A Wellbore Stability Assessment should be on the check list of all well design requirements.

Conducting an offset review to derive the required mud weight is part of the solution. As different inclinations and azimuths change the effective stress on the wellbore wall the onset of failure can easily be induced.  If you can identify two or more of the problems listed you will probably need a WBS.

• Weak formations
• Low / high stresses / high anisotropy
• Elevated pore pressures
• Depleted reservoir
• HP or HT or both
• Fractures
• Coal
• Severe turning geometries
• Extended Reach
• Deep water

• More than 4% hole problem related NPT
• AFE overruns due to hole problems
• Unable to achieve all the subsurface objectives
• Unable to meet technical limit targets
• Evidence of breakout in vertical / low inclination wells (caliper ovality)
• Routine overpull exceeding 20k
• Evidence of pack offs
• ‘Waves’ of cavings
• Backreaming and short trips required