  Hydraulic stimulation is a critical process for increasing the permeability
of fractured geothermal reservoirs. This technique relies on coupled
hydromechanical processes induced by reservoir stimulation through pressurized
fluid injection into the rock formation. The injection of fluids causes
poromechanical stress changes that can lead to the dilation of fractures due to
fracture slip and to tensile fracture opening and propagation, so-called
mixed-mechanism stimulation. The effective permeability of the rock is
particularly enhanced when new fractures connect with pre-existing fractures.
Mixed-mechanism stimulation can significantly improve the productivity of
geothermal reservoirs, and the technique is especially important in reservoirs
where the natural permeability of the rock is insufficient to allow for
commercial flow rates. This paper presents a modeling approach for simulating
the deformation and expansion of fracture networks in porous media under the
influence of anisotropic stress and fluid injection. It utilizes a coupled
hydromechanical model for poroelastic, fractured media. Fractures are governed
by contact mechanics and allowed to grow and connect through a fracture
propagation model. To conduct numerical simulations, we employ a twolevel
approach, combining a finite volume method for poroelasticity with a finite
element method for fracture propagation. The study investigates the impact of
injection rate, matrix permeability, and stress anisotropy on stimulation
outcomes. By analyzing these factors, we can better understand the behavior of
fractured geothermal reservoirs under mixedmechanism stimulation.
