Offshore Seismic Surveys: Why and How

Why are Seismic Surveys Needed in the Atlantic OCS?

The first step in exploring for offshore oil and natural gas resources is often conducted through seismic surveys, which are like ultrasounds of the earth that help scientists “see” below the ocean floor.

• The last surveys of the Atlantic Outer Continental Shelf (OCS) were conducted over 30 years ago. Due to technological advances, the existing estimates of 4.7 billion barrels of oil and 37.5 trillion cubic feet of natural gas are out of date.
• Advances in seismic imaging technology and data processing over the last decade have dramatically improved the industry’s ability to locate oil and natural gas offshore.
• Exploration and development activities generally lead to increased resource estimates. For example, in 1987 the Minerals Management Service estimated only 9.57 billion barrels of oil in the Gulf of Mexico. With more recent seismic data acquisition and additional exploratory drilling, that estimate rose in 2011 to 48.4 billion barrels of oil — a fivefold increase.

Seismic surveys are a safe and proven technology that help make offshore energy development safer and more efficient.

• Governments and the private sector have used this method of exploration in the U.S. and around the world for over 40 years.
• In addition to the oil and natural gas industry, seismic surveys are commonly used by the U.S. Geological Survey, the National Science Foundation, and the offshore wind industry.
• A rigorous permitting process ensures that seismic surveys are properly managed and conducted so they have minimal impact on the marine environment.

How are Seismic Surveys Performed?

Sound waves help scientists map the ocean floor and geology beneath it.

• Surveyors release compressed air into the water to create short duration sound waves that reflect off subsurface rock layers and are “heard” by sensors being towed behind the vessel.
• Scientists analyze the collected data and use it to create maps of geologic structures that could contain energy resources beneath the ocean floor.
• The sound produced during seismic surveys is comparable in magnitude to many naturally occurring and other man-made ocean sound sources, including wind and wave action, rain, lightning strikes, marine life, and shipping.
• Survey operations are normally conducted at a speed of approximately 4.5 to 5 knots (~5.5 mph), with the sound source typically activated at 10-15 second intervals. As a result, the sound does not last long in any one location and is not at full volume 24 hours a day.