Page 128 - Environmental Control in Petroleum Engineering

The Impact of Drilling and Production Operations 115

States (Ayers et al., 1985; Arscott, 1989). These muds have been
approved for use in specific regions without bioassay testing every
time a mud is to be discharged. Special chemical additives like lost
circulation materials and lubricants can also be used if they come from
an approved additive list. The discharge of diesel or free oil is not
permitted under the generic mud program, although cuttings contami-
nated with oil can be discharged if they are washed and do not cause
a sheen. If generic muds are not used, permits must be obtained on a
well-by-well basis under the National Pollutant Discharge Elimination
System. (NPDES).
A number of bioassay studies have been conducted to determine the
toxicity of various drilling muds and their additives. Two sets of
toxicity data for these generic muds are given in Tables 3.2la and 3.2Ib.
From these tables, it can be seen that the generic muds generally pass
the 30,000 ppm toxicity limit on the liquid phase. The 95% confidence
limit on the measured LC 50 toxicities from one set of mysid shrimp
bioassays has been reported to be about 30% of the measured value
(Parrish et al., 1989). Toxicity data from several nongeneric muds are
given in Table 3-22. From this table, it can be seen that muds that

Table 3-21 a
Toxicity of Generic Drilling Muds (96-hr LC 50, ppm)

Suspended
Liquid Phase Particulate Phase
Generic Mud Type Toxicity 1 Toxicity 1

Potassium chloride polymer 58,000-66,000 25,000-70,900
Lignosulfonate seawater 283,500-880,000 53,200-870,000
Lime 393, 000-> 1,000,000 66,000-860,000
Nondispersed > 1,000,000 > 1,000,000
Spud mud (slugged
intermittently with seawater) > 1,000,000 > 1,000,000
Seawater/freshwater gel > 1,000,000 > 1,000,000
Lightly treated lignosulfonate
freshwater/seawater > 1,000,000 > 1,000,000
Lignosulfonate freshwater > 1,000,000 506,000-> 1,000,000

''Mysid shrimp
Source: from Ayers et al., 1985.
Copyright SPE, with permission.