Well sealing via thermite reactions

Abstract

Wells are sealed by means of thermite reaction charges inserted into the wells. The reaction charge can be diluted by addition of metal oxides, silica, or the like control reaction pressure, peak temperature, reaction rate, and expansion characteristics of the resulting thermite plug. The use of dilution of the thermite reactants can take the form of a thermite charge with specific layers, including relatively high and low reaction temperature layers. The ignition source can be oriented to achieve directional control on the product expansion including radial or axial expansion. The charge can be loaded with a large mass to compress the resulting thermite plug into the borehole wall and reduce its porosity during the reaction process. A further variation involves continuous feed of the thermite reactants to the reaction zone. Various combinations and permutations of the above inventive concepts are described.

1 . A thermite plug for a well comprising:
 a thermite reaction charge formed as a generally cylindrical body of length L and a central longitudinal axis α; and   an igniter for the thermite material, wherein the igniter is positioned axially and extends substantially the length L of the general cylindrical body along the longitudinal axis α to trigger an exothermic reaction in the thermite reaction material propagating substantially from the center of the cylindrical body outwardly in a radial direction.   
     
     
         2 . The thermite plug of  claim 1 , wherein the thermite plug further comprises two or more slippage/cleavage planes formed in the thermite reaction charge designed to promoting radial expansion of the thermite reaction charge during combustion. 
     
     
         3 . The thermite plug of  claim 1 , wherein the thermite plug comprises a first section having the thermite reaction charge and igniter as recited in  claim 1 , and a second section comprising a second thermite material and a second igniter disposed to trigger an exothermic reaction propagating substantially in the axial direction. 
     
     
         4 . The thermite plug of  claim 1 , wherein the thermite reaction charge has been diluted by one or more additives to moderate an exothermic reaction produced by the thermite material when ignited, the moderating comprising lowering the reaction temperature to less than 1700° C. and reaction velocity to less than 1 cm/sec within the thermite material from what they would otherwise be without the one or more additives. 
     
     
         5 . The thermite plug of  claim 3 , wherein the second section is positioned below the first section. 
     
     
         6 . The thermite plug of  claim 4 , wherein the second section is positioned above the first section. 
     
     
         7 . Apparatus for sealing a well, comprising:
 a first thermite plug having a igniter, a thermite reaction charge and an upper surface;   an insulating block having upper and lower surfaces, the lower surface of the insulating block proximate to the upper surface of the first thermite plug;   a second thermite plug having an igniter, a thermite reaction charge and a lower surface, wherein the lower surface of the second thermite plug is positioned proximate to the upper surface of the insulating block.   
     
     
         8 . The apparatus of  claim 7 , wherein the first thermite plug comprises a thermite reaction charge having a relatively cooler reaction temperature and wherein the second thermite plug comprises a thermite reaction charge having a relatively hotter reaction temperature. 
     
     
         9 . The apparatus of  claim 7 , wherein the first thermite plug further comprises an expandable metal package enclosing the first thermite plug. 
     
     
         10 . The apparatus of  claim 9 , wherein the igniter for the first thermite plug is disposed substantially along the central axis of the first thermite plug. 
     
     
         11 . The apparatus of  claim 7 , wherein the igniter for the second thermite plug is positioned along the bottom surface of the second thermite plug. 
     
     
         12 . The apparatus of  claim 7 , further comprising a third thermite plug having an igniter and a second insulating block separating the third thermite plug from the second thermite plug. 
     
     
         13 . The apparatus of  claim 12 , wherein the igniter for the third thermite plug is positioned substantially along a central axis of the third thermite plug. 
     
     
         14 . The apparatus of  claim 12 , wherein the third thermite plug includes a thermite reaction charge having a relatively cooler reaction temperature than the reaction temperature of the thermite charge of the second thermite plug. 
     
     
         15 . A method for sealing a well, comprising the steps of
 a) lowering into the well a plug comprising a first thermite plug having an igniter, a thermite reaction charge and an upper surface; an insulating block having upper and lower surfaces, the lower surface of the insulating block proximate to the upper surface of the first thermite plug, and a second thermite plug having an igniter, a thermite reaction charge and a lower surface, wherein the lower surface of the second thermite plug is positioned proximate to the upper surface of the insulating block;   b) igniting the first thermite plug so as to cause a thermite reaction in the first thermite plug, the first thermite plug expanding so as to form a plug in the well;   c) subsequently to step b) igniting the second thermite plug.   
     
     
         16 . The method of  claim 15 , wherein the thermite reaction charge in the first thermite plug comprises a thermite reaction material which has been diluted by one or more additives to moderate an exothermic reaction produced by the thermite material when ignited, the moderating comprising lowering the reaction temperature and reaction velocity within the thermite material from what they would otherwise be without the one or more additives. 
     
     
         17 . The method of  claim 16 , wherein the thermite reaction material in the first thermite plug has been diluted by an amount of between 5 and 75 percent by mass by addition of a metal oxide to the thermite reaction material. 
     
     
         18 . The method of  claim 13 , wherein the plug lowered into the well further comprises a third thermite plug, the third thermite plug separated from the second thermite plug by a second insulation block, the method further comprising the step of igniting the third thermite plug prior to igniting the second thermite plug. 
     
     
         19 . The method of  claim 18 , wherein the third thermite plug is ignited substantially at the same time as the first thermite plug is ignited. 
     
     
         20 . A method for sealing a well, comprising the steps of:
 forming a platform in the well by means of ignition of a first thermite plug lowered into the well and causing the first thermite plug to expand to form the platform in the well; and   subsequently igniting a second thermite plug above the location of the platform.   
     
     
         21 . The method of  claim 20 , wherein the first thermite plug is surrounded by an expandable metal package. 
     
     
         22 . The method of  claim 20 , wherein the first thermite plug is comprised of a thermite reaction material having a reaction temperature substantially less than a reaction temperature of the second thermite plug. 
     
     
         23 . The method of  claim 20 , further comprising the step of igniting a third thermite plug lowered into the well prior to igniting the second thermite plug. 
     
     
         24 . The method of  claim 23 , wherein the third thermite plug is comprised of a thermite reaction material having a reaction temperature substantially less than the reaction temperature of the second thermite plug.