Modeling of fault slip during hydraulic stimulation in a naturally fractured medium

Assessing the intensity of potential seismicity induced by fault slip is a mandatory task in the development of enhanced geothermal systems. In this paper numerical simulations are performed to investigate the propagation of hydraulic fractures and the slip behavior of existing faults due to fluid injection. The cohesive zone model is used in combination with finite cohesive elements to model the hydraulic fractures and the existing faults while the fault shear strength is assumed to follow the Coulomb friction law. Our focus is on the role of the friction conditions on the fault slip behavior. The simulation results show that faults with small friction coefficients tend to slip at low slip rates while faults with a higher friction coefficient tend to slip at rates that are higher than the unstable slip rate threshold. It is also demonstrated that under specific frictional conditions, the sequential stimulation mechanism of permeability enhancement is possible. The results suggest that a good characterization of the fault frictional conditions is required to successfully predict the fault slip pattern and that lowering the fault friction coefficient could potentially reduce the fault slip rate.