Oil and Natural Gas - Energy Policy Analysis: A Conceptual Framework - page 78

to the following conclusion: “Biogenically structured habitats, such as salt marshes and mangrove
forests, are subject to destruction or alteration by acute oiling events. Because the structure of
these habitats depends upon living organisms, when these are killed, the structure of the habitat,
and sometimes the substrate on which is grows, is lost” (NRC 2003, 157). The NRC recommends
that government oil spill contingency plans contain mechanisms for higher levels of prevention
to protect these areas from oil spills than are generally included in them.
Surface oil weathers, loses buoyancy, and sinks down in the water, where it can associate with
particulate matter suspended in the water and eventually sink to the seabed, where it affects the
benthic community (Elmgren et al. 1983). The most sensitive organisms there appear to be crus-
taceans, some of which, like American lobsters, have commercial value. Sedimented oil provides
a long-term pathway for exposure to benthic fisheries (Kingston 1999).
Exploration
Mobile drilling rigs are towed or move under their own power to sites for exploratory drilling
and are anchored at multiple mooring points, or they may be dynamically positioned in deeper
waters. Initial drilling into the seabed to place risers to the surface results in direct discharge of
sediment, drill cuttings, and drilling fluids at the seafloor. After the drilling rig is secured in place,
drilling fluids necessary to cool, lubricate, and transport solids from the drill bit to the surface
are separated from cuttings (pulverized rock from the formation) on the rig. Cuttings are usually
discharged overboard continuously, while drilling fluids are reused and disposed of later, gener-
ally overboard at the drill site. Water drainage from the drill platform may contain drilling fluids,
oil, and small quantities of industrial chemicals. Exploration wells are sparsely distributed and
generally produce brief operational discharges compared to production facilities, in the absence
of a blowout (Neff, Rabalais, and Boesch 1987, 150).
During exploratory drilling, several drilling fluid and cuttings-related effluents are discharged
to the ocean. Used drilling fluids may be discharged in bulk quantities of 1,000 to 2,500 barrels
several times during a drilling operation. Over the life of an exploratory well, 5,000 to 30,000
barrels of drilling fluids may be used, and 50 to 80 percent of this material may be discharged to
the ocean (Neff, Rabalais, and Boesch 1987, 157, 158).
Production
After discovery of a promising reserve of oil or gas, a fixed platform may be placed from which
several development wells may be drilled in different directions, producing more heavily concen-
trated discharges of drilling fluids and cuttings, and greater risks of oil spills. In some near-shore
locations, an artificial island may be built of sand or gravel to support drilling and production, with
resulting destruction of marine habitats (Neff, Rabalais, and Boesch 1987, 151). During drilling
of a 10,000-foot production well, approximately 900 metric tons of drill cuttings are generated
and about 1,000 tons of drilling fluid solids are discharged. As many as fifty to a hundred wells
may be drilled from a single offshore development platform over four to twenty years, resulting
in discharge of about 95,000 metric tons of drilling fluid and cuttings solids to the ocean (Neff,
Rabalais, and Boesch 1987, 159).
Pipeline Construction
Transport of oil and gas across coastal wetlands often entails dredging channels for laying pipelines
and burying them in the seafloor, except where economically impractical. If use of pipelines is