Mitigation of fine migration in low salinity water flooding of clay-rich sandstones Using Fe₃O₄/Saponin/Cu(II) nanocomposite

Fines migration is a major cause of formation damage in clay‑rich sandstones, particularly under low‑salinity waterflooding where electrostatic double‑layer expansion destabilizes clay–mineral adhesion and causes severe permeability loss. This study investigates, at the laboratory scale, the potential of a Fe₃O₄@saponin/Cu nanocomposite to mitigate fines release and permeability loss during simulated low-salinity water flooding of clay-rich sandstone. The nanocomposite was synthesized by co‑precipitating magnetite nanoparticles, coating them with a saponin biopolymer via hydrogen bonding and hydrophobic interactions, and introducing Cu 2 ⁺ through coordination with surface hydroxyl and glycosidic groups. Physicochemical characterization (FT‑IR, TGA, SEM, DLS) confirmed successful functionalization, enhanced thermal stability, controlled particle size, and colloidal stability up to 500 ppm loading. Zeta potential analysis revealed that the nanocomposite shifts mineral surface charge toward neutral or slightly positive values, reducing electrostatic repulsion between fines and the pore matrix. Core flooding of clay‑rich sandstone showed that untreated low‑salinity water caused catastrophic permeability loss (− 69.9%) and tripled injection pressure, whereas adding 500 ppm nanocomposite reduced impairment to − 4.1%, comparable to high‑salinity conditions without treatment. The mitigation mechanism involves synergistic electrostatic neutralization, steric stabilization from the saponin corona, and magnetic/coordination bridging that anchor fines to pore surfaces without plugging. These results demonstrate that Fe₃O₄@saponin/Cu nanofluid enables low‑salinity flooding while suppressing fines migration, providing a practical alternative to high‑salinity injection for enhanced oil recovery.