Page 105 - Environmental Control in Petroleum Engineering

§2 Environmental Control in Petroleum Engineering

it difficult to determine what lasting effects hydrocarbons do have on
ecosystems (National Research Council, 1985).
One ecosystem that is chronically exposed to hydrocarbons from
petroleum production is the Gulf of Mexico. Natural variations in this
ecosystem, however, may completely mask any effects of oil pro-
duction (National Research Council, 1985), Natural variations in the
ecosystem cause large changes in the diversity and number of organ-
isms present at any particular location. These natural variations include
the effects of the Mississippi River discharging into the Gulf. The
Mississippi River has a low salinity, a low oxygen concentration, a
high concentration of nitrogen fertilizers, and a high concentration of
suspended solids. These conditions vary significantly from those of
the marine environment and can have a significant natural impact on
the ecosystem. Because of the chaotic nature of the turbulent discharge
of the Mississippi River, this impact occurs over a large portion of
the Gulf.
A study of hydrocarbon and heavy metal contamination on the
continental shelf of the Louisiana coast in the Gulf of Mexico revealed
contamination of hydrocarbons and heavy metals near offshore plat-
forms (U.S. Bureau of Land Management, 1981). No measurable
impact on the ecosystem could be observed from the presence of the
offshore platforms. In areas having a very low background level of
hydrocarbons in the sediments, elevated hydrocarbon levels were
observed at distances up to 2,000 m from the platform. In areas having
a relatively high background level of hydrocarbons, no concentration
of hydrocarbons in the sediments around the platform was observed.
All levels were, however, below those for public concern. Essentially
no accumulation of hydrocarbons in organisms around platforms was
observed. Some concentration of heavy metals occurred, but insufficient
data were obtained for a reliable statistical analysis. The Mississippi River,
with its fresh water, high sediment load, and low dissolved oxygen
content, had a greater measured impact on the benthic ecosystem than
did the offshore platforms.
Contamination of sediments by polyaromatic hydrocarbons from
routine discharges of produced water into shallow estuaries have been
reported as far away as one kilometer (Rabalais et al., 1990). The
effect of hydrocarbon contamination on the benthic community around
such discharge points was correlated to the hydrocarbon contamination
level. Macrobenthic fauna were missing or greatly affected when the