Cementing – is the placement of a liquid cement slurry in the annulus between a casing and an open hole or previous casing. Providing the well integrity through long-term zonal isolation is the most important function of cement. Without durable zonal isolation the well may never reach its full producing potential. Well cements encounter a wide range of environments, including high temperatures and pressures, corrosive fluids, weak or porous formations. To accommodate for all these conditions various cementing additives have been designed. Additives modify the behaviour of the cement system to allow successful slurry placement and performance.