SOLID GEO MECHANICAL INVESTIGATION OF THE EFECT OF SALT CREEP ON CASING STABILITY USING FNITE ELEMENT METHOD: A CASE STUDY

Abstract

The salt formation creeping can signifcantly afect the casing stability, because of the changes in mechanical and geome chanical parameters. The creeping of Gachsaran salty formation in the south part of Iran has infuences on wells drilled in the region, which should be carefully considered in the casing design process. In this study, the fnite 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. Diferent scenarios were studied to analyze the efect of geomechanical parameters on stress, plastic strain, and casing diameter for a cased cemented well and a well completed with two casings. The efect 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 afected 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 signifcantly For a safe casing design, efect of mechanical parameters should be also considered. Efects 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.