Solid-geo-mechanical investigation of the effect of salt creep on casing stability using finite element method: a case study

The salt formation creeping can significantly affect the casing stability, because of the changes in mechanical and geomechanical parameters. The creeping of Gachsaran salty formation in the south part of Iran has influences on wells drilled in the region, which should be carefully considered in the casing design process. In this study, the finite element analysis technique was applied to study the alteration in mechanical/geomechanical parameters of a well in this formation. The accuracy of the methodology was validated by data available from the reduction in wellbore diameter of another well in the formation. Different scenarios were studied to analyze the effect of geomechanical parameters on stress, plastic strain, and casing diameter for a cased cemented well and a well completed with two casings. The effect of mechanical parameters on casing collapse was studied, where casing eccentricity, ovality, and slenderness ratio were also considered. Our simulation studies showed that casing stability in salty formations is strongly affected by geomechanical and pipe mechanical parameters. To reduce the severity of the casing collapse in salty formation, it is recommended to complete the well with two casings. Our study showed that, this arrangement reduces the plastic strain and the change in casing diameter significantly For a safe casing design, effect of mechanical parameters should be also considered. Effects of parameters such as ovality, eccentricity, and slenderness ratio are noticeable, for example, 2% ovality and 2% eccentricity in L-80 casing, lead to increase in the plastic strain from 0.112 to 0.31 and 0.3, and the overall diameter reduction from 0.455″ to 0.685″ and 0.535″, respectively.