3D Discrete Fracture Network (DFN) models of damage zone fluid corridors within a reservoir-scale normal fault in carbonates: Multiscale approach using field data and UAV imagery

We combined structural data collected in the field and those obtained from a virtual outcrop model constructed from drone imagery, to perform Discrete Fracture Network (DFN) modelling and to characterize the fracture distribution within the damage zone of the low-displacement (similar to 50 m) carbonate-hosted Pietrasecca Fault (PF) (central Apennines, Italy). Both in the hanging wall and in the footwall damage zones, fractures are vertical and parallel to slightly oblique to the fault strike. Fracture length distributions in the footwall damage zone indicate a high degree of fracture maturity, while in the hanging wall damage zone they indicate a low degree of fracture maturity. Pervasive stylolitization in the hanging wall must have hindered the development of through-going fractures, favoring diffuse fracturing characterized by stylolite-bounded fractures. DFN models suggest that permeabilities are 1-2 orders of magnitude greater in the footwall damage zone than in the hanging wall damage zone. As permeability (10(-12) to 10(-15) m(2)) is comparable with those measured in large-displacement (up to 600 m) faults in carbonates, our results show that also damage zones accompanying carbonate faults with similar to 50 m of displacement could be fracture corridors for efficient fluid flow within subsurface reservoirs. Therefore, we propose that jumps in subsurface permeabilities occurring in many carbonate fractured reservoirs could be associated with to the occurrence of high permeability fracture zones developed within damage zones of lowdisplacement faults. As the recent advancement in seismic imaging allow the recognition of faults with displacement in the order of a few tens of meters, reservoir geologists and engineers can apply results of this study to better model the subsurface flow pathways near low displacement faults in carbonate reservoirs.

Automated summary

The study combined field-collected structural data and a virtual outcrop model constructed from drone imagery to characterize the fracture distribution within the damage zone of a low-displacement carbonate-hosted fault in Italy. Results showed that fractures in the damage zone exhibit varying degrees of maturity and permeabilities, with the potential for the damage zone to serve as fracture corridors for fluid flow in subsurface reservoirs. This suggests that changes in subsurface permeabilities in carbonate fractured reservoirs may be associated with high permeability fracture zones developed within the damage zones of low-displacement faults.