We understand that decommissioning can be a complex business. Our approach is to simplify the process as far as possible by focusing on the key drivers whilst adhering to the standards necessary for executing such a large, multi-phase project. This principle has been embedded in the planning and execution of the five main work streams within the Greater Dunlin Area Decommissioning Project.
Platform Wells Plug & Abandonment
The plug and abandonment (P&A) of the 45 platform wells on the Dunlin Alpha is a time-critical and significant work scope, involving numerous technical challenges. The Dunlin Alpha wells will be plugged and abandoned in accordance with Oil and Gas UK recommended standards and the well activity governed by our Well Integrity Management System (WIMS) and Well Operating Procedures (WOPS) standards and procedures to ensure safe and technically appropriate methodologies are applied. We have undertaken interventions on 30 out of the 45 wells on Dunlin since its acquisition from Shell in 2008. A robust planning process accompanied with an inventory of wells with pre-approved P&A programmes is designed to mitigate the schedule risk from specific wells challenges and to maximise productivity.
Subsea Wells Plug & Abandonment
The plug and abandonment (P&A) of the 16 Osprey and Merlin subsea wells will be executed in a single campaign with a Mobile Offshore Drilling Unit (MODU), Transocean 712. These wells will be plugged and abandoned in accordance with Oil and Gas UK recommended standards, with well activity governed by our Well Integrity Management System (WIMS) and Well Operating Procedures (WOPS) standards and procedures to ensure safe and technically appropriate methodologies. The commencement of this campaign has allowed sufficient time for the learnings from the Dunlin Alpha P&A campaign to be incorporated into the design of the well programmes, greatly increasing the availability of original equipment manufacturer (OEM) running tools required for well access.
Subsea Infrastructure Decommissioning
Fairfield is responsible for the management of an extensive Subsea Infrastructure Decommissioning (SID) campaign, associated with the safe, efficient and cost effective decommissioning of the Osprey and Merlin subsea fields, which are tied back to the Dunlin Alpha installation, as well as the subsea infrastructure associated with the platform and Concrete Gravity Base Structure. The SID workstream completed a series of comprehensive stakeholder engagement sessions, including completion of the formal Comparative Assessment process, which culminated in the approval of the Osprey, Merlin and Dunlin Subsea Decommissioning Programmes in December 2017. The associated subsea decommissioning scope of work was competitively tendered by Fairfield in 2017, with Bibby Offshore Limited awarded the contract in early 2018. Detailed engineering and planning preparations will be followed by offshore decommissioning activities later in 2018. Decommissioned infrastructure will be returned to the Port of Cromarty disposal yard, for onward recycling and disposal of recovered materials.
Dunlin Alpha to Cormorant Alpha Oil Export Pipeline (PL5)
The Dunlin Alpha to Cormorant Alpha Oil Export Pipeline (PL5) is a 24” concrete coated trunk pipeline that originally served as an oil export pipeline for comingled production from the Dunlin, Murchison and Thistle platforms respectively. Following decommissioning of the Murchison platform by CNR and Cessation of Production (CoP) from the Greater Dunlin Area fields, as announced by Fairfield in 2015, PL5 currently exports Thistle area production to Cormorant Alpha, where it enters the Brent System ahead of final delivery to Sullom Voe Terminal (SVT).
Use of PL5 as an export pipeline is currently planned to cease in mid-2019, following Fairfield’s agreement to extend the export service for Thistle production, aligned to the Oil & Gas Authority’s Maximising Economic Recovery (MER UK) policy.
In preparation for future final decommissioning of the PL5 export pipeline, Fairfield has commenced stakeholder engagement with industry regulators, external stakeholders and joint venture partners, ahead of formal comparative assessment of decommissioning options for this trunk, currently scheduled to commence later in 2018.
Make Safe and Handover
The Make Safe and Handover team is responsible for transitioning the Dunlin Alpha platform from its operational state to a permanent shutdown state with process equipment cleaned, isolated and ultimately left in a safe state for the topsides removal preparation phase. Key Dunlin engineering and operations personnel provide in-depth asset knowledge and experience that is critical in avoiding abortive work and optimising the efficiency of work executions. Having fully prepared topsides oil and gas processing vessels and successfully completed a programme of equipment isolation and disconnection in the wellheads area, giving free access for an uninterrupted P&A programme, the team are now focussed on conductor removal activities which requires a multi-discipline approach to overcome the technical and integrity challenges.
We will undertake initial feasibility studies to understand the key technical challenges and execution risks associated with each of the available topsides removal methodologies. On completion of methodology evaluation, the work scope for the project Define phase will be informed by the overall execution strategy as well as the outcome of stakeholder consultation and comparative assessment that will determine the key interfaces between infrastructure to be removed and infrastructure planned to be left in-situ. During the Execution phase of the topsides removal work stream, focus will be directed towards ensuring safe and efficient removal of the platform modules in accordance with the agreed removal methodology, sequence and disposal strategy.