Method and apparatus for sealing abandoned oil and gas wells

Abstract

Apparatus and method for forming a solid sealing plug of bismuth-tin alloy material within a well casing for sealing oil or gas wells. Solid alloy material is positioned within a heating tool and lowered to a position within the well casing where the seal is to be formed. The heating tool is heated to liquefy the alloy material and the alloy material then runs out of the heating tool and solidifies on top of a cement plug previously formed within the well casing. A cement slurry or other fluid material may subsequently be deposited on top of the liquefied alloy material to enhance the sealing of the alloy plug, to form a barrier to subsequent creep of the alloy plug when the alloy solidifies and to counteract any pressure acting vertically on the bottom of the plug.

1 . A method for sealing an oil or gas well comprising positioning a melted bismuth/tin alloy material within a casing to form a plug within said casing when said liquefied alloy material solidifies within said casing. 
   
   
       2 . A method as in  claim 1  and further positioning a slurry cement material on the top of said melted bismuth/tin alloy material and allowing said melted bismuth/tin alloy to cool. 
   
   
       3 . A method as in  claim 2  wherein said bismuth-tin alloy material is melted by the application of heat with a heating tool downhole in said oil and/or gas well. 
   
   
       4 . A method as in  claim 3  wherein said bismuth-tin alloy material is positioned within said heating tool in a first solid form prior to being melted. 
   
   
       5 . A method as in  claim 4  wherein said heating tool is lowered within a well casing to an existing cement plug within said well casing with said bismuth-tin alloy in solid form and said force balancing material is positioned on top of said bismuth-tin alloy. 
   
   
       6 . A method as in  claim 5  wherein said bismuth-tin alloy is heated following the lowering of said heating tool within said well casing, said liquefied alloy material exiting said heating tool and said force balancing material exiting said heating tool following said alloy material. 
   
   
       7 . A method as in  claim 1  wherein a cap is initially removed from the top of the outer one of said casing to allow access to said casing. 
   
   
       8 . Apparatus to allow a molten bismuth-tin alloy material to be positioned as a plug within an oil or gas well, said apparatus comprising means to add molten eutectic material to said casing at a predetermined location within said casing so as to form a solid plug within said casing when said liquefied alloy material cools and means to add a force balancing material to said casing on the top of said molten material. 
   
   
       8 . Apparatus as in  claim 7  wherein said molten eutectic material is a bismuth-tin alloy material. 
   
   
       9 . Apparatus as in  claim 8  wherein said means to add said bismuth-tin alloy material is an alloy heater with a first cylindrical cavity to hold said bismuth-tin alloy material in solid form and said means to add a force balancing material is a second cylindrical cavity to hold said force balancing material in a fluid form. 
   
   
       10 . Apparatus as in  claim 9  wherein said heating tool has a heating chamber which allows said bismuth-tin alloy in solid form to be liquefied within said heating tool. 
   
   
       11 . Apparatus as in  claim 10  wherein said means to add molten alloy material to said casing further includes power cables extending to said heating tool and a wireline to allow said heating tool to be raised and lowered within said well casing. 
   
   
       12 . Method of sealing an abandoned oil or gas well comprising removing the cap on the top of the outer casing of said well, lowering and positioning a melted bismuth/tin alloy material within said casing to form a plug within said casing when said liquefied alloy material solidifies within said casing, positioning a force balancing material on the top of said melted bismuth/tin alloy material and allowing said melted bismuth/tin alloy to cool.