Decommissioning in Bass Strait

Planning for the eventual decommissioning of our Bass Strait offshore facilities

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Decommissioning in Bass Strait
The process of decommissioning offshore facilities presents complex challenges. As the operator of some of Australia’s most mature oil and gas fields, ExxonMobil Australia is committed to decommissioning our Bass Strait offshore facilities at the right time, and in the right way.

ExxonMobil has safely and effectively decommissioned offshore facilities to achieve positive outcomes around the globe.

We are leveraging this global experience locally as we start to plan for the eventual decommissioning of our non-producing platforms in Bass Strait. 

While we plan for decommissioning, we continue focus on safely shutting-down platforms as they reach the end of their productive life, ensuring they stay safe until we’re ready to begin the decommissioning process.

We are also keen to share our extensive knowledge and experience in offshore decommissioning around the world with the Australian government as they finalise an enhanced framework for the decommissioning of offshore oil and gas facilities, to ensure a consistent and effective approach to decommissioning across the country.
As the developer and operator of our Bass Strait oil and gas fields we have intimate knowledge of our assets and their environment which will inform our decommissioning campaign.

Recent global decommissioning experience

In 20202, ExxonMobil concluded two, very different but successful offshore decommissioning campaigns in Canada and the Gulf of Mexico

Lena platform in the Gulf of Mexico

In July 2020, ExxonMobil created a new reef site in the Gulf of Mexico outer continental shelf when it toppled-in-place the Lena platform jacket, turning it into a deep water reef.

The ExxonMobil team were able to successfully demonstrate to regulators that, as an artificial reef, the Lena will benefit the environment by continuing to provide habitats for rare marine wildlife in the area, which is similar to what we achieved with the Adelaide refinery wharf in South Australia.

We will continue to work closely with regulators as we finalise our decommissioning approach, so that we can achieve similar successful outcomes for the environment in Bass Strait. 

Closer to home, we recently removed the former Adelaide refinery wharf in South Australia, leaving much of the sea-bed infrastructure in place to minimise disruption to the surrounding marine environment.

Sable field in Canada
In November 2020, ExxonMobil Canada reached a key milestone in the decommissioning of its Sable project with the final removal of all seven offshore platforms which had commenced in May after more than eight years of extensive planning and studies. 

ExxonMobil Australia's decommissioning technical team lead, Emma Ogilvie, was the project manager for ExxonMobil’s decommissioning of the Sable project in Canada during the early planning stages.

“At the Sable field, an enormous semi-submersible crane vessel, Heerema’s Thialf, was used to carry out a sequence of separate lifts of platform components, such as topsides and jackets, using a reverse-installation method,” said Emma.

“During this process, an export barge was used to transport five loads of platform components, weighing a total of approximately 48,000 tonnes, across the Atlantic to a disposal and recycling yard in the U.K.”

“Around 99 percent of the material from Sable will be recycled,” she noted. 

“Importantly, Sable’s best-in-class safety performance continued throughout the removals campaign, with the project maintaining its lost-time incident free status for more than 19 years.”

Similarly to the work we’re currently taking out in Bass Strait, the Sable platform removal campaign followed multiple years of well plug and abandonment activities, as well as parallel activities to prepare offshore platforms for removal.

Planning decommissioning activities in Bass Strait

The process of decommissioning an offshore facility presents complex challenges. 

Decommissioning plans must consider the specific marine ecosystem, the size and weight of facilities and the inherent risks of removing such facilities.

ExxonMobil’s approach to decommissioning varies depending on the type of structure and unique characteristics of a specific site.

We incorporate best practices from other projects and expert advice from relevant stakeholders, including fishing communities, scientific organisations, repurposing and recycling specialists and academia.

Our Australian decommissioning team is using learnings from our experiences in other locations, and liaising closely with our decommissioning centre of expertise, to ensure our local decommissioning activities will meet regulatory, community, government and importantly, our own, high expectations.

Planning and preparation for decommissioning offshore facilities can start up to 10 years prior to actual execution, which is why we’re starting our detailed planning now.

Planning and preparation for decommissioning offshore facilities can start up to 10 years prior to actual execution, which is why we’re starting our detailed planning now. Decommissioning plans must consider the specific marine ecosystem, the size and weight of facilities and the inherent risks of removing such facilities.

Some early decommissioning works are already underway

Over the last few years we’ve made significant progress on our well plug and abandonment work, which puts non-producing platforms in a safer state until final decommissioning occurs. 

A detailed and extensive program of works has seen us successfully plug and abandon our Blackback, Whiting, Seahorse, Tarwhine and Mackerel wells.

Plugging and abandoning wells involves extensive planning and careful execution by specialist vessels, people, technology and equipment. This includes engaging crews who are trained and competent in the operation of semi-submersible, jack-up and platform based rigs and remote operated vehicles. The work requires an extensive logistics support network including a heliport and helicopter fleet for transporting workers as well as a shore base and multiple marine vessels to move the rigs on and off location and transport materials, equipment and supplies to and from offshore locations. All of this work takes place in a challenging remote environment subject to Bass Strait weather and rough sea conditions and is completed in close consultation with regulators and other relevant stakeholders.

After completing a significant plug and abandonment program in 2020, we are mobilising a second platform based rig in Bass Strait during 2021. The two platform based rigs will allow us to plug and abandon wells at our Kingfish B and Fortescue fields, as well as remove platform based conductors from the Mackerel platform.

Over the next few years we will continue to progressively plug and abandon wells as they reach the end of their production life, while we continue to progress the extensive planning and preparation of our final decommissioning program. 

Our significant investment in plug and abandonment activities is in addition to our ongoing work to ensure all our platforms, operating or not, remain in a safe state. In 2021, we will continue to operate a wireline unit in Bass Strait, which allows us to complete well inspection and maintenance activities, 24 hours a day, 365 days a year. The wireline unit is smaller than a platform based rig and can be moved to both operating and non-operating platforms as required, so that we can inspect and maintain the integrity of our wells. 
In 2021, we will continue our early decommissioning works with two platform based rigs that will allow us to plug and abandon wells at our Kingfish B and Fortescue fields, as well as remove platform based conductors from the Mackerel platform.

An enhanced decommissioning framework for Australia

A consistent approach for decommissioning is important to ensure all parties are held accountable for their decommissioning responsibilities.

However, our extensive experience around the globe has shown us that a one-size fits all approach for decommissioning will not deliver the best outcomes.

As outlined above, in two very different environments we achieved two very different, but equally successful decommissioning outcomes in the Gulf of Mexico and Canada during 2020.

Maintaining a flexible approach will ensure the best outcomes are achieved depending on each decommissioning project’s individual factors including the environment and age and type of infrastructure that is being decommissioned.

For example, infrastructure that has been in place for decades, such as many of our Bass Strait platforms, often become sanctuaries for marine wildlife. Simple removal of these well-established facilities could significantly impact the unique marine habitats that have developed in and around them over time.

Any enhanced decommissioning framework should allow for the specific marine ecosystem, size and weight of facilities and inherent risks of removing such facilities to be carefully considered in the approval of any decommissioning activities.

ExxonMobil’s approach to decommissioning varies depending on the type of structure and unique characteristics of a specific site. We hope the Australian government’s enhanced framework will continue to support this flexible approach to decommissioning, while ensuring operators remain accountable as facilities reach the end of their productive life.