Nanoparticles (D ∼ 5 to 50 nm) easily pass through typical pore throats in reservoirs, but physicochemical attraction between nanoparticles and pore walls may still lead to significant adsorption. We conducted an extensive series of nanoparticle transport experiments in core plugs and in columns packed with crushed sedimentary rock, systematically varying flow rate, type of nanoparticle, dispersion concentration, number and sizes of dispersion slugs, and column grain size. Effluent nanoparticle concentration histories were measured with fine resolution in time, enabling evaluation of nanoparticle adsorption in the columns during flow of dispersion and of postflushes. We also apply this analysis to transport experiments reported in the literature.
Our analysis indicates that nanoparticles undergo both reversible and irreversible adsorption. Effluent nanoparticle concentration reaches the injection concentration during slug injection, indicating the existence of an adsorption capacity. Experiments with a variety of nanoparticles and lithologies yield a wide range of adsorption capacities (from 10−7 to 10−2 g nanoparticle/g porous medium) and a wide range of proportions of reversible and irreversible adsorption. Reversible and irreversible adsorption sites are distinct and interact with nanoparticles independently of each other. The adsorption capacities are typically much less than monolayer coverage but are not an intrinsic property of the porous medium nor of the nanoparticle. Instead, they are influenced by operating conditions, i.e., increasing with larger injection concentration and smaller flow rate.