Evaluation of static oxidation characteristics and analysis of displacement efficiency during air injection in light oil reservoirs

Air injection oil displacement is a highly promising enhanced oil recovery technology due to its wide gas source availability, low cost and strong reservoir adaptability. To enhance the application effectiveness of air injection for low-temperature oxidation (LTO) flooding in a specific light oil reservoir in China's Xinjiang oilfield, this study systematically investigates the static oxidation characteristics of crude oil and their influence on oil displacement performance. High-pressure static oxidation experiments and long-core physical simulation tests were conducted to examine the effects of oxidation time, water saturation, oxygen concentration, medium oil components (C₇-C₁₇), and reservoir minerals on the LTO behavior of crude oil. The oil displacement efficiency under different permeability conditions during air flooding was also analyzed. The results indicate that the LTO process exhibits stage-wise characteristics: in the initial stage, oxygen consumption is rapid, light and medium components decrease while heavy components increase, leading to higher viscosity and density of the crude oil. Reservoir conditions significantly influence oxidation pathways-high water saturation, low oxygen concentration, and high medium components inhibit oxidation, whereas reservoir cuttings promote cracking reactions due to their catalytic effect, resulting in oil lightening. Long-core flooding experiments further reveal that air flooding is more suitable for formations with relatively high permeability, which helps delay gas channeling, improve sweep efficiency, and thus achieve higher oil recovery. This research clarifies the intrinsic relationship between oxidation reactions and oil displacement performance during air injection, providing a theoretical basis for the application of air injection technology in light oil reservoirs.