Double-emulsion fabrication of dual-network PTS microspheres with temperature/salt resistance and delayed swelling: Molecular simulation and deep profile control application in reservoir deep zones

High-temperature and high-salinity (HTHS) reservoirs suffer from strong heterogeneity and well-developed preferential flow channels, leading to low water flooding efficiency. Existing profile control microspheres fail to simultaneously achieve high temperature resistance, salt tolerance and delayed swelling. Herein, temperature-resistant, salt-tolerant and delayed-swelling PTS microspheres with a dual “chemical crosslinking-hydrophobic association” network were synthesized via O/W/O double-emulsion polymerization using acrylamide (AM), sodium styrene sulfonate (NaSS), stearyl methacrylate (SMA18) and divinylbenzene (DVB) as monomers. The PTS microspheres had an average particle size of 4.02 μm with good dispersity, maintained structural integrity after 90 days of aging at 120 °C in 2.5 × 10⁵ mg L⁻¹ brine, and exhibited a swelling ratio of less than 20% at 24 h with a final expansion multiple of more than 14. Molecular dynamics (MD) simulations revealed that PTS possessed a more compact conformation (Rg = 1.87 nm) and a stable hydrogen bond network than conventional polyacrylamide (PAM), which was the intrinsic molecular mechanism for its superior temperature and salt resistance. Core flooding experiments showed that PTS effectively blocked high-permeability zones and diverted flow to low-permeability zones, increasing oil recovery by 28.3% to a final oil displacement efficiency of 81.4%. This double-emulsion template strategy realizes a synergistic breakthrough in HTHS resistance and delayed swelling, providing a novel high-performance material for deep profile control in HTHS reservoirs.