  In fractured poroelastic media under high differential stress, the shearing
of fractures and faults and the corresponding propagation of wing cracks can be
induced by fluid injection. Focusing on low-pressure stimulation with fluid
pressures below the minimum principal stress but above the threshold required
to overcome the fracture's frictional resistance to slip, this paper presents a
mathematical model and a numerical solution approach for coupling fluid flow
with fracture shearing and propagation. Numerical challenges are related to the
strong coupling between hydraulic and mechanical processes, the material
discontinuity the fractures represent in the medium, the wide range of spatial
scales involved, and the strong effect that fracture deformation and
propagation have on the physical processes. The solution approach is based on a
multiscale strategy. In the macroscale model, flow in and poroelastic
deformation of the matrix are coupled with the flow in the fractures and
fracture contact mechanics, allowing fractures to frictionally slide. Fracture
propagation is handled at the microscale, where the maximum tangential stress
criterion triggers the propagation of fractures, and Paris' law governs the
fracture growth processes. Simulations show how the shearing of a fracture due
to fluid injection is linked to fracture propagation, including cases with
hydraulically and mechanically interacting fractures.
