Compaction of sand aggregates: mechanical and acoustical characteristics under triaxial conditions

Mechanisms such as grain rearrangement and breakage play a key role in determining porosity and permeability reduction during burial of clastic sediments. In poorly consolidated sandstones, these processes often lead to significant reduction in porosity through the development of compaction bands. The reduced porosity and permeability of such bands produce natural barriers to flow within reservoir rocks. Such time-independent compaction processes operating in highly porous water- and hydrocarbon-bearing clastic reservoirs can exert important controls on production-related reservoir deformation, subsidence, and induced seismicity.
We performed triaxial compression experiments on Ottawa sand aggregates. All tests showed deformation involving elastic grain contact distortion, particle rearrangement, and grain failure. Acoustic data and grain size analysis suggested that at low confining pressure grain rearrangement controlled compaction, with failure focussing along a broad shear plane. At higher confining pressure pervasive grain failure clearly accommodated compaction, though no strain localization was observed and failure appeared to be through cataclastic flow. Chemical environment had no significant effect on compaction in the strain rate range tested. Grain size distribution or grain shape also appeared to not affect the observed mechanical behaviour. Our results can be used to better understand the compaction behaviour of poorly consolidated sandstones.