Meike Bagge

When studying a hydrogen system, it is often difficult to access and characterize the source rocks. In this sense, the greater Münchberg Massif area offers a unique opportunity. East of the Franconian Line, the serpentinites are exposed and easily accessible. West of the Franconian Line, the serpentinites most likely continue and are buried under a thick pile of sediments. In this study, we focus on the area east of the Franconian Fault System. With an interdisciplinary approach, using geology, petrology, geophysics and numerical modelling methods, we aim to characterize the hydrogen source rock in the context of a hydrogen system. The Münchberg Massif – a stack of nappes formed during the Variscan orogeny – consists of stratigraphically inverted metamorphic layers, where the degree of metamorphism decreases with depth. Serpentinites are part of the Prasinit-Phyllit-Serie and are accessible at the outer rim of the Massif. Geological models, seismic and magnetic data suggest that the Prasinit-Phyllit-Serie is present at about 3 km depth throughout the Massif and was partly uplifted by several fault zones in the south. The fault zones in the Münchberg Massif also provide potential pathways for fluid flow. We collected 17 geological samples of the outcropping serpentinites at two locations (Peterleinstein and Zell), about 20 km apart. The results of the petrological analyses (polarization microscope, X-ray diffraction, raman spectroscopy, major and trace element analytic) reveal different degrees of serpentinisation for the two locations. At Peterleinstein, the samples are completely serpentinized with main mineral components of lizardite, magnetite and chlorite. In contrast, the Zell samples are only partly serpentinized with main components of antigorite, magnetite and partly forsterite and clinopyroxene. The chemical composition of the serpentinites is similar at both locations and hints at a depleted mantle protolith. The analyses suggest slightly different serpentinization conditions and degrees of serpentinization throughout the Münchberg Massif. A possible cause for this might be different fluid availability at the locations due to heterogeneities in permeability. It is therefore possible that a residual potential for serpentinization and thus hydrogen formation still exists locally at depth. To get a better understanding of a possible hydrogen system in the subsurface and to illustrate the potential transport processes and pathways, we implemented our results in numerical finite element models using the software package TerrantaLab and TerrantaFlow. We calculated hydrogen flow in a 2D cross-section of the Münchberg Massif, where the Prasinit-Phyllit-Serie was implemented as a hydrogen generating source rock. We performed different scenarios with variations of hydrogen generation rates as well as variations of the petrophysical properties of the geological layers and fault zones. We studied advective and diffusive hydrogen transport (dissolved in water) as well as variations of hydrogen amounts emanating at the surface in these scenarios. Combining outcrop data, laboratory measurements, geophysical data and numerical modelling, contributes to deciphering the hydrogen system and its potential role in the energy system.

Co-authors : Meike Bagge, Peter Klitzke, Maximilian Hasch, Nikola Koglin, Rüdiger Lutz, Andreas Bahr, Daniel Palmowski