Transport and retention of aqueous dispersions of superparamagnetic nanoparticles in sandstone

• Efficient surface coating procedure to superparamagnetic nanoparticles are developed.
• With proper surface coating, nanoparticles can transport through rock long distance.
• Strong anionic polymer coating provides dispersion stability; good transportability.
• Co-polymer coating for targeted delivery of nanoparticles to reservoir was developed.
• Reservoir salinity and pH are key functional nanoparticle design parameters.

We evaluate the transport of surface-treated superparamagnetic iron-oxide nanoparticles in Boise-sandstone rocks by injecting aqueous dispersions of the particles into core plugs. Several different surface treatments yield stable dispersions of these particles, but provide very different transport characteristics. Effluent concentration histories are measured to obtain the particle retention in the rock. The results are used to optimize the particle surface coating so that the reservoir application requirements for the functional nanoparticles can be achieved. The application of interest here requires the nanoparticles to adsorb to oil/water interfaces.Our earlier experiments (Yu et al., 2010) showed that the paramagnetic nanoparticles stabilized with small negatively-charged citrate ligands have little retention in sedimentary rocks, but their preferred adsorption at the oil/water interfaces in rock pores was not achieved. A major improvement in surface coating optimization is achieved by creating a crosslinked polymer film that wraps around the nanoparticle so that it does not detach from the particle surface even under the harsh reservoir conditions. To fine-tune the coating to satisfy the reservoir application requirements, co-polymers and ter-polymers with different constituent monomers are employed. Nanoparticles stabilized with (poly-styrene sulfonate–alt-maleic acid) coating show a good adsorption tendency at the oil/water interfaces, while with very low adsorption at rock surface (~0.02 mg/m2). The dispersion also has long-term stability even at high salinity (8 wt% NaCl). Other polymers, such as (polyacrylic acid–r-butyl acrylate), (polyacrylic acid–b-styrene sulfonic acid), and (polyacrylic acid–r-butyl acrylate–b-styrene sulfonic acid), were also tested. The coating with the last polymer (PAA–PBA–PSS) provides a very low retention of particles in the rock, but only marginal preferred adsorption at oil/water interfaces.

pSS-alt-pMA co-polymer coating to paramagnetic nanoclusters (TEM image) provides good reservoir transportability (blue effluent curve) and preferential adsorption of nanoclusters to oil/water interfaces (red curve).Figure optionsDownload as PowerPoint slide