Firing head with detonation gas release activation

Abstract

A firing head sub for use in explosive well perforation is described. The firing head initiates the firing of a charge within a downhole perforating gun, and also releases the firing head and perforating gun from the tubing string upon firing so as to avoid clogging of the perforating gun with sand and jamming of the perforating gun downhole. The firing head and perforating gun will only be released upon detonation of the charge. This is ensured by a feedback loop that returns spent detonation gas to the firing head to shift a sleeve, thereby unbiasing the firing head latches from their engagement with the tubing string connector, thereby releasing the firing head from the tubing string.

1 . A automatic release firing head sub for attachment between a tubing string and perforating gun to be fired by a charge initiator comprising: 
 a. a tubing string connector adapted to connect a firing head to the tubing string;    b. a firing piston having a firing pin, the firing piston slideably engaged within a cylinder and drivable towards the charge initiator;    c. a piston retainer for applying a retaining force to the firing piston to maintain the firing piston in a non-firing position;    d. a firing mechanism activated by providing pressurized fluid to a side of the cylinder to drive the piston to overcome the retaining force of the piston retainer, thereby releasing and energizing the firing piston and firing pin to strike the charge initiator;    e. a feedback channel for delivering detonation gas under high pressure from the perforating gun to the firing head; and    f. a latching system for releasably attaching the firing head to the tubing string, the latching system unlatching only in response to the delivery of detonation gas to the firing head.    
   
   
       2 . The firing head sub of  claim 1  wherein the latching system includes a collar of flexible fingers, the fingers held by a retention sleeve to engage a recess within the tubing string connector while latched, but biased to disengage when the retention sleeve is moved.  
   
   
       3 . The firing head sub of  claim 2 , wherein the retention sleeve is slideably disposed between the cylinder and the fingers, and is held in place by a shearable link.  
   
   
       4 . The firing head sub of  claim 3 , wherein the retention sleeve is forced from between the cylinder and the fingers by the detonation gas exhausted through the feedback channel.  
   
   
       5 . The firing head sub of  claim 3 , wherein the shearable link comprises a shear pin extending between the tubing string connector and the retention sleeve.  
   
   
       6 . The firing head sub of  claim 1 , wherein the cylinder is a drive housing.  
   
   
       7 . A firing head sub for releasably retaining a perforating gun, the firing head sub comprising: 
 a. a feedback channel adapted to receive detonation gas from the perforating gun; and    b. a latching system adapted to releasably retain the perforating gun, the latching    system adapted to unlatch in response to the detonation gas, wherein the latching system is adapted to unlatch when the detonation gas pressure reaches a threshold pressure.    
   
   
       8 . A method of moving a perforating gun on a tubing string from a perforation zone of a wellbore comprising the steps of: 
 a. activating the perforating gun to generate detonation gases; and    b. directing the detonation gases to trigger the disconnection of the perforating gun and the tubing string,    wherein, the detonation gases must reach a threshold pressure in order to trigger the disconnection of the perforating gun and the tubing string.    
   
   
       9 . The method of  claim 8 , further comprising the step of propelling the perforating gun away from the tubing string, at least in part, using the detonation gases.