Coupled flow-stress-damage simulation of deviated-wellbore fracturing in hard-rock

In this study, the evolution of hydraulic fractures and micro-annuluses around wellbores was simulated using zero-thickness Pore Pressure Cohesive Elements (PPCE). A coupled flow-stress-damage (FSD) nonlinear finite element model which consists of deviated wellbore, perforation hole, micro-annulus, cement sheath and casing was established. The viscoelastic continuum damage induced by hydraulic fracturing is governed by the traction-separation law. Mohr-Coulomb law is used to determine the elastic and plastic behaviors of the cement sheath and surrounding rock. Numerical results show that micro-annulus propagates around the wellbore firstly, then it would gradually close. In addition, the sensitivities of rock parameters and in-situ stresses were also analyzed. It is found that, in the strike-slip stress regime, the width of fracture increases with the increasing deviated angle of wellbore. The fracture length increases with the increasing deviated angle of wellbore if the angle is smaller than 45°. However, if the deviated angle is above 45°, the fracture length decreases when the angle increases. When the bulk modulus is greater than 90 GPa, the fracture geometry keeps nearly unchanged. A higher Poisson's ratio increases the fracture propagation pressure and the in-situ stress differences can not effectively restrict the fracture height growth in hard formation.