Geomechanical Modeling of Wellbore Stability in Anisotropic Salt Formation

Abstract

Abstract Exploration drilling is venturing out into deeper regions of water. While exploring these deeper water depths, large hydrocarbon deposits have been found below salt formations. These reservoirs are located in formations called "pre salts," which are located below the salt formations. Pre-salt reservoirs have been found in Brazil, the Gulf of Mexico, West Africa, and the North Sea. Completions in salt formations can be difficult owing to the creep behavior that the salt formations exhibit. Creep behavior results from the instability of the salt formation, which causes a slow flow and results in permanent deformations. Creep and deformation occur over time and are initiated once the salt formation has been penetrated. Completion of the wellbore does not stop formation creep. The constant creep of the formation causes excess stress on the well completions, which will eventually cause the casing to collapse. This study presents a geomechanical model, which can be used to predict the in-situ casing stress in a salt formation throughout the lifetime of a well. The model incorporates various parameters, like formation and wellbore pressure and formation temperature, as well as casing, cement, and rock properties. In addition, the impact of variations in temperature around the wellbore, drawdown pressure during production, the shape of the wellbore, and formation anisotropic properties are also investigated. The results indicate that many well-established factors that affect wellbore stability in a conventional and non-creep formation may not be valid in salt formations that exhibit creep behavior.