Why are Seismic Surveys Needed in the Atlantic OCS
The Obama administration is currently considering whether to allow seismic surveying in the U.S. Atlantic Outer Continental Shelf (OCS). Offshore seismic surveys are an advanced exploration technique used to locate potential oil and natural gas reserves hidden below the ocean floor. They are also used to site locations for offshore wind facilities.
Seismic surveys have been conducted safely in the U.S. and around the world for decades. The last surveys of the Atlantic OCS took place about 30 years ago. Since that time, technological advances have dramatically improved our ability to pinpoint likely reservoirs, which makes existing resource estimates in that area out of date. New surveys using state-of-the-art techniques and technology would provide a better understanding of the oil and natural gas resource potential in the Atlantic OCS.
How It Works
An offshore seismic survey is performed by a crew aboard a boat that moves along a predefined grid pattern. Behind the boat, the crew tows a sound generator and strings of sound sensors. The sound generator, or airgun, releases compressed air into the water to create sound waves that travel through the water and bounce off subsurface rock layers at the bottom of the ocean. The sensors detect the reflected sound waves, and the information they record produces detailed three dimensional maps that scientists analyze to help locate likely reserves of oil and natural gas. The maps also pinpoint the safest and most efficient drilling locations, eliminating unnecessary drilling and reducing the number of dry wells.
The sound from offshore seismic surveys is comparable to the sound of a sperm whale echolocating for prey and to naturally occurring and other man-made ocean sound sources, including wind and wave action, rain, lightning strikes, marine life, and shipping operations. Survey operations are normally conducted at a speed of approximately 4.5 to 5 knots (~5.5 mph). As a result, the sound does not last long in any one location.
Seismic surveys are highly regulated and performed only in government-licensed areas where operators make great efforts to prevent potential impacts on marine life. Before operations begin, animal movement and behavior patterns are analyzed and any areas of concern are closed to seismic surveys. The surveying process begins with a “soft-start” – a technique that gradually increases sound to full operational levels. This allows animals that may be sensitive to this sound to leave the area. If visual observers or acoustic monitoring devices detect sensitive marine life in the vicinity at any time during the survey, then all operations stop immediately and are restarted only when the area is clear.
Benefits of Seismic Surveys in Oil and Natural Gas Exploration
Today, advancements in seismic technology have helped find, drill and produce oil and natural gas with the least risk and the least possible impact to the earth. As operators explore for oil and gas, the use of geophysical technologies helps to reduce risk in regards to cost, safety and damage to the environment. Seismic information is used to accurately plan locations for wells, reducing the probability of drilling dry wells and consequently the need for further drilling, minimizing the environmental impact of the oil and gas exploration.
See links to the five one-page reports produced by the International Association of Geophysical Contractors (IAGC) below:
- Environmental Benefits of Seismic Surveys
- Fundamentals of Sound in the Marine Environment
- Introduction to Marine Seismic Technologies
- Marine Mammal Strandings
- Seismic Surveys and Fish
- Understanding Marine Mammal 'Takes' Under the US Marine Mammal Protection Act
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