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Structural and Petrophysical Characterization of Mixed Drain/Barrier Fault Zones in Carbonates: Example from the Castellas Fault (SE France)

Christophe Matonti, Juliette Lamarche, Yves Guglielmi, and Lionel Marié
Aix–Marseille Univ, CEREGE Centre Saint-Charles, Marseille, France

During fault activity, strain not only affects the fault plane but also extends into a rock volume called the fault zone. A fault zone is commonly divided into three structural parts accommodating increased strain towards the fault plane (Chester & Logan, 1987): (1) the fault core, a centimeter-to-meter-wide area where pervasive deformation obliterates the initial rock facies; (2) the damage zone, a plurimeter to hectometer-scale wide area containing numerous fractures related to the fault genesis, (e.g Micarelli et al., 2006; Mitchell & Faulkner, 2009); (3) the protolith zone, the surrounding undamaged host rock.

Fault-zone petrophysical characterization is a crucial issue in reservoir exploitation, because fault zones can behave either as hydraulic barriers or as drains. In the first case, fault zones lead to compartmentalizing of the reservoir; in the second case, they connect porous volumes and drain fluids along high permeability corridors. In addition, combining petrophysical analyses with fault-zone structural characterization is a challenge, because faults may display a number of different hydraulic properties, depending on the presence of an impermeable core, the fault-zone width and complexity, and the diffusivity of the fracture pattern (density, connectivity, and strike).

Finally a conceptual model of the fault zone's current hydraulic properties in 3D is proposed, in which the fault zone acts as a mixed drain/barrier element. It takes into account two different scales of permeability: the micrometer matrix scale and the meter-to plurimeter scale of fractures. Three contrasting fluid flow behaviours are defined for the Castellas fault-zone : (1) sealed impermeable barrier to the fluid flow, which is present in site 1; (2) drain behaviour which allow perpendicular and parallel flow with respect to the fault strike and occur in site 2 and 4; (3) and a mixed behavior within which flow can occur only parallel to the fault-zone strike. It’s the case in site 3 and 5.

This model could not only represent relatively small faults with moderate offset, but also suggests the complexity such faults can contribute to fluid flow in carbonate reservoirs.

AAPG Search and Discovery Article #120034©2012 AAPG Hedberg Conference Fundamental Controls on Flow in Carbonates, Saint-Cyr Sur Mer, Provence, France, July 8-13, 2012