370-375Influence 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 105oC, 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