Microscopic seepage mechanism of nanofluids assistant CO2 aerosol foam system flooding after water flooding

CO 2 foam (CF) flooding is a widely adopted enhanced oil recovery (EOR) technique for later stage water flooding reservoirs. However, inadequate mixing of CO 2 and foaming agents often results in uneven and unstable foam, limiting its efficiency. To address this limitation, a novel CO 2 aerosol foam system (CAFS) generated with a custom-designed aerosol foam generator was developed for systematically evaluating CAFS performance following water flooding, with a focus on gas–liquid ratio, pre-injection volume, and solution concentration through core flooding experiments and visualized microscopic flooding experiments. Core flooding experiments show that CAFS achieved an ultimate recovery factor of 62.43 % and reduced water cut by up to 32.51 %, representing improvements over conventional CF by 10.45 % and 20.57 %, respectively. This improvement is attributed to changing rock wettability of nanofluid addition and the high resistance coefficient of aerosol foam. The visualized microscopic flooding experiments further reveal that CAFS produces more uniform and stable foam, enhancing sweep efficiency through mechanisms such as trapping effects, Jamin effects, and pore-throat occupation. Moreover, the emulsification of SDS solution and dissolution viscosity-reducing of CO 2 further improve oil displacement efficiency. Collectively, these findings demonstrate that CAFS outperforms conventional CF flooding and has broad application potential in oilfield development.