Preliminary studies for an integrated assessment of the hydrothermal potential of the Pechelbronn Group in the northern Upper Rhine Graben

Abstract

Abstract. The northern Upper Rhine Graben is due to its tectonic setting and the positive geothermal anomaly a key region for geothermal heat and power production in Europe. In this area the Upper Eocene to Lower Oligocene Pechelbronn Group reaches depths of up to 2800 m with temperatures of locally more than 130 ∘C. In order to assess the hydrothermal potential of the Pechelbronn Group a large dataset is compiled and evaluated. Petrophysical parameters are measured on core samples of eight boreholes (courtesy of Exxon Mobil). Additionally, 15 gamma-ray logs, 99 lithology logs as well as more than 2500 porosity and permeability measurements on cores of some of these boreholes are available. The Lower Pechelbronn Beds are composed of fluvial to lacustrine sediments, the Middle Pechelbronn Beds were deposited in a brackish to marine environment and the Upper Pechelbronn Beds consist of fluvial/alluvial to marine deposits. In between the western and eastern masterfaults of the Upper Rhine Graben several fault blocks exist, with fault orientation being sub-parallel to the graben shoulders. During the syntectonic deposition of the Pechelbronn Group these fault blocks acted as isolated depocenters, resulting in considerable thickness and depositional facies variations on the regional and local scale (few tens to several hundreds of meters). Laboratory measurements of sonic wave velocity, density, porosity, permeability, thermal conductivity and diffusivity are conducted on the core samples that are classified into lithofacies groups. Statistically evaluated petrophysical parameters are assigned to each group. The gamma-ray logs serve to verify the lithological classification and can further be used for correlation analysis or joint inversion with the petrophysical data. Well data, seismic sections, isolines and geological profiles are used to construct a geological 3-D model. It is planned to use the petrophysical, thermal and hydraulic rock properties at a later stage to parametrize the model unit and to determine, together with the temperature and thickness of the model unit, the expected flow rates and reservoir temperatures and thus the hydrothermal potential.

Assessment of deep geothermal research and development in the Upper Rhine Graben

“…The Tertiary (t) fill of the URG was intensively investigated by the hydrocarbon exploration, resulting in a large number of deep wells and seismic lines. Based on this, detailed characterization of the lithostratigraphic units was developed by various authors (Straub 1962;Doebl 1967Doebl , 1979Rothe and Sauer 1967;Illies and Mueller 1970;Sauer and Munck 1979;Illies and Fuchs 1974;Doebl and Olbrecht 1974;Teichmüller 1979;Clauser and Villinger 1990;Durst 1991;Gaupp and Nickel 2001;Derer et al 2003;Hurter and Schellschmidt 2003;Grimm 2005;Grimm et al 2011;Jodocy and Stober 2011;GeORG Projektteam 2013;Reinhold et al 2016;Hintze et al 2018). It should be noted, however, that the stratigraphic classification of the individual horizons has been regularly adapted over the last decades.…”

“…The targets of geothermal exploration in the URG are therefore mainly medium-and coarse-grained horizons, which exhibit sufficiently high permeability and temperature. The Pechelbronn Formation seems to be most suitable in this context, particularly in the northern URG (Hintze et al 2018;Stricker et al 2020). In addition, the Niederrödern Formation and the Meletta Beds of the Froidefontaine Formation may also be a target for deep geothermal projects and underground thermal energy storages (UTES).…”

“…The Pechelbronn Formation, also known as Pechelbronner Schichten or Pechelbronn Group, comprises syn-rift sediments of the Upper Eocene to Lower Oligocene that occur almost throughout the entire URG (Derer et al 2003;Gaupp and Nickel 2001;Grimm 2005;Hintze et al 2018). Due to the locally high oil content within this unit, it has been intensively studied since the nineteenth century.…”

“…The petrophysical properties of the Tertiary succession is described in more detail, by e.g., Gaupp and Nickel (2001), Stober (2011), GeORG Projektteam (2013), Reinhold et al (2016), Hintze et al (2018), Stricker et al (2020) and Bär et al (2021b).…”

The Potential of Depleted Oil Reservoirs for High-Temperature Storage Systems

“…Thermal properties of Tertiary rocks in the URG are very scarce and reveal large variations and uncertainties. Whereas thermal conductivities were measured on core samples [57,66,67], data on heat capacities are only available for comparable lithologies of the same age in the Northern German Basin [68,69].…”