Assessing the Impact of Parameter Interdependence on Wellbore Stability Analysis and Strategic Decisions

Summary The literature on wellbore geomechanics discusses uncertainty analysis of wellbore stability considering uncertain geomechanical parameters. However, the interdependence of these parameters and their impact on decision-making has yet to be addressed. This paper demonstrates how the correlation of input parameters influences drilling decisions. The traditional approach of Monte Carlo simulation and single-factor sensitivity analysis, which assumes independent parameters, was compared to a strategy that considers correlated parameters. The effect of each pair of correlated parameters was assessed using a correlation matrix. A reliable limit for a safe mud window was determined, and the consequences of the best- and worst-case scenarios of wellbore instability were assessed using a decision tree. The findings highlight the crucial impact of parameter correlations on wellbore stability, particularly when drilling relies on percentiles such as P10 and P90. In fracture pressure prediction, strong correlations significantly narrow upper and lower bounds compared to independent parameters. This impact is more significant in fracture pressure than in collapse pressure. Additionally, single-factor sensitivity analysis ranks parameters differently than interdependent sensitivity analysis. The proposed decision-based approach of wellbore stability analysis supports informed decision-making in the planning stage and enhances decision quality.