Finite element analysis of wellbore stability and optimum drilling direction and applying NYZA method for a safe mud weight window

Wellbore stability analysis, selecting the optimum drilling direction, and determining the safe and stable mud weight windows are among the major geo-mechanical challenges in the oil and gas industries. In this study, the wellbore stability analysis and the optimal drilling direction have been numerically modelled by finite element method (FEM) considering the importance of wellbore stability and recognizing instabilities using the data of Sivand oil field. The numerical modeling of wells behaviors has been performed in two modes of elastic and elastoplastic deformations using ABAQUS software. The numerical results have been done using the two failure criteria, namely Mohr-Coulomb and Drucker-Prager and compared together, considering the effect of intermediate principal stress, Drucker-Prager failure criterion has been selected as a suitable failure criterion for this study. In addition, the numerical results have shown that the vertical well is the optimal drilling direction. Then, by applying the NYZA method, the safe mud weight window has been determined. The validity of the proposed mud window for a vertical well has been approved by applying the Mohr-Coulomb analytical method. Finally, the safe and stable mud window for the vertical wellbore has been proposed.