Plasticity-Based Interpretation of Compaction Banding in a High-Porosity Carbonate Rock

Abstract:

Compaction bands are among the most elusive forms of strain localization, especially for what concerns the applicability of laboratory measurements to field problems. It is therefore pivotal to integrate experiments, analytical theories and computational methods to explain laboratory observations and predict the expected strain localization modes for field-specific conditions. Based on this idea, here we provide a mechanistic interpretation of the compaction banding patterns observed in a high-porosity carbonate rock. Such interpretation has been based on an elastoplastic model able to capture the phenomenology of rock deformation in the brittle-ductile transition regime. Data from several axisymmetric stress paths and the strain localization theory have been used to calibrate the model parameters. The model has been then implemented into a finite element code to predict the global response of rock specimens, as well as the characteristics of the localization patterns. The study shows that stress paths able to engage the plastic resources of the rock alter irreversibly the compaction banding potential and affect the geometric features of the deformation bands. Since these effects depend on the constitutive properties, they can be conveniently used to improve the parameter calibration procedure and reduce the number of experiments. The simulations have also shown that specific combinations of boundary conditions and initial heterogeneity exert an important control on the pattern of localized compaction emerging from laboratory experiments. As a result, the interpretation of such localization modes may not be necessarily regarded as a pure product of the constitutive response, but rather as the outcome of interactions between structural effects, boundary conditions, heterogeneities and rock properties.