German Continental Deep Drilling Program

The German Continental Deep Drilling Programme (in German: Kontinentales Tiefbohrprogramm der Bundesrepublik Deutschland), abbreviated as the KTB borehole, was a scientific drilling project carried out from 1987 to 1995 near Windischeschenbach, Bavaria. The main superdeep borehole reached a depth of 9,101 metres in the Earth's continental crust.

The German Federal Ministry of Research funded the project with 528 million DM (270 million Euro). The Lower Saxony LBEG mining office (Landesamt für Bergbau, Energie und Geologie ()) took over the project lead. After the drilling project had ended the used the borehole to install a seismic observatory at depth (Tiefenobservatorium) that was active from 1996 to 2001. The derrick - one of the largest in the world - became a tourist attraction in the region. The two boreholes remain open for further scientific use.

The site of the drilling project is in the ZEV, Zone von Erbendorf-Vohenstrauß, just south of the Erbendorflinie being the contact zone where Laurasia and Gondwana merged into Pangaea. Due to the geological genesis the earth crust consists of a number of layers exhibiting a number of phenomena such as strong magnetic areas and the Erbendorfkörper, a large mass drifting at about eleven kilometres below the surface with a relative high speed and seismic activity.

The project started in September 1987 with an advance borehole using state of the art technology. The borehole reached its target depth of 4,000 metres in April 1989. The results of this drilling were used as parameters for the main borehole - for example the temperature gradient was higher than originally expected. The main drilling started on 8 September 1990 about 200 metres away from the advance borehole for an envisaged depth of 10,000 metres. The first 7,500 metres were using an automatic vertical drill head so that the lateral deviation could be limited to 12 metres. Due to the expected failure of the electronics below that depth a conventional drill head was used below that point. Due to brittleness and ductility the borehole was deforming multiple times, requiring to backfill the hole and start drilling again from a higher place. These operations continued for the last year of the project - the timing and budget constraints put an end to the efforts to go deeper. The drilling ended on 12 October 1994 after 1,468 days at a depth of 9,101 metres and about 300 metres lateral deviation showing a temperature of 265 °C. The planned three main experiments were performed until 31 December 1994. The facilities were being partially dismantled until 31 December 1995.

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