Wellbore-Stability Analysis Considering the Weak Bedding Planes Effect: A Case Study

Wellbore stability in shale is often hampered by the detrimental effect of existing weak bedding planes on shear failure of the rock surrounding the borehole. This paper presents results from an analytical solution to the wellbore-stress problem that incorporates rock failure along weak bedding planes. The solution is used for the case study of a highly inclined well section in a laminated layer of troublesome shale with a strike-slip faulting regime above the target formation in Latin America. Findings indicate improvement in the estimated margin for the wellbore-breakout limit of drilling-fluid density, and, more prominently, the safest drilling direction by accounting for the presence of weak bedding planes in the related wellbore-stability analysis.