Steam injection is the most widely method used for heavy and extra heavy oil production in the oil industry. However, the high temperature of the steam expands the casing and the cement sheath causing mechanical failures such as cracks, loss of zonal isolation and de-bonding between the cement and the casing. To compensate the difference between their respective thermal expansion coefficients and provide better mechanical properties to the sheath, the following work proposes the addition of fluoroelastomer (FKM) by 2%; 5%; 7% and 10% BWOC in the dry blend. All cement slurries have 13 ppg (1,56 g/cm³) density and were designed at 47°C (BHST) for 7 days or 28 days. To simulate the steam injection conditions, the slurries were cured at 300°C and 2000 Psi (13,8 MPa) for the last 3 days of the period of 7 days or 28 days. The FKM was chosen because its appropriated mechanical, chemical and thermal properties for the oil well scenario and it is also used in oil industry like plugs, packers and O-rings. Laboratory tests were performed to obtain the values of compressive strength, Poisson's coefficient and Young's modulus. The identification of the crystalline phases was done through XRD. The morphology and thermal integrity of the FKM at the cement slurry were analyzed through SEM, TGA and DSC. The study shows that FKM is thermally suitable for steam injection conditions, it is chemically inert to crystalline phases of cement. After the steam cycle at 300°C and 2000 Psi,  the compressive strength increased by 15% and the Poisson’s coefficient by 18% when compared to the bottom hole static temperature (47°C).