3D Geomechanical Modeling of Salt-Creep Behavior on Wellbore Casing for Presalt Reservoirs

Exploration drilling is venturing into deeper regions of water. During the exploration of these deeper water depths, large hydrocarbon deposits have been found below salt formations. These reservoirs are called presalts, which are below the salt formations. Presalt reservoirs have been found in offshore Brazil, the Gulf of Mexico (GOM), West Africa, and the North Sea. Completions in salt formations can be difficult because of the creep behavior that the salt formations exhibit. Creep behavior results from the instability of the salt formation, which causes a slow flow and permanent deformations. Creep deformation occurs over time and begins once the salt formation has been penetrated. Completion of the wellbore does not stop formation creep. The constant creep of the salt formation causes excess stress on the wellbore casing, which may eventually cause the casing to collapse. In this study, a 3D geomechanical model is developed, by use of data such as wellbore pressure and temperature; formation stress and temperature; rock, cement, and casing properties, to predict the effects of salt-creep behavior on stress loading in the wellbore casing, which helps to assess the life expectancy of wells in presalt reservoirs. The simulation results of this model can provide quantitative results of casing stress and deformation as a function of time under various temperature, in-situ-stress, and operation conditions, which can be used as useful information for subsequent wellbore-casing design and wellbore-integrity analysis. In addition, possible methods that can mitigate the severity of salt mobility and reduce the risks of casing collapse are discussed.