Yong Zhao, Chenyang Lu, Mingdong Li, Z. X. Li, Xiaochen Zhang, Xiaobin Nie, Daoyi Zhu
In the development of low-permeability petroleum reservoirs, injecting carbon dioxide (CO 2 ) and expanding its conformance volume is one effective approach to enhance recovery and geological carbon storage. Most current studies mainly investigate CO 2 displacement and alternating injection of other chemical agents (e.g., water, surfactant, polymer, and gel) with CO 2 through core displacement experiments, while high-temperature and high-pressure visualized displacement studies are rarely reported. The reservoir adaptability of different chemical alternating systems with CO 2 is also unclear. Therefore, high-temperature and high-pressure visual microfluidic chip experiments were employed. CO 2 displacement features under different chemical alternating CO 2 injection modes were revealed, and the applicability limits of these CO 2 conformance improvement methods were clarified. Results showed that the high-temperature and high-pressure microfluidic chip technique allowed direct and quantitative characterization of microscopic residual oil distribution in pores after CO 2 displacement. Water alternating gas (WAG), foam alternating gas injection (FAG), and polymer alternating gas injection (PAG) all produced multiphase flow resistance in dominant channels (high-permeability breakthrough channels), thereby effectively expanding the CO 2 displacement conformance volume. Among them, the effective permeability-contrast limit of WAG was about 6, that of FAG was about 8, and the reservoir permeability-contrast limit of PAG reached about 24. The findings provide a new approach to alternating injection to improve CO 2 conformance for efficient development of heterogeneous reservoirs. The proposed adaptability ranges of permeability contrast for different alternating injection modes have important engineering application value and reference significance.