Résumé
Understanding fault damage zone (DZ) structure and permeability is fundamental for predicting the distribution and rates of fluid flow in the earth’s crust. Fault conduits in the crust often show evidence for fluid flow localisation at specific structural sites related to fault segment growth and linkage, hence we study here a segmented fault zone with strike-slip kinematics and pluri-decametric displacement, affecting carbonate rocks (Pag island, Croatia). This fault zone has multiple core zones surrounded by a DZ, composed of different types of structure, including wall and link damages. To build discrete fracture networks of these structures (DFNs), we conducted high-resolution fractures mapping and measurements of apertures in five circular areas from the DZ to the background. We also analyzed rock samples from each damage structure using the same method. Fluid flow simulations were performed through all these DFNs, to quantify the permeability and its anisotropy. We show that link damage is about 102 more permeable than the background, and 2 to 5 times more permeable than the wall damage. At the decametric-scale, damage zone permeability can be approximated by a permeability tensor, while at the centimetric scale, this is not the case due to the strong permeability heterogeneity. In the DZ, decametric-scale fracture patterns are 10 to 65 times more permeable than the centimetric-scale fractures, providing conduits for fluid flow. Finally, the maximum permeability strongly correlates with the product of mean aperture and connectivity, suggesting that these parameters could be used as proxy of the permeability in fault DZ. These results provide knowledge to better estimate fault zone permeability, providing constraints for numerical flow modelling in various applications in the energy transition such as, CO2 geological storage, geothermal exploration and the prevention of unwanted leaks to the biosphere.