In geothermal energy, a huge potential lies in hydrothermal reservoirs where ultra-high temperature fluid (400-500 degrees Celcius) can be utilized to multiply the power production output. However, the aggressive fluids and high temperatures encountered in these geothermal reservoirs are tough challenges for any materials and structures to sustain during the operation lifetime of at least 20 years. Improper materials selection and design principles may lead to serious failure events, and loss of the production well. The present paper discussed HotCaSe project, initiated and led by Equinor, with the main objective to solve the challenges related to the well construction for enabling high enthalpy (>2900kJ/kg) hydrothermal power production. At the initiation of the project, a three-day workshop, gathering personnel resources from the involved companies, R&D institutions and other national/international experts, was organized to freely scout for innovative solutions for cost-effective and reliable casing systems. To efficiently screening out the optimal solutions, preliminary modules of a design tool were developed to study the mechanical response in the casing systems under thermal loadings. The tool is currently used to evaluate the identified casing alternatives, by exploring combinations of mainly pre-existing technologies. The functional and mechanical performance of selected well completions solutions will be tested and verified, both in physical laboratory, numerical simulations with help of data computers and field testing. The successful HotCaSe project is going to contribute to access a new dimension in geothermal energy utilization, thus having a significant impact on both society and environment.