Density, cement slurry additives

Foamed cement slurries have been used to provide a low density cement slurry to reduce permeability damage to highly sensitive formations through reduced fluid loss (29). Glass microspheres have also been used to substantially reduce cement slurry density (30, 31). Other additives which reduce cement slurry density to a lesser extent include bentonite, fly ash, silicates, perlite, gilsonite, diatomaceous earth, and oil emulsions (see citations in reference 29). 

The high fluidity (low viscosity) of the slurry is necessary for adequate penetration of the dense fibre array in the mould. By the addition of fly ash and fine sand, the Portland cement content may be diminished and possible shrinkage cracking reduced. Vibration of pre-placed fibres before and after pouring of cement slurry is often advisable in order to improve the density and distribution of reinforcement. External pressure should also be applied. 

Materials formed by acid-base reactions between calcium aluminate compounds and phosphate-containing solutions yield high-strength, low-permeability, C02-resistant cements when cured in hydrothermal environments. The addition of hollow aluminosilicate microspheres to the uncured matrix constituents yields slurries with densities as low as approximately 1200 kg/m, which cure to produce materials with properties meeting the criteria for well cementing. These formulations also exhibit low rates of carbona-tion. The cementing formulations are pumpable at temperatures up to 150° C. 

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