ABSTRACT:

Wellbore instability problems are often encountered during drilling processes of highly deviated wells, although a comprehensive geomechanical model is conducted. The low quality of the input data for the geomechnics models is the root cause of the vast majority of the drilling events. Therefore, the quality control is strongly required to ensure problems-free wellbore. In this regard, uncertainty and sensitivity analysis to the stresses and rock strength parameters are carried out in this study to improve preciseness of the geomechanical model. The Tornado chart is constructed to present the high sensitive parameters of the geomechanical model, while the Monte Carlo simulator is used to determine the less certain parameters. Furthermore, history matching procedure is introduced to validate some key variables in the model. Data from twenty-seven wells in an oil field in southern Iraq is implemented to maintain the wellbore integrity for the upcoming wells. Thus, this work can be presented as decision-making guideline not only to mitigate the drilling problems but also to reduce the unplanned costs.

1. INTRODUCTION
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