The Stag oilfield is located in block WA-15-L on the North-West Shelf, approximately 60km north-west of the coast of Dampier in Western Australia.
The oilfield is operated by Jadestone Energy, which acquired the operatorship license for the block from Quadrant Energy and Santos.
The field has been in production since 1998 and is scheduled for redevelopment via an infill drilling campaign planned for completion by 2020. The $112m redevelopment project is expected to increase the production life of the oilfield up to 2024.
National Offshore Petroleum Safety and Environmental Management Authority issued the license for drilling an additional production well for the project in June 2018.
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Stag oilfield location and reserves
The Stag oilfield is located within a 500m exclusion zone, which allows the off-take vessels to operate at a speed of not more than 5kt.
The oil is hosted within 15.5m oil columns featured in four-way faulted structures in the reservoir.
The field is estimated to hold 22.7 million barrels (Mbbls) of medium crude oil reserves at 19o API.
Stag oilfield redevelopment details
The Stag oilfield is designed to produce 30,000 barrels of oil per day, but is currently producing just 3,750 barrels a day from 11 active oil wells.
The redevelopment project will include the plug and abandonment (P&A) of an existing water injector well (Stag-14H) along with the drilling of a new oil production well (Stag-49H).
The Stag-14H water injector well will be disconnected with a 762mm conductor along with a tubing string recovered from the well. The vacant slot of 14H will make way for the drilling of the Stag 49H oil production well, which will be tied-back to the CPF.
The new oil well is expected to produce 1.2 million barrels (Mbbls) of oil from the Stag oil reservoir. The project includes scope for drilling of four additional production wells.
The drilling activities are being undertaken by the Ensco 107 jack-up drilling rig. The activities were, however, halted temporarily due to an unfavorable condition raised by the tropical cyclone Veronica in March 2019.
Stag oilfield infrastructure details
The Stag field is developed by a central production facility (CPF) connected to a floating storage and offloading (FSO) unit, named Dampier Spirit, along with associated subsea structures.
The CPF is installed at a water depth of 49m and 20m above the sea level. The 6,500t production platform covers a total area of 2,109m² and features a steel hull. It hosts a processing module and living quarters with an accommodation capacity of 58.
Power supply for the CPF is facilitated by three dual-fuel generating units.
Subsea infrastructure and oil export details
The CPF is connected to a total of five sub-surface water injection wellheads, two of which are located 1,110m north-east to the facility and three are located approximately 3km west of the CPF.
Stag’s subsea system comprises manifolds, rigid spools, flexible flowlines, and chemical injection systems accompanied by various electric submersible pumps.
The CPF is connected to a Catenary Anchor Leg Mooring (CALM) buoy, located north-east to the facility, via a 2km-long export pipeline.
A flexible import hose that extends from the CALM buoy supplies the produced oil to the FSO facility, which exports the oil using off-take tankers.
Contractors involved
Jadestone Energy awarded a contract to Ensco Australia, a wholly-owned subsidiary of Ensco, for providing the drilling rig for the new production well in February 2019.
Bouygues Offshore was the engineering, procurement, construction, and installation contractor for the CPF, while CALM buoy for the project was provided by Bluewater.