KWR at the European Geothermal Congress 2025 in Zürich

Both heat production with (deep) geothermal wells were seen as key parts of this ambition and were addressed in many talks and (poster) sessions. Enno de Vries and Stijn Beernink from KWR’s Geohydrology team attended the event to get a good view on current developments and state-of-the-art techniques, and both presented recent work relevant to help facilitate the responsible implementation of these sustainable energy technologies.

This time, in our contributions, we particularly addressed increasing the understanding of the thermal impact of geothermal heat production and heat storage as this is important to support the development of efficient licensing and monitoring (Figure 1).

Image 1: Schematic overview of a monitoring setup to measure the thermal effects in the storage aquifer and overlying quifer(s) with a monitoring well positioned in the vicinity of the wells of a HT-ATES system (developed by G. Schout (KWR)).

Monitoring, measuring and simulating heat losses from hot geothermal wells in the Netherlands

Enno presented KWR’s research conducted for and in collaboration with EBN, where the thermal impact due to conduction losses from a geothermal production well to the shallow groundwater system was determined in the field. This thermal impact has been monitored over the past years (from 2021 onwards) using installed fiber optic cables for distributed temperature sensing (DTS) within close range of geothermal well producing at 85°C,  operational since 2019. There, the vertically temperature profile of the subsurface is measured at 3 distances away from the producer (6, 9 and 63m distance, see Figure 2). KWR analysed the observed temperature data and then was able to reproduce the thermal observations through a site-specific and integrated density dependent groundwater and heat transport model.

The results showed that the heat losses due to conduction from the hot well casing were observed at 6 and 9m distance at T>30 °C at 6m and T>25 °C at 9m from the well after only 3 years of operation. The reference at 63m distance did not show thermal effects. The model simulations agreed very well with the measured data and showed that the convection (upward transport due to density differences) of high temperature heat in permeable sand layers was the main driver for relatively fast radial extension of temperature effects from the wells.

Enno presented this work during the poster session on Wednesday, October 8th, and got involved in nice discussions and interest from other parties in Europe. Other studies presented at the EGC gave new ideas for methods and approaches to decreasing the heat losses from hot casing, which is more inspiration for follow-up work!

Image 2: A figure from the De Vries & Hartog (2024). a) The DTS temperature measurements for the 5 measurement points for GLV1 (distance 6m), GLV2 (distance 9m), and the reference measurement GLV3 (distance 63m) with the boundaries of the geohydrological units; b) the friction factor over the depth of the test sounding (Wiertsema & Partners, 2020); c) conceptual interpretation of identified heat transport processes. An outlier measured on December 1, 2022, at the bottom of GLV2 (28.4°C) is shown separately as an orange star.

PhD in progress: High Temperature Aquifer Thermal Energy storage in the shallow subsurface

Last year, Stijn published an article in the journal Geothermics on how the different heat transfer processes and storage conditions affect the heat losses from High Temperature Aquifer Thermal Energy storage (HT-ATES) wells, and showed that yearly recovery efficiency may vary between 60-90% for reasonably good operating systems. However, this still means that 10 to 40% of the yearly stored heat is lost to the subsurface.

Stijn’s PhD focusses both on maximizing the performance of these systems, as well as looking at the potential effects: where do these heat losses go? And how does this potentially affect the temperature in the shallow subsurface in space and time? The latter was the topic of Stijn’s presentation at the EGC with the aim to show how subsurface hydrogeological conditions affect the thermal impacts of HT-ATES in the shallow subsurface (Figure 3).

The main take-away from his presentation was that the hydrogeological properties of the layers close to the storage aquifer, and especially the sealing clay layer above the storage aquifer mainly determines the potential for quick break-through of high temperature heat to shallower layers. Therefore, to prevent upward migration of high temperature heat and hence relatively strong temperature effects, the hydraulic resistance of the sealing (clay) layers above the storage aquifer is important.

Stijn is currently finalising his PhD at TU Delft, and writing a chapter/manuscript on ‘thermal impact from HT-ATES wells’, under supervision of Niels Hartog, Phil Vardon and Martin Bloemendal, for his thesis.

Image 3: A vertical cross section of the temperature increase due to heat losses from the storage aquifer of a HT-ATES well (at 80 °C) in a 10 °C shallow aquifer from a case-study in Delft after 5 years of operation. The stored heat is mainly distributed towards the top of the aquifer due to buoyancy-driven flow leading to relatively strong upward heat losses into the above lying sealing layer.