Fracturation des carbonates dans la zone de faille normale active d’Aigion (Grèce) à partir des carottes du puits: conséquences sur les propriétés de transfert de fluides

Abstract

The Aigion active fault belongs to a system of north-dipping normal faults that affect the southern shore of the gulf of Corinth. Cores of AIG-10 well crossed the Aigion active fault show the usual presence of a damage zone and a gouge. This work presents a thin section analysis under optical and cathodoluminescence microscopy. It confirms the zonation in terms of fracturing next to the fault zone. Away from the fault zone, fracturing inherited from the Hellenic compressive phase is dominant, even though E-W fractures related to the current extension are observed. All these fractures are sealed and the filling is similar to the limestone host-rock in terms of luminescence. Close to the fault, the number of fault-related fractures increases. Under cathodoluminescence analysis, the fracture filling indicates the passage of several fluids that would be external, and the latest generation of fractures is still open. Beneath 5 m thick of cataclasite and ultracataclasite in limestone and radiolarite (fault core) and 13 m thick of gouge in radiolarite, in the footwall, observations are limited, because the presence of karst has restricted coring opportunities. Nevertheless we can see that the filling of the extension related fractures is different from what has been revealed in the hanging wall fault zone. This suggests that Aigion active fault plane acts as a local transverse seal and has always been. Analysis of cement sequences highlights longitudinal permeability; also, we discussed the role, in terms of fluid transfer, of fault propagation induced features.