Preparation of HPMA stabilized CaCO3 nanofluid and its EOR potential applied in low permeability reservoirs

Nanofluid EOR applications face key challenges including poor stability and clogging in subsurface formations. This study developed a relatively stable CaCO₃-HPMA nanofluid through hydrolyzed polymaleic anhydride (HPMA) modification method using a one-pot method. The CaCO₃-HPMA nanofluid was characterized by FT-IR, TG, particle size analysis, SEM, zeta potential revealing spherical calcite and aragonite phase particles with an average diameter of 164 nm. CaCO₃-HPMA (1000 mg/L) exhibited excellent stability, sustaining a zeta potential exceeding 30 mV after 10 d. The initial median particle size was 164.0 nm, which gradually increased to 201.2 nm after 10 d and reached 314.1 nm after 30 d CaCO₃-HPMA (1000 mg/L) effectively altered the wettability of oil wet core slices to water wet, reducing the contact angle from 103.1° to 77.9°, lowered oil water interfacial tension to 14 mN/m, and achieved a 20 % emulsification index after 240 h at 60 °C. CaCO₃-HPMA (1000 mg/L) nanofluid flooding and the secondary water flooding enhanced oil recovery 18.0 % compared to the primary water flooding in low permeability reservoirs. Notably, when formation clogging occurred, CaCO₃-HPMA nanoparticles were effectively dissolved through acidification, providing a practical and versatile solution for field operations.