CO2-responsive gel microsphere system for carbon sequestration and enhanced oil recovery in harsh reservoirs: Experimental study and molecular dynamics simulation

CO 2 flooding integrates enhanced oil recovery (EOR) and carbon sequestration (CS), yet gas–liquid mobility mismatch deteriorates its performance. While CO 2 -responsive gels mitigate gas channeling, harsh reservoir conditions (e.g., high temperature and salinity) restrict their application. This study aims to develop a novel CO 2 -responsive polymer gel microsphere system to address these challenges. The copolymer microspheres , synthesized via inverse emulsion polymerization using acrylamide (AM), 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and sodium α-olefin sulfonate (AOS), are combined with polyethyleneimine (PEI) to form the responsive system. Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) verify the molecular composition and morphology of the microspheres. Zeta potential analysis reveals a stable negative potential of −98 mV, and particle size measurements show a uniform diameter of 1.4 μm. Rheological tests demonstrate that the system exhibits low initial viscosity but rapidly increases in viscosity after CO 2 injection across wide salinity (20,000–80,000 mg/L) and temperature (20-80°C) ranges. Core flooding tests indicate that a 0.8 wt% gel microsphere system achieves a displacement pressure gradient of 14.67 MPa/m in fractured cores during CO 2 flooding. Molecular dynamics simulations further reveal that electrostatic attraction between the copolymer and protonated PEI enhances cross-linking, improving plugging performance in harsh environments. This work highlights the system’s exceptional stability, high plugging efficiency, and mechanism-driven design, offering a promising solution for EOR and CS in harsh reservoirs.