Integrated Seismic Imaging and Borehole Correlation Reveal the Subsurface Architecture of the GeoLaB Crystalline Geothermal Research Site

The GeoLaB underground research laboratory in the Tromm granite pluton (Odenwald, SW Germany) aims to advance the understanding of thermo-hydro-mechanical-chemical (THMC) processes in crystalline rock for Enhanced Geothermal Systems (EGS). During the 2023–2025 site exploration phase, two orthogonal 2D pre-stack depth-migrated (PSDM) seismic profiles (E–W and N–S) were acquired and repeated alongside two exploration boreholes: vertical well GLB-01 (500 m, fully cored) and deviated well GLB-02 (wireline logged). Because the seismic lines are offset from the borehole collars by 122 to 460 m—representing a significant fraction of the total depth—we present a geometry-aware seismic-to-well tie workflow that explicitly addresses non-coplanar spatial offsets rather than assuming coincident trajectories. Both wells penetrate a shallow granitic unit overlying a metamorphic basement, with the contact identified at ~407 m measured depth (MD) in GLB-01 and within 470–480 m in GLB-02. This boundary generates a prominent high-amplitude, laterally continuous seismic reflector on both PSDM profiles, matching sharp increases in gamma-ray response, P-wave velocity, and bulk density. ... mehrWell correlations highlight two key marker horizons: a thin, uranium-enriched horizon in the lower granite and a distinct marker at the granite–metamorphic interface. Structural interpretation of the E–W seismic profile identifies a primary fault structure (F-1) with associated subsidiary strands, whereas the N–S profile reveals southward thickening of the metamorphic basement and local discontinuity of the lower granite package. These observations were integrated into a preliminary three-dimensional geological model that refines the structural architecture of the proposed underground laboratory, establishing baseline confidence for fault-zone targeting and guiding the design of an upcoming 3D seismic survey to optimize the final research tunnel layout.