Geothermal energy in the Netherlands is growing in general, however, medium deep geothermal (200 - 1500 m depth) is lagging behind while the potential at these depths could be very high. Development is held back by little geologic knowledge of this interval as well as legislative constraints. Better understanding of the reservoir characteristics and well design in this depth range is necessary in order to accelerate the heat transition away from fossil fuels. The Breda Formation is deemed as one of the most promising formations within the medium depth range. Therefore, this formation, particularly the part found in the Zuiderzee Low (ZZL), is the focus point of this thesis. The reservoir characteristics are determined using newly obtained cutting information, novel biostratigraphic analyses, old and new seismic interpretations and petrophysical log data, eventually leading to a static reservoir model. Consequently, the static model is upscaled and used as input for dynamic simulations in the Harderwijk case study area. The static model provides new thickness, depth, porosity, permeability and transmissivity maps of the Breda Formation in the ZZL. These maps were generated using more data (types) than the current ones present in the REGIS model, and should therefore contain less uncertainty. The dynamic model provides insights into doublet lifetimes and flow rates for three different well trajectories in two possible reservoir scenarios. The horizontal trajectory proved superior in terms of doublet lifetime and flow rate for both reservoir scenarios. Finally, the current Dutch legislative framework covering the medium depth is limiting medium deep geothermal development in the Netherlands. A revision of the 500 m depth boundary separating the Mining and Water Law jurisdictions should be considered if the full potential of the medium depth is to be accessed.

Jetted radial wells are a relatively new form of hydraulic stimulation for oil and gas wells, where small diameters holes extend radially from a wellbore. This technique for increasing well connectivity could also be applied to geothermal wells. Radials can be freely placed along a backbone well, making the design of an economically viable well plan time intensive. Numerical optimization has been extensively applied to well design and will be applied for the design of a radial well plan. A simple optimization case is used to compare gradient-based and gradient-free optimization for jetted radial optimization, the gradient-free CMA-ES algorithm is chosen for the workflow. In addition to CMA-ES, mixed integer CMA-ES and uncertainty-handling CMA-ES are incorporated in the workflow. Three reservoir cases are evaluated for optimization using these algorithms. The workflow is able to determine well plans with higher NPV in each of these cases though finding a global optimum remains difficult.