VARYING PROPERTIES ALONG LENGTHS OF TEMPERATURE LIMITED HEATERS

摘要

A system for heating a subsurface formation is described. The system includes an elongated heater in an opening in the formation. The elongated heater includes two or more portions along the length of the heater that have different energy outputs. At least one portion of the elongated heater includes at least one temperature limited portion (240) with at least one selected temperature at which the portion provides a reduced heat output and comprises a ferromagnetic conductor. The heater is configured to provide heat to the formation with the different energy outputs. The heater heats one or more portions of the formation at one or more selected heating rates. A Curie temperature is lower for a portion with temperature limit located in the heater upper part then that for a portion with temperature limit located in the heater bottom part.