Marine seismic surveys

Seismic exploration is undertaken for a range of different purposes

Marine seismic surveys are commonly used around the world:

  • to identify potential oil and gas reservoirs below the seafloor
  • to identify reservoirs suitable for storing waste carbon dioxide to prevent it from entering the atmosphere and contributing to climate change
  • for geological studies of rock layers beneath the seabed
  • for site characterisation for renewable energy developments.

The process of collecting seismic data is known as ‘acquisition’. A marine seismic survey takes place along a series of pre-defined acquisition lines (normally several hundred metres apart) within an overall acquisition area.

Marine seismic surveys are carried out by specialised vessels that tow an array of acoustic sources (airguns) and receivers (hydrophones) across a defined acquisition area.

Airguns work by rapidly releasing compressed air to form a bubble, which creates a pulse of sound. This sound energy is directed at the seafloor and penetrates into the various rock layers beneath.

The reflected soundwaves are then captured by hydrophone receivers, which are towed behind the vessel on a series of cables known as ‘streamers’.

By analysing the soundwaves collected across an acquisition area, geophysicists and geologists are able to build a picture of sub-seabed geological layers, and more accurately define areas that may:

  • hold oil and gas deposits
  • be suitable for storing waste carbon dioxide
  • be appropriate sites for offshore development.

There are a number of lower amplitude sound source technologies in development, such as marine vibroseis, that could be used in marine seismic surveys. While these new technologies have the potential to reduce environmental impacts, they are not yet commercially available and may have other impacts and risks.

Different survey techniques are applied depending on the objectives

Marine seismic surveys can be two, three, or four dimensional (2D, 3D, or 4D).

2D surveys 3D surveys 4D surveys
  • Completed during the early phases of oil and gas exploration
  • Used for larger survey areas
  • Tend to have a smaller sound source and a single streamer
  • Produce a 2D image of a single cross-section through the seabed
  • Consist of multiple acquisition lines, more widely spaced than 3D surveys
  • Completed prior to exploration drilling
  • Used to explore smaller, more defined areas in greater detail
  • Use a larger sound source and multiple streamers
  • Produce a highly detailed 3D image
  • Consist of acquisition lines that are more closely spaced than 2D surveys 
  • Completed during the oil or gas production phase
  • Use the same techniques as 3D surveys
  • Repeated surveying over the same location. Each survey is spaced out in time to provide a time-lapse image
  • Provide insight into changes in the subsurface over time

 seismic survey graphic

National and international requirements ensure the environment is protected

As with any other human activity, marine seismic surveys have the potential for some level of impact on the environment. The type and degree of environmental impact from a seismic survey is influenced by:

  • the nature of the biological, social, economic, and cultural features of the marine environment where the survey is proposed to take place
  • the level of spatial and temporal overlap with environmentally sensitive areas and times
  • the individual survey design (e.g. the nature of the sound source and acquisition line spacing).

The Offshore Petroleum and Greenhouse Gas Storage (Environment) Regulations 2009 (OPGGS Environment Regulations) require companies who wish to conduct a marine seismic survey to address these factors through an environmental impact assessment (EIA) for their specific proposed activity circumstances.

As NOPSEMA can quickly adjust environmental management requirements as the scientific knowledge base grows, the EIA must demonstrate regard to contemporary scientific research when making predictions of impact and determining required control measures.

In addition, there are a number of national and international requirements that are relevant to the environmental management of marine seismic surveys.

The key requirements that apply in Australia are:

There are also a range of international requirements that should be considered, such as:

  • the Convention on the Conservation of Migratory Species (CMS) Family Guidelines on Environmental Impact Assessment for Marine Noise-generating Activities (CMS Guidelines)
  • various technical guidelines on applying thresholds for the impact of received sound levels, e.g. marine mammal acoustic technical guidance
  • various guidelines and codes of conduct for effectively managing environmental impacts from marine seismic surveys, e.g. IUCN guidance on effective planning of geophysical surveys.

Relevant good practice advice from international guidelines is considered through NOPSEMA’s assessment and decision-making processes on environment plans.

Well-designed scientific research can improve environmental management outcomes

There is a large body of international and Australian scientific research into the potential effects of underwater sound generated from seismic surveys, and this knowledge is increasing. However, there are gaps in the science and more research will help to improve the evidence base for industry EIA and regulator decision making.

Early research centred on whales due to their well-developed hearing ability, but in recent years the focus has extended to other fauna groups, including commercially important fish and invertebrates, such as rock lobster and scallops.

The research indicates there are a range of potential impacts of seismic surveys on marine life. This includes physical effects, hearing loss, behavioural disturbance, and masking of communication.

The potential for physical effects is limited to within relatively close range of the sound source, while behavioural disturbance and communication masking effects may be realised at greater distance and lower received sound levels.

However, available evidence shows that, when properly planned and mitigated, seismic surveys do not result in serious or irreversible environmental damage to marine fauna populations.

The Discovery of Sound in the Sea website has good general information on the way marine animals may be affected by sound.

A number of new scientific studies into the effects of seismic on the marine environment are currently under way in Australia. Some key examples include:

The results of these studies will contribute to furthering our understanding of the impacts of seismic surveys on the marine environment.

Industry collaboration to continue funding well-designed research will assist in achieving more efficient and effective regulatory and environmental outcomes. NOPSEMA does not fund research but seeks to influence the research and science agenda to ensure it supports environmental impact assessments conducted by industry and NOPSEMA regulatory activities.

NOPSEMA research priorities of relevance to seismic surveys include improved understanding of:

  • impacts and management thresholds for commercially important invertebrates (e.g. rock lobster and scallops)
  • impacts to zooplankton
  • impacts to southern bluefin tuna and other fish stocks
  • best practice measures to detect whales and mitigate impacts.

Developing an environment plan based on scientific research and stakeholder consultation

Conducting a comprehensive EIA is a vital first step in understanding and managing the potential impacts of a particular seismic survey. It is also the core content of an environment plan.

A critical and often contested part of this process is the interpretation and application of relevant scientific research on the effects of sound on the marine environment.

Companies who want to do a marine seismic survey and those who may be affected by the survey often have different views on the interpretation of the science and the potential scale of environmental impacts resulting from a particular activity.

It is therefore important that the scientific inputs in each EIA:

  • are comprehensive, with consideration of a broad suite of relevant science
  • are based on a defensible and balanced interpretation of the results of important studies
  • are tailored to the specific activity circumstances (e.g. giving consideration to differences in experimental conditions and the specific real-world conditions of the proposed survey)

Another important part of the assessment process is consultation with people who may be affected by the proposed activity. This may help to identify important environmental features, scientific studies, or potential control measures.

Once the potential environmental impacts of a seismic survey are identified and evaluated, the oil and gas company proposing the survey applies management actions to ensure two important tests are met:

1)  those impacts are reduced to as low as reasonably practicable (ALARP)

2)  those impacts are reduced to acceptable levels, in order to ensure the environment is protected.

Management actions may include implementing internationally recognised controls, such as:

  • designing the survey to limit impacts in environmentally sensitive areas
  • avoiding particularly important periods (e.g. migration, fishing season, breeding) for sound-sensitive marine species
  • deploying marine fauna observers to ensure sound emissions are stopped if marine mammals are detected within a certain range
  • implementing exclusion zones to protect environmental features (e.g. offshore reefs)
  • reducing the duration of the survey or changing the way it’s conducted to limit the acoustic energy that’s emitted into the marine environment
  • effectively communicating with other marine users prior to, during, and after the survey.

Find out more about EIA content in environment plans and the assessment process.  

Innovative detection measures improve protection of marine fauna

The mitigation of potential impacts to marine mammals is dependent on an effective marine fauna detection ability. This helps identify the presence, location and behaviour of large marine animals during the course of a seismic survey and allows sound emissions to be ceased/reduced when animals approach the sound source.

There have been, and continue to be, technological advancements in the ability to detect marine mammals at sea. These advancements are considered by those wishing to carry out a marine seismic survey as part of the process of demonstrating ALARP in an environment plan.

The required breadth and effectiveness of marine fauna detection measures increases where there is greater potential to interact with whales and other large marine fauna, particularly during important life stages.

NOPSEMA and the Australian Antarctic Division recently commenced a collaborative project aimed at improving the detection and identification of whales during scientific surveys and maritime activities such as marine seismic surveys.

Technological developments will serve to improve confidence in the management of seismic surveys and the protection of marine fauna, as well as contributing to enhancing knowledge on distribution and behaviour.

Conflict between seismic surveys and commercial fisheries needs to be addressed

Both commercial fishers and companies who wish to carry out seismic surveys are given a ‘licence to operate’ in the Commonwealth marine area. At times, this results in spatial overlap and potential for conflict as the two industries compete for space.

Seismic survey proponents must consult with commercial fishing stakeholders during environment plan preparation and this process is important to identify and address stakeholder concerns.

Concerns commonly raised include potential for target fish species to be displaced by high intensity sound emissions, fishing activity being disrupted, or impacts on fish stocks and reproduction.

The measures adopted to address these concerns are inconsistent, and this has potential to increase conflict between these industries. The development of an effective and consistent framework to manage interactions between licence holders may help reduce conflict and associated time and cost burden.  

Where spatial overlaps occur between licence holders there is a need for:

  • careful planning to minimise the potential for negative interactions (e.g. by avoiding peak fishing areas or times)
  • frequent and effective communications on current and future seismic and fishing operations
  • a mutually respectful relationship where each party seeks to understand the other’s perspectives and challenges, and works proactively to find solutions.

NOPSEMA also sees value in the fisheries and petroleum industries developing mutually-agreed standard arrangements to manage interactions.

This could include:

  • the establishment of regular strategic forums to share information on upcoming operations at a regional level for planning purposes
  • effective communication protocols to manage operations happening at the same time
  • standard protocols for managing claims of financial loss.

NOPSEMA does not have a function to administer or arbitrate disputes between offshore petroleum proponents and commercial fishers but will continue to advocate for the development of such arrangements.

NOPSEMA has an important role to ensure environmental management is effective

NOPSEMA assigns a team of environment specialists to assess each marine seismic survey proposal through the submission of an environment plan.

NOPSEMA’s assessors undertake a comprehensive assessment of each proposal to ensure the facts, reasons, and evidence supporting the case that environmental impacts will be managed to ALARP and acceptable levels are robust. This includes ensuring that:

  • the description of the sound-sensitive marine fauna and socio-economic values (e.g. commercial fisheries) is comprehensive and identifies particularly sensitive areas and times where potential for impact is greater
  • the assessment of impacts to these environmental features is informed by reliable predictions of the sound levels that will be received
  • the scientific basis for conclusions is well founded, there is no cherry picking of papers to support particular arguments, and scientific results are interpreted and applied to the specific activity circumstances appropriately
  • the proposed environmental management measures are tailored to the activity circumstances and will be effective in ensuring impacts are managed to acceptable levels
  • appropriate measures are applied to address areas of uncertainty (e.g. adaptive management, scientific studies, or more protective control measures)
  • information provided by stakeholders has been incorporated into the EIA and, where necessary, control measures have been applied to address concerns.

If NOPSEMA determines that an oil and gas company is not taking appropriate action to protect the environment, we will not accept the proposal and the survey will not be able to commence in the way it was proposed.

Find out more