Offshore safety regualtor NOPSEMA has ordered Woodside to check corrosion on 24-tonne caissons that hang under the North Rankin A offshore platform and could fall onto gas and condensate pipelines below.

The direction was published a week after Woodside chief executive Meg O'Neill targeted a 30 per cent cut in operating costs, with a focus on maintenance.

Woodside reported to NOPSEMA that two caissons on the 37-year old platform were sufficiently corroded to impair their structural integrity and an inspection by the regulator followed.

Caissons are pipes open at the bottom and suspended beneath offshore platforms to either dispose of fluids or suck up seawater for use in processing or fire fighting.

A NOPSEMA direction to Woodside published today requires the company to analyse the structural integrity of four operating caissons and ten that are no longer used and then fix any issues it identifies as soon as possible.

"Failure of one or more of the remaining caissons could lead to dropped object damage to the facility structure or loss of containment from the subsea gas and condensate pipelines," the direction started.

"While the likelihood of pipeline rupture is low, should it occur, loss of hydrocarbon (gas and condensate) from these pipelines may result in a major accident event."

A major accident event is an industry term for an accident that could result in multiple fatalities.  

A Woodside spokesperson said the company has commenced inspection of the final caisson and subsequent analysis and assessment would be completed within several weeks.

The caissons are typically 70m long, 900mm in diameter and weigh 24 tonnes.

The caissons hang about 70m from the seabed near two pipelines, including a 40-inch gas pipeline that is a main supplier of gas to the North West Shelf's five LNG trains near Karratha.

Woodside removed two other caissons in November 2020 and May 2021.

The direction, that is legally stronger than more common inspection notices, requires Woodside to report progress to the regulator every month.  

Unusually, Woodside has been directed to "ensure effective communication with members of the workforce" to reduce risks involved in the caisson work.

Woodside to slash its maintenance budget

A week ago Woodside acting chief executive Meg O'Neill told a conference for investors that Woodside aimed to cut operating costs by 30 per cent within three years.

O'Neill told the Credit Suisse 8th Australian Energy Conference that Woodside needed a "laser-like focus on cost management" for its LNG to be competitive and to allow the North West Shelf to attract third party gas for processing revenue.

"A key focus area for us is maintenance which accounts for a significant portion of our production cost," O'Neill said.

"We have set up teams to tackle each part of the process to make sure we are identifying the right maintenance required for safe and reliable operations, and then execute that maintenance as efficiently as possible."

Woodside acting chief executive Meg O'Neill speaking at the APPEA Conference this week
Woodside acting chief executive Meg O'Neill speaking at the APPEA Conference this week. Source: APPEA.

The planned cuts to operating and maintenance budgets come despite NOPSEMA recently identifying numerous problems with Woodside's operations.

Today's notice is the fifth safety-related action the regulator has taken against Woodside in the last three years. The others were:

  • July 2019 - insufficient capacity to fight fires on the Vincent floating, production, storage, and offloading facility.
  • October 2019 - "Woodside has failed and continues to fail to preserve the condition of the riser turret mooring" used for the Nganhurra FPSO, resulting in the risk of an oil spill and the RTM becoming a navigation collision hazard.
  • November 2019 - Woodside did not properly maintain a crane on the North Rankin A platform and "failed to take all reasonably practicable steps: to ensure the crane was "safe and without risk to health."
  • November 2020 - Woodside failed to conduct an adequate risk assessment of working at heights on the VALARIS DPS-1 drilling rig resulting in "increased exposure to potential for serious injury or death."

The Woodside spokesperson said the safety and wellbeing of its people is Woodside’s highest priority.

"We reject claims of poor safety culture or performance on our facilities, the Woodside spokesperson said.
"For example, in 2020 we achieved our best-ever personal safety performance, including no recordable injuries on our offshore gas platforms."

Rusty caissons a known problem

The risk of caisson failure is well known to Woodside and the wider offshore industry.

Woodside’s 2019 operations plan for the North Rankin complex lodged with NOPSEMA identified internal corrosion of caissons as one of seven possible causes of structural failure that could lead to gas being released.

“Structural damage to the platform resulting from the causes listed…could be minor or could in the most extreme situation result in total loss of the platform,” the plan stated.

Measures to “maintain structural integrity to…prevent structural failures" was identified as necessary to avoid the possibility of an accident that could result in multiple fatalities.

The UK offshore safety regulator has issued a directive that: "Deterioration and failure of caissons, including their supports, has been a significant problem in the UK continental shelf for several decades."

The Bruce platform in the North Sea was shut down for five weeks in early 2020 to fix an unused seawater return caisson that had “parted below the waterline.”

In April 2021 the UK regulator took action against Harbour Energy after one caisson failed, another had “severe corrosion and metal loss” and three more were classed as high risk.

The North Rankin A platform has supplied gas to the North West Shelf LNG plant since 1984. A neighbouring North Rankin B platform commenced operations in 2013.  

The two platforms sit 100m apart in about 125m of water 135km from Dampier.

The NRA platform receives gas, condensate and water from 29 wells on the platform and two subsea wells over the Persephone field, according to Woodside’s operations plan.

The production fluids are piped over a bridge to the NRB platform for processing and compression and then separate streams of gas and condensate flow back to NRA for drying and then are piped to shore.

The North West Shelf project is owned by six equal partners: operator Woodside, BHP, BP, Chevron, Shell, and Japan Australia LNG that is owned by Mitsui and Mitsubishi.


Update: 6:15PM 18 June: Woodside comments added.


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Main image: North West Shelf project's North Rankin A and B platforms. Source: North West Shelf Gas.