Abstract
Wellbore stability problems are one of the major concerns during drilling oil and gas wells. The main factor causing difficulties in wellbore stability analysis is the uncertainty of the downhole conditions and underground formation properties. This work presents a quantitative risk assessment method to evaluate wellbore collapse risks by combining a thermal-poro-elastic model and quantitative risk assessment theory. All related parameters are classified into four categories by using two dimensions: uncertainty and importance. The formation uncertainties are evaluated by using historical data to improve the accuracy of the analysis. Sensitivity analysis is employed to obtain the influence ranking of low confidence parameters on wellbore stability, which provides guidance to recommend efforts in future data collection and analysis. All the analytical results are converted into a collapse risk index, which can be easily understood by the field engineers and provide useful guidance for drilling design and operations. A workflow is developed to apply the method in practical drilling design and real-time drilling operational monitoring, and field validation results show that the model can accurately capture the formations with high wellbore collapses incident rates.
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