Hydrophilic silica nanoparticles

HHSB (C₁₆H₃₃N(CH₃)₂CH₂CH (OH)CH₂SO₃) was procured from Shanghai Nuosong Chemical Co. Ltd., China. Hydrophilic silica nanoparticles (average size of 65 nm) were purchased as a 30% concentration aqueous solution from Sigma-Aldrich. Sodium chloride and calcium chloride were obtained from Beijing Chemical Works, China. Four types of the formation brine (the amounts of dissolved solid were 2 × 10⁴ mg/L, 5 × 10⁴ mg/L, 7 × 10⁴ mg/L, and 10 × 10⁴ mg/L) were prepared by adding NaCl and CaCl₂ (in a ratio of 9:1) into deionized (DI) water.

Hydrophilic silica nanoparticles (non-porous, 25 nm, the specific surface area of 200 m²/g, the density of 2.4 g/cm³, and purity +99.5%), which were purchased from Sigma-Aldrich Company, Taufkirchen, Germany were used in experiments. Transmission electron microscopy (TEM) analysis on the silica powders was performed using a transmission electron microscope (Model: Philips EM208S 100KV, Nicosia, Cyprus). In order to investigate the size distribution of silica NPs, a dynamic light scattering (DLS) test was performed using the Malven ZS Nano analyzer (Malven Instrument Inc., London, UK). Results of TEM and DLS analysis were depicted in Figure 2a,b, respectively. As the results of the DLS test revealed, the size distribution of silica NPs is 18 nm to 38 nm, with an average size of 25 nm. According to the thin pore throats of the carbonate rocks, determination of the maximum radius of flocculated NPs is a crucial matter in NPs flooding. As determined by the DLS analysis, the maximum flocculated size of silica NPs is almost 38 nm, which confirms the ability of NPs to pass through the pore throats (minimum size of 0.05 µm to 2 µm as measured by mercury injection capillary pressure (MICP) tests).