Compaction bands in a porous sandstone sample with pre-induced shear bands

Abstract

Understanding how different modes of deformation bands may interact at the same rock mass is of crucial importance, since such interaction may affect the flow properties within the reservoir rock. In this work we focus on the compaction band nucleation and evolution within a porous sandstone, in which a shear-band has been previously developed. For such a purpose, we performed at the laboratory scale triaxial compression experiments under 20 and 185 MPa confining pressures on a single Bentheim sandstone specimen. Acoustic Emissions (AE) were recorded throughout all experimental stages. AE hypocentre locations and AE source mechanisms were used to describe the spatiotemporal evolution of the developed deformation bands. The shear band evolution was AE controlled. Shear type sources were the prevailing mechanisms up to the peak stress, whereas, the shear band growth was mainly dominated by compressive type sources. The compaction band nucleated at the tip of the pre-existing shear band and evolved towards the circumference of the specimen. A second compaction band nucleated with increasing axial strain at the top part of the specimen and not far from the already developed shear and compaction bands. The dominant mechanisms during the compaction band initiation and formation were compressive type sources.