GEUS’ Well sample laboratory receives and describes more than 13,000 sediment samples a year. They are primarily from water extraction wells, but they also come from raw material wells, geothermal wells, survey wells and geotechnical wells. The laboratory, however, does not deal with contaminated samples.
The descriptions are part of the national well database Jupiter, where geological data from the Danish subsurface from more than 270,000 wells are available on the internet.
Reporting of drilling information and submission of sediment samples
According to law, information about all water supply, raw material, geotechnical and geothermal wells must be reported to GEUS. The information comprises a number of administrative and technical drilling data, closing of wells and submission of sediment samples to GEUS.
Primarily glacial sediments
Most of the wells are between 25 and 100 m deep, although some can reach depths of 200 to 300 m below the surface. The majority of the samples are from Quaternary deposits from glaciations or interglaciations. The deep samples are often from the top of Denmark’s subsurface, primarily Neogene and Palaeogene (Tertiary) deposits and Upper Cretaceous. A few represent Palaeozoic and Precambrian deposits from Bornholm.
Well drilling certificates and list of well drilling companies with A-certificates
Since its establishment in 1888, GEUS has had a fruitful cooperation with well drillers and other drilling in Danish strata. The cooperation means that GEUS sends numbered sample bags to drilling companies and is mainting a list of companies with A-certificates. The Advisory Board for Education and Training for the Building and Construction Industry issues well drilling certificates.
From soil to words
When the samples are described, they are places on long tables. The individual sample is subjected to a systematic sedimentological description. This means: what can be seen, felt and smelled. The tools are restricted to hand sieves, microscope, and hydrochloric acid for detection of calcium carbonate. GEUS’ staff of specialised geologists assist with determination of fossils, dating and stratigraphic issues.
The description, which is entered directly into the Jupiter database, always includes rock type, secondary components, grain size, colour and carbonate content. When relevant, also hardness, sorting of grain size, structures, mineralogical composition and fossils are included.
The description forms the basis for a geological interpretation, in which all samples are given a sediment symbol according to its formation environment and age, and the sample is placed in Denmark’s stratigraphy.
Drilling reports, profiles and use
As the grid of wells grows more finely meshed, the knowledge about the Danish subsurface grows. In the Jupiter database, there are just under five borings per square kilometre. Data can be presented in the form of a report of a geological well log (in Danish only) or as a geological profile, in which several borings are compiled.
Data from wells are an important part of the geological evaluation in a wide range of projects at GEUS. Well data are also used in many connections in private consultancy companies, municipalities and in scientific surveys.
Some major, recent projects where well data from the Jupiter database are used are shown below:
• The National Groundwater Programme
• New Miocene stratigraphy
• Project on shallow geothermal energy