A Comprehensive Uncertainty Assessment of Wellbore Stability Models

Wellbore instability problems are often complicated and costly to solve and may endanger the success of the complete well construction process. For many years, different wellbore stability models are presented to study the state of stresses around the borehole and finally evaluate its stability or failure under the given circumstances. As the majority of the input parameters to the stability models are subjected to errors and uncertainties, therefore the model output, which is the minimum mud pressure required to prevent from the well collapse, is considered as an uncertain parameter. In this work, a Monte Carlo simulation as a quantitative probabilistic method is performed to assess the effect uncertainties in the input parameters on the performance of poroelastic stability model. Results of the Monte Carlo simulation for the given input parameters show that at mud pressures larger than 38 MPa, the probability of the wellbore stability is more than 90% and accordingly the wellbore collapse occurs with a probability of less than 10%. It also can be concluded that the probability of the well stability does not change significantly at different azimuth angles.