The term “deep underground” refers to depths greater than 500 metres, at which very few activities take place other than geothermal projects, storage of waste of all kinds, and the extraction of oil and gas. For these activities, certain rock formations are required that are only found in the deep subsurface. 3D geological models are important tools for the planning, exploration and operation of such projects.

Basic data

Because of the high surveying costs, the volume of data from the deep underground is very low compared to that collected closer to the surface. The main information is provided by seismic surveying and drilling operations. In Switzerland, approximately 12,000 kilometres of seismic profiles have been recorded, and around 40 boreholes to depths of up to 5,300 metres and approximately 200 boreholes to depths of around 2,000 metres have been drilled in the past 50 years.

Uncertainties

Generally speaking, a model is always inaccurate by definition and only represents an approximation to reality. In view of the low volume of available data, this limitation applies in particular to 3D geological models of the deep underground. But thanks to evolving technologies and the scientific progress that has been achieved in the past years, it is nonetheless possible to minimise the existing uncertainties to a large extent. 

The Swiss Geological Survey is aware of this situation and develops 3D geological models with a great deal of consideration and with the incorporation of a wide variety of input data.