Environmental Engineering Reference
In-Depth Information
Fossil water that has been out of contact with the atmosphere for a large part of a geologic
period may accumulate in reservoirs of oil and gas, and some of it may be pumped up during
production as oilfield brine or produced water (White 1957). In older fields, production may be
95 percent water and 5 percent oil and gas (Neff, Rabalais, and Boesch 1987, 159). In 1970 daily
production of produced water in the United States was 3.78 trillion liters. In the northwestern
Gulf of Mexico, an estimated 47.7 million liters per day of produced water were discharged to
outer continental shelf waters, and 47 million liters per day were treated onshore and discharged
to coastal waters (Brooks, Bernard, and Phillips 1977). Produced water discharges from a single
platform are usually less than 1.5 million liters per day, but discharges from large facilities handling
several platforms may be as high as 25 million liters per day (Menzie 1982).
Produced water and oily wastes from platform deck drainage are processed with an oil-water
separator, and domestic sewage is treated in an activated sludge system before discharge. Produced
water treatment systems are designed to remove particulate or dispersed oil and have little effect on
the concentration of dissolved petroleum hydrocarbons, other organics, and metal ions in produced
water (Lysyj 1982; Jackson et al. 1981). Treated water containing up to 48ppm oil and grease is
permitted for discharge to the oceans; consequently, discharges of produced waters often contain
significant concentrations of various aromatic hydrocarbons such as benzene, toluene, ethylben-
zene, xylene, naphthalene, and some alkanes (Neff, Rabalais, and Boesch 1987, 153, 165-166),
many of which are known carcinogens. Other organics found in produced waters include ketones
from solvents used to clean rig structures, phenols, and biocides used to inhibit organic growths
in the production system (Middleditch 1981; Collins 1975). A wide variety of chemicals may be
added to the process stream and appear in effluent water, including coagulents, corrosion inhibi-
tors, cleaners, dispersants, emulsion breakers, paraffin control agents, reverse emulsion breakers,
and scale inhibitors (Middleditch 1984).
Several toxic metals may be present at elevated levels in some produced waters; those pres-
ent at substantially higher concentrations than in seawater include barium, beryllium, cadmium,
chromium, copper, iron, lead, nickel, silver, and zinc, along with small amounts of radionuclides,
principally radium (Neff, Rabalais, and Boesch 1987, 162).
Platform Removal
After development wells have been drilled and transportation or pipeline infrastructure is in
place, drilling platforms are removed, often used in nearby areas for additional drilling, scuttled,
or dismantled for scrap (Neff, Rabalais, and Boesch 1987, 162). Little or no reclamation of the
seabed around offshore well heads is attempted, so these locations remain contaminated by drill-
ing muds and materials discharged from drilling platforms for the indefinite future. Little research
has been completed concerning the distribution or dissolution of such materials after removal of
drilling platforms.
ONSHORE RESOURCES
Preliminary geological exploration on land involves ground and aerial survey of an area, along
with aerial photo and geologic map interpretation. On-the-ground geologic mapping and rock
sampling necessitates use of vehicles and sometimes helicopters to transport geologists into inac-
cessible areas. Geophysical exploration obtains data about subsurface geology. Gravitational and
magnetic surveys are conducted by means of aerial and ground surveys (MDFWP 1983). Small
trucks and jeeps with crews of several people are used at this stage of subsurface data gathering,
and off-road travel is frequent (USDOI 1981a).
 
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