Environment plan for proposed drilling in the Great Australian Bight

About environment plans

An environment plan:
  • details what the operator plans to do
  • identifies the environmental risks
  • explains the plans to manage environmental risks so that they are ‘as low as reasonably practicable’ and acceptable
Operations in the Great Australian Bight can't start unless the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) accept our environment plan.

An environment plan was submitted to NOPSEMA in August 2016.
We expect and welcome scrutiny by regulators and the community to make sure our work is safe and environmentally acceptable. You can contact us online or call us on 1300 130 027.

For more information about regulatory approvals, read our regulatory approval fact sheet.

Oil spill response planning

We don’t expect an oil spill – in fact we plan to not have one. But we also plan to be prepared in meticulous detail should one take place.

The Oil spill response planning strategic overview explains the planning of oil spill response strategies to support preparedness for safe and compliant exploration drilling in the Great Australian Bight.

In the event of an incident, an Australian response team will be stood up within an hour of being notified. We would also work with government bodies for notifications, response support and regulatory oversight as required. Additionally, we have access to support organisations and agencies that can provide resources to support an oil spill response.

A suite of response measures will be activated in response to any oil spill events as required, as soon as practicable and when safe to do so.

Oil pollution emergency plan

The environment plan must contain an oil pollution emergency plan which includes oil spill response arrangements that must be appropriate for the nature and scale of the petroleum activity proposed and for the range of credible spill scenarios that may result from the activity.
As well as meeting our own standards, we must demonstrate to NOPSEMA that the plan has adequately addressed these requirements in order to gain regulatory approval to commence exploration drilling.

Our own requirements for oil spill preparedness, and response planning and crisis management, incorporate what we have learnt over many years of operation and specifically from the Deepwater Horizon accident.

Oil spill modelling

Oil spill modelling is conducted as part of our oil spill response planning process. For more detailed information about oil spill modelling, read Fate and effects oil spill modelling assumptions, parameters and results.

Oil spill trajectory model

A BP global oil spill modelling specialist conducted oil spill modelling for the Great Australian Bight drilling project using the SINTEF OSCAR model, which is our preferred oil spill fate and trajectory model. OSCAR is a three-dimensional model that calculates and records the distribution (as mass and concentrations) of contaminants on the water surface, on shorelines and in the water column.
The model computes surface spreading, slick transport, entrainment into the water column, evaporation, emulsification and shoreline interactions to determine oil drift and fate at surface.

The 3-D current and 2-D wind fields used in the OSCAR simulations to drive pollutant transport were generated using the Imperial College ReEMS model. The model was run in hind cast mode to generate current and wind datasets for the region covering a five-year period (2006 – 2010).

The ReEMS for Australia was set up with the ocean model Regional Ocean Modelling System (ROMS). ROMS is a free-surface, terrain-following, primitive equations ocean model widely used by the scientific community for a diverse range of applications. The atmospheric forcing in the form of six-hourly surface winds, precipitation, radiation and surface air temperature is from the Climate Forecast Reanalysis.

The boundary ocean files are taken from the 1/12 HYCOM re-analysis and the tides from the OTIS Regional Tidal Solutions. Bathymetry is from Global Multi-Resolution Topography and the river input from RiverDis v1.1.

The scope of work for the modelling included:
  • use of stochastic (or probabilistic) modelling to predict the probability of contact to the sea surface, shorelines and water column for each scenario
  • calculation of the likely volume of oil contacting the shoreline
  • review of the stochastic results and present the single spill trajectories with the highest amount of oil reaching the shore for each scenario
  • evaluation of the potential effect of subsea dispersant application in reducing shoreline oiling impacts for each scenario

Modelling thresholds for shoreline, sea surface & water column

Shoreline: 0.1 l/m² or 100 ml/m²

The International Tank Owners Pollution Federation (ITOPF) guidelines for the recognition of oil on shorelines (ITOPF, 2011) were used to define the response threshold for shoreline oiling.

The definition for 'light oiling' is selected as the most appropriate threshold. Light oiling is defined as 1mm thickness of oil with 10 per cent coverage over 5m width. This is equivalent to a threshold of 0.1 l/m2 or 100 ml/m2.

The 100 ml/m2 threshold is assumed as the lethal threshold for invertebrates on hard substrates and sediments (mud, silt, sand, gravel) in intertidal habitats based on Owens & Sergy (1994) and French (2009).

Sea surface: 5 µm (microns) (equal to 5 g/m², 0.005 mm)

The 5 µm  threshold value is derived from the Bonn agreement colour code (ref 4). The code relates the appearance of oil on the water surface and the quantity of oil. This is used as a basic for aerial observation for oil spill response operation.

The minimum thickness of oil that may result in harm to seabirds through ingestion from preening of contaminated feathers, or loss of thermal protection from their feathers, has been estimated by different researchers to range between 10 µm (10 g/m2) to 25 µm (25 g/m2).  Given seabirds are considered sensitive to oiling, this 10 µm threshold is also often applied to other wildlife as a conservative measure.

The selection of the 5 µm threshold thus represents a conservative basis upon which to model an oil spill for spill response planning purposes.

Water column: 58 ppb total hydrocarbons

Carls et al (2008) found that the acute toxicity of water-soluble fraction of oil (LC50) varies from 200 to 5000 ppb total hydrocarbons.

Based on extensive toxicity tests of crude oils and oil components on marine organisms, the Norwegian Oil Industry Association (OLF) guideline for risk assessment of effects on fish from acute oil pollution (2008) concluded that threshold concentration for an expected No Effect Concentration for acute exposure for total hydrocarbons ranges from 50 to 300 ppb.

Work undertaken by Neilson et al (2005, as reported in OLF, 2008) proposed a value for acute exposure to dispersed oil of 58 ppb, based on the toxicity of chemically dispersed oil to various aquatic species, which showed the 5 per cent effect level is 58 ppb.

The 58 ppb threshold for the No Effect Concentration for oil dissolved and entrained oil in the water column was thus selected based on the conclusion in the OLF guideline.

Stochastic modelling

Stochastic modelling was conducted as part of the oil spill modelling work scope. Stochastic modelling is used to predict the probability of contact with a receptor.

The stochastic oil spill modelling that was undertaken for the Great Australian Bight wells was conducted for three separate weather ‘seasons’ which best grouped the likely prevailing weather conditions. Ten simulations were run per month – each varying in start time – using data for winds and currents from January 2006 to December 2010.
This ensures that the predicted transport and weathering of an oil spill simulation is subjected to a range of prevailing wind and current conditions that is historically representative of the time period in question.
We ran:
  • 270 individual simulations during summer (October to March) when there are predominantly south and south-east winds
  • 181 individual simulations during winter (June to September) when there are mainly north and north-west winds
  • 100 individual simulations during the transitional season (April and May) when there is no real wind pattern
Although each simulation uses the same release information, they have differing trajectory paths due to the varying start times and associated conditions, such as tides and temperature. The stochastic model reports a summary of all the predicted individual simulations and therefore is used to determine the probability of spill direction based on these aggregated results.

Water depths

The exact drilling locations have not been determined yet. Drilling will be conducted in the area of the previously conducted seismic survey. Water depths in this area range from approximately 1000m to 2500m.

Preventing a well control incident

There could be various causes leading to a well control incident, such as defective well design or execution, drilling into shallow gas, an influx of hydrocarbons into the wellbore or collision with an offshore vessel.
For each of these causes we will have multiple barriers in place. All of these barriers are verified before operations commence.
Some examples of these barriers are: having a detailed well program in place, selecting and managing appropriate contractors, maintaining a hydrostatic overbalance, and a fully operational blow out preventer system including an Emergency Shut Down operation.

These barriers will be tested and verified during the well construction process.

Capping & containment plan

Capping stacks are devices that interface with a well to curtail the flow resulting from a well control event. As part of the lessons learned from the Deepwater Horizon accident there has been significant advances in subsea technology and capping stacks are now proven technology for oil spill control during a subsea well control event.

There are a number of capping stacks available to the industry strategically placed around the world. Oil Spill Response Limited, of which BP is a member, has capping stacks positioned in Singapore, Brazil, Cape Town, and Stavanger. Further, there are around 20 other capping stacks globally that are owned by a number of different operators and industry associations.

As we finalise the well locations and well designs for the Great Australian Bight, we will identify capping devices that are fit-for-purpose for the wells to be drilled. A capping and containment plan to document the plans for mobilising and installing various capping devices to the Great Australian Bight will be finalised before drilling commences. The decision of when to deploy a fit-for-purpose capping stack will be part of our capping and containment plan. It is expected that mobilisation activities will commence very shortly after a notification of a loss of well control event.
Along with a capping and containment plan, we will have a full suite of oil spill response measures available.
The detailed plans for mobilising and deploying various response strategies will be documented in our oil pollution emergency plan.

Subsea first response toolkit

The Australian subsea first response toolkit is financed by 13 offshore oil and gas companies including BP, and is stored in Fremantle, Western Australia, for immediate mobilisation if required for a well control event.

The toolkit contains specialised equipment required to clean the area around the wellhead, enable intervention, and prepare for relief well drilling and safe installation of a well capping or containment device. We will mobilise the equipment to site in the event of a loss of well control event.
Our first responder vessel – one of the support boats for the Ocean GreatWhite rig – will be equipped with a remote operating vehicle and will be available at the well site within 48 hours should it be required.
Once finalised, the oil pollution emergency plan will detail the first response equipment required locally to support the first responder vessel.

Relief well

As members of APPEA, BP and other oil and gas operating companies have signed a Mutual Aid Agreement whereby the industry will make assets (including rigs) available to other members in the event of an emergency. Vessels also form part of the response and the Australian Maritime Safety Authority can secure any assets in Australia if required.
A relief well plan will be in place before we start drilling and the plan would be initiated immediately in the event of a loss of well control.

Sound generation & marine life

We have modelled sound attenuation from proposed drilling operations, which includes both rig thrusters and vertical seismic profiling.

Cetaceans use sound for navigation, communication and prey detection, and are therefore considered to be a sensitive receptor of anthropogenic underwater sound. The level of potential impact to marine fauna depends on multiple factors, such as the intensity and duration of underwater sound, distance from the source, hearing sensitivity of the fauna species and activity at the time of sound exposure (for example migrating or feeding) as well as any mitigation measures that may be employed.

The key cetacean species identified as sensitive receptors in the drilling area (i.e. those that are listed as threatened under the Environment Protection and Biodiversity Conservation Act or have ‘biologically important areas’ recorded in the region) are blue, southern right, humpback and sperm whales. Key aggregation areas for these whales in the Great Australian Bight are along the shelf break, at the head of the Bight and at Kangaroo Island’s pools and canyons.

We commissioned the Centre for Marine Science and Technology at Curtin University in Perth to undertake a study to predict the level of underwater sound associated with the drilling operations. Modelling results predict that the sound pressure level dropped below 160 dB re 1 μPa RMS within 100m of the drilling rig, and below 120 dB re 1 μPa RMS between 10km and 40 km from the drilling rig. With the MODU at the most northern point of the proposed drilling area, the sound level is predicted to be less than 115 dB re 1 μPa SPL RMS at the shelf break and less than 106 dB re 1 μPa SPL RMS at the Head of Bight and the Kangaroo Island’s pools and canyons.

Studies conducted regarding potential impacts on whales from continuous sound indicate that no or limited response is likely for sound levels below 120 dB re 1 µPa sound pressure level RMS while sound levels greater than 160 dB re 1 μPa SPL RMS have been recorded as causing behavioural responses in baleen whales (Southall et al, 20071). A threshold of 160dB re 1uPa SPL RMS is often used as a threshold for assessment of potential behavioural disturbance.

Given these predicted sound levels, it is unlikely that whales in key aggregation areas will be disturbed by the drilling program. In the unlikely event that individuals passing through the immediate drilling area were disturbed by increased sound levels, this would not affect the species at the population level.
Although modelling predicts that sound levels are below any levels that are likely to cause disturbance to sensitive marine fauna, we will examine options to conduct sound recording during our operations.

Decibel scale

The decibel (dB) scale is a logarithmic scale that expresses the ratio of two values of a physical quantity. It is used to measure the amplitude or loudness of a sound. As the dB scale is a ratio it is denoted relative to some reference level, which must be included with dB values if they are to be meaningful. The reference pressure level in underwater acoustics is 1 micropascal (µPa). Whereas the reference pressure level used in air is 20 μPa, which was selected to match human hearing sensitivity.

As a result of these differences in reference standards, sound levels in air are not equal to underwater levels. To compare sound levels in water to sound levels in air, it is necessary to subtract 62 dB from the sound level in water to account for the difference in reference levels and absorption characteristics of the two mediums.

Sound pressure & sound exposure levels

Underwater sound is typically measured in terms of instantaneous pressure, or sound pressure level, in dB re 1µPa (Richardson et al., 2005). Sound pressure level can also be expressed as a root mean squared (RMS) measure, which is an average pressure over a duration of time.

Source level is a measure of sound at a nominal distance of 1m from the source and is denoted in dB re 1µPa@ 1 m. 

Sound pressure level is used in this impact assessment wherever possible as it has historically been used to assess potential impacts to marine life. However sound exposure level is increasingly used for assessing impacts to marine life as it accounts for duration of sound exposure and enables comparison between sound from different sound signals – and therefore sound sources – with different characteristics.

Sound exposure level is a metric used to describe the amount of acoustic energy that may be received by a receptor, such as a marine animal, from an event. This level is the dB level of the time-integrated, squared sound pressure normalized to a one-second period, and is expressed as dB re: 1 μPa2-s.

Given the multiple measures commonly used to express sound levels, it’s important to ensure any comparisons between specific sound level values are made using the same measures; for example peak sound pressure level compared with peak sound pressure level, or RMS sound pressure level with RMS sound pressure level.

Cumulative sound

We have not conducted any research regarding cumulative sound from multiple operations in the Great Australian Bight. We are not aware of any other oil and gas activities that will be conducted at the same time as our drilling operations. However, we have regular meetings with other oil and gas operators in the Great Australian Bight and will discuss such cumulative sound studies in the event that multiple operations overlap.
1: Southall, B L, A E Bowles, W T Ellison, J J Finneran, R L Gentry, C R Green Jr, D Kastak, D R Ketten, J H Miller, P E Nachtigall, W J Richardson, J A Thomas and P L Tyack (2007).  Marine Mammal Noise Exposure Criteria: Initial Scientific Recommendation. Aquatic Mammals, 33 (4): 411 – 414

Benthic smothering

Drill cuttings are generated during drilling operations as the drill bit penetrates into the earth displacing rock and sand particles from the well. These cuttings are contained within drilling fluids (or muds) which transport cuttings to the surface. Drilling fluids also cool and lubricate the drill bit, and seal the walls of the well in sections with permeable rock in order to prevent cave-ins and flow of formation fluids which could cause a blowout.

Cuttings and the associated fluids are discharged directly onto the seabed during drilling of the top-hole section (riserless operations), before circulating infrastructure is installed, which enables cuttings and fluids to be returned to the MODU for separation such that the fluids can be reused, and the cuttings discharged overboard via a chute.
Smothering of benthic habitat and fauna may occur close to the well where cuttings settle on the seabed.

Deposition of greater than 9.6mm is considered likely to cause smothering impacts on benthic ecosystems.
The modelling used to predict dispersion of drill cuttings and fluids predicts that less than 1km squared around each well will be affected by this 1mm to 10mm sediment deposition thickness.
Studies indicate that benthic infauna and epifauna recover relatively quickly, with substantial recovery in deepwater benthic communities within three to 10 years. However, recovery is dependent on the type of community affected; the physical structure and persistence of the cuttings pile itself, the presence and nature of any toxic components within the cuttings and the availability of colonising organisms.


In Australia, the Australian Maritime Safety Authority’s Protocol for the Register of Oil Spill Control Agents is the recognised standard for the acceptance of chemical dispersants. This standard has been prepared to screen chemical dispersants for use in marine pollution incidents with the intent of covering a range of possible oil types and environmental conditions.
Given this focus, the dispersants registered are accepted for general purpose response activities with application dependent on the specific incident.