Oilwell cements must be adjusted to the correct density in order to provide a suitable combination of pressure control during placement and low permeability and strength after setting. For some densities this can be done simply by choosing the water/cement ratio that gives the required density value. However, for low densities this would lead to sedimentation, free water and a weak set cement. Mineral extenders are added to low density slurries to increase the low-shear slurry viscosity and thus prevent settling, and if they also exhibit pozzolanic activity to strengthen the set cement. Hollow mineral spheres may also be used to increase the effective solid volume fraction of the cement without increasing its density.
Our bentonite, ECCAgel, is a non-treated (or natural) sodium bentonite which meets the requirements of API specificaion 13A/ISO 13500 section 11 (OCMA grade) for drilling fluids. At low doses it will increase the low shear viscosity of a cement slurry substantially, thus preventing sedimentation, but such slurries will be highly shear-thinning and thus remain straightforward to pump.
Calcined diatomite is an extremly lightweight pozzolan which both increases the low shear viscosity of a cement slurry and strengthens the set cement. It is particularly recommended for high temperature applications, even in excess of 450°F.
Expanded perlite consists of hollow spherical particles which contain both open and closed pores. All particles contribute to the raising of slurry viscosity, and those with closed pores - which do not fill with water under moderate pressure - can also raise the solid volume fraction whilst simultaneously lowering slurry density.
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