Title : Viscoelastic and flow properties of CO? foams stabilized by surfactant–nanoparticle systems
Abstract:
Foams have emerged as a promising method for gas mobility control in subsurface reservoirs, particularly in Enhanced Oil Recovery (EOR) operations and for carbon dioxide (CO₂) storage. However, the practical implementation of CO₂ foams is often limited by their inherent instability. Adding nanoparticles (NPs) into surfactant solution has been widely employed in improving foam stability in CO2-EOR applications. In this study, the rheological behaviour of nanoparticle (NP)-stabilized CO₂ foams was experimentally investigated to assess their potential for improved stability and flow performance in porous media. CO₂ foams were generated using a natural surfactant mixed separately with three different types of nanoparticles (0.1–0.5 wt.%) and the stability experiments were carried out at room temperature and pressure. The results showed that the CO₂ foams exhibited non-Newtonian shear-thinning behaviour with a 9 – 20% increase in apparent viscosity upon increasing NP concentration for all the three types of NPs used. Viscoelastic measurements revealed dominant elastic behaviour (G′ > G″) at low strain (< 100%) and a transition to viscous behaviour (G″ > G′) at higher strains (> 100%), indicating strong structure–property dependence. Dynamic rheological tests showed a maximum reduction of 60% in G′ during strain sweeps and a 40% reduction during frequency sweeps. Microscopic analysis further revealed foam coarsening, with bubble sizes increasing from 30–50 μm to 250–600 μm within 2 hours due to coalescence. The enhanced viscosity and viscoelasticity of NP-stabilized foams suggest improved resistance to gas channelling and effective pore-blocking potential, underscoring their applicability in improving sweep efficiency in heterogeneous reservoirs.
