Boreholes
Boreholes provide information about the composition of the ground. They also serve a particular purpose: for example, for the production of natural gas or as preparation for construction methods.
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Summary
Boreholes (also known as drill-holes) are mostly drilled vertically into the ground. Special methods also allow directional (curved) holes to be sunk.
Boreholes provide important clues
Underground Information is obtained from:
- drill core
- the cuttings (also known as “chips”), which are extracted with the drilling fluid
- the drilling advance rate
- measurements in the borehole.
With downhole surveys, a sensor (e.g., a temperature sensor) or a camera is passed down the hole; the signals can be assigned to the appropriate depth. Some methods also make it possible to test the surrounding rock in the borehole.
Documentation using a borehole log
The borehole is documented by means of a borehole log. The header of this document typically includes summary hole information such as the borehole identifier, location, date and name of the drill foreman.
The body of the document contains the downhole log which is a downwards scaled record of the sequence of intersected strata, together with depth measurements.
This includes a schematic diagram as well as a description of the retrieved material (e.g., core, chips or mud) and the quality of the recovery. These "raw data" are used to interpret the subsurface and to make specific statements about the fundamental questions of the investigation.
Archiving drilling data for the future
Drilling – in particular core drilling – is expensive. Therefore records and data are archived in order to be able to reinterpret them for subsequent questions. Geological bureaus, the cantons and geological information centers keep drilling archives.
These archives should in the future be able to exchange borehole data in a simple manner. For that, a standardized data model for boreholes and an exchange format must be developed and implemented.
Boreholes with concrete benefits
Besides for the purposes of research, boreholes have a variety of functions – for example:
- Downhole heat exchangers
- Groundwater wells
- Production wells for hydrocarbons, natural gas or petroleum
- Pumping of grout for example, concrete for drilled piles
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Who is who
Boreholes drilled for exploration, as well as those used for the utilization of heat and water, are subject to approval. The cantons administer maps for the authorization of downhole heat exchangers.
Authorization, planning and geological surveying
- Professional register of CHGEOL
- Services directory of the Swiss Geosciences: Geoscience Switzerland
- Overview map for the utilization of underground heat: cantonal geoportal
See also Geothermal Energy
Borehole Archive
- See Data section
- Borehole data of the Swiss Geological Survey
Company Directory for Geothermal Energy Utilization
Data
Borehole data archive
Borehole data are archived and made accessible by various authorities:
- map.geo.admin.ch
- Canton Bern geological portal for hydrogeological documentation
- Canton Vaud geological cadastre
- Canton Geneva InfoGESDEC
This list is not exhaustive.
Borehole cores
Special drill cores, whose replacement would be disproportionally expensive, are preserved by the Geological Survey in a core repository for future examination. This includes e.g., the exploration results of the AlpTransit base tunnels of the Lötschberg and Gotthard rail axes.
Data exchange
In Switzerland, there is a standard data model for borehole data, but the exchange between the archives is not yet regulated. The professional association CHGEOL and the Swiss Geological Survey are however thinking about the exchange and utilization of borehole data (CHGEOL publication borehole logs in the internet):
© swisstopo, 2011
