Stability Analysis of Wellbore in Shale Layers, Case Study: Ahwaz Oil Field

Shales are found in over 75 % of drilled profiles and create 90 % of wellbore stability problems. During drilling in shale formation using numerical and analytical methods and considering correct and logical parameters one can decrease the costs of wellbore walls instability. This study has been performed on the effect of physical and geomechanical properties of shale on wellbore stability in one of Iranian oil fields. In this study, a stability analysis of unstable shales has been done in a well section by numerical (FESTO3 software) and analytical methods. The mud weight window for different states of in situ stresses was suggested using analytical method. One of these states was studied and the optimum mud weights were proposed by numerical method and the results were compared. The research shows that understanding the state and magnitude of principal stresses can drastically affect the analyses.