HT-ATES (high-temperature aquifer thermal energy storage) systems target seasonal storage of large amounts of thermal energy enabling to meet the demand of e.g. industrial processes or district heating systems. The high injection temperatures or pressures of HT-ATES systems, however, cause thermo- and poroelastic stress changes close to the injection well, which may induce fault reactivation and seismicity. In this contribution, we focus on assessing the risk of fault reactivation and induced seismicity of the planned HT-ATES demonstrator DeepStor in the Upper Rhine Graben close to Karlsruhe, Germany, which aims at utilizing a former oil reservoir for HT-ATES. The risk assessment starts with a geological model of the planned storage site as input for thermo-hydraulic numerical modeling. The resulting changes in reservoir pressure and temperature are entered in a semi-analytical calculation of stress changes on a fault next to the HT-ATES system. A parameter sensitivity and subsequent Monte Carlo analysis with 1000 realizations show that the strongest influence is related to uncertainties in the stress state, especially the horizontal–vertical stress ratio and the orientation of the maximum horizontal stress. The calculated slip tendency on the fault next to the injection well, however, exceeds the friction coefficient only for c. 1 % of all parameter combinations of the Monte Carlo analysis, i.e. only for a very unfavorable combination of reservoir and operational parameters. Thus, the risk of fault reactivation and subsequent induced seismicity for HT-ATES at the DeepStor demonstrator can be expected to be relatively low.

We like to present calculated results for a hypothetical ATES system based on a geological reservoir model for the Breisgauer Bucht in the southwest of Germany. The storage configuration consists of two 8” horizontal filter sections with a length of 500m at a distance of 100m within the Buntsandstein in a depth of 700m below surface. Calculations were made with the FEA-Program COMSOL..

The seasonal storage system is powered by a solar thermal field (4ha) based on extrapolated hourly heat power data from 2016 to 2020, published for the solar thermal field in Vojens, Denmark. On the consumer load side, the monthly heat demand of 1000 households in Munich 2013 were taken.

Aim of the study was to calculate time dependent flow rates, pressure changes and temperature distributions to derive a realistic estimation of the production heat power, the storage capacity and the storage efficiency during operation. Dependent on the input data, storage efficiencies between 60% and more than 80% were calculated.

Since the optimal operation of an ATES is a trade-off between storage production power and storage efficiency, these models can be a powerful tools during the planning, construction and operation of an ATES system and, after validation in early operation phases, result in a digital twin for control (and cost) optimisation.

The City of Vienna is committed to become climate-neutral by the 2040. Its vast district heating grid, with a pipe length of over 1,300 Km connects more than 400,000 households and prevails in the heating sector by using 50% of the energy demand. Amongst other technologies, ATES is deemed one important building block in decarbonising the energy sector.

Evaluation of Neogene strata for ATES usage in the Vienna Basin involved interpretation of a modern 3D seismic survey and a large pre-existing dataset from oil & gas wells. Although the hydrocarbon prospective areas are generally situated in more proximal parts of the depositional systems, sedimentological interpretations can be extrapolated into the ATES study area with limited well control when applying sequence stratigraphic principles.

A geological concept is proposed for three sequences, each representing one specific depositional system. Each system contains a defined number of architectural elements such as slope, channel, fan, prodelta and delta plain. The geometry of the potential reservoirs is then assessed, whilst depositional environments have been calibrated with sedimentological data available from cores. Additionally, wireline log data from key wells have been used to calculate reservoir properties. Modelling of subsurface temperature data from offset wells resulted in a temperature model in 3D, which allows for accurate predictions of the reservoir temperatures.

By integrating data from all the disciplines, several GDE maps (Gross Depositional Environment) have been created. These maps highlight the high potential areas for ATES applications, in which leads and prospects will be explored in the near future.

Aquifer Thermal Energy Storage (ATES) systems are recognized for their substantial storage capacity at relatively low costs, making them an increasingly appealing technology. In densely populated urban areas like Berlin, where excess heat resources are abundant, geothermal district heat supply is of utmost importance. Therefore, ensuring the sustainable operation of ATES systems necessitates precise evaluation and prediction of hydraulic and heat transport processes.

Our research primarily focuses on the Adlershof ATES site located in the south-eastern region of Berlin. This ATES utilizes fine-grained Jurassic and Triassic sandstones to store and provide heat for the district heating network. To investigate the interaction between fluid and solid phases in porous media and their influence on storage behavior, we adopt an integrative approach that combines multiscale field measurements, laboratory experiments, core analysis, and numerical modeling.

Field measurements and laboratory experiments contribute to establishing the parameter ranges and identifying critical values for a medium-scale model. This model is employed for stochastic simulations to study the relevant system parameters, providing insights into sensitive parameters and their potential values. We confirm the hypothesis that the influence of dispersivity and porosity is dominating over the heat capacity. The model calibration can be improved by high-resolution measurements. Subsequently, a 3D large-scale model incorporates this information to facilitate the optimal design of the ATES system and ensure accurate long-term forecasting of its performance. Simulations account for varying injection temperatures and distances between wells to show the shared effect of these parameters and facilitate technical solutions.

Surplus heat as stored in an MTES (Mine Thermal Energy Storage) system in summer could partly meet the increasing demand of energy in winter. Better understanding the process of heat and mass transfer in the subsurface of an MTES during the injection-production cycles helps improving the budgeting of the stored mass and heat, and permits sustainable operation of such systems. Therefore, a concurrent injection and production test was conducted at a doublet wellbore system built in a previous mine site, Bochum, Germany. In this test, water of defined temperatures up to 55 °C was injected into the gallery of a horizontal mine drift down to 64 m in the subsurface, and the temperature of the concurrent produced water was below 25 °C. The depth-resolved temperature at both wellbores as monitored using the distributed temperature sensing (DTS) technique revealed such a heat transition in the storage that was much faster than the one which could be presumed for the porous rock matrix in the studied subsurface. By numerical modelling, it could be shown that the fracture flow-dominated heat transition in the storage yielded wellbore temperatures comparable to the values as monitored throughout the present test. Flow of water along the fractures as well as the concomitant heat transition into the surroundings resulted in lower temperature of the produced water as compared to the concurrent injected water.