Design and application of messenger nanoparticle tracers for multi-parameter reservoir exploration

The inaccessibility of geothermal reservoirs makes the accurate determination and monitoring of reservoir properties and conditions difficult and is a major problem in reservoir engineering. We present an approach for the development of messenger nanoparticle tracers for the simultaneous determination of flow paths ("tracer") and reservoir properties ("messenger"), with a proof-of-concept example of flow-through experiments and temperature detection under controlled laboratory conditions. For this, silica particles are synthesized with a two-layer architecture, an inner closed core and an outer porous shell, each doped with a different fluorescent dye to create a dual emission system. Temperature detection is achieved by a threshold temperature-triggered irreversible release of the outer dye, which changes the fluorescence signal of the particles. The flow-through experiments were conducted in a sand packed-bed column. The breakthrough curves of the nanoparticle tracers show minor tailing and a faster breakthrough compared to conservative, conventional molecular tracers such as Uranine and Eosine. The presented particle system thus provides a direct, reliable and fast way to determine reservoir temperature and flow paths in the reservoir. The system has a sharp threshold for accurate measurement and allows detection in concentration ranges as low as a few micrograms of nanoparticles per liter.