Conventional thermal recovery techniques face challenges in low-permeability heavy oil reservoirs due to low recovery factors and poor economic viability. To address these challenges, low-temperature oxidation (LTO) during oxygen-reduced air flooding was employed to achieve in situ oil upgrading and enhance oil recovery. Static oxidation tests at oxygen concentrations of 5%, 10%, 15%, and 21% were designed to analyze the produced gas composition and the physical properties of the oil following oxidation. We further employed Differential Scanning Calorimetry (DSC) and Thermogravimetric (TG) analysis to evaluate the oxidation behavior of crude oil under the same oxygen concentration conditions. Finally, long-core displacement experiments were performed to assess how the oxygen concentration influences the recovery efficiency. The results showed that under the tested conditions, oxygen consumption exceeded CO2 generation, indicating that low-temperature oxygen addition reactions (formation of oxygenated species) dominated over complete oxidation. As the oxygen concentration increased, the oxidized crude oil exhibited a higher viscosity. At higher oxygen concentrations (15% and 21%), the asphaltene content increased significantly, resulting in poorer fluidity. The activation energy in the LTO stage decreased with increasing oxygen concentration, as revealed by kinetic analysis over the range of 5% to 21%. The LTO stage dominated the crude oil oxidation process. However, the heat release during this stage was less affected by the oxygen concentration. Consequently, increasing the oxygen concentration contributed only marginally to elevating the reservoir temperature. For the studied reservoir, oxygen-reduced air flooding with a 5% oxygen concentration achieved a final recovery factor of 34.82%. This represented a 1.76% improvement over conventional air flooding, thereby enabling economically efficient reservoir development.
Zhang et al. (Fri,) studied this question.