Santos WA PVG Pty Ltd (Santos) proposes to temporarily suspend or decommission the VGA-4H GI ST1 well within the Van Gogh Coniston Novara (VGCN) fields (production licence WA-35-L), with the Operational Area also extending into WA-28-PL. The permit areas are within Commonwealth waters approximately 285 km west-southwest of Dampier and 60 km north of Exmouth, Western Australia. The water depths in the field range from approximately 360 m to 380 m.
This EP will focus on activities required to undertake well intervention to suspend the single barrier VGA-4H GI ST1 well, or, alternatively, decommissioning of the well. In either case, the objective is to return the VGA-4H GI ST1 well to a two-barrier status. The well decommissioning activity will place permanent barriers in the well. To do so, some components of well infrastructure will be removed (e.g. crown plugs, completion tubing). Additionally, some subsea infrastructure may also be removed (e.g. electrical flying lead, hydraulic flying lead) between the xmas tree (XT) and the subsea manifold to facilitate the safe and effective removal of the XT, if it is removed during the well decommissioning activity.
Well suspension will be carried out using a light well intervention vessel (LWIV), or alternatively, well decommissioning activities will be carried out using a mobile offshore drilling unit (MODU). Both the LWIV and MODU will require support vessels and helicopters. Both activities may also include use of a remotely operated vehicle (ROV).
The activity is planned to commence between approximately Quarter (Q)3 2026 and Q4 2027 with an expected duration of approximately 10 to 40 days. Both the commencement date and duration may vary depending on approvals, MODU/LWIV availability, operational efficiencies and weather conditions This EP has evaluated impacts and risks of the activity for any time of the year to allow for operational flexibility.
In general, a MODU based well decommissioning program may consist of:
+ Preparatory activities
+ Survey activities (including geophysical surveys)
+ Mobilisation and positioning
+ Establishing and testing connection with the well
+ Ddisplacing hydrocarbons from the well
+ Install permanent isolation barriers to the reservoir
+ Remove subsea tree from the wellhead
+ Install permanent isolation barrier to non-hydrocarbon zones (if required)
+ Recover riser and BOP
+ Recovery of subsea well infrastructure
+ Demobilisation of MODU.
In general, up to three anchor handling type vessels will be used for the duration of a MODU assisted well abandonment campaign. One of the vessels will remain on location with the MODU/LWIV at all times, however all three vessels may be present simultaneously in the field.
An Operational Area for the activities covered by the EP is defined as within a 2,500 m radius of the VGA-4H GI ST1 subsea well.
Helicopters will be used to transfer crew and equipment to and from LWIV/MODU.