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2 M. Antonellini et al. / Marine and Petroleum Geology xxx (2013) 1e16
strategies have been adopted to image SSRF from seismic data; they the direction parallel to its plane (Antonellini and Aydin, 1994,
include the use of seismic attributes such as coherency or curvature 1995).
(Astratti et al., 2012; Lohr et al., 2008; Pearce et al., 2011), analysis of Excellent rock exposures located along the Northwest Sicily
amplitude variations in 3D seismic models (Lohr et al., 2008), the shoreline provide a unique opportunity to study in detail the fluid
use of stochastic techniques to extrapolate the SSRF from seismic flow properties of a high porosity, Pleistocene carbonate grainstone
resolution faults (Marrett and Allmendinger, 1992), and interpre- rock crosscut by a strike-slip faults system (Fig. 1). The outcrops
tation of the fault traces from seismic profiles and logs (Lohr et al., allow investigating the effects of small offset sub-vertical faults on
2008). Non-geophysical techniques employed to image SSRF are an aquifer/reservoir-scale permeability analogue during production
based on paleo-stress analysis, structural restoration, studies of by designing accurate numerical experiments for single-phase fluid
outcropping analogues and fractal/stochastic analysis of fault at- flow. The strike-slip faults nucleated from compactive shear bands
tributes (Agosta et al., 2010; Cello et al., 2000, 2003; Kattenhorn (sensu Aydin et al., 2006). Single compactive shear bands represent
and Pollard, 2001; Maerten et al., 2002; Maerten and Maerten, the incipient stage of faulting in porous rock (Aydin, 1978; Aydin
2006; Maerten et al., 2006; Roberts, 2007; Saillet and Wibberley, and Johnson, 1978; Aydin et al., 2006). These structures evolve
2013; Schultz et al., 2008, 2013; Shipton et al., 2002). Since the forming zones of compactive shear bands, which have offsets
late 90s, a large number of studies on SSRF have been produced <0.5 m, well below the limit of seismic resolution. Eventually at an
after analysis of, mainly, sandstone and siliciclastic rocks (Fossen offset larger than 0.5 m, according to fault/rock type, lithologic
and Bale, 2007; Morris et al., 2012 and references therein). Some characteristics, and stress state (Aydin et al., 2006), zones of com-
studies have also been presented for carbonate rocks (Farran et al., pactive shear bands become well-developed faults (sensu strictu)
2005; Morris et al., 2009; Penney et al., 2005; Putz-Perrier and containing discrete slip surfaces along which cataclasis occurs. It
Sanderson, 2010), and for the effects of fault geometry, damage follows that many faults formed by the aforementioned process fall
zones and SSRF on fluid flow (Matthäi et al., 1998; Fossen and Bale, below the limit of seismic resolution in the outcrops of Northwest
2007; Rotevatn et al., 2009; Fossen et al., 2010). Sicily (Tondi, 2007; Tondi et al., 2012).
Besides the inherent risk or advantages that SSRF cause during The objectives of this paper are the following. (1) Characterize in
oil exploration in terms of migration, fault sealing, top-seal the field the sub-seismic resolution strike-slip fault network by
breaching, and reservoir quality enhancement/degradation means of structural mapping, scan lines/areas surveys and mini-
(Manzocchi et al., 2008; Walsh et al., 1998), SSRF may play an permeametry. (2) Define methodologies to up-scale and/or elabo-
important role during the phase of oil production, Enhanced Oil rate the structural and permeability properties measured in the
Recovery (EOR), and geologic CO 2 sequestration (Ambrose et al., field, so that they can be imported in a standard single-phase fluid
2008; Damsleth et al., 1998; Esposito et al., 2010). Antonellini flow simulator (i.e. MODFLOW 2005) used in ground water
et al. (1999) have shown that deformation bands faults in the oil modeling under an equivalent porous medium approach. (3)
field of Arroyo Grande (California, USA) were controlling the effi- Compare two methodologies, one based on a deterministic fully
ciency of the steam injection production scheme employed for EOR. descriptive approach (field maps), the other one on a Discrete
Structural heterogeneities and SSRF have also been shown to affect Fracture Network (DFN) obtained with a stochastic approach
the water circulation in aquifers within siliciclastic (Haneberg, (MOVEÔ), to describe both structural and petrophysical properties
1995; Rawling et al., 2000) and carbonate rocks (Celico et al., 2006). of the network of structures (i.e. compactive shear bands, zones of
Focusing on deformation bands, characteristic structural fea- compactive shear bands, and faults). The comparison will be done
tures of porous rocks that deform like granular media (Aydin et al., by testing the same field area with the two aforementioned
2006), they have been a matter of interest due to their pronounced methods and using simple boundary conditions in the fluid flow
control on fluid flow in reservoir rocks (Nelson, 2001). The litera- numerical experiments. (4) Evaluate the importance of the sub-
ture characterizing the petrophysical properties of deformation seismic resolution strike-slip fault networks on single-phase flow
bands in siliciclastic rocks is rather extensive (Antonellini and during well production at a reservoir-scale.
Aydin, 1994; Faulkner et al., 2010; Flodin et al., 2001, 2004;
Fossen and Bale, 2007; Fowles and Burley, 1994; Lothe et al., 2. Study area
2002; Main et al., 2000; Ngwenya et al., 2003; Shipton et al.,
2002; Sternlof et al., 2004; Taylor and Pollard, 2000). Conversely, The studied outcrops, located in Northwest Sicily (San Vito lo
only in recent times some work has been done for deformation Capo peninsula and Favignana Island) are roughly oriented northe
bands in carbonate rocks (Cilona et al., 2012; Micarelli et al., 2006; south (see Fig. 1 for location). The northwestern corner of Sicily
Rath et al., 2011; Rustichelli et al., 2012; Tondi et al., 2006b, 2012; represents the most external sector of the Sicilian orogenic belt,
Tondi, 2007). Field, numerical, and theoretical studies investi- which is mainly comprised of south-verging, Neogene fold-thrust
gated how deformation bands may affect the subsurface fluid flow, tectonic elements (Giunta et al., 2000). The most recent faults
and at what scale their effect is most influential (Ahmadov et al., outcropping in the area form a system comprised of high-angle,
2007; Antonellini and Aydin, 1994, 1995; Jourde et al., 2002; strike-slip structures oriented either WeNW or NeNE (Abate
Manzocchi et al., 1999; Sternlof et al., 2004; Manzocchi et al., et al., 1993, 1997; Giunta et al., 2004; Nigro et al., 2000; Tondi
2008; Matthäi et al., 1998). et al., 2006a). The former faults are characterized by a right-
In siliciclastic rocks, the permeability values of deformation lateral kinematics, the latter by a left-lateral one. The kinematics
bands measured normal to the plane of the band range from less of such a fault system is compatible to the current regional stress
than 0.1 mD to a few tens of mD (Antonellini and Aydin, 1994; field, which is made up of an NWeSE oriented principal horizontal
Fossen and Bale, 2007). The aforementioned values are consistent compression direction (Giunta et al., 2009).
with the deformation bands decreasing the host rock permeability In the study area, deformed Triassic to Miocene platform car-
by one to four orders of magnitude. In carbonate rocks, Rath et al. bonates, which pass upwards into deep-water marls and lime-
(2011) documented that permeability is reduced as much as three stones, are the basement units underlying Plio-Pleistocene marine
orders of magnitude in the direction normal to the band with deposits comprised of Upper Pliocene shales overlain by 20e30 m
respect to the host rock. Slip surfaces associated to thick zones of thick, Lower Pleistocene carbonate grainstones (Abate et al., 1993,
deformation bands are discontinuities in the rock that may act, in a 1997). The latter rocks include beds, characterized by a thickness
way, similarly to an open fracture enhancing the permeability in ranging between 20 cm and 100 cm, made up of eroded carbonate

Please cite this article in press as: Antonellini, M., et al., Fluid flow numerical experiments of faulted porous carbonates, Northwest Sicily (Italy),
Marine and Petroleum Geology (2013), http://dx.doi.org/10.1016/j.marpetgeo.2013.12.003