EIA for North Sea seismic surveys

12th May 2014

Related Topics

Related tags

  • Noise ,
  • Natural resources ,
  • Biodiversity


Margo Mosley

ERM's Mike Fraser and Steve Mitchell describe how noise propagation modelling was key in assessing how a seismic survey could impact marine fauna in the North Sea and helped obtain consent for the procedure

A 3D seismic survey is to be carried out in UK and Norwegian waters to explore for hydrocarbons in the south of the Statfjord licence block. Written consent to undertake the survey is required from the secretary of state under the Offshore Petroleum Activities (Conservation of Habitats) Regulations 2001, as amended in 2007, and an application has to be made to Decc to obtain this.

Information regarding environmental issues must be supplied including the effects of underwater noise. Potential disturbance and damage to the hearing of whales, dolphins, porpoises and turtles from underwater noise generated by air guns was a key issue. ERM prepared the necessary environmental impact assessment (EIA) justification for Statfjord Licence Group.

Our approach

In line with UK guidelines, a study was carried out to identify whether any marine species were likely to be significantly affected by the seismic survey. In particular, it examined whether the survey would cause deliberate disturbance, injury or death of any marine species protected under European legislation.

The study provided a description of the proposed survey, the baseline conditions and an assessment of the potential impacts from planned and accidental events, including: emissions to air; discharges to sea; the physical presence of the survey vessel and support vessels; and noise generated by vessel engines and air guns. Most potential impacts were identified as not significant, but further assessment was needed on underwater noise disturbance.

Marine noise exposure modelling

Underwater noise propagation from the seismic air gun array was predicted using ERM’s marine noise exposure model.

The model has been developed to simulate the propagation of sound taking into account the local marine environment, including water temperature, salinity, bathymetry, seabed absorption and the underlying bedrock characteristics, all of which affect the propagation or reflection of sound waves.

Sound propagation is modelled down to frequencies of 10Hz to address the hearing range of all relevant species. After defining the local environment, the model produces transmission-loss results for a set of vertical transects through the study area. These are used to compute frequency-weighted sound levels as a function of water depth around the noise source.

This process yields instantaneous noise levels. However, to consider disturbance and potential damage effects fully, it is necessary to also consider the dose of noise an animal will experience over time.

To do this ERM has developed a noise exposure model that sums the noise levels as an animal moves through the water. In this case a “swim away” model was used (see figure above) assuming the animal moves away from the noise source at a given speed at a depth where the noise level is highest.

This process allowed a cautious, but robust, calculation of the noise dose and the impact on the various species known to be in the area of the survey activity.

The likelihood of animals being close enough to the noise source to be significantly affected was then estimated from known animal sightings and population data for the area. A suitable soft-start process to the seismic survey was adopted to give sufficient time for animals to move away from the exclusion zone so that the potential for significant effect was minor.

Outcomes and lessons learned

In keeping with other projects, the modelling indicated that noise from seismic operations can potentially lead to impacts over a wide area unless mitigation measures are adopted.

It is important to model the noise impact zone taking into account site-specific factors that affect noise propagation to ensure that effects are realistically assessed.

It is also necessary to consider animal movement within the sound field, which affects the accumulated noise exposure and potential for injury.

To assess the potential for an offence, the likelihood of animals being sufficiently close to the airgun array must be taken into account. There is inherent uncertainty in this process even if a detailed study of the marine baseline is available. It was critical for marine biologists and acousticians to work together so that robust assumptions could be made.

With appropriate good practice mitigation consent was given in time for the survey to proceed on schedule.

Mike Fraser (michael.fraser@erm.com) is a principal consultant at ERM and Steve Mitchell (steve.mitchell@erm.com) is a technical director at ERM.

Transform articles

National climate plans could see fossil fuel demand peak by 2025

Demand for fossil fuels will peak by 2025 if all national net-zero pledges are implemented in full and on time, the International Energy Agency (IEA) has forecast.

15th October 2021

Read more

The Green Homes Grant is set to deliver only a fraction of the jobs and improvements intended, leading to calls for more involvement from local authorities in future schemes.

23rd September 2021

Read more

COVID-19 recovery packages have largely focused on protecting, rather than transforming, existing industries, and have been a “lost opportunity” for speeding up the global energy transition.

23rd September 2021

Read more

Half of the world's 40 largest listed oil and gas companies will have to slash their production by at least 50% by the 2030s to align with the goals of the Paris Agreement, new analysis has found.

9th September 2021

Read more

None of England’s water and sewerage companies achieved all environmental expectations for the period 2015 to 2020, the Environment Agency has revealed. These targets included the reduction of total pollution incidents by at least one-third compared with 2012, and for incident self-reporting to be at least 75%.

30th July 2021

Read more

The UK’s pipeline for renewable energy projects could mitigate 90% of job losses caused by COVID-19 and help deliver the government’s ‘levelling up’ agenda. That is according to a recent report from consultancy EY-Parthenon, which outlines how the UK’s £108bn “visible pipeline” of investible renewable energy projects could create 625,000 jobs.

30th July 2021

Read more

Billions of people worldwide have been unable to access safe drinking water and sanitation in their homes during the COVID-19 pandemic, according to a progress report from the World Health Organisation focusing on the UN’s sixth Sustainable Development Goal (SDG 6) – to “ensure availability and sustainable management of water and sanitation for all by 2030”.

30th July 2021

Read more

The oil and gas industry is set to burn through its allocated carbon budget 13 years early unless decisive action is taken immediately, new analysis has found.

22nd July 2021

Read more

The UK will no longer use unabated coal to generate electricity from October 2024, one year earlier than originally planned, the Department for Business, Energy & Industrial Strategy has announced.

2nd July 2021

Read more

Media enquires

Looking for an expert to speak at an event or comment on an item in the news?

Find an expert