Wellbore Stability of Salt and Anhydrite Formation of Fauqi Oilfield in Iraq

Abstract

Salt and anhydrite formation of Fauqi oilfield in Iraq contains salt, anhydrite and shale. Complex situations have occurred in drilling process, such as overflow and sticking. The cores of the three lithology rock are fetched and their strength and creep mechanical properties are tested. Anhydrite is with higher strength and lower creep properties, and shale and salt is with lower strength and higher creep properties. The collapse pressure and fracture pressure of the three lithology rock are calculated. The safe density window of anhydrite is the most widest and there is no risk of wellbore instability, and the safe density window of shale is the narrowest and wellbore instability easily occur. The low limit of mud density to prevent shale and salt creep are calculated by power law model. The safe drilling density window is determined and successfully applied in drilling field.