Approaches to closure for offshore infrastructure

How we approach closure in a marine environment

Every one of BHP’s operated assets interacts with the marine environment in some way during its operational lifecycle. Whether it is the floating facilities or subsea infrastructure of our petroleum assets, coastal infrastructure for loading and shipping our suite of mined products, or the extraction of seawater for water supply for mining activities at Escondida and Spence, we continually interact with the ocean and its ecosystems. We are working to ensure our marine interactions have sustainable outcomes throughout the lifecycle of our operated assets, including the closure phase.

One of the challenges during the closure phase is when we make decisions about infrastructure no longer required for production. The way we respond to marine closure is set out in our internal closure standard, which helps drive optimised closure outcomes for our sites by combining consideration of our social and environmental values, obligations, safety, costs, risk management and the expectations of external stakeholders.

In a marine environment, the balance required to achieve an optimised closure can be complex. Our closure work is required to incorporate an assessment of the associated threats and opportunities, with possible outcomes ranging from a full removal of facilities at the end of their operational life, to understanding the conservation benefits of existing infrastructure or repurposing selected infrastructure for further socio-ecological benefits, where appropriate to do so.

Recycling the Hay Point coal-loading trestle structure

Where full removal is the selected closure option, the primary focus is the removal of subsea infrastructure and the restoration of the marine environment to baseline conditions.

An example of this is the dismantling and full removal of the coal-loading jetty at Hay Point in Queensland, which was ongoing in FY2020. This marine closure project is adjacent to the Great Barrier Reef Marine Park and subject to strict environmental controls that were embraced by the dismantling team. For example, the team implemented marine fauna observation procedures whenever humpback whales or turtles were sighted, to avoid disturbance to these creatures while in the vicinity of the works.

 landward end of trestle-straight


Hay Point trestle before and after the closure project (Credit: BHP)

The old jetty trestle structure was 1.9 kilometres long and made up of 243 piles, 5,311 tonnes of steel and 921 tonnes of non-ferrous materials. All materials recovered from the demolition project have been returned to shore for further processing, with 100 per cent of the steel and non-ferrous materials recovered to date processed for recycling at licensed recycling facilities.

Understanding the relationship between fishery abundance and the BHP-operated Griffin subsea gas pipeline

While removal of marine infrastructure is the starting point, we recognise that sometimes leaving some subsea infrastructure in place can be beneficial to the environment, and we use research and evidence to determine this.

For example, research undertaken with the University of Western Australia (UWA) on the Griffin subsea gas pipeline in Western Australia found the pipeline had been a catalyst for increased local ecological diversity. It has provided a habitat for corals and sponges to prosper, creating a breeding ground and home for endangered species and fish of commercial importance.

The research indicated the pipeline’s removal could adversely affect marine ecosystems that had thrived around this subsea infrastructure, which has been in place since 1993, and cause more environmental disturbance than if the pipeline was left in place. It also found fish assemblages recorded in the pipeline zone had two to three times the value of commercial fish species in depths beyond 80 metres than in surrounding habitats comprising bare, sandy sediments. Commercially important fish species such as snapper were common on the pipeline. For more information on this research, please see our Prospects story, How an underwater gas pipeline become a fish haven.

Tiger shark  Tiger sharked observed during the Griffin pipeline fish surveys (Credit: UWA)

In FY2020, we extended our research partnership with the UWA to better understand the socio-ecological value of offshore infrastructure. We committed to a three-year partnership helping to support three PhD students to investigate the biodiversity conservation value of subsea structures. This program will be the first socio-ecological investigation to compare fish assemblages around subsea infrastructure and compare them with nearby restricted and open-access areas in natural environments within marine parks. It will enable a better understanding of the role of subsea infrastructure and no-take zones or restricted access areas in biodiversity conservation, particularly for endangered and protected species.


Leopard shark observed during the Griffin pipeline fish surveys (Credit: UWA)

The outcome of this research will enable BHP to combine consideration of our values, obligations, costs and risk management with environment, health and safety considerations and external stakeholder expectations to achieve an optimised closure outcome for the Griffin pipeline, and extend this knowledge to other submerged marine infrastructure.

Evaluating the benefits of retained infrastructure at King Reef

The Exmouth community in Western Australia had been advocating for an artificial reef that would create additional recreational opportunities in the region by providing a fishing and diving experience for the local community and tourists in the sheltered waters of the Exmouth Gulf.

This was recognised by BHP, and the Exmouth Integrated Artificial Reef, known as King Reef, was constructed two years ago from selected sections of redundant BHP infrastructure. The reef was formed from a combination of six giant steel structures from the BHP-operated Griffin oil and gas facility that had been decommissioned and cleaned, and concrete modules supplied by an artificial reef installation company who project managed the works. These steel structures were repurposed and deployed on the ocean floor within the Exmouth Gulf. Community volunteers have continued to monitor the reef since then through a BHP-funded project called Reef Vision, sending data back to the community-based recreational fishing organisation Recfishwest and Curtin University for scientific assessment and reporting.

Griffin mid-depth buoy after cleaning,

Griffin mid-depth buoy after cleaning, Exmouth (Credit: BHP)

Conceptual layout of Exmouth Integrated Artificial Reef

Conceptual layout of Exmouth Integrated Artificial Reef (Credit: Subcon)

Two months after the reef’s deployment, volunteer videos revealed over 20 fish species on the structures. After four months, the volunteers captured over 40 fish species. In January 2020 (just under two years after deployment), volunteers recorded over 90 fish species living on the artificial reef, with a large portion being fish species popular with recreational fishers.

Location of Integrated Artificial Reef in Exmouth Gulf

Location of Integrated Artificial Reef in Exmouth Gulf (Credit: Recfishwest)

With an area of two acres, the reef provides more than 27,000 cubic metres of underwater habitat, providing food and shelter for a variety of fish, sea turtles, sea snakes, sharks and rays. Since its deployment, the artificial reef has continued to develop and support a thriving marine ecosystem. It continues to have a direct positive impact on tourism and local businesses and is popular among fishing enthusiasts. For more information on the reef’s construction, please see our Prospects story How old BHP infrastructure creates a fishing playground.

Delivering optimised marine closure outcomes

With the marine environment facing increasing risks or pressures from potential physical climate change impacts, fishing activities and habitat modification and destruction, we understand we need to take a holistic approach to identify and achieve sustainable outcomes for our marine closures to address shared challenges in the catchments and basins where we have been operating.

Our objective is to achieve an optimal marine closure outcome in consultation with local communities and other stakeholders. We seek to ensure we have a detailed evidence and knowledge base to enable informed assessment and management of the threats and opportunities identified, to develop a suite of options and undertake a closure options assessment.

From full removal (such as at Hay Point) to the repurposing of infrastructure to provide enduring socio-ecological benefits (such as the Exmouth Integrated Artificial Reef), we aim to balance our social and environmental values, obligations, safety, costs, risk management and the expectations of external stakeholders, to inform an optimised marine closure outcome.

Juvenile red emperor fish

Juvenile red emperor inside a King Reef repurposed mid-depth buoy (Credit: Subcon)