Heat Transport in Fractures and Fracture Networks – Simulation, Inversion, Measurements

Fractured reservoirs are targets for enhanced geothermal systems (EGS), because a network of fractures in an otherwise solid rock is an optimal pathway for circulating the working fluid while efficiently extracting heat. The main ambition of HeatSIM (Heat Transport - Simulation, Inversion, Measurements) is to increase our comprehension of coupled thermal-hydraulic processes and the resulting heat transfer in fractured rocks over different scales, by experimental imaging, numerical simulation and inverse modeling of lab data. The first work package (WP1) will measure heat transfer in laboratory experiments, focusing on the influence of fracture wall topographies and local fracture apertures, dead-end fractures, fracture network topology, and fracture intersections. To this aim, a novel optical thermometry measurement technique, based on the temperature-dependent fluorescence of phosphor colloids, will provide the evolving temperature field within the fluid domain and solid matrix with high spatial and temporal resolutions. A sensitivity analysis will allow quantifying the influence of the various geometric parameters on the outflow temperature. HeatSIM’s WP2 will then propose conceptual simplifications to the experimental geometries, coupled to numerical simulation to predict outflow temperatures. Different such models will be implemented, and their hydraulic and thermal properties will be calibrated from the experimental thermal breakthrough curves. Their outflow temperature prediction capabilities will also be compared. Thanks to the applicant’s strong background in EGS, numerics and inverse modeling, and the host team’s expertise in fractured media, subsurface heat transport and lab experiments, HeatSIM will thus decipher the impact of fractured media’s geometry on heat transfer efficiency, and provide new insights into the prediction of geothermal sites’ efficiency and the optimization of geothermal energy energy extraction.