Rheology and Flow Visualization of Temperature-Responsive Volume-Phase Transition Microgels and their Implications in Geothermal Systems*

Geothermal energy remains a largely untapped indigenous resource for nations across the globe to increase their energy security and simultaneously reduce their carbon footprint. The introduction of enhanced geothermal systems has amplified the potential for geothermal extraction in previously overlooked regions, but also presents significant uncertainty with the inherent risk of premature thermal breakthrough. Previous simulations have suggested a temperature-responsive change in aperture to redirect flow around flow paths which are prematurely drained of their thermal energy can significantly boost system efficiency and life expectancy. Volume-phase transition microgels present a real world implementation of this change in aperture through their ability to reversibly swell and shrink in response to temperature changes. Rheometry combined with visualization techniques are performed to understand the microstructure, macro-rheological properties, velocity, and volume fraction. Particularly, we will show how yield stress varies as a function of volume fraction of soft hydrogels and temperature.