Wellbore stability analysis and application to optimize high-angle wells design in Rumaila oil field, Iraq

Abstract

Mechanical wellbore instability is one of the main issues during the drilling operations, this problem causes around 14% of drilling nonproductive time (NPT) for new wells in Rumaila oil field; these breakouts were commonly observed in the shale and weak shaly sandstones along Rumaila geological column. In this study, a quantitative wellbore failure analysis was carried out through applying modified Lade criteria on five wells in Rumaila oil field (A, B, C, E and F). The results gave a prediction of the appropriate mud density that can control the wellbore shear failure for any well type in order to eliminate or minimize wellbore instability and indicated that the preferred direction to drill deviated and horizontal wells should be parallel to maximum horizontal stress (NE–SW). The study also introduced the recommended drilling mud weight for vertical and deviated wells in Rumaila oil field for the sake of gaining wellbore stability which requires raising the drilling mud weight to more than 1.27 gm/cm3 starting from bottom of Sadi Formation to the well total depth. The results also showed that wells with low inclination (less than 30°) are less stable than highly inclination wells (more than 30°).