Compaction bands simulated in Discrete Element Models

Compaction bands, i.e. tabular zones that accommodate compaction but no shear, have recently been observed in high-porosity sandstone, where the dominant micromechanism is grain breakage and crushing. Such bands are extremely important for hydrocarbon extraction, forming barriers that might inhibit the flow. They have further been associated with borehole stability problems. However, compaction band initiation and propagation remain poorly understood, while the necessary material conditions for their formation require further investigation.Three-dimensional Discrete Element Method simulations of the stressing of a sandstone sample were conducted. These successfully reproduced a discrete compaction band; its initiation and propagation are shown. An investigation into the effects of the cementation bond strength and the post-fragmentation behaviour of the grains on the observed behaviour is also presented. Well-localised discrete bands were observed when both the bond strengths were high and the grains lost their load-bearing capacity after being broken. On the contrary, an advancing crushing front resembling a diffuse compaction band was observed in simulations where the broken grain could still carry force. The data presented here provide the micromechanical insight necessary for a better understanding of conditions leading to compaction band initiation and propagation, which might facilitate identification of rocks that might form them.