Seamless Fracture Characterization with Virtual Outcrop Models: Fracture Geometry and Vertical Persistence at Creux-du-Van, Swiss Jura Mountains

Deep geothermal energy is emerging as a key component of Switzerland’s Energy Strategy 2050. In the Canton of Vaud, projects target natural hydrothermal systems at depths of 800 to 1,000 meters, with temperatures ranging from 35 to 100°C, in Upper Malm limestone reservoirs. These limestones, with low matrix porosity and permeability, rely on well-connected fracture networks and karstic features to enhance fluid flow. However, subsurface data from seismic surveys and well data do not fully cover scale intervals that are relevant for reservoir characterization and modeling. To address this limitation, we use a virtual outcrop model (VOM) to characterize fractures in 3D, explore its potential to bridge the length-scale gap, and compare fracture patterns and kinematics between scales of observation. 
At Creux-du-Van, a unique continuous, 3D exposure of fractured and gently folded Upper Malm limestones in the Central Internal Jura Fold and Thrust Belt provides an exceptional opportunity for fracture characterization at the decimeter to hundreds of meters scale, allowing comparisons with previous structural interpretations at the regional, 1:500,000 to 1:25,000 scale. Approximately 700 fractures were interpreted from high-resolution VOMs, i.e., point clouds (~110 points/m²), of Creux-du-Van, derived from terrestrial LiDAR scanning. These fractures were classified based on vertical persistence, which is a relative measure for the extent to which they propagate across mechano-stratigraphic boundaries. Geometric parameters such as orientation, dimensions (length, width, and aspect ratio), and spacing were also quantified. Field-based structural analysis complements the digital dataset by providing kinematic and chronological interpretations of brittle structures linked to the tectonic evolution of the fold and thrust belt.
The lengths of regional strike-slip fault traces span four orders of magnitude, ranging from tens of meters to tens of thousands of meters, with a median of 177 meters. Their orientation, kinematic, and length relationships align with the multi-scale Riedel shear model (Ruhland, 1973)   forming the regional structural framework. Fractures in the VOM span scales from 0.1 to hundreds of meters, with a median length of 5 meters. Regional faults and VOM-derived fractures show an overlap in length distributions and consistency in fracture orientations and kinematics. Both align with the NW-SE compression inferred from field-based kinematic data and regional restorations associated with the Jura shortening event, demonstrating seamless characterization of brittle features across scales. 
This study seeks to further investigate the role of mechanical boundaries (e.g., stratigraphic boundaries, regional structures) in controlling reservoir compartmentalization. It also showcases the potential of outcrop analogues such as Creux-du-Van to support 3D characterization and analyses of fracture properties such as length distributions, orientation, and vertical persistence, ultimately contributing to the advancement of structural modelling of subsurface reservoirs for sustainable energy solutions.