Method and system for sealing a void in an underground wellbore

Abstract

Voids ( 14 ) in a underground wellbore ( 1 ) are sealed by:—inserting a corrosion prone object ( 10 A-C, 12 ) in the void injecting an oxidizing agent into the void ( 14 ); and—allowing the oxidizing agent to induce corrosion of the corrosion prone object and to thereby generate corrosion products ( 13 A-E) that are physically larger than the corrosion prone object ( 10 A-C, 12 ) and that seal the void ( 14 ).

1 . A method of sealing a void in an underground wellbore, the method comprising:
 inserting a corrosion prone object in the void;   injecting an oxidizing agent into the void; and   allowing the oxidizing agent to induce corrosion of the corrosion prone object and to thereby generate corrosion products that are physically larger than the corrosion prone object and that seal the void.   
     
     
         2 . The method of  claim 1 , wherein the void has an annular shape and the corrosion prone object comprises a ring which is inserted into the void. 
     
     
         3 . The method of  claim 2 , wherein the annular shaped void is located adjacent to a ferrometallic well conduit and the corrosion prone object comprises an aluminum ring arranged in the void adjacent the conduit. 
     
     
         4 . The method of  claim 3 , wherein a series of aluminum rings is arranged at selected longitudinal intervals along the length of an annular void at the outer and/or inner surface of the ferrometallic well conduit. 
     
     
         5 . The method of  claim 4 , wherein the ferrometallic well conduit is a well casing, well liner, or an electrical or hydraulic conduit provided with a ferrometallic lining. 
     
     
         6 . The method of  claim 5 , wherein the ferrometallic well conduit is a well casing or well liner made of a low alloy steel, such as L80 or P110 steel. 
     
     
         7 . The method of  claim 1 , wherein the oxidizing agent comprises an electrolyte and oxygen and/or an oxygen generating agent. 
     
     
         8 . The method of  claim 7 , wherein the electrolyte comprises a brine. 
     
     
         9 . The method of  claim 7 , wherein the oxidizing agent comprises a chemical oxygen generating agent selected from the group consisting of H 2 O 2 , NaClO 3 , KClO 4 , NaNO 3  and combinations thereof. 
     
     
         10 . The method of  claim 9 , wherein the oxidizing agent comprises a microbial oxygen generating agent. 
     
     
         11 . The method of  claim 10 , wherein the microbial oxygen generating agent comprises thermophilic chlorate reducing micro-organisms. 
     
     
         12 . The method of  claim 11 , wherein the thermophilic chlorate reducing organisms comprise bacteria of the genus  Archaeoglobus, Geobacillus  and/or  Thermus , which use hydrogen (H) and electrons(e) provided by brine and/or other fluids in the void followed by dismutation of chlorite (ClO 2   − ) by the micro-organisms on the basis of the reactions:
   ClO 3   − +2H + +2e→ClO 2   − +H 2 O
     ClO 2   − →Cl − +O 2 
   
     
     
         13 . The method of  claim 12 , wherein the thermophilic chlorate reducing micro-organisms multiply at an ambient temperature of at least 80° C. and comprise bacteria of the genus  Archaeoglobus fulgidis.    
     
     
         14 . A system for sealing a void in an underground wellbore, the system comprising:
 a corrosion prone object arranged in the void;   means for injecting an oxidizing agent into the void to allow the oxidizing agent to induce corrosion of the corrosion prone object and to thereby form the corrosion products that are physically larger than the corrosion prone object and that seal the void.   
     
     
         15 . The system of  claim 14 , wherein the annular shaped void is located at the outer surface of a ferrometallic well conduit, the corrosion prone object comprises an aluminum ring arranged around the conduit and the means for injecting an oxidizing agent comprises means for injecting an electrolyte and oxygen and/or an oxygen generating composition into the void.