Explosive shock dissipater

Abstract

A method of dampening stress waves propagated from the detonation of an explosive device in a wellbore to protect a device positioned downhole including the steps of positioning a shock dissipater between an explosive device and a package; detonating the explosive device propagating a stress wave toward the shock dissipater and the package; and reflecting a portion of the stress wave in the shock dissipater. The shock dissipater may have one or more interface formed between materials of dissimilar acoustic impedances. The shock dissipater may reflect a compressive portion of the stress wave at one interface and a tensile portion of the stress wave at another interface.

1 . An apparatus for dampening a stress wave, the apparatus comprising a first interface formed between a first layer of material and a second layer of material, the first and second layers of material having dissimilar acoustic impedances. 
   
   
       2 . The apparatus of the  claim 1 , further including a third layer of material positioned in contact with the second layer of material to form a second interface, the second and third layers of material having dissimilar acoustic impedances. 
   
   
       3 . The apparatus of  claim 2 , wherein the acoustic impedance of the first layer of material and the acoustic impedance of the third layer of material are dissimilar. 
   
   
       4 . The apparatus of  claim 2 , wherein the acoustic impedance of the first layer is less than the acoustic impedance of the second impedance layer and the second acoustic impedance is greater than the acoustic impedance of the third layer of material. 
   
   
       5 . The apparatus of  claim 4 , wherein the acoustic impedance of the first layer of material and the acoustic impedance of the third layer of material are dissimilar. 
   
   
       6 . The apparatus of  claim 2 , wherein the acoustic impedance of the first layer is greater than the acoustic impedance of the second impedance and the second acoustic impedance is greater than the acoustic impedance of the third layer of material. 
   
   
       7 . A wellbore tool string, the tool string comprising:
 an explosive device,   a package; and   a shock dissipater positioned between the explosive device and the package, the shock dissipater including a first interface formed between a first layer of material and a second layer of material, the first and second layers of material having dissimilar acoustic impedances.   
   
   
       8 . The tool string of  claim 7 , wherein the shock dissipater is a sub assembly. 
   
   
       9 . The tool string of  claim 7 , further including a housing having an axial bore and a longitudinal axis, wherein the shock dissipater is positioned across the axial bore such that the first interface is oriented substantially perpendicular to the longitudinal axis. 
   
   
       10 . The tool string of  claim 7 , further including a conduit formed through the shock dissipater, the conduit being oriented substantially parallel to the longitudinal axis of the housing. 
   
   
       11 . The tool string of  claim 7 , further including a third layer of material positioned in contact with the second layer of material to form a second interface, the second and third layers of material having dissimilar acoustic impedances. 
   
   
       12 . The tool string of  claim 11 , wherein one of the layers of material is a metal, another one of the layers of material is an elastomeric material, and another one of the layers of material is foam. 
   
   
       13 . The tool string of  claim 11 , wherein the acoustic impedance of the first layer of material and the acoustic impedance of the third layer of material are dissimilar. 
   
   
       14 . The tool string of  claim 11 , wherein the acoustic impedance of the first layer is less than the acoustic impedance of the second impedance and the second acoustic impedance is greater than the acoustic impedance of the third layer of material. 
   
   
       15 . The tool string of  claim 14 , wherein the acoustic impedance of the first layer of material and the acoustic impedance of the third layer of material are dissimilar. 
   
   
       16 . The tool string of  claim 11 , wherein the acoustic impedance of the first layer is greater than the acoustic impedance of the second impedance and the second acoustic impedance is greater than the acoustic impedance of the third layer of material. 
   
   
       17 . The tool string of  claim 11 , further including a housing having an axial bore and a longitudinal axis, wherein the shock dissipater is positioned across the axial bore such that the first interface is oriented substantially perpendicular to the longitudinal axis. 
   
   
       18 . The tool string of  claim 17 , further including a conduit formed through the shock dissipater, the conduit being oriented substantially parallel to the longitudinal axis of the housing. 
   
   
       19 . A method of dampening stress waves propagated from the detonation of an explosive device in a wellbore to protect a device positioned downhole, the method comprising the steps of:
 positioning a shock dissipater between an explosive device and a package;   detonating the explosive device propagating a stress wave toward the shock dissipater and the package; and   reflecting a portion of the stress wave in the shock dissipater.   
   
   
       20 . The method of  claim 19 , wherein the step of reflecting includes:
 reflecting a tensile wave portion of the stress wave at one interface between layers of material; and   reflecting a compressive wave portion of the stress wave at another interface between layers of material.   
   
   
       21 . The apparatus of  claim 2 , wherein the acoustic impedance of the first layer of material and the acoustic impedance of the third layer of material are similar.