Geotechnical News • December 2017
31
THE GROUT LINE
• greater insurance for long term
blockage
• act as a stepping stone for more
challenging treatments
The majority of the trials with 4.5
ratio sodium silicate has been as a
compliment to a cement squeeze.
The 4.5 ratio material was diluted
1:1 with water for a total volume of
500 to 1000 litres. This material was
squeezed using a pressure pump-
ing unit. (see figure 3). Typically,
the setting process would begin as
the squeezed silicate was exposed
to calcium rich environment of the
microchannels. As injection pressure
increased a small volume of fresh
water would be pumped behind the sil-
icate to act as a spacer for the cement.
Field trials showed a high first-time
success rate using the 4.5 ratio but
more trials would be necessary to
determine if success rate was statisti-
cally higher vs. conventional silicate.
The 4.5 ratio sodium silicate has also
been used as a standalone product to
block gas migrating inside and outside
of the casing. It should be noted that
successful blocking of gas or water
is not just about having an effective
sealant, success is dependent on good
diagnostics to pin point the source(s)
of gas and their pathways. Once com-
munication is established with gas
pathways then proper placement of
the treatment chemical is critical to
success. Trials have been equally split
between using the high ratio mate-
rial by itself or with a setting agent.
Placements of the silicate have been
done with a pressure pumping unit or
with chemical injection pumps (see
figures 3). The advantage of chemical
injection pumps is it allows for low
pump rates over long period times.
The other advantage is it is a low cost
pumping technique. For well abandon-
ment, success requires that venting
gas be reduced to zero. Based on the
limited number of trials the success
rate at achieving total blockage on the
first squeeze is ~66%. In cases where
the volume of venting was reduced
but not eliminated it is felt there were
secondary sources of gas and not all
pathways were available for entry.
Conclusions
The experimental study at GRC pro-
vided a good starting point to assess
the performance of cementation of
clean quartz sand by 4.5 ratio silicate
vs. conventional sodium silicate. The
setting agents used in the study were
citric acid and triacetin. The next
phase of study will look at longer gela
Table 3. Permeability of pure sand vs. consolidated sand with
4.5 ratio and citric acid
Sample
Curing time
Permeability
Control, quartz
sand
N/A
2.30x10¯
⁴
m/s
50% S45-Citric
7 days
2.73x10¯
8
m/s
50% S45-Citric
14 days
7.55x10¯
8
m/s
Figure 2: gas pathways in cement.
Figure 3: Silicate squeeze with cement.
