Wellbore-stability analysis made easy and practical

Recent years have seen much scientific and technical progress in the understanding of wellbore stability. The main causes of instabilities have been identified, models have been developed, and practical remedies proposed and often tried successfully in the field. Yet despite this scientific effort, extra drilling costs associated with wellbore instabilities remain very high. This demonstrates that until now, scientific and technical progress has somehow failed to reach final technical and economical objectives. This paper shows that the main reason for such a state of affairs is the complexity of wellbore-stability analysis, which cannot be performed for every single well on a worldwide basis. Having identified this, Agip undertook a vast effort of field-data back analysis to identify from historical records the best way to optimize its drilling planning, practice, and post-evaluation procedures. The paper presents part of this effort and in particular the back analysis of four clusters drilled in southern Italy (a total of 38 wells). It then draws conclusions for procedure optimization. Finally, it shows how the approach is used during the field-appraisal phase to speed up the learning curve and significantly cut the development-drilling costs.