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Cement additives
Research during the past decade has shown that the permeability of the set cement
can be greatly reduced if correct additives are used in a standard cement mixture
(Talabani. 1995). Gas migration in the annulus between the formation and the casing has
bee. +.minated by four new cement additives: ironrc. sponge, XC-polymer, synthetic
ruc i.'ld Anchorage clay. The ironite sponge has been shown to eliminate the
mic!'.:.i1ulus between C.'Je casing and the cement body by magnetically bonding the
casing with ironite spcCige in the cement. XC-polymer has shown great results as a
filtrate control agent. The Anchorage clay, when added to some ultrafme cement, has
been shown to reduce the permeability of the cement body due to illcc:.age of pores.
Synthetic rubber added to the mixture compensates for the expansion-eontraction cycles in
the cement during setting. The elastic behavior of the rubber reduces or eliminates the
second final presstire-vc'l.e shift. '
X-9
It ;.5 believed that future efforts will cc
in temperature and pressure to optimize thiclc: c
length of the annulus.
·ntrate on designing cement for variations
of the cement body along the entire
Cement mixing
Until the mid-1980s, the instant jet mh.:: of cement powder with additives and
water resulted in a non-homogeneous slurry that m many cases caused an incomplete
cement-water reaction. As a result, cement powder with war'" created low applied shear
on the cement particles, in which the peel was the only pan ;·::i·;;ting with water and the
core stayed dry.
To solve the problem a new unit was made that cycles the slurry through a jet and
then a high shear is applied to the cement slurry in the mixing tank. The high shear rate
creates a homogeneous cement slurry in which most of the ;:cwder p:m.icles react
completely with water.
Ultrafmc cement manufactured and introduced to the oil field in the 19805 has
pa.:1icles 20 to 26 A in diameter, which is one third the particle size of the other cement
classes. Complete cement-water boDdir·c -' more easily achieved using a mixture of this
new cement type.
Perforation
Perforation technology in the pas :ecade has become better as more successful
jobs were performed. Th:.:. was due to better designed charges as well as the use of better
centralizers and magnets. Perforation theory for 'directional wells with partial penetration.
different possible charges, spacing, and shots-per-foot is better understood and therefore
the perforating job can be optimized (Economides, 1989). The use of acid has also shown
good results; however, extreme care is suggested in terms of time ane. pressure when
using acid. The issue of overbalanced; underbalanced perforation is still
unrescIved.
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