Injection-driven deformation of a fractured material

Hydraulic fracturing, or fracking, involves injecting fluid into a low-permeability reservoir rock at high pressure in order to open a network of fractures, which act as high-permeability pathways. However, most reservoir rocks have a pre-existing network of natural fractures. The impact of these existing fractures on the hydraulic fracturing process is difficult to predict, involving the nonlinear coupling of fluid flow with rock deformation and failure in a complex (fractured) geometry. Here, we study this problem experimentally in a model system: fluid injection into a cemented packing of soft particles, which behaves as a cohesive poroelastic material. We insert "natural" fractures into the system by manually cutting the bonds between particles in specific places. We then inject fluid into the packing at a constant rate and measure the dynamic strain field at high resolution using particle tracking. Comparison of the strain field with and without pre-existing fractures reveals their strong and nonlocal impact on both flow and deformation.