Discrete fracture network modeling of background deformation in Apulian carbonates (Altamura Fm., Murge area, Italy)

We present the first results of an ongoing project aimed at better deciphering the role played by background fractures on subsurface fluid flow within Cretaceous Apulian carbonates. Taking advantage of 3D exposures present in the Murge area of southern Italy, which is part of the southern Apennines foreland, we were able to accurately map the fracture network that pervasively crosscut the Cretaceous limestone of the Altamura Fm. (Coniacian – Campanian inf.). There, bed-perpendicular fractures consist of strata-bound joints and sheared joints and no strata-bound, throughoing, small-scale strike-slip faults with cm offsets. Often, the strata-bound joints and sheared joints abut against bed-parallel stylolites present within individual limestone beds. For each fracture/fault set, we assessed its dimensional, spatial and scaling properties from mesoscale structural data (scan line and scan area). Structural data were gathered along artificial walls and pavements of inactive quarries. By computing the mean orientation, size distribution, aspect ratio, aperture, N (number of fractures per sample volume), P32 (fracture area for sample volume) and fractal dimension of each fracture/fault set, we were able to build up a multiple DFN (Discrete Fracture Network) model of a representative rock volume of 10 m-side. In particular we construct different DFN model for each mechanical unit and for strata-bound and non strata-bound fractures. The resulting model was then used to compute the overall 3D permeability (Kx, Ky, Kz) of each individual layer (single limestone beds) and of the representative rock volume comprised of several mechanical units. The results of this work will be key to define, in the next future, an appropriate REV (Elementary Representative Volume) model aimed at simulating the fluid flow properties of such a representative rock volumes at reservoir conditions, which means given values of lithostatic loading under specific tectonic stress states.