The exploration risk for geothermal wells is high, as the desired flow rates can often not be achieved due to insufficient permeability of the rocks in production horizons. Processes are already known from the oil and gas industry that can in principle be used to increase the permeability of a reservoir. These include pressurised water-based methods (e.g. Radial Jet Drilling (RJD)), with which small-calibre deflection wells are produced from the main well in order to hydraulically connect surrounding fault zones, especially fractures, to the well. The known methods offer solutions for soft reservoir rocks that are easy to drill with conventional methods. However, these conditions, which are typical for oil and gas reservoirs, cannot simply be transferred to geothermal reservoirs. These are often formations of hard rock where the water jet technology used in the RJD process has no or too low drilling performance.