Brittleness of shales: Relevance to borehole collapse and hydraulic fracturing

Plasticity plays an important role to stabilize a borehole against collapse. Borehole stability modeling shows that a decrease in brittleness (corresponding to increased plasticity) may stabilize a borehole which otherwise could not have been drilled in stable conditions. In fracturing operations, the local state of stress, geological heterogeneities (including natural fractures) and the anisotropic poro-elasto-plastic behaviour of the shale formation, controls the resulting efficiency. This includes brittleness, but requires a better understanding of the complex mechanics of the fracturing process.