Remaining opportunities in medium-deep reservoirs of the North German Basin – lessons learned from the new development in Schwerin

The North German Basin yields enormous resources of heat in place bound to the Palaeozoic–Mesozoic succession and to fault systems. Early exploration campaigns have identified highly permeable Mesozoic sandstones at depth of <2,300 m with temperatures of <100°C. Despite the fundamental knowledge established by these campaigns, the development of hydrothermal reservoirs remained limited due to considerable pre-drilling risks resulting from uncertainties in reservoir predictions at individual localities.

To minimise risks associated to subsurface uncertainties, an interdisciplinary work flow integrating sedimentological, geophysical, and petrophysical methods was designed to re-evaluate the six Mesozoic reservoir complexes of the North German Basin. Within the projects Sandsteinfazies, GeoPoNDD and mesoTherm this work flow was applied to an extensive database of cores and wireline logs leading to high-resolution maps depicting facies, thickness and quality of individual hydrothermal reservoirs. These maps enable reliable predictions of key parameters, i.e. net-thickness and permeability, on regional to local scales and, thus, make a significant contribution to the reduction of subsurface uncertainties. The potential of these subsurface reservoir maps to increase the utilisation of geothermal energy is demonstrated on the example of the reservoir development at Schwerin, a previously underexplored locality. There, reservoir predictions enabled targeting a highly productive sandstone at 1,250 m depth. The operation combines a conventional doublet system with industrial heat pumps to supply 7 MW_th to the local heating grid. The lessons learned from Schwerin demonstrate significant opportunities in medium-deep reservoirs enabling a sustained increase of developments for heat supply in North Germany.