Application of the Damage Theory to the Modeling of Hydrofracture-associated Microseismicity

In this paper, we present a numerical model of geomechanical response of the reservoir to the propagating hydraulic fracture. The model includes the effect of the main fracture, poroelasticity, and new-forming fractures, and is capable of predicting microseismic activity. The paper has two parts. In the first one, we investigate how to model deformation of fractured poroelastic media using the damage theory by comparing the numerical results with analytical solutions of fracture opening in impermeable, porous, and jointed media. In the second part, we apply the damage theory to a simple case of unfractured wellbore to assess and understand the behaviour under simple conditions. The tests show that a continuous fracture can be modelled assuming the damage parameter D=1 in the fracture, and that the poroelasticity can be modelled using the damage parameter D=0 in the medium. The damage parameter of fractures that do not fully open, such would be shear fractures or fractures on a small scale, is smaller the damage of the open fracture. The new fractures have influence on the opening of main fracture such that more fracturing (microseismic events) tend to decrease opening of the main fracture.