Wellbore stability analysis made easy and practical

Recent years have seen many scientific and technical progress in the field of wellbore stability understanding. The main causes of instabilities have been identified, models developed and practical remedies proposed and often tried successfully in the field. Yet despite this scientific effort, drilling extra costs associated with wellbore instabilities remain very high. This in turn demonstrates that until now, scientific and technical progress have somehow failed to reach their final technico-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 in order 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 -i.e. 38 wells in total. It then draws conclusions in terms of procedure optimization. Finally, it presents how the approach is used during the appraisal phase of a field in order to speed up the learning curve and hence significantly cut the development drilling costs.