Continental deep drilling program of the Federal Republic of Germany

from Wikipedia, the free encyclopedia
Continental deep drilling program of the Federal Republic of Germany (Germany)
Red Dot.svg
The 83 m high derrick of the 9 km deep borehole near Windischeschenbach

The continental deep drilling program of the Federal Republic of Germany ( KTB ) was a major geoscientific research project carried out between 1987 and 1995 . The then Federal Ministry for Research and Technology financed the project with 528 million DM (270 million euros), the project sponsor was the Lower Saxony State Office for Soil Research . The borehole of the main borehole is the deepest in Germany and one of the deepest in the world with a depth of 9,101 meters . The deep drilling program brought extensive and partially accepted hypotheses contradicting new findings about the earth's crust . The successor to the program is the International Continental Scientific Drilling Program (ICDP).

From 1996 to 2001 the GeoForschungsZentrum Potsdam (GFZ) operated a depth observatory in the facility, which supervised the further scientific use of the two boreholes as part of the ICDP. Since then, the property and the building have been owned by the GEO-Zentrum Foundation at the KTB , which has been running the GEO-Zentrum as a public information and educational facility since 1998. Visitors can view what is still the world's largest land drilling rig and are informed about current geoscientific and geotechnical topics at events and special exhibitions . Scientific use of the two boreholes is also possible.

Goals of the continental deep drilling program

The main aim of the continental deep drilling program, which included many individual scientific projects, was the precise exploration of the earth's crust . For this purpose, special drilling and monitoring technology had to be developed and tested. The KTB was the first major German project for basic geoscientific research.

planning

It was planned to drill to a depth at which the temperature would be 300 ° C, as the electronic measuring devices (magnetic field, temperature, etc.) would only work up to this temperature. At least 8000 meters depth and 250 ° C should be reached. Decisive for the choice of the location in the Upper Palatinate versus a location in the Black Forest, which was considered to be equivalent from the point of view of the possible geological gain of knowledge up to the end, was that the critical temperature of 300 ° C in the Upper Palatinate only expected at a depth of about twelve kilometers was five kilometers deeper than in the Black Forest.

geology

ZEV with KTB
Central European variscides
Geological map with a focus on the Rump Mountains and the eruptions of the Central European Variscides. The Erbendorf-Vohenstrauß zone (marked in red) is located on the western edge of the crustal section of the Moldanubian zone called Tepla-Barrandium .

The Windischeschenbach location (near Weiden in the Upper Palatinate ) is in the so-called zone of Erbendorf - Vohenstrauß (ZEV). In the north this tectonic unit ends at the Erbendorflinie, in the west on the Franconian line and in the south on the Luhe-Linie . The Erbendorf and Luhe lines emerged as a result of the emergence of the Variscan mountains , whose hulls are exposed here and in the other German low mountain ranges , during the convergence of the continents Laurussia and Gondwana . The Erbendorf line, shown in dashed lines in the graphic opposite, is the boundary between the two large clods of the Saxothuringian and Moldanubian clods that belong to the contact zone of the former continental plates and run parallel to it . The actually drilled unit, the ZEV, consists of an alternating layer of metabasites and para- gneiss , these units were probably deposited on a continental slope , the former belonging to the Saxothuringian, Bohemian (Teplá-Barrandian) or Moldanubic i. e. S. is controversial. Due to its history, the earth's crust has a strongly structured structure here, and several geophysical anomalies have been detected, such as the Erbendorf body, which is about eleven kilometers deep at this point, with increased seismic reflectivity and speed. Above it lie several strongly magnetized areas, some of which were drilled and some of which were discovered through their long-range effects.

In 1987, residents of the Windischeschenbach community feared that harmful gases could escape from the nearby drilling site. According to information from the scientists, the fear was unfounded, as only the smallest amounts of hydrogen, methane and helium-3 were released.

Drilling path

Model in the information center

Between September 1987 and April 1989, a fully core hole pilot hole was drilled to a depth of 4,000 meters. The findings of the pilot bore determined the technical concept of the main bore. This also showed a significantly higher temperature gradient than expected.

The main bore that followed from September 8, 1990 at a distance of 200 meters should therefore only reach a little over 10,000 meters. A total of 35 isolated core samples were only taken below 4,000 meters, but the cuttings were continuously examined. In order to limit the friction of the drill string so that the planned depth could be reliably reached at all, an independently controlled vertical drill head was used up to 7,500 meters, with which the lateral deviation could be limited to 12 meters. Due to the expected temperature-related failure of the electronics, conventional drilling had to continue below this depth. From this depth on, the rock was in the brittle-ductile transition area, so that the borehole was partially deformed by differently directed horizontal stresses. The drill got stuck several times and had to be reattached after the borehole had been filled in pieces. These operations took about a year to complete. Budget and the associated time constraints were ultimately decisive for the completion of the well.

The main drilling of the continental deep drilling program was completed on October 12, 1994 after 1,468 days at a depth of 9,101 meters, about 300 meters of lateral deviation and a temperature of 265 ° C.

The three planned large-scale tests were carried out by December 31, 1994, thus completing the main part of the deep drilling program. After that, the plant was partially decommissioned and other smaller tests were carried out.

The program as a whole ended on December 31, 1995.

Results

The results led to widespread recognition of the zone structure and the postulated paleoplate configuration based on it in the Central European part of the Variscan basement (the deep borehole is in the seam area of ​​several formerly separate lithospheric plates ). The more rapid increase in temperature with increasing depth goes well with the strong structure of the overall geological system that can be seen in this picture. Due to the temperature limitation to ≈ 300 ° C, the originally hoped-for depth of 12 km was only reached to 75%. The technology push through the project has increased as a result.

6-roller drill bit with drill core

Individual results are, for example, the knowledge that the rock has gaps down to great depths and that deep water is significantly more mobile than initially assumed. This should be taken into account when planning underground storage facilities for radioactive waste, for example. An abnormally strong increase in the magnetic field was already evident in the pilot hole, which was interpreted as a result of a deep, previously not suspected magnetized area and was then also drilled in the main hole. The joint interpretation of various borehole measuring methods, the results of which could be checked using drill cores and cuttings, also made great progress. The joint interpretation of surface and borehole measurements provided improved methods, e.g. B. in the field of seismics, geoelectrics , magnetotellurics , magnetics and earthquake observation.

literature

Web links

Commons : Continental deep drilling program of the Federal Republic of Germany  - collection of images, videos and audio files

Individual evidence

  1. ↑ M. Füßl, B. Weber: Northern Upper Palatinate. Forays into the history of the earth. Quelle & Meyer Verlag, Wiebelsheim, 2009. p. 12
  2. ^ A. Dörr, WA Zulauf: Elevator tectonics and orogenic collapse of a Tibetan-style plateau in the European Variscides: the role of the Bohemian shear zone. International Journal of Earth Sciences March 2010, Volume 99, Issue 2, pp 299-325, doi : 10.1007 / s00531-008-0389-x
  3. ↑ Further results can be found in the article What the scientists found - KTB results on scinexx.de

Coordinates: 49 ° 48 ′ 55 ″  N , 12 ° 7 ′ 14 ″  E