Polymer-Stabilized Multi-Walled Carbon Nanotube Dispersions in High-Salinity Brines

Carbon nanotubes (CNTs) exhibit promising properties for potential applications in oil and gas reservoirs. CNTs can be used as delivery vehicles for contrast agents or catalyst nanoparticles deep inside the reservoir. Dispersing 100 ppm of CNTs in deionized water is easily achieved by sonication of CNTs using properly selected surfactant or polymer solutions. These surfactants and polymers are non-covalently adsorbed to the nanotube surface, inducing dispersion stability. In oil reservoirs, high salinity is the norm; therefore, because the electrostatic double layer is compressed as a result of the high ionic strength found in a typical reservoir brine, colloid CNT dispersions lose stability and CNTs flocculate and precipitate. To maintain a stable colloidal dispersion of CNTs, a dispersant with functionality providing steric repulsion between the dispersed tubes is needed to prevent aggregation. In this work, suspensions of multi-walled carbon nanotubes (MWNTs) were generated using two polymers, gum arabic (GA) and hydroxyethyl cellulose (HEC-10), in 10% API brine (8 wt % NaC1 and 2 wt % CaC1(2)). GA was used as a primary dispersant, which is able to debundle the tube aggregates. After the first sonication with GA, the secondary dispersant, HEC-10, is added to provide the steric repulsion needed to keep the tubes dispersed in high-salinity brines. Polymer adsorption to the nanotube surface was observed using scanning electron microscopy. Focusing the electron beam for an extended period of time induced damage to the polymer layer around the individual nanotubes, leaving the tubes intact, as clear evidence of polymer adsorption. Adsorption experiments showed low to negligible adsorption of MWNTs to crushed Berea sand at 80 degrees C in both 10 and 20% brines. Dispersion injection in column and coreflooding tests showed successful propagation of CNT dispersions through porous media, with total nanoparticle recovery exceeding 80% in reservoir rock. This work demonstrates the potential of using polymer-stabilized carbon nanoparticle dispersions in a range of applications to advance current oilfield technology.