Re-evaluation of data from old deep boreholes with the aim of possible reuse for geothermal energy – advances in the TRANSGEO project

The ongoing structural transformation from the hydrocarbon industry to sustainable green energy is one of the challenges Europe is facing recently.In Germany, there are about 15,000 boreholes with depths ≥ 400 m (deep wells).Transgeo, a transnational project funded by the EU-program Interreg, aims to identify the potential of such boreholes for geothermal energy extraction in Germany and four other Central European countries.One of the main aspects of the project is the collection of data from deep wells, which will then be compiled into databases and fed into a web-based IT tool to demonstrate to potential investors the possible deep wells for geothermal energy extraction.The reuse of old boreholes, especially former oil or gas wells, is particularly attractive, as it can potentially reduce the costs of otherwise very costly geothermal drilling while making use of existing infrastructure.

The deep drillings in the eastern part of the North German Basin are mostly several decades old, as economic independence was sought especially during the GDR era and great efforts were put into the exploration and mapping of national raw material deposits. Hence, several comprehensive studies and data collections are still available in the archives. The value of analyses of taken samples, measured parameters, among other things is priceless. Such data is the basis for modelling, and also for the validation of existing models. Parameters here displayed, include temperature, porosity and permeability in identified pay zones within formations interesting for geothermal energy extraction. Also, the technical data about the borehole construction, as well as the detailed information about the location of cement bridges (abandoned wells), and geological or technical issues during, or after the drilling process are crucial, if considering a reuse or planning a new drilling project nearby an existing borehole.