation gun  202   b , and a third perforation gun  202   c , it is understood that the perforation tool assembly  200  may comprise any number of perforation guns  202 . Each perforation gun  202  comprises one or more explosive charges  203  that desirably perforate the casing  16  and the subterranean formation  14  when the perforation gun  202  is activated and/or fired. The perforation tool assembly  200  may further comprise a firing head (not shown) that initiates a detonation train and/or an energy train to fire the perforation guns  202 . The perforation tool assembly  200  may further comprise tandems or other coupling structures (not shown) that are used to promote coupling between perforation guns  202 , spacers  204 , and/or other components in the perforation tool assembly  200 . In an embodiment, the perforation tool assembly  200  may comprise one or more structures for managing the propagation of the shock wave through the perforation tool assembly  200  in response to the perforation guns  202  being fired. 
     The explosive charges  203  may be shaped charges that focus energy in a preferred direction, for example radially outwards. The explosive charges  203  may be designed to have a relatively unfocused energy projection to produce big, shallow holes in the subterranean formation  14 , which may be referred to in some contexts as big hole charges. Alternatively, the explosive charges  203  may be designed to provide highly focused energy projections to produce narrower, deeper penetrations into the subterranean formation  14 , which may be referred to in some contexts as deep penetrating charges. In some embodiments, both big hole charges and deep penetrating charges may be mixed in the perforation tool assembly  200  in various ways. For example, one perforation gun  202  may comprise all big hole charges, and another perforation gun  202  may comprise all deep penetrating charges. Alternatively, in an embodiment, the perforation gun  202  may comprise both big hole charges and deep penetrating charges. The perforation gun  202  may comprise a charge carrier that retains the explosive charges  203  within a tool body of the perforation gun  202 . The tool body may feature scallops or regions of thinned wall proximate to where the explosive charges  203  will fire through the tool body. 
     The spacers  204  may be incorporated in the perforation tool assembly  200  to align the perforation guns  202  desirably with different production zones  40 . For example, it may be desirable to penetrate the casing  16  to produce from a first zone at between 10200 feet and 10230 feet, to penetrate the casing  16  to produce from a second zone at between 10360 feet and 10380 feet, and to penetrate the casing  16  to produce from a third zone at between 10460 feet and 10480 feet. In this case, a first spacer 130 feet in length may be incorporated between the first perforation gun  202   a  and a second spacer 80 feet in length may be incorporated between the second perforation gun  202   b  and the third perforation gun  202   c . The spacers  204  may comprise a plurality of connected pipes and/or tubular bodies. In an embodiment, the perforation tool assembly  200  may not have spacers  204 . 
     In an embodiment, the charges  203  in the perforation guns  202  are detonated by the propagation of an energy train  220  directed downwards and parallel to the axis of the perforation tool assembly  200 . In this case, the first perforation gun  202   a  is activated by the energy train  220  first, the second perforation gun  202   b  is activated by the energy train  220  second and after the first perforation gun  202   a  is activated, and the third perforation gun  202   c  is activated by the energy train  220  third and after the second perforation gun  202   b  is activated. Assuming that the speed of propagation of the energy train  220  parallel to the axis of the perforation tool assembly  200  is approximately equal to the speed of propagation of a shock wave traveling in a tool body of the perforation tool assembly  200 , for example a steel tool body, as each successive perforation gun  202  is fired, a shock wave  222  is created in the perforation tool assembly  200  that propagates downwards and may add to or accumulate with the amplitude of the shock wave already propagating downwards from the previously fired perforation gun  202 . It is understood that in some embodiments this accumulation of amplitude or building of the shock wave may be limited or not occur, for example when the detonation speed in the energy train  220  is faster than or slower than the speed of propagation of the shock wave traveling in the tool body of the perforation tool assembly  200 . Further, additional shock wave interactions may also be created during the detonation of the perforation guns. For example, a portion of the resulting shock waves can comprise a multi-frequency wave distribution (e.g., distributed in frequency and/or amplitude), which may add or cancel at various locations at various times. Since these additional interactions may not contribute to an overall accumulation of the shock wave, they will not be discussed further herein even though one of ordinary skill in the art will recognize that they are present. 
     The graphic arrow  222  conceptually represents this building and/or accumulating amplitude of the shock wave as increasingly thick arrows. Note that the explosion of the charges  203  also creates shock waves that propagate up the tool body and up the workstring  30 , but these shock waves do not overlap in time and hence do not accumulate in amplitude. When the shock wave  222 , which is compressive as it travels downwards, reaches the foot  206  of the perforation tool assembly  200  it reflects back upwards as a tensile shock wave  224 . 
     It is understood that in other embodiments, the perforation guns  202  may be detonated by the propagation of an energy train  220  directed upwards such that the third perforation gun  202   c  is activated by the energy train  220  first, the second perforation gun  202   b  is activated by the energy train  220  second and after the third perforation gun  202   c  is activated, and the first perforation gun  202   a  is activated by the energy train  220  third and after the second perforation gun  202   b  is activated. A shock analysis similar to that for firing from top to bottom can be performed for this firing sequence as well as for other firing sequences, for example where the energy train  220  is first activated between perforation guns  202  and propagates both upwards and downwards at the same time. 
     The structures that alter the propagation of the shock wave may be incorporated into the perforation tool assembly  200 , for example to attenuate the peak magnitude of the shock wave, to change the speed of the shock wave, to change the timing of the shock wave, or to tune the dynamic response of the perforation tool assembly  200  to reduce the shock load on the perforation tool assembly  200 . Some of the structures may promote an acoustic impedance mismatch with the remainder of the perforation tool assembly  200  such that some of the shock wave energy is reflected, thereby attenuating the shock wave energy that is propagated in the direction of detonation propagation. 
     The structures may comprise one or more energy mass absorbers where a mass is suspended within a segment of tubing with energy absorbing elements supporting the mass on one or both ends. When subjected to a large acceleration, for example when the shock wave accelerates the segment of tubing enclosing the mass, the large inertia of the mass resists motion, thus imparting a load on the energy absorber elements supporting the mass. The energy absorbed by the energy absorbing material, for example crushable structures, removes energy from the shock wave. The structures may comprise a deformable energy absorber having non-linear elasticity. This deformable energy absorber may flex very little in response to shock loads up to a threshold level and then, for shock loads above this threshold, yield readily. 
     The structures may comprise one or more energy mass absorbers where a mass is suspended within a segment of tubing with springs (e.g., elastic elements) supporting the mass on either end. The mass-spring system may comprise a natural resonance frequency based on the properties of the mass and the springs. The shock wave may cause the mass to oscillate within the segment of tubing, thereby damping the perforation tool assembly  200  motion at or near the natural resonance frequency. The properties of the mass and/or the springs could be tuned to match the characteristics of the perforation tool assembly  200  and the expected shock and/or loads within the system. One or more of the energy absorbing elements may be used with the springs to further dampen and/or dissipate the energy within the system. 
     Turning now to  FIG. 3 , a shock accumulation  240  is represented as a function of a ratio V e /V s    242  of a speed of the energy train propagation in the direction parallel to the axis of the perforation tool assembly  200 , V e , to a speed of the shock wave propagation in the tool body in the direction parallel to the axis of the perforation tool assembly  200 , V s . Note that the example discussed with reference to  FIG. 3  is directed to a tool gun string  200  that does not employ the structures and methods of energy propagation management described herein. When V e  is substantially less than V s  or substantially greater than V s , the shock waves associated with the detonation of the charges in the perforation guns  202  do not align sufficiently to significantly boost the amplitude of the shock wave. When V e  and V s  approach an equal value, however, the shock waves associated with the detonation of the charges in the perforation guns  202  begin to accumulate in magnitude, an effect which may be referred to as shock accumulation  240  and/or shock gain. The shock accumulation  240  may be mapped to a shock load which may be quantified in units of force. 
     It is understood that the function depicted in  FIG. 3  is exemplary and that in different specific implementations of the perforation tool assembly  200 , a different relationship between the ratio V e /V s    242  and the shock accumulation  240  may be applicable. The maximum amplitude gain  244  may depend upon the total charge load, which may depend at least in part on the number and properties of the charges that are exploded, and/or the distribution of the charge load within the perforation guns. Additionally, the maximum amplitude gain  244  may further depend on the elasticity of the tool body and/or the extent to which the energy in the shock wave is dissipated and/or decays in the tool body. A shock load imparted by exploding charges may initially have a short duration, high amplitude but may become spread out in time as a lower amplitude, longer duration wave as the shock wave propagates in the tool body. The present disclosure teaches managing shock load propagation by absorbing shock load energy and/or frequency shifting some of the shock load energy, which may reduce the shock accumulation  240 . 
     Turning now to  FIG. 4A  and  FIG. 4B , an assembly  100  is described. In an embodiment, the assembly  100  comprises a tool string connector  102  and a perforation gun  104 . The assembly  100  may be made-up or coupled together on a floor of the servicing rig  20  before running the workstring  30  into the wellbore  12 . Alternatively, the assembly  100  may be coupled together below the floor of the servicing rig  20 , for example within a Christmas tree over the wellbore  12 . The assembly  100  may form a portion of the perforation tool assembly  200  described above. In some embodiments, the assembly  100  may comprising an auto-latch coupling. An auto-latching coupling may reduce the time of making connections among some assemblies in the perforation tool assembly  34 . For further details about auto-latching couplings, see U.S. Pat. No. 5,778,979, entitled “Latch and Release Perforating Gun Connector and Method,” by John D. Burleson, et al.; U.S. Pat. No. 5,992,523, entitled “Latch and Release Perforating Gun Connector and Method,” by John D. Burleson, et al.; U.S. Pat. No. 5,823,266, entitled “Latch and Release Tool Connector and Method,” by John D. Burleson, et al.; and U.S. Pat. No. 5,957,209, entitled “Latch and Release Tool Connector and Method,” by John D. Burleson, et al.; each of which is hereby incorporated by reference in its entirety. 
     In an embodiment, the perforation gun  104  comprises a stinger  116  and a circumferential groove  110 . In some contexts, the stinger  116  and  110  may be referred to as a latch mate of the perforation gun  104 . It is understood that the perforation gun  104  further comprises a tool body and a plurality of explosive charges  203  that are retained in a charge carrier within the tool body. The charge carrier may be fabricated from a thin metal tube that has holes cut out to receive and retain the explosive charges  203 . The charge carrier may be secured within the tool body of the perforation gun  104  by materials that serve as shock absorbers to protect the charge carrier and charges  203  from axial and/or radial accelerations that may be experienced during run-in of the workstring  30 . The distinction between the shock absorbers that protect the charge carrier and charges  203  during run-in and the mechanical energy absorber components discussed further below that reduce the shock load associated with the firing of the perforation guns  202  and/or  104  will be readily appreciated by one skilled in the art of perforation guns and downhole operations. The accelerations associated with run-in are orders of magnitude less intense than the accelerations associated with the shock load resulting from firing the perforation guns  202 ,  104 . Additionally, in an embodiment, the shock absorbers may protect the charge carriers, which may not be in the primary load path of the perforation tool assembly  34  and consequently may not significantly affect the shock wave propagation in the primary load path of the perforation tool assembly  34 . Still further, the shock absorbers within the perforation guns are effectively destroyed by the detonation of the explosive charges, thereby removing any shock absorbing capabilities once the explosive charges are detonated. 
     In an embodiment, the tool string connector  102  comprises a collet  106  and associated collet fingers  108 , a sleeve  112 , a collet prop  114 , and a one or more shear pins  118 . In some contexts, the collet  106 , collet fingers  108 , sleeve  112 , collet prop  114  may be referred to as a latch component. When the tool string connector  102  is lowered onto the perforation gun  104 , the collet  106  receives the stinger  116 , the collet fingers  108  flex to allow the collet  106  to slide over the outside of the stinger  116 , and the collet  106  engages with the groove  110 . The assembly  100  is illustrated in  FIG. 4A  during the course of this engagement, just before the collet  106  engages with the groove  110 . Once the collet  106  engages with the groove  110 , the sleeve  112  may be raised so that the collet prop  114  props the collet  106 , as illustrated in  FIG. 4B . The sleeve  112  may be shifted or slid upwards by springs that form part of the tool string connector  102  or by a tool that grips the outside of the sleeve  112  and lifts it. When the tool string connector  102  and the perforation gun  104  are in the state illustrated in  FIG. 4B , the latch mate of the perforation gun  104  and the latch component of the tool string connector  102  may be said to be engaged or to engage each other. The perforation gun  104  is coupled to the tool string connector  102  in the state of the assembly  100  illustrated in  FIG. 4B . 
     It is understood that in other embodiments the tool string connector  102  may comprise additional components. In an embodiment, the sleeve  112  may be retained in position by a latching mechanism or by engaging with another mechanism of the tool string connector  102 . This latching mechanism may be manipulable by a tool at the surface to allow the sleeve  112  to be retracted and to un-make the coupling between the tool string connector  102  and the perforation gun  104 . In an embodiment, the latching mechanism may be configured to remain latched in the presence of high shock loads and to not rattle into an unlatched state during a perforation event. It is understood that the tool string connector  102  may be either up-hole or down-hole of the perforation gun  104 . The tool string connector  102  may have a threaded end (not shown) that may couple threadingly to another perforation gun  202 ,  104 , for example at an end opposite to the latch component of the tool string connector  102 . 
     Turning now to  FIG. 5 , a range of motion R of the tool string connector  102  relative to the perforation gun  104  is illustrated. The range of motion R may promote decoupling the shock load between perforation guns  202 ,  104 . In an embodiment, the range of motion R may be limited to an axial motion of less than about 5 inches. In another embodiment, the range of motion R may be limited to an axial motion of less than about 2 inches. In another embodiment, the range of motion R may be limited to an axial motion of less than about 1 inch. 
     Turning now to  FIG. 6A  and  FIG. 6B , the assembly  100  is illustrated with mechanical energy absorbing structures. In an embodiment, the assembly  100  may comprise a first energy absorber  130  between the stinger  116  and an interior of the tool string connector  102 . In an embodiment, the assembly  100  may comprise a second energy absorber  132  between the collet  106  and a shoulder of the circumferential groove  110  of the perforation gun  104 . The energy absorbing structures may be dimensioned to prevent relative motion between the tool string connector  102  and the perforation gun  104  during run-in, as seen in  FIG. 6A . Alternatively, the energy absorbing structures may be dimensioned to allow some relative motion between the tool string connector  102  and the perforation gun  104  during run-in, as seen as first energy absorber  136  and second energy absorber  138  in  FIG. 6B . The energy absorbing structures  130 ,  132 ,  136 ,  138 , generally, may be designed to withstand compression and tensile forces up to a threshold, where the threshold is much greater than the customary run-in forces and/or accelerations. The energy absorbing structures  130 ,  132 ,  136 ,  138  may be designed to deform, to allow motion of the perforation gun  104  relative to the tool string connector  102  by non-restorative deforming, for example compressing, while under a relatively high load such as that presented during a perforation event. The energy absorbed is related to the force applied to the absorbing structure multiplied by the distance by which the structure  130 ,  132 ,  136 ,  138  is non-restoratively compressed: force times distance. The energy absorbing structures  130 ,  132 ,  136 ,  138  may absorb energy in the shock load and/or shock wave propagating in the perforation tool assembly  200  and associated with firing one or more perforation guns and/or associated with an induced dynamic underbalance condition. 
     Turning now to  FIG. 7A  and  FIG. 7B , the first energy absorber  130 ,  136  is discussed further. In an embodiment, the first energy absorber  130 ,  136  may comprise a plurality of disks  140 , for example a first disk  140   a , a second disk  140   b , and a third disk  140   c . It is understood that the first energy absorber  130 ,  136  may alternatively comprise a single disk, two disks, or more than three disks. The disks  140  may have a hole  142  that allows primacord or detonation cord to pass through the first energy absorber  130 ,  136 . The disks  140  may comprise honeycomb material that acts as an energy absorber when crushed. The disks  140  may comprise ductile metal that acts as an energy absorber when compressed beyond the elastic limit and/or beyond the yield point of the ductile metal. 
     The disks  140  and/or the first energy absorber  130 ,  136  may be designed to sustain multiple shock loads, for example shock loads that may be separated in time. For example, in an embodiment, the first energy absorber  130 ,  136  may be designed to sustain shock load peaks that are separated by at least one second, by at least about two seconds, at least about three seconds, at least about ten seconds, or at least about thirty seconds. In the case of multiple shock load peaks or multiple shock hits, the first energy absorber  130 ,  136  may deform a fraction of a deformation capacity of the absorber  130 ,  136  during each hit. In an embodiment, the first energy absorber  130 ,  136  may be designed to sustain a maximum number of shock load hits, for example three shock load hits, five shock load hits, ten shock load hits, or some other number of shock load hits. The disks  140  may comprise frangible material that acts as an energy absorber when crushed. In an embodiment, one or more of the disks  140  may comprise a nonlinear spring, for example a wave-type spring and/or a Belleville-type spring. The disks  140  may be referred to in some contexts as washer-shaped. 
     Turning now to  FIG. 8 , the second energy absorber  132 ,  138  is discussed further. In an embodiment, the second energy absorber  132 ,  138  may be embodied in a form substantially similar to that of the first energy absorber  130 ,  136  described above and may be designed to sustain a plurality of shock wave hits. The second energy absorber  132 ,  138  may comprise a plurality of disks. The disk or disks may comprise honeycomb material, crushable tubes, ductile metal, and/or frangible material. The second energy absorber  132 ,  138  has a large opening that corresponds to the outside diameter of the circumferential groove  110 . In an embodiment, the second energy absorber  132 ,  138  may have the form of a split ring that may be opened to put the second energy absorber  132 ,  138  onto the circumferential groove  110 . Alternatively, the second energy absorber  132 ,  138  may be provided in two halves that are assembled into the circumferential groove  110  at the wellbore  12 . In an embodiment, the second energy absorber  132 ,  138  may comprise one or more nonlinear springs, for example a wave-type spring and/or a Belleville-type spring. The second energy absorber  132 ,  138  may be referred to in some contexts as washer-shaped. 
     Turning now to  FIG. 9A ,  FIG. 9B ,  FIG. 10 , and  FIG. 11 , examples of a disk  140  are described. In an embodiment, one or more of the disks  140  may be formed of a ductile metal that has grooves or flutes cut or cast into the disk  140 , as illustrated in  FIG. 9A  and  FIG. 9B . When a compression or crushing force is applied to the faces of the disk  140 , the force is borne initially by the peaks of the grooves or flutes. As the disk  140  flattens, the resisting force of the disk  140  increases as the peaks of the grooves or flutes are flattened out and the force is distributed across a greater area. The crushing of the disk  140  may be said to be non-restorative. Energy in the shock load propagation is consumed during the process of flattening the peaks of the grooves or flutes, and therefore the shock load that propagates from the perforation gun  104  to the tool string connector  102  or from the tool string connector to the perforation gun  104  is reduced. The same analysis of the crushing of the ductile disk  140  can be adapted to apply to a disk  140  that has a crenellated surface with a square or rectangular pattern as illustrated in  FIG. 10  or that has a knurled surface as illustrated in  FIG. 11 . Any ductile metal may be used to form the disk  140 , for example brass. The second energy absorber  132  may be formed of a ductile metal having similar grooves and/or irregularities in one of its surfaces. 
     In an embodiment, a set of disks  140  may be available at the location of the wellbore  12 . The set of disks  140  promotes composing the first energy absorber  130 ,  136  out of a set of different designed disks  140 , for example disks that have different amounts of compliance or different amounts of resistance to compression forces, according to a design or recipe for building the assembly  100 . Likewise, a set of different second energy absorbers  132 ,  138  having different energy absorption characteristics may be available for building the assembly  100 . In some contexts, the set of disks  140  having different energy absorption characteristics may be referred to as interchangeable energy absorption components or as interchangeable components. 
     Turning now to  FIG. 12 , a method  400  is described. At block  402  the wellbore  12  is modeled. At block  404  the perforation gun string  202  is modeled. At block  406 , a perforation job is simulated based on the wellbore model and the perforation gun string model. The results of the simulation are analyzed to determine the effectiveness of the simulated perforation job, comparing the simulated results to the preferred results. At block  408 , a mechanical energy propagation management device is designed based on the simulation and/or based on the wellbore model and the gun string model. For example, one or more energy absorbers  130 ,  132 ,  136 ,  138  are designed. For example, a mass energy absorber system, as described further below, is designed. The processing of blocks  402 ,  404 , and  408  may be repeated or iterated a plurality of times to improve or optimize the design of the mechanical energy propagation management device or other parameters of the perforation gun string  202 . The design of the energy absorbers  130 ,  132 ,  136 ,  138  may be based on absorbing the shock wave peaks of multiple independent perforation gun  202 ,  104  firings, for example multiple hits. In an embodiment, the processing of blocks  402 ,  404 ,  406 , and  408  may be omitted. 
     At block  410 , a mechanical energy propagation management device is placed between the perforation gun and a tool string connector, for example, the mechanical energy propagation management device designed in block  408 . For example, one or more energy absorbers  130 ,  132 ,  136 ,  138  designed in block  408  above are placed between the perforation gun and a tool string connector. At block  412 , the perforation gun  104  is coupled to the tool string connector  102 , wherein the perforation gun and the tool string connector are configured to move relative to each other within a limited range of motion when the mechanical energy propagation management device is not present. The term mechanical energy propagation management device may comprise one or more of energy absorbers  130 ,  132 ,  136 ,  138  and/or a mass energy absorber system, as described further below. At block  414 , a perforation gun is placed in the wellbore  12 . For example, the perforation gun designed in block  408  is placed in the wellbore  12 . 
     Turning now to  FIG. 13 , a mass energy absorber  380  is described. In some contexts, the mass energy absorber  380  may be referred to as a tuned mass energy absorber. The mass energy absorber  380  may be designed through modeling and simulation as described above. The mass energy absorber  380  is suitable for incorporation into the perforation tool assembly  200  to alter the propagation of the shock wave through the perforation tool assembly  200 . For example, the mass energy absorber  380  may be provided between other components of the perforation tool assembly  200 , for example between perforation guns  202  and/or spacers  204 . The mass energy absorber  380  may be coupled to a first component up-hole and to a second component down-hole from the mass energy absorber  380 . A plurality of mass energy absorbers  380  may be coupled to each other. It is understood that a plurality of mass energy absorbers  380  may be placed at one or more positions within the perforation tool assembly  200 . 
     In an embodiment, the mass energy absorber  380  comprises a mass  382  and at least one absorber disposed between at least one end and the tool body  386 . For example, the mass energy absorber  380  may comprise a mass  382  supported in a first end by a first absorber  384   a  and supported on a second end by a second absorber  384   b . The mass  382  may be centralized within the tool body  386  by soft polymeric stand-off buttons or rings or other structures that exhibit low axial coupling between the mass  382  and the tool body  386 . The mass  382  may comprise tungsten, depleted uranium, or other dense materials. The absorbers  384   a ,  384   b  are coupled to and support the mass  382  within a tool body  386  without deformation during normal displacements of the mass energy absorber  380  and/or the perforation tool assembly  200 , for example during run-in. When a shock wave propagates to the mass energy absorber  380  via coupling of the tool body  386  to the perforation tool assembly  200 , the inertia of the mass  382  resists displacement, the absorbers  384  deform, energy is removed from the shock wave, and the shock load that propagates on beyond the mass energy absorber  380  is attenuated. 
     The absorbers  384  may comprise crushable structures such as a non-linear stiffness device that is designed to be relatively stiff until a critical load or stress level is reached, at which point the absorber loses its stiffness and absorbs energy. The absorbers  384  may comprise materials that deform non-restoratively. The absorbers  384  may comprise devices similar to those described above with reference to assembly  100 : honeycomb structures, crushable tubes, deformable washers of ductile metals, deformable washers of ductile metals having a grooved, fluted, crenelated, or knurled surface. While the absorbers  384  are illustrated in  FIG. 9  as substantially similar is dimension, the first absorber  384   a  may have different dimensions, different compliance, and/or different energy absorption characteristics. For example, if the expected shock wave is simulated to propagate from above and down through the mass energy absorber, the first absorber  384   a  may be called upon to absorb more energy than the second absorber  384   b . Additionally, the sense of the stress placed upon the absorbers  384  may be different. For example, the first absorber  384   a  may experience a greater compression stress than a tensile stress, while the second absorber  384   b  may experience a greater tensile stress than compression stress. In an embodiment, hence, the first absorber  384   a  may be designed differently than the second absorber  384   a.    
     The absorbers  384  and/or the mass  382  may be designed for altering shock waves associated with a plurality of separate, distinct shock events. For example, the absorbers  384  may partially crush in response to and alter the propagation of a first shock wave associated with firing a first perforation gun; the absorbers  384  may further crush in response to and alter the propagation of a second shock wave associated with firing a second perforation gun after the firing of the first perforation gun; and the absorbers  384  may yet further crush in response to and alter the propagation of a third shock wave associated with firing a third perforation gun after the firing of the second perforation gun. In some contexts, such separate, distinct shock events may be referred to as time separated shock events or as time separated perforation gun firings. In an embodiment, the second shock wave may be associated with firing a second perforation gun at least about 1 second later, at least about 10 seconds later, or at least about 30 seconds later than the firing of the first perforation gun. In an embodiment, the third shock wave may be associated with firing a third perforation gun at least about 1 second later, at least about 10 seconds later, or at least about 30 seconds later than the firing of the second perforation gun. 
     In an embodiment, the mass energy absorber  380  may further comprise linear springs or non-linear springs, which may replace or be used in combination with one or more of the energy absorbers between the mass  382  and the tool body  386 . In an embodiment, mass energy absorber  380  comprises a mass  382  suspended within the tool body  386  by one or more springs (e.g., elastic elements, restorative springs, absorbing springs, etc.) supporting the mass  382  on either end. The configuration of the mass energy absorber  380  may be the same as illustrated in  FIG. 13 , with the elements  384   a ,  384   b  comprising springs rather than absorbers. In some embodiments, the springs may act as energy absorbers by either having some degree of resistance and/or incorporating resistive or deformative elements. 
     The mass energy absorber  380  may comprise a natural resonance frequency based on the properties of the mass and the springs. The shock wave may cause the mass to oscillate within the segment of tubing, thereby damping the perforation tool assembly  200  motion at or near the natural resonance frequency. The properties of the mass and/or the springs could be tuned to match the characteristics of the perforation tool assembly  200  and the expected shock and/or loads within the system. One or more of the energy absorbing elements may be used with the springs to further dampen and/or dissipate the energy within the system. Further, a plurality of mass energy absorbers  380  may be disposed in the tool string, each with the same or different properties, for example, to dampen the shock load at various natural resonance frequencies along the string. The mass energy absorbers may be disposed in a single tool body  386  or a plurality of tool bodies, and the tool bodies may be coupled to each other and/or distributed throughout the perforation gun string. 
     When a shock wave propagates to the mass energy absorber  380  via coupling of the tool body  386  to the perforation tool assembly  200 , the inertia of the mass  382  resists displacement, but will begin to oscillate at the natural frequency based on the properties of the one or more springs and the mass. The resulting oscillation may serve to convert the shock wave into different frequencies and/or change the amplitude of the shock wave (e.g., spread out the shock wave to thereby reduce the peak amplitude) as the mass energy absorber  380  begins to oscillate and thereafter transfers the energy back to the tool body  386 . As noted above, due to the natural losses in the springs and if one or more absorbers are present, the energy may be dissipated prior to being transferred back to the tool body  386 . 
     It is understood that the mass energy absorber  380  may be implemented in other configurations than those described with reference to  FIG. 13 . For further details about energy absorbers and shock load mitigation, see U.S. patent application Ser. No. 13/377,148, filed Dec. 8, 2011, entitled “Shock Load Mitigation in a Downhole Perforation Tool Assembly,” by Timothy S. Glenn, et al., which is hereby incorporated by reference in its entirety. 
       FIG. 14  illustrates a computer system  580  suitable for implementing one or more embodiments disclosed herein. For example, the analysis performed in blocks  402 ,  404 , and/or  406  of method  400  described above with reference to  FIG. 12  may be promoted by executing a modeling application on the computer system  580 . Further, the designing performed in block  206  may be performed at least in part using a design application executing on the computer system  580 . The computer system  580  includes a processor  582  (which may be referred to as a central processor unit or CPU) that is in communication with memory devices including secondary storage  584 , read only memory (ROM)  586 , random access memory (RAM)  588 , input/output (I/O) devices  590 , and network connectivity devices  592 . The processor  582  may be implemented as one or more CPU chips. 
     It is understood that by programming and/or loading executable instructions onto the computer system  580 , at least one of the CPU  582 , the RAM  588 , and the ROM  586  are changed, transforming the computer system  580  in part into a particular machine or apparatus having the novel functionality taught by the present disclosure. It is fundamental to the electrical engineering and software engineering arts that functionality that can be implemented by loading executable software into a computer can be converted to a hardware implementation by well-known design rules. Decisions between implementing a concept in software versus hardware typically hinge on considerations of stability of the design and numbers of units to be produced rather than any issues involved in translating from the software domain to the hardware domain. Generally, a design that is still subject to frequent change may be preferred to be implemented in software, because re-spinning a hardware implementation is more expensive than re-spinning a software design. Generally, a design that is stable that will be produced in large volume may be preferred to be implemented in hardware, for example in an application specific integrated circuit (ASIC), because for large production runs the hardware implementation may be less expensive than the software implementation. Often a design may be developed and tested in a software form and later transformed, by well known design rules, to an equivalent hardware implementation in an application specific integrated circuit that hardwires the instructions of the software. In the same manner as a machine controlled by a new ASIC is a particular machine or apparatus, likewise a computer that has been programmed and/or loaded with executable instructions may be viewed as a particular machine or apparatus. 
     The secondary storage  584  is typically comprised of one or more disk drives or tape drives and is used for non-volatile storage of data and as an over-flow data storage device if RAM  588  is not large enough to hold all working data. Secondary storage  584  may be used to store programs which are loaded into RAM  588  when such programs are selected for execution. The ROM  586  is used to store instructions and perhaps data which are read during program execution. ROM  586  is a non-volatile memory device which typically has a small memory capacity relative to the larger memory capacity of secondary storage  584 . The RAM  588  is used to store volatile data and perhaps to store instructions. Access to both ROM  586  and RAM  588  is typically faster than to secondary storage  584 . The secondary storage  584 , the RAM  588 , and/or the ROM  586  may be referred to in some contexts as computer readable storage media and/or non-transitory computer readable media. 
     I/O devices  590  may include printers, video monitors, liquid crystal displays (LCDs), touch screen displays, keyboards, keypads, switches, dials, mice, track balls, voice recognizers, card readers, paper tape readers, or other well-known input devices. 
     The network connectivity devices  592  may take the form of modems, modem banks, Ethernet cards, universal serial bus (USB) interface cards, serial interfaces, token ring cards, fiber distributed data interface (FDDI) cards, wireless local area network (WLAN) cards, radio transceiver cards such as code division multiple access (CDMA), global system for mobile communications (GSM), long-term evolution (LTE), worldwide interoperability for microwave access (WiMAX), and/or other air interface protocol radio transceiver cards, and other well-known network devices. These network connectivity devices  592  may enable the processor  582  to communicate with the Internet or one or more intranets. With such a network connection, it is contemplated that the processor  582  might receive information from the network, or might output information to the network in the course of performing the above-described method steps. Such information, which is often represented as a sequence of instructions to be executed using processor  582 , may be received from and outputted to the network, for example, in the form of a computer data signal embodied in a carrier wave. 
     Such information, which may include data or instructions to be executed using processor  582  for example, may be received from and outputted to the network, for example, in the form of a computer data baseband signal or signal embodied in a carrier wave. The baseband signal or signal embodied in the carrier wave generated by the network connectivity devices  592  may propagate in or on the surface of electrical conductors, in coaxial cables, in waveguides, in an optical conduit, for example an optical fiber, or in the air or free space. The information contained in the baseband signal or signal embedded in the carrier wave may be ordered according to different sequences, as may be desirable for either processing or generating the information or transmitting or receiving the information. The baseband signal or signal embedded in the carrier wave, or other types of signals currently used or hereafter developed, may be generated according to several methods well known to one skilled in the art. The baseband signal and/or signal embedded in the carrier wave may be referred to in some contexts as a transitory signal. 
     The processor  582  executes instructions, codes, computer programs, scripts which it accesses from hard disk, floppy disk, optical disk (these various disk based systems may all be considered secondary storage  584 ), ROM  586 , RAM  588 , or the network connectivity devices  592 . While only one processor  582  is shown, multiple processors may be present. Thus, while instructions may be discussed as executed by a processor, the instructions may be executed simultaneously, serially, or otherwise executed by one or multiple processors. Instructions, codes, computer programs, scripts, and/or data that may be accessed from the secondary storage  584 , for example, hard drives, floppy disks, optical disks, and/or other device, the ROM  586 , and/or the RAM  588  may be referred to in some contexts as non-transitory instructions and/or non-transitory information. 
     In an embodiment, the computer system  580  may comprise two or more computers in communication with each other that collaborate to perform a task. For example, but not by way of limitation, an application may be partitioned in such a way as to permit concurrent and/or parallel processing of the instructions of the application. Alternatively, the data processed by the application may be partitioned in such a way as to permit concurrent and/or parallel processing of different portions of a data set by the two or more computers. In an embodiment, virtualization software may be employed by the computer system  580  to provide the functionality of a number of servers that is not directly bound to the number of computers in the computer system  580 . For example, virtualization software may provide twenty virtual servers on four physical computers. In an embodiment, the functionality disclosed above may be provided by executing the application and/or applications in a cloud computing environment. Cloud computing may comprise providing computing services via a network connection using dynamically scalable computing resources. Cloud computing may be supported, at least in part, by virtualization software. A cloud computing environment may be established by an enterprise and/or may be hired on an as-needed basis from a third party provider. Some cloud computing environments may comprise cloud computing resources owned and operated by the enterprise as well as cloud computing resources hired and/or leased from a third party provider. 
     In an embodiment, some or all of the functionality disclosed above may be provided as a computer program product. The computer program product may comprise one or more computer readable storage medium having computer usable program code embodied therein to implement the functionality disclosed above. The computer program product may comprise data structures, executable instructions, and other computer usable program code. The computer program product may be embodied in removable computer storage media and/or non-removable computer storage media. The removable computer readable storage medium may comprise, without limitation, a paper tape, a magnetic tape, magnetic disk, an optical disk, a solid state memory chip, for example analog magnetic tape, compact disk read only memory (CD-ROM) disks, floppy disks, jump drives, digital cards, multimedia cards, and others. The computer program product may be suitable for loading, by the computer system  580 , at least portions of the contents of the computer program product to the secondary storage  584 , to the ROM  586 , to the RAM  588 , and/or to other non-volatile memory and volatile memory of the computer system  580 . The processor  582  may process the executable instructions and/or data structures in part by directly accessing the computer program product, for example by reading from a CD-ROM disk inserted into a disk drive peripheral of the computer system  580 . Alternatively, the processor  582  may process the executable instructions and/or data structures by remotely accessing the computer program product, for example by downloading the executable instructions and/or data structures from a remote server through the network connectivity devices  592 . The computer program product may comprise instructions that promote the loading and/or copying of data, data structures, files, and/or executable instructions to the secondary storage  584 , to the ROM  586 , to the RAM  588 , and/or to other non-volatile memory and volatile memory of the computer system  580 . 
     In some contexts, a baseband signal and/or a signal embodied in a carrier wave may be referred to as a transitory signal. In some contexts, the secondary storage  584 , the ROM  586 , and the RAM  588  may be referred to as a non-transitory computer readable medium or a computer readable storage media. A dynamic RAM embodiment of the RAM  588 , likewise, may be referred to as a non-transitory computer readable medium in that while the dynamic RAM receives electrical power and is operated in accordance with its design, for example during a period of time during which the computer  580  is turned on and operational, the dynamic RAM stores information that is written to it. Similarly, the processor  582  may comprise an internal RAM, an internal ROM, a cache memory, and/or other internal non-transitory storage blocks, sections, or components that may be referred to in some contexts as non-transitory computer readable media or computer readable storage media. 
     ADDITIONAL DISCLOSURE 
     The following are nonlimiting, specific embodiments in accordance with the present disclosure: 
     In a first embodiment, a perforation tool assembly comprises a perforation gun, and a mass energy absorber coupled to the perforation gun and configured to alter the propagation of mechanical energy released by firing one or more perforation guns. The mass energy absorber comprises a mass and at least one absorber, and the at least one absorber is disposed between the mass and the perforating gun. 
     In a second embodiment, which is the perforation tool assembly of the first embodiment, the mass comprises at least 80% by weight tungsten or depleted uranium. 
     In a third embodiment, which is the perforation tool assembly of the first embodiment or the second embodiment, the at least one absorber is configured to alter shock waves associated with a plurality of time separated perforation gun firings. 
     In a fourth embodiment, which is the perforation tool assembly of any of the first embodiment to the third embodiment, the at least one absorber is a crushable material. 
     In a fifth embodiment, which is the perforation tool assembly of any of the first embodiment to the third embodiment, the at least one absorber is a frangible material. 
     In a sixth embodiment, which is the perforation tool assembly of any of the first embodiment to the fifth embodiment, the at least one absorber is a material that deforms non-restoratively. 
     In a seventh embodiment, which is the perforation tool assembly of any of the first embodiment to the sixth embodiment, the at least one absorber comprises a first absorber on a first end of the mass energy absorber and a second absorber on a second end of the mass energy absorber. 
     In an eighth embodiment, which is the perforation tool assembly of the seventh embodiment, the first absorber has a different compliance than the second absorber. 
     In a ninth embodiment, a perforation tool assembly comprises a plurality of perforation guns, and a mass energy absorber disposed between at least two of the plurality of perforation guns. The mass energy absorber is configured to reduce the propagation of mechanical energy across the mass energy absorber, and the mass energy absorber comprises a mass and at least one absorber. The mechanical energy is released by firing one or more perforation guns. 
     In a tenth embodiment, which is the perforation tool assembly of the ninth embodiment, the mass comprises one or more of tungsten or depleted uranium. 
     In an eleventh embodiment, which is the perforation tool assembly of the ninth embodiment or the tenth embodiment, the at least one absorber is a material that deforms non-restoratively. 
     In a twelfth embodiment, which is the perforation tool assembly of the eleventh embodiment, the at least one absorber is at least one of a crushable material or a frangible material. 
     In a thirteenth embodiment, which is the perforation tool assembly of any of the ninth embodiment to the twelfth embodiment, the mass energy absorber comprises a first absorber and a second absorber, and/or the first and second absorber are configured to absorb energy and reduce the mechanical energy that propagates across the mass energy absorber. 
     In a fourteenth embodiment, which is the perforation tool assembly of the thirteenth embodiment, the first absorber has a different mechanical energy absorption characteristic from the second absorber. 
     In a fifteenth embodiment, a method of perforating a casing string in a wellbore comprises modeling a wellbore; modeling a perforation tool assembly, wherein the perforation tool assembly comprises at least one perforation gun and a mass energy absorber; simulating firing the at least one perforation gun; designing the mass energy absorber based on the simulating; firing the first perforation gun when the first perforating gun is disposed in a wellbore; and attenuating a mechanical energy that propagates across the mass energy absorber, wherein the mechanical energy is associated with firing the first perforation gun. 
     In a sixteenth embodiment, which is the method of the fifteenth embodiment, designing the mass energy absorber comprises designing a crushable component based on the simulating. 
     In a seventeenth embodiment, which is the method of the fifteenth embodiment or the sixteenth embodiment, designing the mass energy absorber comprises designing a frangible component based on the simulating. 
     In an eighteenth embodiment, which is the method of any of the fifteenth embodiment to the seventeenth embodiment, designing the mass energy absorber comprises designing the mass energy absorber to attenuate mechanical energy that propagates across the mass energy absorber at different times, and/or the different times are separated by at least 1 second. 
     In a nineteenth embodiment, which is the method of any of the fifteenth embodiment to the eighteenth embodiment, designing the mass energy absorber comprises selecting from a plurality of dense materials based on an analysis of energy attenuation and cost of the dense material. 
     In a twentieth embodiment, which is the method of the nineteenth embodiment, the dense materials are selected from tungsten and depleted uranium. 
     In a twenty first embodiment, a perforation tool assembly comprises a perforation gun string; and a mass energy absorber coupled to the perforation gun. The mass energy absorber comprises a mass disposed within a tool body; and at least one spring, where the at least one spring is disposed between the mass and the tool body. 
     In a twenty second embodiment, which is the perforation tool assembly of the twenty first embodiment, the springs comprise restorative springs. 
     In a twenty third embodiment, which is the perforation tool assembly of the twenty first embodiment or the twenty second embodiment, the springs comprise at least one energy absorber. 
     In a twenty fourth embodiment, which is the perforation tool assembly of the twenty third embodiment, the at least one energy absorber is a crushable material. 
     In a twenty fifth embodiment, which is the perforation tool assembly of the twenty third embodiment, the at least one energy absorber is a frangible material. 
     In a twenty sixth embodiment, which is the perforation tool assembly of the twenty third embodiment, the at least one energy absorber is a material that deforms non-restoratively. 
     In a twenty seventh embodiment, which is the perforation tool assembly of any of the twenty first embodiment to the twenty sixth embodiment, the mass energy absorber is configured to convert at least one shock wave frequency into a natural resonance frequency of the mass energy absorber. 
     In a twenty eighth embodiment, a method of absorbing energy during a perforation event comprises detonating at least one explosive charge in a perforation gun to create a shock wave; transferring the shock wave to a mass energy absorber coupled to the perforation gun, wherein the mass energy absorber comprises: a mass disposed within a tool body, and one or more retaining elements disposed between the mass and the tool body, and wherein the perforation gun and the mass energy absorber are disposed in a perforation gun assembly; inducing movement of the mass based on the transferring of the shock wave; and removing energy from the perforation gun assembly in response to the movement of the mass. 
     In a twenty ninth embodiment, which is the method of the twenty eighth embodiment, the one or more retaining elements comprise springs. 
     In a thirtieth embodiment, which is the method of the twenty ninth embodiment, removing energy from the perforation gun assembly comprises temporarily removing energy from the perforation gun assembly. 
     In a thirty first embodiment, which is the method of any of the twenty eighth embodiment to the thirtieth embodiment, the one or more retaining elements comprise one or more energy absorbers. 
     In a thirty second embodiment, which is the method of the thirty first embodiment, removing energy from the perforation gun assembly comprises permanently removing energy from the perforation gun assembly using the one or more energy absorbers. 
     In a thirty third embodiment, which is the method of any of the twenty eighth embodiment to the thirty second embodiment, the one or more retaining elements comprise non-linear energy absorbers. 
     In a thirty fourth embodiment, which is the method of any of the twenty eighth embodiment to the thirty third embodiment, the one or more retaining elements comprise crushable energy absorbers. 
     In a thirty fifth embodiment, which is the method of any of the twenty eighth embodiment to the thirty fourth embodiment, inducing movement in the mass comprises inducing an oscillation in the mass. 
     In a thirty sixth embodiment, which is the method of the thirty fifth embodiment, the oscillation occurs at a natural frequency of the mass energy absorber. 
     While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted or not implemented. 
     Also, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.