The Stybarrow field is located in the Commonwealth waters of the Exmouth subbasin, Australia, within the production licence WA-32-L that is owned and operated by Woodside Energy.
The field was developed by a 50:50 joint venture between BHP and Woodside until the merger of BHP’s oil and gas portfolio (BHP Petroleum) with Woodside Energy in June 2022.
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Crude oil production from the Stybarrow field commenced in November 2007 and ceased in July 2015 while the floating production storage and offloading (FPSO) unit departed from the field in the following month. All wells were bullheaded and valves were pressure-tested and closed upon cessation of production.
The environmental plan for cessation activities in the field was approved by the national government’s National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA) in April 2016.
The plug and abandonment (P&A) activities are scheduled to be completed by September 2024 alongside the decommissioning of subsea infrastructure, with the removal of disconnectable turret mooring scheduled to be completed by March 2025.
The P&A and subsea decommissioning work is expected to start in the fourth quarter of 2023 upon approval by NOPSEMA.
Location
The Stybarrow field is located in Australia’s North West Shelf. It lies approximately 51km north-west of North West Cape at water depths from 810m to 850m.
Stybarrow oil field infrastructure
Oil production at the Stybarrow field was carried out using the MV16 Stybarrow Venture, a floating, production, storage and offloading (FPSO) vessel installed on a spider buoy.
The subsea infrastructure consisted of six production wells, a gas injection well, and three water injection wells, all within four drill centres connected to DTM through flowlines. Five subsea distribution units were installed with one electrohydraulic umbilical per drill centre.
The subsea trees and the spider buoy were connected to the distribution units via a system of flexible flowlines and eight risers.
The 160,000-tonne MV16 Stybarrow Venture FPSO has a production capacity of 100,000 barrels of liquids per day with a storage capacity of 900,000 barrels. The vessel is equipped with a disconnectable internal turret mooring system designed by SOFEC.
Stybarrow field decommissioning details
The decommissioning of the field includes the plugging and abandonment of wells, and removal of the subsea equipment, including field deviation activities.
The well P&A activities include the removal of wellheads and Christmas trees, and the plugging and abandonment of ten wells with cement to prevent hydrocarbon release.
The decommissioning work also includes the removal of nine direct-to-metal legs, nine support buoys, eight flexible flowlines and nine risers. Also to be removed are umbilicals and flowlines, a water injection manifold, subsea distribution units, and anode skids.
The DTM lies on the sea bed due to loss of buoyancy and is proposed to be towed to shallower waters of WA-12-L placed onto a vessel.
The Stybarrow field deviation environment plan is under assessment, which proposed to leave nine suction bases, nine anchors, and the Eskdale-1 exploitation wellhead in place.
Contractors involved
McDermott, an energy engineering and construction solutions provider, was awarded the engineering, procurement and removal contract for the decommissioning works in July 2023.
The contract involves the full removal of the turret mooring. McDermott will deploy its derrick lay vessel DLV2000 for the removal works. The scope of the contract includes the provision of services recovery, transportation, and onshore offloading of the DTM buoy for dismantling and disposal.
Transocean, a drilling contractor, was awarded the contract for the permanent plug and abandonment of wells of the Stybarrow field in May 2023.
