Special Additives

There are a number of additives that do not fit neatly into functional groupings. Fibers are used for controlling lost circulation. Special types of fibers also improve the impact resistance and tensile strength of cement. The flexibility of cement can be improved by the use of special additives. This increase in flexibility provides increased resistance to failure by mechanical stresses imposed on the cement during well operation. Granular salt (sodium chloride) and potassium chloride are used primarily to change the ionic nature of the water in the slurry, which helps to minimize adverse formation interactions. In cases where the formation is salt, high concentrations of salt, up to saturation, are commonly

used to prevent leaching salt from the borehole wall.

Silica is used to combat strength retrogression, which is a change in the hydration products that are formed when cement is exposed to high temperatures (>110°C [230°F]). Silica is available in coarse or fine grades for cementing.