Discrete Fracture Network Modelling of Faulted and Fractured Apulian Platform Carbonates (Altamura Formation, Southern Italy)

In order to better understand the relative contribution of background and localized deformation on the petrophysical properties of fractured tight carbonates, Discrete Fracture Network (DFN) models of representative outcrops were build up by using a stochastic approach. The study carbonates, which crop out along the vertical walls and pavements of an abandoned quarry of southern Italy, represent a surface analogue of the hydrocarbon reservoirs currently developed in nearby areas of Italy. The outcrops expose a well-layered, tight, Cretaceous limestone crosscut by both background (diffuse) and fault-related (localized) deformation. Fractures show a high variability of their spatial and dimensional properties (length, intensity, aspect ratio and aperture), according to the different structural domains (fractured host rock, fault damage zone and fault core) in which they were surveyed. Such variability highlights the different scales at which the structural domains affect the tight carbonates, and can be considered a key challenge to construct a realistic reservoir model. DFN modelling of representative rock volumes of the fractured host rock showed that both volumetric (P32 and porosity) and hydraulic properties (correspondent permeability) are mainly affected by the two main sets of Non-StrataBound fractures (NSB). Equivalent porous media modelling, which include both fractured host rock and fault zones, showed that the overall permeability of the Fault Damage Zones (FDZ) is 2-to-4 orders of magnitude higher than the fractured host rock permeability. The FDZ can be therefore interpreted as fluid conduits that enhance fluid flow, which is controlled by both the dimensional properties of the fractures and by their aperture values.