Page 132 - Environmental Control in Petroleum Engineering

The Impact of Drilling and Production Operations 119

Table 3-23
Toxicity of Drilling Fluids to Hard Clams, EC 50
Drilling Fluid Type 1 Concentration (micro!/!)
Seawater lignosulfonate 100
Seawater lignosulfonate 1
Seawater lignosulfonate 10
Lightly treated lignosulfonate 10
Freshwater lignosulfonate 100
Lime 10
Freshwater lignosulfonate 100
Freshwater/ seawater lignosulfonate 100
Reference drilling fluid 1
1
Duplicate drilling fluid types are from different formulations.
Source: U.S. Environmental Protection Agency, 1983.

3.6.2 Impact of Drilling Fluid Disposal

Drilling fluids used for onshore wells are primarily disposed of in
reserves pits, while in many areas drilling fluids from offshore plat-
forms have been dumped overboard. A number of studies have been
conducted on the impact of these discharges.
For most drilling muds, sodium has the greatest potential to impact
the environment from the onshore disposal in reserves pits (Miller,
1978). Heavy metals are also of concern, although their potential to
leach away from the pit and contaminate the groundwater is limited
by their low concentration and low solubility (Mosley, 1983; Branch
et al., 1990; Crawley and Branch, 1990; Candler et al., 1990; American
Petroleum Institute, 1983). Extensive field studies have suggested that
the onshore disposal of drilling wastes in reserves pits poses no serious
threat to human health or the environment (American Petroleum
Institute, 1983). In some cases, crop yield was improved following the
disposal of drilling wastes.
A number of field studies have been conducted to measure the
impact of discharging drilling fluids on the benthic community around
offshore platforms. These studies have revealed elevated levels of
hydrocarbons and heavy metals in the sediments surrounding plat-
forms. Most of these hydrocarbons and heavy metals are associated
with cuttings, making it possible to estimate the deposition of these