Environmental Engineering Reference
In-Depth Information
and produce for several years; then wells may be drilled to a deeper pay zone, thus creating a new
field beneath the old field.
Reclamation
When a well field is abandoned, drilled holes are sealed and surface markers are established to
record the well name and location. Disturbed land surfaces are restored to their previous grade
and productive capability, and necessary measures are taken to prevent adverse hydrological ef-
fects from the wells.
Transportation
It has been estimated that activities associated with oil and gas transportation (including refining
and distribution) of crude oil or refined products results in the release of about 44 million gallons
of oil to the seas worldwide each year, about 2.7 million gallons to North American waters (NRC
2003, 3). This includes spills from onshore production and transportation facilities that run off
into rivers and streams. Oil and gas transportation activities account for about 45.2 percent of all
input of petroleum to the environment worldwide from all sources, including natural seeps (Neff,
Rabalais, and Boesch 1987, 170).
Offshore oil and gas development carries with it the risk of oil spills at the platform and in trans-
porting the oil from the platform to shore. Spills at the platform result from leaks or blowouts
during both exploratory and production drilling. Most oil and gas produced offshore is trans-
ported ashore through pipelines. Oil spills result from pipeline ruptures or chronic leaks. Where
technologically difficult or economically infeasible, transport of oil by pipelines is replaced by
storage of the product offshore, then transfer to tankers or barges. This method is commonly
viewed as less safe than pipelines. (Neff, Rabalais, and Boesch 1987, 167)
Most oil and gas produced onshore is transported through pipelines or by tank trucks on roads
and highways used by other vehicles. Large spills from outer continental shelf production and
onshore production are rare. Although the number of small spills from transportation activities is
larger, the total amount of oil from these is relatively small compared to the total amount attribut-
able to large offshore spills (Neff, Rabalais, and Boesch 1987, 169).
For example, the largest oil spill in the Gulf of Mexico prior to 2010 was from a blowout of an
exploratory well, IXTOC-I in the Bay of Campeche, Mexico, in June 1979, which released about
140 million gallons of crude to the marine environment, fouling largely uninhabited shorelines in
Mexico and beaches in Texas. Less than 10 percent of the oil from this spill was recovered (Neff,
Rabalais, and Boesch 1987, 170).
IXTOC-I was dwarfed in comparison by the BP Macondo well blowout after the Deepwater
Horizon rig exploded and sank on April 20, 2010, releasing over 205 million gallons of crude oil by
July 15 at a rate estimated at that time of about 2.52 million gallons per day (Henry 2010). This was
easily the largest oil spill ever directly affecting the United States and ranks as the second-largest
known release of oil in world history. Although the final tally of oil released during this incident
is as yet unknown, its effects on the Gulf of Mexico will be profound for many years to come.
Early surveys in May 2010 discovered large subsurface plumes of oil droplets had formed in
deep waters of the Gulf of Mexico, some ten miles long, three miles wide, and 300 feet thick in
spots. Some plumes contained a great deal of oil in multiple layers in the water column. Scientists
 
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