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Nanoparticles can improve the stability of CO 2 foam and increase oil recovery during CO 2 flooding in reservoirs. The synergistic effect of hydrophilic SiO 2 nanoparticles and hexadecyltrimethylammonium bromide (CTAB) on CO 2 foam stability was examined in this study. Experimental results show that the synergistic effect requires a CTAB/SiO 2 concentration ratio of 0.02−0.07, with 0.033 representing the best concentration ratio. With the increase in the concentration ratio, the synergistic stabilization effect of CTAB/SiO 2 dispersion first increases and then decreases. In the monolayer adsorption stage (concentration ratio from 0.02 to 0.033), when the hydrophobicity of SiO 2 nanoparticles increases with the concentration ratio, the nanoparticles tend to adsorb on the gas−liquid interface and the stability of CO 2 foam increases. In the double-layer adsorption stage (concentration from 0.033 to 0.07), when the hydrophobicity of SiO 2 nanoparticles decreases with an increase in the concentration ratio, the nanoparticles tend to exist in the bulk phase and the stability of CO 2 foam decreases. The CTAB/ SiO 2 dispersion stabilizes CO 2 foam via three mechanisms: decreasing the coarsening of CO 2 bubbles, improving interfacial properties, and reducing liquid discharge. CTAB/SiO 2 foam can greatly improve oil recovery efficiency compared to water flooding. Experimental results provide theoretical support for improving CO 2 foam flooding under reservoir conditions.

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Soft robots, compared to traditional rigid-bodied robots, are constructed with physically flexible/elastic bodies and electronics to mimic nature and enable novel applications in industry, healthcare, aviation, military, etc. Recently, building...