CO2-Responsive Tunable Phase Changing Nano-Scale Fluids for Subsurface Energy Recovery

Rising consumption of water for subsurface energy recovery has motivated the exploration of novel fluids to enhance the permeability of the subsurface geologic reservoirs. Advancements in developing novel nanofluids will allow us to enhance heat recovery from geothermal reservoirs and reduce water use for hydraulic fracturing operations. Specifically, we explore the design of CO₂-responsive phase changing nanofluids. These nanofluids are constructed from SiO₂ nanoparticles tethered with poly(allylamine) (PAA), which form hydrogel upon reaction with CO₂. The presence of SiO₂ nanoparticles enhances the CO₂ absorption capacity when compared with the pure PAA solution. The CO₂ absorption on PAA and SiO₂-PAA was governed by the formation of carbamate, protonated primary and secondary, and bicarbonate ions using infrared spectroscopy. Time resolved USAXS/SAXS measurements showed an increase in the sizes of SiO₂-PAA aggregates during CO_2­ loading and hydrogel formation. Additionally, the effect of nanoparticle size and concentration of polymeric chains on CO₂ absorption was also investigated. These observations point to the feasibility of enhancing hydrogel formation with these novel nano-scale fluids to enhance permeability in the subsurface environment.