A series of ‘firsts’ on North Sea subsea well abandonment project

PROJECT OVERVIEW 

A major operator required through tubing abandonment of three wells across two fields in the UK sector of the North Sea during Q4 of 2021. 

The project required a subsea well abandonment full back deck equipment spread incorporating Claxton’s suspended well abandonment tool (SWAT™), perforation, pumping and cementation tooling and well fluid management systems. This was the vessel operator’s first well abandonment project and the first-time the end-client would utilise the SWAT tool in a unique first-time overboard deployment as opposed to through the moon pool. 

Claxton, a Cutting and Decommissioning brand in Acteon’s Energy Services division managed third-party interfaces to provide cement and pumping services for the vessel-based well abandonment work scopes and used SWAT for well fluid management to minimise well fluids returned to shore. 

THE CHALLENGE

The project requirement was for the removal of oil-based mud (OBM), filtration of the well fluids and placement of an environmental plug in the bore and annuli between 400 ft and 1229 ft below the mudline. To minimise the number of tanks on board, and the volume of well fluids that were required to be returned to shore for processing, a well fluid management spread was used onboard to enable returned OBM to be cleaned and once the permitted levels were achieved the clean fluid was discharged overboard. 

Bespoke equipment was developed for the project including an over-boarding platform which Claxton provided their experience and knowledge to design and successfully deploy SWAT from the vessel. 

The client had experienced issues with over-perforation of their casing on a previous project therefore Claxton implemented gun testing to ensure this didn’t happen on this project.

Other challenging factors to the project included adverse weather conditions, a significant wave height of 3.5 m and a congested back deck. 

CUSTOMER GOAL 

The operator’s goal was to use a vessel-based approach to the abandonment of three wells and by doing so achieve significant cost and time savings compared to that of a rig.  

They needed to safely clean up the wells and recover well fluids such as OBM back to the surface whilst minimising the impact on the environment. 

OUR SOLUTION AND ITS COMMERCIAL BENEFITS TO THE PROJECT 

We develop market-leading services and integrated solutions 

• Claxton successfully provided the full vessel back deck spread with SWAT, cementing tools and well fluid management. 
• In-house well engineering and analysis expertise was applied to aid third-party bespoke technology development to reduce operational risk. 

We work at scale with a proven track record for delivery 

• Claxton leveraged experience from their track record of over 100 suspended wells successfully abandoned and recovered to safely clean up the wells and recover well fluids such as OBM back to the surface. 

We optimise the project to increase commercial value 

• Management of cementing design and supply simplified the supply chain. 
• Local presence enabled us to mobilise equipment from our UK bases in Great Yarmouth and Aberdeen. 
• Provided a rigless, vessel-based abandonment operation to minimise cost and carbon footprint. 

We minimise the environmental impact  

• The time-efficient rigless vessel operations provided project carbon footprint reduction. 
• Bespoke technology provided reliable environmental plugging of suspended wells and reduced operational risk. 

PRODUCTS USED 

SWAT™

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