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The Dowell Drilling Fluids Team on the Hibernia project,
off the coast of Newfoundland, faces some interesting challenges.
As the platform is located in an environmentally sensitive
area, discharges to the sea must be carefully monitored.
There are three major types of drilling fluids: water-based
mud (WBM), oil-based mud (OBM) and synthetic-based mud (SBM).
The drilled cuttings from water-based muds are much less
damaging to the environment and are normally discharged o
the sea. Water base systems are not always as effective as
oil- or synthetic-based fluids, especially for solving the
problems associated with these particular wells. |
In the most recent wells a combination
of water-based and oil-based muds have been used. Water-based
mud is used early in the drilling process. Then oil-based
mud is substituted as the well gets deeper and reaches the
limit of the water-based mud, in terms of lubricity and well
bore stabilization.
Since oil-based muds, while effective as a drilling fluid,
can be toxic to marine plants and animals so their use is
normally tightly controlled. For the Hibernia project , the
cuttings from the mud have to be washed (on the platform),
in order to remove the oil, prior to discharge. This washing
process takes time, and has proved to be a factor limiting
the rate of drilling. |
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In the future, government legislation may allow for discharge
of cuttings using synthetic-based mud, which exhibits similar performance
to the oil-based mud, but has a better environmental profile. Although
the initial cost of the fluid will be approximately double that
of oil-based mud, substantial time and dollar savings will be achieved
due to the fact that these cuttings do not have to be washed.
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