COMPACTION BANDS AS ANTICRACKS IN SANDSTONE: TAMING COMPLEXITY THROUGH INTEGRATED OBSERVATION, EXPERIMENTATION AND PROCESS-BASED SIMULATION

Compaction Bands (CBs) are distinct, tabular, bounded features of highly localized porosity loss that occur as systematic to chaotic arrays in deformed sandstone. Abundant field evidence suggests that individual CBs propagate and interact as closing-mode anticracks within a nominally elastic granular medium. In order to test and develop this conceptual model, we are investigating CB behavior both experimentally and numerically. As constrained by field evidence, our experimental results indicate that stress concentrations generated at random depositional flaws in response to tectonic loading at low confining pressures can initiate a self-sustaining domino-like pore collapse accommodated by granular rearrangement in uncemented sands and poorly cemented sandstones. Our numerical modeling results, based on linear elastic fracture mechanics and the displacement discontinuity boundary element method, further demonstrate that, once started, CBs will tend to self organize via mechanical interaction to form systematic patterns. Striking similarities between the simulated and outcrop CB patterns argue strongly in favor of the anticrack conceptual model. Previous numerical studies have demonstrated that typical patterns of low-porosity CBs can reduce effective bulk permeability by as much as two orders of magnitude, while inducing equivalent degrees of permeability anisotropy. Given this potential to restrict subsurface fluid flow, developing a predictive mechanical understanding of how and under what conditions CBs form is of prime importance for optimal aquifer and reservoir management.