Hydraulic properties of fault zones in porous carbonates, examples from central and southern Italy

Emanuele Tondi (1), Andrea Rustichelli (1), Antonino Cilona (2), Fabrizio Balsamo (3), Fabrizio Storti (3), Giuseppe Napoli (4), Fabrizio Agosta (5), Pietro Renda (4) & Maurizio Giorgioni (6)
(1) Scuola di Scienze e Tecnologie, Università di Camerino, Italy. Corresponding author e-mail: andrea.rustichelli@unicam.it; tel: +39 0737 402619; fax: +39 0737 402644.
(2) Department of Geological and Environmental Sciences, Stanford University, USA. Now at Shell Global Solution, Rijswijk, Netherlands.
(3) Dipartimento di Fisica e Scienze della Terra "Macedonio Melloni", Università di Parma, Italy.
(4) Dipartimento di Scienze della Terra e del Mare, Università di Palermo, Italy.
(5) Dipartimento di Scienze, Università della Basilicata, Italy.
(6) Shell Italia, E&P, Rome, Italy.

We present the results of in situ permeability measurements performed, using a portable field permeameter, on normal and strikeslip fault zones that crosscut high-porosity carbonate grainstones. The measurement sites expose in the Cretaceous Orfento Formation of the Majella Mountain (Abruzzo, Italy), and the Lower Pleistocene deposits of the Favignana Island (Sicily, Italy). Nine small-displacement, compactive shear banding-based fault zones have been tested in the field. The fault offset ranges between 10 and 200 centimeters. The acquired permeability data indicate a two orders of magnitude decrease of porosity and permeability from the host rock to the cataclastic fault cores. A clear dependence of the fluid circulation paths through porous carbonates is therefore inferred at depth due to orientation, density and connectivity of the fault zones. Moreover, this study indicates the key role played by the pore network characteristics (pore dimensions above all) of undeformed host rocks on determining extremely different permeability values of the faulted porous carbonate grainstones. Accordingly, the results presented in this study may be helpful in applications such as geofluids management for improving the forecasting of carbonate reservoir quality and understanding the extent of reservoir compartmentalization.

permeability, sub-seismic resolution faults, compactive shear banding, Favignana Island, Majella Mountain.