Downhole trigger device

Abstract

A trigger device keeps a downhole tool from setting until it is properly positioned. Regardless of the type of tool or the type of associated trigger, the retainer of the present invention is combusted. The material is preferably one that combusts readily such as a material used in fuses for explosives. The battery requirements are to simply create the brief spark that starts the combustion, making the battery size significantly smaller than what would be needed to power a heater to melt materials that were used in the past.

1 . A trigger device for a downhole tool for selectively actuating the tool, comprising: 
 a body;    an actuating member mounted to said body whose movement sets the tool;    a restraining member to selectively directly or indirectly restrain movement of said actuating member with respect to said body, said restraining member when subjected to an initial energy input initiates a process within said restraining member that continues without further energy input to the point of allowing said actuating member to move.    
   
   
       2 . The device of  claim 1 , wherein: 
 said process releases heat.    
   
   
       3 . The device of  claim 1 , wherein: 
 said process comprises a chemical reaction.    
   
   
       4 . The device of  claim 1 , wherein: 
 the response of the restraining member to energy input is pyrotechnic.    
   
   
       5 . The device of  claim 1 , wherein: 
 said restraining member comprises an explosive material.    
   
   
       6 . The device of  claim 1 , wherein: 
 said energy input comprises a spark.    
   
   
       7 . The device of  claim 6 , wherein: 
 said spark is supplied by a battery supported by said housing.    
   
   
       8 . The device of  claim 6 , wherein: 
 said spark is generated mechanically.    
   
   
       9 . The device of  claim 1 , wherein: 
 said actuating member comprises a piston that is subjected to an initial force.    
   
   
       10 . The device of  claim 9 , wherein: 
 said restraining member comprises a wire that initially retains said piston.    
   
   
       11 . The device of  claim 10 , wherein: 
 said wire passes through said piston.    
   
   
       12 . The device of  claim 1 , wherein: 
 said restraining member comprises a wire fuse.    
   
   
       13 . A method of selectively actuating a downhole tool, comprising: 
 retaining directly or indirectly a triggering member with a restraining member;    applying energy to the restraining member to initiate a response in said restraining member;    removing said applied energy while said response continues; and    defeating said restraining member to let the triggering member move.    
   
   
       14 . The method of  claim 13 , comprising: 
 releasing heat from said response.    
   
   
       15 . The method of  claim 13 , comprising: 
 creating a chemical reaction as said response.    
   
   
       16 . The method of  claim 13 , comprising: 
 using a wire fuse for said restraining member.    
   
   
       17 . The method of  claim 13 , comprising: 
 making said response a pyrotechnic one.    
   
   
       18 . The method of  claim 14 , comprising: 
 obtaining said response without the presence of oxygen.    
   
   
       19 . The method of  claim 13 , comprising: 
 creating a spark for said applying energy.    
   
   
       20 . The method of  claim 19 , comprising: 
 using a piston as said triggering member;    using a wire to retain said piston;    passing said wire around or through said piston; and    allowing said response to break said wire.    
   
   
       21 . The device of  claim 1 , wherein: 
 said restraining member opens a port as a result of being subjected to said energy input.    
   
   
       22 . The device of  claim 21 , wherein: 
 said actuating member comprises a piston flanked by chambers; said restraining material is disposed initially in a port in one of said chambers such that application of said energy input opens said port to create a net force on said piston to set the tool.    
   
   
       23 . The device of  claim 22 , wherein: 
 said port, when opened admits hydrostatic well pressure to one of said chambers.    
   
   
       24 . The device of  claim 22 , wherein: 
 said body further comprises a pressurized chamber, said port, when opened allows pressure from said pressurized chamber to reach said piston via one of said chambers to set the tool.    
   
   
       25 . The device of  claim 24 , wherein: 
 the other of said chambers is exposed to well hydrostatic pressure.    
   
   
       26 . The device of  claim 2 , wherein: 
 said restraining member comprises a final element that is in contact with the actuating member and said heat compromises said final element to allow the actuating member to move.    
   
   
       27 . The device of  claim 26 , wherein: 
 said final element comprises a cord connected to the actuating member that fails from said heat.    
   
   
       28 . The device of  claim 10 , wherein: 
 said wire holds a plurality of sleeve segments together until said initial energy input starts a process that undermines said wire.    
   
   
       29 . The device of  claim 10 , wherein: 
 said wire holds a split ring together around said piston until said initial energy input starts a process that undermines said wire.