In the development of low-permeability petroleum reservoirs, injecting carbon dioxide (CO2) and expanding its conformance volume is one effective approach to enhance recovery and geological carbon storage. Most current studies mainly investigate CO2 displacement and alternating injection of other chemical agents (e.g., water, surfactant, polymer, and gel) with CO2 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 CO2 is also unclear. Therefore, high-temperature and high-pressure visual microfluidic chip experiments were employed. CO2 displacement features under different chemical alternating CO2 injection modes were revealed, and the applicability limits of these CO2 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 CO2 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 CO2 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 CO2 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.
Zhao et al. (Fri,) studied this question.