Thermo-hydro-mechanical response of the operation style in a faulted Malm reservoir: Storage triplet vs. hydrothermal doublet

Abstract The existing heat in the earth can be considered as an abundant source of clean energy. Geothermal applications have extracted this resource via various approaches, such as petro- and hydrothermal systems or heat pumps. In recent years, thermal energy storage systems (ATES), which balance the temporal mismatch of the energy demand and supply were widely developed, primarily in the Netherlands. Herein we compared the fully elastic thermo-hydro-mechanical response of two different geothermal systems: a hydrothermal doublet and a high-temperature (HT) ATES triplet, both located in the karstified and faulted Malm aquifer in the north of Munich (south of Germany). Both systems have a negligible impact on the pressure field of the Malm reservoir due to its high permeability. The geomechanical responses at the scale of the reservoir are primarily governed by thermoelasticity, with only minor poroelastic effects due to low pressure variations. In our linear elastic constitutive framework, the cyclic injection and production of the HT-ATES triplet lead to slightly lower stress-field perturbations than the continuous operation of the hydrothermal doublet under the investigated operating conditions. As a result, lower fault destabilization and smaller induced displacements were computed in the HT-ATES scenario. These differences are attributed to the cyclic thermal loading and reduced cumulative thermal perturbation associated with the storage operation. Additionally, the heterogeneity of the reservoir, represented by differences in the permeability of the layers, has a notable impact on both thermal recovery and the fault stability in the HT-ATES triplet.