Page 272 - Pipeline Pigging Technology

Pig-tnto-place plugs and slugs

A large variety of different gel formulations and concentrations were
evaluated both in the test loop and also in the laboratory. During the testing
programme, the following parameters were evaluated:

1. the length of time required for the gel to hydrate;
2. the effect of dynamic transport of the gel along the pipeline;
3. the gellation characteristics of the gel once transportation had
stopped and the gel was allowed to sit and develop;
4. the effect of biocide in the gel;
5. the time required to break the gel, and the break mechanisms
required to be employed.

At the present time, Nowsco has developed a gel with the following
characteristics:

1. the gel can be mixed and injected into a pipeline in a controlled
manner;
2. the gellation time can be accurately controlled for anywhere be-
tween 2 and 18 hours;
3. the viscosity of the gel can be accurately controlled, enabling known
differential pressures to be withstood;
4. the gel will break within a predetermined time, enabling its removal
from the system.

In the experiments undertaken in the laboratory and field loops, a 50-ft
plug of gel was able to withstand 10-bar differential pressure for 52 days.
Additional work is continuing with this system, but at present a low-pressure
differential barrier system is available for systems where water contamination
is not considered a serious problem.
As an alternative to aqueous-based gel systems, hydrocarbon gels were also
evaluated. The advantage of using hydrocarbon systems is that no water is
introduced into the line, no bacterial potential exists, and therefore the
recommissioning process following the positioning of the barrier in the
system is quicker and cheaper, as water contamination of the system is
minimized. In early experiments it was attempted to develop hydrocarbon-
based gel with similar characteristics to the aqueous-based gel. This research
proved more complicated, due to the nature of both the hydrocarbon fluids
and the base chemicals, and it has proved significantly more difficult to obtain
repeatable results using the hydrocarbon-based system; research, though, is
continuing. It was thought at this time that the possibility of developing a

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