Scientific drilling is an important method in the geosciences. It is used to obtain data and samples from the geological subsurface to investigate scientific questions.

Scientific drilling is necessary to observe and measure processes such as the formation of earthquakes or the sustainable use of resources under natural conditions. Drillings are also used to obtain rock samples that can be used to reconstruct past environmental and climatic conditions.

The deepest borehole to date reaches a depth of 12,266 m and was drilled on the Kola Peninsula near Zapolyarni in north-west Russia. It was drilled from 1970 to 1989 as a scientific borehole (Teufe = depth in miner's jargon) to explore the structure of the Earth's interior and, for example, ore deposits down to great depths. Today, there are some "longer" wells drilled to produce natural gas under the sea from land, but these commercial wells are horizontally deviated at 1000 or 2000 m depth, and thus their actual vertical depth is only about 2000 to 3000 m.

Thanks to 150 years of experience in drilling technology, drilling on land is very safe today. In Germany and Europe, mining authorities approve and monitor deep drilling in great detail so that environmental hazards can be largely ruled out. Moreover, research drilling is only undertaken where very extensive preliminary investigations have ruled out risks such as pressurized gas.

Basically, a so-called fluid exchange is to be prevented. This is understood as a possible mixing of salt water and groundwater or the rise and escape of natural gas or crude oil. To prevent this, plastic or metal pipes are cemented into the borehole wall in sections and a system of sealing cocks is attached to the head of the borehole, thus sealing the borehole. The mud circulating within the borehole is monitored for signs of pressure increase or gas rise. If necessary, the density of the drilling fluid is adjusted with weighting agents to prevent breakout. Boreholes must be sealed with cement from bottom to top after use to guarantee for the permanent closure of the hole.

Risks must also be minimized when using boreholes. When oil or hot water is extracted, or when water or gas is injected, the underground pressure conditions in the cracks and pore space of the surrounding rock change. This can lead to crack widening or even fracturing in the rock, which manifests itself as microseismicity or earthquakes. Fortunately, today it is possible to detect even the smallest precursors of magnitude -2, called microquakes, with particularly sensitive seismometers and to throttle back or stop the injection before larger quakes occur. Slow pressure equalization then leads to the release of stresses without quakes noticeable at the surface.

Such test procedures, called "adaptive stimulation", are carried out, for example, in research boreholes to explore the creation of artificial heat exchangers for geothermal use. Rocks at greater depths are hotter (the temperature rises by 30° per kilometer deep), and they are also denser. So you cannot simply inject cold water into one borehole and pump hot water into an adjacent borehole without having created an artificially high permeability. To this end, the GFZ is conducting the GEOREAL experiment in its KTB deep laboratory, for example. In geothermal projects, we speak of hydraulic stimulation. In this process, water — sometimes with additives (some sand, others chemical thickeners) — is injected into boreholes at high pressure to create fractures in the subsurface for better flow and heat exchange. In geothermal energy, artificial additives are usually not used during injection.

Research wells are only occasionally drilled for specific scientific questions. For the exploration and use of geothermal energy, however, drilling has been increasing in southern Germany for some years, for example in the Munich area and in the Upper Rhine Valley Graben. There, the potential to hit high temperatures of over 100°C already at a depth of 3000 to 5000 m is high. The rocks have good permeability, which means that these reservoirs serve as good, natural heat exchangers. In the north and east of Germany, permeable rocks are also often found between a depth of 1000 and 2000 m, from which 40 to 70 °C hot water can be extracted to supply modern low-temperature heating systems, for example. In the winter of 2022/2023 the company EWP in Potsdam drilled a borehole for geothermal use. This borehole is over 2000 m deep and was drilled on the Heinrich-Mann-Allee in Potsdam, very close to the GFZ. 

Existing boreholes are also needed for experiments in the long term. The GFZ is using the 4 and 9.1 km deep boreholes of Germany's Continental Deep Drilling Programme as a deep laboratory to test the possibility of creating artificial heat exchangers by injecting water at a depth of 4 km. There are similar projects in the North German Basin in Brandenburg near Gross-Schoenebeck, where geothermal energy is being researched.