The Effect of Cement Type on the Occurrence and Nature of Compaction Localization in Three High-porosity Sandstones

Compaction bands are a type of strain localization structure which form perpendicular to the maximum principal stress in the subsurface and can significantly disrupt fluid flow in porous sandstone reservoirs, potentially impacting on industrial fluid injection/extraction. Although recent studies have highlighted the control that certain microstructural properties have on compaction band formation, the role of cement has generally been overlooked. To examine this problem, we performed triaxial tests on three sandstones, with very similar microstructural properties, such as porosity (~26-29%) and grain size (~230-300 µm), but with different cement types. Each sample formed discrete compaction bands when taken to 5% axial strain at a starting effective stress equivalent to 85% of its hydrostatic yield (P*) value. However, the location and distribution of the compaction bands differed within each sample. In Bentheim, which is cemented with strong syntaxial quartz overgrowths, the compaction bands were only located at the sample ends. By contrast, in Castlegate, which is weakly cemented with clays, the compaction bands were distributed throughout the whole sample and in the amorphous quartz-cemented synthetic sample, the bands were only present across the sample center. Our results suggest that the cement type plays a significant role in the micromechanics of deformation within each of the samples, which in turn, determines where the compaction bands nucleate and grow. Additionally, since all the compaction bands identified were discrete (≤3 grain diameters in width), rather than diffuse (>3 grain diameters in width) as typically seen in nature, we suggest that cement is not the primary control regarding the preference for the formation of diffuse or discrete compaction bands. Our study highlights the potential importance of cement in compaction band nucleation in sandstones.