Given the increasing worldwide demand for energy, it is crucial to focus on the development of energy storage technologies that are both efficient and sustainable. Thermal energy storage systems are an economically viable and environmentally beneficial solution to meet this need. Hereby Aquifer Thermal Energy Storage (ATES) systems are notable for their exceptional storage capacities, especially when it comes to managing changes in seasonal heat use. Although low-temperature ATES systems have received attention, there is still minimal research on high-temperature ATES (HT-ATES) applications, which utilize fluid temperature at a higher level than traditional ATES systems. To ensure smooth and cost-effective operations, it is essential to thoughtfully plan the setup of these systems. Therefore, this thesis specifically examined HT-ATES systems, with a specific emphasis on well completion and surface facilities. It has also explored the influence of reservoir characteristics on the overall system to analyze and improve the design for HT-ATES applications. The study includes evaluations of technology, economics, and operations to ensure the long-term efficiency of these systems. Computer simulations using the software PIPESIM from Schlumberger provide a comprehensive analysis of the behavior, performance, and dynamics of different completion designs, enabling the assessment and improvement of alternative techniques.