To operate aquifer thermal energy storages in a sustainable way, we located an artesian aquifer other than the aquifer storage in a research wellbore by analyzing the subsurface temperature as monitored with a fiber optic cable in three artesian flow tests. The positioning of the artesian aquifer was validated via numerical modelling. Analyses of the temperature data and numerical modelling enabled determining the profile of flow velocity, flow rate and the depth interval of inflow.

A systematic laboratory experiment elucidates two-phase heat transport due to water flow in saturated porous media to understand thermal propagation in aquifers. Results reveal delayed thermal arrival in the solid phase, depending on grain size and flow velocity. Analytical modeling using standard local thermal equilibrium (LTE) and advanced local thermal non-equilibrium (LTNE) theory fails to describe temperature breakthrough curves, highlighting the need for more advanced numerical approaches.

We compute a realistic three-dimensional model of the temperatures down to 75 km deep within the Earth, below the Caribbean Sea and northwestern South America. Using this, we estimate at which rock temperatures past earthquakes nucleated in the region and find that they agree with those derived from laboratory experiments of rock friction. We also analyse how the thermal state of the system affects the spatial distribution of seismicity in this region.

This study focuses on the optimization of open-loop shallow geothermal systems to improve their efficiency and sustainability. Different approaches to solve optimization problems in this field are explored, their strengths and limitations are highlighted, and recommendations are given for their use and future developments. The study can be a valuable basis for researchers and practitioners involved in the management and optimization of shallow geothermal systems.

In 2019, a fiber optic cable was installed in the middle of a deep geothermal production well to the reservoir in Munich, Germany. This cable hangs freely below the pump and allows continuous measurements of the temperature at every meter of the cable. The well was put into operation for the first time in the summer of 2021. We used the fiber optic cable to monitor the temperature profile during production in the reservoir and to quantitatively interpret the flow zones using an inverse model.