CO2-Triggered In Situ Silica Particle Formation for Proactive Profile Control between Waterflooding and CO2 Flooding in Harsh Reservoirs

Early gas breakthrough during CO2 flooding is often aggravated by dominant flow channels formed in prior waterflooding. We developed a CO2-triggered silicate system (SAS) for proactive profile control in high-temperature and high-salinity reservoirs. Owing to its low initial viscosity, SAS can be preferentially placed in high-permeability channels before CO2 injection. Dissolved CO2 then lowers pH and triggers silicate condensation, leading to in situ formation of silica particles that selectively plug dominant flow paths. The generated inorganic Si–O–Si network endows the system with strong thermal and salinity tolerance. Characterizations including FTIR, XPS, TGA, SEM, particle size analysis, pH/conductivity monitoring, HOMO–LUMO analysis and molecular dynamics simulations were conducted to reveal the acid-triggered structural evolution induced by CO2 dissolution. Sand-pack displacement experiments further demonstrate that SAS pretreatment increases total oil recovery from 49.5% to 67.2%. This CO2-triggered in situ particle system provides a simple and effective strategy for mitigating gas channeling and enhancing CO2 flooding performance in harsh reservoirs.