In 2006, a feasibility study was carried out by ERDWERK on behalf of the community of Holzkirchen to analyze the deep geothermal potential. In 2011, the first concrete development plan was prepared on the basis of the available data (reprocessed 2D seismic surveys, borehole data).
The First 3D Seismic by a Municipality
From February to March 2011, for the first time in Germany, a new 3D seismic survey was carried out commissioned by a community. The geophones were placed over an area of about 66 km². On the basis of the seismic data, ERDWERK designed a detailed reservoir model that was used to create the well design and to specify the drilling sites. The drilling site is located directly east of the business park (called “Alte Au”).
Due to changes in basic conditions, new variants of the project had been developed and tested on their profitability in collaboration with the specialist lawyers GGSC. The regional council of Holzkirchen decided on the 30th of April 2015 to realize a smaller version of the project (multi-pad well site and a final borehole diameter of 6.1/8"). After completion of the detail planning and the EU-wide tendering procedure, the construction of the well site began in autumn of 2015.
Well Site Construction and SPUD
The well site was built in late autumn 2015 by the company Dobler GmbH. Due to the favorable weather in November / December 2015 and the professional work of the construction company, the drilling site could be completed before the Christmas holidays and accepted by the mining authority. Assembly of the drilling rig could begin between Christmas and New Year, so that the drilling work could begin on 27.01.2016.
The drilling operations of the Th1 started on the 27th of January in 2016 and went quite well until March of 2016, when an unexpected gaskick in the layer of the "Rupel-Bändermergel" stopped them abruptly at a depth of 4,200 m. To continue the drilling, a sidetrack (Th1a) was required. It was successfully drilled until the mid May of 2016 and reached a final depth of 5,600 m. The pumping tests, which proved the drilling success, were carried out in June of 2016.
The drilling operations for the well Th2 also began well, however in the 3. section casings became stuck during the installation of the liner. As a result, costly fishing and milling was necessary to remove the casings. This took several months and to the detriment of the project schedule. Further problems with pipe sticking during a check-trip through the sidetrack of the third section, which required a further sidetrack and lead to more delays. In the beginning of March 2017, the well reached its final depth of 6,084 m MD. Thereby, the well in Holzkirchen is the longest and deepest in the Southern Molasse Basin and of its kind in Europe.
The following short-term pumping tests delivered a thermal water temperature of > 150 °C. A first short-term circulation step test showed a delivery rate of up to 50 l/s. The drilling rig was completely dismantled and demobilized by mid April in 2017.
In mid December 2018, trial operation of the thermal water circuit was started and geothermal energy was fed into the district heating network for the first time. The first electricity production took place at the beginning of July 2019. The current commissioning phase, including trial operation with optimization of the process flows, is to continue into the coming year.
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