Abstract: It is necessary to optimize the parameters of gas injection heating during the gas injection-heating process in situ
combustion. A transient model is proposed to simulate the flow and the heat exchange of air in the well tube and oil reservoirs
including the mixing process of air and oil reservoirs，change of component and phase state such as evaporation of hot water
and condensation of cold wet air，the heat exchange among different oil reservoirs and rock. A solving method based on Rung-
Kutta and a simulation program is programmed. After the verification of simulating injection，this mathematical model and its
solving method are applied to the simulation and monitoring of gas injection heating process in situ combustion at actual oil
field. It was found that the extension of heating zone is slow (radius of heating zone is less than 0.6 m after a 5-day injection)
and greatly influenced by the moisture content of oil reservoir，and the temperature of it is almost constant and determined by
the power of electric heater and gas flow rate. The power of electric heater and gas flow rate should keep in a stable state during
the heating process.

Key words: in situ combustion, gas injection-heating, monitoring system, mathematical model, Rung-Kutta method