CO2-in-water foams at elevated temperature, pressure and salinity are very unstable since the CO2 bubbles undergo rapid coalescence and coarsening. We have designed a system of liked-charged surfactant and surface-modified nanoparticles to make ultra-stable CO2 foam at 60 °C, 15 MPa and an extreme salinity (230 g/L TDS) with an ultralow nanoparticle concentration (0.05 wt%). We modified the silica nanoparticle surface by covalently bonding two amines: one for interfacial activity and another for colloidal stability in brine. The nanoparticles were characterized with thermogravimetric analysis, NMR and conductimetric titration. The nanoparticle size was measured by dynamic light scattering in brine at 60 °C for 2 weeks. The foam stability was measured with optical microscopy at 60 °C and 15 MPa. In the presence of only 0.05 wt% nanoparticles, the initial foam bubble growth rate was similar to the surfactant only condition. However, after the initial fast bubble coalescence and coarsening, the nanoparticle interfacial concentration increased sufficiently to sustain a strong elastic CO2-water interface, which decreased the bubble growth rate by 2 orders of magnitude. The surfactant adsorption on the liked-charged nanoparticle is low, making the nanoparticle amphiphilicity independent of the surfactant. The tuning of the nanoparticle surface for both colloidal stability in brine and high amphphilicity at the CO2-water interface over a wide range of surfactant concentration and an ultralow nanoparticle concentration is novel and of great interest for both fundamental advancement and commercial applications, for example mobility control in CO2 sequestration and oil recovery.

Stable CO2/water foam with ultralow concentration of amine-coated-nanoparticles and surfactant

ACS Spring 2022

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