Method and apparatus for sealing wells in co2 sequestration projects

Abstract

Method for forming a downhole plug within an abandoned well casing for preventing the flow of gas through the plug and reaching the surface, particularly for CO2 sequestration projects. A milling tool mills out a longitudinal section of the perimeter of the well casing and surrounding cement and detritus to expose the well bore. A heater containing solid metallic alloy is lowered into the casing and the alloy is melted so that it fills the milled out area and flows into the face of the well bore. The heater is removed to allow the alloy to solidify. The upper casing acts to restrain any movement of the plug following solidification of the alloy.

1 . A method of forming a metal alloy plug within the well casing of a well bore of an abandoned oil or gas well to prevent the flow of gas through said metal alloy plug comprising the steps of dropping a casing milling tool down said well casing to a predetermined depth within said well casing, said well casing having a plug below said predetermined depth, milling out a longitudinal section of said well casing and the well cement and detritus surrounding said well casing and above said plug so as to expose the wall of said well bore while leaving the upper portion of said well casing above said milled out area and while leaving the bottom portion of said well casing below said milled out area, removing said casing milling tool and dropping a heater into said well casing to said predetermined depth, said heater carrying a solid metallic alloy plugging material, increasing the temperature of said heater to melt said metallic alloy and maintaining said increased temperature until said melted metallic alloy has flowed from said heater and permeated said well bore to a desired depth, removing said heater from said well casing and allowing said melted metallic alloy to solidify within said well bore, said casing and said milled out area. 
     
     
         2 . Method as in  claim 1  and further comprising applying pressure on said liquid metallic alloy following said melting of said solid metallic alloy and allowing said pressure to assist said melted alloy to flow from said heater. 
     
     
         3 . Method as in  claim 2  wherein said metallic alloy comprises bismuth as a principal component. 
     
     
         4 . Method as in  claim 1  wherein the quantity of melted metallic alloy is sufficient to entirely fill said milled out area between said upper and lower portions of said well casing, said upper well casing restraining movement of said metal alloy plug following said solidification of said metal alloy within said milled out area. 
     
     
         5 . Apparatus used to form a metallic alloy plug within a well casing, said apparatus comprising a milling tool used to mill out a longitudinal section of a well casing at a predetermined depth within said well casing and leaving the upper and lower portions of said well casing above and below said milled out area and a heating tool operable to carry solid metallic alloy billets, to melt said billets at an elevated temperature of said heating tool to form liquid alloy and to maintain said elevated temperature of said heating tool until said liquid alloy flows into said milled out area for a desired time period, said heating tool having a connected power cable to supply power to said heating tool and to lower and raise said heating tool within said well casing. 
     
     
         6 . Apparatus as in  claim 5  and further comprising means to apply pressure on said liquid alloy to assist flow of said liquid alloy from said heating tool and into said milled out area.