Graphene is a 21st Century super material, that continues to break the ceiling in the materials world, as well as increase the strength of cement-based materials. Wellbore cement is brittle and subject to mechanical failure from variations in temperature and pressure. The thin sheets of graphene are suggested to occupy the space left by water during cement hydration and further improve the sealing capacity of the cement since graphene is hydrophobic and may not react within the hydration process. The objective of this study is to add natural high-grade graphene with carbon content ~ 92.8 wt, different from graphene oxide 41.5-72.6 wt%C, to cement and assess its mechanical and microstructural properties. Our target is to provide experimental evidence for improved mechanical durability, toughness, and scientific explanation of the mechanism that leads to more ductile wellbore cement. Electron microscopy was used to determine the structure and morphology of graphene and EDS to assess the chemical content and hence the purity of the graphene. SEM analysis was carried out on the samples to determine any alteration in the morphology of the graphene after contact with these solutions. Small amounts from 0.004% to 0.1% graphene are then added to class H cement (16.4 ppg enhanced) in preparation of cement core samples that were cured for 28 days, at 900C, and 95%RH. CT scans were obtained from fully saturated samples before any sample destruction. Microstructural characterization was performed on fractured and polished surfaces. A mechanical test was conducted under subsurface pressures and temperatures. Graphene greatly improved the shear strength of thecement by ~30% under triaxial loading with 0.1%wt added and reduced porosity of cement by ~12% with 0.05%wt. We are suggesting that the mechanisms by which graphene strengthens the cement are by settling in the pore spaces as well as provide a template for hydration to begin.