A geomechanical study of Bakken Formation considering the anisotropic behavior of shale layers

In this study, the geomechanical behavior of the shale layers is investigated in various capacities under isotropic and anisotropic scenarios. Primarily, an accurate estimation of geomechanical properties is carried out. Different geomechanical parameters including Young's modulus, Poisson's ratio, and rock strength for both isotropic and anisotropic modes are estimated based on field investigations for all three members. Dynamic elastic moduli are estimated from advanced acoustic log tests, and static moduli are measured in the laboratory. Then, a comparison is made, and a correlation is developed to convert dynamic to static elastic properties. Consequently, stress alteration and deformation changes around the boreholes are modeled in response to drilling. Measured parameters are utilized in a finite difference numerical model to predict rock deformation and stress variation. Based on the geomechanical models, stress regimes and medium deformations around the borehole are compared in both anisotropic and isotropic circumstances. Moreover, the effects of wellbore inclination on stress distribution, wellbore deformation, and yielding zones are discussed. The effects of wellbore inclination on stress distribution are monitored by studying horizontal principal stresses. According to the results, the relative plasticity radius of the medium is determined by dividing maximum radius of the yielded zone by the primary radius of the wellbore. Consequently, the failure zones and relative plasticity radiuses are compared for different well inclinations from vertical to horizontal wellbores. The relative plasticity radiuses are shown constant from vertical borehole to the borehole with 45 degrees of inclination with a gradual increase in values towards a horizontal borehole.