Australia's offshore safety regulator has issued Italian major Eni with a notice after equipment from the offline Woollybutt oilfield off Western Australia was found to be floating on the ocean surface.

The National Offshore Petroleum Safety & Environmental Management Authority (Nopsema) issued the operator with a general direction after a floating mid-depth buoy (MDB) was found floating on the sea surface.

Nopsema confirmed in the direction, dated 4 September, that it had been notified by Eni of an object floating on the sea surface within WA-25-L, which was later confirmed on 3 September to be one of two MDBs located at the field.

Eni has confirmed with the regulator the MDB is within the gazetted petroleum safety zone, under 24-hour observation and is still connected to the Woollybutt subsea infrastructure.

An Eni spokesperson confirmed to Upstream on Tuesday that there was no evidence of any hydrocarbons leaking at the field.

"Eni is progressing with third parties to conduct further activities required to mitigate potential risks arising from this occurrence including removal of the navigational hazard, in accordance with regulatory requirements and in the shortest possible time," the spokesperson said.

Safety concerns

The approximately 40-tonne piece of equipment was designed to be tethered by chains at a depth of 50 metres, and Nopsema believes it now poses a risk to the safety of vessels in the area and potentially to the integrity of the subsea infrastructure, including the wells.

The regulator has confirmed it has opened an investigation into what led to the failure of the tethering system, but it has also issued Eni with three separate directions to ensure the safety of the area.

This includes taking “all reasonable measures” to mitigate the risk from the floating MDB to vessels in the area, as well as to “equipment, structures and property within the title area”.

Nopsema also directed Eni to carry out an assessment of the condition of all equipment, structures and property within the title area “as soon as reasonably practicable” to determine any potential risks to safety, well integrity and the environment.

Finally, Eni has also been ordered to notify Nopsema of any change to risks of navigation in the area, or to the condition of other equipment in the title area.

Operator previously warned

Nopsema had already identified the potential hazard the MDB posed in an improvement notice issued to Eni in May of this year after the regulator carried out an inspection following the sinking of the detachable single-point mooring at the field in January.

Inspectors found the sinking of the single-point mooring buoy was likely due to a failure to maintain adequate cathodic protection which protects the buoy from corrosion.

The inspection also found a number of deficiencies related to the integrity management of the two MDB mooring systems at the field.

The MDB mooring systems had a design life of five years and fatigue life of 15 years, but had been in place at the field for 17 years, since commencing production in 2003.

The regulator noted, at the time, it could find no evidence the MDB’s design and fatigue life had been reassessed and certified as fit for service beyond 2016.

Nopsema inspectors also found that Eni could not demonstrate effective inspection and maintenance activities were being carried out on the MDBs, mooring chains and mooring systems to ensure their integrity or that they were fit for service.

Following the improvement notice, Nopsema gave Eni 180 days to prevent or reduce the risk of an MDB floating to the surface and ensure the MDBs mooring chains and mooring systems were fit for service.

Woollybutt lies roughly 40 kilometres west of Barrow Island off Western Australia and was discovered in 1997.

The field came online in 2003 and was produced via four subsea wells tied back to a floating production, storage and offloading vessel. The field was shut-in nine years later in 2012 following several years of natural decline.

Eni received approval from Nopsema last year to carry out decommissioning activities at the field, with the aim of having all plug and abandonment activities of the shut-in wells to be completed by 2021.