Physical properties of carbonate fault rocks, fucino basin (Central Italy): implications for fault seal in platform carbonates

Abstract

We documented the porosity, permeability, pore geometry, pore type, textural anisotropy, and capillary pressure of carbonate rock samples collected along basin-bounding normal faults in central Italy. The study samples consist of one Mesozoic platform carbonate host rock with low porosity and permeability, four fractured host rocks of the damage zones, and four fault rocks of the fault cores. The four fractured samples have high secondary porosity, due to elongated, connected, soft pores that provide fluid pathways in the damage zone. We modeled this zone as an elastic cracked medium, and used the Budiansky-O'Connell correlation to compute its permeability from the measured elastic moduli. This correlation can be applied only to fractured rocks with large secondary porosity and high-aspect ratio pores. The four fault rock samples are made up of survivor clasts embedded in fine carbonate matrices and cements with sub-spherical, stiff pores. The low porosity and permeability of these rocks, and their high values of capillary pressure, are consistent with the fault core sealing as much as 77 and 140 m of gas and oil columns, respectively. We modeled the fault core as a granular medium, and used the Kozeny-Carmen correlation, assigning the value of 5 to the Kozeny constant, to compute its permeability from the measured porosities and pore radii. The permeability structure of the normal faults is composed of two main units with unique hydraulic characteristics: a granular fault core that acts as a seal to cross-fault fluid flow, and an elastic cracked damage zone that surrounds the core and forms a conduit for fluid flow. Transient pathways for alongfault fluid flow may form in the fault core during seismic faulting due to the formation of opening-mode fractures within the cemented fault rocks.

Hydrogeological properties of fault zones in a karstified carbonate aquifer (Northern Calcareous Alps, Austria)

“…11b) due to secondary dissolution. The present data set unfortunately does not allow to clarify whether cataclasites with higher porosities have elevated permeabilities and if yes, whether a process different from secondary dissolution could be responsible for that; however, examples from the literature treat fine-grained cataclastic rocks as impermeable (Agosta and Kirschner 2003;Agosta et al 2007;Agosta 2008;Storti et al 2003).…”

“…However, the subsurface hydrogeological behaviour of faults in carbonate aquifers is very difficult to determine (e.g. Celico et al 2006) as water/rock interactions (dissolutional weathering) produce transient, heterogeneous and anisotropic permeability structures (Agosta et al 2007;Agosta 2008).…”

“…Agosta and Kirschner 2003;Agosta et al 2007;Agosta 2008;Billi and Di Toro 2008;Storti et al 2003). In the damage zone, porosity and permeability are expected to increase and are controlled by connectivity and anisotropy of fracture networks (Agosta et al 2010;Billi 2005b) and/or breccia zones (e.g.…”

Tectonic control on the petrophysical properties of foredeep sandstone in the Central Apennines, Italy

“…However, studies dedicated to the kilometer‐scale variation of their petrophysical properties with respect to tectonic structures are rather scarce [e.g., Benson et al ., ; Chang et al ., ; Mavko et al ., ]. Concerning the Central Apennines, a Tertiary‐Present fold‐and‐thrust belt characterized by the occurrence of several carbonate ridges thrusted onto siliciclastic foredeep deposits [ Cosentino et al ., ], studies dedicated to the experimental evaluation of the petrophysical properties mainly focused on evaporites [ Trippetta et al ., , ], carbonates [ Ciccotti and Mulargia , ; Ciccotti et al ., ], and fault rocks [ Agosta et al ., ]. It is worth noting that foredeep sandstones are common in mountain belts and represent the most common reservoir rocks worldwide.…”

Fractured reservoir modeling: From well data to dynamic flow. Methodology and application to a real case study in Illizi Basin (Algeria)

“…Fault arrays and natural fractures distribution exert an important influence on subsurface fluids migration, trapping and production mechanism since they may play a key role in changing the original petrophysical properties -such as porosity and permeability-of reservoir rocks (Caine et al, 1996;Aydin, 2000;Agosta et al, 2007). This becomes even more critical in present-day exploration and appraisal campaigns that are increasingly focused on tight or low (primary) porosity reservoirs and for which the knowledge of the fracture distribution represents a major step in the production forecast.…”