One of the
flashpoints in the debate over developing possible offshore oil and
gas centers on seismic surveying, an effective but controversial
method used in the search for energy deposits.
meetings have been scheduled this month about using “air guns”
off the N.C. coast. The first was earlier this week in Wilmington,
the second is today in Morehead City, and the last one is on Monday,
April 27, in Kill Devil Hills.
primer to help you understand what all the noise is about.
exploration method that uses pulses of sound that are projected into
the earth’s crust. As the sound rebounds, the pulses are analyzed
and from that data images of the layers of sediment, rock and
hydrocarbons up to 10,000 feet below the surface can be created.
is used to search for hydrocarbons on land and in marine
environments. It is also used by doctors when giving ultrasound
examinations to pregnant women.
a new technique?
Land-based seismic surveying has been in use since the 1920s,
although the early methods used to create the pulses of sound would
be considered downright primitive by today’s standards—the survey
team would set off dynamite at the bottom of a shaft they had
surveying was developed in the 1960s. Technology had advanced to the
point that a method of sending a bubble of sound to the bottom of the
ocean had been developed and the returning sound waves could be
interpreted by the improving computer technology.
marine seismic surveying work?
An array of “air
guns” are towed behind a ship, and at timed intervals, a pulse of
sound is directed to the seabed. The term air gun may not be quite
correct, though, according to Stanley Labak, an expert in marine
acoustics with the Bureau
of Ocean Energy Management, or BOEM. That’s the
federal agency that regulates offshore energy exploration and
“Air gun is
the terminology in the industry since its inception . . . in the
early ‘60s. But it’s not really a gun. It’s a chamber that has
pressurized air in it and at a set time they release that air and it
forms a bubble and it creates sound,” he said.
The pulses of
sound penetrate the ground, and as the echoes of the sound come back
to the ship, they are analyzed. From the data, the returning pulses
of sound create a remarkably detailed map of the earth beneath the
is no alternative technology that maps the seabed and the resources
that may there. To potential bidders planning to participate in
BOEM’s planned sale of oil and natural gas leases off the N.C.
coast, the information seismic surveying can provide is considered
some people opposed to it?
marine mammals and many other species of marine life use sound to
communicate and navigate the oceans, many people are worried that the
sound coming from the air guns will harm whales, dolphins, sea
turtles and fish. The pulse of sound is very loud, typically between
200-300 decibels. To put that in perspective, normal conversation
occurs at about 60 decibels; the noise of a passing truck is about
100 decibels; and the roar of a jet at takeoff is around 180
any evidence that any of these fears are real?
Here is where it
gets a bit confusing.
There are no
peer-reviewed studies that have shown a definitive link between
seismic surveying and injured or dead marine life. However, there
have been a considerable number of incidental events where seismic
surveying has occurred that coincides with changes in behavior in
marine life and large increases in dead animals.
seismic surveying point out that the wave length of the sounds are
well below threshold of what almost all marine mammals can
hear—higher frequencies will not penetrate beneath the seabed. They
also argue that very little sound escapes from the air gun pulses,
noting that the more focused the pulse is the more accurate and
useful the rebounding echo will be.
observe that laboratory tests on marine life subjected to sounds
similar to those emitted during seismic surveys are adversely
affected and there is a considerable body of evidence pointing to
injured and dead marine life occurring during seismic surveying.
A 1996 study in
Norway showed a marked decrease in fish catch over a 2,000
square-mile area following seismic surveying. There are also,
worldwide, well-documented beachings of whales and dolphins
concurrent with survey activity.
likely to hear the booms while walking the beach or fishing offshore?
although anything is possible. Because the seismic surveying that is
being contemplated is so far offshore—a minimum of 50 miles for oil
and gas—there is no possibility that the sound would travel back to
the shore. If a seismic survey was done closer to shore and in
shallower water, it is possible that the pulse could bounce off the
bottom and be heard along the shoreline.
being proposed for North Carolina?
shelf off the North Carolina coast is clearly in the bull's-eye of
where oil and gas are thought to exist.
There are two
basic types of seismic surveying: two dimensional and three
dimensional. A 2D survey is really an outline of an area where the
possibility of oil or gas is thought to exist. A 2D survey consists
of a ship with a single pulse source sailing a grid pattern. The
survey information is less detailed but also takes less equipment and
expertise to interpret.
The 3D array,
which provides more detailed information, requires multiple air guns
on towlines behind the survey ship.
There are permit
requests for 2D- and 3D-surveys in N.C. waters.
state and federal permits been issued?
Getting a permit
to engage in what’s called “geological and geophysical,” or
G&G, surveying is a time consuming and detail-oriented process.
Because the areas under consideration are not within the three-mile
jurisdiction of the state, there are no state permits required.
state has a federally approved coastal management program. That
allows the state to review any action that requires federal permits
to make sure it’s consistent with state laws and regulations. BOEM
couldn’t immediately issue permits for seismic testing if the state
officials determined that it would violate the state program.
BOEM in February
of 2014 issued a so-called Record of Decision outlining what the
government will be seeking in a G&G permit application. A
detailed recital of mitigations and precautions, the document is 12
surveying permits have been issued, although there are currently four
permit requests. Petroleum
Geo-Services has requested a 3D-permit. Spectrum
Technology have asked for 2D-permits.
request is the only such request on the Eastern seaboard.
will it start?
to say when or even if seismic surveying will begin. It is possible
that BOEM will move quickly after the public hearings and seismic
surveying could begin as early as this summer. It is also possible
that the concerns of the public and problems with the permit
applications will slow the process down, or bring it to a halt.
Public Meeting Scheduled for April
The Bureau of
Ocean Energy Management will sponsor a public meeting on seismic
offshore seismic testing at Ramada Plaza Nags Head Oceanfront, 1701
S. Virginia Dare Trail, Kill Devil Hills. One meeting starts at 3
p.m. and the other at 5:30 p.m. Each lasts about 90 minutes.
article is provided by Coastal Review Online, an online news service
covering North Carolina's coast. For more news, features, and
information about the coast, go to www.coastalreview.org.)