Shape and surface property effects on displacement enhancement by nanoparticles

This work studies the mechanisms of shape and surface property effects on multiphase displacement enhance-ment by nanoparticle suspensions in porous media. Three representative nanoparticles with promising industry applications, namely silica nanoparticles, graphene oxide and hydroxylated carbon nanotubes have been considered comprehensively. The correspondence between particle shape and surface property, interfacial adsorption behaviors, and displacement patterns has been analyzed systematically. Significant differences in adsorption tendencies and consequences are revealed via adsorption characterizations with theoretical deriva-tions and microscopic modeling. For liquid-liquid interfacial adsorption, sheet-like and fibrous shapes with amphiphilicity are more beneficial to adsorption and retention at interface, which promotes dynamic interfacial tension reduction and emulsion stabilization. For solid surface adsorption, spherical and fibrous shapes with hydrophilicity are more favorable for formation of nanoscale rough structures, which induces the development and maintenance of wetting films. Visualization and quantification of multiphase displacement in complex structures via microfluidic experiments enable us to evaluate the relative performances and unravel displacement enhancement modes. Hydroxylated carbon nanotubes exhibit optimal performance, followed by graphene oxide and then silica nanoparticles, with clear distinction in interfacial phenomena. Enhanced liquid-liquid interfacial adsorption behaviors result in the invasion into un-swept regions with sweeping efficiency enhancement, whereas enhanced solid surface adsorption behaviors drive the detachment of defending phase in the form of isolated ganglia.