Page 170 - Environmental Control in Petroleum Engineering

Planning for Environmental Protection 1SI

these new drilling muds may still be prohibited, even though they
provide significantly improved environmental protection. Many of the
regulations covering the discharge of drilling muds were established
before the development of these alternative mud systems and have not
been changed to reflect these new technologies.
One way to lower the toxicity of diesel oil muds is to increase the
amount of water in the mud emulsion. This will reduce the amount
of oil that is available to be retained on cuttings. Water contents in
new mud formulations have been reported to be as high as 65%
(Friedheim and Shinnie, 1991). Traditional muds have water contents
typically around 10% or less. Another way to lower the toxicity of
oil-based muds is to use a less toxic base oil. Mineral oils having a
low concentration of aromatic hydrocarbons have been successfully
used (Jacques et al., 1992), as have esters, ethers, and polyalphaolefins
(Peresich et al., 1991; Candler et al., 1993). Cationic surfactants can
also be added to the mud to reduce the amount of oil trapped on
cuttings (Friedheim and Shinnie, 1991).
A variety of new water-based muds are being developed as possible
substitutes for oil-based muds. The additives for these muds have
included various low-toxicity polymers and glycols (Bland, 1992;
Bleter et al., 1993; Enright et al., 1991; Reid et al., 1993). Substitu-
tions can also be made with the additives used in water-based rnuds.
For example, dolomite can be used instead of barite as a weighting
agent. Additives made from water-soluble combinations of silicon,
phosphorus, aluminum, and boron can replace some conventional
additives (Zakharov and Konovaiov, 1992). New pipe dopes are being
developed that do not contain heavy metals; these new pipe dopes have
included micron-sized alumina-ceramic beads in a lithium grease.
Drilling muds can be reformulated to improve shale stability. This
will reduce wellbore washouts, minimize the degradation of solids (the
breaking into smaller, harder-to-separate particles), reduce the amount
of material brought to the surface to be handled, and lower the mud
volume requirement of the well (Alford, 1991; Thurber, 1992). Potas-
sium acetate or potassium carbonate can be used instead of potassium
chloride for shale stability problems to minimize the chloride content
of the drilling mud (Gillenwater and Ray, 1989). Other mud additives
and suggested substitute materials are given in Tables 5-1 and 5-2.
A variety of opportunities are available during production operations
to substitute less toxic materials for more toxic, traditional materials. For