Delayed Swelling Polymer Microspheres for CO₂ Channeling Control under High-Temperature and High-Salinity Environment

Gas channeling during the CO₂ flooding process significantly reduces both oil recovery and the level of CO₂ storage. Polymer microspheres have emerged as gas channeling control agents due to their superior strength and injectability. However, the rapid and uncontrolled swelling of most reported polymer microspheres impedes their in-depth transportation and effective plugging in porous media under high-temperature and high-salinity environments. To address these challenges, a series of CO₂-triggered and delayed swelling polymer microspheres (denoted as DVP), incorporating dimethylaminopropyl methacrylamide (DMAPMAm), N-vinyl-2-pyrrolidone (NVP), and N,N'-methylenebis-(acrylamide) (MBA) as the CO₂-responsive monomer, salt- and temperature-resistant component, and cross-linker, respectively, were prepared using inverse microemulsion polymerization. The impacts of monomer composition and cross-linker content on the morphology and swelling behavior of DVP in aqueous solutions were investigated, and the gas channeling control capacity of DVP was evaluated in an artificial core. The results showed that the CO₂-induced swelling ratio of DVP augments with higher contents of DMAPMAm and cross-linker yet decreases when the dosage of cross-linker exceeds 0.5%. After aging for 8 days at 140 °C and in 15,000 mg/L brine, the particle size of DVP, having a DMAPMAm dosage of 50% and an MBA content of 1%, gradually expands from 280 to 701 nm with a swelling ratio of 2.50. In this case, using this DVP aged in situ for 8 days within a fractured core with an original permeability of 10 mD leads to a plugging efficiency as high as 99%. This work provides a new idea for the development of materials for the control of CO₂ gas channeling.