Design of silica nanoparticle tracers with optimized dispersion stability, sorption and deposition properties based on (X)DLVO and filtration theory

Functional nanoparticles emerged as potential new tracers for geoscientific applications, such as geothermal reservoir exploration. In this study, optimization strategies based on DLVO, extended DLVO (XDLVO) and filtration theory are presented. Our results show that nanoparticle material should have a low Hamaker constant, making metallic nanoparticles unfavorable. To ensure dispersion stability and minimize sorption on commonly negatively charged reservoir minerals, the nanoparticles should exhibit ζ-potentials below -30 mV. Decreasing the size of nanoparticles increases the diffusion-driven collisions with minerals grains and the probability of deposition while keeping the particle-to-grain size ratio below 0.008 prevents size exclusion effects. The impact of gravity on particle deposition is negligible for nanoparticles, making higher-density nanoparticle tracers viable. Experimental findings and XDLVO theory confirm the applicability of surface modifications to form a steric barrier that lowers attachment efficiencies while increasing colloidal dispersion stability. The impact of temperature cannot be assessed in a straightforward manner as it depends on multiple factors that can have contradicting effects. The presented study can serve as a guideline for the design of stable nanoparticle tracers with predictable transport properties in reservoirs. It shows that selecting appropriate materials, adapting ζ-potentials or employing effective surface modifications are key strategies to improve the performance of engineered nanoparticle tracers for geothermal exploration.