Thermal processes for subsurface formations

A heater system for heating a subsurface formation, comprising:

• a first conduit;
• a second conduit positioned in the first conduit;
• a plurality of oxidizers to oxidize fuel and oxidizing fluid mixture to heat a portion of a subsurface formation, the plurality of oxidizers positioned between the first conduit and the second conduit, the oxidizers in fluid communication with the first conduit and the second conduit;
• wherein the second conduit supplies fuel to the oxidizers;
• and
• wherein the first conduit supplies oxidizing fluid to the oxidizers.

A heater system for heating a subsurface formation, comprising:

• an oxidizer conduit;
• a fuel conduit positioned in the oxidizer conduit;
• and
• a first oxidizer coupled to the fuel conduit and positioned between the fuel conduit and the oxidizer conduit;
• the first oxidizer configured to mix fuel from the fuel conduit and oxidizing fluid from the oxidizer conduit to produce a combustible fuel mixture that is oxidized in the first oxidizer to produce heat and combustion products, wherein the combustion products pass downstream from the oxidizer through the oxidizer conduit;
• and
• a second oxidizer coupled to the fuel conduit, wherein the second oxidizer is configured to mix fuel with fluid from the oxidizer conduit to produce a combustible fuel mixture that is oxidized in the second oxidizer to produce heat and combustion products.