In this study, a high-temperature and high-pressure microscopic visualization model was used to simulate water flooding, CO₂ flooding and water-alternating-gas (WAG) flooding using CO₂ at 60℃ and 18 MPa in complex reservoirs. Multiphase fluid displacement features in porous media were described in detail by observing the multi-phase fluid flow and residual oil distribution in the process of water flooding, CO₂ flooding and WAG flooding. The residual oil ratio at each process was quantitatively analyzed using image processing technology and software analysis. The experimental results show that WAG flooding not only decreased fluid slipstream in water flooding, but also reduced gas breakthrough along the high permeability pore in CO₂ flooding. WAG flooding made the advantages of water flooding and CO₂ flooding complementary to each other, increasing the oil recovery by 12.31% compared with CO₂ flooding.

high temperature and high pressure  /  microscopic visualization simulation  /  gas/water alternating flooding  /  improve the recovery efficiency