Estimating the Optimum Mud Pressure by Using the Different Failure Criteria in Deviated Wells

Wellbore instability is one of the important problems in drilling operations. Because this problem can delay drilling operation، increase drilling cost and in some cases can be the cause of the loose well. The cost of these problems is estimated to be more than two billion dollars in a year in the world. If proper physical and chemical mud properties are selected، more stable wells can be obtained. By using the rock mechanics sciences along with the complete cognition of the mechanical properties of the formation، the optimum well trajectory and mud weight window will be determined. Many ingredients are influential in well trajectory design; thus knowing and correctly using these ingredients can affect the design of the optimum mud pressure and well stability. The analytical methods are more usable than the numerical methods، because they are simple and usable without knowing some parameters of rock and formation، which are not usually available at the beginning of typical project. In this paper، we are trying to analyze the stability of the 2SK5 well in the Salman oil field by using three failure criteria، namely Mohr-coulomb، magi-coulomb، and drucker-prager، and to compare the usage of these criteria in wellbore stability analyses. Finally، some suggestions for drilling in this oil field are made.