Unplanned Events
Shell has designed and developed Prelude to operate with the lowest possible risk to the environment. Mitigation strategies outlined in the Environment Plan (EP) document submitted to NOPSEMA describe the various ways Shell is managing environmental impact and risk.
Shell has identified there is a risk of unplanned loss of containment events which may have environmental impacts. For the purpose of the EP Shell has used industry standard modelling to assess areas of risk and the potential impacts.
For more information on modelling emergency events view a video or factsheet (PDF), created by NOPSEMA.
Risk
The risk of an emergency event as a result of unplanned loss of containment is very remote.
The chances of a worst-case scenario event, such as those modelled by Shell, is even more unlikely.
Shell is confident that sufficient management, technical and design systems have been put in place to protect the environment from any unplanned release of harmful material.
What is loss of containment?
There are different kinds of petroleum products stored on Prelude which could have environmental impacts if they were accidentally released into the environment.
There are different types of loss of containment scenarios which have a range of potential impacts.
- Subsea infrastructure – production well loss incidents are rare and range from minor breaches from pinhole leaks, through to a well blowout.
- Product storage and offloading – Prelude’s product streams may have an impact on the environment if there is an accidental release during storage or offloading.
- Fuel oil – There is a chance of loss of fuel oil if there is a collision with a tanker. However, given the impact energy required to result in a tank breach the risk is considered very remote.
- Diesel – there is a risk of loss of diesel during operations. The only scenario that might result in this kind of loss is a collision with a vessel.
- Other hazardous liquids – there is a risk of materials other than hydrocarbons, being released accidentally during operations.
For more information on the management of waste or liquid discharges click below.
- Waste
- Liquid Discharges
For a detailed summary, select your area of interest:
Environment
Environment
Sediment quality
Sediment quality is not expected to be significantly affected by any worst-case scenarios of materials release at the sea’s surface. It is expected that any loss scenario at or above the surface, is unlikely to reach the seabed due to the water depth in the operational area.
Loss of containment at the seabed, such as loss of well control, may contaminate sediments. For larger scale releases near shorelines there is a chance of long-term contamination depending on the type of material released.
Water quality
Some hydrocarbon compounds will have a greater impact on water quality than others, should they be accidentally released. Overall, regardless of release type, the concentrations of hydrocarbons in the water column will decrease over time following control of the release source.
Air quality
A worst-case loss of well containment scenario would result in a gas cloud if released material reached the water’s surface. In the offshore environment the gas cloud would be expected to disperse rapidly.
Modelling results indicated no key ecological features would be exposed to floating hydrocarbons at a level resulting in an adverse impact. However, several key ecological features may be exposed to other types of hydrocarbons at levels which would result in an adverse impact. The full Environment Plan describes which key ecological features have a high likelihood of a significant impact during an emergency event.
Key ecological features are most likely to be impacted by a loss of materials in the subsea infrastructure, such as loss of well control, due to the potential scale of such a blowout.
It is expected that potential impacts would be limited to submerged features, as floating oils are not predicted to contact key ecological features at levels which would cause impacts.
Benthic communities
Benthic communities
Sediments
The seabed in the Prelude operational area is largely sediments which are home to low density epibenthic fish and crustaceans. These species may be subject to health impacts from exposure to hydrocarbons. However, it is expected that any affected habitat will be limited to areas in close proximity to the location of a subsea release. Filter feeders are particularly susceptible to health impacts, due to their method of feeding.
Corals
Impacts to coral from hydrocarbons vary from no visible injury, through to significant coral deaths. Some coral types are more sensitive than others, and their stage in the lifecycle will also make them more or less susceptible to impacts.
Subtidal corals are likely to be less impacted by releases at the surface and although reef coral habitats are more likely to be impacted by a severe spill, they are also less sensitive to impact. Volume and duration of an unplanned release will play a big factor in the extent coral communities are potentially affected.
Macroalgae and sea grass
Although seagrass and macroalgae may be impacted by a loss event, studies have shown that recovery rates are rapid.
In the case of macroalgae, research has also indicated, in some instances, recovery is faster in cases where oil is left to degrade naturally.
Mangroves
Mangrove habitats throughout the Kimberley are highly susceptible to oil pollution. However, given the significant distance between potential release locations and the nearest mangroves, any materials reaching mangroves would be highly weathered. As such, even in worst-case modelled releases mangrove communities are not likely to be impacted.
Marine fauna
Marine fauna
Marine mammals
There are eight species of marine mammals which may be found within the zone of potential impact. There are biologically important areas for several species within 145km of Prelude. Despite the vulnerability of marine mammals to hydrocarbons, it is not anticipated that impacts resulting from a loss event would affect any significant portion of any species’ population.
Marine reptiles
Marine reptiles, including sea snakes and turtles are known to live in or traverse through the adverse exposure zones. Saltwater crocodiles are also identified as potentially occurring within this zone. Both sea snakes and turtles have the potential to experience health impacts from encounters with materials released during loss events.
Seabirds and shorebirds
Seabirds and shorebirds are known to be present within the zone of potential influence. Seabirds are known to be particularly vulnerable to hydrocarbon spills due to their contact with the water’s surface during feeding, resting or moulting. Shorebirds are less likely to be impacted as they usually remain on shorelines to feed. Should any bird come into contact with material following a LOC event, they are likely to suffer severe health impacts. Mass mortalities are not expected given the low number of birds in the area, and distance from any known breeding colonies.
Different types of plankton are likely to be impacted by a worst-case scenario loss event. The impacts are likely to consist of short-term acute toxic effects. However, the compressed lifecycle of the species is likely to result in a rapid recovery in the population. Species that have planktonic larval phases are likely to be impacted in a worst-case scenario, with increased larval mortality, however this is not expected to result in population scale impacts.
Pelagic fish
Fish that encounter material from a loss release may experience health impacts, which will vary on the concentration and duration of exposure. The conclusion supported by studies of fish stocks following large-scale spills shows little evidence of severe impacts at the population level.
Human activities
Human activities
Commonwealth Heritage Places and Marine Protected Areas
Several offshore islands and reefs listed as Commonwealth Heritage Places and Marine Protected Areas are within the areas modelled and may be impacted in the event of a loss. The value of these locations occurs in their unique ecology, habitats and sea scapes. As such, the potential impact to these areas would be significant.
Commercial fishing
A number of commercial fisheries operate within the adverse exposure zone. In the event of a significant loss, it is likely locations affected would be temporarily closed. The nature of the closure would depend on the extent and type of spill. Any spill is unlikely to result in the complete closure of a fishery. Fish exposed during a loss event may become “tainted”, which would require ongoing monitoring. In some instances, the perception of possible tainted stock would be sufficient to reduce prices and lower income for commercial fishers.
Tourism and recreation
There are currently no known tourism activities within the operational area. Some tourism activities may take place within the zone of potential influence. Worst-case scenario impacts would be displacement of activities, temporary exclusions zones or avoidance of areas which are aesthetically impacted as well as flow-on revenue impacts to tourism operators. Any impacts to activities is expected to be slight.
Defence and shipping
Defence activities are unlikely to be impacted by even the worst-case scenarios modelled by Shell. Vessels in the area may be temporarily diverted to accommodate spill response operations.
Oil and gas industry
There are other petroleum activities in the region. A worst-case scenario spill may affect the operation of the facilities if water quality is impacted and is no longer suitable for use in the other operations. There may also be impacts on routine operations, such as reduced production. A clean-up operation may result in increased competition for vessels and drill rigs if well intervention is required.
Clean-up activities
Some clean-up activities have their own associated environmental impacts. New or unique impacts associated with the implementation of spill response strategies are considered acceptable where they present a net environmental benefit compared to the “do nothing” approach.
