gorgon gas development backfill fields
Chevron Australia is the operator of the Gorgon Project (Gorgon), one of Australia’s largest natural gas projects located off the northwest coast of Western Australia.
As outlined in the initial development approval for Gorgon, we are planning to install a subsea gathering network for seven backfill fields in the Greater Gorgon region. A backfill field is a supply of natural gas from an alternative source that will support the continued use of an existing facility.
The Gorgon Gas Development Backfill Fields (the Development) represents the next phase of the Gorgon Project, and the intent is to maintain current rates of liquefied natural gas (LNG) and domestic gas production at the Gorgon Gas Facility on Barrow Island.
We are seeking initial feedback from stakeholders to help us prepare an Offshore Project Proposal (OPP) for submission to the National Offshore Petroleum Safety and Environment Management Authority (NOPSEMA).
location and water depth
The seven fields are located about 200 kilometres north of Onslow and 100 kilometres north-northeast of Barrow Island, at depths of 150 metres to 1,230 metres. Most of the fields are in water depths greater than 800 metres. The fields are: Chandon, Chrysaor, Dionysus, Eurytion, Geryon, Semele and West Tryal Rocks. The operational area includes a five-kilometre buffer around the most conservative indicative location of the backfill fields’ infrastructure (figure 1).
schedule and duration
Activities to start the development of the first field are proposed to commence in 2025. Field development will be staggered so all fields will not be developed in a single campaign. The order of the development of the seven fields has not yet been finalised.
During development periods, work will occur in stages throughout the year and activities could occur during the day or night.
The Development intends to tie in the seven backfill fields with the existing subsea gathering infrastructure which connects the two currently operational gas fields, Gorgon and Jansz-Io, with the Gorgon Gas Facility. From the facility, gas is processed and liquefied for export as LNG or piped to the mainland for Western Australian domestic gas users.
Planned activities in the fields include:
- drilling wells
- installing a subsea gathering network that connects the wells to the existing Gorgon and Jansz-Io pipelines
- conducting geotechnical and geophysical surveys
- commissioning and start-up
- maintaining and repairing infrastructure
- operating vessels, helicopter and remotely operated vehicles
Subsea infrastructure will include:
- wells and associated infrastructure
- flowlines carrying gas from the fields to the Gorgon and Jansz-Io pipeline tie-in locations
- lines to convey electricity, fibre-optic cables, and hydraulic and other fluids, called umbilicals.
No permanent structures will be above the sea surface.
EMBA – environment that may be affected
Planned activities will have the potential for environment interactions, known as ‘aspects’
Planned aspects result in environmental impacts and changes to the environment and may present environmental risks.
Unplanned releases and events may occur while conducting activities.
The size of the ‘environment that may be affected’ also known as an ‘EMBA’ is based on an emergency condition’s worst case environmental scenario. In this case, the EMBA has been defined through combining 300 simulations from a loss of well control event from each of the seven fields under different hydrological and meteorological conditions representative of summer, winter and transition seasons in the north west. Figure 1 shows the EMBA.
Control measures to prevent a loss of control event are in place, however, Chevron Australia is required to assess this highly unlikely scenario.
In this scenario, cultural, ecological and social values and sensitivities may be exposed to hydrocarbons. These are considered environmental risks because they are not planned to occur.
Table 1 lists potential environmental impacts and risks and control measures.
The Gorgon Gas Development primary approval under the Environmental Protection and Biodiversity Conservation Act 1999 (Cth) and Environmental Protection Act 1986 (WA) included developing the Gorgon and Jansz-Io fields and constructing the Gorgon Gas Facility (also known as the Gorgon Gas Treatment Plant) on Barrow Island
The backfill fields were envisaged in the initial Gorgon Gas Development approvals process and will tie into existing subsea gathering infrastructure and be processed in the existing Gorgon Gas Facility.
The fields do not increase the life or capacity of the Gorgon Gas Facility beyond the approved Gorgon Gas Development.
Chevron Australia is preparing an OPP to develop the seven backfill fields for submission to NOPSEMA.
The OPP will include:
- an assessment of environmental impacts and risks to show that the activities are environmentally acceptable
- identification and assessment of feasible alternatives including a comparison of environmental impacts and risks
- clearly defined and measurable environmental performance outcomes
- sufficient information to allow the public to provide informed comment.
After submission, NOPSEMA first checks that there is enough information for members of the public to make an informed comment.
NOPSEMA then sets a public consultation period of at least four weeks, during which stakeholders can submit comments. After comments have been received and addressed, NOPSEMA begins their assessment to decide whether to accept or reject the OPP.
NOPSEMA’s acceptance of the OPP is a general indication of the development’s environmental acceptability, however, it does not allow Chevron Australia to commence work.
Before commencing work, we must conduct further and more detailed consultation with relevant persons as part of the process of preparing an environment plan. That environment plan then needs to be reviewed and accepted by NOPSEMA before work can commence.
Stakeholders are invited to provide details of any additional aspects or potential control measures they consider relevant or ask for additional information or consultation.
You can contact us toll free on 1800 225 195 or leave feedback online below.
If you choose to provide feedback, Chevron Australia will collect your name and contact details, for the purposes of maintaining contact with you and including your feedback in our submission to NOPSEMA. Provision of this information is purely voluntary, however if you choose not to provide it, we may not be able to contact you in the future. Chevron may transfer your information to NOPSEMA if required and, if you do not identify it as sensitive, to other Chevron affiliates including our head office in the United States.
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