ATES (Aquifer Thermal Energy Storage) medium-depth geothermal technology uses aquifers to store and extract thermal energy. It allows regulating seasonal temperatures by means of hot and cold wells. This technology principally uses matrix aquifers, due to their good thermal conductivity and ability to effectively store and release heat.
This process is being considered by Services Industriels de Genève (SIG) in the fractured and karstified limestones of the Upper Mesozoic series in the Satigny area (Geneva, Switzerland). By planning a new geothermal doublet, SIG would like to store the residual heat of a heating network in summer and use it in winter. The GEo-01 exploration borehole drilled in 2018, located close to the study area, indicated favorable characteristics for the implementation of such a system, such as high permeabilities and low hydraulic flow.
However, the heterogeneity and complexity of fractured aquifers, as well as the presence of preferential conduits in this geological context can complicate the implementation of this technology. To assess its feasibility, a DFN (Discrete Fracture Network) model was built using offset well data (including GEo-01), 2D seismic data and outcrop analog (Jura mountains) data. This model needed to mitigate hydrogeological uncertainty in the project area by integrating spatial, field, geophysical and well data to assess the equivalent parameters of the dual environment present in the targeted geological formations.
The hydrogeological parameters were dynamically calibrated. An uncertainty analysis was run to determine which of the geological, hydrogeological or operational parameters could have the major influence on the pressure and temperature conditions to be expected, with a view to optimize the energy efficiency of the exploitation. The main outcomes of this analysis are as follows: Fracture permeability and production rate essentially control pressure differentials across wells; Block size and production rate mainly influence production temperature evolution; Sustainable and even enhanced production parameters are found in both wells of the doublet over 30 years, with limited impact on GEo-01.
These promising results allowed the launch of the execution phase of this ATES project. Additional drilling data from the doublet boreholes, as well as the integration of 3D seismic interpretation data in the Satigny area will help updating the simulation of this reversible exploitation and specifying the production.
