The Challenge
Three mature offshore fields reached end of economic life together, leaving a combined inventory of 27 platforms, 32 pipelines and associated subsea cables to be decommissioned under a single programme. The assets spanned several decades of construction vintage, with incomplete as-built records on the older structures and pipelines whose burial status had not been surveyed in years.
The operator needed a FEED that would survive tender — a programme that installation contractors could price with confidence, that regulators could approve, and that would not unravel when the first vessel spread mobilised.
Our Approach
Every removal concept was screened against a real vessel, a real cut method and a real disposal route before it entered the estimate.
VORYX team members managed the Tier-1 FEED contractor on behalf of the operator, running technical assurance across the full asset stack rather than accepting deliverables at face value. Every removal concept was tested against an available vessel class, a real cut technology and a confirmed onshore reception route before it was allowed into the cost estimate.
The programme was built as a multi-season campaign portfolio. Weather windows, heavy-lift vessel availability, well readiness and yard reception capacity were sequenced together, so that the schedule reflected the constraint that actually governed each season rather than the optimum for any single scope.
Structured comparative assessment was applied across the pipeline inventory, where removal, trench-and-bury and leave-in-place options each had to be argued on safety, technical feasibility, environmental impact, societal impact and cost — with the evidence traceable back to survey data and quantified estimates.
What We Delivered
- FEED management and technical assurance of a Tier-1 contractor
- Asset register and data gap closure across 27 platforms and 32 pipelines
- Removal method selection and constructability screening per structure
- Multi-season campaign sequencing and vessel spread strategy
- Comparative assessment across the pipeline and subsea cable inventory
- Bottom-up CAPEX estimate with probabilistic schedule and risk register
- Waste, disposal and recycling strategy with onshore reception planning
- Execution strategy, Scope of Work and tender-ready ITT package
The Outcome
- A decommissioning programme priced from execution reality rather than analogue scaling
- Regulator-facing justification for each pipeline and structure end-state
- Contractor-ready tender package covering the full three-field inventory
- Cost and schedule risk quantified and owned rather than absorbed as contingency
Standards Applied
- IMO Res. A.672(16)
- UNCLOS Art. 60
- London Protocol
- ISO 19902
- DNV-ST-N001
- NORSOK D-010
- AACE RP 18R-97
Operator and project names are anonymised for confidentiality and disclosed on request. Experience described is that of VORYX team members.
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