Location and Timing
Shell proposes to remove wellheads: Crux 2ST1, Crux 3, Crux 4 and Auriga West-1 located in AC/RL9, Crescendo-1 located in WA-371-P, Prelude-1a located in WA-44-L, and Trio-1 outside of existing Shell permit area in block 1338. All seven (7) wellheads are situated in Commonwealth marine waters ~460km north-north east of Broome (Figure 1).Removal of the wellheads will remove the visual and structural evidence of the wells from the seabed, and eliminate presence or future hazards to the environment or other users of the area.
The wellhead removal activity is scheduled to commence in Q1-Q3 2017, and is planned to take ~3 weeks to complete. However, due to unforeseen delays and operational complications, the scope could occur up to 3 months anytime during 2017 and 2018.
Details of Light Well Intervention Vessel
The wellhead removal activity will be conducted using a light well intervention vessel. The vessel will be equipped with remotely operated vehicles (ROVs), dynamic positioning (DP) system, moon pool, helideck and accommodation (for personnel onboard of ~120 crew).
Length overall : 117.35 mBreadth moulded : 22.0 mPOB: 120 personsEnclosed lifeboats : 4 x 60 manDP System: Kongsberg Maritime AS, SDP21Shell will ensure that such a vessel shall have required vessel documentation accepted by the various legislative bodies for use offshore in Australian waters.Helicopter flights to and from the vessel will be conducted on an ad-hoc basis and in the case of emergencies.
Operational Scope
The Trio-1, Prelude-1a, Crescendo-1, Auriga West-1 wells were permanently abandoned by Shell in 2007, 2007, 2009 and 2015, respectively. The Crux 2ST1, Crux 3 and Crux 4 wells were permanently abandoned by Nexus Energy Ltd in 2006, 2007 and 2008, respectively.The light well intervention vessel will deploy an ROV supported wellhead retrieval package to cut and recover the wellheads for onshore disposal. The wellheads will be cut with an abrasive cutter utilising high pressure water and abrasive sorted grit particles. This method of wellhead removal has been used in offshore Australian since 2003 and is designed for the removal of multi-casing wellheads, piles and platform conductors without the need for a rig or explosives.Each wellhead is expected to take a minimum of 2 days to remove.Once onshore, the wellheads will be managed and disposed of by a licensed waste facility.