Methods to remove alloy plugs and annular seals and associated apparatus

Abstract

The present invention provides methods for removing metal alloy plugs and/or a metal alloy annular seals from a target zone of a subterranean well bore and in particular the removal of such so that completion tubing and/or completion equipment can be retrieved from the target zone. The present invention provides for the use of both heat and acid compounds in the removal of the metal alloys. In addition, the present invention provides a downhole tool for delivering acid compounds to a target zone of a subterranean well bore to enact the methods of the present invention.

1 . A method of removing a metal alloy plug and/or a metal alloy annular seal from a target zone of a subterranean well bore, said method comprising introducing an acid compound into the target zone to break down the metal alloy of said plug and/or annular seal. 
     
     
         2 . The method of  claim 1 , further comprising perforating a well tubing at a location in, or proximal to, the target zone in order to allow access to an annular space in which said metal alloy annular seal is set, wherein the perforating step takes place prior to the introduction of the acid compound. 
     
     
         3 . The method of  claim 2 , wherein the well tubing is perforated at a location that is up-hole of the metal alloy annular seal. 
     
     
         4 . The method of  claim 2 or 3 , wherein the well tubing is perforated at a location that is adjacent to the metal alloy annular seal. 
     
     
         5 . The method of any one of  claim 1 to 3 , wherein the acid compound is introduced into the target zone using a dump bailer delivered down the well bore. 
     
     
         6 . The method of any one of  claim 1 to 3 , wherein the step of introducing the acid compound comprises pumping the acid compound into the target zone. 
     
     
         7 . The method of any one of  claim 1 to 3 , wherein the step of introducing the acid compound comprises deploying the acid compound down the well bore to the target zone in a delivery container that is configured to break upon impact within the target zone and disperse the acid compound in the target zone. 
     
     
         8 . The method of any one of  claims 1 to 3 , further comprising a step of at least partially isolating the target zone within the subterranean well bore to retain said acid compound within the target zone long enough to break down the metal alloy. 
     
     
         9 . The method of any one of  claims 1 to 3 , wherein said further comprises heating the target zone and/or the acid compound. 
     
     
         10 . The method of  claim 9 , wherein the acid compound is heated before it is introduced into the target zone. 
     
     
         11 . The method of any one of  claims 2 to 3 , further comprising subjecting the well tubing to additional loads via tension, compression, internal pressure and/or external pressure either before or after the acid compound is introduced to the target zone. 
     
     
         12 . A method of removing a metal alloy annular seal from an annulus within a target zone of a subterranean well bore, said method comprising:
 perforating a well tubing at a location adjacent to said annular seal; and   delivering heating means downhole to the target zone via the well tubing and operating such to melt the metal alloy annular seal.   
     
     
         13 . The method of  claim 12 , further comprising the step of providing a junk basket a location down hole of the heating means prior to the operation of the heating means such that any molten alloy flowing through the perforations can be collected by the junk basket. 
     
     
         14 . (canceled) 
     
     
         15 . (canceled) 
     
     
         16 . A downhole tool for use in the removal of metal alloy plugs and annular seals from a target zone of a subterranean well bore, said tool comprising a dump bailer with an internal cavity that is resistant to an acid compound used to break down the metal alloy of said plugs and annular seals;
 wherein dump bailer further comprises release means that, in use, are actuatable to facilitate the egress of the acid compound from the internal cavity into the target zone.   
     
     
         17 . The downhole tool of  claim 16 , wherein the internal cavity is formed from stainless steel and/or is provided with a protective coating or lining that is resistant to said acid compound. 
     
     
         18 . The downhole tool of  claim 16 or 17 , wherein the tool further comprises a heater that is configured to heat an acid compound housed within the internal cavity. 
     
     
         19 . The downhole tool of any one of  claim 16 or 17 , wherein the tool further comprises at least one isolation device configured to engage with a well tubing within the well bore and form a barrier to retain said acid compound within the target zone. 
     
     
         20 . The downhole tool of any one of  claim 16 or 17 , wherein the tool further comprises a piston configured, in use, to eject an acid compound from within the internal cavity of the dump bailer and introduce it into the target zone. 
     
     
         21 . (canceled)