Effect of formation strength anisotropy on wellbore shear failure in bedding shale

The shale gas/oil is playing an important role in the current energy resources. However, the wellbore instability problems bring a high risk to drilling engineering especially in the formation with bedding planes. A normal wellbore stability analysis approach is based on elasticity, which is not enough to recognize the mechanisms. In this paper, the poroelasticity was adopted to present the hydro-mechanical coupling effect in shale formation, meanwhile, the permeability anisotropy which could affect the effective stresses around the well was considered. A three-dimensional finite difference model was developed to simulate arbitrary directional well in shale by the coordinate transformation method. The jointed material model was proposed to character the strength anisotropy and plastic behavior of bedding shale. Additionally, the effects of well trajectory, bedding plane orientation and mud weight on shale wellbore stability were discussed, thus some implications for improving wellbore stability in bedding shale formation were obtained from the proposed model.