Annular-sealant mechanical properties are critical factors in well success. High-pressure/high-temperature (HP/HT) conditions place unique demands on the mechanical design of a sealant. Finite element models (FEM's) were used to determine the influence of wellbore stability and the effect of loading on sealant integrity. Sealant mechanical properties considered were elasticity, and tensile, shear, and bonding strengths. Typical oilwell cement, latex, foamed, and hybrid slurries were investigated. The study indicated a strong relationship between sealant behavior, formation in-situ stresses, formation properties, and well-completion parameters.