Over the last two decades, there has been an increased focus on the stability of the cement sheath under the influence of shear stresses imposed during the lifetime of the well.Shear stresses can occur on pressure testing or due to temperature fluctuation on the casing during well production, fracturing and in extreme cases on geological shifts over time.In order to mitigate the effect of shear stresses, the mechanical properties of the cement sheath are investigated and improved on addition of fibers for tensile strength and elastomeric material for enhanced Youngs modulus and Poissons ratios.It has also been demonstrated that modification of the C-S-H matrix, as on addition of nano-particles, can also improve the mechanical properties and resistance to external stresses.