Pore Network and Hydraulic Behaviour Characterization of Fractured Sandstones

Hydraulic behaviour is controlled, in fault zones, by fracture and pore network properties but the interactions between parameters of the pore, fracture and fault networks and fluid-flow are not fully understood, due to the strong dependence to rock characteristics and external conditions (stress and pressure field, physical and chemical conditions of fluid-flow). To determine the control of these factors on fractured sandstone hydraulic behaviour, an outcrop was selected on the Upper Rhine Graben western border, in the footwall of a normal fault affecting Triassic sandstones. On samples belonging to the damage zone of this fault, pore and petrophysical properties were determined using mercury intrusion porosimetry (MIP), NMR relaxometry and petrography (SEM, cathodoluminescence). The matrix pore network dimensions vary depending on the distance between the sample and the closest fracture plan, and the behavior is different for the two facies identified. These variations are linked with differing mechanisms of deformation and diagenesis for each facies, but both result in an enhanced drainage in the “damage” zone around the fracture. At the fault scale, the hydraulic behaviour can be determined by combining the global fracture intensity and the effect of each single fracture damage zone.