Method and apparatus for plugging a wellbore

Abstract

The present invention provides a method and apparatus for plugging a wellbore in a trip saving manner. In one aspect, the invention includes a cement retainer disposed on a run-in string and a radially expanded perforating assembly disposed below the cement retainer. In a single run, the apparatus provides for perforating a wellbore and squeezing cement through the perforations and into the formation therearound. In another aspect, a method of plugging the wellbore includes running a cement retainer and a radially expanded perforating assembly into a wellbore on a run-in string. After the cement retainer is set, a firing head is actuated to cause the perforating gun to discharge. After perforations are formed, cement is introduced from the cement retainer into the isolated area and squeezed through the perforations. Thereafter, the run-in string disengages from the cement retainer leaving behind the plug formed. In yet another aspect, a firing head capable of being actuated by different means is used to discharge the perforating assembly.

1 . A firing head for igniting a charge in a wellbore, comprising: 
 a body having a central channel therethough;    a two position firing pin disposed in the bore, the firing pin constructed and arranged to ignite the charge in a second position; and    a frangible member disposed in the bore above the pin, the frangible member dividing the bore into an upper and lower portions, the upper portion having a higher pressure therein than the lower portion.    
     
     
         2 . The firing head of  claim 1 , further including a fluid path between the wellbore and the upper portion.  
     
     
         3 . The firing head of  claim 2 , wherein the fluid path comprises at least one aperture formed in a wall of the body.  
     
     
         4 . The firing head of  claim 3 , whereby the charge is ignited by increasing the pressure in the upper portion to a predetermined level at which level the frangible member ruptures, exposing the lower portion to the higher pressure of the upper portion and moving the pin to the second position.  
     
     
         5 . The firing head of  claim 1 , further including an axially movable member mounted at an upper end of the body, the member movable by mechanical force applied thereto to break the frangible member, exposing the lower portion to the higher pressure of the upper portion and moving the pin to the second position.  
     
     
         6 . The firing head of  claim 5 , whereby the movable member is held in a first position by a shearable member extending between the movable member and the body.  
     
     
         7 . The firing head of  claim 1 , whereby the pin is held in a first position by a shearable member extending between the pin and the body.  
     
     
         8 . The firing head of  claim 1 , wherein the charge is a perforating charge.  
     
     
         9 . A firing head for discharging a perforating assembly, comprising: 
 a body;    a channel disposed in the body;    a plug at least partially disposed in the channel;    a rupture disc assembly disposed below the plug;    a firing pin disposed below the rupture disc assembly;    a roll pin at least partially disposed in the body and the plug; and    a retention pin at least partially disposed in the firing pin.    
     
     
         10 . The apparatus of  claim 9 , wherein the plug comprises a hollow T-shaped snout.  
     
     
         11 . The apparatus of  claim 9 , wherein the rupture disc assembly comprises: 
 a snout channel disposed in the rupture disc assembly; and    a membrane disposed in the rupture disc assembly, wherein the membrane prevents fluid communication in the snout channel.    
     
     
         12 . The apparatus of  claim 9 , wherein the body comprises: 
 a first set of holes disposed in an upper portion of the body; and    a second set of holes disposed in a middle portion of the body, wherein the first and second set of holes are in fluid communication with the channel.    
     
     
         13 . The apparatus of  claim 10 , wherein a pressure above and below the firing pin is below a hydrostatic pressure.  
     
     
         14 . A method for actuating a firing head for discharging a perforating assembly, comprising: 
 supplying a force to break a membrane disposed above a firing pin;    increasing a pressure above the firing pin; and    causing the firing pin to strike a primer cap.    
     
     
         15 . The method of  claim 14 , wherein supplying a force to break a membrane comprises: 
 striking a plug disposed at a first position above the membrane;    causing a roll pin securing the plug to the first position to break;    moving the plug from the first position to a second position; and    breaking the membrane with the plug.    
     
     
         16 . The method of  claim 14 , wherein supplying a force to break a membrane comprises: 
 increasing a hydrostatic pressure above the membrane;    breaking the membrane.