Characterization of shear and compaction bands in a porous sandstone deformed under triaxial compression

The study of localized deformation in porous sandstones at the laboratory scale can yield valuable insights into the internal structures and mechanisms of shear zones and compaction bands that might impact on flow at a reservoir scale. Herein, we report results of a laboratory study of shear and compaction band formation in a porous sandstone using a range of full-field experimental techniques: acoustic emissions, ultrasonic tomography, X-ray tomography, and 3D volumetric digital image correlation, plus thin section and Scanning Electron Microscope observations. The two main mechanisms involved in shear and compaction band formation, grain breakage (damage) and porosity reduction (compaction), are both well captured by the combination of all these laboratory techniques. The combined use of these techniques demonstrated the processes of shear and compaction band generation and the associated strain components that developed in the laboratory, and potentially also increased understanding of the naturally developed equivalents. The physical mechanisms of shear and compaction involved seem to be similar, but at the laboratory scale they show differences in the proportions and the order of occurrence in time.

Research Highlights
► Combination of full-field methods to study shear and compaction bands in sandstones.
► Strain, density & ultrasonic velocity changes indicate cracking & porosity decrease.
► Similar mechanisms in both shear and compaction bands.
► Differences in their proportions and their order of occurrence in time.
► Quantification of shear and volumetric strain fields in both deformation bands.