Seismic Surveys & Marine MammalsJoint IOGP/IAGC position paper

The oil and gas and geophysical industries are committed to operating in an environmentally responsible manner. This requires thorough attention to the potential impacts on the marine environment, including sounds generated by upstream activity.

This paper focuses on the sound introduced into the marine environment as a result of marine seismic surveys. It discusses potential interactions with marine life, how widely adopted mitigation measures can reduce impact to marine life and how research efforts contribute to improving understanding of effective techniques to avoid any potential negative effects of sound on marine life.

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• The importance of both marine life and marine anthropogenic activities to society underscores the need to identify, assess and manage interactions between seismic surveying and marine mammals. The oil and gas and geophysical industries work to protect the world’s oceans while exploring for new hydrocarbon resources.

• Oil and gas provide a significant proportion of the world’s energy and will do so for some time to come.

• Marine seismic surveys are a critical tool for identifying valuable energy resources with high precision – they reduce the number of wells drilled.

• Mitigation measures for seismic surveys are carefully designed and implemented to address potential site-specific safety and environmental impacts identified during project planning.

• After more than 50 years of worldwide seismic surveys and more than 15 years of extensive peer-reviewed scientific research, there remains no evidence that sound from properly mitigated seismic surveys has had any significant impact on any marine populations.

• The oil and gas and geophysical industries continue to invest considerable resources in research and technology to further understand the effects of sound on marine life.

1. We work to meet the world’s growing energy demand

The world will rely on oil and gas as part of a balanced energy mix for decades to come.

According to the International Energy Agency, in 2040 oil and gas will probably meet about half the world’s growing energy needs. Natural gas, in particular, will be required as a backup fuel for the variable output of renewable sources such as solar and wind.

World energy consumption by source, 1990-2040quadrillion Btu

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01990 1995 2000 2005 2010 2015 2020 2025 2030 2035 2040

2012history projections liquid fuels

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Figure 1: Global energy need is expected to grow over 50% through 2040. Renewable energy will not be able to replace the need for oil and gas by that time.

As global demand for energy increases, the search for more oil and gas will continue. According to World Ocean Review [1], approximately one third of the oil and gas extracted worldwide currently comes from offshore sources. This figure is expected to rise over the coming decades, especially given recent significant deepwater hydrocarbon discoveries.

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2. Marine seismic surveys are an essential tool for safely locating and producing oil and gas resources

Marine seismic surveys create images of the geological structure beneath the ocean floor, using a method that is similar to ultrasound in medicine.

Employed primarily to explore for and produce oil and gas, seismic surveys are also used by the military, marine and offshore extractive industries and academic researchers for a variety of other purposes. These include scientific studies of the earth’s geological history, the identification of national maritime zones and boundaries offshore, assessment of seabed foundations for offshore construction and accurate placement of offshore renewable energy infrastructure [2].

The seismic survey process is straightforward. A vessel tows an acoustic source array (usually a set of compressed air chambers) that creates predominantly low-frequency pulses of acoustic energy. The release of compressed air sends sound waves into rock layers beneath the ocean floor. Hydrophones towed behind the seismic vessel record reflected and refracted sound waves, which constitute the seismic data.

Figure 2: Seismic surveying is used to image the subsurface.

Once collected, the raw seismic data are processed to generate subsurface images. These high resolution images are then used to identify areas where oil and gas may be present.

More than 50 years of experience demonstrates that this method of exploration is the most reliable means for locating possible oil and gas reservoirs.

Just as important, seismic surveying helps to exclude areas where there are likely no recoverable oil and gas resources. Effectively identifying the most prospective areas reduces industrial interaction with the marine environment and the need for drilling.

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3. Industrial activity is one of many sources of sound in the marine environment

There are many natural sources of sound within the marine environment: wind, rain, waves, marine mammal vocalizations and the sounds made by other marine life all contribute to relatively high levels of ambient sounds. Other natural events such as volcanic eruptions, earthquakes and lightning strikes produce short-lived high intensity sounds underwater.

In addition, there are many man-made (anthropogenic) sources of sound in the ocean. These include shipping, fishing, sonar (used for navigation, fishing and defence), construction, dredging, military activities as well as seismic surveys. Each of these sources, whether natural or anthropogenic, has different frequencies and intensities in the marine environment.

Since sound is common in the marine environment, animals have evolved strategies to use sound and manage successfully in sound-filled environments. Potential impact, if any, of a specific sound depends on its characteristics, the species receiving the sound and other characteristics of the marine environment.

Sound characteristics (see inset overleaf) include how loud a sound is perceived, the duration and sound type, whether the sound is considered impulsive (transient) or continuous (ongoing) and the sound’s frequency (pitch).

A seismic acoustic source array emits a sound that lasts less than 0.1 second. It is typically repeated every 10 to 15 seconds as the seismic vessel moves along a straight ‘data acquisition’ line at a speed of about 5 knots for many kilometres. After which the vessel will move to another acquisition line and may return to the area many hours later.

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Characteristics of soundPerception of sound – How loud a sound is perceived is dependent on the amplitude of the sound and the ear’s sensitivity to the particular frequencies contained in the sound. The amplitude is normally determined as the pressure, measured in pascal (Pa).

Since sounds detectable by human ears can have a wide range of pressures from less than 0.00002 Pa to over 20 Pa, scientists have historically used a logarithmic decibel scale (dB) to describe the intensity of sounds for convenience of display. The number of dB is ten times the logarithm to base 10 of the ratio of a measured pressure squared to a reference pressure squared (10 log10 (p2/p02) dB) = 20 log10 (p/p0).

For underwater sound, scientists have agreed to use the intensity of a sound wave with a pressure of 1 micropascal (µPa) as the reference pressure p0. In air, however, scientists agreed to use 20 µPa as the reference pressure. This difference can lead to misunderstandings when comparing the loudness of sounds in air and water.

When comparing sounds for strength, it is important to use the same measurement convention. Sound level values in air and in water are not directly comparable due to differences in propagation characteristics. A correction factor of approximately 62 dB must be subtracted from the water dB to account for the physical differences between air and water and the different reference levels. A seismic source at 220 dB in water would thus be comparable to a source producing 158 dB in air.

For any sound, including seismic surveys, the amplitude diminishes as sound waves travel away from their source, much like ripples on the surface of a pond. The rate of decrease depends on various physical characteristics, such as water depth, temperature, salinity and, in shallow water areas, seabed conditions.

Impulsive sounds are short duration pressure pulses with rapid rise time, followed by decay that may include oscillating maximum to minimum pressure. The sounds made by acoustic source arrays are impulsive. Other impulsive sounds include pile strikes and snapping shrimp.

Continuous sounds do not have the rapid rise time of a distinct pulse, but persist for long periods of time. Examples of continuous sources of sound include ships and waves crashing.

Frequency, as measured in cycles per second or hertz (Hz), is related to the pitch of sound. To help ensure quality imaging deep beneath the ocean floor, predominantly low frequency (less than 200 Hz) is used for seismic imaging. Of the total energy in each pulse, more than 98% is low frequency. Low frequency sounds – such as earthquakes, baleen whale calls and, under rare circumstances, seismic pulses – can be detected at distances [5] thousands of miles from the source. Although detectable, the sound level at these great distances is very low and there is no research to suggest that sound from distant sources negatively affects whales or other marine life.

Find out more at www.dosits.org.

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4. Industry mitigation measures reduce impact on marine life

Industry experience with marine seismic surveying worldwide, combined with several decades of international scientific research, suggest an extremely low likelihood of biologically significant harm to marine life from seismic surveying. To date, there is no research showing that serious injury, death or stranding of marine animals has occurred from exposure to sound from seismic source arrays.

Many countries and regional authorities have established regulations and associated guidelines specifically designed to protect marine mammals during seismic operations.

The geophysical and wider oil and gas industries also adopt:• measures recommended by industry organizations• individual company internal practices• site-specific measures to mitigate risks identified during project planning.

A joint industry IOGP−IAGC recommended practice describing monitoring and mitigation measures for cetaceans during marine seismic survey and geophysical operations is currently in development.

Pre-programme planning assesses safety and environment aspects related to proposed operations as well as geophysical and commercial objectives. Risk assessments identify potential likelihood of events and consequences. Measures are then designed to either eliminate or greatly reduce any potential impacts. A scientific understanding of each potential risk is essential to this process. As research studies increase scientific understanding, the findings are used to refine risk assessment and management.

Sound modeling may be conducted at an early phase of project planning. This helps to inform decisions related to scheduling surveys in order to minimize the likelihood of a survey activity and marine life sensitivity occurring in the same location and the same time. Potential sound exposure of marine life is assessed by first determining how sound propagates through the water column over various distances from the sound source. This process predicts sound loudness. Predicted sound levels are then compared to relevant scientific knowledge to determine potential impacts of sound on marine life.

During operations, mitigation measures such as soft starts, exclusion zones and monitoring help to avoid the risks identified during project planning.

Soft-start involves a gradual increase in the loudness of the sound source to full operational levels at the beginning of the survey – usually over 20 to 40 minutes. The soft-start procedure allows time for any animal that may be close to the sound source to move away as the sound grows louder. This reduces the likelihood of exposure to higher sound levels.

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Exclusion zones are typically established and monitored around the acoustic source array as an additional precautionary measure. This further reduces the risk of potential physical harm to marine life. The size of the circular zone is either predetermined by regulation or, in absence of regulations, a minimum of 500 metres is widely used. If no animals are detected within this zone a soft-start can commence.

Figure 3: Observer scanning for marine mammals.

Visual monitoring by Marine Life Observers – also known as Marine Mammal Observers (MMOs) [3] or Protected Species Observers (PSOs) [4] – is common during seismic survey programmes. These trained personnel may initiate appropriate action, such as silencing the arrays, if a species of concern enters the exclusion zone.

Towed Passive Acoustic Monitoring (PAM) [6] may be used to complement visual monitoring. Hydrophones are towed through the water to detect the vocalizations of marine mammals.

Figure 4: Spectrogram display (frequency vs time) of a vocalization signal for a humpback whale, recorded offshore Brazil.

This allows detection of certain marine mammals in the exclusion zone at night or when visibility is poor. If an animal is detected in the exclusion zone, the PAM observer alerts the crew, who can then initiate appropriate action.

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5. Research informs protective measures for responsible seismic operations

While there is a wealth of information on marine life and sound from seismic surveys, the oil and gas and geophysical industries continue to support scientific research to address the remaining knowledge gaps.

Since 2006, a group of international oil and gas companies, in partnership with the geophysical industry, have funded a US$55 million research programme to advance the understanding of the interaction between sound from oil and gas operations and marine life.

Under the auspices of the International Association of Oil & Gas Producers (IOGP), this Exploration & Production Sound and Marine Life Joint Industry Programme (JIP) has become the largest non-governmental research programme in this field.

The JIP commissions independent studies and promotes the publication of the results in peer-reviewed literature. These studies are designed to better understand how sound travels in water; the possible physical and behavioural effects of sound on marine life; and new technologies and methodologies to mitigate potential impacts of sound from seismic survey activities.

The JIP has studied and developed a range of tools that are used to help understand the behaviour of marine mammals in their environment. These tools include animal tracking satellite tags, improved passive acoustic detection and classification tools. The JIP has also developed methodologies for assessing subtle behavioural and physiological responses to anthropogenic sound as well as potential long-term consequences, should they exist.

More information on industry’s commitment to science and the results of recent studies can be found at www.soundandmarinelife.org.

Individual oil and gas companies also support and participate in other research efforts as part of their internal global or regional programmes. They also work at local level to support specific operations or projects. Regulatory agencies, academics, and the military have also been engaged in studies to understand how sound affects the marine environment. Research from each of these entities helps to reduce remaining uncertainty and increases the understanding of effective techniques to avoid any potential negative effects of sound on marine life.

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Emerging technologies Emerging technologies may have the potential to provide even more effective protection of the marine environment during industry operations. Although compressed air acoustic source arrays provide the only efficient, robust and safe sound source that is currently viable for conducting large scale seismic surveys, efforts are underway to investigate alternative sound source methods and technologies.

In recent years, industry has invested significant research funding into the development of innovative seismic sound sources and alternative geological imaging technology.

The goal of this research is to determine whether there are alternative technologies that can better serve the world’s need to identify oil and gas reserves while further minimizing impacts on the marine environment.

Before any of these potential innovations become commercially available, each will need to demonstrate the ability to meet geophysical data quality objectives, operational safety and reliability requirements, and stewardship of environmental sensitivities. They must also meet regulatory compliance standards.

6. ConclusionFor decades to come, the oil and gas and geophysical industries will rely on seismic imaging technology to find and develop the hydrocarbon resources needed to meet the global energy demand.

With appropriate planning and mitigation measures, seismic surveys can be executed safely and without significant impacts to marine life in general and marine mammal populations in particular.

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References

[1] World Ocean Review. http://worldoceanreview.com/en/

[2] The First Global Integrated Marine Assessment, World Ocean Assessment I. http://www.worldoceanassessment.org/?page_id=14

[3] Discovery of Sounds in the Sea. http://www.dosits.org See: http://www.dosits.org/science/soundmovement/sofar/

[4] Marine Mammal Observer Association. http://www.mmo-association.org/

[5] US Department of Commerce. National Oceanic and Atmospheric Administration. See: http://www.nmfs.noaa.gov/pr/publications/techmemo/observers_nmfsopr49.pdf

[6] The E&P Sound & Marine Life Joint Industry Programme (JIP). http://www.soundandmarinelife.org See http://www.soundandmarinelife.org/innovation/pamguard.aspx

Learn more

API. See: http://www.api.org/policy-and-issues/policy-items/jobs/energizing-america

The Australian Petroleum Production & Exploration Association. See: http://www.appea.com.au/oil-gas-explained/operation/seismic-surveys/

Bureau of Ocean Energy Management. See: http://www.boem.gov/BOEM-Science-Note-August-2014/

International Association of Oil and Gas Producers. http://www.iogp.org

International Association of Geophysical Contractors. http://www.iagc.org

International Energy Agency. Energy Technology Perspective (2014). http://www.iea.org/etp/explore/

National Oceanic & Atmospheric Administration. See: http://oceanexplorer.noaa.gov/explorations/sound01/background/acoustics/acoustics.html

Petroleum Exploration & Production Association of New Zealand. See: http://www.seismicsurvey.co.nz/

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AcknowledgementsEnvironment Committee Sound and Marine Life Subcommittee

Photography used with permission courtesy of: Front page: ©cookelma/iStockphoto Page 3: PGS, Courtesy of IAGC Page 4: ©RobertPlotz/iStockphoto Page 7: CGG, Courtesy of IAGC

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