Study on associated gas combustion characteristics and inert gas influence rules in air-foam flooding process

Air-foam flooding technology is a potential tertiary oil recovery technology. However, enhancing oil recovery through air injection still indicates risks of explosion. In this study, the upper and lower flammability limit (UFL and LFL) and limiting oxygen concentration (LOC) of the associated gas during air-foam flooding are investigated. The change rules of these combustion characteristics are tested under different initial pressures and temperatures using a high-pressure experimental device. The measurement results indicate that with the increase of initial temperature and pressure, the LFL and LOC decrease, whereas the UFL increases. The flammability limits of the associated gas measured at 15 MPa and 80 degrees C are ranging from 1.14% to 56.67%, far exceeding the calculated value under the room temperature and pressure. The empirical formula of the associated gas combustion performance is also fitted to immediately identify the risk levels of associated gases with similar components. The change in initial pressure and temperature only slightly affects the LOC when CO2 is the inert gas. By contrast, it greatly reduces the LOC when N2 is the inert gas. The maximum difference value of 2.55% between the LOC of the two inert gases is observed at 4 MPa and 80 degrees C. Overall, the findings of this study can serve as test data for the combustion limits and limiting oxygen content of associated gases in the process of air-foam flooding.