Potential for deep geothermal heat production in clastic rocks of the southern North German Basin – A case study from Hoya, Germany

Deep geothermal aquifers can be a good source for industry applications with a high heat demand in the course of the energy transition. Industries such as paper production require heat sources that are independent of global market fluctuations, with predictable, reliable and green long-term supply. A number of clastic aquifers have been identified as potentially feasible for geothermal use within the North German Basin ranging from the lower Cretaceous to Middle Bunter Sandstone. Due to the extensive hydrocarbon exploration in the North German Basin, it is often possible to provide a local subsurface analysis of the geothermal potential at the location of the required use.

In this work, we present a case study from the town of Hoya in the southern North German Basin, where an abandoned hydrocarbon exploration well is available, as well as numerous wells in the vicinity (20 km) and some 2D seismic lines. From well log analysis, well reports, seismic data and an available 3D model of Lower Saxony, we evaluate the quality of different clastic reservoirs in the study area. We found? that many of the reservoirs that are known for good quality sandstones in the North German Basin are presented as shales at the paper mill in Hoya. Potentially usable sandstone reservoirs include the lower Cretaceous Aptian (top ca. 1600 m) and Valendis Sandstone (top ca. 1700 m), the middle Jurassic Dogger Delta 2 (top ca. 1950 m) and the Lower Triassic Hardegsen Sandstone (top ca. 3850 m). Surrounding well data, however, show a large spatial heterogeneity for these lithologies over relatively short distances. We include these geological uncertainties, temperature measurements from wells, permeability measurements from well tests and the specific requirements of a paper production company to evaluate the geological and economic feasibility, based on geothermal energy estimations and levelized costs of heat for the individual reservoirs.