Modeling fracture propagation from brittle to ductile layers

In this study, we use empirically-derived formulae based on linear elastic fracture mechanics to calculate the time and rate of propagation of a fracture across the boundary between a brittle and a ductile layer, as a function of strain, layer thickness and mechanical contrast between the layers. We show the fractures are most likely to be arrested at the interface in thin layers, or when the contrast in subcritical propagation index or crack energy between the layers is high. They are more likely to propagate into the ductile layer if the brittle layer is thick, or if the applied strain is increasing. These results can be used to predict potential for pressure communication between isolated reservoir beds, or risk of top-seal failure by subcritical hydraulic fracture propagation.