Deciphering Diffuse Fractures from Damage Fractures in Fault Zones and Their Effect on Reservoir Properties in Urgonian Carbonates

In carbonate reservoirs, fracture networks impact reservoir properties. Unlike background fractures, fault-related fractures are heterogeneously distributed along the fault zone and can form drains or barriers depending on the diagenetic history. The aim of this study is to identify the structural and diagenetic attributes of both types of fractures and to determine their respective impact on the reservoir properties. To this end, our study focused on an outcrop of Urgonian carbonates in SE France which affected by poly-phase tectonics (burial, extension, folding and strike-slip). We made a 290m scan-line along the outcrop to characterize fracture network inside and outside five fault zones and a diffuse shear zone. The diagenetic analysis on 45 thin sections in LPA and cathodoluminescence evidenced diagenetic stages that have affected the host rocks since the Barremian. This study allowed to identify 2 sets of diffuse early fractures. One set was reactivated by the faults while neo-formed fractures appeared. The diagenetic processes in faults zones and diffuse fractures differ too, and specifically affected the petrophysical properties of the host carbonates.