Rock Mechanical Characterization of an Offshore Mudrock from Haltenbanken, Mid-Norway

Abstract

Rock mechanical tests and subsequent investigations in scanning electron microscopy (SEM) have been carried out on samples retrieved from the Late Cretaceous Springar Fm offshore Mid-Norway. Mineralogical and petrophysical analyses pertinent to this study have been conducted according to standard methods. The Springar Fm has a clay content of 45–50%, with smectite rich mixed-layer illite/smectite as the dominating clay mineral. Consolidated undrained (CU) triaxial tests show a geomechanically brittle behaviour at all test conditions. The brittle behaviour is mainly due to diagenetic siderite cement. During the rock mechanical consolidation phases only minor reductions in the pore volumes took place. During the induced shear deformation local orientation of small mica grains parallel to the direction of shear occurred in the vicinity of the failure zone. The small fabric changes observed in the SEM are in agreement with the low deformations seen from the CU triaxial test data of the Springar Fm.