Multi-parameter screening study on the static properties of nanoparticle-stabilized CO2 foam near the CO2 critical point

The important role of nanoparticles (NPs) on foam stabilization under harsh geological conditions has been well recognized. In this paper, the Orthogonal Experimental Design (OED) method is adopted to investigate the synergy effects of six parameters, including NP concentration, surfactant concentration, oil concentration, salinity, temperature, and pressure, under five levels in the range of 0–0.2 wt%, 0.1–0.5 wt%, 0–4 wt%, 0–8 wt%, 20–60 °C, and 5.5–9.5 MPa respectively. K values and B values obtained in the OED experiments are employed to show the single parameter effect and the importance of each influential factor on foam static properties. It is concluded that system temperature and pressure, which has the highest B values of 22 mm and 18 mm on foam height results, are the dominant parameters on foamability, whereas temperature with B values of 80% on foam decay rate is the dominant factor on foam stability. It is observed when the system condition is close to the CO₂ critical point, the foamability and stability of the NP-stabilized foam are much worse than under conditions far from the critical point. At last, optimal formulation of surfactant and NP concentration is proposed and validated for two geological cases of 45 °C and 55 °C with salinity and oil presence. It is expected the experimental technique, as well as the research results, reported in this paper could help the laboratory screening and formulation optimization of the complex NP-stabilized ScCO₂ foam system.