Primary cementing is the process of placing cement in the annulus between the casing and the formations exposed to the wellbore. The major objective of primary cementing has always been to provide zonal isolation in the wellbore of oil, gas, and water wells to exclude fluids such as water or gas in one zone from oil in another zone. To achieve this objective, a hydraulic seal must be obtained between the casing and the cement. And between the cement and the formations, while at the same time preventing fluid channels in the cement sheath. This requirement makes primary cementing the most important operation performed on a well. Without complete zonal isolation in the wellbore. The well may never reach its full producing potential. Remedial work required to repair a faulty cementing job may do irreparable harm to the producing formation.