Nanoparticle delivery to porous media via emulsions and thermally induced phase inversion

Abstract We report a novel payload delivery technique based upon surfactant-stabilized emulsions to transport nanoparticles into geological formations. Such nanoparticles are useful for facilitating oxidation of organic phases, such as crude oil. The number of variables that affect transport makes it difficult to predict how particles behave in a complex hydrocarbon reservoir; for most applications, this understanding is critical to maintaining the nanoparticle size distribution necessary for success. Our technique decreases particle interactions with other elements in the reservoir by providing a protective microcapsule that releases nanocatalysts at specified conditions (e.g., temperature or salinity). The capsules are the dispersed phase of an oil-in-water emulsion and move readily through water-filled pathways in the porous medium. We show that an established semi-empirical formulation parameter is useful to manage and plan for different subsurface conditions that affect delivery-capsule stability. Observations of both transport and delivery are made using microfluidic devices with representative sandstone pore network patterns and sand packs. We also quantify particle-particle interactions experimentally in different media using zeta potential, dynamic light scattering, and cryo scanning electron microscope measurements. These observations provide insight into the relative strength of net attractive/repulsive forces of particles in potential solvents. Our microfluidics results show that delivery occurs by destabilizing the emulsion at temperatures near or slightly greater than formation temperature. Once the emulsion ‘breaks,’ particles move freely in a continuous oil phase and mix with the in-situ crude. We also show that an essential benefit is that the temperature that triggers the release is tunable to reservoir conditions with the appropriate choice of solvent, surfactant, and fluid ratio. In the absence of an easily accessible crude-oil phase, particles deposit readily on grains or clay minerals. The results from the sand pack experiments confirm that the ultimate emplacement distribution is fairly uniform.