Selecting Safe Mud Weight Window for Wellbore in Shale While Drilling Using Numerical Simulation

Abstract

Abstract In conventional drilling, the lower bound of the safe mud weight window is usually chosen for preventing compressive shear yielding evaluated by applying various failure criteria, such as the Mohr-Coulomb criterion on the elastic stresses, while the upper bound is typically determined by the fracture initiation pressure. For the wellbore drilled in shale formation, however, the lower bound calculated using a conventional method becomes unsafe because of the complications introduced by various shale issues, such as bedding planes. In this paper, two approaches are used for computing the safe mud weight window for wellbore drilled in shale formations. In the first approach, the effect of bedding planes is absorbed in the equivalent rock strength properties in the theoretical analysis. The second approach involves performing direct numerical simulation with bedding planes modeled explicitly in the constitutive model. A case study indicates that the two approaches provide consistent results.