Bridging reservoir physics and energy system operation: A cross-scale numerical framework for high-temperature aquifer heat storage

High-Temperature Aquifer Thermal Energy Storage (HT-ATES) is increasingly considered as a key technology to enhance the flexibility of heat supply systems and to support the decarbonization of District Heating Networks (DHN). In this study, we present a physics-based numerical modeling framework for the consistent assessment of HT-ATES performance across scales, from reservoir physics to energy system modeling.

Coupled thermal-hydraulic numerical models are developed to simulate the storage of high-temperature fluids in a stratified geothermal reservoir. This layered configuration captures key subsurface heterogeneity and enables the systematic evaluation of zone-specific contribution to fluid migration, heat transfer, and associated heat losses. The models consistently account for temperature- and pressure-dependent fluid density and viscosity, allowing density-driven effects and their interaction with forced convection to be resolved.

The numerical analysis captures the spatial and temporal evolution of the thermal perturbation induced by the cyclic HT-ATES operation. Beyond conventional thermal performance metrics, the approach additionally quantifies the hydraulic performance of the HT-ATES system via computing the productivity and injectivity indices, thus enabling the assessment of heat recovery and well performance within a unified framework. The geometry of the thermally influenced rock volume and the developing surface area between the thermal front and undisturbed rock are shown to critically affect heat losses. The hydraulic performance is primarily controlled by the reservoir transmissibility, while variations in fluid properties introduce an additional transient component to the system response.

Building on the reservoir-scale model, the HT-ATES system is exemplarily integrated into a multicomponent energy network, in which a geothermal plant provides the base load and gas boilers supply peak demand. To enhance the energy flexibility in the system, the seasonally operated HT-ATES system is combined with a short-term Thermal Energy Storage (TES) tank. In this hybrid storage configuration, the HT-ATES charges the TES tank, which in turn manages short-term fluctuations in peak heat demand. A coupled simulation framework links the reservoir-scale HT-ATES model with the network-scale thermal-hydraulic models of the DHN and the TES. The dynamic interaction between subsurface storage and heat demand is resolved through the exchange of transient mass fluxes and fluid temperature. Simulation results demonstrate that the integrated HT-ATES/TES storage system can flexibly respond to fluctuating heat demand, covering the greatest portion of the annual peak load and thus significantly reducing reliance on gas boilers.

This integrated approach enables the evaluation of HT-ATES as an active energy system component for seasonal heat shifting, peak-load management, and reduction of fossil-fuel-based heat generation. The presented methodology provides a transferable framework for linking detailed reservoir physics models with energy system models, supporting the design and assessment of multicomponent energy systems and advancing strategies toward flexible, decarbonized heat supply schemes.