| Title | The Deep Hydrogeothermal Project in Holzkirchen, Molasse Basin, Germany |
|---|---|
| Authors | Klaus DORSCH, David LENTSCH, Christoph NIEDERSEER, Albert GÖTZ |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | medium enthalpy geothermal resource, deep hydrothermal exploration, Southern German Molasse Basin, carbonate reservoir, pore pressure variance, drilling challenges, municipally project, district heating, ORC power plant |
| Abstract | In Holzkirchen, a market town in the south of Germany close to the Alps, the currently deepest producing hydrothermal doublet in central Europe can be found. The Upper Jurassic carbonate reservoir in this region (Malm-Aquifer) is located between 4600 m and 5200 m depth and is known to have good transmissivity and a geothermal fluid with low salinity suitable for geothermal production (StMWIVT 2004). All in all, the project took 13 years to complete - from early conception in 2006 to the commencement of power production in 2019. Drilling of the two deviated wells in the deep sedimentary (Molasse) basin close to the Alps was a big challenge. The first well was spudded in January 2016. Following an intense gas kick while drilling the third section (of five in total) in the Lower Rupelian (Tertiary), the complete third section (1600 m) had to be abandoned and a sidetrack was drilled following a new well path to avoid the potential gas-bearing high-pressure zone. The final depth of 5600 m MD (5079 m TVD) was reached in May. After testing of the first well, the second well commenced in June. This well also proved problematic in the third section, where parts of the 9.7/8†liner as well as a drilling BHA were lost in two separate incidences due to differential sticking. Two sidetracks were drilled and after a total drilling period of about eight months, the final depth of 6084m MD was reached and followed by a circulation test of both wells which verified the required productivity and temperature. The most significant drilling challenge was the extremely high variance in pore pressures and the difficulty in foreseeing these pressures within the Oligocene and Cretaceous (approx. 3000 - 4500 m TVD), despite data from hydrocarbon offset wells. In spite of those drilling challenges, the success of the doublet in Holzkirchen represents the current peak of reservoir exploration in the southern part of the German Molasse Basin. Permeability is much lower compared to shallower wells that exploit the Malm-reservoir further north. The productivity of the Holzkirchen wells is strongly associated with a fault system. Nevertheless, the productivity (55 l/s) in combination with temperatures of more than 150°C is ample and sufficient to supply the district heating network of Holzkirchen with geothermal energy and to operate a small 3.4 MW ORC power plant. |