From pilot site knowledge via integrated reservoir characterization to utilization perspectives of a deep geothermal reservoir: 3D geological model at the research platform Groß Schönebeck in the Northeast German Basin

Abstract

The Groß Schönebeck site in the North German Basin serves as research platform for studying the geothermal potential of deeply buried Permian reservoir rocks and the technical feasibility to extract their geothermal heat. The structural setting of the site was investigated in more detail by studying a newly acquired 3D-seismic survey to improve the structural picture that was based on several old 2D seismic lines so far. The new data allows a revision of the geological interpretation of the site, enabling the set-up of a new reservoir model and providing base information for a possible further site development of the Permian and Permo-Carboniferous targets. The 3D seismic of Groß Schönebeck allows for the first time a consistent geological interpretation and model parameterization of the well-studied geothermal site. Main reflector horizons and the corresponding stratigraphic units were mapped and the structural pattern of the subsurface presented in the 8 km x 8 km x 4 km large seismic volume. While some fracture and fault patterns are visible in the upper Zechstein and post-Permian units, formerly hypothesized large offset faults are not present in the Rotliegend reservoir itself. However, a well-established graben-like structure at the top of the Zechstein succession is most likely related to broken anhydritic Zechstein stringers. Most reflectors above the salt show a rather undisturbed pattern. The main reservoir sandstone of the Dethlingen Formation (Rotliegend) was mapped and characterized. The base of the underlying Permo-Carboniferous volcanic rock sequence and hence its thickness could not be depicted reliably from the geophysical data. Based on the new seismic data and the available reconnaissance drilling, logging, and laboratory data of the Groß Schönebeck research site, the thickness and distribution of the sedimentary Rotliegend (with emphasis of the sandy reservoir section) and of the volcanic rock sequence was modelled and parameterized with petrophysical properties (i.e., total and effective porosity, fluid permeability, bulk density, thermal conductivity, thermal diffusivity, and specific heat capacity), providing a more realistic reservoir description. The data and interpretation constitute the basis for a better understanding of the dominating processes at the site and for future measures. Further site development could include a deepening of one well to give evidence on the volcanic rock sequence and consider deviated wells into favourable zones and the design of a fracture-dominated utilization approach.