Heater well method and apparatus

A method to heat a formation, the formation lying below a surface of the earth, the method comprising the steps of:

• providing a wellbore within the formation to be heated, the wellbore comprising
• a casing within the formation to be heated,
• a tubular defining, in the inside of the tubular, a flowpath for hot gases from the surface to a point in the wellbore near the bottom of the formation to be heated, and a volume between the tubular and the casing providing a flowpath for hot gases from near the bottom of the formation to be heated to the top of the formation to be heated, wherein the flowpaths are in communication with each other near the bottom of the formation to be heated and the volume between the casing and the tubular at the top of the formation to be heated is in communication with a point above the surface, and
• insulation for a portion of the length of the wellbore within the formation to be heated between the flowpath for hot gases from the surface to the point in the wellbore near the bottom of the formation to be heated and the flowpath for hot gases from near the bottom of the formation to be heated to the surface;
• supplying a flow of hot gases to the flowpath for hot gases from the surface to a point in the wellbore near the bottom of the formation to be heated;
• and
• returning the hot gasses to the surface through the volume between the tubular and the casing and thereby heating the formation.