2. Conventional cement
The function of cement is for isolating production zone and to provide support for the casing .Portland cement is made up of calcium oxide (CaO), silicon dioxide (SiO) and water (H2O) which the composition of calcium carbonate is around 75-80 wt% and 20-25 wt% of clay ,.. Compressive strength of Portland cement is developed through hydration. Hydration is chemical reaction between water and cement compound. The rheology and early strength of cement is developed from reaction of aluminate compound at the beginning of hydration. Rate of hydration can be control by adding gypsum. It is for preventing the premature hardening of cement. Gypsum will react with aluminate and hydroxyl ion to form ettrigate. Ettrigate will prevent hydration process by forming needle shaped crystal on the aluminate and creating induction period .
Some addictive can be added to the cement to enhance the properties of cement. There are accelerator, retarder, extender, weighting agent, dispersant, fluid loss control agent and loss circulation agent .
Accelerator Use to speed up the early stages of hydration. Applicable in shallow well.
Retarder Inhibit hydration and slow the setting time of cement. Applicable in deep well.
Extender Reduce slurry density, thus reduce the hydrostatic pressure during cementing operation. Extender use to prevent break down and loss of circulation of weak formation.
Weighting agent Increase cement density by adding high