Banner image

Woollybutt Field Decommissioning

Activity type Decommissioning, dismantling or removing a facility
Activity subtypes
Submitted by Eni Australia Limited
Submission date 30 September, 2021
Subtype New
Decision date
RMS ID 6768
Status Under assessment (with titleholder)
Link to previously accepted EP
Keith Cook
Phone: 08 9320 1111
Location map (click to enlarge)
Location map - Activity: Woollybutt Field Decommissioning (refer to description)

The Woollybutt Field is located approximately 80 km off the northwest coast of Western Australia in Lease Area WA-25-L. The Field is approximately 30 km west of the Barrow Island Marine Management Area and Marine Park boundary, and more than 50 km south-west of the Montebello Islands Marine Park.

The scope of this Environment Plan (EP) covers the decommissioning of the following infrastructure within Permit Area WA 25 L: six steel mooring anchors and chains, eight concrete umbilical crossing mattresses and 16 grout bags, approximately 10 km of umbilicals and jumpers, and approximately 20 km of flexible flowlines and jumpers.

Six anchors and chains were installed for mooring the FPSO via a DSPM buoy. The anchors remain located at a horizontal distance of 780 m from the centre of the buoy. Each chain has a total length of approximately 850 m and diameter from 92 mm to 162 mm. Anchor dimensions are approximately 8.1 m long, 2.9 m wide and 3.1 m in length, and have a unit weight of approximately 35.5 te.

Eight concrete mattresses and 16 grout bags were installed over umbilical and flowline infrastructure for stabilisation during operations. The mattresses are approximately eight feet by 20 feet by 4.5 inches in size and constructed predominantly of concrete, with small amounts of stabilised copolymer extruded fibre rope and polyvinylchloride. The grout bags are plastic bulk bags made from polypropylene and are typically 0.9 m by 0.9 m by 0.9 m in size. The bulk bags are packed with dry cement bags and each typically weigh 400 kg in air.

During production, the subsea control modules included control umbilicals which contained cores for hydraulic fluid, chemical injection and power and signal cores for control and data recovery from the wells. Flowlines and jumpers were used for transporting gas from the wells. At the time of decommissioning under this EP, the umbilicals, flowlines and jumpers will have been disconnected, laid on the sea floor and contain only seawater.

This EP proposes to leave the above Woollybutt field infrastructure in situ. The decommissioning strategy has been developed based on the outcomes of an options assessment, equal or better outcomes assessment and assessment against the principles of Ecologically Sustainable Development.

Other Details
Locations North West
Commonwealth waters adjacent to Western Australia
Titles (or other instruments) WA-25-L
Current Documents (Under assessment)
EP Document

Location map