Experimental analysis of electrostatic and hydrodynamic forces affecting nanoparticle retention in porous media
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There have been significant advances in the research of nanoparticle technologies for formation evaluation and reservoir engineering operations. The target applications require a variety of different retention characteristics ranging from nanoparticles that adsorb near the wellbore to nanoparticles that can travel significant distances within the porous medium with little or no retention on the grain substrate. A detailed understanding of the underlying mechanisms that cause nanoparticle retention is necessary to design these applications. In this thesis, experiments were conducted to quantify nanoparticle retention in unconsolidated columns packed with crushed Boise sandstone and kaolinite clay. Experimental parameters such as flow rate, injected concentration and sandpack composition were varied in a controlled fashion to test hypotheses concerning retention mechanisms and enable development and validation of a mathematical model of nanoparticle transport. Results indicate nanoparticle retention, defined as the concentration of nanoparticles remaining attached to grains in the porous medium after a volume of nanoparticle dispersion is injected through the medium and then displaced with brine, is a function of injected fluid velocity with higher injected velocities leading to lower retention. In many cases nanoparticle retention increased nonlinearly with increasing concentration of nanoparticles in the injected dispersion. Nanoparticle retention concentration was found to exhibit an upper bound beyond which no further adsorption from the nanoparticle dispersion to the grain substrate occurred. Kaolinite clay was shown to exhibit lower retention concentration [mg/m2] than Boise sandstone suggesting DLVO interactions do not significantly influence nanoparticle retention in high salinity dynamic flow environments.