Numerical modeling of casing collapse in Gachsaran formation in Sirri-E oilfield in Persian Gulf

Casing collapse is a costly phenomenon in drilling industry that occurred in different geological environment with different geomechanical property. Geomechanical and numerical analysis of casing collapse in Sirri-E, one of the offshore Iranian oilfield in Persian Gulf has been investigated in this work. In this study we tried to model several collapse loading of rock-cement-casing system under real condition of in-situ stress and geomechanical property of different lithology, cement and casing, to decrease simplified modeling assumption. A mechanical earth model is built to determine the accurate amount of in-situ stresses and different mechanical property of rock. This geomechanical data extracted from 1D geomechanical earth model and entered to numerical model involved formation, cement and casing. Furthermore the interactions between the casing and surrounding formation are simulated by applied elastic-plastic behavior for rock and cement. Also Joint property between different media considered to increase the accuracy of model to real condition of borehole at the collapsing depth. The result show that over pressured marl and salt have high potential for casing collapse and the maximum external load applied to the casing is very more than maximum mud weight that usually considered in API standard for design of casing. So it is necessary to use coupled data from mechanical earth modeling and numerical analysis to determine maximum lithostatic pressure applied to the casing.