Fault zones characterization and fluid flow numerical experiments in carbonates rocks

Faults zones are important pathways for hydrocarbon migration and could behave as complex conduit-barrier systems in hydrocarbon reservoirs. Within fault zones, mechanical (i.e. fracturing, compaction, and comminution) and chemical (i.e. dissolution, and cementation) processes could enhance or decrease hydraulic properties. In this regards, characterizing fault zones properties is imperative during oil reservoir planning and development. In order to assess hydraulic properties within fault zones, useful sub-surface data could be derived from seismic attributes, well logs, and production tests; however, this information is limited by seismic resolution and distribution of well data. For this reason, information from outcrops analogues are normally entered in reservoirs model. This research is focus on assessing the hydraulic properties of faults zones and their influence on fluid flow in deformed reservoirs. The studied rocks could be considered as analogues of currently exploit carbonate reservoirs localized in Italy. Fault zones hosted in both tight and porous carbonates are investigated by using different methods, for instance field-based fractures analysis and discrete fracture modelling, permeability measurements, three-dimension imaging techniques (Synchrotron X-ray micro-tomography) and computer fluid dynamics experiments. Studied tight carbonates (Altamura Fm, Cretaceous) could develop well-fractured damage zones and discontinuous fault cores. In the case of investigated porous carbonates (Lower Pleistocene and Cretaceous Grainstones localized in Sicily and Maiella Mt., respectively), shear strain is often localized in deformation bands, where porosity and pore connectivity are modified. Eventually, deformation bands could evolve in faults, developing fault core and damage zone. Based on results, processes that take place in faults zones could be favorable or adverse to fluid flow. For instances, in tight carbonates open and well connected fracture networks within fault damage zone could increase permeability about three orders of magnitude. By the contrary, the permeability in fault zones hosted in porous carbonates decrease in the same rate due compaction and cementation. In general, fault cores could generate localized barriers, though some processes, such as fracturing and dissolution, could make a positive contribution to fluid flow. Additionally, permeability anisotropy is a consistent factor among the studied fault zones, where fluid flow parallel to faults is much more suitable that in the normal direction. To summing up, the implemented methodologies and outcome results are useful for a better understanding of the contribution of fault zones to hydrocarbons migration and storability in carbonates reservoirs.