Deformation style and fluid flow behaviour in a faulted siliciclastic-carbonate sequence

Abstract

Understanding fluid flow behaviour of faults is important for resource exploitation and management. Most studies analysing fluid flow behaviour in fault zones focus on either high-porosity or low-porosity sequences. In this study, we analyse various mechanical layers within alternating siliciclastic-carbonate sequences in fault zones in the Oligo-Miocene Logudoro basin, located in northern Sardinia (Italy). We combined a variety of methods, including field measurements of structures, in-situ permeability and Schmidt Hammer rebound measurements converted to uniaxial compressive strength. Furthermore, we performed thin section analysis, to characterize grain size, porosity, and mineral compositions. We used the gathered data to model the fluid flow conditions within deformation patterns present in one fault-zone. Deformation styles are related to mechanical properties of the rocks at the time of faulting, juxtaposition and differences in intergranular space and porosity in sandstones. The permeability is influenced by the presence of deformation structures such as fractures (high permeability), compactional shear bands (low permeability) and fault rocks within fault core (high and/or low permeability). The fluid flow model highlights the significant influence of deformation bands on the flow field and hydraulic gradient, demonstrating the importance of including these structures in the analysis.