Salt- and temperature-stable quantum dot nanoparticles for porous media flow

The transport of colloidal nanoparticles (NPs) through porous media is a well-studied phenomenon at ambient temperature and in low-to-zero salinity water found in aquatic systems. Little is known at much higher temperatures and salinities such as conditions found in petroleum reservoirs, thus limiting the possible use of NPs in downhole oilfield applications. Using 3-nm CdSe quantum dots (QDs) as a model material, we report that NPs can be prepared with excellent colloidal stability at high ionic strengths and elevated temperatures. QDs with an outer coating of a nonionic ethoxylated alcohol surfactant showed little aggregation in synthetic seawater with ionic strength of 0.55 M and 1 M NaCl brine solution based on dynamic light scattering analysis. They showed colloidal stability up to 70 degree C, close to the cloud point temperature of the nonionic surfactant. They further showed nearly unimpeded flow behavior when carried in high-salinity water through a packed column of crushed calcite or sandstone mineral at room temperature. QDs were successfully passed through a medium-permeability Berea sandstone core (100 mDa) at 17 atm, 25 degree C, and 8 mL/h. The preparation strategy for salt- and temperature-stable QDs is applicable to a wide range of particle sizes and compositions, toward the general handling and use of functional NPs in high-salinity environments.