  Shear dilation based hydraulic stimulations enable exploitation of geothermal
energy from reservoirs with inadequate initial permeability. While contributing
to enhancing the reservoir's permeability, hydraulic stimulation processes may
lead to undesired seismic activity. Here, we present a three dimensional
numerical model aiming to increase understanding of this mechanism and its
consequences. The fractured reservoir is modeled as a network of explicitly
represented large scale fractures immersed in a permeable rock matrix. The
numerical formulation is constructed by coupling three physical processes:
fluid flow, fracture deformation, and rock matrix deformation. For flow
simulations, the discrete fracture matrix model is used, which allows the fluid
transport from high permeable conductive fractures to the rock matrix and vice
versa. The mechanical behavior of the fractures is modeled using a hyperbolic
model with reversible and irreversible deformations. Linear elasticity is
assumed for the mechanical deformation and stress alteration of the rock
matrix. Fractures are modeled as lower dimensional surfaces embodied in the
domain, subjected to specific governing equations for their deformation along
the tangential and normal directions. Both the fluid flow and momentum balance
equations are approximated by finite volume discretizations. The new numerical
model is demonstrated considering a three dimensional fractured formation with
a network of 20 explicitly represented fractures. The effects of fluid exchange
between fractures and rock matrix on the permeability evolution and the
generated seismicity are examined for test cases resembling realistic reservoir
conditions.
