| CPC E21B 36/008 (2013.01) [E21B 29/002 (2013.01); E21B 33/1208 (2013.01)] | 14 Claims |

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1. A downhole tool assembly system for use in deploying alloy plugs and/or seals in oil and gas wells, said system comprising:
a tubular heater with an exothermic chemical reaction heat source, wherein the tubular heater is provided with a running tool at an up-hole end thereof;
a tubular mandrel in which a down-hole portion of the tubular heater is removably retained such that the tubular heater and the tubular mandrel are in thermal communication; and
a mill arranged on the outside on the tubular heater at a location proximal to the up-hole end thereof and separated from the tubular mandrel by a clearance space, wherein the mill comprises at least one flow port that by-passes the tubular heater and provides access to the clearance space from an up-hole location.
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