Dunlin Alpha - a decommissioning challenge turned collaborative solution

This has not always been the case. While those involved in the early days of North Sea exploration and production considered the full asset lifecycle, the primary focus was on designing for safety, reliability and operability. Then through asset operation, wells and facilities were repaired and modified in a fit-for-purpose manner with limited focus on the consequences of ageing infrastructure 30 – 40 years down the line.

As a result, there are many assets – in the UK and beyond – that are approaching the end of their economic lives without an integrated life of asset plan, or an approach in place to deal with decommissioning.

Unlike today, where a design for decommissioning approach is encouraged, those seeking to deliver well decommissioning across older assets are having to dig deep to come up with innovative ways to more efficiently execute these programmes of work.

While that brings with it challenges, there are opportunities too. With more than 750 suspended inactive wells in the UKCS today, we have the chance to learn from these projects and really move the needle – whether that is in driving the development of innovative solutions within our supply chain, to building the capabilities needed to standardise best practice into how we understand, manage and prepare our late life assets for efficient decommissioning.¹

Further, with the wide variety of field and infrastructure types, state of asset degradation, water depths and environmental conditions we are exposed to across the UKCS, the experience that we are developing in this region will be applicable to virtually all other offshore provinces – knowledge that could be a valuable export commodity.

The Greater Dunlin Area decommissioning project is one such example. Taking the Dunlin Alpha platform, satellite fields and infrastructure from cessation of production to final site remediation has been a multi-year undertaking, with a decommissioning programme that has called for innovative thinking and an integrated approach between ourselves and our supply chain partners.

Installed in 1977, Dunlin Alpha is a four-leg gravity base structure, located in the Northern North Sea. A crucial part of decommissioning this asset has involved the removal of 45 well conductors – a process that began in 2018 and is set to conclude later this year.

Not your typical conductor removal

During a routine conductor removal programme, a drill crew would routinely pull all the casing strings and conductor once a well has been successfully abandoned. For Dunlin Alpha, however, many of the conductors – due to the excessive span between topsides and the -10 m guideframe, and poor performance of 1^st generation conductor connectors – have been repaired over the years by temporary braces, clamps and grouted-sleeves; installed principally by the previous operator in order to extend the asset’s operational life.

This has made their removal far more complicated, with a relatively straightforward drill rig pull rendered unviable due to there being insufficient clearance to pass these various attachments through the sleeves within the modular support frame (MSF).

A collaborative approach

Due to the complexity of the project, a collaborative approach was adopted. Representatives from companies including The WellGear Group, AquaTerra, Atkins, Worley, Rever Offshore, Scopus Engineering, and Underwater Cutting Solutions (UCS), all joined Fairfield in brainstorming solutions for how to best overcome the challenges presented.

Seven potential solutions were taken from concept through a series of decision gates, before the team decided on a hybrid – one that enabled operations to begin in just nine months. Without over-engineering, it was a fit-for-market solution for Dunlin Alpha’s challenges.

The adoption of a combination of new and proven technologies enabled the project team to reduce the overall campaign schedule by a year, also delivering major cost savings, with the following innovations among those contributing to this result:

• The AquaTerra supplied ‘QuikDeck’ system was utilised to access the conductors from underneath the platform. This system was able to be installed and deconstructed in less than half the time of traditional scaffolding, significantly optimising operations. Further, due to the ability to raise and lower the deck as required, Fairfield was able to navigate the time constraints typically posed by weather conditions in the North Sea, allowing operations to extend into the late-autumn, compared to just the summer months with a more traditional scaffold and rope access method. Nets were suspended below the connectors, catching loose grout and preventing it from falling – thereby improving safety and environmental parameters.
• The significant quantity of clamps and braces that had to be removed would have resulted in a number of summer seasons being required for the drilling package to recover the conductors. Instead, WellGear’s Rigless Intervention System (RIS) was installed to enable pulling of conductors with clamps in parallel with the P&A activity. This continual use of a pulling unit, without interfering with the drilling package well programme, removed conductors from critical path and optimised the schedule. The integration of the WellGear and Fairfield teams, both on and offshore, led to a more cohesive approach.
• A temporary marine crane from Brimmond Group was mobilised to support the WellGear RIS unit and supplement the existing platform craneage. This enabled Dunlin Alpha’s main crane to focus support on Rig P&A work with the RIS unit following behind to remove the casing and conductors, further optimising the execution schedule.

Progress through adversity

Despite schedule changes stemming from COVID-19, 29 conductors (as of 5 May 2021) of a total 45 have now been pulled, testament to the ability of the Fairfield team and its supply chain partners to work collaboratively and provide an innovative, integrated and cost-effective solution. The task will be completed within 2021.

Dunlin Alpha demonstrates that Fairfield’s strategy – of focusing on a North Sea solution that is fit-for-purpose, without over-engineering – is one with potential to bring great advantage to the UKCS’ decommissioning arena. And, if we can master the domestic market and achieve competitiveness within the North Sea region, we will be able to export that knowledge and experience further afield.

For further information regarding the decommissioning of Dunlin Alpha platform, please visit: http://www.fairfield-energy.com/operations/greater-dunlin-area/

Author: John Wiseman, Managing Director, Fairfield Energy

Reference

1.https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/943765/strengthening-uk-decommissioning-cfe-govt-response-.pdf

Read the article online at: https://www.oilfieldtechnology.com/offshore-and-subsea/24062021/dunlin-alpha--a-decommissioning-challenge-turned-collaborative-solution/