Downhole tool shock absorber with electromagnetic damping

Abstract

A technique facilitates absorption of shock experienced by a tool in a borehole. The technique comprises coupling a tool into a tool string sized for delivery into the borehole. A shock absorber is positioned along the tool string to absorb shock loads incurred by the tool. The shock load experienced by the tool induces an electromagnetic force in the shock absorber which acts in a direction to mitigate the shock load.

What is claimed is: 
     
         1 . A system for absorbing shock, comprising:
 a tool string deployed in a wellbore, the tool string comprising a well tool and a shock absorber positioned to absorb shock loads incurred by the well tool, the shock absorber comprising:
 an electromagnetic coil; 
 a permanent magnet positioned for relative movement with respect to the electromagnetic coil when shocks are incurred by the well tool and translated to the shock absorber, the relative movement inducing an eddy current in the electromagnetic coil which generates a magnetic field resisting the relative movement with sufficient force to absorb the shock loads acting on the well tool. 
   
     
     
         2 . The system as recited in  claim 1 , wherein the electromagnetic coil is part of an outer sleeve. 
     
     
         3 . The system as recited in  claim 2 , wherein the permanent magnet is positioned on an inner rod received within the outer sleeve. 
     
     
         4 . The system as recited in  claim 1 , wherein the electromagnetic coil is received within a sleeve comprising the permanent magnet. 
     
     
         5 . The system as recited in  claim 1 , wherein the permanent magnet comprises a stack of permanent magnets. 
     
     
         6 . The system as recited in  claim 1 , wherein the shock absorber further comprises a resistor coupled to the electromagnetic coil to provide a control with respect to the rate of energy dissipation. 
     
     
         7 . The system as recited in  claim 1 , wherein the relative movement creates electrical energy which is dissipated via heating. 
     
     
         8 . The system as recited in  claim 1 , wherein the shock absorber further comprises a spring to bias the permanent magnet toward a predetermined position relative to the electromagnetic coil. 
     
     
         9 . The system as recited in  claim 1 , wherein the shock absorber further comprises a magnetic cushion working in parallel with the electromagnetic coil and the permanent magnet. 
     
     
         10 . A method for absorbing shock in a borehole, comprising:
 coupling a tool into a tool string sized for delivery into the borehole;   positioning a shock absorber along the tool string to absorb a shock load acting on the tool; and   using a magnetic field to create a force in the shock absorber, the force acting in a direction which mitigates the shock load.   
     
     
         11 . The method as recited in  claim 10 , further comprising forming the shock absorber with an electromagnetic coil and a permanent magnet positioned for relative movement with respect to the electromagnetic coil when the shock absorber is subjected to the shock load. 
     
     
         12 . The method as recited in  claim 11 , further comprising locating the electromagnetic coil on a sleeve. 
     
     
         13 . The method as recited in  claim 12 , further comprising locating the permanent magnet on an inner rod received within the sleeve. 
     
     
         14 . The method as recited in  claim 10 , wherein using comprises mitigating the shock load by converting kinetic energy to electrical energy which is dissipated through heating. 
     
     
         15 . The method as recited in  claim 11 , further comprising coupling a resistor to the electromagnetic coil to establish a desired rate of energy dissipation. 
     
     
         16 . The method as recited in  claim 10 , further comprising moving the tool string downhole into a borehole. 
     
     
         17 . The method as recited in  claim 10  further comprising employing magneto-rheological fluid to establish the force via increased viscosity of the magneto-rheological fluid when exposed to the magnetic field. 
     
     
         18 . A system for absorbing shock, comprising:
 a shock absorber which may be coupled into a tool string, the shock absorber having a first component with an electromagnetic coil and a second component with a permanent magnet, the first component and the second component being mounted in the shock absorber for relative movement with respect to each other under a sufficient shock load, the electromagnetic coil and the permanent magnet acting, when subjected to the relative movement, to create a counterforce which slows the relative movement.   
     
     
         19 . The system as recited in  claim 18 , wherein the first component comprises a sleeve and the second component comprises a rod. 
     
     
         20 . The system as recited in  claim 18 , further comprising a well tool, wherein the shock absorber works in cooperation with the well tool to dissipate shock loads incurred by the well tool.