| Keywords |
deep geothermal projects, hydrothermal, success rate, stock take, Bavaria, south German Molasse Basin, wells, drilling, costs |
| Abstract |
In the last decades, the number of geothermal heat and power installations worldwide increased and the trend seems to continue. In Germany, three regions qualify for the installation of deep hydrothermal wells: the Upper Rhine Graben, the North German Basin and the South German Molasse Basin. 29 deep geothermal projects have been realized in the Bavarian part of the South German Molasse Basin between 1998 and July 2019. In this paper, we provide an updated analysis of the current status of the southern Bavarian deep geothermal projects. The existing 29 hydrothermal geothermal projects have been evaluated in an empirical approach with respect to drilling success and other related parameters. We find that a differentiation should be made between projects that are designed for heat and those that are designed for power or combined power/heat production, especially when it comes to success rates. Based on the available data the success rate of heat projects is 100 %, 15 out of 15 projects were successful. For power or combined power/heat projects the success rate is 71 %, 10 out of 14 projects. Power projects in the South German Molasse Basin target greater depths ( more than 3000 m) to reach higher reservoir temperatures and require relatively high yields. This causes quite elaborate and rather long (sub-) horizontal drilling paths. Regarding the drilling success rate, our study shows that the success rate of first-try boreholes for heat projects is 91 %, three times higher than for power or combined power/heat projects with 32 %. Below a drilling depth of 3000 mTVD the probability of encountering low yields increases from 4 % to 25 % and of encountering technical drilling problems from 4 % to 20 %. Regarding additional drilling costs due to sidetracks or deepenings, analyses show that on average the additional costs for heat projects are about 40 € per drilled meter and for power projects about 265 € per drilled meter. On the subject of drilling rate, analysis show an overall average of 46 m/day, with heat projects showing a slightly higher drilling rate of 49 m/day compared to 41 m/day for power projects. Thus far, four projects in Bavaria were unsuccessful. There are two reasons causing the failure of those projects: insufficient yields and for one project the natural gas content. All four unsuccessful projects are power projects and situated in the deeper southwestern part of the South German Molasse Basin. Apart from exploration risks, higher thermal water temperatures that are naturally associated with power projects and higher yields are more likely to produce cost-intensive scalings than lower temperature thermal waters which are sufficient for direct heating use. Observed induced microseismicity has occurred in both heat and power or combined power/heat operations, mainly at the reinjection well locations. Overall eight microseismic events with magnitudes between ML = 2,0 and 2,5 and intensities between EMS II and EMS III have been observed at three locations thus far. Power or combined power/heat projects are more ambitious than heat projects and awareness should be raised for the associated uncertainties and drilling risks. However, power production from geothermal resources especially in combination with heat production remains an important pillar for the energy transition in Germany. In order to increase the economic feasibility, drilling risks and the accompanying costs have to be reduced by a better understanding of the reservoir and the consideration of targeted small-scale stimulations. |