New Analytical Model for Predicting the Unstable Zone Around the Borehole

Abstract

Summary In this study, a new analytical model, which is computationally lower in cost than current numerical methods, is presented to calculate the radius of the plastic zone around the borehole in underbalanced drilling (UBD) to prevent borehole instability. With this model, it is also possible to analytically calculate the optimal drilling-mud weight, which is the amount of mud weight with no plastic zone. The presented model is based on the Mouhr-Coulomb failure criterion. The model can be used in both vertical and inclined wells and in poroelastic formations with anisotropic horizontal stresses. Predictions from the model provide a reasonable match to the field data and numerical solution results.