A number of reservoirs around the globe are in deep environments, and often it is necessary to drill and cement through salt sections to reach them, such as in offshore Brazil. These reservoirs are mainly in deep water and are commonly referred to as pre-salt zones. It can be very challenging to drill and cement the salt section. The salt zones could be a few hundred meters thick, creep at high rates, and when in contact with drilling fluid and cement slurry, their chemical properties can change. The effect of salt movement or creep is addressed in this work.

Salt formations pose a unique challenge to the structural integrity of the wellbore by applying a time varying load on the cement sheath and casing. This load is caused by the existence of deviatoric stress and temperature variations. Deviatoric stress is the difference between formation in-situ stress and the wellbore fluid’s hydrostatic stress. When a salt formation creeps during a well operation, it does so to achieve a hydrostatic state such that the deviatoric stress is zero.

The present work is a study of cement sheath integrity under downhole thermo-mechanical loading conditions using finite element analysis (FEA). The effect of salt creep on the stresses experienced by the cement sheath at various stages in the life of the well, including drilling, cementing, shut-in, completion, and production, are simulated. A material model for salt creep is validated against experimental data reported in the literature. Multiple cement systems are compared for their effectiveness in providing zonal isolation for the life of the well. The effect of structural and thermal loads due to salt creep on cement are quantified through stresses in cement.

The method discussed in this paper should help the industry select cement formulations that can withstand stresses caused by salt movement during the life of the well. Method and case studies pertaining to offshore Brazil are presented and discussed in this paper.

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