This thesis is about the design and optimization of a High-Temperature Aquifer Thermal Energy Storage (HT-ATES) system in the Vienna Basin, with a focus on the aquifer component. There are numerous parameters that influence the thermal recovery efficiency (R) of ATES, one main characteristic for the successful implementation of this kind of underground thermal energy storage (UTES). Therefore, the objective of this thesis is to determine the most influencing parameters and find the optimal combination of these to maximize the efficiency. To investigate the impact, assumptions are made on parameters and their respective range in agreement with a local geologist and numerical simulations are conducted to evaluate their influence on the performance of the aquifer. Ultimately, a design of experiments (DoE) approach is used to obtain a thorough analysis of the results. By analyzing the simulations, statements about the pressure and temperature distribution within an aquifer are made and the combination of parameters within the specified range that yield the highest performance are determined.