Silica Nanoparticle-Reinforced Wormlike Micellar Gels for High-Temperature Flow Redistribution in Heterogeneous Porous Media

Maintaining the rheological performance of wormlike micellar fluids at elevated temperatures remains challenging. Conventional viscoelastic surfactant (VES) systems may undergo thermally induced micellar scission and loss of gel-like viscoelasticity at elevated temperatures. In this study, we investigate the size-dependent reinforcement of long-chain C22+ wormlike micellar systems by silica nanoparticles under a temperature-ramp protocol reaching 160 °C. Under the applied temperature-ramp protocol, the formulation containing 0.10 wt% of 15 nm SiO2 nanoparticles exhibited the highest measured rheological response among the tested formulations, retaining an apparent viscosity of approximately 210 mPa·s and a plateau storage modulus of approximately 18.5 Pa during the 20 min isothermal holding period at 160 °C, compared with a plateau storage modulus of approximately 11 Pa for the corresponding VES system. At equal nanoparticle mass loading, the 15 nm particles produced approximately 18% and 6% higher G′ and G″, respectively, than the 500 nm particles. The rheological results, together with qualitative electrokinetic measurements after dilution, are consistent with nanoparticle-surfactant association that may promote micellar entanglement and network reinforcement. The nanoparticle-enhanced viscoelastic surfactant (N-EVES) formulation reduced the acid-rock reaction rate to approximately 25% of that measured for conventional HCl while showing an apparent effective H+ diffusion coefficient of the same order. Scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDS) detected Si- and N-containing species on the treated carbonate surface, suggesting that surface adsorption or deposition may contribute to reaction retardation. Parallel dual-core flooding under a permeability contrast of approximately 13 showed fluid redistribution toward the low-permeability core. Based on the axial wormhole penetration length obtained from the CT reconstruction, the normalized axial wormhole penetration fraction of the low-permeability core was approximately 70% for the 0.10 wt% formulation. These results provide experimental evidence of nanoparticle-size-dependent rheological reinforcement, acid-rock reaction retardation, and core-scale flow redistribution under strongly acidic and high-temperature conditions.