New Insights into CaO-swelling Cements

Abstract

Influence of CaO in improving slurry swelling is studied, using high pressure-high temperature (HP-HT) expansion cells, and compared with previous results. For varying temperatures and pressures the beginning and end of expansion and the duration, of expansion are observed. The expansion values are determined. The extent to which cement shrinks is found to be a balance between the chemical reaction of water and clinker mineral, and the physical reaction of gel dipole water attached to the electrically charged cement surfaces. An optimum water cement factor (WCF) of 0.45 ensures pumpability during oil well cementing, without causing increased hardened-paste porosity and permeability. Specially stable matrix is needed to use the swelling agent, and the smaller the CaO reactivity, the earlier the ‘‘Time-window’’ attains high temperature. Depending on the retarders used to suppress shrinkage, cement expands at an average value of 6 per cent for 19, 16, 15 and 6 min, at 60, 80, 90 and 105^oC, respectively. Calcium oxide quantity between 12 and 14 per cent by weight of cement is recommended for good swelling. A second method of gradually mixing cement slurry components in stages represents an improvement of the CaO swelling ability over the old lump method which is quite useful.