Abstract
This study reports the size-dependent interactions of silica nanoparticle (NP) dispersions with oil, which facilitate oil recovery from sandstone rock. Herein, we studied various 7–22 nm sized colloidal silica NPs (CSNPs; the colloidal state when dispersed in aqueous solutions) and fumed silica nanoparticles (FSNPs; the dry powder state). Interfacial tension at the oil-nanofluids interface declined with decreasing NP size in a range from 7 to 22 nm. This is because NP spatial density at the interface increased with smaller particle size, thereby, the interface area per NP decreased to approximately 1/30, and interfacial energy had reduced enough. In addition, smaller NPs more strongly were adsorbed to the rock because of improved diffusion in suspension and increased adsorption density. This caused creating a wedge film between oil and rock, which changed the oil contact angle. Due to this effect, core flooding experiments indicated that oil recovery increased with decreasing particle size. However, FSNP dispersions exhibited low recovery factor because of particle aggregation. This phenomenon may facilitate massive permeability reduction, thus causing oil trapping inside rock pore. We found that both the sizes and types of CSNPs and FSNP affected the Interfacial tension at oil-water interface and rock surface wettability, which influenced ultimate oil recovery.
Highlights
This study focused on the effect of nanoparticle size on interfacial tension and rock wettability
When NPs were suspended in colloidal silica NPs (CSNPs), brine, 12 nm 12 mean nm fumed silica nanoparticles (FSNPs), and 22were nm approximately
We found that all silica NPs remained in stable emulsions for ten days, and and readily adsorbed to the oil–water interface, included
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Nanotechnological applications have attracted great attention in the context of oil reservoirs with small pores and pore throats [1,2,3,4,5,6,7,8]. Nanoparticle (NP) dispersions change the wettability of porous media. Wettability controls the fluid flow, affecting oil recovery during water flooding. Many studies have shown that NPs render rock surfaces more hydrophilically wettable [9,10,11,12].
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