Fluid-driven fractures in layered hydrogels

The formation of fractures in low permeability rocks facilitates fluid transport and storage. Reservoir rocks, including shale exhibit strata or layers of varying composition and mechanical properties. To model how liquid-filled fractures propagate through layered media, we use laboratory-scale experiments. We study the geometry of the fracture that forms and propagates upon injection of a low-viscosity fluid in a block of hydrogel composed of two layers with different stiffness or Young's modulus. Our experiments show that the fracture geometry depends on the layer in which it is initiated. A fracture formed in the soft layer does not propagate in the stiff layer. A fracture formed in the stiff layer rapidly transfers into the soft layer when it reaches the interface between the two layers. Scaling arguments are provided to explain the experimental results and provide insights into the propagation of fractures in geological rock formations.