Page 258 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 234

[ ] Well Programming
2.5.8

Diesel normally contains approximately 26% total aromatics of
which more than 5% of the total are polycyclic aromatics. Most poly-
cyclic aromatics with three or more aromatic rings are toxic and car-
cinogenic. Low-aromatic mineral oils normally will contain less than
5% total aromatics of which less than 5% of the total aromatics are
polycyclic aromatics. In some low-aromatic mineral oils, the concen-
tration of hazardous polycyclic aromatics may be less than 5 ppm. The
resultant toxicity of the formulated oil mud is less (than those based
upon diesel).
The use of diesel as a base oil was outlawed in most areas by the
Paris Convention. There are still some countries that permit its use,
however, most of the big operators are so environmentally conscious
that even in unregulated areas, they do not use diesel in mud.
Low-aromatic mineral oil. These oils superceded diesel in offshore
operations because their toxicity was substantially lower (at least 10
times lower for most marine organisms tested).
The development of low-aromatic mineral oil systems was greatly
advanced (particularly in the North Sea) in the early eighties as it
allowed PDC turbine combinations to be used on offshore rigs which
did not have cuttings washing systems. Early PDC bits required the use
of oil muds as a flush.
Nonmineral oils and synthetic oils. These were developed to address
the problem that a substantial amount of hydrocarbon material in a
cuttings pile will cause an environment that is not conducive to a ben-
thic population and where anaerobic conditions may be set up.
In this group of hydrocarbon liquids there are vegetable oils, stabi-
lized esters, ether systems, and oils synthesized and formulated to pro-
vide for stable oil muds with low toxicity, biodegradability aerobically,
and in some cases anaerobically.
Early work on these “oils” was directed to fish oils and vegetable
oils. However, these oils showed very high kinematic viscosities
with high plastic viscosities in the formulated muds. The resultant
muds showed poor system stability. Stabilized ester systems later
developed, followed by ether systems and liquids synthesized to
specific specifications.
This group of oils is very diverse and it is recommended to inves-
tigate them further for specifications, performance, and environmental
acceptance of local legislation through contact with the drilling fluids
companies and legislative bodies.

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