Page 127 - Environmental Control in Petroleum Engineering

114 Environmental Control in Petroleum Engineering

Table 3-20
Toxicity of Gas Treatment Chemicals (96-hr LC 50 , mg/L)

Chemical Fresh Water Salt Water
Methanol 8,000-> 10,000' 12,000-28,000
Ethylene glycol > 10,000 >20,000'
Diethylene glycol >5,000~>32,000 2
Triethylene glycol > 10,000-62,600 >1,000 J

'48-hour text
2
24-hour test
'23-dav test
Source: after Hudgins, 1992.
Copyright SPE, with permission.

(text continued from page 107)
a 0.45 micron filter and designated the "liquid phase." The remaining
unfiltered fluid is designated the "suspended particulate phase." The
settled material at the bottom of the mixing vessel is called the "solid
phase." Chemical additives, if any, are then mixed with this liquid for
the toxicity test.
Mysid shrimp are used as the test organisms for the liquid and sus-
pended particulate phases, while hard-shell clams are used for the solid
phase. The U.S. Environmental Protection Agency has set a mysid shrimp
toxicity limit (96-hour LC 50) for drilling mud discharge into the United
States outer continental shelf (OCS) waters of 30,000 ppm (3%) for
suspended particulate phase (after the 9:1 dilution with sea water).
Materials with LC 50 values greater than one million ppm do not kill
at least one half of the mysid shrimp during the 96-hour test.
Testing drilling fluids for toxicity in aquatic systems is difficult,
however, because much of the material settles rapidly, and what
remains suspended may partition into two or three discrete layers. This
makes repeatability of the exact test conditions difficult. The condition
of the test animals prior to exposure to the drilling fluids is also an
important factor in determining the test repeatability. Laboratory tests,
however, have shown similar results from different labs for the toxicity
of various materials in drilling fluids (Parrish and Duke, 1988).
To speed permitting of new offshore wells and eliminate the need
for bioassays on every drilling fluid prior to discharge, a set of eight
generic drilling muds were developed for offshore use in the United