Abstract: There are two combustion states of in-situ combustion, namely low-temperature and high-temperature oxidation of crude oil. To address the problems of unstable low-temperature oxidation process, low thermal efficiency and low recovery percent, indoor physical simulation and numerical simulation experiment were carried out with the in-situ combustion in Du 66 Block as the study object, a kinetic model of in-situ combustion reaction was established through the historical fitting of oxygen consumption and different-component exhaust gas data, and a transform boundary chart of high- and low-temperature oxidation was constructed based on the initial temperature and ventilation intensity at the front edge of the in-situ combustion. The results of the study showed that in high-temperature oxidation, the apparent H/C atomic ratio of crude oil in Du 66 Block was 0.5 to 2.0 and the CO/CO₂ volume ratio was 0.13 to 0.40; the combustion during low-temperature oxidation was unstable and easily extinguished; the initial temperature and ventilation intensity at the critical front edge of high- and low-temperature oxidation of in-situ combustion in Du 66 Block were 280°C and 1.0 m³/(m²·h) respectively; if lower than or close to the critical value, there may be a risk of low-temperature oxidation or even extinction; development countermeasures were put forward based on in-situ combustion in Du 66 Block, including maintaining the minimum ventilation intensity and stratified in-situ combustion. The study provides a theoretical basis for the engineering design of in-situ combustion reservoirs.

Key words: in-situ combustion, numerical simulation, high-temperature oxidation, low-temperature oxidation, technological limit, Du 66 Block