Imbricated Structure and Hydraulic Path Induced by Strike Slip Reactivation of a Normal Fault in Carbonates

Fault zones strongly impact basin reservoir properties as they can act as drains or barriers depending of their structural and diagenetic properties. In the case of reactivated faults, newly develop fracture and fault systems reworked and cross-cut preexisting structures generated by the first fault activity potentially result in new fluid pathways. The study focalized on the polyphase Castellas fault affecting Barremian calcarenites (Urgonian facies). We performed a 870m-long high resolution mapping along the Castellas fault zone with a data of 586 measurements, including 56 fault planes, 460 fractures and 70 bedding planes. We realized a geological map and a stratigraphic log and fifteen cross-sections perpendicular to the fault zone, to capture fault architecture variations. The Castellas fault structure, observed on map and cross-sections exhibit large lateral variations of fault core and fault geometry. It is composed of a complex anastomosed architecture made of 8 main fault planes striking from N047° to N078°, with secondary fault planes, horse tail structures and imbricated lenses. Fault zone hydraulic signature change from a porous fault rock with a tight damage zone during normal faulting to a fracture network and fault core enhanced permeability during strike-slip deformation.