Heating device for passage through subterranean asphalt and method of use

Abstract

A lowermost casing segment in a tubular casing string, capped with a cast iron end cap, has an ignitable thermite mixture within the interior of such casing segment which, when ignited, superheats the end cap and the casing segment, to allow the casing segment and the end cap to be lowered completely through a subterranean asphalt formation without allowing the asphalt to enter the interior of the casing segment. The cast iron end cap is then drilled out to allow further drilling through the casing segment into oil and gas formations beneath the asphalt formation. In a first embodiment, the casing segment has a top cap to constrain the thermite mixture. In a second embodiment, the thermite mixture is located within a metal capsule which can be lowered into the casing segment to rest against the bottom end cap, and then be removed by a wireline.

1 . A system for allowing a casing string to be lowered through a subterranean asphalt formation, comprising:
 a tubular joint of casing at the lowermost end of said casing string, said tubular joint of casing having a first end and a second end, said first end having a first cap sealing said first end against entry of asphalt through said first end into the interior of said joint of casing;   a second cap within the interior of said tubular joint of casing, and located between said first and second ends of said tubular joint of casing; and   a thermite mixture within the interior of said tubular joint of casing, between said first and second caps, for heating the first cap and at least a portion of said tubular joint to allow said tubular joint of casing to be lowered through said asphalt formation.   
   
   
       2 . The system according to  claim 1 , including in addition thereto, a firing head for igniting the thermite mixture. 
   
   
       3 . The system according to  claim 2 , wherein said first cap comprises cast iron. 
   
   
       4 . The system according to  claim 3 , wherein said second cap comprises cast iron. 
   
   
       5 . The system according to  claim 1 , wherein said thermite resides within an envelope which can be lowered into and removed from the interior of said joint of casing by a wireline running from the earth's surface down to the envelope. 
   
   
       6 . An apparatus for melting through a subterranean asphalt formation comprising;
 a lower casing assembly with side walls, a top end, and a bottom end capable of being lowered into said asphalt formation;   said bottom end being covered by a bottom cap;   a top cap between said top end and said bottom end, therein creating a substantially hollow chamber within the lower casing assembly as defined by the side walls, the top cap and said bottom cap, said hollow chamber housing a thermite mixture capable of producing heat significant to reduce asphalt to a soft, viscous, flowing material upon ignition; and   a firing head in contact with said top cap and with said thermite mixture, and being capable of igniting said thermite mixture, wherein when said firing head is actuated the thermite mixture ignites and produces heat which heats the bottom cap and the lower casing assembly significantly to reduce asphalt to a soft, viscous, flowing material, thereby allowing the lower casing assembly and bottom cap to be lowered through the asphalt layer.   
   
   
       7 . The apparatus of  claim 6  further comprising:
 a first drop bar located in the hollow chamber and attached to the top cap, and said first drop bar being capable of igniting said thermite mixture, said firing head being in communication with the first drop bar, wherein upon actuating said firing head the first drop bar is dropped in the thermite mixture, thereby igniting the thermite mixture.   
   
   
       8 . The apparatus of  claim 6 , further comprising:
 a second drop bar located at the earth's surface, above the firing head, wherein when said second drop bar contacts the firing head the firing head is activated.   
   
   
       9 . The apparatus of  claim 6 , further comprising:
 an exhaust port for releasing gases from the hollow chamber, wherein said exhaust port runs through the top cap and into the hollow chamber.   
   
   
       10 . The apparatus of  claim 6 , further comprising:
 an ignition cord capable of igniting a thermite mixture, wherein said firing cap is connected to the ignition cord and said ignition cord is in contact with the thermite mixture.   
   
   
       11 . The apparatus of  claim 10 , further comprising:
 said ignition cord being capable of igniting said thermite mixture from the top of the thermite mixture downwardly.   
   
   
       12 . The apparatus of  claim 10 , further comprising:
 said ignition cord being capable of igniting said thermite mixture from the bottom of the thermite mixture upwardly.   
   
   
       13 . A method for lowering the bottom end of a tubular casing string through a subterranean asphalt formation, comprising the steps of:
 capping the said bottom end of said casing string;   heating the capped bottom end and at least an additional portion of the lowermost joint of casing in said casing string, by igniting a thermite mixture located with said lowermost joint of casing; and   lowering said tubular casing string through said asphalt formation during said heating step.   
   
   
       14 . The method according to claim  15 , including in addition thereto, the step of drilling through the said capped bottom end, and then drilling further into the formations beneath the said asphalt formation.