New cement slurry formulations containing colloidal silica have been used in North Sea primary cementing operations to help control annular gas migration, enhance slurry "turbulent flow" characteristics without solids settling, and aid cement bonding to formation and casing. Colloidal silica slurries have been successfully placed as lightweight lead cements in intermediate casing operations, and have effectively sealed annuli in gas storage wells and in horizontal completions.

Silica cementing additives have been used often for gas migration control, slurry stability, and high-temperature applications in the North Sea. However, because of its extensive specific surface area (500m2/g), colloidal silica adds additional benefits. Colloidal silica is more efficiently handled in offshore operations because less bulk material is required. The reduced volumes also reduce overall slurry cost. Because colloidal silica particles are so fine, there is virtually no settling of the base material in containment offshore.

A discussion of colloidal silica slurry properties is contained in this paper. Performance properties are presented in relation to each of its various well applications. A case history of a horizontal well is also given that describes the practical use of colloidal silica cement.

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