CO2 geosequestration or enhanced oil recovery (EOR) by CO2 injection in hydrocarbon reservoirs is suggested as a short-term solution for limiting CO2 atmospheric accumulation. In the case of oxy-combustion CO2 capture, the main annex gas associated with CO2 is O2 in important proportion (≤7%). Even if hydrocarbon oxidation processes by O2 are well-known in high-temperature–low-pressure (HT-LP) conditions, scarce data are available under reservoir conditions (high-pressure–low-temperature, HP-LT). To predict the hydrocarbon evolution in the presence of O2 in an oil-depleted reservoir, it is necessary to investigate their reactivity. As a matter of fact, a double approach combining experimentation and modeling was performed in this study. Experiments were carried out on a model compound (n-octane), by injecting O2/N2 gas mixtures in a HP-LT titanium reactor. In parallel, a detailed kinetic model for n-octane, generated by the software EXGAS, was applied. Several reactions were added, and some rate parameters have been adjusted to adapt the model to reservoir conditions. The modified model was validated by experiments performed at different reaction temperatures and O2 concentrations. The consistency between experimentations and modified oxidation model is promising for the development of a tool allowing the prediction of hydrocarbon reservoir stability.

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CO 2 geosequestration [carbon capture and storage (CCS)] and enhanced oil recovery (EOR) by CO 2 injection in hydrocarbon-depleted reservoirs could limit the CO 2 atmospheric accumulation. In the case of CO 2 capture by oxy-combustion, the main annex gas associated with CO 2 is O 2 . O 2 that remains in the flue gas for injection can induce the oxidation of the hydrocarbons contained in the reservoirs. The effect of O 2 must be studied in terms of benefit and/or risk for CCS or EOR. To investigate the mechanism of hydrocarbon oxidation, it is essential to analyze the distributions of the formed oxygenated compounds. That is why experiments have been performed with a model compound (n-octane) in a closed reactor under high pressure at different temperatures and with different oxygen concentrations. The product distribution suggests two pathways of n-alkane oxidation, with (i) the preservation of the aliphatic chain length of the initial n-alkane, which generates oxygenated products with the same number of carbon, and (ii) the breakdown processes of the initial n-alkane, which generates lowmolecular-weight oxygenated products. The new understanding of the mechanism of n-alkane oxidation could be incorporated into the detailed kinetic model of our previous study, which is specific to the reservoir conditions.