Discrete fracture network modelling of faulted and fractured Apulian platform carbonates (Altamura Formation, southern Italy)

Hydraulic properties of representative volumes of fractured/faulted Upper Cretaceous Apulian platform carbonates were modeled using a stochastic approach (DFN), with the aim to decipher the contribution of background and localized deformation on fluid flow in tight platform carbonates at outcrop-scale. The study rocks crop out in quarries located at Murge area, Italy, and correspond to excellent analogues of the hydrocarbon reservoirs currently exploited in southern Italy. The outcrops expose a well-layered limestone affected by both diffuse (background) and fault-related (localized) deformation. Background deformation consists of bed-parallel and bed-perpendicular stylolites, four sets of stratabound joints and two sets of non-stratabound fractures. The fault-related deformation is represented in the small scale by sub-vertical sheared fractures with few-cm offset and mostly characterized by the absence of fault core and discontinuous damage zones. In a larger scale, the fault related deformation is localized in strike-slip fault zones striking N120° (right-lateral) and N160° (left-lateral), which are characterized by a vertical separation above seismic resolution (> 20m), high fractured damage zone (about 30m thick) and well-developed fault core of about 1m of thickness. The field work consisted of obtaining both spatial and dimensional properties of individual fracture sets (length, intensity, aspect ratio and aperture) pertaining to either background or localized deformation. Posterior analysis consisted of finding useful relationships, such as, dependency of fracture aperture on both orientation and length, fracture intensity variations along the fault zones, fracture length relationship with orientation. Discrete fracture network (DFN) models for host rock (at different scales) and damage zones were obtained with a stochastic approach by using MOVE™ software and the outputs of individual DFN models consist on volumetric fracture intensity (P32) fracture porosity and 3D hydraulic conductivity (Kx, Ky, Kz) upscaled using the method of Oda (1985). The studied carbonates show an high variability of these properties at various scales and among different zones (host rock, damage zone and fault core) highlighting the importance of both sub-seismic and seismic resolution strike-slip fault networks on flow during well production at a reservoir-scale.